construction estimating i bct 1770

The beginning is the most
important part of the work.
Plato
CONSTRUCTION
ESTIMATING I
BCT 1770
CHAPTER 4
SITEWORK
CSI DIVISION 2
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SITE WORK – DIVISION 2
General Information
 Earthwork starts with the soils report and finishes with landscaping.
 Included in between are demolition, clearing and grubbing, excavating and grading, and paving
 On-site work usually includes all construction on a project, including the structure and work within a
5 lf wide perimeter surrounding it
 Site improvements includes any and all other construction within the boundaries of the property but
beyond the 5 lf on-site perimeter.
 Off-sites refer to items outside the property lines such as street improvements, driveway entrances,
curb and gutter etc.
Site Work Includes
 Subsurface Exploration
 Site Preparation
 Clearing and Grubbing the Site
 Excavation and Grading
 Backfill
Subsurface Exploration
 Knowledge of the soil at various depths below the surface


A soils engineering firm takes samples of the surface and makes test borings
The two primary pieces of information being sought are the type and stability of the soil
 A soil report states the conditions of the earth on, and immediately adjoining, the property
 The soils engineer is also responsible for information regarding hazardous materials that may be
present
Site Preparation
 Demolition – A specialty contractor or excavating contractor may be contracted for structure and
debris removal.
 The demolition crew dismantles structures or parts of structures and removes or caps existing
utilities.
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 It is also the demolition crew’s responsibility to see that all hazardous wastes are completely
removed from the site
 Demolition costs include labor and equipment, as well as transportation and disposal of the
materials
 The demolition is sometimes accomplished by a salvage company; the company recoups some of
the expense of the demolition by reselling the salvageable materials
Clearing and Grubbing
 Like demolition, clearing entails removal of structures and debris
 The costs involved in clearing are the same as those considered for demolition
 Grubbing refers to removal of the vegetation
 The work includes removal of trees, shrubs, and other vegetation
 The costs involved for grubbing include labor, equipment and transportation
 The owner or architect determines which form of vegetation is to be saved, moved, or removed
 Remove trees and shrubs as shown on plans and protect the ones that remain
 Box and protect all trees in the construction area
 Remove all debris from the site; do not use it for fill
 The site is cleared and topsoil stripped within the limits of the building area
 Stripping line will be set back to allow any excavation
30’
30’
25’
STRUCTURE

Example: A basement
Approx. 25’ around the perimeter (when applicable)
Volume = 80’ X 80’ X .5 = 118.6 c.y.
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Excavating and Grading
 It is difficult to determine the cost of excavating

Cost varies with the type of soil, water, disposal etc.

Most surprises will increase costs
 There is little or no materials required, with the exception of stakes or flags for identifying grade
levels and carpentry materials for mass or trench excavation.
 The major costs in the excavating and grading estimate are labor and equipment, of which the
equipment makes up the largest part.
 The equipment necessary is dependent on the size of the project and the type of soil encountered.
 The contractor may need only a small bulldozer or may require a large earthmover and grader
Excavating


It is difficult to determine the cost of excavating

Cost varies with the type of soil, water, disposal etc.

Most surprises will increase costs
By code Footing excavation must go to solid, stable earth

Footing on soft or wet soil or fill will result in cracks in the foundation

Organic matter under a footing will decay

Price the job in cubic yards not by linear feet - Deeper footings should not come out of your
pocket

Normal excavation is based on sandy loam or light soil

Light clay or loose rock - add 50%

Tough clay or rock - cost plus

De-watering extra
 Swellage - increase in volume due to the handling of disturbed soil
 A variation in soil quantities is called “loose” soil and results from expansion caused by braking the
soil up and mixing with air
 The loss varies with the type of soil and the compaction requirements. A swell factor must be
added to account for the “loose” soil variance.
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
Using a swellage factor on the example above


Volume = 118.6 X 1.30 = 154.18 = 155.00 c.y.
NOTE: 36.5 c.y. increase due to swellage

The excavation line around a building must be kept back to allow formwork and the sloping of the
cut

Sloping of the cut

Is based on the soil, water, etc.
Undisturbed soil, no water

(ratio = horizontal : vertical)




Sand and gravel - 1:1
Ordinary clay - 1:2
Stiff clay - 1:3 or 1:4
Where sloping is not possible, it may be necessary to sheet and brace the banks to prevent caveins

OSHA - excavation of five feet or over requires soil supports

Hand dressing
Backfill

Compute the displacement volume of the construction within the limits of the excavation (footing,
piers, basement walls, etc.)


Deduct this volume from the sum of the mass excavation

Remainder is volume of backfill

Add a shrinkage factor
Shrinkage - when loose material is placed as a backfill material and compacted. - It is compressed
into a smaller volume and shrinkage occurs

Shrinkage factor:




Sand and gravel
Loam
Dense clay
Solid rock
0.10 - 0.15
0.15 - 0.20
0.25 - 0.30
0 .0 0
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Example - Backfill
 Example: 1. Backfill a channel - 6’ deep, 15’ wide, 5,280’ long
2. Backfill with dense clay
3. Construction volume = 6,000 c.y.


