1.2 Structure of the Field Testing Manual

Transcription

Field Testing Manual - 2003 - Ministry of Works TANROADS, Tanzania
April 2003
ISBN 9987-8891-4-X
THE UNITED REPUBLIC TANZANIA
MINISTRY WORKS
��
Field Testing Manual - 2003
THE UNITED REPUBLIC OF TANZANIA
MINISTRY OF WORKS
Field Testing
Manual - 2003
TANROADS
Central Materials Laboratory (CML)
i
April 2003
ISBN 9987-8891-4-X
Reproduction of extracts from this Manual may be made subject
to due acknowledgement of the source.
Although this Manual is believed to be correct at the time of
printing, Ministry of Works does not accept any contractual,
tortious or other form of liability for its contents or for any
consequences arising from its use. People using the information
contained in the Manual should apply and rely on their own skill
and judgement to the particular issue that they are considering.
Printed by: Elanders Novum AS, Oslo Norway
Layout: Jan Edvardsen, Interconsult ASA Oslo Norway
ii
TANROADS
Preface
An important part of a quality assurance system in civil construction works is a complete description of test procedures. This
involves having a Laboratory Testing Manual and a Field Testing Manual comprising a precise and simple description of test
procedures and necessary forms for records and presentation of the test results. It is in this context that this Field Testing
Manual has been prepared. The Laboratory Testing Manual was prepared and launched in the year 2000 to form a complete
system of testing standards for road works. This system is complemented by the launching of the Pavement an Materials
Design Manual-1999 and the Standard Specifications for Road Works-2000 from where test limits for material quality and
extent of testing programmes are specified.
These manuals form part of the development of Tanzanian National Standards and Guidelines under the Institutional Cooperation in the Road Sector Programme Agreement between the Government of the United Republic of Tanzania and the
Kingdom of Norway.
The Field Testing Manual describes techniques to be applied during testing in the field of geotechnique, material prospecting
and alignment surveys, construction control, pavement evaluation and axle load surveys. The testing and sampling procedures are clearly specified and their fields of application and limitations are clearly described. Moreover, the test procedures
are simplified to a practical approach, without compromising the correct procedure to be followed for each test.
This Manual will provide an invaluable documentation of field techniques to the benefit of both engineers and technicians
working in the road construction industry in the country and also other areas related to foundations for structures.
Dar es Salaam,
April 2003
F. Marmo
a.g Chief Executive Officer
TANROADS
TANROADS
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Acknowledgements
The Field Testing manual – 2003 has been prepared as a component under the Institutional Cooperation between TANROADS, CML and the Norwegian Public Roads administration (NPRA). The Government of Tanzania and the Norwegian
Agency for International Development (NORAD) have jointly financed the project, which forms a part of a programme to
establiosh technical standards and guidelines for highway engineering.
This Manual has been prepared by a Working Group consisting of the following members:
Mr. C. Overby
Mr. S. Rutajama
Mr. S. Nergaard
Mr. R. Johansen
NPRA
CML
Noteby, consultant
ViaNova, consultant
Chairman
Member
Member
Secretary
The Working Group wish to acknowledge engineers and technicians at CML for their valuable comments during the preparation of this Manual.
Photographs were provided by:
C. Overby
NPRA
M. T. Keganne
Roughton International
- Rolf Johansen
Vianova
- M. Besta
CML
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Summary of Terminology
Definitions of terms and abbreviations are presented in full in Appendix 7. Selected terms, definitions and abbreviations are
tabulated below for ease of reference in the use of this manual.
Base course
Materials testing methods
Bituminous binders
Bitumen emulsion (anionic, cationic, inverted)
Cutback bitumen (e.g. MC3000, MC800, MC30)
Penetration grade bitumen (e.g. 60/70, 80/100)
Bituminous layers
Asphalt concrete surfacing
Bitumen emulsion mix
Dense bitumen macadam
Foamed bitumen mix
Large aggregate mix for bases
Penetration macadam
AC
BEMIX
DBM
FBMIX
LAMBS
PM
Bituminous seals
Emulsion fogspray
Slurry seal
Surface treatments:
Surface dressing
Cape seal
Otta seal
Sand seal
Cemented materials (lime or cement)
C4
Stabilised,
UCS >4
C2
Stabilised,
UCS >2
C1
Stabilised,
UCS >1
CM
Modified,
UCS >0.5
Climatic zones
Dry
Moderate
Wet
MPa
MPa
MPa
MPa
Design depth
Earthworks
Fill
Improved subgrade layers
Roadbed
Environmental Impact Assessment
Fogspray (Sprayed on a surface dressing)
Granular materials
CRR Crushed fresh rock
CRS Crushed stones and oversize
G80 Natural gravel CBR >80%
Gravel roads
GC Grading coefficient
GW Gravel wearing course
SP Shrinkage product (LSx%pass.75mm)
Materials for earthworks
DR Dump rock: un-sorted rock
G15 Natural gravel/soil CBR >15%
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(cold)
(hot)
(cold)
(hot)
(cold)
CBR
GM
ICL
LL
LS
MDD
OMC
PI
PL
TFV
UCS
-
California bearing ratio
Grading modulus
Initial consumption of lime
Liquid limit
Linear shrinkage
Maximum dry density
Optimum moisture content
Plasticity index
Plastic limit
Aggregate strength (10% fines value)
Unconfined compression strength
Materials testing standards
AASHTO
-
ASTM
BS
CML
NPRA
TMH
-
Issued by the American Association for State Highway Of
ficials
Issued by the American Society for Testing and Materials
British Standard
Central Materials Laboratory (Ministry of Works),
Norwegian Public Roads Administration
Technical Methods for Highways (South African series of
standards)
Prime (Sprayed on granular layers)
Problem soils
Expansive soils
Dispersive soils
Saline soils/water
Subbase
Subgrade
Improved subgrade layers
In-situ subgrade and fill
S15
CBR > 15%
S7
CBR > 7%
S3
CBR > 3%
Surfacing
Binder course, bituminous hot mix
Gravel wearing course
Surface treatments
Wearing course, bituminous hot mix
Tack coat (Sprayed on bituminous layers)
Traffic
Design period
E80 - Equivalent standard axle (8160 kg)
Heavy vehicles:
> 3t un-laden weight
Very heavy goods vehicles: 4 or more axles
Heavy goods vehicles:
3 axles
Medium goods vehicles: 2 axles
Buses:
> 40 seats
Light vehicles:
< 3t un-laden weight
VEF Vehicle equivalency factor (the number of E80 per
heavy vehicle)
Unfavourable subgrade conditions
Cavities, termites, rodents
High water table and swamps
Wells
Wet spots
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Pavement Details
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Table of Contents
1
2
3
4
5
6
INTRODUCTION...........................................................................................................................................................3
1.1 Background, purpose and scope .............................................................................................................................3
1.2 Structure of the Field Testing Manual 2003 ...........................................................................................................4
1.3 Layout.....................................................................................................................................................................4
GEOTECHNIQUE .........................................................................................................................................................7
2.1 Planning of investigations - methodology..............................................................................................................7
2.2 Ground investigations.............................................................................................................................................9
2.3 Soundings ............................................................................................................................................................12
2.4 Borings .................................................................................................................................................................13
2.5 Sampling ..............................................................................................................................................................15
2.6 Handling, transport and storage of samples .........................................................................................................19
2.7 Recording ............................................................................................................................................................19
2.8 Geotechnical test methods....................................................................................................................................20
PAVEMENT EVALUATION .......................................................................................................................................39
3.1 Pavement distress .................................................................................................................................................39
3.2 Methodology ........................................................................................................................................................42
3.3 Detailed condition surveys .................................................................................................................................. 45
3.4 Pavement strength – structural surveys ............................................................................................................... 49
3.5 Test pit profiling and sampling ............................................................................................................................52
3.6 Homogenous sections...........................................................................................................................................55
AXLE LOAD SURVEYS..............................................................................................................................................58
4.1 Introduction ..........................................................................................................................................................58
4.2 Resources for axle load surveys ...........................................................................................................................58
4.3 Condition of survey sites......................................................................................................................................59
4.4 Weighing...............................................................................................................................................................62
4.5 Recording and reporting .......................................................................................................................................64
MATERIAL PROSPECTING AND ALIGNMENT SURVEYS...............................................................................71
5.1 Introduction ..........................................................................................................................................................71
5.2 Methodology ........................................................................................................................................................71
5.3 Alignment soil surveys.........................................................................................................................................77
5.4 Soils and gravel sources .......................................................................................................................................80
5.5 Rock Sources ........................................................................................................................................................83
CONSTRUCTION CONTROL...................................................................................................................................89
6.1 Introduction ..........................................................................................................................................................89
6.2 Earthworks and unbound layers ...........................................................................................................................89
6.3 Cemented Layers ..................................................................................................................................................94
6.4 Bituminous Layers ...............................................................................................................................................95
6.5 Bituminous Seals..................................................................................................................................................98
6.6 Concrete..............................................................................................................................................................101
6.7 Construction control test methods......................................................................................................................104
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Appendix 1:
Appendix 2:
Appendix 3:
Appendix 4:
Appendix 5:
Appendix 6:
Appendix 7:
Appendix 8:
CML laboratory and field test methods ..............................................................................................................121
Soil profiling descriptions after Brinks and Jennings.........................................................................................123
CUSUM method for delineation of homogenous sections.................................................................................124
The MERLIN method for measuring roughness. ...............................................................................................125
Layout of survey sites and traffic safity measures..............................................................................................128
Design Traffic Loading - example......................................................................................................................129
Definitions, terms, prefixes and basic units ........................................................................................................131
Abbreviations .....................................................................................................................................................135
Appendix 9: Worksheets .........................................................................................................................................................138
LIST OF TABLES
Table 2.1: Samples of soils or rock using various methods of sampling. Expected classifications. .....................................18
Table 3.1: Typical types of distress associated with pavement performance. .......................................................................39
Table 3.2: Possible causes of traffic-associated distress........................................................................................................41
Table 3.3: Possible causes of non-traffic-associated distress. ...............................................................................................41
Table 3.4: Minimum required test frequencies for pavement evaluation. ............................................................................44
Table 3.5: Data obtained in the detailed conditions survey. ..................................................................................................45
Table 3.6: Condition rating, visual evaluation. .....................................................................................................................46
Table 3.7: Condition rating, rut depth measurements. ..........................................................................................................47
Table 3.8: Condition rating, roughness measurements..........................................................................................................48
Table 3.9: Condition rating, maximum surface deflection, Benkelman Beam......................................................................52
Table 4.1: Heavy vehicle categories......................................................................................................................................62
Table 4.2
Traffic load distribution between lanes. ...............................................................................................................66
Table 4.3
Traffic Load Classes - TLC ..................................................................................................................................74
Table 5.1: Required size of sample. ......................................................................................................................................76
Table 5.2: Design depth measured from finished road level. ...............................................................................................78
Table 5.3: Sampling frequency. .............................................................................................................................................79
Table 5.4: Borrow pit investigations, minimum test frequency.............................................................................................82
Table 6.1: Methods and purposes of the field testing activities.............................................................................................90
Table 6.2: Sampling Frequencies, earthworks and layerwork. .............................................................................................90
Table 6.3: Density test methods. Inherent weakness of method and common operator errors. ............................................92
Table 6.4: Testing frequencies, field density for earthworks and layerwork.........................................................................93
Table 6.5: Test methods for moisture content. Features of each method ..............................................................................93
Table 6.6: Sampling frequencies for bituminous materials. ..................................................................................................95
Table 6.7: Testing frequencies for field density testing of bituminous materials..................................................................96
Table 6.8: Sampling frequencies for bituminous seals........................................................................................................100
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LIST OF FIGURES
Figure
Pavement Details ...................................................................................................................................................vi
Figure 2.1: Example of areas influencing the works at a far distance from the site. ..............................................................10
Figure 2.2: Principle of vane testing. ......................................................................................................................................26
Figure 2.3: U100 (U4) core sampler assembly. ......................................................................................................................30
Figure 3.1: Sequence of pavement evaluation leading to rehabilitation design......................................................................43
Figure 3.2: Rebound deflection measurements using Benkelman Beam................................................................................51
Figure 3.3: Assessing data for determination of homogenous sections..................................................................................55
Figure 4.1: Sources of error at the weighing site – surface gradient. .....................................................................................60
Figure 4.2: Sources of error at the weighing site – surface evenness. ....................................................................................60
Figure 4.3: Sources of error at the weighing site – surface evenness by the scale. ................................................................61
Figure 4.4: Sources of error at the weighing site – surface evenness, consequences. ............................................................61
Figure 4.5: System for recording axle configurations.............................................................................................................64
Figure 5.1: Use of information from field surveys in pavement design. ................................................................................72
Figure 5.2: Principle of required quantity for material prospecting vs. theoretical quantity from the project drawings .......72
Figure 5.3: Minimum sample size of soils as a function of particle size................................................................................74
Figure 5.4: Method of sampling from trial pit.. ......................................................................................................................75
Figure 5.5: Reducing the sample size by quartering...............................................................................................................75
Figure 5.6: An example of good labelling. .............................................................................................................................76
Figure 5.7: Examples, longitudinal profile. Information from trial pits. ................................................................................78
Figure 5.8: Theoretical material volumes - without loss - in natural, loose and compacted states. ......................................81
Figure 5.9: Typical ‘loss’ of available material volumes during the process of winning natural gravel
for pavement layers. .............................................................................................................................................82
Figure 5.10: Core box before placing wooden rods for marking core loss...............................................................................86
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1
INTRODUCTION
1
Introduction
2
Geotechnique
3
Pavement evaluation
4
Axle load surveys
5
Material prospecting and
alignment surveys
6
Construction control
Appendices
Chapter 1: Table of Contents
1.1 Background, purpose and scope .......................................................... 2
1.2 Structure of the Field Testing Manual - 2003 ..................................... 3
1.3 Layout .................................................................................................... 3
2
Chapter 1
Introduction
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1
INTRODUCTION
1.1
Background, purpose and scope
The Field Testing Manual - 2003 forms part of the development of Tanzanian
Standards, Specifications and Guidelines for roads, that Ministry of Works and
Tanroads are conducting under the programme for institutional cooperation with
the Norwegian Public Roads Administration. The following documents have
already been prepared and were launched under endorsement by the Ministry of
Works:
► Pavement and Materials Design Manual - 1999
► Laboratory Testing Manual - 2000
► Standard Specifications for Road Works - 2000
It is vitally important that the documents are firmly based on the same platform
regarding methods of testing, interpretation of results and application in the process for planning, design, construction and maintenance of roads. An important
part of this process is the work being carried out in the field, to form the basis
for road design, quality control and methods applied during construction and
maintenance.
The Field Testing Manual - 2003 serves the purpose of setting standards for
field investigations and field testing, and is a reference book providing advice
for engineers and technicians involved in such work. The Manual is prepared
with links to the above documents in respect of method and minimum requirements for investigations and data collection. This includes investigations for
new projects as well as evaluation of existing roads with the purpose of utilising
the pavement structure in rehabilitation and upgrading of the road. Appropriate
standards of workmanship in road construction and maintenance, as described
in the above documents, is reflected in the Field Testing Manual - 2003 in descriptions of appropriate construction quality control.
The Manual is prepared with emphasis on being a practical handbook that
provides appropriate cost effective investigations of sufficient accuracy for the
purpose.
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Chapter 1
Introduction
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1.2
Structure of the Field Testing
Manual - 2003
The Field Testing Manual – 2003 is divided into its major chapters according to
the purpose of collecting the information in the field, i.e.:
1 Introduction:
Purpose: Introduction to the Manual with backgraound and purpose and
scope.
2 Geotechnique:
Purpose: Investigations related to stability of foundations for e.g. bridges
and other structures, stability of embankments and cuttings.
3 Pavement evaluation:
Purpose: Assessment of the condition of existing pavements, to form
basis for optimal design of rehabilitation measures.
4 Axle load surveys:
Purpose: Assessment of existing traffic loading to form the basis for
projection of future traffic loading for the purpose of pavement
design and design of rehabilitation measures.
5 Material prospecting and alignment surveys:
Purpose: Pavement design of new roads and supply of construction
materials for both new road construction and rehabilitation.
6 Construction control:
Purpose: Quality Control during construction.
1.3 Layout
Parts of the Manual are printed with the same layout as the method sheets of the
Laboratory Testing Manual - 2000. This is considered a superior layout where
a number of standardised methods are being described, but is not ideal way of
presenting large amounts of informative text. A mixed layout has therefore been
chosen for the Field Testing Manual - 2003 in order to make a user friendly
format and to capture the best of both layouts. Wherever practical, the method
sheet layout has been applied due to its more concise format.
4
Chapter 1
Introduction
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2 GEOTECHNIQUE
1
Introduction
2
Geotechnique
3
Pavement evaluation
4
Axle load surveys
5
alignment surveys
6
Appendices
2.1
Planning of investigations - methodology....................................... 7
2.1.1 General ................................................................................... 7
2.1.2 Objectives............................................................................... 7
2.1.3 Type, extent and stages of site investigations ........................ 7
2.1.4 Desk study.............................................................................. 8
2.1.5 Site reconnaissance ................................................................ 8
2.1.6 Detailed studies ...................................................................... 8
2.1.7 Construction and performance appraisal................................ 9
2.2
Ground investigations ...................................................................... 9
2.2.1 Purpose of ground investigations ........................................... 9
2.2.2 Project stages.......................................................................... 9
2.2.3 Requirements.......................................................................... 9
2.2.4 Procedures .............................................................................. 9
2.2.5 Types of ground investigations ............................................ 10
2.2.6 Extent of ground investigations ........................................... 10
2.2.7 Choice of methods for ground investigation........................ 11
2.2.8 Personnel .............................................................................. 11
2.3
Soundings ........................................................................................ 12
2.3.1 General ................................................................................. 12
2.3.2 Static soundings ................................................................... 12
2.3.3 Sounding tests in boreholes.................................................. 12
2.3.4 Dynamic soundings.............................................................. 12
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Chapter 2
Geotechnique
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2.4
2.5
2.6
Handling, transport and storage of samples ................................ 19
2.7
Recording ........................................................................................ 19
2.7.1 Field recording ..................................................................... 19
2.7.2 Reporting.............................................................................. 19
Geotechnical test methods ............................................................. 20
2.8
6
Chapter 2
Geotechnique
Borings............................................................................................. 13
2.4.1 General ................................................................................. 13
2.4.2 Boring methods .................................................................... 13
Sampling .......................................................................................... 15
2.5.1 Sampling techniques ............................................................ 15
2.5.2 Sample disturbance classes .................................................. 15
2.5.3 Disturbed samples ................................................................ 16
2.5.4 Un-disturbed samples........................................................... 17
2.5.5 Choice of sample method depending on soil conditions...... 17
2.5.6 Field classification and sample size ..................................... 18
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2
GEOTECHNIQUE
2.1
Planning of investigations methodology
2.1.1
General
It is now common to use the term site investigation in a wide sense, considering
not only the sampling or exploration of the ground, but the complete aspect of
investigations to assess the suitability of a site for executing civil works.
Geotechnical ground investigation covers a series of investigation types from
engineering geological mapping by various means to detailed boring and sampling for laboratory testing or in situ testing of soil/rock engineering properties.
The extent and method of investigation should first be decided based on the
technical requirements of the project, as established through the initial evaluation stages. This initial phase may include a preliminary ground investigation.
Ground investigation specialists should be consulted at this stage.
The investigation programme thus planned by the specialist may be changed to
utilize the available resources. However, the Client must be made aware of any
particular aspects of the project which may not be properly investigated due to
lack of resources, either financial or technical, so that this may be properly accounted for in the design and subsequent construction of the works.
2.1.2
Objectives
The primary objective of most site investigations is to secure sufficient information to enable a safe and economical design to be made. Thereby the construction can proceed without any difficulties and in-service performance or safety is
not adversely affected.
An important objective of site investigations is to determine the effect of
changes to the surroundings that will incur as a consequence of implementing
the project. E.g. the construction of high embankments may affect large areas
beyond the project location.
2.1.3
Type, extent and stages of site investigations
Type and extent
The type and extent of site investigation depends on:
● Proposed works.
● Conditions of the site.
● Project stage.
● Available resources.
By proceding in stages the investigation can always seek to verify and expand
information collected previously.
Procedure
The general investigation procedure is proceeding in stages:
1. Desk study.
2. Site reconnaissance.
3. Detailed study for design, including ground investigations.
By proceding in stages the investigation can
always seek to verify and expand information
collected previously.
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Chapter 2
Geotechnique
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During and after construction, the investigations may continue:
4. Follow up during construction.
5. Post-construction appraisal/performance evaluation.
2.1.4
Desk study
The objectives of the desk study are:
● Τo collect all existing information regarding the proposed works and the
conditions of the site.
● Τo learn as much as possible from previous experience and studies, and
about adjacent property that may be affected by the works. This includes
a study of the previous use of the site and of previous projects in the area,
their design, construction and performance.
The desk study should also obtain information regarding existing services etc.
that must be considered for the project and when conducting the actual ground
investigations. The following information may be required:
● Land survey, i.e. maps, aerial photographs, ownership, present use, existing
structures.
● Permitted use and restrictions, i.e. land acquisitions, general and local regulations and rights of way.
● Approaches and access.
● Climate, i.e. temperature, rainfall, seasons etc.
● Ground conditions, i.e. geology, soil and vegetation, maps and reports and
hydrogeology.
● Sources of material for construction, e.g. existing borrow pits.
● Services, i.e. drainage, water, electricity, telephone.
2.1.5
Site reconnaissance
The site or project area should be inspected thoroughly, preferably by foot. The
objective of such a reconnaissance is to gather as much information as possible,
by observation of the ground and geological features and the performance of
any existing constructions. A note of local practices and resources is important.
Vegetation, river courses, erosion gullies, existing borrows and cuttings can
reveal important information, such as signs of swell or collapse, settlement and
cracks, in existing structures. Vehicles and even light aircraft may be appropriate in the case of large project areas.
Site reconnaissance prior to ground investigations is of paramount importance.
2.1.6
Detailed studies
This investigation stage includes the ground- and materials investigations proper, and other investigations that may be appropriate, like a topographical survey.
In the case of a dam or a bridge for example, the question of possible flooding,
erosion or changes to the surroundings may require hydrological and other
environmental studies. The kind of detailed information required for design and
construction is as follows:
Detailed Land survey
● Aerial photography.
● Ground conditions.
● Hydrogeology and hydrography.
● Climate.
● Sources of materials for construction.
● Disposal of waste and surplus materials.
● Adjacent properties and services.
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Chapter 2
Geotechnique
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2.1.7
Construction and performance appraisal
This stage is primarily to ensure that the design is adjusted as required if the
conditions revealed by the construction differ from the results and assumptions
of the pre-construction investigations.
2.2
Ground investigations
2.2.1
Purpose of ground investigations
Site and ground investigations of several types may be required in a road construction project:
● Sites for new works.
● Defects or failures of existing works.
● Safety of existing works or structures.
● Materials for constructional purposes.
2.2.2
Project stages
Engineering construction projects are usually carried out through different
stages, normally identified as:
● Feasibility study and preliminary design.
● Detailed design.
● Construction stage.
The various planning stages are most distinct in major projects. The contractor
or builder may be engaged at an early stage and thus take part in the final design
or more commonly come in after the final design.
2.2.3
Requirements
To meet the primary objectives of the site investigation, the ground investigation should generally satisfy the following basic requirements:
● Clarify the geology of the site.
● Establish the soil and rock profile.
● Establish the ground water profile.
● Establish the engineering properties of the ground.
● Cover all ground which may be permanently or temporarily changed by the
project.
There may also be other requirements particular to each project, and the basic
requirements must be detailed.
2.2.4
Procedures
The general procedures for ground investigations are as follows, based on the
results of the desk study, site reconnaissance and an evaluation of the project
type and stage:
1. Define the objective of the investigation.
2. Decide the extent of the investigation.
3. Decide the method of investigation.
4. Carry out field and laboratory work, possibly by stages.
5. Reinstate all pits etc. by carefully backfilled, and any pits that have to be
left open and unattended should be fenced off or properly secured with
other appropriate methods.
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The results should be continuously evaluated
to see if the objectives are met, and plans and
methods should be corrected if necessary.
Chapter 2
Geotechnique
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Laboratory testing forms a considerable part of the total cost of investigation
and the laboratory test programme shall therefore be devised by the engineer responsibility for the overall execution of the project including the financial side.
The extent of investigation conducted at the various planning stages may vary
widely. Some feasibility studies may not require a detailed ground investigation
at all, if all the necessary information is available from the desk study and site
reconnaissance.
2.2.5
Types of ground investigations
The type of ground investigations and the methods used will of course vary
widely from case to case. The different methods of ground investigation are as
follows:
● Trial pits, shafts and headings.
● Soundings, borings. Tests in boreholes.
● Other in situ or field tests.
● Sampling, laboratory tests.
● Geophysical methods.
● Remote sensing.
The method of investigation to be used is decided by the:
● Character of the ground.
● Technical requirements.
● Character of the site.
● Availability of equipment and personnel.
● Cost.
Drill rig in position on site.
2.2.6
Extent of ground investigations
General
The extent of investigations required, will vary from case to case depending on
the project type and stage, the ground conditions and previous knowledge about
the conditions. It is important that an experienced engineer carries out a field
assessment to locate areas affected by the works that are not obvious at first
sight. An example of such a situation is illustrated in Figure 2.1. Some general
guidelines are given below.
Mass influencing the works
Mass influenced by
the works
Figure 2.1: Example of areas influencing the works at a far distance from the site.
10
Chapter 2
Geotechnique
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Location
The exploration points pits or boreholes should be located such that the general
conditions of the site are established, at the same time ensuring that sufficient
detailed information is obtained. Consequently, the greater the ground variations
the greater the number of exploration points required. For ordinary structures a
grid pattern of spacing 10 to 30 metres is often used. Minor structures covering
a small area should be investigated in a minimum of three points.
The exploration points, borings or pits should be positioned so as not to interfere with the proposed construction by disturbing the ground at the foundation
level or by opening up for water from deep aquifers.
Depth of investigation
The general rule is to investigate to the depth which may be affected by the
works
For foundations of structures, the stressed depth is normally one and a half
times the loaded area, measured below the base of the foundation. In the case of
light structures the project may influence the ground moisture regime, causing
swell or collapse to greater depths. It is therefore always desirable to determine
the total thickness of deposits of such soils.
For pile foundations simple rules cannot be given. The investigation depth has
to be decided and revised on the basis of results of the investigations in each
individual case. Sufficient capacity to carry the pile loads has to be proven, and
investigations for pile foundations may include test piling and load testing.
Investigation of ground water level by
simple methods.
Embankments should be investigated to a depth sufficient to check possible
shear failures through the foundation strata, evaluate settlements and, in the case
of dams, check seepage conditions. Cuts and excavations should be investigated
to a depth sufficient to evaluate the deformation and stability conditions, giving
due regards to ground water and any soft strata.
2.2.7
Choice of methods for ground investigation
The following issues should be taken into consideration in the choice of method
for ground investigations:
● Project requirements.
● ground conditions.
● project budget.
● available time, equipment and personnel resources.
When evaluating alternative ground investigation methods the logistics of
operating in the local environment is important, such as access to water for drilling. E.g. both core drilling and cable percussion methods require water, whereas
augers don’t.
2.2.8
Personnel
Ground investigations should be planned and directed by a senior engineer or
geologist also responsible for assessing and interpreting the results. The supervision of field work may be delegated to qualified engineers or geologists assisted
by trained senior field technicians or drilling supervisors. This personnel should
be conversant with field description and classification of soils and rock and the
investigation methods used.
Borehole/test pits logging and field material descriptions are normally the responsibility of the driller/technician and should be checked by the field supervisor.
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2.3
Soundings
2.3.1
General
The sounding tests are purely empirical. They are simple to perform and have
been in use for many years. Consequently there is a wealth of experience,
data and correlations from all parts of the world, linking the test results to soil
parameters and performance of structures, to ensure a reasonably confident
interpretation of the results.
Soundings from the surface without sampling and without pre-boring, may be
carried out by several means; and consists in its simplest form of the driving
of a steel rod into the ground until hard stratum is located. However, standard
procedures have been developed to enable the systematic recording of relative
resistance of various soil layers and the accumulation of empirical relationships
between sounding resistance and soil engineering characteristics. Such methods are:
● Dynamic soundings.
● Static soundings.
● Weight- and Rotary soundings.
Both static and rotary sounding systems with electronic or hydraulic recording
of the resistance to penetration have lately been developed.
2.3.2
Static soundings
Static soundings or cone penetration tests (CPT) of several types are in wide
spread use. The tests are known by a number of terms depending on manufacturer etc., for example Dutch cone testing. The basic principle of all such tests
is that a rod is pushed into the ground and the resistance on the point and/or the
shaft is measured by various means. The equipment is either anchored to the
ground by screws and/or employ heavy dead weights/drill rigs to give the necessary reaction forces for the penetration.
2.3.3
Sounding tests in boreholes
Borehole tests are of several kinds and varies from the determination of resistance to penetration (SPT or CPT) to direct measurement of shear strength of
clays. Some soundings normally carried out without the use of independent
boreholes, may also be performed from the bottom of boreholes.
2.3.4
Dynamic soundings
The main use of all direct dynamic soundings i.e. soundings not requiring boreholes, is to give a rapid and cheap test of relative conditions within a site or to
compare different sites.
The simple method of driving a steel rod into the soil until it meets resistance is
only useful for determining the depth to a hard stratum like rock or calcrete/hard
laterite, under a relatively shallow layer of softer soil. The most widely used
dynamic sounding test is the Standard Penetration Tests (SPT). The sample
obtained in SPT is used for soil identification.
Simple soundings may give a relative measure of the hardness of the ground
provided the penetration depth per hammer blow or within a certain time when
using the percussion drill, is recorded. The resistance to penetration depends on
the soil type, and experienced drillers may be able to distinguish cohesive and
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frictional materials by the feel and sound of the drill steel. The dynamic sounding method has limited penetration in firm ground and are not suitable for use in
coarse soils or soils containing rock fragments etc.
Standardisation of the sounding procedure and equipment; the drill steel rods
and point, the hammer weight, drop height and blow rate etc., has increased the
use of dynamic soundings to give a better indication of the type of soil present
and to determine the bearing capacity of the ground by empirical means in the
case of sands and gravels (frictional soils), particularly for the design of piles.
2.4
Borings
2.4.1
General
Borings are required for sampling the ground or to provide a hole in which to
conduct tests of the in-situ properties. The type of boring to be used depends on
the purpose and the ground conditions. The most important ground parameters
affecting the boring operations are:
● The self supporting ability of the ground.
● The content of larger particle size, cobbles etc.
In general cohesive soils are self supporting, so are some cemented sands and
silts, whereas granular materials below the ground water level are unstable.
The borehole sides may be supported by inserting linings of steel casing, or
by filling the borehole with a head of water or heavy liquids like a bentonite
suspension called mud or slurry. The worst ground conditions to drill through
are layers of boulders.
2.4.2
Boring methods
Borings may be carried out by various methods:
● Auger borings. By hand or mechanical.
● Percussion boring. Cable rig.
● Rotary drilling. Core drilling.
● Wash borings.
● Other methods.
Auger borings
Auger borings may either be conducted by hand or by mechanical means, and
there are various types in use.
Hand augers are used in self supporting ground without large gravels or cobbles,
down to a depth of 2 to 5 metres. Disturbed samples may be obtained and open
tube samplers may be used from the bottom of the hole. Small portable power
augers may drill to depths exceeding 10 metres and casings may be used if
necessary.
Disturbed samples may be obtained by lifting the auger out of the ground or by
spinning the material up in case of the continuous flight auger. Auger borings
are mainly used in cohesive (self supporting) soil. Casings may be inserted in
cohesionless soil.
Some augers have a hollow stem, permitting the use of a drive sampler through
the stem. This type of auger acts as a casing of internal diameter 75 to 150 mm
and may also be used for deep drilling below the water table.
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Two types of Auger.
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A disadvantage with samples from mechanical augers is that the material
brought up becomes mixed, layering is thus difficult to detect and so is the
transition to rock particularly in the case of soft, weathered rocks so common in
Tanzania. The basement gneisses for example will often appear as a sand.
Percussion borings
Percussion borings loosens the ground with a drop chisel. The spoils are mixed
with water and lifted out of the hole by a shell or baler.
The shell may be used as a boring tool in loose granular materials below the
ground water level. Other tools used are a clay cutter.
The clay cutter and shell bring up disturbed material that are sufficiently representative to identify the strata. Samples may also be taken from the bottom of
the hole. However, some of the percussion boring procedures, such as adding
water to a dry hole in clay or working with a water level other than the ground
water level, may not be acceptable from a soil exploration point of view.
There is usually some disturbance of the soil below the bottom of the borehole,
from which samples are taken, and it is very difficult to detect thin layers of soil
and minor geological features with this method. Percussion boring can be employed in most types of soil, including those containing cobbles and boulders.
The rig for percussion boring is very versatile and can normally be fitted with a
hydraulic power unit and attachments for mechanical augering, rotary core drilling and cone penetration testing.
Rotary drilling
Rotary drilling is the traditional drilling method for investigations of rock, but
the method is also used in soils. It is particularly useful in the kind of layered
hard/soft strata typical for the regions of volcanic rocks, tuff and ashes.
There are two forms of rotary drilling, open hole drilling and core drilling. Open
hole drilling, which is generally used in soils and weak rock, uses a cutting bit
to break down all the material within the diameter of the hole. Water or mud is
used to flush out the material. Open hole drilling can only be used as a means of
advancing the hole, the drilling rods can then be removed to allow tube samples
to be taken or in situ tests to be carried out. In core drilling, which is used in
rocks and hard clays, the bit cuts an annular hole in the material and an intact
core enters the barrel, to be removed as a sample. However, the natural water
content of the material is liable to be increased due to contact with the drilling
fluid. Typical core diameters are 41 mm, 54 mm and 76 mm, but can range up to
165 mm. The larger diameters are used in difficult rock.
The advantage of rotary drilling in soils is that progress is much faster than with
other investigation methods and disturbance of the soil below the borehole is
slight. The method is not suitable if the soil contains a high percentage of gravel
(or larger) particles as they tend to rotate beneath the bit and are not broken up.
A core size of 76 mm is usually satisfactory,
but 100 to 150 mm and the triple barrel
technique gives the best results in weak,
watered or fractured rock.
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Rock core samplers
Rotary core samples are obtained by the core drilling method, mainly used for
sampling of rock. Sampling is done by double or triple tube core barrels. As
for soil, greater diameter gives better samples. A core size of 76 mm is usually
satisfactory, but 100 to 150 mm and the triple barrel technique gives the best
results in weak, watered or fractured rock.
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Wash boring
Wash borings break up the ground by the percussive action of a chisel in combination with the erosive force of water being jetted out through narrow holes in
the chisel. The water also washes the soil particles to the surface.
Wash boring is mostly used in sand and finer soils. Casing or drilling mud is
used in collapsing ground. The method cannot be used to obtain soil samples as
the soil brought to the surface is not representative of the strata being worked.
However, this boring technique causes no or little disturbance to the soil immediately below the bottom of the hole, enabling tube samples to be taken or in
situ tests like the SPT to be carried out. The method is also used to determine
the depth to rock below fine grained soils.
2.5
Sampling
2.5.1
Sampling techniques
There are four main techniques for sampling the ground:
● Taking disturbed samples from the drill tools or from excavating equipment
in the course of boring or excavation.
● Drive sampling, in which a tube or split tube sampler having a sharp cutting
edge at its lower end is forced into the ground either by a static thrust or by
dynamic impact.
● Rotary sampling, in which a tube with a cutter at its lower end is rotated
into the ground, thereby producing a core sample.
● Taking block samples specially cut by hand from a trial pit, shaft or heading.
The principal types of tube samplers are:
● Open tube samplers
● Stationary piston samplers
● Continuous sampler
● Compressed air sampler
● Rotary core sampler
2.5.2
Sample disturbance classes
There are five disturbance classes for samples depending on the degree to which
they have been disturbed by the process of sampling, handling and transport
until finally laboratory testing:
Class 1 Classification, moisture content, density, strength, deformation
and consolidation characteristics.
Class 2 Classification, moisture content, density.
Class 3 Classification, moisture content.
Class 4 Classification.
Class 5 None – sequence of strata only.
Within the five classes there are two main categories for practically denoting the
samples:
● Disturbed samples.
● Undisturbed samples.
Class 1
Class 1 samples for precise determination of strength and deformation characteristics may be impossible to obtain in sensitive cohesive soils, and of non-cohesive soils from below the water table.
Residual soils represent a particular problem for Class 1 sampling as they tend
to swell during sampling, often resulting in permanent damage to the soil strucCentral Materials Laboratory (CML)
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ture. This swell is due to lack of internal suction in partly saturated soils, and
even in the case of saturated soils, an open structure with large voids will not be
able to maintain suction without volumetric expansion and desaturation.
Class 2
Class 2 is taking of disturbed samples with additional requirements to obtain
field/bulk density of the soils. Determination of the field density may be executed by:
● Block sampling.
● Core cutter method (shoe cutter).
● Split spoon sampler.
Classes 3 to 5
Classes 3 to 5 are the commonly called disturbed samples. Apart from the actual
sampling, the quality also depends on how the sample is sealed, transported,
stored, and treated in the laboratory. The most important consideration is to
observe that class 3 requres sealed packaging for measuring moisture content in
the laboratory.
2.5.3
Disturbed samples
Objectives
Disturbed samples, which are used mainly for soil classification tests, visual
classification and compaction tests. Disturbed samples have the following features:
● Τhe same particle size distribution (grading) as the in-situ soil.
● Τhe soil structure has been significantly damaged.
● Τhe water content may be different from that of the in-situ soil.
Safety precautions must be observed, esecially
sloping or supporting of the sides of deep pits before personnel are allowed to enter trial pits. Sampling and inspection should be done immediately
upon excavation of unsupported pits.
Sampling methods
Disturbed samples can be excavated from trial pits or obtained from the tools
used to advance boreholes (e.g. from augers and the clay cutter) and from the
sampler of the SPT tests. The soil recovered from the shell in percussion boring
is deficient in fines and is therefore unsuitable for use as a disturbed sample.
Trial pits, shafts and headings supply the most detailed and reliable data on the
soil in-situ conditions, enabling visual examination of strata boundaries and soil
fabric.
Trial pits
Trial pits may be dug by hand or a light mechanical excavator in all soil types
above the ground water level. Excavation below the ground water level in
permeable soils will require dewatering, and the safe excavation depth is very
limited.
Shafts and headings
Shafts are deep pits, normally hand excavated and supported by timbering or
bored by piling rigs. Headings or edits are inspection galleries excavated laterally into the side of a shaft or from the surface of a steep hill. Both roof and
sides are supported.
Shafts and headings are not excavated below the ground water level of permeable ground. Because of the expense, they are normally only used for very large
and costly structures; dams, tunnelling projects etc. Headings are frequently
used for the investigation of rock or soil/rock in the case of dam abutments.
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2.5.4
Un-disturbed samples
Objectives
Undisturbed samples are required to determine the strength and volume stability
characteristics of the soil. Undisturbed samples must preserve both the in-situ
structure and water content of the soil.
Sampling methods
Undisturbed samples can be cut by hand from trial pits or obtained by special
samplers, refer sample techniques b), c) and d) above. However, the quality of
such samples can vary considerably, depending on the sampler, the sampling
technique used and the ground conditions.
The highest quality samples are obtained by block
sampling.
Open tube samplers. U4 core sampling
U4, i.e. general purpose 100 mm diameter sampler, is used in all cohesive soils
and weak rock. A sample catcher or core-catcher is used to aid the recovery of
silty or sandy soil which tend to fall out upon withdrawal of the sampler.
The U4 sampler may either be forced down in one continuous movement or
be hammered down. When forced down, samples of non-sensitive, fine cohesive soils of stiff or lower consistency may give Class 1 samples (highest class
undisturbed). However, the normal quality is Class 2 or even lower if hammered
into hard ground.
Open tube samplers other than U4
Other open tube samplers of varying diameters, but of the same general working
principle as the U4 type are also in use. Special thin walled samplers have been
developed to improve the sample quality, but piston samplers are preferable.
Piston samplers
The standard 54 mm sampler (Geonor type) is designed to be driven down to
undisturbed soil well below the bottom of the borehole, where the thin walled
cylinder is pressed down in one continuous movement. The sampler is used in
silt and clay and will give Class 1 samples in soft to medium ground.
U4 core sample.
42 mm penetration sampler for use with dynamic sounding equipment of the
percussion drill type, may give Class 3 samples for classification and natural
moisture content.
Other piston samplers of sample diameter up to 100 mm or greater may be used
in special cases, for example to obtain samples of research quality.
2.5.5
Choice of sample method depending on soil conditions
Table 2.1 indicates which methods for ground investigations are suitable for
different types of soil conditions, and the class of disturbance to the sample that
can be expected for each method
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Table 2.1: Samples of soils or rock using various methods of sampling. Expected classifications.
Soil type, rock
Non-cohesive soils
containing boulders,
cobbles or gravels
Samplers, tests
• Pit is desirable.
Classification, comments
• Percussion rigs with shell and chisel,
with casing to support the borehole sides
• CPT tests are preferable to SPT below GWL.
• Test pits or augers are useful, with casing or
hollow stem below GWL.
Sand
Silt
Hard, weathered tropical,
or over-consolidated clay
• Piston samplers or U4 tubes with core catcher.
Thin walled piston sampler
U4 tubes without core catcher
Vane test
CPT tests are preferable to SPT.
Augers or cable percussion methods can be used.
U4 tubes
Sample pit, cut block sampling
Core drilling equipment
Soft clay
Augers or cable percussion methods can be used.
U4 tubes
Vane test or CPT
Clays with gravel, cobbles
Test pit is preferable.
or boulders
Normally core drilling equipment is used.
Rock
Cable percussion methods, sampled using U4
tubes with reinforced cutting shoe.
• Class 5 disturbed sample only
• Penetration tests are of imited use in
ground with boulders and cobbles, but are
useful in gravel and sand
Class 2 sample
Class 3 sample
Un-drained shear strength of clayey silt
Below GWL
Class 1 to 2
Class 1 to 3
Well suited
In very stiff materials (sample is affected by
drilling water).
Class 1
Class 2
In-situ shear strength.
In weak and weathered rocks, tuffs etc
2.5.6
Field classification and sample size
Classification of samples in the field should follow the method after Brinks and
Jennings as described in Appendix 2.
Determination of the field density as part of the classification may be executed
by:
● Block sampling.
● Core cutter method (shoe cutter).
● Split spoon sampler.
The required size of sample for indicator and compaction tests in the laboratory
tests are given in Chapter 5.2.3 - Sampling for various types of soils. Minimum
sample sizes are specified in the Laboratory Testing Manual - 2000 for each
geotechnical laboratory test.
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2.6
Handling, transport and storage of
samples
Laboratory testing of samples shall be carried out as soon as possible after sampling. Any necessary storage and handling must be such that the quality of the
sample is not reduced or the class of disturbance of the sample is not changed
by the time they reach the laboratory. Undisturbed samples shall be cushioned
against jolting and vibrations, especially during transportation when there is a
great risk of such damage to the samples.
Purpose made box for storage and shipment
of core samples.
Loss of moisture from samples shall be prevented by appropriate means such as
use of waxing, rubber capping, plastic cling foil or other means as appropriate.
Special care should be taken if the samples have to be stored for an extended
period of time before testing.
2.7
Recording
2.7.1
Field recording
Sample description
Field sample description and classification is part of the sampling procedure and
shall be carried out as set out in Chapter 5 - Materials prospecting and alignment surveys.
The aims of field descriptions, in-situ testing and laboratory testing of samples
of soil and rock are:
1. To identify and classify the samples with a view to making use of past experience with materials of similar geological age, origin and condition; and
2. to obtain soil and rock parameters relevant to the technical objectives of the
investigation.
Recording
Proper field procedures include accurate setting out with reference to an identifiable permanent physical object which should also be shown on the plan drawing of the investigation. Normally, the ground level of test pits, bore holes etc.
should be determined.
All samples must be labelled with a unique sample identification including:
1. Project name.
2. Date.
3. Location and elevation of borehole.
4. Depth.
5. Method of sampling.
6. Description.
7. Remarks etc.
2.7.2
Reporting
General
All field work should be reported on standardised forms, which will also serve
as check lists for the personnel, to ensure that all relevant data for interpretation of the results are collected. A copy of the report should always follow the
samples to the laboratory.
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Soils and materials distribution maps
In most investigations, the preparation of special soils and materials maps is a
very powerful way to compile, analyse and present all site investigation data.
On maps one should combine on one map all known topographical and soils/
materials features, such as:
● General geology.
● Εxisting borrow pits.
● Κnown areas of clay.
● Rock outcrops etc.
The technique of compiling data on maps is particularly useful for feasibilityor preliminary studies, but will also aid the efficient planning and execution of
detailed ground investigations. Such maps are also very useful in locating the
optimal road alignment or position of a dam or bridge site.
2.8
Geotechnical test methods
Field Tests
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Chapter 2
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F2.01
Soundings
Cone penetration - CPT
BS1377: Part 9: 1990
BS5930: 1999
F2.02
Soundings
Standard penetration test - SPT and
continuous core penetration test - CCPT
BS1377: Part 9: 1990
BS5930: 1999
F2.03
Soundings
Vane test
BS1377: Part 9: 1990
BS5930: 1999
F2.04
Boring
U100 (U4) sampling, undisturbed samples
BS5930: 1999
F2.05
Ground water
Pore pressure, ground water level
BS5930: 1999
F2.06
Ground water
Permeability tests for soils and rocks
BS5930: 1999
F2.07
Ground water
Ground water sampling
BS5930: 1999
F2.08
In-situt strenght
Plate loading test
BS1377: Part 9: 1990
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Field investigations
2 Geotechnique
Central Materials Laboratory
Test Method no F 2.01
Soundings:
Cone Penetration Test - CPT
Objective
The uses of the CPT test have traditionally been to predict pile driving resistance,
skin friction and end bearing capacity of driven piles in non cohesive soils regardless of the groundwater conditions. The test with continuous resistance
recording is also commonly used to investigate clays. As with other probing
systems, the test only gives an indication of the soil type, and traditional boring
and sampling is required for a positive soil determination, using the CPT for
rapid interpolation between boreholes.
��
��
� ��
Description of method
��
The basic test procedure is to record the resistance when pushing the cone a
fixed distance into the ground ahead of the outer rods, and then to push the
outer rods down into contact with the point and further advancing the cone and
outer rods together to the next test depth. The resistance when advancing the
outer rods may also be recorded. The latest equipment registers the point resistance electrically by sensors inside the point, enabling the recording of a continuous resistance profile, including the pore water pressures. This type of equipment may detect very thin soil layers. The cone or penetrometer point is at the
end of a string of inner rods running inside hollow outer rods sleeve or shaft.
� � � ��
Without friction sleeve
Use of the CPT test is limited by the safe load that can be carried by the cone,
and the force available for pushing the penetrometer into the ground. Penetration will normally have to be terminated when dense sand or gravel, coarse
gravels, cobbles or rock is encountered. Going from soft ground directly into
rock or cobbles may break the point.
Cone penetration tests may also be conducted in boreholes.
References
● BS 1377 : Part 9 : 1990 gives details on test procedure for CPT.
● BS 5930 describes the procedure for a test variety called the Static
Dynamic Probing, combining the advantages of the CPT with the greater
penetration in firm ground of the dynamic penetration test.
��
Note that although the results of the CPT test may be analysed by soil mechanics theory, the correlations between cone resistance bearing capacity, settlement and shear strength are partly based on experience with certain soil types
and should thus be used with caution for other types of soil.
��
��
��
��
��
� ��
��
� � � ��
Witht friction sleeve
CPT test assembly.
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2 Geotechnique
Soundings:
Standard penetration test - SPT and
Continuous Cone Penetration Test - CCPT
Objective and description of method
No disturbance may be impossible to achieve in
granular soils below the ground water level, which
may be loosened by flow towards the borehole. In
such conditions, in-situ tests performed independently of a borehole should be considered, e.g.
the CPT test.
BS 1377 : Part 9 : 1990 denotes the CCPT test
SPT(C).
The standard penetration test (SPT) is a dynamic penetration test for determination of relative strength or relative density of soils and weathered rock, and
for taking samples for identification of soils in the ground. The test is carried out
using a thick-walled sample tube with an open ended point “split spoon or split
barrel sampler”. The outside diameter of the sampler is 50 mm. This is driven
into the ground at the bottom of the borehole by blows from a standard weight
falling through a standard distance. The blow count gives an indication of the
density of the ground. The small sample that is recovered will have suffered
some disturbance but can normally be used for identification purposes.
The basis of the test consists of dropping with a free fall a hammer of mass
63.5 kg on to a drive head from a height of 760 mm. The number of such blows
necessary to achieve a penetration of the split-barrel sampler of 300 mm,
following a 150 mm seating drive, is regarded as the penetration resistance (N).
The SPT test may be carried out with a solid cone point suitable for hard
ground. This test is denoted Continuous Cone Penetration Test (CCPT).
CCPT
SPT sampler.
The Continuous Cone Penetration Test (CCPT) is performed in gravel and
coarse soils and is conducted in the usual way as for SPT except that the
sampler is replaced by a solid steel cone of the same outside diameter, with a
60° apex cone. The continuation of this description refers to the SPT test.
Advantages and limitations
The test is sometimes carried out in boreholes
considerably larger in diameter than those used for
ground investigation work, e.g. in the construction
of bored piles. The result of the SPT is dependent
upon the diameter of the borehole. Tests should
not be regarded as SPT when performed in
boreholes with diameter larger than 150 mm.
Boreholes with reduced diameter shall continue
for min. 1m before SPT commences.
In conditions where the quality of the “undisturbed”
sample is suspect, e.g. very silty or very sandy
clays, or hard clays, it is often advantageous to
alternate the sampling with standard penetration
tests to check the strength.
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The SPT is probably the most widely used in-situ test in the world. The test
assumes a carefully cleaned out borehole, established by a method which will
not disturb the ground below the bottom of the hole.
Advantages
● Great merit of the test.
● Simple and inexpensive test.
● The soil strength parameters which can be inferred are approximate, but
may give a useful guide in ground conditions where it may not be possible
to obtain borehole samples of adequate quality, e.g. gravels, sands, silts,
clay containing sand or gravel and weak rock.
Limitations
● Samples are disturbed, thus the soil strength parameters which can be in
●
ferred are approximate.
When the test is carried out in granular soils below groundwater level, the
soil may become loosened.
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Apparatus
Boring equipment.
The boring equipment shall be capable of providing a clean hole before insertion
of the sampler and shall ensure that the penetration test can be performed in
relatively undisturbed soil. When wash boring, a side-discharge bit shall be used
and not a bottom-discharge bit. The process of jetting through an open tube sampler and then testing when the desired depth is reached shall not be permitted.
When boring in soil that will not allow a hole to remain stable, casing and/or
mud shall be used. The area that is exposed in the base of the borehole prior to
testing may influence the result and consequently the borehole diameter shall
always be reported.
� ��
��
��
� �� " ��
��
�� " ��
��
Drive rods
The rods used for driving the sampler assembly shall be tightly coupled by
screw joints and shall comply with BS 4019.
● Minimum stiffness, general:.............................. type AW drill rods
● Minimum stiffness, holes deeper than 20 m: .... type BW drill rods
● Maximum rod weight: ....................................... 10.0 kg/m
Only straight rods shall be used and, the relative deflections shall not be greater
than 1 in 1000 when measured over the whole length of each rod.
��
��
��
��
The sampler assembly shall have the shape and dimensions shown in the
figure to the left. The drive shoe and split barrel, both having a uniform bore of
the same diameter, shall be made of steel with a smooth surface externally and
internally. The drive shoe shall be made of hardened steel. It shall be replaced
when it becomes damaged or distorted to avoid the test result being affected.
The coupling shall contain a 25 mm nominal diameter ball check valve seated in
an orifice of not less than 22 mm nominal diameter which shall be located below
the venting. The ball and its seat shall be constructed and maintained to provide
a watertight seal when the sampler is withdrawn. Alternative designs of check
valves are permitted provided they give equal or better performance.
��
Split barrel sampler assembly
�
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Drive assembly
The drive assembly of an overall mass not exceeding 115 kg shall comprise the
following.
● A hammer made of steel and weighing 63.5 + 0.5 kg.
● A pick-up and release mechanism which shall ensure that the hammer has a
free fall of 760 + 20 mm, and shall not influence the acceleration and deceleration of the hammer or the rods. The velocity of the hammer shall be negligible when the hammer is released at its upper limit.
● A guide arrangement which shall permit the hammer to drop with minimal
resistance and to ensure the hammer strikes the anvil squarely.
● A drive-head (anvil) made of steel, with a mass between 15 kg and 20 kg,
which shall be tightly screwed to the top of the drive rods.
SPT slip barrel sampler assembly.
Periodic checks for rod straightness shall be
made on site, including the threaded connections
between consecutive rods.
Procedure
Preparing the borehole
Clean out the borehole carefully to the test elevation using equipment that will
ensure the soil to be tested is not disturbed. When boring below the groundwater table maintain at all times the water or mud level in the borehole at a
sufficient distance above the groundwater level to minimize disturbance of the
TANROADS
Chapter 2
Geotechnique
23
ch2
Withdraw the drilling tools slowly from the ground
and up the borehole (when filled with water) to prevent suction and consequent loosening of the soil
to be tested. When casing is used, do not drive it
below the level at which the test is to commence.
soil at the base of the borehole. Maintain the water or mud level in the borehole
throughout the test to ensure hydraulic balance at the test elevation.
Executing the test
Lower the sampler assembly to the bottom of the borehole on the drive rods
with the drive assembly on top. Record the initial penetration under this total
dead-weight. Where this penetration exceeds 450 mm omit the seating drive
and test drive and record the’ N’ value as zero. After the initial penetration, carry
out the test in two stages:
The rate of application of hammer blows shall not
be excessive such that there is the possibility of
not achieving the standard drop or preventing
equilibrium conditions prevailing between successive blows.
1. Seating drive: Using standard blows the seating drive shall be a penetration
of 150 mm or 25 blows whichever is first reached.
2. Test drive: The number of blows required for a further penetration of 300
mm and this is termed the penetration resistance (N). If the 300 mm penetration cannot be achieved in 50 blows terminate the test drive. For test driving in soft rock the test drive should be terminated after 100 blows if a penetration of 300 mm has not been achieved.
Interpretation
Interpretation is part of foundation design, that should contain an site investigation report including interpretation of the data. There is a lack of enforced and
consistent international standardization for the drilling technique and SPT tests
equipment. SPT results and soil parameters derived from data outside Tanzania
may therefore not correlate with results from SPTs derived in accordance with
practices in the country.
References
● BS 5930 : 1999
● BS 1377 : Part 9 : 1990
● Review of relevant literature:
CLAYTON, C.R.I. The standard penetration test (SPT): Methods and use.
CIRIA Report no. 143. London: CIRIA 1995.
24
Chapter 2
Geotechnique
TANROADS
ch2
2 Geotechnique
Soundings:
Vane test
Objectives
Vane tests are used for determining the in-situ shear strength of fully saturated
cohesive soils (clays). The test can be extended to measure the re-moulded
strength of the soil.
A steel vane at the end of a high tensile steel rod is pushed into the clay below
the bottom of the borehole and torque is subsequently applied to induce shear
failure of the clay cylinder contained by the blades of the vane. With this type it
is not always possible to penetrate to the desired stratum without the assistance
of pre-boring. The torque required to rotate the vane can be related to the shear
strength of the soil.
In soft to medium strength clays this test may be carried out independently of
a borehole by jacking the vane into the ground in a protective casing. At the
required depth, the vane is advanced ahead of the casing, the test conducted,
and the vane and casing forced to the next test depth.
Vane.
The vane test is normally restricted to fully saturated clays of un-drained shear
strength up to about 100 kN/m2, and is particularly useful in soft, sensitive
clays where sample disturbance may influence laboratory results. It has little
applicability to partly saturated and cemented soils.
Advantages
A main advantage is that the test itself causes little disturbance of the ground
and is carried out below the bottom of the borehole in virtually undisturbed
ground.
Limitations
If the test is carried out in soil that is not uniform and contains only thin layers
of laminations of sand or dense silt, the torque may be misleadingly high.
Results are unreliable in materials with significant coarse silt or sand content.
The results are questionable in stronger clays or if the soil tends to dilate on
shearing or is fissured. The presence of rootlets in organic soils, and also of
coarse particles, may lead to erroneous results.
TANROADS
Small hand operated vane test instruments
are available for use in the sides or bottom
of an excavation.
The un-drained shear strength determined by
an in-situ vane test is normally not equal to the
average value measured at failure in the field,
e.g. in the failure of an embankment on soft clay.
The discrepancy between field and vane shear
strengths is found to vary with the plasticity of the
clay and other factors.
Chapter 2
Geotechnique
25
ch2
Apparatus
The vane test apparatus shall be either the borehole or penetration type, as
illustrated. Small hand held equipment is only suitable as indicator tests.
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Principle of vane testing.
26
Chapter 2
Geotechnique
TANROADS
ch2
Vane
The vane of cruciform shape, should be of preferably of high grade stainless
steel with the following measurements, (reference to illustration).
Length (H):
Shall be twice the overall blade width D
Shear strength of soil
< 50 kPa
50 - 100 kPa
Suitable vane size, approximately
150 mm long by 75 mm
100 mm long by 50 mm wide
The design of the vane shall be such that it causes as little remoulding and
disturbance as possible when inserted into the ground for a test. The blades
shall be as thin as possible, consistent with the strength requirements, and
have a cutting edge at the lower end. The rod on which the vane is mounted,
normally of high tensile steel, shall preferably not exceed 13 mm in diameter.
Rods
The vane rod shall be enclosed by a suitably designed sleeve from just above
the blades and throughout the length it penetrates the soil to exclude soil
particles and the effects of soil adhesion. The sleeve shall be packed with
grease. This sleeve shall commence above the blades at a distance equivalent
to about two diameters of the vane rod.
Extension rods about 1 m in length. These shall be sufficiently strong to be able
to stand axial thrust, allow a reasonable amount of lack of linearity, and be fitted
with a coupling which makes it impossible for the rods to tighten or twist relative
to each other.
Instrument
Calibrated torque measuring instrument preferably with height adjustment and
capable of being clamped in the required position. The base of the instrument
shall be capable of being fixed to the ground. The instrument shall have a
torque capacity of approximately 100 Nm and an accuracy of 1 % or better of
the indicated torque from 10 Nm to the instrument’s maximum reading.
Procedure
The following is specified for performing the test.
● Place steady bearing minimum every 3 m in the case of tests in a borehole.
● Rotate the torque head throughout the test at a rate within the range 0.10°/
second to 0.20°/second (equal to 6° /minute to 12° /minute).
● Rotate the torque head until the soil is sheared by the vane. Read the
gauge at maximum deflection, thus indicating the torque required to shear
the soil.
Remoulding
Test of re-moulded strength of soils is done by removing the torque-measuring
instrument from the extension rods and turning the vane through six complete
rotations. A period of 5 min is permitted to elapse after which the vane test is
repeated in the normal way.
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Chapter 2
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27
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Calculations and reporting
The shear strength of the soil, (kPa) is calculated from the following equation:
M
S= K
where
M
K
is the torque to shear in the soil (in Nm);
is a constant depending on dimensions and shape of the vane.
Assuming the distribution of the shear strength is uniform across the ends of a
cylinder and around the perimeter then:
K=
� D2H (1+
2
D
3H
) 10
-6
where
D
H
is the measured width of vane (mm)
is the measured height of vane (mm)
As the ratio of length to width of the vane is 2 to 1 the value of K may be
simplified in terms of the diameter so that it becomes:
K = 3.66D3 X 10 –6
The test report shall contain the following information:
(a) The method of test used.
(b) The vane shear strength (in kPa) to two significant figures.
(c) The type of vane test apparatus.
References
• BS 5930 : 1999
• BS 1377 : Part 9 : 1990
28
Chapter 2
Geotechnique
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2 Geotechnique
Boring:
Objectives
Undisturbed samples are required to determine the strength and volume
stability characteristics of the soil. Undisturbed samples must preserve both the
in-situ structure and water content of the soil.
Description of method and equipment
Open tube samplers: U100 core sampling
Open-tube samplers consist essentially of a tube that is open and made
sharp at one end and fitted at the other end with means for attachment to the
drill rods. General purpose 100 mm U100 (also called U4 after the imperial
measurements) diameter sampler is used in all cohesive soils and weak rock. A
sample catcher or core-catcher is used to aid the recovery of silty or sandy soil
which tend to fall out upon withdrawal of the sampler. The U100 sampler may
either be forced down in one continuous movement or be hammered down.
Refer to Chapter 2.5.2 for definition of disturbance
classes:
Class 1 (undisturbed)
Class 2 (classification, moisture, density)
Class 3 (classification, moisture)
Class 4 (classification only)
Class 5 (none, sequence of strata only)
When forced down, samples of non-sensitive, fine cohesive soils of stiff or lower
consistency may give Class 1 samples (highest class, undisturbed). However,
the normal quality is Class 2 or even lower if hammered into hard ground.
Other open tube samplers of varying diameters, but of the same general
working principle as the U100 type, are also in use. Special thin walled
samplers have been developed to improve the sample quality, but piston
samplers are preferable.
Piston samplers
The standard 54 mm sampler (Geonor type) is designed to be driven down to
undisturbed soil well below the bottom of the borehole, where the thin walled
cylinder is pressed down in one continuous movement. The sampler is used in
silt and clay and will give Class 1 samples in soft to medium ground.
42 mm penetration sampler for use with dynamic sounding equipment of the
percussion drill type, may give Class 3 samples for classification and natural
moisture content.
Other piston samplers of sample diameter up to 100 mm or greater may be
used in special cases, for example to obtain samples of research quality.
TANROADS
U100 (U4) core sampler with extracted core.
Piston samplers are currently not commonly used
in the country and for further detail refer to relevant
literature and BS 5930:1999.
Chapter 2
Geotechnique
29
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U100 (U4) core sampler assembly.
References
● BS 5930:1999
30
Chapter 2
Geotechnique
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2 Geotechnique
Groundwater:
Objective
One of the most important parts of any ground investigation is the determination
of ground water levels or ground water pressures. In layered ground, permeable
layers separated by impermeable stratum may have different ground water
pressures and some may be artesian. Seasonal variations in the ground water
pressures should also be determined or evaluated.
Description of methods
General
The ground water conditions should always be observed as part of any borehole
operation. However, borehole observations may not be correct due to the time
required for the water level to stabilize, particularly in ground of low permeability.
Furthermore, it may not be possible to determine the levels or strata from which
the water is entering the borehole. Use of casings or mud may also interfere
with the results.
Piezometers - general
To measure ground water pressures accurately it is generally necessary to install
special measuring devices called piezometers. Piezometers may be installed to
different depths in the same location to study pressures in various layers. There
are several types of piezometers in the market as described below. Piezometers
are important parts of pumping tests, and the standpipe and hydraulic type may
also be used for in-situ permeability tests as described for boreholes.
Standpipe piezometers
Standpipe piezometers consist of a porous filter tip sealed into the ground at the
appropriate level and with an open tube (standpipe) to the surface for plumbing
the water level. The response time of this type of piezometer is long in soils of
low permeability due to the large volumes of water in the system. Some piezometers (e.g. type BAT) are designed to facilitate sampling.
Hydraulic piezometers
Hydraulic piezometers are closed systems where the pressure is measured by
a manometer, having a short response time.
Electrical and pneumatic piezometers
Electrical and pneumatic piezometers also have rapid response time. These
systems use a porous element in which the water pressure is detected by an
electrical transducer or balanced by air pressure, respectively.
Electrical level detector
Electrical equipment is available for lowering into boreholes or standpipes, and
thereby detect the surface of free water level in the well (picture).
References
Electrial ground water level detector.