Excavated Volume = 6 x 15 X 5280 = 17,000 c.y.
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
Volume of Backfill = excavated volume - const. Volume

1.00 - shrinkage factor

= 17,600 - 6,000 = 11,600 = 16,571.43
1.00 - .30
.7 0
= 16,572 c.y.
Swales and Basins
 A swale may be a natural or excavated dip or shallow sloped area in the earth, a swallow sloping
of paved parking areas and driveways, or a concrete trench through the center of such areas used
to direct the drainage away from any structure located on the property.
 A detention basin is an area, on or off the property, that is either a natural basin, or an excavated
one and that is several feet lower than the surrounding area.
Swales and Basins
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Grading

Plot plans and survey - mostly commercial




Finish grade levels of main corners of the property and
the building’s finished floor



Dimensions of plot
Location and dimensions of all structures
Location and dimensions of all walks, driveways, etc.
Location of a bench mark and its elevation
Location of utilities, such as electric, water, gas, and sewer
Finish grading



Spread topsoil
Prepare topsoil to receive sod, etc. by removing stones and debris
Hand rake
Soil Treatment
 Soil treatment against termites and rodents, is included in the work of the excavating contractor
 The location of the treatment and the quantities of chemical are determined by the soil conditions,
by local codes and ordinances.
 The treatment is usually confined to the area under and immediately adjacent to the structure
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Paving
 After the grades have been completed and established, the finished surfaces for traffic are
constructed.
 The materials required include:



A sub-base
An aggregate base
The surfacing material with a seal coat
 The surfacing materials used may either be of concrete or a bituminous product (asphalt)
Landscaping

Landscaping includes everything within the site improvements and, possibly, off-sites on a project.

The identification of paving, sidewalk, patios, plazas, and so on is called the hardscape

The remaining areas – lawns or other ground cover, shrubbery, or trees – are the softscape
THE ESTIMATE
The Estimate – Demolition
 Demolition – This portion of the estimate is for demolition, clearing and rubbing and normally
involves only labor and equipment.
 The demolition estimate includes clearing and grubbing of trees and vegetation.


Check specification to determine what vegetation is in good enough condition to save
The remainder is unwanted vegetation and debris
The Estimate – Grading
 The calculation for grading is determined in cubic feet or cubic yards
 The calculation needs to show whether soil is to be removed or added

Soil that is to be removed is called cut.
 Cut areas are always positive quantities in calculations
 Soil that has to be added is referred to as fill
 When a negative quantity is calculated, it is identified with the symbol (<>)
 A large property with many contour changes is difficult to estimate without the use of some form of
reduction of area.

The simplest technique for reducing areas ids through the use of a grid system
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
Grids are usually drawn in 50 lf. squares directly on the site plan or on an overlay.
Grid Averaging Method
 The averaging method uses the cross sectional view of the whole grid and the elevations noted on
the four corners of the grid
 The section should cut through the grid in as nearly a perpendicular line to the contours as
possible
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Grid Averaging Method
 Elevations of 4 corners – grid 1:
 Section 1A-88.00’; Section 2A-91.75’; Section 1B-90.33’; Section 2B-94.25’
 88.00 ft. + 91.75 ft. + 90.33 ft. + 94.25 ft. = 364.33 ft.
 364.33 ft. / 4 = 91.08 ft.






T.O.W . is 95.0 ft.; the rough grade is 8” below the T.O.W ., therefore:
95.0 ft. – 0.67 ft. = 94.33 ft.
94.33 ft. – 91.08 ft. = <3.25> ft.
<3.25> ft. X (50 ft. X 50 ft.) =
<3.25> ft. X 2500 sq.ft. X 1.20
<8125> cu.ft. / 27 cu.ft. X 1.20 = <361.11>cu.yd.
 The 20% soil expansion shall be used for all remaining grading and excavating calculations
The Estimate - Excavation
 The quantity of material to be moved and efficiency of the crews and equipment determine both the
labor and the equipment costs
 The quantity of materials moved is determined with points of information picked up by the estimator
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from the soils report and/or a job-site visit. W ithout this report, a viable estimate of excavating costs
cannot be made.
 The efficiency of crews is based on historical data and the soil report.
The Estimate - Paving

In making estimates for paving, the estimator must note the following:




The type and thickness of the base material
The cementitious aggregate
Surfacing
The estimator should determine the slope, possibly including any small swale
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EXERCISE I
Estimate the amount of excavation in cubic yards required for the topsoil, basement, and
footings for the building foundation below.
1 Compute the cubic yards of topsoil that must be removed to a depth of 8”. In making
this computation, it is necessary to include a swellage factor.
2 Compute the amount of earth to be removed in order to form the basement walls
(Swellage factor for wet clay).
3. Determine how many cubic yards of earth must be removed for the footing for this
foundation. (Do not use any swellage factor).
4. Compute the amount of backfill (loam) that will be required after the foundation is in
placed. In making this computation, it is necessary to include a shrinkage factor.
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CONSTRUCTION PHOTOGRAPHS
CORE DRILLING SAMPLE
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LASER
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TREE SHREDDER
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BULL DOZER
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TRACK EXCAVATOR
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FRONT LOADER
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GRADER
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DUMP TRUCK
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EXCAVATOR
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EXCAVATING – UTILITIES
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EXCAVATING – WATER LINES
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STEAM ROLLER
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