● BS 5930:1999
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31
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2 Geotechnique
Groundwater:
Permeability tests for soils and rock
Objective
In-situ permeability testing is generally more
reliable than tests performed on samples in
the laboratory due to the large mass of ground
involved and the lack of sample disturbance.
However, permeability testing requires expert
knowledge both to select the correct method and
to evaluate the results.
Permeability tests are carried out for the purpose of measuring underground
flow characteristics of ground water through in-situ soils or rock. Pumping
tests may be carried out to study the permeability, transmissivity and storage
of an area of several square kilometres, as may be required in the evaluation
of ground water resources or the design of subterrain cut-off barriers in dam
design.
Of the variety of in-situ permeability tests in boreholes the common tests are:
A. Permeability of soils below the ground water level by the variable head
methods.
B. Permeability of soils below the ground water level by the constant head
methods.
C. Permeability of soils or rock by pumping tests.
D. Permeability of rock subjected to water pressure, Packer test.
As a rule, constant head borehole tests are likely
to give more accurate results than variable head
tests, but variable head tests are simpler to perform. The more elaborate and expensive pumping
tests with observation of the drawdown levels, give
the most reliable results.
Tests A and B both apply a hydraulic pressure in the borehole different from that
in the ground and observe the effect in the borehole.
Test C - pumping test for the permeability of the ground - involves a steady
flow pumping from a well and observation of the drawdown effect on ground
water levels in inspection wells (piezometers), at some distance away from the
pumped well. The drawdown in ground water level thus created is termed the
“cone of depression”.
Some particular problems encountered in in-situ permeability testing are:
● High test pressures may fracture, open up, the ground.
● Layers/fissures in the ground, and water tightness of the complete test
system greatly affects the results.
● Test holes may erode, use of filters, screens etc. may be required.
● Results are affected by the effective stress which in turn will be effected by
the test, in the case of compressible soils.
● The influence of partial saturation on permeability needs to be taken into
account in interpreting results as long term inflow tests are likely to give
permeabilities which are close to those for the saturated soil.
References
● BS 5930:1999
32
Chapter 2
Geotechnique
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2 Geotechnique
Groundwater:
Objective
Ground water sampling is carried out for the purpose of chemical analysis, either
for evaluation as a water source for consumption or use in the works. Water for
earthworks, layerworks or concrete requires testing against deleterious matter
such as e.g. soluble salts or other substances causing damage.
A sample should be taken immediately the water bearing stratum is reached
during boring. It is preferable to obtain samples from the standpipe piezometers
if these have been installed. It is important to ensure that samples are not contaminated or diluted.
Some piezometers (e.g. type BAT) are designed to
facilitate sampling.
References
● BS 5930:1999
TANROADS
Chapter 2
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33
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2 Geotechnique
Deformation test:
Plate loading test
Objectives
The plate loading method is used for determination of the vertical deformation
and strength characteristics of soil, primarily for foundation footings, but may
also be requested for determination of in-situ E-modulus of pavement layers of
for support of the pavement.
The test is conducted by penetrating a rigid, circular, plate into the soil insitu and measuring the force and deformation strength of density of soils and
compacted layers of primarily clay and soft materials. Core cutting gives volume
by predetermining the size of the excavated hole with a calibrated core of
known volume.
Advantages
The method is a simple way of determining foundation support at shallow
levels for smaller structures or for investigation of small areas. The test may be
useful on construction sites during establishment of method specifications for
compaction control of earthworks.
Limitations
● The test is slow to perform and requires a considerable input of resources.
The method is therefore not well suited for investigations of large areas.
● The results are only valid for the site conditions under which the test is
performed, e.g. with regards to moisture conditions.
Apparatus
General
The apparatus for determining penetration is normally the same as used for
Benkelman beam testing. A hydraulic jack is used for applying the force, that
is measured by aid of a calibrated manometer on the jack. Support to the jack
may be a truck or other heavy equipment. Quick-setting plaster is required for
preparation of the test site. Equipment for sampling and field density measurement
is required if such tests are requested at the same location as the plate loading
test.
The depth to which the measurement has effect is
approximately1,5 times the diameter of the plate,
as a rule of thumb.
The test plate
34
TANROADS
Chapter 2
Geotechnique
The plate shall be circular and the diameter normally ranges between 150 and
300 mm. The plate diameter should be larger than five times the diameter of the
larges particles normally found in the soil. In case of measurement of fissured
clay the plate diameter should be larger than five times the spacing between the
fissures, and have a diameter of minimum 300 mm.
ch2
Procedure
1. Carefully trim off and remove all loose material and any embedded fragments
so that the area for the plate is generally level and as undisturbed as possible. Hollows shall not be infilled with soil. For tests on cohesive soils proceed
as soon as possible thereafter to pour and spread the paste of the quicksetting plaster to obtain a level surface not more than 15 mm to 20 mm thick.
Immediately the paste is spread, bed the plate. For tests on granular soils
fill any hollows with clean dry sand to produce a level surface on which to
bed the plate.
If excavation to the test level as is required, carry
out this work as quickly as practicable to minimize
the effects of stress relief, particularly when in
cohesive soils.
2. Apply a film of oil on the plate and place it in postion. Rotate and tap the
plate to bed it properly, and remov all surplus plaster.
The increment loading method gives the strength
characteristics under drained conditions.
3. Put in postion all equipment for loading and measurement of deformation.
4. Apply an initial load of 20 kN/m2 for a few secondes and thereafter set the
measurement gauge to zero.
5. Load the plate in five increments. The table below suggests increments to
use in the test. The load at each increment shall be maintaned intil deformation is negligible. Record the load and deformation at each load increment.
6. Off-load the plate slowly and repeat the test after the arm of the force gauge
has settled.
Increment
1
2
3
4
5
It is desirable to load the plate at equal increments
whereby the maximum load is near the design
pressure. This is possibly to obtain where site
conditions are familiar.
Load (kN/m2)
50
180
300
420
600
1. Calculate the bearing pressure (in kN/m2)at the load that causes failure. If
failure is not clearly defined, use the pressure causing a penetration of 15%
of the diameter of the plate.
2. Calculate the E-modulus as follows:
Plot the pressure (kN/m2) against deformation, and determine the points on
the curve that represent 30% and 70% respectively, of the maximum pressure. Calculate as follows:
P1 = P70 – P30
S1 = S70 – S30
E1 =
where:
P70
P30
S70
S30
D
3
4
x
P1
S1
xD
is the pressure (kN/m2) at 70% of the maximum pressure
is the pressure (kN/m2) at 30% of the maximum pressure
is the deformation (metres) at 70% of the maximum pressure
is the deformation (metres) at 30% of the maximum pressure
is the diameter of the plate (metres)
References
● BS 1377 : Part 9 : 1990
TANROADS
Chapter 2
Geotechnique
35
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36
Chapter 2
Geotechnique
TANROADS
ch3
3
PAVEMENT EVALUATION
1
Introduction
2
Geotechnique
3
Pavement evaluation
4
Axle load surveys
5
alignment surveys
6
Appendices
3.1 Pavement distress ...................................................................................... 39
3.1.1 Types of distress....................................................................... 39
3.1.2 Cause of distress....................................................................... 40
3.2
Methodology ........................................................................................ 42
3.2.1 Purpose of pavement evaluation .............................................. 42
3.2.2 Evaluation procedure ............................................................... 43
3.2.3 Test frequencies........................................................................ 43
3.2.4 Desk study................................................................................ 44
3.2.5 Initial assessment ..................................................................... 44
3.3
Detailed condition surveys.................................................................. 45
3.3.1 General ..................................................................................... 45
3.3.2 Condition rating and reporting ................................................. 45
3.3.3 Visual evaluation...................................................................... 46
3.3.4 Rut depth measurements .......................................................... 47
3.3.5 Roughness measurements ........................................................ 47
3.4
Pavement strength – structural surveys............................................ 49
3.4.1 General ..................................................................................... 49
3.4.2 DCP measurements .................................................................. 50
3.4.3 Deflection measurements ......................................................... 50
TANROADS
Chapter 3
Pavement Evaluation
37
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3.5
3.6
Test pit profiling and sampling in existing pavements..................... 52
3.5.1 General ..................................................................................... 52
3.5.2 Test programme, frequency and location ................................. 52
3.5.3 Size and depth of test pits......................................................... 53
3.5.4 Sampling and testing in the trial pit ......................................... 53
3.5.5 Description and logging of the soil profile,
analysis and presentation.......................................................... 54
Homogenous sections .......................................................................... 55
3.6.1 General ..................................................................................... 55
3.6.2 Procedure.................................................................................. 55
Field Tests
Chapter
Visual evaluation
3.3.3
Rut depthe measurements
3.3.4
Roughness measurements
3.3.5
DCP measurements
3.4.2
Deflection measurements
3.4.3
Test pit profiling and sampling in existing pavements
3.5
References
● Pavement and Materials Design Manual - 1999, Ministry of Works,
Tanzania
● Guideline no. 2 Pavement Testing, Analysis and Interpretation of Test
Data. Roads Department, Botswana, 2000
38
Chapter 3
Pavement Evaluation
TANROADS
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3
PAVEMENT EVALUATION
This chapter should be read in close relation to the Pavement and Materials
Design Manual - 1999 Chapter 9-Pavement Rehabilitation, and in particular
sub-Chapter 9.1-Pavement Evaluation. The Pavement and Materials Design
Manual – 1999 sets out requirements and places the evaluation activities in prospective with the actual use of the collected data in the rehabilitation process.
3.1
Pavement distress
3.1.1
Types of distress
General
The typical types of pavement distress associated with functional and structural
pavement performance are summarised in Table 3.1.
Table 3.1: Typical types of distress associated with pavement performance.
Pavement performance
Distress indicators
Structural performance
- Deformation
- Cracking
- Surface disintegration
Functional performance
- Riding quality
- Skid resistance
- Surface drainage
The structural failure of a pavement is usually indicated by development in rutting and cracking, and may eventually lead to surface disintegration, ravelling
and/or shear failure in the pavement. However, failure may also be a result of
surface defects that initiate other structural defects after ingress of moisture.
The functional performance of a structurally sound pavement is taken care of by
regular maintenance. However, if structural defects are allowed to develop, they
will start affecting the functional pavement performance adversely.
The needs for a pavement evaluation usually arise as a result of one or more of
the following conditions:
● Poor functional performance that appears to be a result of structural defects.
● Poor structural performance, potentially requiring costly intervention in
order to arrest further deterioration.
● Εxpected dramatic increase in traffic in the short term.
● Strategic reasons related to the funding situation or network strategies.
Types of cracks
Development of cracking may be a primary cause of subsequent ingress of
moisture and weakening of structural layers, leading to rapid deterioration of a
pavement. This is why identification of cracking is a key element of any pavement evaluation. Different forms of cracking can be due to different fundamental causes, so cracks can be a good indicator of the distress mechanism in the
pavement. It is therefore vital to be able to identify the various types of cracks
in the field, and for practical purposes, four different types are defined, as indicated below.
Pavement and Materials Design Manual
- 1999
The mode of distress and failure of pavements
is a function of the type of pavement, primarily
related to the subbase, base and surfacing type.
I.e. stabilised materials behave in a different manner to granular materials, and asphaltic concrete
behaves differently to thin bituminous seals. These
aspects are discussed at further depth in the
Pavement and Materials Design Manual -1999.
By carrying out visual inspection immediately after rainfall, pavement defects such
as rutting/depression clearly shows up.
Block cracking at an early stage.
TANROADS
Chapter 3
Pavement Evaluation
39
ch3
● Crocodile and Map cracking
Longitudinal cracking caused by volumetric
(wetting and drying cycles) movements in
the subgrade.
Traffic associated crocodile cracking (interconnected polygons less than 300
mm diameter) normally starts in the wheel paths as short longitudinal cracks.
● Block cracking
Block cracks are not confined to the wheel paths, are not initiated by traffic
loading, and are usually caused by the shrinkage of pavement layers, especially made of stabilised materials.
● Longitudinal cracking
Longitudinal cracks are associated with shrinkage and movements from the
subsoil, however they may be traffic-associated and an early stage of structural distress if only confined to wheel tracks. Poor construction techniques
of e.g. joints or previous road widening may also be the cause of longitudinal
cracking.
● Transverse cracking
Transverse cracking is usually caused by temperature-associated shrinkage
and movements in surfacings and sometimes bound layers.
Pumping in cracks
Pumping occurs when water pressures generated in the pavement by traffic
loading, causing water containing fine material to be pumped to the surface
through cracks. It indicates loss of fine material from the pavement materials,
leading to loss of support to cemented layers in particular and distress.
3.1.2
Cause of distress
A distinction should be made between non-traffic associated distress and traffic
associated distress.
Severe block cracking.
Tell-tale discolouration around cracks can be a
good indication of previous pumping.
A favourable combination of material types with
regards to resistance against shrinkage cracking is
e.g. to use a granular material above a cemented
layer in order to stop reflection of inevitable cracks
in the cemented layer.
Traffic associated distress is usually restricted to the wheel paths while nontraffic-associated distress tends to occur over the full width of the road or occurs
at the pavement edges and adjacent to culverts. As a loaded wheel moves over a
road, the pavement surface deflects downwards before returning to its original,
or close to its original, position. This deflection is a function of the magnitude
of the load applied, and the stiffness of the pavement structure and subgrade.
The performance of bituminous surfacings is often related to the deflection in a
pavement and shape of the deflection bowl as repeated flexing results in fatigue
of the surfacing and subsequent development of cracking. This mode of distress
is however only one aspect out of a complex combination of environment,
material properties of each pavement layer and the manner in which the loading
is being applied to the pavement structure. It is therefore not possible to only
study aspects related to pavement deflection, but rather to consider the broad
range of mechanisms affecting pavement performance.
Non-traffic associated distress tends to occur over the full width of the road or
occurs at the pavement edges and adjacent to culverts. The cause of such distress is usually directly caused by environmental effects such as movements due
to temperature fluctuations, shrinkage and swelling, or e.g. hardening of binders,
material types, or combination of material types, being used in the pavement.
Table 3.2 indicates possible causes of traffic-associated distress. Table 3.3 indicates possible causes of non-traffic-associated distress
40
Chapter 3
Pavement Evaluation
TANROADS
ch3
Table 3.2: Possible causes of traffic-associated distress.
Type of
distress
Distress
indicators
Possible cause
Cracking:
Longitudinal in the
wheeltracks
Structural
Structural
(functional
when severe)
Functional
•
•
•
•
Cracking: Crocodile •
•
Pumping in cracks
•
•
Ravelling of surface
•
•
•
Rutting
•
•
•
•
Surface potholes
•
•
•
Deep potholes (into •
the base course)
•
•
Bleeding/flushing
•
Subgrade problems.
Poor construction.
Start of failure in stabilised base course.
Fatigue failure of surfacing or base.
Poor drainage/high moisture content.
Poor bond under bituminous surfacing.
Moisture/drainage problems with significant movement in upper pavement layers.
Insufficient or dry binder.
Poor aggregate adhesion.
Insufficient compaction of subgrade.
Insufficient compaction of pavement layers.
Insufficient pavement strength.
Shear failure of bituminous surfacing or granular base course.
Poor bonding surfacing/base course.
Disintegration of weak aggregates.
Damage caused by soluble salts.
Vehicular damage.
Spalling around cracks.
Insufficient shear strength of base course or subbase.
Excessive moisture.
Excessive application of bitumen.
Soft base resulting in punching of aggregate.
Table 3.3: Possible causes of non-traffic-associated distress.
Type of
distress
Distress
indicators
Longitudinal
cracking
Structural
Transverse
cracking
Block cracking
Map cracking
Star cracking
Possible cause
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
Shrinkage through ageing.
Reflection of stabilisation cracks from base or subbase.
Shrinkage of natural gravels through drying or self cementation.
Volumetric movement beneath shoulder (expansive clays).
Settlement of fills.
Shrinkage of bituminous surfacing through ageing.
Volumetric shrinkage associated with leaking culvert.
Shrinkage of natural gravels through drying or self cementation.
Tearing by paver or steel wheeled rollers (asphalt).
Settlement at culverts or structures.
Shrinkage through ageing.
Shrinkage through ageing of surfacing.
Soluble salt blistering.
Water vapour blisters.
Chemical reactions or surface ageing.
Structural
(functional
when severe)
Deep potholes
(into the base
course)
•
•
Insufficient shear strength of base course or subbase.
Excessive moisture.
Functional
Surface
irregularities
•
•
•
Collapsible sand.
Expansive soil.
Subsoil mole or insect activity.
TANROADS
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3.2
Methodology
3.2.1
Purpose of pavement evaluation
General
The purpose of pavement evaluation is to determine why the present condition
prevails so that appropriate rehabilitation measures can be identified, i.e. to
provide the input for pavement rehabilitation designs. Before embarking on any
pavement evaluation it is essential to understand its objective in each case, and
to make use of evaluation techniques that will best achieve this objective. Planning of pavement evaluations must be aimed at satisfying the requirements of
the specific evaluation, which normally calls for a functional evaluation as well
as a structural evaluation.
Functional evaluation
Functional evaluations identify the capability of the pavement structure to
provide a comfortable and safe service to the road user. The primary parameters
determined in functional evaluations are the riding quality, skid resistance and a
visual evaluation of aspects such as potholes and edge break.
Structural evaluation
Structural evaluations are carried out to determine whether the pavement will
carry the traffic it has been designed for and can be carried out at any time in
the pavement’s life. The remaining structural capacity can be determined and
compared with the traffic that the pavement has carried, or is expected to carry,
over the remainder of its life.
Structural evaluations involve the use of field testing and detailed investigations. Structural surveys may consist of pit excavations with associated laboratory testing, deflection measurements and probing by e.g. Dynamic Cone
Penetrometer (DCP).
Structural evaluations require an investigation of the strengths and thicknesses
of the individual pavement layers as well as the overall interaction of the layers
within the pavement structure. These evaluations may require testing of parameters such as:
● Probing with Dynamic Cone Penetrometer (DCP).
● Profiles or test pits.
● Deflection.
● Deflection bowl parameters may give additional information to explain e.g.
the mode of distress when assessed together with layer thicknesses.
Visual evaluations of cracking, disintegration and potholing are necessary inputs
for a structural evaluation. It is possible to obtain a preliminary indication of the
possible causes of distress in a pavement from a simple visual evaluation.
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3.2.2
Evaluation procedure
Pavement evaluation should be carried out in the sequence given in Figure 3.1:
��
��
��
��
��
��
��
��
��
��
��
��
��
��
��
��
��
��
��
��
��
��
��
��
��
See figure 3.3 in “Chapter 3.6.2”
��
��
��
��
��
��
��
��
��
Figure 3.1: Sequence of pavement evaluation leading to rehabilitation design.
3.2.3
Test frequencies
The minimum frequency of site investigations depend on the type of road
shown below.
SCHEME A:
All trunk roads.
Other important main roads, e.g. strategic routes or major links
in towns, deemed to be of particular importance.
SCHEME B:
Other roads.
The minimum required test frequencies for pavement evaluation is given in
Table 3.4. The test frequencies are the minimum acceptable. Additional tests
may be required depending on site conditions, i.e. where there are particularly
varying conditions or the sections are short. Any anomalies in the test results or
poor statistical basis due to few results warrant additional tests. Demarcation of
homogenous sections should be revised after analysis of the test results.
TANROADS
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Table 3.4: Minimum required test frequencies for pavement evaluation.
Min. test frequency (m)
Test
Detailed condition
surveys
Rut depth measured both sides in outer wheel path only.
Surface defects (visual evaluation)
Roughness, IRI
Scheme
A
Scheme
B
50
100
Continuously measured
500
DCP, measured on the side with highest rutting values.
Structural surveys
1000
Minimum 3 per homogenous
section
Maximum surface deflection, measured on the side with highest rutting
values, in outer wheel path only.
100
200
Test pits, excavated to design depths as defined in Chapter 5.3.3.
1000
2000
The variability of the pavement structure and
condition as well as the length of the project will
normally dictate the number of sample/ readings
- short projects will need more observations per
kilometre on average than long projects.
3.2.4
Desk study
The desk study comprises collection and processing of all relevant existing
information that can be made available before going to the field. Considerable
amounts of information regarding road projects may be available from the road
authorities (MOW/Tanroads), including:
● Τhe original design, should however to be used with care as considerable
changes may have been made in the course of the implementation of the
project.
● Αs-built records or completion data.
● Ιnformation on traffic and climate, preferably collected over many years.
● Ρeports from previous investigations.
● Μaintenance records and data in operational road management systems.
Other information such as the climatic records over the life of the road can be
obtained from the relevant source and provide important information for planning of the most effective evaluation procedure.
3.2.5
Initial assessment
The initial assessment involves visual inspections on site, seen in conjunction
with information from the desk study, for the purpose of establishing sections
with obvious performance characteristics and condition. No comprehensive
field testing programme shall be commissioned without completion of the initial
assessment. This stage is important for an optimal field programme to be established, and to prevent waste of resources on e.g. carrying out comprehensive
tests on sections of road where the pavement cannot be salvaged and therefore
requires investigations with the view of designing and constructing a new pavement.
● For pavement management data collection: from a moving vehicle (usually not exceeding 20 km/h) with periodic stops to get information that is
more detailed.
● For pavement evaluation purposes for rehabilitation design: at walking
pace.
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3.3
Detailed condition surveys
3.3.1
General
Detailed condition surveys involve work to establish the surface characteristics of the exiting pavement and all other information that can be gathered by
visual inspection and measurements on the surface, but not involving structural
surveys such as deflection measurements, DCP and trial pits.
Typically, pavement conditions surveys include observation and recording of
the parameters listed in Table 3.5.
Table 3.5: Data obtained in the detailed conditions survey.
Parameters to be rated against criteria in the Pavement
and Materials Design Manual-1999
Other important observations
Rutting
(measurements)
Pumping in cracks
(visual evaluation)
Potholing / failures
(visual evaluation)
Deformation
(visual evaluation)
Cracking
(visual evaluation/measure)
Edge-break
(visual evaluation)
Ravelling
(visual evaluation)
Bleeding (flushing)
(visual evaluation)
Patching
(visual evaluation)
Surfacing condition
(visual evaluation)
Roughness
(measurements)
Drainage
(visual evaluation)
The parameters in Table 3.5 can be grouped into the following categories that
practically are being measured or observed at the same time or with similar
types of resources.
● Visual evaluation.
● Rut depth measurements.
● Roughness measurements.
Reference points
It is of utmost importance to tie in the measured data with fixed physical
features along the road, as there is likely to be a difference between vehicle
distance and project road distance. Established chainages may also be changed
over time, rendering measured data unusable due to lack of reference. Any difference in reference points should be accommodated during data processing to
ensure all field data can be directly correlated to fixed field features.
3.3.2
Condition rating and reporting
The condition rating for a section shall be reported in a standardised form in accordance with threshold values given for each type of distress and for two traffic
loading categories respectively:
● TLC 1 and lower.
● TLC 3 and higher.
This means in practice traffic loading lower or higher than 1 million E80s over
the design period. Ref. Pavement and Materials Design Manual-1999.
The ratings are reported as:
Sound:
Warning:
Severe:
Adequate condition
Uncertainty exists about the adequacy of the condition
Inadequate condition
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3.3.3
Visual evaluation
General
The visual evaluation is an important part of the pavement evaluation process,
that involves collecting visual evaluation data in a conventional manner:
Visual evaluation.
Visual evaluation requires a rating of degree and extent of the various distress
parameters in order to use the data in a rational manner in the subsequent rehabilitation design. The work requires an experienced person or preferably a team
of two or more. It is essential that all persons carrying out rating use a standard
rating system and are ‘calibrated’ periodically against each other for consistency.
Typical pavement conditions evaluated visually include:
● Failures/potholing (RATED)
● Deformation (NOT RATED)
●
●
●
●
Cracking (RATED)
Ravelling (RATED)
Patching (RATED)
Pumping in cracks (NOT RATED)
●
●
●
●
Edge-break (NOT RATED)
Bleeding (flushing) (NOT RATED)
Surfacing condition (NOT RATED)
Drainage (NOT RATED)
Some of the data are not rated, as indicated above, as they do not
directly form part of the input to the rehabilitation design. These data are
nevertheless useful, providing the designer with valuable information as a
basis for deciding on appropriate rehabilitation measures.
Definitions in accordance with the World Bank
HDM-4 model.
Definitions of cracks
Cracks measured in square metres are defined as the length of the crack plus
500 mm multiplied by 250 mm. All cracks, wide and narrow, are measured in
this manner. Overlapping areas where cracks are close to each other shall not be
counted several times, i.e. a fully cracked up area with crocodile cracks will be
measured as the surface area of the carriageway that is cracked, plus 125 mm
extending outside the area to be accurate, however not outside the perimeters of
the carriageway.
A WIDE crack is defined as being wider than 3 mm. Such areas are part of the
total recording of cracks, but shall in addition be recorded separately as the
proportion of wide cracks in relation to the total cracked area.
Rating criteria and reporting
The distress criteria for visual evaluation are given in Table 3.6.
Table 3.6: Condition rating, visual evaluation.
Parameter
Condition rating (sound / warning / severe).
Threshold values (in % of carriageway area , except for Wide Cracks)
Traffic class TLC 1 or lower
Traffic class TLC 3 or higher
Sound
Warning
Severe
Sound
Warning
Severe
Potholes/failures
<0.01
0.01-0.20
>0.20
<0.01
0.01-0.10
>0.10
All cracks
<20
20-50
>50
<10
10-30
>30
Proportion wide cracks >3mm
<20
20-50
>50
<10
10-30
>30
(in % of all cracks)
1)
Loss of stone, ravelling
<5
5-15
>15
<5
5-10
>10
Patching
<0.3
0.3-1.0
>1.0
<0.2
0.2-0.6
>0.6
1) Loss of stone on pavements with a surface treatment over a base course made of unbound materials shall be rates ’Severe’
wherever the affected area exceeds 5%. This tightening of rating is necessary in this type of pavement due to its rapid deterioration
experienced when the thin seal starts to show signs of distress.
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3.3.4
Rut depth measurements
General
Changes in rut depth over time is a good indicator of pavement distress taking
place, and in combination with a cracked surface there is likelihood of accelerated deterioration due to water collection and ingress of water. High rutting
values also affect the functional condition of the pavement negatively. The
measurement of rut depth is best carried out using a standard straight edge and
a calibrated wedge. On the basis of its general use and its ease of handling and
transportation, a 2-metre straight edge is the most practical equipment for rutting measurements.
Automated rut depth measurement devices are
available, usually towed behind or a component
of some other pavement evaluation device e.g.
high-speed profilometers.
Test procedure
It is recommended to use a standard 2-metre straight edge with a calibrated
wedge for rut depth measurements. Where no 2-metre straight edge is available,
it is possible that a length of string be substituted, however this technique is not
generally recommended as it requires considerable practice to avoid over-reading.
Normally it is sufficient to measure the maximum rut in the outside wheel paths,
which in most cases have the greater rut depth. On most roads, it is usually
found that the heaviest trafficking occurs in one direction but ruts should nevertheless be recorded for both directions.
For single carriageway (two lane) roads, the
remedial action will be governed by the worst
case, while for dual carriageways it may be possible to have different remedial actions for each
carriageway.
Analysis, rating criteria and reporting
Data from different wheel paths must be kept separate and no attempt made to
combine or statistically simplify them. The highest value is reported, normally
the outer wheel path. Data from separate lanes must not be mixed in any way
and shall be reported separately.
The 90%-ile value of the rut depth per section should be reported. The distress
criteria for rutting are given in Table 3.7.
Table 3.7: Condition rating, rut depth measurements.
Condition rating (sound/warning/severe).
Threshold values (mm rut depth)
Parameter
Rutting, 90%-ile
value over a section
(mm)
Traffic class TLC 1
or lower
Sound
Warning
Severe
<10
10-20
>20
Traffic class TLC 3
or higher
Sound Warning
<5
5-15
Severe
>15
3.3.5
General
The roughness of a road pavement is a major measure of its functional condition
and a high level of roughness is the largest contribution to the part of the road
user costs that are affected by road conditions. Different roughness of roads
with similar pavement construction is a good measure of the relative pavement condition, but does not identify the nature or the causes of distress. Most
pavement defects contribute in some way to increasing the roughness of the
road pavement, either directly from a deformed surface or indirectly as a result
of repair work of e.g. cracks and potholes. Changes in roughness over time is a
good indicator of pavement distress taking place.
TANROADS
Workmanship during construction of a road, and
subsequent maintenance, is contributing to the
level of roughness of a road pavement.
Chapter 3
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47
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Equipment types
The following types of equipment are use for roughness measurements:
● Measurement of surface geometry, e.g. MERLIN.
● High speed equipment operating on vehicle motion, e.g. Bump Integrator.
● High speed equipment for measurement of surface geometry operating with
laser or ultrasound.
All alternative equipment shall be calibrated against the MERLIN.
Own established chainage needs to be tied
to fixed features such as culverts, for sufficiently secure identification of the site.
MERLIN
The MERLIN is a simple equipment for measuring surface roughness by manual methods, providing reliable data without input of expensive technology, albeit
at a rather low output. The MERLIN should be used for research and monitoring purposes, or routine evaluations of short pavement sections, preferably less
than 20 km. The equipment can be maintained - and even manufactured - from
readily available materials using moderately skilled artisans. The time and effort
required for longer sections will normally make high speed devices more cost
effective and practical.
Before use, the MERLIN shall be calibrated using a standard piece of steel,
6 mm thick placed under the measuring foot on a flat surface (floor). Further
detail on the procedure is given in Appendix 4.
Analysis, rating criteria and reporting
Data from different wheel paths must be kept separate and no attempt made to
combine or statistically simplify them. The highest value is reported, normally
the outer wheel path. Data from separate lanes must not be mixed in any way
and shall be reported separately.
Calibration of MERLIN.
The roughness measurement unit shall be reported as the International Roughness Index (IRI) in metres per km over each section. The distress criteria for
roughness measurements are given in Table 3.8.
Table 3.8: Condition rating, roughness measurements.
Parameter
Roughness, IRI
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Threshold values ( IRI value m/km )
All traffic classes
Sound
Warning
Severe
<3
3-6
>6
ch3
3.4
Pavement strength – structural
surveys
3.4.1
General
Methods
There are three alternative, approaches for assessing the strength of a pavement,
meaning the estimated ability of the pavement to withstand repetitive wheel
loads. The basic methods involves carrying out:
● Probing into the pavement (by e.g. DCP) and thereby measuring the strength
characteristics of each layer. Then relate this information to empirical data
on similar types of pavement under similar physical conditions.
● Measurement of the surface deflection and shape of the deflection bowl
under loading. Then relate this information to empirical data on similar
types of pavement under similar physical conditions.
● Excavation of trial pits, measure layer thickness and obtain laboratory
data to characterize the properties of the materials in pavement and subgrade. Then apply this information to current pavement design methods
or relate the information to empirical data on similar types of pavement
under similar physical conditions.
In addition one may combine the above methods and also apply theoretical
calculation models to the data.
This chapter 3.4 deals with measurements of pavement strength by use of direct
methods:
● DCP.
● Deflection measurements.
Measurements of pavement strength by plate
bearing tests and in-situ CBR are now uncommon
in pavement evaluation because the tests are
destructive, are costly and time consuming for the
field work.
Determination of potential strength characteristics by excavation of trial pits for
laboratory testing is presented in Chapter 3.5.
Validity of the results
It is important to be aware that there are fundamental differences between the
test methods. Some give pavement strength measured directly in the field under
local conditions as they are at the time of measurement. Other methods give potential strength as the output, where local conditions have to be assumed, rather
than having a direct effect on the test results.
● DCP measurements, deflection measurements and all other direct field measurements of strength give results that are only valid for conditions as they
are at the time of measurements.
● When carrying out laboratory testing of samples taken from the pavement
one has to reproduce field conditions with regards to e.g. moisture content
and density. Alternatively one has to test the material under standardised
conditions, such as 4 days soaked CBR or at OMC, and apply the results to
design methods based on such standardised testing, plus make assumptions
on future moisture regime in the pavement. Variations in moisture content,
condition of the surface at the test location compared to other areas of the
road, local drainage conditions, time of the year, weather conditions, etc.
have to be carefully considered in assessment of the validity of the collected
information.
TANROADS
Old pavements with granular materials and a
defective and pervious bituminous surfacing may
have very high moisture contents at certain times
of the year, but exhibit high strength during dry
conditions at other times.
Chapter 3
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49
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3.4.2
DCP measurements
Introduction
The Dynamic Cone Penetrometer (DCP) can be used for estimation of an approximate strength of the individual layers in a pavement structure, rapidly and
with minimal disturbance to the pavement. In this way, many results can be
obtained quickly and the statistical evaluation of these will generally provide a
relatively representative measurement of the pavement strength. The side of the
road with the highest rutting values should be subjected to DCP testing, normally in outer wheel path.
DCP testing apparatus in operation.
Test procedure and equipment
The normal procedure regarding use of the equipment is familiar and should be
followed, however particular attention is drawn to:
● Τhe condition of the apparatus (cone not worn, rods not bent, all fasteners
tight).
● Τhe device shall be held vertically during the test, and the rod shall not
jammed towards the sides of the hole during testing, two condition that
easily occur where there are large stones in the ground.
● Large stones could affect the readings and should be recorded.
● The hammer should be just touching the upper stop prior to release.
● A minimum depth of 800 mm, or refusal, should be achieved.
● The DCP holes shall be backfilled with fine, dry, sand and the upper 50 mm
of the hole patched with asphalt premix or cement slurry.
It should be noted that DCP MEASUREMENTS WILL IN ALMOST ALL CASES GIVE A
TOO OPTIMISTIC IMPRESSION OF THE PAVEMENT STRENGTH wherever there has been
poor procedure or problems during the site work. This is true if e.g. the cone is
worn, the weight has not been lifted all the way to the top during testing, the rod
gets jammed in the hole, the equipment is not held vertically, the readings are
disturbed due to stones and sometimes if there fasteners in the equipment are
not tight.
Drop hammer of DCP.
The standard DCP apparatus can be adapted to use disposable cones, which are
left in the hole on completion of the test. These have the advantage of:
● Reducing damage to the apparatus, as withdrawal after testing is a major
strain on all parts of the equipment.
● Ensuring that the tip of the cone is always in good condition.
● Greatly reducing the time spent on testing, as withdrawal after testing is
often a time consuming part of the procedure.
Analysis and presentation
The derived CBR data characterising the spatial variation of the DCP profiles
along the project length should be presented graphically both for each location.
In addition the CBR strength over a section of road should be plotted in order
to evaluate variations in layer strengths and thicknesses along the project and
allow identification of uniform sections.
Disposable cone for DCP, i.e. without
threads.
3.4.3
General
Deflection measurements are useful in helping to identify the cause and extent of any differential condition along a road and for design of rehabilitation
measures in accordance with the Pavement and Materials Design Manual-1999.
50
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Deflection measurements shall however not be used as the only tool for designing pavement rehabilitation or overlays, and requires confirmation by the use of
the structural number method. Normally the maximum deflection is measured,
but surface curvature (shape of the deflection bowl under load) gives useful
additional information to explain the mode of distress, but is not applied in the
rehabilitation design method.
Temeraure should be routinely measured in
asphaltic layers thicker than 50 mm. Such data are
however not critical for assessment of pavements
with granular base course.
Equipment
The simplest methods for deflection measurement is the Benkelman Beam. The
principle operation of the equipment is by measurement of surface deflection
between the dual wheels of an axle loaded to 8175 kg. If this axle load cannot
be applied for any reason, the readings shall be adjusted linearly to the values of
a 8175 kg load.
The following should be adhered to if possible, with regards to the wheels on
the rear axle of the truck:
● 11.00 x 20 or 10.00 x 20 tyre dimensions.
● Road contact length: 200 mm.
● Spacing between the walls of the tyres in the dual wheel combination:
75 – 90 mm.
● Tyre pressure 590 kN/m2 (85 psi)
Falling Weight Deflectometer (FWD) measurements are obtained faster than with the Benkelman
Beam, but requires a considerably higher level of
mechanical skills and cost in operating hardware.
The deflection values obtained using alternative test methods such as Falling
Weight Deflectometer (FWD) differ significantly, and each manufacture of
FWD may give different results.
Test procedure
Two methods for measuring deflection with the Benkelman Beam are in use,
respectively rebound and transient deflection, that give slightly different responses.
● Rebound: Should normally be used, is easy and quick. The wheel is
stationary at the tip of the beam and measurement is taken
after it has moved away.
● Transient: The method is only required on newly constructed pavements (less than 3 years). The method is more difficult and
with higher risk of damage to the equipment compared to
the rebound method. The loaded wheel moves towards past the
tip of the beam, and the maximum value is measured.
1. Zero-reading under the static load.
Measuring temperature of asphaltic layers.
2. Reading after the truck has moved forwards, and the beam moved to the next
location.
Figure 3.2: Rebound deflection measurements using Benkelman Beam.
TANROADS
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Analysis and condition rating
In order to utilise a common rehabilitation design method the deflection values
shall be converted to equivalent Benkelman Beam values irrespective of equipment being used. Values are reported as 90%-ile values for homogenous sections calculated with minimum 20 measurements. Table 3.9 shows distress criteria in respect of maximum deflection values for pavements with granular base
course and lightly cemented pavements respectively. For other types of pavements the maximum deflection method is not a reliable measure of pavement
condition or a suitable basis for prediction of future pavement performance.
Table 3.9: Condition rating, maximum surface deflection, Benkelman Beam.
Pavement type
Threshold values (mm maximum deflection 90%-ile value)
Traffic class TLC 1 or lower
Traffic class TLC 3 or higher
Sound
Warning
Severe
Sound
Warning
Severe
Granular base course
<0.70
0.70 - 1.30
>1.30
<0.50
0.50 – 1.00
>1.0
Lightly cemented base course
<0.55
0.55 - 1.15
>1.15
<0.35
0.35 - 0.85
>0.85
3.5
The excavation and testing of test pits is probably
the most costly part of a routine pavement evaluation. It is imperative therefore that optimum locations are tested, and that the maximum information
is obtained from each test pit.
Test pit profiling and sampling
in existing pavements
3.5.1
General
The excavation of pits through the pavement with testing and sampling of the
materials comprising each layer is an essential part of structural pavement
evaluation for the purpose of pavement rehabilitation design in accordance with
the Pavement and Materials Design Manual-1999.
It should also be noted that, unless specially treated, the material is tested at
an in-situ moisture condition that, may differ considerably from the laboratory
soaked CBR normally used for the pavement design. The soaked condition can
dramatically influence the CBR result.
3.5.2
Test programme, frequency and location
Test programme
Sample collection and laboratory testing is normally the most costly component
of the pavement evaluation. It is therefore essential to develop the pavement
evaluation programme to obtain all the information necessary to carry out the
rehabilitation design (or any other purpose for which the evaluation is being carried out) with the minimum amount of data collection and field and laboratory
testing. A balance needs to be struck between the cost of the evaluation and the
required amount/quality of information.
Frequency
The frequency of the sample pits shall be minimum that given in Table 3.4 in
Chapter 3.2.3, i.e. for trunk roads and other important roads the frequency is
higher than other roads. The given frequency is however the minimum acceptable, and additional tests are likely to be required in order to form a proper
basis for the rehabilitation design. No hard and fast rules can be laid down for
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the required test pit frequency, as it varies with the mode of distress, length of
uniform sections, pavement materials, variability and possibly others depending
on site conditions.
Location
The location of test pits should be carried out once sufficient information is
available to divide the road into a number of preliminary uniform sections. At
each location, test pits are usually excavated in the outer wheel path of the more
heavily loaded lane.
3.5.3
Size and depth of test pits
Area
The area of the test pit should be as small as possible so as to cause minimal
disturbance to the pavement and subsequent patching, but large enough to:
● Permit a sample of sufficient size to be collected. A 100 mm thick layer of
typical material will provide a sample of 180 to 200 kg per square metre.
● Αllow enough space to carry out in situ testing and excavation at depth.
Depth
Test pits shall be excavated to the following depth, whichever is smaller:
● Μinimum to the full depth of the existing pavement.
● Μinimum to the depth as defined in Table 5.2 in Chapter 5.3.3.
At least one test pit at each site should be excavated to a depth at which the insitu material can be inspected and sampled.
Sample size
Minimum sample size depending on particle size of the material and laboratory
test programme is given in Chapter 5.2.3. The required sample size may well
be exceeded if the laboratory testing programme that the samples will undergo
includes specialised testing.
3.5.4
Sampling and testing in the trial pit
Preparing the site before excavation of the trial pit
The investigation of test pits should follow a standard procedure:
1. The surfacing type shall be accurately described, including the condition of
the road surface as described in Table 3.5.
2. Rut depths shall be measured.
3. Condition of shoulders and drainage system at the site shall be recorded.
4. Road widths and shoulder widths shall be measured and recorded.
Procedure
Reference is made to Figure 5.4 and Figure 5.5 in Chapter 5.2.3, where the procedures for taking samples in a trial pit, and quartering of samples is illustrated.
The procedure having direct reference to sampling of an existing pavement is as
follows:
1. The surfacing should be carefully removed causing minimal disturbance of
the upper base course.
2. Immediately on exposure of the base course to the atmosphere, an in situ
density determination should be carried out on the base course using either
a nuclear method or sand replacement. With both methods, it is essential
TANROADS
Chapter 3
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53
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to obtain samples for accurate gravimetric moisture content determinations.
These samples should be at least one kilogram in mass and should be oven
dried to constant mass. All dry densities should be calculated using the
gravimetric moisture content and not the nuclear moisture contents.
3. Once the density of the base has been determined, the material should
be loosened and sampled with sufficient material being collected for the
laboratory testing envisaged.
4. The test pit should then be carefully trimmed and cleaned until the next
layer is exposed. If the materials in the two layers differ significantly, it is
easy to prepare a suitable surface on the next layer for density testing. If
the material comprising the underlying layer is similar to the base, difficulty
is sometimes experienced in locating the top of the underlying layer. Welldefined compaction planes are, however, commonly observed.
5. Each pavement layer should then be tested and sampled in turn until the
required depth is reached.
6. Test pits should be carefully reinstated with materials of at least similar
quality to those removed, compacted well in layers as appropriate, and the
hole sealed with cold-mix asphalt or other appropriate methods for surfacing as required.
During sampling of test pits a summary of all samples collected with their depth
and description should be made. This can be included on the soil profile description form. The samples removed from the test pits should be carefully bagged
and labelled prior to submitting to the laboratory for appropriate testing.
3.5.5
Description and logging of the soil profile, analysis and
presentation
The seal removed from the trial pit should be closely inspected and descriptions
of the bituminous surfacing (type of surfacing, binder condition, adhesion to the
base and to chippings, prime penetration depth, etc.) recorded.
Once the pit has been tested and sampled, one “wall” of it should be scraped
clean with a spade and the pavement profile described and measured. The description should follow the method after Brink and Jennings as shown in
Appendix 2. Graphic illustrations of the pit profiles, including depths and material descriptions, must be provided.
The condition and shapes of the layer interfaces should be examined to determine the layer from where rutting and failure originates.
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3.6
Homogenous sections
3.6.1
General
An important part of pavement evaluation is to identify sections that behave
similarly in respect of one or more aspects of pavement condition and distress.
It is not possible to make exact rules for this part of the process because site
conditions, type of pavement and loading may vary tremendously between projects and within individual projects. This chapter however sets out a proposed
procedure that is found useful in most cases and includes the use of CUSUM as
a rational means of assessing a set of measurement data along the road to delineate into sections having approximately similar values.
The CUSUM is a method to establish homogeneous sections by analysis of one parameter at the
time. The method utilises plotting of the cumulative
sum of difference from the average value and the
interpretation of data is simple.
3.6.2
Procedure
Figure 3.3 sets out the procedure for assessing data from the pavement evaluation for the purpose of establishing homogenous sections. The procedure for
carrying out CUSUM calculations for each individual set of measured data is
given in Appendix 3 where also an example is presented, showing a set of data
where CUSUM has been used for delineation into homogenous sections.
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Figure 3.3: Assessing data for determination of homogenous sections.
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56
Chapter 3
Pavement Evaluation
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4
AXLE LOAD SURVEYS
1
Introduction
2
Geotechnique
3
Pavement evaluation
4
Axle load surveys
5
alignment surveys
6
Appendices
4.1
4.2
4.3
4.4
4.5
Introduction......................................................................................... 58
Resources for axle load surveys............................................................ 58
4.2.1 Staff .......................................................................................... 58
4.2.2 Equipment ................................................................................ 58
Condition of survey sites..................................................................... 59
4.3.1 General ..................................................................................... 59
4.3.2 Site location for mobile weighbridges ..................................... 59
Weighing .............................................................................................. 62
4.4.1 Duration of the survey.............................................................. 62
4.4.2 Origin and Destination (O/D) surveys ..................................... 62
4.4.3 Vehicle categories..................................................................... 62
4.4.4 Accuracy .................................................................................. 62
4.4.5 Procedure for weighing ............................................................ 63
Recording and reporting .................................................................... 64
4.5.1 General ..................................................................................... 64
4.5.2 Axle configuration.................................................................... 64
4.5.3 Equivalency factor ................................................................... 65
4.5.4 Axles loaded to above 13 tonnes.............................................. 65
4.5.5 Traffic growth........................................................................... 65
4.5.6 Lane distribution ...................................................................... 66
4.5.7 Construction traffic................................................................... 66
4.5.8 Traffic Load Classes (TLC)...................................................... 66
4.5.9 Presentation of Data ................................................................. 67
References
● Pavement and Materials Design Manual - 1999, Ministry of Works, Tanzania
● Guideline no. 4 Axle Load Surveys. Road Department, Botswana - 2000
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Axel Load Surveys
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The Pavement and Material Design Manual-1999
requires that all pavement design of bitumen surfaced roads shall be based on project dedicated
axle load surveys.
The axle load weighing described in this chapter
only deals with static weighing, and not weight
of moving vehicles, commonly termed Weigh -in
-motion (WIM).
4
AXLE LOAD SURVEYS
4.1
Introduction
Tanzania has over the last decades made great efforts in expanding and improving the road network as part of developing the infrastructure, thus enabling sustainable economic and social development throughout the country. In order to
secure and preserve this valuable asset timely and appropriate maintenance and
rehabilitation measures are essential. Accurate information on traffic loading is
one of the basic inputs for management of this network. Such data are required
for design of new pavements and for pavement rehabilitation as well as forming
a basis for making decisions on the most economical and appropriate management strategy for individual road links and for the network as a whole.
The main purpose of this chapter is to provide a practical guidance on how to
conduct an axle load survey that gives sufficient information for both pavement
management and design purposes. Guidance is given for collection and presentation of the data in a manner that ensures all input to the pavement design is
secured and no vital information is being lost or obscured through inappropriate
summarisation of data. Since such surveys can be expensive they must be carefully planned and organised to minimise resource wastage.
4.2
In conjunction with a border gate the survey will
follow the border post gate opening and closing
schedules.
Resources for axle load surveys
4.2.1
Staff
Due to 24-hour operation of the axle load surveys, the team normally requires
about 15 people working on a three shift basis with 4 -5 people on each shift.
Proper training must be completed prior to letting the team operate on their own
in the field. Such training should be conducted by an experienced engineer fully
conversant with the technical and logistics details. The minimum qualifications
of the team members are as follows
Team leader: .......................................................... 1 technician or engineer
Scale reading and data recording: ......................... 6 technician/assistant
Traffic control: ....................................................... 5 assistant/labours
Vehicle operation: .................................................. 3 drivers
The exact number of people on a shift will vary depending conditions on site,
such as traffic intensity. The number of shifts will vary depending on the total
survey schedule, i.e. the number of all-night measurements and also special site
conditions such as border gates.
4.2.2
Equipment
The following equipment is required to conduct an axle load survey. Personal
equipment, water and fuel is not included in the listing:
General, for all surveys
● flatbed truck .....................................................(no 1)
● pick-ups ...........................................................(no 2)
● reflective traffic safety vests ............................(no 15)
● traffic cones .....................................................(no 20)
● red stop flags ....................................................(no 2
● road signs ..................................................... (no 10)
● generator for lights ....................................... (no 1)
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●
●
●
●
●
●
●
electrical lamps ............................................ (no 2) incl. cables
torches incl. spare batteries .......................... (no 2)
axle survey forms, pens and other stationary
spade ............................................................. (no 1)
pick ............................................................. (no 1)
broom ........................................................... (no 1)
camera .......................................................... (no 1)
Addition for mobile weigh bridges
In case where the mobile weigh bridges are used the following additional
equipment is required:
● weigh pads and peripheries
● 2 metre long straight edge..............................(no 1)
● spirit level .....................................................(no 1)
● ramps .............................................................(no 4)
● bags of fine sand to level mobile weigh bridge
● tent and or umbrella
4.3
Condition of survey sites
4.3.1
General
The ease with which an axle load survey can be carried out depends largely on
the conditions of the site and the possibility to weigh the vehicles easily and
safely. The survey should be carried out on a road stretch with good visibility so
the traffic is made aware of the need to stop well in advance.
Details on layout for survey sites and traffic safety
measures are given in appendix 5.
The site location for the stationary weigh bridges were carefully selected to
cater for the activities normally taking place at these sites at the time they were
established and therefore require no further comment in this chapter.
4.3.2
Site location for mobile weighbridges
General requirements
Axle load surveys using mobile weighbridges require sites to be selected by the
team leader to give the best possible working conditions, safety and effectiveness of the survey, and it is important to ensure that:
● The survey site covers the road section from which data is required.
● Traffic in both directions can be surveyed.
● The traffic safety aspects have been considered and found acceptable.
● There is no access to detours that bypass the survey site.
● The local police is informed of the survey location and duration.
● The location is as level as possible.
There are many different types of mobile weigh
bridges available, however the required measuring
position is similar for all types.
The requirements listed above should be carefully addressed prior to conducting
the axle load survey.
Sources of error
The surface gradient on the weighing site should not exceed 2% in order to
comply with normal weighbridge requirements. In addition to this general requirement, there are several other physical features on site that may be sources
of error, such as those shown in Figures 4.1, 4.2, 4.3 and 4.4 below.
TANROADS
Mobile weighbridge site.
Chapter 4
Axel Load Surveys
59
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Figure 4.1: Sources of error at the weighing site – surface gradient.
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Figure 4.2: Sources of error at the weighing site – surface evenness.
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Figure 4.3: Sources of error at the weighing site – surface evenness by the scale.
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Careful preparation of the site for mobile
weigh bridges is essential for reliable
results.
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Figure 4.4: Sources of error at the weighing site – surface evenness, consequences.
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4.4
Weighing
4.4.1
Duration of the survey
Axle load surveys should be carried out for seven consecutive days and for 24
hours a day. This is done to ensure a representative sample of the traffic loading
over each of the days in the week, and axle load surveys less than seven days
duration are not recommended. If the axle load survey is carried out in conjunction with a border gate station, the hours of the survey should be in accordance
with the opening hours of the border gate.
Weighing at night requires preparation
of light systems, power supplies, torches,
reflective vests etc. for safe operations.
O/D-surveys are being carried out at the
same time as axle load surveys.
A new axle load survey for provision of new vehicle
equivalence factors is required if there is a great
change in type or amount of goods or type of
vehicles being used along the route.
4.4.2
Origin and Destination (O/D) surveys
Conducting an O/D (origin and destination) survey by interviewing the
driver in parallel with an axle load survey will not involve extra resources or
disturbance to the traffic. The type of load the vehicle is carrying should also
be recorded. Normally the O/D information is not reported in the axle load
survey report, however the information remains on the field worksheets and
can be useful for future feasibility studies or for other purposes.
4.4.3
Vehicle categories
Besides giving the cumulative axle loads (E80) and the load distribution, the
axle load survey will for practical use in design give an average number of E80s
for each of the categories of heavy vehicles shown in Table 4.1, i.e. the Vehicle
Equivalence Factors (VEF). These figures can be applied to simple traffic count
data for the route at a later time and thereby greatly enhance the value of routinely and cheaply collected information from traffic counts.
Heavy vehicles are defined as:
● Vehicles having an un-laden registered weight of 3 tonnes or more.
● Buses having a seating capacity of 40 or more.
Table 4.1: Heavy vehicle categories.
Heavy vehicle category
Definition
Medium Goods Vehicle MGV
2 axles. incl. steering axle, and
3 tonnes empty weight, or more
Heavy Goods Vehicle HGV
3 axles. incl. steering axle, and
Very Heavy Goods Vehicle VHGV
4 or more axles. incl. steering axle, and
Buses
Seating capacity of 40, or more
All vehicles that are defined as heavy vehicles shall be included in the axle load
survey, whether they are loaded or not. I.e. there shall be no selection of loaded
vehicles over empty ones for inclusion in the survey, as this will give a distorted
value for the average Vehicle Equivalence Factor for the category of vehicle.
4.4.4
Accuracy
The accuracy of weighed individual axles depends greatly on the issues discussed above, thus every effort should be made to have all the wheel of a
vehicle to rest on an equally level plane. If the weighing plane raises, or alternatively lowers, the level of the wheels to be weighted compared to the plane of
the remaining wheels of a vehicle, the measured weight will be inaccurate.
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The accuracy of the weighing procedure will mainly depend on the following:
● The gradient of slope or plane of the weighed axle.
● The wheel base.
● Spacing between dual wheels.
● The equality in tyre pressure.
● The equality in the wear and tear of the tyres.
● The height of the load above the centre of the axle.
The weighbridge to be used, whether it is a stationary or a mobile, shall be
properly calibrated according to the manufacturers specifications.
4.4.5
Procedure for weighing
Vehicle control and weighing
Two flag men (traffic controllers) should stand on the road where they are
clearly visible to the oncoming traffic. They must wear reflective traffic safety
vests and during the night they should be equipped with a flash torch showing a
red light. The flag men are stationed at a distance of 30 metres on either side of
the weigh bridge. They should force the vehicles to be weighed to a complete
stop before reaching the weighbridge. The traffic controller instructs the truck
driver on how to approach the weighbridge at slow walking speed. All vehicle
categories shown in Table 4.1 shall be directed towards the mobile weigh bridge
where the weighbridge officer stands in front of the weighbridge to direct the
vehicle onto the weighbridge platform
After the front axle of the vehicle has been positioned accurately on the platform and has come to a complete stop, the weighbridge officer ask the questions
regarding the O/D survey, and pass the answers to the recording officer.
Weigh bridge site.
After completing the weighing the front axle, the weighbridge officer directs the
driver of the vehicle to position the next wheel (axle ) on the platform. This procedure continues until all the wheels (axles) of the vehicle have been weighed.
When the weight of the last axle load has been
recorded, the driver must be told to drive off the
platform slowly. Acceleration on departure from the
platform may cause damage to the equipment.
Special for stationary weighbridges
Stationary weighbridges are normally well marked by the use of traffic sign
boards and drivers of heavy vehicles know that they must report at the weighbridge. However, this only applies when the vehicle is loaded, and empty trucks
are normally free to pass the weighbridge station, whereas for the purpose of
axle load surveys empty trucks must also be weighted. This appears as a new
procedure for the drivers and it is therefore particularly important to position the
flag men on either side of the turn-off access roads to the weighbridge.
The work of the staff normally assigned to operate the weighbridge shall not be
interferred with, but the recording officers shall take their own recordings from
the scale showing the axle load figure and make their own observations of the
weighing procedure.
Special for mobile weighbridges
The mobile weighbridges are often established where the road users are not
used to observe them, unlike the stationary weighbridges. The flag men therefore have an even more demanding and important task than for stationary
weighbridges, and proper layout of the site in accordance with Appendix 5 is
essential for their safety and effective operation of the weighbridge. It is particularly important to observe that the driver is told to drive slowly on and off
the platform of mobile weighbridges because these are usually less sturdy than
stationary ones and easily get damaged by breaking and acceleration.
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Chapter 4
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4.5
At CML a computer programme is being offered for
calculation of axle loading.
Recording, reporting and calculation
4.5.1
General
The following points are particularly important to observe during recording:
● Traffic travelling in opposite directions shall be recorded on separate sheets.
● Εach axle is dealt with separately, hence each axle is recorded separately on
the pre-made survey form.
4.5.2
Axle configuration
Each vehicle is given a simple axle configuration code for ease of defining and
processing the axle load data. The code is made up by the following system:
● Each axle is represented by a digit, ‘1 ‘ and’ 2’ depending on how many
wheels are on the end of the axle.
● Tandem axles are indicated by recording the digits directly after each other;
● a decimal point ‘ . ‘ is placed between code digits for a vehicle’s front and
rear wheels.
● The code for semi-trailers and articulated trailer are recorded in the same
way as for trucks but is separated from the truck code by a minus ,-, sign.
● Similarly, for trailers a plus ‘+’ sign is used.
The system is illustrated by examples in Figure 4.5 showing some of the common axle configurations seen in the country.
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Figure 4.5: System for recording axle configurations.
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4.5.3
Equivalency factors
The damaging effect of an axle passing over the pavement is expressed by the
equivalency factor related to an equivalent standard axle (E80) of 8160 kg load:
Equivalency factor = [Axle Load (kg) / 8160] 4.5
The Vehicle Equivalency Factor (VEF) for every vehicle in the axle load survey
is determined and an average value is subsequently calculated for each heavy
vehicle category, for each lane separately. The average VEF for each heavy
vehicle category, for each lane, can then be applied to the results from traffic
counts to give the cumulative E80s traffic loading the pavement is subjected to
over a given period.
4.5.4
Axles loaded to above 13 tonnes
The proportion of the design traffic loading as a result of axles loaded to above
13 tonnes shall be calculated from axle load survey data. If this proportion is
50% or higher then the design traffic loading is defined as Heavy, denoted by an
index to the Traffic Load Class as input to the pavement design catalogue. One
should not confuse the proportion of the design traffic loading as a result of axles loaded to above 13 tonnes with the counted proportion of these axles in the
traffic stream, the latter being incorrect. A moderate number of very heavy axles
will make up a considerable proportion of the design traffic loading.
The percentage of the design traffic load (E80) attributed to axles loaded to
above 13 tonnes shall be calculated based on detailed data from project dedicated axle load surveys. The axle load data from the lane with the highest value
of E80 shall be used.
Chapters 5, 8, 9 and 10 in the Pavement and
Materials Design Manual - 1999/ set out measures
in the design of pavement and improved subgrade
layers to offset the effect of a large proportion of
very heavy axle loads.
The heavy axles’ proportion of E80 is calculated as follows:
Heavy Axles’
Proportion =
of E80 [%]
4.5.5
Number of E80 from axles of 13 t and heavier in the survey
Total number of E80 from all heavy vehicles in the survey
x 100
Research is not yet conclusive on issues related to
the effect of very heavy axle loads on a variety of
pavement types.
Traffic growth
General
The following estimations of future growth are required:
● Growth in the number of heavy vehicles.
● Growth in the number of E80 per vehicle (Vehicle Equivalency Factor).
Types of traffic
The forecasting of traffic growth shall include separate estimates for the 4 vehicle categories. It is necessary to assess future traffic in respect of the following
types:
There is a considerable uncertainty and risk of
making large errors in estimations of traffic growth
since a number of individually uncertain factors
are brought together in the analysis. Where little
information is available Historical data, origindestination surveys and records from Ministry of Works
Tanroads and Statistical Bureau are among the
sources of information for assessment of traffic
growth. The designer may have to resort to the
use of growth figures for GDP in the estimation of
movement of goods.
● normal traffic:
that would use the route regardless of the condition of the road
● diverted traffic:
that moves from an alternative route due to the improvement of the
road, but at otherwise unchanged origin and destination
● generated traffic:
additional traffic occurring due to the improvement of the road
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Total growth rate
For each heavy vehicle category the total E80 growth rate is calculated from the
formula:
E80 growth rate = [(1+h/100) x (1+v/100) - 1] x 100
where:
h=
growth rate in traffic volume for the heavy vehicle category
v=
growth rate in vehicle equivalency factor (E80 per vehicle) for the heavy
vehicle category
4.5.6
Lane distribution
The design traffic loading shall be corrected for the distribution of heavy vehicles between the lanes in accordance with Table 4.2.
Table 4.2 Traffic load distribution between lanes.
Cross
section
Single
carriageway
More than
one lane in
each direction
Loading from construction traffic can have a
significant effect on pavements designed for
low traffic.
Paved
width
Corrected design traffic Explanatory notes
loading – E80
< 3.5 m
Double the sum of E80 in The driving pattern on
both directions
this cross section is
very channelled
Min. 3.5 m,
but less
than 4.5 m
The sum of E80 in both
directions
Traffic in both directions
use the same lane
Min. 4.5 m,
but less
than 6 m
80% of the sum of E80 in
both directions
To allow for overlap in
the centre section of the
road
6 m or wider
Total E80 in the heaviest
loaded direction
Minimal traffic overlap
in the centre section of
the road
90% of the total E80 in
the studied direction
The majority of heavy
vehicles use one lane in
each direction
-
4.5.7
Construction traffic
The calculation of design traffic loading shall include construction traffic and
public traffic that is expected to use the completed pavement before the start of
the design period.
4.5.8
Traffic Load Classes (TLC)
After finally determining the design traffic loading, E80, and the heavy axles’
proportion of E80, the values are placed into their correct class in accordance
with Table 4.3.
Table 4.3 Traffic Load Classes - TLC
Design traffic loading [E80 x 106]
< 0.2
0.2 to 0.5
0.5 to 1
1 to 3
3 to 10
10 to 20
20 to 50
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Traffic Load Class (TLC)
TLC 02
TLC 05
TLC 1
TLC 3
TLC 10
TLC 20
TLC 50
ch4
Where the heavy (>13 t) axles’ proportion of E80 is 50% or higher the Traffic
Load Class shall be given an index, i.e.:
TLC 05-H
TLC 1-H
TLC 3-H
TLC 10-H
TLC 20-H
TLC 50-H
Insufficient sample of data for these low traffic
roads < 0,2 million E80, makes it difficult
to achieve a realistic traffic loading design.
Hence, a traffic load class TLC 0,2 -H is not
established.
4.5.9
Presentation of Data
The following information for each direction of the road shall be presented in
the detailed design report for paved roads:
● Cumulative E80 over the design period.
● The proportion of the design traffic loading that is a result of axles
above 13t (in %).
● Assumed construction traffic before the start of the design period.
● The Traffic Load Class for use in the pavement design.
The above is the minimum information required. Additional information may be
necessary.
The following details shall be presented, for each of the four heavy vehicle
categories classified
● Weighing data for all axles on heavy vehicles as obtained in the axle
load survey.
● Summary of traffic counts.
● Vehicle Equivalency Factors used.
● Growth rate in average E80 per vehicle.
● Total growth rate in E80 for each heavy vehicle category.
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Axel Load Surveys
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5
MATERIAL PROSPECTING
AND ALIGNMENT SURVEYS
1
Introduction
2
Geotechnique
3
Pavement evaluation
4
Axle load surveys
5
Material prospecting
and alignment surveys
6
Appendices
5.1
5.2
5.3
5.4
5.5
Introduction......................................................................................... 71
Methodology ........................................................................................ 71
5.2.1 Planning.................................................................................... 71
5.2.2 Soil descriptions and profiling ................................................. 73
5.2.3 Sampling .................................................................................. 73
Alignment soil surveys ........................................................................ 77
5.3.1 Introduction .............................................................................. 77
5.3.2 Establishment of centreline ...................................................... 77
5.3.3 Sampling depth......................................................................... 78
5.3.4 Sampling frequency ............................................................. 79
Soils and gravel sources...................................................................... 80
5.4.1 Introduction .............................................................................. 80
5.4.2 Environmental considerations and occupied land.................... 80
5.4.3 Desk study for gravel and soil surveys .................................... 80
5.4.4 Quantity estimates.................................................................... 81
5.4.5 Minimum requirements, sampling frequency .......................... 82
Rock Sources ....................................................................................... 83
5.5.1 Introduction .............................................................................. 83
5.5.2 Desk study for rock quarry surveys ......................................... 83
5.5.3 Quantity estimates.................................................................... 83
5.5.4 Rock quality ............................................................................. 84
5.5.5 Surface sampling...................................................................... 84
5.5.6 Drilling ..................................................................................... 85
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Material Prospecting and
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References
● Pavement and Materials Design Manual - 1999, Ministry of Works,
Tanzania
● Guideline no. 2 Pavement Testing, Analysis and Interpretation of Test Data.
Road Department, Botswana - 2000
● Guideline no. 3 Methods and Procedures for Prospecting for Road Construction Materials. Road Depratment, Botswana - 2000.
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5
MATERIAL PROSPECTING
AND ALIGNMENT SURVEYS
5.1
Introduction
5.2
Methodology
In order to maintain, construct, rehabilitate or upgrade a road network, large
quantities of soils and gravel materials are required and normally alignment soil
surveys are needed for a reliable design of improved pavement layers, estimates
of earthworks quantities to be made and the pavement design to be validated.
This chapter describes the methods and procedures that are appropriate in Tanzania for the location and proving of material sources for road construction as
well as setting out procedures for alignment field surveys.
5.2.1
Planning
General
It important to gather as much information as available about the intended construction project where alignment surveys or material surveys are to be carried
out. Large amounts of time consuming and expensive field work may be carried
out unnecessarily if the planning in advance has not been properly undertaken.
The following general points should be given attention in the planning of alignment soils surveys and surveys for pavement and earthworks materials:
The parameters pavement layer thickness and
pavement material types are not determined
on the basis of the alignment soils survey, but
by the availability of pavement materials, traffic
loading and climate. Ref. the pavement design
method of the Pavement and Materials Design
Manual-1999.
1. Establish the type of road (bituminised/gravel/earth), whether trunk road or
not, road width, design traffic loading and the designers’ preliminary views
on alternative pavement types and material quantities for pavement construction.
2. Establish whether the horizontal alignment is fixed, or can be moved, or is
likely to be moved after the soil survey has been carried out.
3. Obtain as much information as possible about the vertical alignment and areas of likely cut or fill, and the likely depth of cut and fill and locate these
areas on maps for use in the field.
4. Estimate the need for earthworks fills and their likely position along the
road line.
Use of field data in the pavement design
Special attention is drawn to the awareness of the exact purpose of each part
of the field survey in accordance with the design method of the Pavement and
Materials Design Manual-1999 as outlined below and illustrated in Figure 5.1.
As shown in Figure 5.1, the alignment soils survey does not determine the pavement structure, i.e. the layer thickness and required material type in subbase,
base course and surfacing. The pavement structure is determined by traffic loading and climate. The availability of pavement materials in the area is important
for choice of the most economical pavement structure within a range determined
by the traffic loading and climate.
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The alignment soils survey however determines the number of improved
subgrade layers that are required before the pavement can be placed. Climate
is an important input in these considerations. Also the need for special
attention to poor in-situ soils is determined in the alignment soils survey.
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Figure 5.1: Use of information from field surveys in pavement design.
Alignment soils survey - purposes
The main purposes of the alignment soil survey are the following:
● Make available background data to form the basis for determining the number of improved subgrade layers required before the pavement is placed.
This means the required amount of earthworks may depend on the alignment soils survey.
● Establish the occurrence of problem soils in the road corridor.
● Establish any potential drainage problems such as e.g. perched water table.
This means the amount of sampling during alignment soils surveys may be reduced considerably in areas where drainage or geometric considerations are the
overriding factors determining the amount of earthworks.
Availability of pavement materials is in-formation
the designer needs very early in the design
process in order to make cost comparisons and
fundamental decisions on the implementation of
the project.
Survey for pavement and earthworks materials - purposes
The survey for available pavement material sources forms the basis for the
pavement design, see Figure 5.1, and is an essential tool in the selection of construction method and alternative pavement types. Provision of this information
shall therefore be made a high priority in the field investigations.
Survey for pavement and earthworks materials - required quantity
Figure 5.2 shows the principle of required quantity for material prospecting
being twice the theoretical amount from the project drawings. Further detail
on quantity estimates and ‘loss’ of material during winning of natural gravel is
given in Chapter 5.4.4 - Quantity estimates.
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Figure 5.2: Principle of required quantity for material prospecting vs. theoretical quantity from the project drawings.
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5.2.2
Soil descriptions and profiling
General
Soil descriptions and profiling shall be carried out in accordance with the
method outlined in Appendix 2 after Brink & Jennings. All pit logs shall be
drawn to scale in columns, with the result of the soil description written on them
or referred to in a table.
Borrow pits
The data obtained from trial pit logs should be used to subdivide borrow pits
into areas comprising materials of similar characteristics. At least one sample
should be taken from each different material unless they are clearly unusable.
When profiling the pit, the following factors should be taken into consideration:
● Colour
● Soil type
● Origin
Overburden should always be sampled.
Colour
The colour of the material may reflect the gravel type, and the colours should be
based on a standardised colour chart.
Soil type
The grain size proportion of the material determines the engineering properties
of the material and its behaviour within the pavement. The particle shape is also
important in this regard.
Origin
Where the origin of the material can be clearly defined, especially in terms of
residual, transported or pedogenic materials, then it should be used to refine the
grouping further. This should e.g. include the parent material if possible. The
degree of induration or development of pedogenic materials should be noted e.g.
calcified sand or nodular calcrete.
The material could be described as boulders,
gravel, sand, silt, clay or some combination of
these e.g. clayey gravel with boulders, gravelly
sandy clay, etc. In addition, the prospector’s
knowledge of the local soil types in terms of
performance should be used.
5.2.3
Sampling
Representative samples and sample size
It is particularly important to ensure that the sample is representative for the
material. A common source of error is to sample in a vertical profile, but not
take the same amount of material from each depth over the layer that is being
sampled. E.g. by sampling more of the material that easier to excavate rather
than a fully equal amount at all depths.
Sufficient size of sample is important in order for the sample to accurately represent the original material and to enable the required laboratory tests to be performed. The larger the grain size the larger sample is required in order to represent the original material and because more material will be discarded as oversize in the laboratory. See Figure 5.3. The required minimum sample size given
in Figure 5.3 does not take account of the laboratory test programme. Additional
quantities of sample material may be required depending on the requirements of
the tests to be carried out. Table 5.1 indicates the approximately required sample
size depending on tests to be carried out.
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Sampling with excavator.
Chapter 5
Alignment Surveys
73
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Table 5.1: Required size of sample.
Purpose of sample
Indicator testing, i.e.
Atterberg limits, grading,
moisture content
Compaction tests, CBR
Comprehensive examination
of construction material
including stabilization.
Strength, shape, etc
Soil type
Clay, silt, sand
Fine and medium gravel
Coarse gravel
All soils
Mass (kg)
1
5
30
70
All soils
150
Rock
40-100
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Figure 5.3: Minimum sample size of soils as a function of particle size.
The suitability of the overburden for use as road
building material shall be assessed and samples
taken as required depending on potential use and
uniformity of the overburden.
74
Chapter 5
Alignment Surveys
Sampling procedure from trial pits
Care shall be taken to avoid contamination of different strata during sampling.
The following procedure should be followed:
A. Choose one section of the trial pit that contains a representative profile of
the material.
B. Remove the topsoil (usually 0-200 mm thick) in order to expose a groove
that will yield sufficient quantities of material from each of the layers below.
C. Clean the bottom of the trial pit.
D. Refer to Figure 5.4. When sampling the overburden, place a sample bag
(flat) at the bottom of the pit. Using a shovel or pick, break the material
along the groove such that the material falls on top of the sample bag at the
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bottom of the pit. Put the material into a clean bag and place it outside the
trial pit. The exercise should be repeated until sufficient quantity of material
has been collected. Make sure that the layer being sampled is not contaminated by material accidentally falling in or scooped up with the sample.
E. To prepare the next stratum for sampling, clean the groove to the top of the
stratum to be sampled, also clean the bottom of the pit. Break the material
along the groove as above until sufficient quantity of the material has been
collected.
F. Place another sample bag at the bottom of the pit and repeat (E) above.
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Guideline no. 3, Roads Department, Botswana
- 2000.
Figure 5.4: Method of sampling from trial pit.
Quartering
If necessary, collect a large sample and quarter it down to the required size
((Figure 5.5).
Figure 5.5: Reducing the sample size by quartering.
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Labelling
Whenever there is doubt about the identity of a sample it shall be discarded and
any laboratory testing is a waste of resources. There is often great cost and time
spent on obtaining the sample in the field, and re-sampling on account of poor
practice in handling and marking should never occur. It is therefore of great
importance that labels must be clearly written with permanent ink and contain
all necessary information and minimum the following:
● Name of project.
● Chainage or borrow pit number.
● Sample pit number.
● Sample depths from/to.
● Sampling date and name of responsible officer.
Labels shall always be kept inside the bag
even when additional marking is made on
the outside.
The label shall always be placed in a plastic bag in
order to be kept dry.
Figure 5.6: An example of good labelling.
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5.3
Alignment soil surveys
5.3.1
Introduction
Design input
The alignment soil survey provides background data for the design of earthworks layers for improved subgrade and for treatment of areas with problem
soils. Besides enabling earthworks design to be carried out, the soil survey also
provides valuable information to the designer of the geometric alignment. It is
therefore important that following a thorough desk study, the field work on the
soil survey is carried out in the following sequence:
1. Reconnaissance.
2. Initial survey with limited sampling.
3. Detailed centreline soil survey related to an established centreline in the
field.
It is also vital that engineering staff utilises time spent in the field at the time
of the survey to go back and extend previous reconnaissance to further detail,
and thereby gather knowledge of the project area. Such knowledge can lead to
changes in the design, making cost savings possible.
An alignment soil survey carried out with consciousness to any potential cost
savings can make major improvements to the project economy by adjustments
to the alignment. Examples of changes having potential for cost savings on the
basis of a good alignment soil survey are the following:
● Αvoiding areas with poor soil conditions or poor drainage conditions.
● Ιmproved utilisation of material in the road corridor by making cuttings
where economies can be made, and minimising cutting in areas where spoiling of the material is likely.
● Μinimising cuttings to depths which may cause increased spoiling of mate-
rial, such as shallow cuttings in topsoil where small quantities or poor material quality leads to spoiling or uneconomical utilisation for earthworks.
● Minimising filling in areas where earthworks material is scarce.
Alignment surveys as basis for gravel surveys
The alignment soil survey often gives one of the most important clues for starting the survey for construction materials. This information can prove to be vital
knowledge when surveying for construction materials outside the alignment.
The test pits excavated in the alignment survey
gives the field staff knowledge of material types
available in the area and clues to their location.
5.3.2
Establishment of centreline
A detailed alignment soil survey can be wasted cost and effort if it is not possible to establish the exact location of each sample on subsequent detailed plans
for the road project. This means the centreline soil survey should preferably
start after the initial centreline has been established in the field. Where it is not
possible to wait for surveyors to establish the centreline, it is vital to find some
other reliable means of giving the samples an identity that makes it possible to
trace back their location to the alignment and chainage once established.
If proper identification of samples in the field is not possible, then further field
work on alignment soil surveys should be limited to a reconnaissance survey
with a reduced sampling programme, carried out to get an overview of the soil
conditions in the project area.
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5.3.3 Sampling depth
The sampling depth depends on the vertical alignment in relation to ground
levels, plus road type and envisaged traffic loading. The sampling depth should
cover the design depth of the pavement, which is the depth measured from the
FINISHED ROAD LEVEL down to the depths shown in Table 5.2.
Field sampling of centreline.
It is impossible to know the depth measured from GROUND LEVEL to the depth of
sampling unless there is knowledge about the approximate vertical alignment
of the project road. E.g. the values in Table 5.2 may translate into prohibitively
large pit depths in a cut, making sampling impossible, or the design depth may
be entirely within the depth of an embankment fill, where quality of available
fill materials decide the required pavement design rather than in-situ soils. Special consideration should however be made where there is occurrence of expansive soils. In such
cases
ter 5 it is necessary to also sample below design depth. I.e.
Chap
expansiveness of soils deeper than the design depth will have an effect on the
performance of the pavement due to seasonal movement rather than strength,
and this information is an important design input affecting project cost.
Subgrade
ter 5
Chap
Subgrade
s
Pavement and Material
General
5.0
Comments:
t Rehabilitation/
/Chapter 9 – Pavemen
below the design
Propertie s of soils affect pavement
depth may indirectly
are generally unrelated
per-formance, but
to traffic loading.
Design Manual - 1999
al
e evaluation for structur
es the methods for subgrad g and laboratory
samplin
This chapter describ
new roads, conventional basis of CBR values. Strength
pavement design of
is classified on the
tely
testing. Subgrade strength may be used provided they are adequa
CBR
Works at
indicators other than
d by the Ministry of
approve
are
and
correlated to CBR values
project level.
ne subgrade strength
ation methods to determi
overlay
Alternative field investig purpose of pavement rehabilitation or
the
may be employed for
design.
5.1
Design Depth
level to
from the finished road an effect
defined as the depth
the soil no longer has
The design depth is
bearing strength of
c loading. Figure 5.1
the depth that the load
of
ance in relation to traffi
structural components in
on the pavement’s perform
in relation to the main
values
shows the design depth and Table 5.1 gives the design depth
rks
pavement and earthwo
type.
relation to design road
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Table 5.2: Design depth measured from finished road level.
Design depth from finished road level (m)
Road type
General requirements
Paved trunk road
Other roads
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5.2
eys
Centreline Soil Surv
available information
be carried out to gather , geology, soils, known
climate
A desk study shall always
ations, topography,
c load
d and expected traffi
about previous investig
type, design standar
are likely).
material sources, road large number of very heavy axle loads
r
structures shall be
of
ion
conditions (i.e. whethe
foundat
stability and
Issues related to slope
addressed separately.
classified
General
g strength, shall be
their properties, includin excavated along the road
Subgrade soils and
by the use of trial pits
based on soil surveys
line.
Works
5.2.0
Ministry of
5.2
Pavement and Materials Design Manual
- 1999.
0.8
0.6
Heavy traffic load classes
TLC05-H to TLC50-H
1.2
1.0
Figure 5.7 shows examples of longitudinal profiles of two sections of road,
one through a fill area and one through deep cut area. Common for both
these examples is that NONE OF THE TEST PITS GIVE INFORMATION FOR THE PURPOSE OF PAVEMENT DESIGN OR DETERMINATION OF IMPROVED SUBGRADE LAYERS.
5.3
Example: High Fill
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Extensive laboratory testing for the purpose of
structural pavement design in the examples shown
in Figure 5.7 is likely to be a waste of money.
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Example: Deep Cut
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Figure 5.7: Examples, longitudinal profile. Information from trial pits.
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5.3.4
Sampling frequency
Distribution of pits and sampling locations
The sampling frequency depends on a number of factor, where available funds
for the actual survey work is one of them. This means the number of locations
one can afford to sample has to be used to the maximum and distributed wisely
to bring forward the following information that the alignment soil survey should
give the designer:
● Location of significant changes in soil conditions.
● Ρepresentative information about each significant soil condition, sufficient
to design the pavement for the area.
In order to utilise the resources optimally the following measures may be employed by the field staff:
● Making uneven spacing of the sample pits to detect significant changes in
soil conditions and reduce work in areas with similar conditions.
● Excavating more pits than what is sampled and using soil descriptions to
reduce the need to carry out laboratory testing of material having the same
characteristics.
Minimum requirements, average sampling frequency
The average sampling frequency given in Table 5.3 is a measure of the total
effort put into soil alignment surveys that one would expect for average conditions and project type.
There will be considerable variation in sampling frequency along the road line
for one project, and there will also be a varying need for effort on soil surveys
from project to project depending on site conditions and project type.
Table 5.3: Sampling frequency.
Road type
Indicator testing
Minimum number of CBR tests for any
homogenous section
CBR strength
testing
Min. for statistical
analysis
Paved trunk roads
Minimum 4 per km
Minimum 2 per km
Other trunk roads
Minimum 2 per km
Minimum 1 per km
Gravel roads
Minimum 2 per km
Minimum 1 per 2 km
5 tests
Absolute minimum
3 tests
Additional investigations or specialised tests shall be scheduled separately as
required.
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5.4
Commen land form in the country, where
“good” gravel is found.
Soils and gravel sources
5.4.1
Introduction
There is no map covering Tanzania to show construction materials for road
works, similar to a geological map. Gravels often occur in relatively small
localised deposits, scattered around the landscape and often hidden under overburden. Material prospecting involves looking for clues to the occurrence of
useful materials and then digging to see what may be there. Learning to identify
features that indicate the presence of gravel from the interpretation of maps and
other information is a central activity in prospecting. However, the most important parts are:
1. Desk study, collect existing data and information about project requirements
regarding quantities and quality.
2. Field reconnaissance.
3. Field survey, detailed investigations.
4. Pit excavation, sampling.
5. Testing, material evaluation and reporting.
5.4.2
Environmental considerations and occupied land
Resources
Construction materials are among non-renewable resources and in view of the
increasing importance of protecting the natural environment and resources, it is
important to make the best use of a source, once found. This implies mapping
it and describing it accurately so that it can be correctly classified and therefore
correctly applied to a specification.
Borrow pit of natural gravel. Careful
stockpiling is essential to obtain good
quality material.
Conflict of interest
The conduct of Environmental Impact Assessment (EIA) is a mandatory requirement in Tanzania, for new roads and road up-grading, as for other substantial developments. The purpose of EIA is to ensure that a project does not
achieve its own goals at the expense of loss or inconvenience to non-beneficiaries or future generations.
It is important to foresee potential conflicts of interest with the environment and
occupants of land in the area already at the time of prospecting for materials.
The responsible field staff is required to obtain all required permissions according to legislations before starting their work. Wherever possible occupied land
and sensitive areas should be avoided even though permission to prospect has
been granted. Such areas are likely to be banned from full material exploitation
at the time of construction and it does not gain the project to have its design
based on material sources that are unlikely to be available.
5.4.3
Desk study for gravel and soil surveys
It is vital for an economical and successful field survey that a thorough desk
study is carried out. Normally the major cost of the survey is in the field work,
secondly the laboratory work, which value depends entirely of the quality of the
field survey.
The most important information required prior to the field survey is in the answer to the following questions:
● What alternative types of pavement that may be constructed and what are
the required material quality for the various pavement alternatives?
● What quantities of material do we look for?
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● Do we also look for sources of sand and rock for concrete structures or
pavement layers?
In order to increase the likelihood of finding construction materials, the following sources should be checked for any relevant information prior to carrying out
field work:
● Geological maps, aerial photos and soil maps where available. What types
of material can we expect to find?
● Previous surveys in the area which could have been undertaken by a variety
of organisations and companies for a variety of purposes.
● Previous exploitation of material sources in the area, such as quarries, borrow pits or mines.
● Previous construction projects in the area, where as-built data or informa-
tion from the time of construction could be of vital importance. Both supervision and construction staff should be approached in addition to government staff that may have information.
5.4.4
Quantity estimates
It is important to make an appropriate allowance for wastage when making
resource estimates. Wastage may typically vary from 5% to 30%. In addition to
wastage it is important during field investigations to take into account a considerable “loss” in the case of marginal qualities of materials, whereby parts of
a material source may be rejected after laboratory testing. On this basis one
should aim at a DOUBLING OF THE REQUIRED QUANTITIES of materials for pavement
layers at the time of prospecting in order to take account of wastage, losses and
rejected materials Figure 5.9 illustrates the total ‘loss’ of available quantity one
may experience from the investigation stage to construction.
Main causes of wastage or ‘loss’ of excavated
material at borrow pits are loss or contamination
during overburden clearance and from the lower
surface of the borrow area by over excavation, in
addition to loss at the floor of stockpiles. When
accurately calculating volumes of pit excavation
required for a specific construction layer, it is also
necessary to make an allowance for wastage at
the construction site. The amount of wastage will
depend on a number of factors including loss by
removal of oversize material, loss associated with
loading, transport and over placement of material
on the road.
In addition to wastage there may be a significant change of material volume
from the Borrow pit or cutting to the compacted road. This is due to expansion
of the volume by excavation and reduction by subsequent compaction on the
road. Such change of volume depends on material type and Figure 5.8 gives
typical bulking/shrinkage factors for various material types.
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Figure 5.8: Theoretical material volumes - without loss - in natural, loose and compacted
states.
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Figure 5.9: Typical ‘loss’ of available material volumes during the process of winning
natural gravel for pavement layers.
As a rule, the gravel prospecting should realistically AIM FOR THE DOUBLE
QUANTITY of the theoretical requirements from the crossection. Even doubling
the theoretical quantity may be insufficient in areas where:
● The material quality is marginal, thereby increasing the loss after laboratory
testing.
● Τhe sources are small and scattered or appearing in thin layers, thereby
increasing the loss during borrow pit operations.
● Τhere is a large proportion of oversize material, thereby increasing the loss
due to removal during processing on the road.
5.4.5
Minimum requirements, sampling frequency
Potential borrow pits shall be surveyed by trial pit investigations and sampling.
The survey shall prove sufficient quantities for all earthworks and pavement
materials as outlined in Chapter 5.4.4 Quantity estimates. Minimum sampling
and testing frequency for detailed borrow pit investigations is shown in Table 5.4.
Table 5.4: Borrow pit investigations, minimum test frequency.
Intended use
Maximum cubic metres to be
represented by one test
CBR
Grading and PI Aggregate strength
Bituminous basecourse
5 000
3 000
Cemented base-course
5 000
5 000
Cemented subbase
10 000
10 000
Base course - natural
5 000
3 000
gravel
Subbase - natural gravel
10 000
5 000
Improved subgrade
10 000
10 000
Fill
20 000
20 000
No less than four trial pits shall be excavated in each borrow pit.
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Chapter 5
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20 000
20 000
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5.5
Rock Sources
5.5.1
Introduction
Rock source prospecting involves looking for clues to the occurrence of useful
materials. The engineer should be able to identify features that indicate the presence of hard rock from the interpretation of available topographical and geological maps and even more important, the careful assessment of aerial photographs. Based on the initial study and field reconnaissance sampling, laboratory
testing and finally drilling is required where the initial samples are encouraging.
A natural sequence of an investigation programme will be:
1. Desk study.
2. Field reconnaissance.
3. Initial sampling and testing of surface rock materials.
4. Drilling and/or seismic refraction traversing to prove overburden, quantity,
uniformity and quality of rock (proof drilling and core drilling).
5. Testing, material evaluation and reporting.
Normally the overriding cost of quarry prospecting
is in the drilling activity of the field work, secondly
the laboratory work, which value depends entirely
of the quality of the field survey.
The contractor may not opt to open more than one
rock source on a project. However, identifying several potential quarry sites, increases the chance of
receiving competitive bids from contractors having
plant with higher mobility.
The selection of hard rock sources for road projects is a major consideration,
and the engineer and geologist must be aware of all the factors which together
produce a satisfactory hard rock source for full scale production. The nature,
extent and accessibility of rock sources play an important role in construction
costs. Transport of material is a major cost factor in all road construction, and to
ensure economical construction it is important that sources of suitable rock are
found in one, or preferably several, locations along the alignment.
5.5.2
Desk study for rock quarry surveys
It is vital for an economical and successful field survey that a thorough desk
study is carried out. The following sources of information should be checked for
any relevant data prior to carrying out any field work.
● Topographical maps and Geological maps where available.
● Aerial photographs.
● Collect existing data and information about project requirements regarding
quantities and quality.
● Previous surveys in the area which could have been undertaken by a variety
of organisations and companies for a variety of purposes.
● Previous construction projects in the area, where as-built data or information from the time of construction could be of vital importance. Both super
vision and construction staff should be approached in addition to government staff that may have information.
● Information on commercial or governmental exploitation of material
sources in the area such as quarries, borrow pits or mines.
● Information on type of pavement to be constructed and required material
quality for the various pavement alternatives.
Potential quarry site at a rock outcrop.
5.5.3
Quantity estimates
When selecting a hard rock quarry for construction the quality and volume are
naturally important factors. These factors must be revealed during the investigations of the quarry. Sufficient drilling to prove a quarry is most important.
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What might first have appeared as an extensive
body of rock, could prove to be a confined body,
limited in size, when quarrying commences. For
some volcanic rocks, unsuitable soft ash may be
located underneath a hard rock cover of considerable thickness.
Old quarry rock face. Samples of fresh rock
from these sites give very reliable laboratory
test results.
It is in the interest of both Employer and Contractor that an adequate volume of
rock meeting the specifications is available. There is a significant expansion in
material volume from the in-situ quarry to blasted and crushed material ready
for road construction as shown in Figure 5.8. However, when making quantity
estimates, wastage and loss must be considered, due to e.g. unrevealed substandard material. At the time of prospecting, a volume of minimum 50 % in excess
of the required quantities of construction materials should be proven in all cases
of rock quarry investigations, in order to take account for wastage, loss and
rejected materials. This safety factor in respect of available rock quantity is necessary due to the severe consequences for implementation of the project if the
source runs out during construction. If the quarry shall solely be used for single
sized aggregate production, the proven volume should preferably be double the
required quantities, due to production of undesired fines.
5.5.4
Rock quality
In the selection of a hard rock quarry, the question of quality is naturally of
prime importance. Adequate investigations are essential if problems are to be
avoided during quarrying. It is therefore necessary not only to pit and drill the
rock body adequately to prove the QUANTITY available, but to ensure that rock
body of acceptable and uniform QUALITY is present throughout the selected rock
mass. Pit excavation, proof drilling and seismic refraction would show depth of
overburden, and whether the rock body is uniform and of adequate size. In addition to surface sampling, further samples to prove rock quality in depth must be
taken from rock cores obtained by core drilling.
5.5.5
Surface sampling
Where to sample
The field reconnaissance is followed by an initial sampling programme. Based
on the initial reconnaissance, it is important that only those sites which appear to
have material in adequate quantities and of adequate quality should be sampled.
Quarry waste should always be sampled
and tested. Depending on the properties of
the material, the material may be used in the
pavement layers or as surfacing aggregate.
For security reasons it may be difficult to obtain
permission for use of dynamite required for
blasting.
Representative samples
Only samples considered representative of the material which is considered
usable shall be taken. Selected material of the site of better quality but low
in quantity shall be avoided. Samples should preferably be taken at several
locations of the potential quarry site.Where overburden is encountered pits or
trenches must be excavated down to the hard rock surface. Sampling is usually
performed by chiselling out pieces of fresh rock using a chisel or a pickaxe. It
is recommended, however, to excavate samples by means of blasting. Holes for
the required explosives can be drilled by petrol propelled hand held equipment,
e.g. a Pioneer or Cobra percussion drill.
Weathered/fresh
Weathering is a general term referring to the breaking down of rocks into smaller
particles. The process can involve chemical and/or physical breakdown. Weathering typical results in an accumulation of natural gravel and soil. Weathered
rock are usually rippable with bulldozers and excavators. When prospecting
for a rock source it is important to sample fresh and hard rock and to avoid the
weathered material.
Boulders and oversize material in coarse
gravel should not be overlooked as a source
for e.g. surfacing aggregate.
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Sample size
The size of samples will depend on the number and type of tests to be performed
on the material. Typically a normal sized sample shall be approximately 40 kg.
However, for an extensive testing programme samples of 100 kg or more are
required.
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5.5.6
Drilling
General
If test results on initial samples are encouraging, a drilling programme shall be
set out to prove the quantity available and uniformity and quality of the rock in
depth. At this stage in the prospecting seismic refraction traversing may be used
to provide information on the depth of overburden, weathered rock and the hard
rock profile.
Proof drilling
Proof drilling using rotary percussion drilling equipment may be used to determine overburden, weathered rock and the depth to hard rock. By drilling into
hard rock one may also get an indication of the relative quality of the rock in
depth. Core drilling should, however, be regarded as the preferred method for
the latter purpose. For determination of overburden and extent of weathered
rock, both pit excavation and seismic profiling may be employed.
Rock cores.
Core drilling
Core drilling is a costly, but the most effective method of confirming geology
and obtaining information of the bedrock below the hard rock profile. Core
drilling is rotary boring with core extraction where core samples are taken from
progressively increasing depth in order to obtain a complete record of the subsurface rock, and samples for laboratory testing of the rock mechanical properties.
Generally, drilling is helped with water as a circulating medium. Double extractor “swivel type” core barrels with bottom discharge are recommended for good
core recovery. For drilling in solid and stable rock core sizes down to 45 mm
may be used, but larger diameter gives better samples. A core size of 76 mm is
usually satisfactory, but 100 to 50 mm and the triple barrel technique give the
best results in weak, weathered or fractured rock. Refer to BS 5930 and BS 4019.
Core recovery is seldom complete over the length of the borehole. In such cases,
experience is employed in assessing the nature and quality of the rock that has
not been recovered.
Core sampler with extracted rock core
box for storage and transportation of core
samples.
Logging
The logging and description of core samples varies considerably, and the methods employed are always dependant on the type of information required for a
particular project. The logging should be given a graphical presentation. For
rock source prospecting the following are the most important data required by
the engineer.
1. Drilling date. Type of machine, drilling method, size of core and depth of
casing installed. Elevation of the borehole and its coordinates. Its orientation - vertical or inclined in degrees and direction.
2. Core recovery. The percentage length of core recovered in relation to the
length of the drill run. The volume of the sample recovered in relation to the
volume drilled.
3. Rock quality designation (RQD). The length of core sections greater than
10 cm as a percentage of the total length drilled.
4. Rock weathering grade. Usually shown on a scale of 1-5, where 1 is fresh
and unaltered hard rock and 5 is very weak weathered rock. Assessments
are subjectively based on the degree of weathering and fracturing.
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5. Discontinuities. Faults, shear zones and jointing are indicated, and their
orientation.
6. Fracture index. The number of fractures or joints per meter of core recovered.
7. Geological description of strata. Individual rock horizons are described in
terms of consistency, structure, colour and type; e.g. unweathered, steeply
dipping (giving degrees and direction) pale brown granitoid gneiss. Rock
horizons shall be described and not the rock in each drill run.
8. Symbolic log. A log in which easily recognizable symbols are used to designate various rock types.
9. Sampling. Rock types or areas from which samples have been taken for
laboratory testing.
The extracted cores should be placed in core boxes, see Figure 5.10. It is good
practice on completion of an investigation to photograph the cores recovered
from each borehole. This provides both a permanent record for each borehole,
as well as being a useful reference in conjunction with the study of core logs.
Containing of core samples
Core samples extracted from the drill holes shall be placed in adequate core
boxes (e.g. wood or plywood), with partitions, in the same position as they occurred in the ground, see Figure 5.10. All weak material shall be placed in plastic sleeves immediately after extraction and placed in its proper place in the core
box. Core loss shall be marked by a wooden rod of the same length as the core
loss. The core boxes shall be clearly marked with drill hole number, inclination
of the hole and depths of the corresponding cored zone, as well as the original
number of the box in the series of cores boxes from the same hole.
Figure 5.10: Core box before placing wooden rods for marking core loss.
Reporting
After the rock sources have been delineated and sampled, a geometric surveyed
should be carried out to locate, the pits and drill holes. The results should be
recorded on a plan including borehole/pit elevation. Similarly the geologist
should incorporate all relevant information on the plan, i.e. depth of overburden,
volume of usable material, test results and pit and drill hole logs.
This information forms the basis for assessing the necessity for carrying out further exploration in order to locate additional sources or increase those already
located.
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6
CONSTRUCTION CONTROL
1
Introduction
2
Geotechnique
3
Pavement evaluation
4
Axle load surveys
5
alignment surveys
6
Appendices
6.1
6.2
6.3
6.4
6.5
Introduction......................................................................................... 89
Earthworks and unbound layers ....................................................... 89
6.2.1 Introduction .............................................................................. 89
6.2.2 Sampling on the road ............................................................... 90
6.2.3 Density measurement ............................................................... 90
6.2.4 Testing of moisture content...................................................... 93
6.2.5 Direct strength measurements .................................................. 94
Cemented Layers................................................................................. 94
6.3.1 Scope ........................................................................................ 94
6.3.2 Sampling .................................................................................. 94
6.3.3 Density ..................................................................................... 94
6.3.4 Control of site operations ......................................................... 94
6.3.5 Coring....................................................................................... 95
Bituminous Layers .............................................................................. 95
6.4.1 Scope/introduction ................................................................... 95
6.4.2 Sampling .............................................................................. 95
6.4.3 Temperature.............................................................................. 96
6.4.4 Density ..................................................................................... 96
6.4.5 Moisture- and bitumen content in cold bituminous mixes....... 96
Bituminous Seals ................................................................................. 98
6.5.1 Scope ........................................................................................ 98
6.5.2 Application rate (binder, tack coat, prime and fogspray)......... 98
6.5.3 Temperature (binder, air, surface) ............................................ 99
6.5.4 Aggregate spread rate............................................................. 100
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6.6
6.7
6.5.5 Sampling (binder/prime) ........................................................ 100
6.5.6 Application of precoater......................................................... 100
6.5.7 Equipment control and calibration ......................................... 100
Concrete ............................................................................................. 101
6.6.1 Introduction ............................................................................ 101
6.6.2 Sampling of fresh concrete..................................................... 101
6.6.3 Slump of concrete .................................................................. 101
6.6.4 Making and curing specimens for compression test .............. 102
6.6.5 Taking core samples of hardened concrete ............................ 102
6.6.6 Special tests............................................................................ 103
Construction control test methods................................................... 104
References
● Pavement and Materials Design Manual - 1999. Ministry of Works, Tanzania.
● Standard Specifications for Road Works - 2000. Ministry of Works,
Tanzania.
● Guideline no. 2 Pavement Testing, Analysis and Interpretation of Test Data.
Roads Department, Botswana - 2000
● Guideline no. 3. Methods and Procedures for Prospecting for Road Construction Materials, Roads Department, Botswana - 2000.
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6
CONSTRUCTION CONTROL
6.1
Introduction
This chapter should be read in close conjunction with the Standard Specifications
for Road Works-2000, where the requirements for testing and quality control is
set out in full detail.
Construction control for contract roadworks is divided into:
Production control: Production control is carried out by the contractor for the
purpose of satisfying himself that chosen methods and
materials meet the specified standards. The production
control serves as an early warning for the contractor and
helps reduce his risk of failure and associated additional
cost to himself of remedial work. The contractor may be
obliged to submit results from the production control to
the supervising engineer and may in some cases be taken
as part of the acceptance control.
Acceptance control: Acceptance control is carried out by the supervising
engineer, or on his behalf, to ensure compliance with the
specified standards and to enable payments to be made.
Results from acceptance control will normally form part
of the as-built data as documentation of quality submitted
to road inventories of the agency.
This chapter contains guidelines for field testing carried out in the acceptance
control, whereas the production control is mentioned where appropriate, however at lesser detail.
It is essential for an effective construction control that there is sufficient and
equal motivation for achieving correct quality of the final product on the sides
of both the contractor and the representatives for the controlling authority. One
should always aim for a situation whereby all parties see benefits in striving for
the highest possible quality of materials and workmanship under the circumstances.
6.2
Having to re-do work, or replace material (picture), is a loss to all involved in the
construction.
Earthworks and unbound layers
6.2.1
Introduction
Testing on the road and sampling from the road is carried to provide documentation of the quality of materials and workmanship as part of the acceptance
control. The following categories of field testing work are described here:
● Sampling for laboratory testing.
● Density tests.
● Tests of moisture content.
● Strength measurements of compacted layers or in-situ.
Sampling from stockpiles or production plant is normally part of the production
control carried out by the Contractor and choice of type and amount of control
lies with him unless otherwise specified or directed.
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Table 6.1 shows the main methods and purposes of the field testing activities
during quality control on the road.
Table 6.1: Methods and purposes of the field testing activities.
Field testing activity
Sampling
Moisture testing
Shovel and bag
−
Sand replacement
−
Auger or coring (in
rare cases)
−
Nuclear gauge
−
Water balloon
−
Core cutting (in rare
cases)
−
Compaction control
−
−
Indirect test of
strength
−
Methods
Main purpose
Density testing
−
−
Laboratory testing for
quality
−
Reference for density
testing
6.2.2
Strength testing
−
Sampling for ovendrying
−
Speedy moisture
−
Nuclear gauge
−
Sampling for frying
pan (in rare cases)
Part of the
compaction control
Indirect test of
strength
−
Plate bearing test
−
DCP
−
Field CBR
−
Clegg hammer
−
Documentation of
pavement strength
−
Indirect control
of compaction or
moisture content
Sampling on the road
General
Sampling from the road includes sampling from compacted or un-compacted
layers and is normally part of the acceptance control. Production control will
normally be carried out before material has been brought to the road and sampling for this purpose is done at the material source.
Sampling frequency
The sampling frequency depends on the layer under construction and tests
intended to be carried out. Table 6.2 shows the minimum frequency for acceptance control on trunk road contracts. A lower frequency of sampling may be
employed on contracts for construction of secondary roads.
Table 6.2: Sampling Frequencies, earthworks and layerwork.
Layer and nominal class of material
Tests to be carried out
CBR
MDD, PI, grading
CBR, PI, grading
MDD
CBR, PI, grading
MDD
CBR, PI, grading
MDD
CBR, PI, grading
MDD
UCS, PI
MDD
CBR, PI, grading
MDD
UCS, PI
MDD
Roadbed
Earthworks fill using soils: (G3)
Backfill to culverts and structures
Improved subgrade (G7, G15) or
Gravel wearing course (GW)
Subbase: (G25, G45)
Subbase: (CM, C1)
Base course: (G60, G80)
Base course: (CM, C1, C2)
Base course using crushed aggregate: (CRS)
Base course using crushed aggregate: (CRR)
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LS, grading
MDD
LS, grading
Apparent density, TFV
TANROADS
Sampling frequency, minimum
10000
5000
2000
1000
500
200
10000
5000
m2
m2
Cu.m.
Cu.m.
Cu.m.
Cu.m.
m2
m2
1
sample per
1
sample per
1
sample per
1
sample per
1
sample per
5000
m2
1
sample per
5000
m2
1
sample per
1
sample per
5000
2500
5000
2500
m2
m2
m2
m2
1
sample per
5000
m2
2500
m2
1
sample per
5000
m2
10000
m2
ch6
Sampling procedure
Sampling from the road should be carried out at one chainage profile, i.e. not
by taking many partial samples along the road to make up a combined sample.
Sampling from chainage profiles gives the correct impression of the variability
of the material whereas adding small amounts of material along the road will
make a mixture of material that in practice will not be mixed on the road by
the processing equipment. Effective deliberate mixing of different materials on
the road can be expected only where the material has been dumped in the same
profile chainages by dumping one material on top of the other, or by dumping in
separate rows next to each other.
Samples for tests of grading and Atterberg limits should be taken AFTER COMPACTION
on the road. This is particularly important where the material contains soft particles that break down easily during compaction. The alternative, if this is not
possible, is to ensure that the sample for tests of Atterberg limits are taken after
the material has been compacted in the laboratory.
The risk of errors by mixing material of different
types when changing material source is minimised
by adherence to the procedure of taking samples
in chainage profiles.
Time of sampling
Tests
After compaction
Grading,
Atterberg limits
Before compaction
CBR, MDD
Samples for tests of MDD and CBR should always be taken BEFORE COMPACTION
on the road as the MDD reference value and measured CBR strength will be
incorrect if the material is compacted for the second time in the laboratory.
In all cases samples should preferably be taken AFTER MIXING of the material by
the equipment on the road. If this is not possible, sampling should be carried out
by taking several partial samples within the vicinity of the chainage profile that
is the reference identification of the sample.
6.2.3
Density measurement
General
The principle of the conventional methods to measure density is to excavate a
hole in the layer - which gives the weight of material - and to measure the volume of the hole. The difficulty is associated with finding the volume in the layer
that the excavated material occupied.
● Sand replacement and the water balloon methods rely on finding the volume
by replacing the excavated material with a medium of known density, either
water or loose, dry sand. The water balloon method is today not very common due to practical problems in execution of the test and is generally not
recommended.
● Density measurements with nuclear gauges rely on the instrument’s interpretation of differences in resistance to penetration of nuclear radiation
through media of different density.
● Core cutting gives volume by predetermining the size of the excavated hole
with a calibrated core of known volume.
Sand replacement testing is slow, but is the
reference method that most contract specifications revert to in case of disputes.
In all cases the DRY density is the parameter that shows degree of compaction,
i.e. describing how closely the solid particles are packed together, and is the
reported result of density measurements for construction control. The moisture
content of the tested material is therefore an essential part of the measurements
and will have a direct influence on the reported results. See further in Chapter
6.2.4.
Choice of method
In Table 6.3 the weaknesses and common errors of the various methods are
described, and the consequences of errors are described in broad terms.
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Table 6.3: Density test methods. Inherent weakness of method and common operator
errors.
Method
Inherent weakness of the test
method
•
•
Common operator error while
performing the test
Small sample size
Variable
Variation in the density of reference medium (sand or water)
Wrong shape of the hole, usually
narrower towards the bottom
Sand replacement or
water balloon
Irregular sides of the hole, especially
in materials with high content of
coarse particles
•
•
Nuclear gauge
•
Leaving out stones when
measuring moisture content of
the excavated material
Failure to take account of irregularities in the surface of the
layer
Failure to compensate for
inherent statistical variation
in nuclear radiation counts by
repeating the counts
Failure to carry out regular
calibration and service of the
instrument
Wrong or inaccurate reference counts
Location near vertical structures while measuring
•
•
•
Too low density
Variable
Too high density
Location near vertical structures
while taking daily standard
counts
Failure to apply moisture
correction
Too low density
Air gap between source and
measured material
Small sample size
Core cutting
Varies, usually too
high density
Too high density
•
Depth of measurement does not
coincide with thickness of measured
layer
Consequences
for the test
results
Change of soil density during coring
Leaving out stones when measuring
moisture content of the excavated
material
Variable
Varies, usually too
high density
Too low density
Test frequency
Table 6.4 shows the minimum frequency of field density testing for acceptance
control on trunk road contracts. A lower frequency of density testing may be
employed on contracts for construction of secondary roads. The frequencies in
the Table 6.4 are set out for conventional methods such as sand replacement and
water balloon. Required test frequency will depend on e.g. the capacity of the
equipment in use, and one should take advantage of high capacity equipment
such as nuclear gauges by increasing the frequency well above the minimum set
out in Table 6.4.
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Table 6.4: Testing frequencies, field density for earthworks and layerwork.
Frequency, minimum
Absolute minimum
1000 m2
3 tests per section and
1 test per 50 m
Roadbed
1
test per
Earthworks fill using soils: (G3)
1
test per
200 Cu.m.
Backfill to culverts and structures
2
tests per
10 Cu.m.
Fill or improved subgrade layers using dump rock: (DR)
Method specification
Improved subgrade layers using gravel/soils: (G7, G15)
1
test per
1000 m2
4 per section per layer
Gravel wearing course used on gravel roads: (GW)
1
test per
1000 m
2
4 per section
Subbase: (G25, G45, CM, C1)
1
test per
750 m2
5 per section
Base course: (G60, G80, CRS, CRR, CM, C1, C2)
1
test per
500 m
6 per section
2
3 per section per layer
2 per section
Frequencies should be increased when using high capacity equipment such as nuclear gauges.
6.2.4
Testing of moisture content
Table 6.5 shows the weaknesses and common errors of the various methods for
testing field moisture content in construction control, and the consequences of
errors are briefly described.
Table 6.5: Test methods for moisture content. Features of each method.
Method
Sampling and oven-drying
Speedy moisture
Features of methods for testing moisture content:
Advantages: +
Limitations:
Large sample size is possible.
+
Results are reliable when sampling testing is carried out correctly.
+
Results take long to be available, normally over night.
Results are obtained very fast.
+
+
+/-
Nuclear gauge
-
Sampling and pan-drying
+
+
-
Coarse material cannot be included and requires correction in order to find moisture
content of total sample. This leads to lesser accuracy and may introduce errors.
Results vary more than tests by oven-drying.
Small sample size reduces accuracy.
Calibration is required.
Results are obtained very fast.
The accuracy of the results depends on applying moisture correction against oven-drying
for each new tested material type.
The depth of measurement is normally varying depending on the moisture content (moist
makes shallow and dry makes deep) and measurements cannot normally be directed to a
certain desired depth by the operator unless special equipment is used.
Calibration is required.
Large sample size is possible.
Results are obtained fast.
Results are not reliable on materials having high organic contents, that will combust and
give a wrong impression of the moisture content.
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6.2.5
Direct strength measurements
Direct strength measurement carried out in construction control is normally required to document pavement strength for the purpose of making road inventory
rather than for acceptance control.
Plate loading tests and field CBR tests are
slow and therefore loosing popularity due to
high cost of investigating a limited number
of locations.
The following methods of direct strength measurements are the common ones:
● Dynamic Cone penetrometre (DCP).
● Clegg hammer.
● Field CBR.
● Plate bearing tests.
● Deflection measurements.
Testing of direct strength is more commonly applied during pavement evaluation and further description of the methods are given in Chapter 3.
6.3
Cemented Layers
6.3.1
Scope
This chapter includes construction control of layers made of materials cemented
by the use of cement, lime or other hydraulic binders such as pozzolans. The
material classes are denoted CM, C1 and C2 in the Pavement and Materials
Design Manual - 1999.
6.3.2
Sampling
Reference is made to Chapter 6.2.2 - Sampling on the road as procedures for
sampling are similar for cemented as for unbound layers. There are however
additional precautions when sampling fresh cemented materials. Samples for
compaction in the laboratory shall be tested not later than the time limit set for
compacting and finishing off the layer on the road. This time limit depends on
the type of layer and the type of stabiliser in use and is measured from the time
the stabiliser gets into contact with the material. In certain cases the Engineer
may direct that compaction of the sample in the laboratory shall be delayed
until the latest possible allowed time for compaction and finishing on the road
according to the Specifications.
6.3.3
Density
Reference is made to Chapter 6.2.3 - Density measurement as procedures for
density measurements are similar for cemented as for unbound layers.
6.3.4
Control of site operations
Timing of mixing operations
All hydraulic stabiliser require that the layer is mixed, compacted and finished
off within a certain period of time measured from the time the stabiliser came
into contact with the material. This type of control requires accurate record
keeping on site.
Stabiliser content
Laboratory testing of stabiliser content should be avoided by help of measurement records of operations on site. The Contractor’s production control can be
utilised for this purpose under the supervision of the Engineer if the procedure
are to the satisfaction of the Engineer. In the cases where control of quantities
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has been insufficient, or the effectiveness of the mixing process is under dispute,
the Engineer may instruct sampling for the purpose of testing the stabiliser
content. In such cases the sample and testing programme should be devised for
each individual case.
100 mm
6.3.5
Coring
Coring is normally not part of the acceptance control as the results will become
available too late to make decisions whether the material is acceptable and also
too late for remedial work to be carried out. In particular situations on site the
Engineer may however use tests on cores to satisfy himself that a layer meets
the required technical quality and make decisions whether the material needs to
be rejected and removed on this basis.
Interpretation of the coring results are however at the Engineers discretion as
coring is normally not part of the requirements investigated by the acceptance
control, that the Contractor is required to fulfil. The following tests are normally
carried out on cores taken from cemented layers.
● Density
● Compressive strength (UCS)
● Specialied tests, e.g. durability ref.
6.4
Bituminous Layers
6.4.1
Scope/introduction
The procedures for sampling and site control of bituminous layers will depend
on the type of material being used. The site control of cold mix types requires
procedures that differ from hot types. This caper gives an overview of the required site control for the two basic types of material, whereas the extent of the
control programme will depend on type of project and site management.
6.4.2
Sampling
Frequency
Table 6.6 gives the minimum sampling frequencies for layers made of bituminous materials.
Core through bituminous and cemented
layers.
Cores from stabilied pavement layers.
Table 6.6: Sampling frequencies for bituminous materials.
Layer and nominal
class of material
Base course of a bituminous mix or asphalt
concrete surfacing
Test
Extraction, grading
Marshall test
Sampling frequency,
minimum
1 Sample per
100 mm
10 000 m2
5 000 m2
Coring
Cores can be taken from the completed layer after some time after compaction depending on material type. Hot mixed material can be cored as soon as
the layer has cooled, whereas cold mixes require a considerable length of time
before cores can be retrieved. This period may vary from a few weeks to several
months depending the mix properties.
Asphalt concrete core.
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6.4.3
Temperature
Correct temperature at the time of compaction is essential to achieve a good
result for hot types of bituminous mixes, and requires that all loads arriving on
site are being checked. Where there has been delays during the paving operation, additional measurements may be taken from the hopper of the paver.
Thermometers with a sufficiently long and pointy measurement device shall by
penetrated into the load at three locations maximum 300mm apart and the average value shall be the reported temperature at this location. Several temperature
measurements should be taken from each load where variable results are experienced or the operation procedures are unsatisfactory for any reason.
6.4.4
Density
To achieve sufficient density at the time of construction is essential for the
strength and durability of the layer. Most types of bituminous mixes will show
increased density after some time under traffic. However excessive densification
by traffic loading will lead to poor riding quality and rutting, and is a sign of
insufficient compaction during construction or instability in the mix. In the case
of instability of the mix, shoving, excessive rutting and damage may result.
Measurement of field density is normally carried out by the nuclear gauge
method, but in cold mixes a volumetric method such as sand replacement may
be employed. See Chapter 6.2.3-Density measurement.
Table 6.7 gives the minimum testing frequencies for layers made of bituminous
materials.
Table 6.7: Testing frequencies for field density testing of bituminous materials.
Testing frequency,
minimum
Absolute
minimum
Base course of bituminous mix:
(BEMIX, FBMIX, DBM, LAMBS)
1 test per
6 per section
Base course of penetration macadam:
(PM80, PM60, PM30)
Method specification
Asphalt concrete surfacing
(AC20, AC14, AC10)
1 test per
500 m2
400 m2
6 per section
Frequencies should be increased when using high capacity equipment such as
nuclear gauges.
The density of the layer immediately after the
paver, but before rolling, is normally not measured.
The density at this position is however decisive for
the riding quality and close control of paver operation and maintenance is essential.
It is important for obtaining a good riding quality that as much as possible of the
densification of the layer is carried out by the screed of the paver before rolling.
The condition of the paver and maximum uncompacted layer thickness placed
in one operation are essential parameters in this regard.
6.4.5
Moisture- and bitumen content in cold bituminous mixes
Cold bituminous mixes contain both water and bitumen and therefore requires
careful attention to definitions. Soil mechanics and asphalt technology use different principles in definitions of liquid contents, and there should be a clear
agreement in cases where both water and bituminous binder are present. Definitions are given below.
Moisture content - definitions
The following sets out the ordinary definition of moisture content for soils and
gravel materials that DO NOT CONTAIN BITUMEN, such as aggregates for bituminous
mixes before bitumen is added:
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wN =
where:
wN
mW
mS
mW
mS
x
100
is moisture content where bitumen is NOT present in the material, i.e. before adding of bitumen (in % )
is mass of water (in g )
is mass of dry material (in g )
The following is the definition of moisture content for cold bituminous materials, i.e. AFTER BITUMEN IS ADDED:
wB =
where:
wB
mW
mSB
mW
mSB
x
100
If moisture content of materials containing bitumen
was calculated on the basis of dry aggregate
weight without bitumen, one would have to carry
out bitumen extraction test every time moisture
content was to be determined.
is moisture content where bitumen is present in the material,
(in % )
is mass of water (in g )
is mass of dry material including bitumen (in g)
This means the dry density of a cold bituminous mix is defined as the density of
the material including bitumen, but excluding water.
Method for measuring moisture content
Cold bituminous mixes contain water as an important part of the composition
of the materials. In order to obtain the density value of the material excluding
water, it is necessary to find the moisture content. Due to the presence of bitumen (that contains hydrogen) the nuclear gauge cannot be used for measuring
moisture content, and drying of a sample is required.
Bitumen content - definition
The following is the definition of bitumen content for cold bituminous materials:
B =
where:
B
mB
mSB
mB
mSB
x
100
It is worth noticing that moisture content is a
percentage of the mass of material without water,
while bitumen content is a percentage of the total
dry mass including the bitumen itself.
is bitumen content (in % )
is mass of bitumen (in g )
is mass of dry material including bitumen (in g)
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6.5
Bituminous Seals
6.5.1
General
This chapter includes procedures for sampling and site control of all work
where bituminous distributors are in use, i.e. surface treatments, tack coat,
prime, fogspray and work with related aggregates for these seals.
Surfacing operation.
Measurement of application rate by volume
requires further clarification of the temperature to
which the rate applies in order to be a meaningful
parameter.
6.5.2
Application rate (binder, tack coat, prime and fogspray)
General
Control of application rates of bituminous binders requires knowledge about the
aimed application rates and sometimes the relationship between weight, volume
and temperature of the sprayed material. Bituminous materials change their density as a function of temperature and it is important to clarify whether the aimed
application rate is by weigh in kg per area, or whether it is a volume measure in
litres per area.
It is important to obtain field testing results that are either directly comparable
with the aimed spray rates, or to make sure that reliable conversion factors are
applied where field results are not comparable with the aimed results. Examples
of conversion using dipstick measurements and respectively sample plates, are
given below, with the following legend:
Cold binder refers to the standard temperature
at which density testing of the binder has been
performed, usually 20oC.
Legend:
RVC is corrected rate, cold binder (in l/m2 )
RVH is corrected rate, hot binder, i.e. spraying temperature (in l/m2 )
RM is corrected rate, (in kg/m2)
MVH is measured rate, hot binder, i.e. spraying temperature (in l/m2)
MM is measured rate, (in kg/m2)
ρH
is the density of hot binder, i.e. spraying temperature (in Mg/m3)
ρC
is the density of cold binder (in Mg/m3)
Site measurement by volume (dipstick)
Measurement by DIPSTICK gives the application rate in VOLUME AT SPRAYING
TEMPERATURE. This is usually the most convenient and reliable method for
site control, but requires that the Contractor’s equipment is calibrated to the
satisfaction of the Engineer. Measurement by dipstick has a further advantage
that it gives a measure of consumed material. This eliminates any temptation
to under-apply binder and compensate for this by manually adjusting the spray
rate where sample plates are placed.
● Where aimed (specified) application rate is given in l/m2 COLD rate:
RVC =
Spraying tack coat.
MVH
ρH
ρC
x
● Where aimed (specified) application rate is given in kg/m2:
RM =
MVH
x
ρH
● Where aimed (specified) application rate is given in l/m2
rate:
Dipstick measurements in l/m at spraying temperature is used directly without
correction.
HOT
2
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Site measurement by weight (sample plates)
Measurement BY SAMPLE PLATES gives the application rate in MASS AT ANY
TEMPERATURE. This method has to be employed where the contractor cannot
produce certificates of reliable calibration of his spraying equipment.
RVH =
rate:
MM
ρH
RVC =
HOT
COLD
rate:
MM
ρC
● Where aimed (specified) application rate is given in kg/m2:
Sample plate measurements in kg/m2 is used directly without correction.
6.5.3
Temperature (binder, air, surface)
Sufficiently high temperature of the binder at the time of spraying is essential for
the spray nozzles to spread the binder properly and avoid stripes. The pumping
system and type of nozzles are selected to fit a certain range of viscosity and will
not operate properly at the higher viscosity of a too cold binder. Any tendency of
the spray ramp to make stripes will get worse at low spraying temperatures because there will be no aid of flowing on the surface during the initial few seconds
after the binder has reached the road. All problems associated with the spraying
temperature of the binder are aggravated by using low application rates.
The spraybar shall be tested before start
and sprayed binder shall be removed.
The temperature of the sprayed binder will normally reach the road temperature
before there is time to spread aggregate, which means the road temperature is
the controlling factor for choice of binder viscosity in relation to aggregate type
and weather conditions. This also means one cannot select a binder with too
high viscosity for the site conditions, and subsequently attempt to compensate
for this by increasing the spraying temperature. The air temperature and wind
conditions have an effect on the length of time before the binder reaches the
road temperature.
Temperature of the binder should be recorded at least twice during the spraying of
one distributor tank and as required depending on stoppage of the operation, etc.:
1. Record temperature just before starting to spray and after the binder has
been circulated sufficiently to give a reliable reading. No spraying shall start
before the lowest temperature in the permitted range is reached. Preferably
the highest limit in the permitted range should be reached before starting.
2. Record temperature at the time the level of binder in the distributor tank
approaches the minimum amount for re-heating the binder to be possible.
At this time decisions must be made whether to stop the spraying for reheating, or if the tank can be emptied without any stop that can cause the
temperature to fall below the lowest in the allowed range. Any stoppage of
work after this point requires that the tank is refilled and reheated before
work can resume.
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6.5.4
Aggregate spread rate
It is suggested to measure aggregate spread rate in connection with visual
inspection at the time of starting to use each new aggregate type or size or as
required when there are changes in the production. Measurement of aggregate
spread rate for site control should as a rule be carried out by consumption and
visual inspection unless there are cases of dispute which requires special measures. Commonly there is experience of over-application of aggregate by the
site staff rather than the opposite.
Application of aggregate.
Site measurement of spread rate for starting up and special control is best carried out with a plate of known area and weighing of aggregate that is covering
the plate. Aggregate spread rate is commonly specified and paid for by volume
and this method requires that a reliable bulk density of the aggregate is applied
in the calculations following weighing of the sample plates.
6.5.5
Sampling (binder/prime)
Binder, tack coat and prime
Sampling of binder from distributors is carried out with a sampler device that
can remove material from the middle of the tank or from special sampler cocks
on distributors where this is fitted. If no such equipment is available one can
sample by opening one spray nozzle separately into a bucket. It is particularly
important that at least one third of the tank has been sprayed immediately before
sampling is done and that the nozzle where the sampling is take was in use during the operation. The sample size should be minimum 4 litres and appropriate
safety precautions are required due to the hazardous nature of this operation.
Useful equipment can be obtained for control of aggregate spread rate.
Sampling of bituminous binders is normally carried
out before start of operations and whenever there
is a change in the supplies or there has been
events of suspected overheating or contamination
on site.
Aggregates
Sampling of aggregate is carried out for the purpose of confirming the validity
of the surfacing design and quality of materials. Table 6.8 gives the minimum
sampling frequencies for sprayed bituminous seals.
Table 6.8: Sampling frequencies for bituminous seals.
Layer
Surface treatments
Test
Aggregate strength
(TFV)
Grading, flakiness
Sampling frequency, minimum
1 Sample per
20 000 m2
5 000 m2
6.5.6
Application of precoater
Precoater is normally applied days in advance of the spraying operation and site
control is as much a requirement to ensure sufficient mixing as to ensure correct
quantity of precoater. Normally the desired result is a fully coated aggregate at
the smallest amount of precoater that can provide such a result.
Site control should be carried out by visual inspection and record keeping of
mixing time, material consumption and end result at the production site.
6.5.7
Equipment control and calibration
All equipment used for the work with bituminous materials shall be checked
and calibrated to meet the requirements set out in Standard Specifications for
Road Works-2000, Sections 4100 and 4300, where the procedures are described
in some detail. The status on calibration of tank and dipstick of bitumen dis-
100 Chapter 6
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tributors will determine whether the site control can be undertaken by volume
measurements with dipstick or whether control by sample plates on the road has
to be undertaken. The two methods are described in Chapter 6.5.2- Spray rate
(binder, tack coat, prime and fogspray).
6.6
Concrete
6.6.1
Introduction
The main objective of concrete control is to prove that the concrete itself or
structural members meet given requirements. In order to do so, representative
sampling and uniform test performances are of great importance. This chapter
describes procedures for appropriate sampling and testing methods of fresh and
hardened concrete in the field.
6.6.2
Sampling of fresh concrete
A sample of fresh concrete is normally taken as close to the construction as
possible. The sample is extracted from the transporter by taking 3 part samples
from the middle of the batch. The sample is to be taken continuously in clean
and dry plastic buckets, 11⁄2 times the volume required for the tests to be performed. The samples are to be protected from drying, direct sunlight or rain and
are to be covered by a lid, plastic sheeting or other suitable item.
The part samples should be homogenized before any testing take place. Consistence, air-entrainment and temperatures are to be measured immediately after
sampling.
Registration and identification
The following data shall be registered for each sample:
● Sample identification.
● Place, time and date of the sampling.
● Batch and recipe identification (concrete class).
● Concrete and air temperatures, weather conditions.
● Construction member to be cast.
6.6.3
Slump of concrete
The slump test is used for determining the workability of fresh concrete. The
test procedure for testing is similar for testing both in the laboratory and in the
field, ref. test 2.11 in the Laboratory Testing Manual-2000. The working sheet
in the Manual may be used. The apparatus shall consist of a specimen mould
made of metal and in the form of the lateral surfaces of the frustum of a cone
and a tamping rod, all to measures given in the Laboratory Testing Manual2000. The method is regarded as suitable up to aggregate size of approximately
35 mm within normal range of consistency.
Slump specimens that break or slump laterally give incorrect results. In such
cases, the test shall be repeated with a new sample. A shearing slump is a
sign of poor cohesion in the concrete and the slump test may in such case be
inapplicable.
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Chapter 6 101
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Reference is made to Test 2.12 in the Laboratory
Testing Manual-2000
6.6.4
Making and curing specimens for compression testing
Scope
The scope of this method is to give procedures for making and curing compression test specimens to obtain a uniformity of the specimens with respect to
homogeneity and storing. Homogeneity and the storing conditions of the specimens have a strong influence on the results of compression tests.
Moulding
Moulds shall have a non-absorbent surface and be substantial enough to hold
their shape during the moulding of the specimens. Re-usable steel moulds covered with a thin layer of mineral oil as a form release material are preferred. The
moulds shall be watertight and made of a rigid material. The cross-section of
the specimen shall be at least three times the maximum size of the aggregates.
Commonly used sizes are 100 mm cubes or 150 mm cubes. The concrete shall
be placed in either two or three layers depending on the sizes, using a scoop or
blunted trowel. Each layer is consolidated by tamping, 25 strokes per layer for
100 mm cubes and respectively 35 strokes per layer for 150 mm cubes. The
required method for consolidation of the concrete is a tamping rod, 16 mm in
diameter and length 450 mm with a hemispherical tip. Finishing shall be performed, to produce a flat, even surface, level with the rim of the mould.
Concrete cube moulds.
Curing
Moulds shall be placed on a rigid horizontal surface, free from vibration and
other disturbances. Initial curing shall be performed in a controlled environment
that maintains the temperature preferably at about 25°C and prevents loss of
moisture. Under final curing, the specimens shall be stored under moist conditions with free water maintained on all surfaces, preferably at a temperature of
about 25°C.
6.6.5
Taking core samples of hardened concrete
Scope
Concrete cores are mainly used for evaluating the condition of a structure with
respect to deterioration or to determine strength properties. The scope of this
method is to give procedures for concrete coring and patching to secure proper
core dimensions and patching of the boreholes.
Interpretation of test results
It is important that the method for interpreting the compression strength of cores
is decided in advance in the case of a contractual dispute. A number of factors will cause the compression strength of cores to be different from the cube
strength, such as time of curing, curing temperature and curing moisture. One
may not therefore be able to apply the specified cube strength directly in the
evaluation of the test results in the same manner as core strengths.
Coring equipment.
Before drilling, it is recommended to locate reinforcement in order to avoid cutting the steel
102 Chapter 6
Coring operation
The drill bit shall be a diamond-tipped, thin-walled core drill with provision for
a cooling liquid (e.g. water).
If the determination of compressive strength is the purpose of the core drilling,
the core diameter should be at least 3 times the maximum aggregate size. The
core length (without reinforcement etc.) should be at least 1,5 times the core
diameter to secure an ideal length of the prepared test specimen after sawing
and grinding the core ends.
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Proper core dimensions have to be decided in each case with respect to:
● Τhe purpose of coring.
● Τhe dimensions of the structure (mainly thickness).
● Ιnternal obstructions, e.g. reinforcement, cable ducts etc.
● Μaximum aggregate size of the concrete.
Desirably the ratio length: diameter should ideally
be 1:1. Diversion from a 1:1 ratio requires correction of the test results before compression strength
is reported.
A specimen taken perpendicular to a horizontal surface shall be located, when
possible, so that its axis is perpendicular to the bed of the original concrete as
placed. A specimen taken perpendicular to a vertical or battered surface shall be
taken near the central portion of the concrete element.
The concrete cores should be sealed in PVC film or airtight container to prevent
moisture loss and be protected from sudden strokes etc. before transported to
the laboratory.
Depending on type of structure or member, one
should consider if epoxy resin is required to create
satisfactory bond or water tightness.
Patching
Generally patching is to be performed with a mortar with strength properties
equal to the concrete itself. Vertical holes shall be repaired with a repair mortar
with adequate flow properties after removal of any cooling agent and drilling
waste. Horizontal holes shall be repaired with a mortar having the property to
flow into the borehole. At the concrete surface, a suitable formwork shall be
made (mail-box type) to allow the mortar to rise above the top cylinder surface.
Proper action to avoid loss of moisture must be taken.
6.6.6
Special tests
General
Various types of field testing equipment is available for investigating the properties of concrete structures. They shall, however, be regarded only as instruments
giving indicative values/results, but are useful tools in the progress of investigating the properties of a structure. The results should be treated with a care,
and in many cases must be checked by other methods.
Surface impact test (Schmidt hammer)
The test involves recording the rebound of a spring-activated plunger that
strikes the concrete surface. Several tests should be performed prior to calculating a mean value of the concrete strength. The method is rapid and economical,
and large areas can be tested quickly. It is however important to agree on how to
interpret the test results in the case of a contractual dispute.
Concrete cover of reinforcement bars
Several types of field testing instruments are available to locate reinforcement
bars and measure the concrete cover. Some are rather advanced and claimed to
be capable of also measuring the bar dimensions. The purpose of the measurements is essential on how to proceed. Generally, several tests should be taken to
locate the reinforcement bars and measuring the depth. The test should include a
detailed mapping of a square of approximately 0.5 m2 and marking the location
of the reinforcement bars with a colour marker or chalk. The high – low values
and a mean value are registered when the purpose is to check the concrete cover.
Results from the Schmidt hammer are
affected by the surface conditions, such as
moisture content and carbonation, and do
not necessarily give a reliable correlation
with the core strength values.
Carbonation
Carbonation is a natural reaction between the lime, Ca(OH)2 in the cement and
the surrounding carbon dioxide, CO2 in the air. A consequence is a reduction of
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the alkaline level in the pore water from pH 13 to below 12.4, which may result
in reinforcement corrosion. The depth of carbonation (front) will vary for one
particular surface.
The test is preferably applied on split cores or
concrete pieces that have been chiselled out.
The test method is based on the use of an indicator fluid, consisting of 1
gramme of phenolphthalein, dissolved in 50 ml ethanol and diluted with 50 ml
water. The carbonation front is shown as the boundary between original colour
and a pinkish taint representative for the un-carbonated concrete after applying
the fluid.
6.7
Construction control test methods
Field Tests
104 Chapter 6
F6.01
Density
Sand replacement
B51377: Part 9: 1990
F6.02
Density
Nuclear gauge
B51377: Part 9: 1990
ASTM D2922
ASTM D 2950 - 91
ASTM D3717
F6.03
Density
Core cutting
BS 1377: Part 9:
1990
F6.04
Preparation
for bituminous
sealing
Sand patch test
TMH6: Method ST 1
F6.05
Preparation
for bituminous
sealing
Ball preparation test
TMH6: Method ST 4
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6 Construction control
Density tests:
Sand replacement method
Objectives
The sand replacement method is used for measurement of the in-situ density
of soils and pavement layers. The test is very common in control of density in
compacted layers on construction sites.
The water balloon method utilizes similar principles
of measurement as the sand replacement method,
but is not recommended due to practical difficulties in obtaining reliable results, and commonly
problems with the equipment.
The principle of the sand replacement method is to excavate a hole in the layer
- which gives the weight of material and moisture content - and to subsequently
measure the volume of the hole by filling it with a medium (sand) of known bulk
density
Test cone.
The sand replacement method has long merits in control of density in
compacted layers on construction sites, and is often the reference method that
most contract specifications revert to in case of disputes. The test assumes
careful adherence to procedure, and its accuracy depends heavily on good
workmanship.
BS-type:
Advantages
● There is a general confidence in the test, that is justified when performed
properly and in suitable types of material (i.e. not too coarse grained).
● No advanced instrument and special skills are required.
Container for calibration
Limitations
● The test is slow to perform.
● Sensitive to workmanship and material type being tested, e.g. irregular
sides of the hole in materials with high content of coarse particles gives
inaccurate results (too high density).
Apparatus
The equipment for sand replacement testing varies in size and type. The BS
type is described her, however the principles are valid also for alternative types
of approved equipment. The BS type of equipment is available in a large and a
small type that is chosen according to the following guideline:
● Small type for testing layers with thickness maximum 150 mm.
● Large type for testing layers with thickness 150 mm to 250 mm.
One kit of equipment contains:
● Pouring cylinder.
● Base plate, nails for securing to the surface are also recommended.
● Calibrated measuring container.
Two types of sand replacement equipment.
In addition suitable tools are required for excavating and sampling the hole
(spoons, chisel, hammer, airtight containers for samples).
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Sand
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The density-sand shall be a clean closely graded silica sand which provides a
bulk density that is reasonably consistent. It shall be free from flaky particles,
silt, clay and organic matter. The grading of the sand shall be such that:
●
●
100% passes a 600 µm test sieve and
100% is retained on a 63 µm test sieve.
Before use it shall have been oven dried and stored in a loosely covered container for minimum 7 days to allow its moisture content to reach equilibrium with
atmospheric humidity. The sand should not be stored in airtight containers and
should be mixed thoroughly before use.
Sand salvaged from holes in compacted soils after carrying out this test shall
be sieved, dried and stored as described above before it is used in further sand
replacement tests.
��
��
Pouring cylinder, large type.
�
Procedure
Calibration of the sand and weight of sand in the cone
This procedure of determining the bulk density of the sand and determining
the weight of sand in the cone is carried out once for a batch of density-sand
and repeated whenever there is significant change in humidity. If tests are not
carried out on a regular basis, say every week, then this procedure should be
repeated for each new set of measurements.
Fill the calibrating container from the pouring cylinder, subsequently strike off
the top and determine the weight of sand. Repeat these measurements at least
three times and calculate the mean weight. Calculate the mean density of the
sand by use of the calibrated volume of the container.
Measurement cylinder, large type.
Sand replacement equipment, BS - type.
Determine the weight of sand in the cone by placing the base plate on a flat
surface, preferably a glass plate, fill sand from the pouring cylinder and weigh
before and after. Repeat these measurements at least three times and calculate
the mean weight of sand in the cone.
Measurements on site
Expose a flat area, approximately 600 mm square, of the soil to be tested and
trim it down to a level surface. Brush away any loose extraneous material. Lay
the metal tray on the prepared surface and nail it to the surface. Excavate a
round hole to the perimeter of the base plate and to the full depth of the layer
or as limited by the size of the equipment. Make sure that e.g. the chisel is not
levered against the sides of the hole. NB: Make sure the hole has:
●
●
●
Vertical walls.
As smooth walls as possible.
Flat surface at the bottom.
Carefully collect ALL the excavated material from the hole and keep it in an airtight container for determination of moisture content. It is important that no
material, stones etc. is thrown away during field testing or laboratory testing of
the excavated material.
Fill with sand from the pouring cylinder and determine the total weight of sand in
hole and cone by weighing before and after.
By following the calculations in the attached form determine density as follows:
106 Chapter 6
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1. Calculate the mass of sand in the hole (m1):
m1 =
m2 - m3 - m4
where:
m2 is the mass of sand and pouring cylinder before pouring (in g)
m3 is the mass of sand and pouring cylinder after pouring (in g)
m4 is the mass of sand in the cone, determined by previous calibration (in g)
2. Calculate the volume of the hole (V) in mL:
m1
V=
ρS
where:
m1 is the mass of sand in the hole (in g)
ρS is the density of the sand, determined by previous calibration (in Mg/m3)
3. Calculate the bulk density of the soil, ρ (in Mg/m3), from the equation:
mS
ρ=
V
where:
mS is the mass of all the soil in the hole (in g)
V is the volume of the hole (in mL)
4. Calculate the dry density ρd (in Mg/m3), from the equation:
ρd =
100ρ
100+w
where:
w
is the moisture content of the material in the hole (in %)
(b) The in-situ bulk and dry densities of the soil (in Mg/m3) to the nearest 0.01
Mg/m3.
(c) the moisture content, (in %), to two significant figures.
References
● BS 1377 : Part 9 : 1990
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Density tests:
Nuclear gauge method
Objectives
General
There is a variety of manufactures and designs of
the nuclear gauges. It is therefore impossible to
detail fully the operation of the gauge and reference is made to the manufacturer’s handbook.
Problems caused by the effect of underlying
materials often occur in construction of new roads
Also overlays where vastly different aggregate
sources have been used in the underlying pavement compared to the new bituminous layer may
give the same errors.
The objective of this method is determination of the in-situ density and moisture
content of fine-, medium-, and coarse-grained soils by means of a nuclear gauge.
Such gauges provide a rapid non-destructive technique for determining in-situ
bulk and dry density as well as the moisture content.
Bituminous materials
The nuclear gauge method is also suitable for determination of bulk density of
bituminous layers. For bituminous layers, with thickness up to maximum 75 mm,
measurement in ‘backscatter’ mode is common. Layers thicker than 75 mm
require ‘direct transmission’ mode. See figure. Errors may occur when measuring
the bulk density of thin bituminous layers overlying a pavement layer with a
considerably different density. When measuring bituminous materials containing
water (e.g. cold mixes), the moisture content needs to be determined using
conventional sampling and laboratory testing in each location.
Safety
Transportation of radioactive material in e.g. aircraft is restricted.
A manufacturer’s handbook and an approved
transport case shall be kept with the gauge.
Routinely move back a couple of steps while taking counts with the gauge.
The equipment used in this test utilizes radioactive materials emitting ionising
radiations which may be hazardous to health unless proper precautions are
taken. Before testing starts it is essential that users of this equipment are aware
of the potential hazards and comply with all applicable government regulations
concerning the precautions to be taken and routine procedures to be followed
with this type of equipment. This includes regular tests for radioactive leakage
according to manufacturer´s specification.
The following are general guidelines that are valid in handling of nuclear gauges
in order to minimize radiation effects:
● Keep at a distance to the gauge when it is not necessary to be near during
operation of the equipment.
● Keep the time spent near the gauge to a minimum.
● Store the equipment away from people, i.e. use a locked store room and not
a room used regularly by personnel.
Moisture content by mass of soil is not measured
directly by the gauge, but is being calculated by
the on-board calculator that is fitted in most brands
of equipment.
108 Chapter 6
Description of equipment and method
The nuclear gauges normally measure both bulk density and moisture content
using respectively two nuclear sources with corresponding sensors. See figure
below Some types of gauges have sensors that can be inserted into the ground
in the same manner as for the nuclear sources, and the moisture source is
movable. These gauges are normally used for research purposes due to elaborate calibration procedures and high cost.
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Measurement of density and moisture content is normally made at the same
time in the same locations. All measurements are direct comparisons with an
appropriate calibration with a daily standard count on a calibration block bearing
the same serial number as the gauge. I.e. no measurement is more accurate
than this daily standard calibration count.
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Principle and nuclear gauge measurements.
● Bulk density: In most types of equipment the sensor for density is located
inside the gauge, while the nuclear source can be either operated while
exposed at the surface of the gauge (‘backscatter’
backscatter’ mode) or inserted into
the soil on the tip of a rod (‘direct transmission’ mode).
● Moisture: In most types of equipment the source and sensor for moisture
The moisture content is derived from measurements of the presence of hydrogen nuclei.
Therefore, any presence of hydrogen that is
not in the form of water that can be evaporated
by standard laboratory tests causes errors that
must be corrected in proper calibration procedures for each type of soil. See below.
are both located inside the gauge (always ‘backscatter’).
backscatter’). The effective
backscatter
depth of measurement of moisture content varies with the moisture content.
The manufacturers handbook refers for further detail to quantify the depth
of influence. General:
high moisture contents
è
shallow
depth of influence
low moisture contents
è
deep
zone of influence
Normal procedure for use of the nuclear gauge in construction control of layer
work and earthworks is as shown in the flowchart, with further details given in
the text.
Ensure gauge is safe,
serviced and calibrated
less than 24 months ago.
Apply moisture correction for material to be
tested.
Apply maximum dry
density from lab-tests of
the material.
Carry out daily standard
count and observe if
trench measurement
applies on site.
Carry out measurement
of field density and
moisture content.
Record relative field
density and apply
statistical assessment.
TANROADS
Report the results with
reference to the requirments of the tested layer.
Chapter 6 109
ch6
Advantage
Chapter 6.2.4 presents the relative advantages/
limitations of various types of methods for measuring field density.
The main advantage of measurements with nuclear gauges is that the results
are obtained very fast. The accuracy of the results depends on applying correct
procedure including moisture correction against oven-drying for each new
tested type of material. Measurement of bulk density is generally far more
reliable than for moisture content.
Materials and over-sized particles
The test is suitable for most fine-, medium- and coarse grained soils where the
surface is sufficiently even to provide a smooth base for the gauge. The test is
valid where the material falls within both the following limits in respect of oversized particles:
Sieve size (mm)
Maximum amount retained on sieve (%)
37.5
10
20
30
Field measurements include all particles present in the material at the test
location. It is important to observe that material with larger amounts of oversized particles than given in the above table will give field test results that do
not correspond with the reference value for Maximum Dry Density found in
the laboratory. In such case the relative density measured in the field will be
incorrect (normally too high). The presence of occasional over-sized particles in
the soil will also give unusually high field density results when encountered at
the test location. Inspection holes should be excavated in case of doubt.
Use of direct transmission instead of backscatter
mode gives a better result in respect of density
measurements, especially where the material is
inhomogeneous.
Limitations
Measurements on materials with special chemical composition of soil, such as
blast furnace, is unsuitable for testing with nuclear gauges. Material that is very
inhomogeneous and having large variation in density or moisture at different
depths is not suitable for testing with nuclear gauges because the zone of
influence of the nuclear rays is not exactly defined.
Compensation shall be made by applying moisture correction for materials
containing hydrogen which is not removed during the standard oven-drying
process. However, where the material contains very large and varying amounts
of hydrogen the nuclear gauge shall not be used for measurement of moisture
content, and a sample shall be taken for laboratory testing of moisture at each
location. Examples of such materials are those containing:
● Βitumen.
● Large amounts of organic matter.
● Οther materials where the moisture correction shows large variation.
This calibration is necessary in order to compensate for the normal long-term ageing of the nuclear
sources and to check the stability of electronics
besides carrying out mechanical service under
safe conditions by specially trained personnel.
110 Chapter 6
Periodic calibration
Minimum every 24 months the nuclear gauge shall be serviced and calibrated in
accordance with ASTM D2922 and ASTM D3017 at a workshop facility with
appropriate equipment and skilled staff, preferably approved by the manufacturer
of the equipment. A valid certificate of calibrations less than 24 months old shall
be kept with the gauge.
TANROADS
ch6
Daily standard counts
Measurements with a nuclear gauge are actually comparisons with an appropriate calibration obtained by applying a daily standard count on a calibration
block having the same serial number as the gauge. I.e. the calibration block
provided with the gauge is not interchangeable and no field measurement is
more accurate than the daily standard count. A daily standard count shall be
carried out before measurements start, and shall be repeated after 8 hours of
continuous use of the gauge. A standard count should also be taken at the end
of the day’s measurements in order to check for any instability in the gauge.
It is important to carefully observe the manufacturer’s instruction for positioning of the gauge on the
block for daily standard counts.
After switching on the gauge, a normalization period of minimum 15 minute is
normally required, confer with the manufacturer’s handbook. Do not switch the
gauge off if the gauge shall be used during the day.
Four-minute counts are normally used for standard
counts, however the manufacturer’s guidelines
apply.
Perform the standard count with the gauge located minimum:
● 7 m away from other nuclear gauges.
● 1.5 m from any large structure which may affect the gauge readings.
The manufacturer sets out detailed procedures for carrying out daily standard
counts and interpretation of the results to detect any instability in the gauge.
Special procedures for establishing gauge stability are described in the manufacturer’s handbook. In the case of instability giving values outside the manufacturer’s quoted range, the gauge shall be sent for periodic calibration irrespective of the time since the previous calibration.
A record of the daily standard counts should be
kept for reference in case instability in the gauge
is suspected.
Measurement in trenches or by vertical structures
No measurements shall be undertaken if the gauge is less than 150 mm from
any vertical projection. Se figure below.
��
If measurements are carried out in narrow trenches or in locations within 1.5 m
of a building or other structure, then a special procedure is required: Carry out
daily standard count procedure (see above) with the reference block located in
the same position and orientation as the proposed test locations prior to each
such field test.
��
��
��
��
��
Using nuclear gauge near structures and in trenches.
Density correction
Density correction is unnecessary under normal conditions for measurements
of soils and crushed aggregate. Where materials have a special chemical
composition, such as e.g. blast furnace slag, the use of nuclear gauge shall be
abandoned, and no attempts should be made to use the method by the help of
density corrections.
TANROADS
The procedure for density correction is elaborate
and carries a considerable risk of errors.
Chapter 6 111
ch6
Moisture correction
FrequencyNo measurements of moisture content are reliable unless moisture
correction has been carried out. Moisture correction shall be carried out when:
● Use of a new material source is about to start.
● Τhere is change in material type or properties within a material source.
● Α period of 3 months has elapsed since the last time moisture correction
for the particular material was determined.
● Whenever there is doubt or dispute over test results.
Procedure
Select 5 locations on a smooth, newly (same day) compacted layer
constructed with the material for which moisture correction shall be
determined. In each of the 5 locations carry out the following procedure:
Validation:
If the correction shows that the nuclear gauge
gives a substantially lower moisture content
than the laboratory test results, there is a great
possibility of errors in the procedure. Most likely
the error is with the handling of the sample for
laboratory testing. Do check in particular that the
large particles have not been removed from the
material sample by field- or laboratory staff prior
to testing moisture content.
1. Place the gauge in a location with an even surface.
2. Carve a line on the surface along the outline of the gauge.
3. Measure moisture content using the nuclear gauge as described under
Field measurements below. Use backscatter mode (direct transmission
mode only applies to density measurements and is not of interest for this
procedure).
4. Remove the gauge from the surface.
5. Take a sample in the centre of the outline of the gauge for the purpose of
measuring field moisture content by oven drying in the laboratory, i.e. the
sample shall be placed in a water tight container immediately. The sample
shall be taken from a circular hole approximately 100 mm in diameter and
cylindrical approximately 100 mm deep. Where the material has a considerable proportion of particles larger than 20 mm the size of the hole
should be widened to 150 mm diameter. If a single, large, particle is encountered, then abandon the measurement and find an alternative
location.
6. Test the sample for moisture content in the laboratory by standard oven drying of the entire sample including all large particles. Test no. 1.1. of the Laboratory Testing Manual-2000 shall be applied.
After the above procedure is completed for all 5 locations, calculate the moisture correction factor for the material by combining the laboratory test results
with the results from the nuclear gauge in accordance with procedures set out in
the manufacturer’s handbook. Apply the correction factor in all subsequent field
measurements of materials from the same source unless determination of a
new moisture correction factor is required for reasons given above.
Field measurement using nuclaer gauge.
Field measurement
General
Direct transmission is preferred due to its ability
to test equally all parts of the layer to the total
depth to which the gauge probe is inserted.
Direct transmission mode shall be used where field density will be measured,
due to the better accuracy of measurement compared to backscatter mode.
Select the depth of gauge probe insertion that corresponds with the thickness of
the layer to be measured.
Preparation of the site
If the layer has a very coarse texture giving poor contact with the bottom surface
of the gauge, and better alternative locations cannot be found, the surface should
be sprinkled with fine, dry, sand that is subsequently levelled to a smooth sur-
112 Chapter 6
TANROADS
ch6
face where the gauge is to be bedded. It is important that the sand is used in
moderation and shall not form an added layer. I.e. the higher points of the layer
to be tested shall be seen protruding through the sand across the entire surface
area before the gauges is placed.
Use of sand is normally not required, but where it
is needed the sand should be of similar geological
origin as the material to be tested, preferably made
of screened fines from the same material source.
Use suitable tools, such as trowel, straightedge and scraping plate for levelling
the surface at the site of the test as required. Make a hole for the direct
transmission measurement by use of a hammer and a steel drive pin to produce
a hole with diameter up to 3 mm larger than the gauge probe. The hole should
be slightly deeper than the depth to which the gauge probe will be inserted. It is
important to use a suitable guide tool made from a pipe welded on a steel plate
to direct the drive pin accurately true to the surface without disturbing the sides
of the hole. Take particular care not disturb the hole and the surface when the
drive pin is extracted. Use spanners to turn the drive pin at the same time as it
is gradually withdrawn from the hole.
Positioning of the gauge
Place the gauge on the surface and insert the gauge probe into the whole to the
required depth. After the gauge is properly seated, pull the gauge back in order
for the probe to obtain proper contact with the wall of the hole. See figure below.
��
��
��
��
��
��
��
��
��
Placing nuclear gauge into position.
Measurement counts
After the gauge is properly positioned, take a one-minute measurement count
and record the results for density and moisture. Repeat the measurement count,
record the result and use the average of the two results as the reported value at
the location. If there is considerable difference between the two measurements,
take two more counts and use the average value. Retract the extendable probe
into the gauge, ensure the shutter is closed and check that the radioactive
source is safely housed. A procedure whereby the gauge is rotated and repositioned between each repeated measurement at the same location, should be
avoided because it may increase the risk of errors.
One-minute counts are normally used for field
measurements, however the manufacturer’s
guidelines apply. Longer count duration statistically improves the test result, thereby the accuracy
increases.
By repeating the count and using the average
value with the gauge in the same position, one
does improve the accuracy of the measurement
considerably.
Apply the relevant moisture correction if the gauge does not provide calculation
of corrected values on the basis of user-determined calibration values.
Patch the hole by pouring fine sand in the hole and tamp with a steel rod until
level with the surface of the layer.
TANROADS
Chapter 6 113
ch6
Reporting
The attached worksheet shall be filled in and the test report shall contain the
following information:
Equipment
● Μodel and serial number of the gauge.
● Date of last calibration, reference to certificate.
● Μethod of test being used (backscatter or direct transmission, depth of
measurement and whether trench procedures have been applied).
● Standard count values.
Location
●
●
●
●
Τype of layer (e.g. earthworks, type of pavement layer, material type).
Μaterial source being used.
Μoisture correction value and date of its determination.
Τime since compaction was completed (in the case of construction control).
Test
● Maximum Dry Density and Optimum Moisture Content (CML test no 1.9)
in the respective locations where measurements are carried out.
● Average percentage over-sized particles larger than 20 mm and 37.5 mm
respectively.
● Τest results from the field density and moisture tests using the nuclear gauge.
In the case of construction control the field density and moisture content values
shall be calculated and reported using statistical methods as appropriate to
meet the requirements of the Standard Specification for Road Works-2000.
References
●
●
●
●
114 Chapter 6
BS 1377:Part 9:1990
ASTM D2922
ASTM D2950-91
ASTM D3717
TANROADS
ch6
Density tests:
Core cutting method
Objectives
The core cutting method is used for measurement of the in-situ density of soils
and compacted layers of primarily clay and soft materials.
��
Core cutting gives volume by predetermining the size of the excavated hole with
a calibrated core of known volume.
��
Advantages
The core cutting method is fast and simple to perform in soft materials.
� ��
Limitations
● In coarse materials the test is difficult to perform.
● The method is less accurate than e.g. the sand replacement test and should
only be used as an indicator of in-situ density.
�
��
� ��
��
��
Apparatus
� ��
The apparatus is a 100 mm diameter steel cylinder, a steel dolly and a steel
rammer, as shown in the figure.
� ��
1. Expose a small area, approximately 300 mm square, of the soil layer to be
tested and level it. Remove loose extraneous material. Place the core cutter
with its cutting edge on the prepared surface. Place the steel dolly on top of
the cutter, and ram the latter down into the soil layer until only about 10 mm
of the dolly protrudes above the surface, care being taken not to rock the
cutter. Dig the cutter out of the surrounding soil taking care to allow some
soil to project from the lower end of the cutter. Trim the ends of the core flat
to the ends of the cutter by means of the straightedge.
2. Determine the mass of the cutter containing the core to the nearest 1 g.
��
Procedure
��
��
�
�
Core cutting assembly.
3. Remove the core from the cutter, crumble it and place a representative
sample in an airtight tin and determine its moisture content w, using the
method specified in the Laboratory Testing Manual-2000 method 1.1.
1. Calculate the internal volume of the core cutter in cubic centimetres from its
dimensions which shall be measured to the nearest 0.5 mm.
Where driving causes shortening of the sample
in the cutter, or there is difficulty in digging out
the cutter, it may be found preferable to remove
the soil from around the outside of the cutter and
slightly in advance of the cutting edge as it is
driven down.
2. Weigh the cutter to the nearest 1 g.
TANROADS
Chapter 6 115
ch6
Calculate the bulk density of the soil, ρ (in Mg/m3), from the equation:
mS - mC
ρ=
VC
where:
mS is the mass of soil and core cutter (in g)
mC is the mass of core cutter (in g)
VC is the internal volume of core cutter (in mL)
Calculate the dry density ρd (in Mg/m3), from the equation:
100ρ
ρd =
100+w
where:
w
is the moisture content in the soil (in %)
(b) The in-situ bulk and dry densities of the soil (in Mg/m3) to the nearest 0.01
Mg/m3.
(c) The moisture content, (in %), to two significant figures.
References
● BS 1377 : Part 9 : 1990
116 Chapter 6
TANROADS
ch6
Preparation for bituminous sealing:
Sand patch test
Objectives
The objective of the method is to measure the texture depth of a road surface
for the purpose of establishing correction of binder spray rate for subsequent
application of surface dressing.
The sand patch test result is not directly referred
to in the design method for surface dressings in
the Pavement and Materials Design Manual-1999
and is therefore not a requirement for surfacing
design.
The method describes the procedure for spreading a known volume of sand, on
the surface and measuring the area covered.
The method offers a rational method for determination of correction of the
binder spray rate and valuable building-up of experience. The test only gives
an approximate estimate of texture depth and is only useful as a help for the
designer of the surfacing.
Apparatus
●
●
●
●
●
●
A container with a known volume, when filled, of approximately 500 ml.
Alternatively, a simple apparatus made from
readily available materials, consisting of a 300
mm wide sledge with rubber blades for spreading
sand is described in TMH6, method ST1. The
apparatus is convenient if a large number of tests
is required.
A rubber squeegee
Measuring tape
A board measuring 500 mm x 1500 mm
A carpet brush, a spatula and strait edge
A supply of sand passing 0,3 mm sieve and retained on 0,075 mm sieve.
Procedure
Choose a test site which is representative of the section of road to be tested.
Chalk two parallel lines, 500 mm apart and approximately 3 m long, using the
board. Fill the 500 ml container with sand, without jarring it to prevent compaction of the sand, and level it off with a spatula or straight-edge. Pour the sand
in a zig-zag pattern between the parallel lines. Spread the sand with the rubber
squeegee between the lines to as great a length as possible. The spreading
should be done in such a manner that the surface voids are filled without leaving an excess or a continuous layer of sand. Try not to let the last bit of sand tail
off but keep the finishing line as straight and regular as possible. Measure the
length of the patch covered with sand and record it to the nearest 5 mm on a
suitable recording sheet. If a tail of sand is formed, the area of the tail should be
calculated and added to the area of the rectangular portion of the patch.
If several tests are to be done in the field, it is more
convenient to determine the mass of the known
volume of sand in the laboratory and then to weigh
off in clean containers as many separate portions
as are needed for field work.
Calculation and reporting
Texture depth (mm) T =
a = volume of sand, in ml.
a
1000
b
b = area covered, in m2.
References
● NITRR, Council for Scientific and Industrial Research, Republic og South
Africa, 1984. Technical Methods for Highways (TMH) no. 6: Special methods for testing roads.
TANROADS
Chapter 6 117
ch6
Preparation for bituminous sealing:
Ball penetration test
Objective
The ball penetration test result is not directly
referred to in the design method for surface dressings in the Pavement and Materials Design
Manual-1999 and is therefore not a requirement
for surfacing design.
The objective of the method is to obtain a measure for estimating the depth
to which surface dressing aggregate can be expected to penetrate into the
underlying surface and thereby give valuable input for design of surface
dressings.
Penetration into the underlying surface is among
the correction parameters having the greatest
effect on required bitumen stray rates.
The method offers a rational method for determination of correction of the
binder spray rate and valuable building-up of experience. The test provides
useful a help for the designer of the surfacing but does not give exact
penetration depth for the aggregate after a specific period in service.
It should be noted that the relationship is valid
for all road surfaces and temperatures (T,) lying
between 25 and 55 °C.
This method describes a test for measuring the penetration resistance of a road
surface using a steel ball with a diameter of 19,0 mm. The result may be used
when designing a surface treatment for a road.
Apparatus (see figure below)
Α.
B.
C.
D.
A circular (127 mm) tripod stand and cross-bar.
A steel ball with a diameter of 19,0 mm.
A depth gauge graduated in mm.
A standard Marshall compaction hammer in compliance with the Laboratory
Testing Manual 2000, test 3.18.
E. A surface thermometer graduated in degrees Celsius (25 to 55 °C).
D
C
A
B
118 Chapter 6
TANROADS
ch6
Procedure
Subdivide the road into a number of representative sites. Toss the steel ball
onto the road at each site in a random manner.
Place the circular tripod stand over the ball at the point where it comes to rest
so that the ball is in the centre of the circular frame. Place the cross-bar in the
slots provided on the stand so that the forward edge of the bar is vertically
above the centre of the ball. Take an initial reading by means of a depth gauge
from the top of the cross-bar to the top of the ball and remove the bar without
disturbing the tripod stand.
Give the ball one blow with the Marshall hammer and replace the cross-bar in
the same position as before. Take a second reading as above. The depth of
penetration is the difference between the two readings. Repeat the procedure at
least 10 times at each site and report the mean depth of penetration of the steel
ball.
Take the temperature of the road surface at each site for each set of penetration
readings.
Calculation and reporting
Correct the penetration reading by means of the following formula:
PenT0 = PenT1 - K(T1 – T0)
Where:
Pen T0
Pen T1
T1
T0
K
= penetration depth at suggested road surface temperature (mm)
= penetration depth at measured road surface temperature (mm)
= temperature of road at time of ball test ( 0C)
= temperature of road suggested for particular location ( 0C)
= temperature-susceptibility of penetration (mm/OC).
The following K-factors are recommended:
0,04 mm/0C
Single and multiple seals (not fatty)
0
0,05 mm/ C
Slurry seals (not fatty)
0
0,07 mm/ C
Cape seals (not fatty)
0,08 mm/0C
Fatty roads and premix surfacings.
References
● NITRR, Council for Scientific and Industrial Research, Republic og South
Africa, 1984. Technical Methods for Highways (TMH) no. 6: Special
methods for testing roads
TANROADS
Chapter 6 119
APPENDICES
1
Introduction
2
Geotechnique
3
Pavement evaluation
4
Axle load surveys
5
alignment surveys
6
Appendices
Appendix 1:
Appendix 2:
Appendix 3:
Appendix 4:
Appendix 5:
Appendix 6:
Appendix 7:
Appendix 8:
Appendix 9:
CML Laboratory and test methods
Soil profiling descriptions after Briks and Jennings
CUSUM method for delineation of homogenous sections
The MERLIN method for measuring roughness
Layout of survey sites and traffic safety measures
Design Traffic Loading - example
Definition of terms
Abbreviations
Worksheets
References
● Pavement and Materials Design Manual - 1999, Ministry of Works, Tanzania
● Laboratory Testing Manual - 2000, Ministry of Works
● Guideline no 2
Pavement Testing, Analysis and Interpretation of Test Data, Roads Department,
Botswana - 2000
● Guideline no 3
Methods and Procedures for Prospecting for Road Construction Materials, Roads
Department, Botswana - 2000
● Guideline no 4
Axle Load Surveys, Roads Department, Botswana - 2000
120
TANROADS
Appendix 1: CML LABORATORY AND FIELD
TEST METHODS
The following test methods are described in the Laboratory Testing Manual - 2000 and Field Testing Manual
- 2003, and are being referred to in the Standard Specifications for Road Works - 2000 and the Pavement
and Materials Design Manual - 1999 issued by TANROADS, Ministry of Works, Tanzania.
CML test
number:
Name of test:
Reference to test method:
Tests on Soils and Gravel:
1.1
1.2
1.3
1.4
1.5
1.6
1.7
1.8
1.9
1.10
Moisture Content
Liquid Limit (Cone Penetrometer)
Plastic Limit & Plasticity Index
Linear Shrinkage
Particle Density Determination - Pyknometer
Bulk Density for undisturbed samples
Particle Size Distribution - Wet sieving
Particle Size Distribution - Hydrometer Method
Compaction Test - BS Light and BS Heavy
CBR Test - One point method
1.11
CBR Test - Three point method
1.12
1.13
1.14
1.15
Consolidation Test - Oedometer
Triaxial Test
Shear Box Test
Permeability Test - Constant Head
1.16
Organic Content - Ignition Loss Method
1.17
1.18
Crumb Test
pH Value (pH meter)
1.19
Preparation of Stabilised Samples for (UCS)
1.20
Compaction Test - Stabilised Materials
1.21
1.22
UCS of Stabilised Materials
Initial Consumption of Lime - ICL
BS1377:Part 2:1990
BS1377:Part 2:1990
BS1377:Part 2:1990
BS1377:Part 2:1990
BS1377:Part 2:1990
BS1377:Part 2:1990
BS1377:Part 2:1990
BS1377:Part 2:1990
BS1377:Part 4:1990
BS1377:Part 4:1990
BS1377:Part 4:1990 and
TMH1:method A8:1986
BS1377:Part 5:1990
BS1377:Part 7:1990
BS1377:Part 7:1990
BS1377:Part 5:1990
BS1377:Part 3:1990 and
NPRA 014 test 14.445
BS1377:Part 5:1990
BS1377:Part 3:1990
TMH1:method A14:1986 and
BS1924:Part 2:1990
TMH1:method A14:1986 and
BS1924:Part 2:1990
TMH1:method A14:1986
BS1924:Part 2:1990
Tests on Aggregates and Concrete:
2.1
2.2
2.3
2.4
2.5
2.6
2.7
2.8
2.9
2.10
2.11
Moisture Content of Aggregates
Relative Density and Water Absorption
Sieve Tests on Aggregates
Flakiness Index (FI) and Average Least Dimension (ALD)
Elongation Index
Aggregate Crushing Value (ACV)
Ten Percent Fines Value (TFV)
Aggregate Impact Value (AIV)
Los Angeles Abrasion Test (LAA)
Sodium Soundness Test (SSS)
Slump Test
BS812:Part 109:1990
BS812:Part 2:1975
BS812:Part 103.1:1985
BS812:Section 105.1:1989
BS812:Section 105.2:1990
BS812:Part 110:1990
BS812:Part 111:1990
BS812:Part 112:1990
ASTM C535-89
ASTM C88-90
BS1881:Part 102:1983
2.12
Making of Concrete Test Cubes
BS1881:Part 108:1983
2.13
Concrete Cube Strength
BS1881:Part 116:1983
TANROADS
121
CML test
number:
Name of test:
Reference to test method:
Tests on Asphalt and Bituminous Materials
3.1
3.2
3.3
3.4
3.5
3.6
3.7
3.8
3.9
3.10
3.11
3.12
3.14
3.15
3.16
3.17
3.18
3.19
Preconditioning of Bitumen Samples Prior to Mixing or Testing
Density of Bituminous Binders
Flash and Fire Point by Cleveland Open Cup
Thin-Film Oven Test (TFOT)
Penetration of Bituminous Materials
Softening Point Test
Ductility
Viscosity Determination using the Brookfield Thermosel Apparatus
Density and Water Absorption of Aggregates Retrieved on a 4.75 mm Sieve
Density and Water Absorption of Aggregates Passing the 4.75 mm Sieve
Calibration of Glass Pycnometers (0.5-1 litre)
Mixing of Test Specimens; Hot Bituminous Mixes
Determination of Maximum Theoretical Density of Asphalt Mixes
and Absorption of Binder into Aggregates
Bulk Density of Saturated Surface Dry Asphalt Mix Samples
Bulk Density of Paraffin-Coated Asphalt Mix Samples
Bulk Density of Asphalt Mix Samples, Calliper Measurements
Calculation of Void Content in Bituminous Mixes
Marshall Test
Marshall Mix Design
3.20
Refusal Density Mix Design
3.21
Indirect Tensile Strength Test
3.22
3.23
Determination of Binder Content and Aggregate Grading by Extraction
Effect of Water on Bituminous Coated Aggregates, Boiling Test
3.13
NPRA 014 test 14.511
ASTM D70-97
ASTM D92-90
ASTM D1754-87
ASTM D5-86
ASTM D36-70
ASTM D113-86
ASTM D4402-91
ASTM C127-88
ASTM C128-88
NPRA 014 test 14.5922
NPRA 014 test 14.5532
ASTM D2041-95 and D4469-85
ASTM D2726-96
ASTM D1188-89
NPRA 014 test 14.5622
ASTM D3203 and AASHTO pp19-93
ASTM D1559-89
ASTM D1559-89
TRL Overseas Road Note 31, app. D:
1990
ASTM D3967 and NPRA 014 test
14.554
ASTM D2172-88, method B
ASTM D3625-96
Field Tests
F2.01
Soundings
Cone penetration - CPT
B51377: Part 9: 1990
B55930: 1999
F2.02
Soundings
Standard penetration test - SPT and continuous core
penetration test - CCPT
B51377: Part 9: 1990
B55930: 1999
F2.03
Soundings
Vane test
F2.04
F2.05
F2.06
F2.07
Boring
Ground water
Ground water
Ground water
Permeability tests for soils and rocks
F2.08
Deformation test
Plate loading test
F6.01
F6.02
Density
Density
Sand replacement
Nuclear gauge
F6.03
Density
Preparation for bituminous
F6.04
sealing
Preparation for bituminous
F6.05
sealing
Pavement evaluation
122
TANROADS
Core cutting
B51377: Part 9: 1990
B55930: 1999
B55930: 1999
B55930: 1999
B55930: 1999
B55930: 1999
BS 1377:
Part 9: 1990
B51377: Part 9: 1990
B51377: Part 9: 1990
ASTM D2922
ASTM D 2950 - 91
ASTM D3717
BS 1377: Part 9: 1990
Sand patch test
TMH 6: Method ST 1
Ball penetration test
TMH 6: Method ST 4
Visual evaluation
Rut depth measurements
DCP measurements
Test pit profiling and sampling in existing pavements
Chapter 3.3.3
Chapter 3.3.4
Chapter 3.3.5
Chapter 3.4.2
Chapter 3.4.3
Chepter 3.5
Appendix 2: SOIL PROFILING DESCRIPTIONS
AFTER BRINKS AND JENNINGS
TANROADS
123
Appendix 3: CUSUM METHOD FOR DELINEATION
OF HOMOGENOUS SECTIONS
The CUSUM is a method to establish homogenous sections by analysis of one parameter at the time. The method utilises plotting of
the cumulative sum of difference from the average value. The calculations, plotting and interpretation of data are illustrated below in
an example where rutting measurements are analysed and plotted.
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The figure below shows a realistic example of a CUSUM plot for rut depth measurements on a project:
124
TANROADS
Appendix 4: THE MERLIN METHOD FOR
MEASURING ROUGHNESS.
Introduction
The standard measure of road roughness is the International Roughness Index (IRI) was developed during ‘The International Road
Roughness Experiment’ in Brazil. It is a mathematical quarter car simulation of the motion of a vehicle at a speed of 80 kph over
the measured profile and can be calculated directly from road levels measured at frequent intervals. High-speed equipment used
for such measurements must be periodically calibrated to allow the values of roughness to be reported in terms of IRI. Methods of
calibration include either a rod and level survey, a standard instrument, such as the TRL Profile. Beam, the MERLIN (Machine for
Evaluating Roughness using Low-cost Instrumentation), the Face Dipstick or the ARRB Walking Profiler.
Description of the MERLIN
The MERLIN is a low cost, but accurate equipment available in Tanzania and is described below. A diagram of the equipment is
shown in the figure.
The MERLIN has a rear footing, 1.8 metres apart from the front wheel made of a bicycle wheel. A moveable probe is placed on the
road surface mid-way between the resting point of the wheel and the rear footing, that measures the vertical distance ‘y’ between the
road surface under the probe and the centre point of an imaginary line joining the resting point of the wheel and the footing.
It is assumed that the MERLIN has a mechanical amplification factor of 10. up to the pointer where the deviation from a true line of
the road surface is marked.
Pointer
Chart
Handles
Wheel with marker in
Rear foot
Pivot
Weight
Moving arm
Probe
TANROADS
125
Operation of the MERLIN
The result is recorded on a data chart mounted on the machine. By
recording measurements along the wheel path, a histogram of ‘y’ can
be built up on the chart. The width of this histogram can then be used
to determine the IRI. To determine the IRI, 200 measurements are
usually made at regular intervals, (one measurement at each wheel
revolution). For each measurement, the position of the pointer on the
chart is marked by a cross in the box in line with the pointer and, to keep
a count of the total number of measurements made, a cross is also put
in the ‘tally box’ on the chart. When the 200 measurements have been
made the distribution is graphically marked on the chart. The procedure
is repeated for the other end of the distribution. The width of the scatter
of 200 marks, excluding the outer 10 marks at each end of the scatter, is
then measured in millimetres and denoted D.
For earth, gravel, surfaced dressed and asphaltic concrete roads, the
IRI can be determined using the following equation.
IRI = 0.593 + 0.0471 D
Calibration of the MERLIN
This equation for calculation of IRI from MERLIN test results assumes that the MERLIN has a mechanical amplification factor of 10.
In practice this may not be true because of small errors in manufacturing. Therefore, before the MERLIN is used the amplification
has to be checked and the value of D corrected. The instrument is rested with the probe on a smooth surface and the position of the
pointer carefully marked on the chart. The probe is then raised and a calibration block approximately 6 mm thick placed under the
probe. The new position of the pointer is marked. If the distance between the marks on the chart is called S, and the thickness of the
block T, then measurements made on the chart should be multiplied by the following scaling factor:
Scaling factor
=
10 T
S
6 mm calibration block made of steel.
126
TANROADS
Length of section when using the MERLIN to calibrate alternative
high-speed equipment
The length of test section used in the calibration should be approximately 415 m, on account of the following:
When 200 measurements are taken using a MERLIN with a wheel having an outer diameter of 26-inches (660 mm), then the length
of the surveyed section will be 415 metres (one measurement at each wheel revolution). For shorter or longer sections, a different
procedure will be required. The guiding principles are:
●
●
●
●
The test section should be a minimum of 200 metres long.
Take approximately 200 readings per chart. With less than 200 readings the accuracy will decrease and with more the chart
becomes cluttered. If the number of readings differs from 200, then the number of crosses counted in from each end of the
distribution, to determine D, will also need to be changed. It should be 9 crosses for 180 readings, 11 for 220 readings etc.
Always take measurements with the marker on the wheel in contact with the road. This not only prevents errors due to any
variation in radius of the wheel but also avoids operator bias.
Take regularly-spaced measurements over the full length of the test section. This gives the most representative result.If
taking repeat measurements along a section, try to avoid taking readings at the same points on different passes. e.g. start
the second series of measurements half a metre from where the first series was started.
Tally box
1 2 3 4 5 6 7 8 9 10
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
TANROADS
127
Appendix 5: LAYOUT OF SURVEY SITES AND
TRAFFIC SAFETY MEASURES
WORKING
AREA
0
20 m
50 m
100 m
PREPARE
TO STOP
Left
Right
150 m
200 m
WEIGHBRIDGEAHEAD
300 m
400 m
SLOW DOWN
500 m
Standard layout for placing of traffic warning signs.
128
TANROADS
Appendix 6: DESIGN TRAFFIC LOADING EXAMPLE
Input data
Design period = 20 years.
Pavement construction is expected to be completed 3 years after the time of traffic survey.
Traffic growth rate = 3.5% (for all heavy vehicle categories).
n
n
n
Direction 1
Direction 2
Vehicle category/counts
Buses
0
11
15
13
11
14
16
17
92
13
Day 1
Day 2
Day 3
Day 4
Day 5
Day 6
Day 7
Day 8
Total
Daily
MGV
13
17
28
19
36
18
9
11
151
19
HGV
11
5
11
15
9
15
8
4
78
10
Vehicle category/counts
VHGH
24
17
20
24
26
33
11
2
157
20
Buses
13
14
15
10
15
13
13
0
93
13
MGV
24
26
13
29
30
25
16
5
168
21
HGV
11
9
16
9
10
12
13
7
87
11
VHGH
9
12
20
26
38
21
28
9
163
20
Summary of axle load survey and equivalency factors. Assessment of axles heavier than 13
tonnes. (Chapters 4.5.2, 4.2.3 and 4.5.4 in the Pavement and Materials Design Manual - 1999)
Vehicle
category
Direction 1
Avg.
Gross
wt.(ton)
Avg.
VEF
(80 kN)
Total
No. of
veh.
Direction 2
E80 from all
axles
E80 from
Avg.
axles heavier Gross
than 13 tonnes wt.(ton)
Avg.
VEF
(80kN)
Total
No. of
veh.
E80 from all
axles
E80 from
axles heavier
than 13 tonnes
Buses
17.396
3.922
92
360.824
0
17.265
4.033
93
375.069
13.25
MGV
12.217
3.705
151
559.455
280.19
12.615
3.262
168
548.016
220.93
HGV
23.146
8.959
78
698.802
282.40
22.480
8.557
87
744.459
359.15
39.196
8.087
114
921.918
133.57
45.160
13.81
131
1809.11
128.35
40.548
10.031
43
431.333
204.72
33.987
7.936
32
253.952
173.58
0.000
0.000
0
0
0
0.000
0.000
0
0
0
39.566
8.620
42.966
12.657
VHGV-SEMI
-TR
-ST
Avg. of all
VHGV’s
SUM of
VHGV’s
157
1353.25
338.29
163
2063.06
301.93
Total
478
a=2972.33
b=900.88
511
a=3730.60
b=895.26
From the heaviest loaded direction, proportion of E80 made up from axles heavier than 13tonnes (in direction 2):
= (b/a) x 100 = (895.26/3730.60) x 100 = 24%
This value is less than 50%, thus the Traffic Load Class will not be denoted heavy (-H) and no special measures are required
in the pavement design or design of improved subgrade.
Traffic growth and design traffic loading (Chapters 4.5.5 and 4.5 in the Pavement and Materials
Design Manual - 1999)
TANROADS
129
Direction 1
Buses
Daily counts
VEF
E80/day
MGV
Direction 2
HGV
VHGV
Buses
MGV
HGV
VHGV
13
19
10
20
13
21
11
20
3.922
3.705
8.959
8.620
4.033
3.262
8.557
12.657
50.986
70.395
89.590
172.400
52.429
68.502
94.127
253.140
Total E80/day
383
468
Use the heaviest direction in axle loading for calculating the traffic loading, in this case direction 2. The cumulative
number of standard axles, E80 = 365 x t1 x (1 + I)N - 1
i
where:
t1 =
average daily number of standard axles in the year of traffic survey
i =
annual growth rate expressed as a decimal fraction
Substituting:
N =
calculated period in years
t1 =
468
i
0.035 for all heavy vehicle categories
=
The cumulative number of E80 for the design period and the time from present until completed pavement construction is
calculated using (20 + 3) = 23 years, and let be denoted as E8023.
E8023 = 365 x 468 x (1 + 0.035)23 –1 = 5.9 million E80
0.035
The cumulative E80 for the time from present to completion of pavement construction is calculated using 3 years, and let be
denoted as E803.
E803 = 365 x 468 x (1 + 0.035)3 –1 = 0.5 million E80
0.035
Hence E80design = E8023 - E803 = 5.9 – 0.5 = 5.4 million E80
Construction traffic (Chapter 4.5.7 in the Pavement and Materials Design Manual - 1999)
On the completed pavement 90,000 m3 of construction materials is expected to be transported using trucks of a capacity of
15 m3 and having an equivalency factor (VEF) of 12.5 when fully loaded.
Therefore 6000 loads will be required.
E80construction = 6000 x 12.5 = 0.075 million E80
Hence Total E80design = 5.4 + 0.075 = 5.475
i.e. say 5.5 million E80
Traffic Load Classes (TLC) (Chapter 4.5.8 ) in the Pavement and Materials Design Manual - 1999.
Design traffic loading of 5.5 million E80 puts the project road into TLC 10. (Table 4.3 Pavement and Materials Design
Manual - 1999)
130
TANROADS
Appendix 7: DEFINITIONS AND TERMS
Asphalt Concrete (AC)
A group of hot bituminous mixtures used for surfacing. They normally consist of a well
graded mixture of coarse aggregate, fine aggregate and filler, bound together with
penetration grade bitumen.
Base course
The layer(s) occurring immediately below the surfacing and above the subbase or, if there
is no subbase, above the improved subgrade layers.
Behaviour
The function of the condition of the pavement with time (see also performance).
Binder course, bituminous
The surfacing layer immediately below the bituminous wearing course above the base
course.
Bitumen emulsion
A binder in which bitumen has been dispersed in finely divided droplets in water by the
aid of mechanical means and an emulsifying agent. Bitumen emulsion is made in an
anionic and a cationic type depending on the particle charge of the bitumen droplets in
solution. Bitumen emulsions are classified according to percentage of bitumen in the
material and the physical properties related to their behaviour during construction, (See
also break).
Bitumen stabilised material
A material made of natural- or crushed aggregate with a bituminous binder admixed. Used
in pavement layers - primarily for base course.
Bitumen-rubber
A binder in which bitumen is modified with more than 15% ground rubber. (See also
modified binder).
Bituminous binders
Petroleum derived adhesives used for sealing of surfaces and binding of aggregates in
pavement layers. Classified according to their composition and physical properties. (See
also penetration grade bitumen, cutback bitumen, bitumen emulsion, bitumen rubber, and
modified binders).
Bituminous seals
A general term for thin bituminous wearing courses made of surface treatments or slurry
seals, or a combination of these.
Borrow pit
A borrow pit is a site from which natural material, other than solid stone, is removed for
use in construction of the works. The term borrow area is also used.
Break of emulsions
‘Break’ of a bitumen emulsion is when the water and bitumen separates so that the water
will evaporate, leaving behind the bitumen to perform its function.
Buses
All buses with a seating capacity of 40 or more.
Cement- or lime modified
material (CM)
Naturally occurring gravel and soils which are modified by the addition of either lime or
Portland cement so that their engineering properties such as strength and plasticity are im
proved, but the materials still remain flexible. Used in pavement- and improved subgrade
layers. (See also Cement- or lime stabilised material).
Cement- or lime stabilised
material (C4, C2, C1)
A material that consists of snatural- or crushed gravel stabilised with ordinary Port
land cement or lime such that a semirigid material is produced. Classified according
to their minimum unconfined compressive strength. Used in pavement layers. (See
also Cement- or lime modified material).
TANROADS
131
Crushed rock (CRR)
Crushed material made from fresh quarried rock or clean, un-weathered boulders of
min 0.3 m diameter. All particles shall be crushed. The material is compacted to a
specified percentage of the aggregate’s apparent density.
Crushed stone (CRS)
Crushed stones. Min 50% by mass of particles larger than 5 mm shall have at least
one crushed face. Made from crushing of stones, boulders or oversize from natural
gravel. Max 30% of the fraction passing the 4.75 mm sieve can be soil fines. The
material is compacted to a specified relative density of BS-Heavy.
Curing membrane
A bituminous binder, usually made of bitumen emulsion, applied immediately after
construction of a completed surface of modified or stabilised materials with lime or
cement. Its purpose is to prevent early drying out of the cemented layer and to minimise adverse effects of the stabiliser’s contact with CO2 in the air.
Cutback bitumen
A penetration bitumen which viscosity has been temporarily reduced by blending
with solvents. The solvents are expected to evaporate during the early part of the
pavement’s service life. Classified according to their viscosity.
Cutting
A cutting is a section of the road where the formation level is below the original
ground level.
Deflection (surface)
The recoverable vertical movements of the pavement surface caused by the application of a wheel load.
Deformation
A mode of distress, unevenness of the surface profiles.
Degree of distress
A measure of severity of the distress.
Distress
The visible manifestation of deterioration of the pavement with respect to either the
serviceability of the structural capacity.
Dry Density and Moisture Content of bituminous materials
The moisture content, in %, to use for calculation of dry density of materials that
contain both bitumen and water, e.g. FBMIX and BEMIX, is defined as follows:
MC =
(weight of water)
(weight of aggregate + weight of bitumen)
x 100
Dump rock (DR)
Un-graded rock or boulder material with a sufficiently low fines content so that the
large particles are in contact with each other when placed in earthworks layers. Used
in fill and improved subgrade layers.
Dynamic Cone Penetrometer
(DCP)
An instrument for assessing the in-situ CBR strength of granular materials/soils.
Shrinkage Limit
The saturated moisture content corresponding to the void ratio of a dried sample. In
practise this is the moisture content below which little or no further volume change
occurs in a soil being dried.
Skid resistance
The general ability of a particular road surface to prevent skidding of vehicles.
132
TANROADS
Slurry seal
A cold premixed material of creamy consistency in a fresh state, made of crusherdust, bitumen emulsion and cement filler. Water is added for adjustments of the con
sistency. If constructed in combination with a new surface dressing, it is named a
Cape seal.
Structural capacity
The ability of the pavement to withstand the effects of climate and traffic loading.
Structural design
The design of the pavement layers for adequate structural strength under the design
conditions of traffic loading, environment and subgrade support.
Structural distress
Distress pertaining to the load bearing capacity of the pavement.
Structural evaluation
The assessment of the structural capacity of a pavement.
Subbase
The layer(s) occurring below the base course and above the improved subgrade
layer.
Subgrade
The completed earthworks within the road prism before the construction of the
pavement layers.
Surface dressing
A surface treatment made of single sized aggregates of crushed material. Can be
constructed in single- or multiple layers.
Surface treatment
A general term for thin bituminous wearing courses made by lightly rolling aggregate into a sprayed thin film of bitumen. Aggregates can alternatively be made of
crushed or natural material with a grading depending on the desired type of surface
treatment to be produced. Can be constructed in single- or multiple layers.
Surfacing integrity
A measure of the condition of the surfacing as an intact and durable matrix (it includes values of porosity and texture).
Surfacing, bituminous
The uppermost pavement layer(s), which provides the riding surface for vehicles.
Includes bituminous wearing course and bituminous binder course where used.
Tack coat
An application of bituminous binder to a bituminous surface subsequent to placing
a bituminous layer. Usually made of bitumen emulsion with the purpose to improve
the bond between bituminous layers.
Terminal level
A minimum acceptable level of some feature of the road in terms of its serviceability.
Types of distress
The sub-classification of the various manifestations of a particular mode of distress.
Vehicle Equivalency Factor (VEF)
The total number of equivalent standard axles calculated for one vehicle.
The average of all these values within one vehicle category is subsequently
calculated for ease of reference to traffic count data.
Very Heavy Goods Vehicles (VHGV)
All goods vehicles having 4 axles or more.
Wearing course, bituminous
The uppermost surfacing layer. Can consist of a bituminous mix or a bituminous
seal, or both in combination.
TANROADS
133
Prefixes
The standard units of measurement to be used are based on the International System (SI) units. However, the units applicable to road design also include some units which are not strictly part of SI. Multiples and sub-multiples of SI units are
formed either by the use of the indices or prefixes. Definition of prefixes
Prefix
Symbol
Multiplying factor
mega
M
106
kilo
k
103
hecto
h
102
deca
da
10
deci
d
10-1
centi
c
10-2
milli
m
10-3
micro
µ
10-6
Basic units
Basic units, multiples and sub-multiples
Quantity
Unit
Symbols
Recommended Multiples
and Sub-Multiples
Length
metre
M
km, mm
Mass
kilogram
KG
Mg, g, mg, t (1t = 103kg)
Time
second
S
day(d), hour (h), minute(m)
Area
square metre
m
Volume(solids)
cubic metre
m3
Volume (liquid)
litre
l
Density
kilogram per Cubic metre
kg/ m
Mg/ m3 (1 mg/ m3 = 1 kg/l)
Force
Newton
N
MN, kN (1N = 1 kgm/s2)
Pressure and Stress
Pascal (N/m2)
Pa
MPa, kPa
Electric conductivity
Siemens per metre
S/m
mS/cm
Angle
degree or
grade
o
minute (‘), second (‘’)
(3600 circle), (400g circle)
Temperature
degree Celsius
o
Viscosity (dynamic)
Pascal.second
Pa.s
mPa.s
m /s
mm2/s, St (stokes)
1 cSt = 1 mm2/s
Kinematic viscosity
134
TANROADS
km2, mm2, hectare
(1ha = 10,000 m2)
2
cm3, mm3
ml, (1 ml = 1 cm3)
3
g
C
2
Appendix 8:
ABBREVIATIONS
10%FACT
See TFV
kN
AADT
Average Annual Daily Traffic
AASHO
Former name of AASHTO
AASHO-Road Test
Pavement research project conducted by AASHO to test the performance of
various pavements on a full scale
AASHTO®
American Association of State Highway and Transportation Officials
AC
Asphalt Concrete
ALD
mm
Average Least Dimension
ASTM
American Society for Testing and Materials
BEMIX
Classification of a material stabilised with bitumen emulsion (Bitumen
Emulsion MIX)
BS
British Standard
BS-Heavy
Compaction effort for soils, standardised by the CML test method 1.9
BS-Light
Compaction effort for soils, standardised by the CML test method 1.9
Cx
Classification of cement- or lime stabilised material, ‘x’ denoting the minimum
UCS value (7 days, at 97% MDD of BS-Heavy)
CBR
[%]
California Bearing Ratio, described by the CML test method 1.11
CBRdesign
[%]
CBR value for a homogenous section of subgrade, calculated
statistically or by subjective judgement, to use in pavement design
CBRsoaked
[%]
California Bearing Ratio measured after standardised 4 days soaking of
specimens in water, described by the CML test method 1.11
CI
Coarseness Index, used for classification of materials for gravel wearing
courses.
CM
Classification of cement- or lime modified material (low UCS strength)
CML
Central Materials Laboratory, Dar es Salaam
CRR
Material denotation for blasted, crushed, rock
CRS
Material denotation for crushed stones
CUSUM
Cumulative sum, statistical calculation method
DCP
Dynamic Cone Penetrometer
DBM x
Classification of a hot mixed bituminous base course material (Dense Bitumen
Macadam) ‘x’ denoting the upper nominal particle size in the material
dMAX
TANROADS
[mm]
Maximum particle size of soils and aggregates
135
dMIN
[mm]
Minimum particle size of soils and aggregates
dX
[mm]
The sieve size through which ‘x’% of all particle pass
E80
Equivalent Standard Axle (8160 kg)
EIA
Environmental Impact Assessment
EIS
Environmental Impact Statement
E-Modulus
[MPa]
Elasticity Modulus, describing stress/strain properties of structural pavement layers
ESA
Equivalent Standard Axle (=E80)
FBMIX
Classification of a material stabilised with foamed bitumen (Foamed Bitumen MIX)
FDD
[%]
Field Dry Density
FI
[%]
Flakiness Index, described by the CML test method 2.4
FMC
[%]
Field Moisture Content
Gx
Classification of gravel and soil materials, ‘x’ denoting the minimum CBR
GC
Grading Coefficient = [ (%pass28mm) – (%pass0.425mm) ] x (%pass5mm) /100
GDP
Gross Domestic Product
GM
Grading Modulus = (300 - %pass2mm - %pass0.425mm - %pass0.075mm) / 100
GW
Gravel Wearing course materials
ICL
[%]
Initial Consumption of Lime, derived from laboratory test CML 1.22
IRI
m/km
International Roughness Index
ISO
International Standard Organisation
lab
Laboratory
LAMBS
Classification of a hot mixed bituminous base course material (Large Aggregate
Mixes for Base)
LL
[%]
Liquid Limit, described by the CML test method 1.2
LS
[%]
Linear Shrinkage, described by the CML test method 1.4
max
Maximum
MC
[%]
MC x
Moisture Content
Medium Curing (type of cutback bitumen), ‘x’ denotes the upper nominal
viscosity limit
MDD
[kg/m3] Maximum Dry Density (compaction effort shall be stated)
MoW
Ministry of Work
min
Minimum
MSS
Magnesium Sulphate Soundness test
NEMC
National Environment Management Council
136
TANROADS
NPRA
Norwegian Public Roads Administration
NORAD
Norwegian Agency for International Development
OMC
[%]
pen
Optimum Moisture Content (at MDD of BS-Heavy unless stated)
Penetration, used to identify a type of bitumen (penetration grade)
PI
[%]
Plasticity Index, described by the CML test method 1.3
PIw
[%]
Plasticity Index, weighted for the sample’s amount of material passing 0.425 mm,
based on the CML test method 1.3
PMx
Penetration Macadam, ‘x’ denoting the upper nominal particle size in mm
PSI
Pavement Serviceability Index
RAP
Resettlement Action Plan
RC x
Rapid Curing (type of cutback bitumen), ‘x’ denotes the upper nominal
viscosity limit
Sx
Subgrade classification, ‘x’ denoting minimum CBR value
SC x
Slow Curing (type of cutback bitumen), ‘x’ denotes the upper nominal viscosity limit
SI
International standardisation by International Organization for Standardization
SIA
Social Impact Assessment
SL
Shrinkage Limit
SP
Shrinkage Product = [ LS x (%pass 0.425mm) ]
ST
Surface Treatment, a general term for all types of sprayed bituminous seals
SSS
Sodium Sulphate Soundness test
TFV
kN
Ten percent Fines Value, described by the CML test method 2.7
TFVdry
kN
As TFV. Used when dry test conditions need to be emphasised in the text
TFVsoaked
kN
As TFV. Ten percent Fines Value measured after 24 hours soak in water
TLCX
[million E80]
Traffic load class, ‘x’ denoting maximum number (in million) of E80 in the class
TLCX -H
[million E80]
Traffic Load Class, ‘x’ denoting maximum number (in million) of E80 in the class, ‘-H’
denoting that there is a large proportion of very heavy loads in the traffic stream
TMH
UCS
VEF
TANROADS
Technical Methods for Highways (South African series of standards)
[MPa]
Unconfined Compressive Strength, described by the CML tests 1.9 and 1.21
method for cement- or lime stabilised materials
Vehicle Equivalency Factor
137
Appendix 9: Worksheets
BORE LOG
TEST PIT LOG
FIELD DENSITY, Sand replacement method
FIELD DENSITY, Nuclear gauge metod
DCP
ROUGHNESS, MERLIN method
DEFLECTION, Benkelman Beam
138
TANROADS
BORE LOG
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TANROADS
139
TEST PIT LOG
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140
TANROADS
FIELD DENSITY
Sand replacement test
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TANROADS
141
FIELD DENSITY
Nuclear gauge method
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Mod. AASHTO
MDD/OMC
THICKNESS
mm
CHAINAGE
Km
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TROXLER
WD
DD
%M
%PRO
AVER
Aver
Comp
AVERAGE:
142
TANROADS
DCP
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BLOW No.
READING mm
DN mm/BLOW
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BLOW No.
READING mm
DN mm/BLOW
0 (zero-reading)
Sign. Technician:...............................................................................
TANROADS
143
Roughness measurments
MERLIN
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Tally box
1 2 3 4 5 6 7 8 9 10
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
144
TANROADS
DEFLECTION
Benkelman Beam
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Deflection reading, x 10-2
Inside wheeltrack
Chainage
Initial
reading
TANROADS
Max.
reading
Final
reading
Outside wheeltrack
Defl.
mm -2
Initial
reading
Max.
reading
Final
reading
Defl.
mm-2
145
Field Testing Manual - 2003 - Ministry of Works TANROADS, Tanzania
April 2003
ISBN 9987-8891-4-X
THE UNITED REPUBLIC TANZANIA
MINISTRY WORKS
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1.2 Structure of the Field Testing Manual

Transcription

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