CE 5320- Advanced Geotechnical Engineering

CE 5320Advanced Geotechnical
Engineering
Instructor: Reza Ashtiani, Ph.D.
Liberal Arts Bldg. Room 210
TR 6:00 pm- 7:20 pm
Fall 2016
3
4
Employment of civil engineers is projected to grow 20 percent from 2012 to 2022, faster than the
average for all occupations. As infrastructure continues to age, civil engineers will be needed to
manage projects to rebuild bridges, repair roads, and upgrade levees and dams.
Industries that employed the most civil
engineers in 2012, Bureau of Labor statistics
Civil engineers held about 272,900 jobs in 2012.
Course Structure
Text:
Advanced Soil Mechanics, by Braja M. Das, Fourth
Edition, Publisher: CRC Press-Tylor & Francis, 2014.
Class Website:
Site Password:
www.rezasalehi.com/CE-5320
students
Grading:
1.
2.
3.
4.
Final Comprehensive Exam (400 points)
Homework Assignments (300 points)
Term Project (300 points)
Critical Assessment (attendance and
involvement in class discussions) (50 points)
__________________________________________
Total: 1050 Points
General Concepts
Mechanical
Compaction
CE5320 - Advanced
Geotechnical Engineering
Soil Water
Interactions
Physical Properties of Soils
Field Compaction
Laboratory Compaction
Capillary Action
Diffuse Double Layer
Suction Profile
Hysteresis Behavior
Soil Water
Characteristic Curve
Applications of SWCC
Mohr Circle and Failure Criteria
Stress Path Testing
of Geomaterials
Types & Components of
Stress Path Tests
Shear Strength and Soil Suction
Laboratory Testing
Shear Strength of
Soils
Subsurface Soil
Explorations
Reliability in
Geotechnics
Skempton’s Pore Water Pressure
Parameters
N-s Rule
Probability of Failure
In-Situ Shear Strength
Rankine’s Theory
Lateral Earth
Pressure
Coulomb’s Theory
Soil Suction and Earth
Pressure
Seismic Loads and Earth
Pressure
Failure Mechanisms
Bearing Capacity of
Shallow
Foundations
Bearing Capacity Theories
Soil Suction and Bearing Capacity
Item Description
Quantity
Lecture Topics
13
Lecture Segments
15
PowerPoint Slides
739
Homework Assignments
3
Term Project
1
Exams
1
Size Limits in Soil Classification Systems
Particle Size Limits by Various Systems
Particle Size Classifications
Mechanical Sieve Analysis
A sieve analysis is conducted by taking a measured amount of dry, wellpulverized soil and passing it through a stack of progressively finer
sieves with a pan at the bottom. The amount of soil retained on each
sieve is measured, and the cumulative percentage of soil passing
through each sieve is determined.
Particle Size Distribution Curve
Note that the grain diameter, D, is plotted on the logarithmic scale and the
percent finer is plotted on the arithmetic scale.
Hydrometer Analysis
 Hydrometer
test is performed on the fine portion of
the mix (particles passing sieve #200 or smaller than
0.075 mm).
 Stoke’s
law of settling is the basis for developing the
gradation chart for the fine grained soils.
 According
to Stoke’s law, the sedimentation velocity
of suspended particles is proportional to the square
of their diameter.
Hydrometer Test
 Hydrometer test entails the measurement of the specific
gravity of a dispersed soil suspension, contained in a
sedimentation cylinder, by a hydrometer bulb immersed in
the suspension.
 Sodium Hexametaphosphate is typically used as a
dispersing agent.
 As larger soil particles settle, the specific gravity of the
suspension decreases, approaching the specific gravity of
water.
 Hydrometer readings are then correlated to the “percent
finer” and the grain size distribution curve is plotted
similarly to the method used in sieve analysis.
Hydrometer Test
The standard test methods for both mechanical sieve analysis and
hydrometer tests are described in detail in ASTM D422.
Combination of Mechanical Sieve Test
and Hydrometer Test
 When these results are combined, a
discontinuity generally occurs in the
range where they overlap. This
discontinuity occurs because soil
particles are generally irregular in
shape.
 Sieve analysis gives the intermediate
dimensions of a particle; hydrometer
analysis gives the diameter of an
equivalent sphere that would settle
at the same rate as the soil particle.
Laser Particle Size Analyzer
 The central idea in laser diffraction is that
a particle will scatter light at an angle
determined by that particle’s size.
 Larger particles will scatter at small angles
and smaller particles scatter at wide
angles.
 A collection of particles will produce a
pattern of scattered light defined by
intensity and angle that can be
transformed into a particle size
distribution result.
Different Types of
Particle Distribution Curves
Definition of D60, D30, and D10
Gradation Parameters

Coefficient of Uniformity (Cu )

Coefficient of Curvature (Cc )
D60
Cu 
D10
2
30
D
Cc 
D60  D10

D10 : The diameter corresponding to 10% finer in the particle-size
distribution curve.

D30 : The diameter corresponding to 30% finer in the particle-size
distribution curve.

D60 : The diameter corresponding to 60% finer in the particle-size
distribution curve.
Determination of Gradation
Parameters- Example
D60  0.41
D30  0.185
D10  0.09
D60 0.41
Cu 

 4.56
D10 0.09
(0.185) 2
Cc 
 0.93
0.41  0.09
Simultaneous Requirements for Well Graded
Soils based on Gradation Parameters
Well  graded soil
for gravels :
1  Cc  3 and Cu  4
for sands :
1  Cc  3 and Cu  6
Aggregate Geometry
 Particle

Describes flat and elongation of the aggregate
particles.
 Particle


Shape
Angularity
Relates to the broken edges of the aggregate particles.
Surface Macro-Texture

Relates to the asperities on the particle surface.
Plasticity of Soils
Consistency Limits of
Fine Grained Soils in Presence of Water
 At
low moisture content soil behaves more like
a brittle solid and can resist shear stresses.
 At
high moisture content soil and water may
flow like a liquid.
 Depending
on the moisture content, soil
behavior can be: solid, semisolid, plastic, or
liquid.
Atterberg Limits
 When a clayey soil is mixed with an excessive amount of water, it may
flow like a semiliquid.
 If the soil is gradually dried, it will behave as plastic, semisolid, or solid
material, depending on its moisture content.
 The moisture content, in percent, at which the soil changes from a liquid to
a plastic state is defined as the Liquid Limit (LL).
 The moisture content, in percent, at which the soil changes from a plastic
state to a semisolid state is defined as the Plastic Limit (PL).
 The moisture content, in percent, at which the soil changes from a
semisolid state to a solid state is defined as Shrinkage Limit (SL).
Atterberg Limits
Plasticity Index or PI
solid
liquid
The plastic zone
PL
0%
LL
Moisture content
Max
Definition of Atterberg Limits
Strength Comparison of the Same Soil
at Different Moisture Contents
Atterberg Limit Tests
Liquid Limit, LL
 Moisture content (in percent) required to close a distance of 12.7 mm (0.5 inch)
along the bottom of the groove after 25 blows.
 Basically the moisture content below which the soil can be sheared.
Plastic Limit, PL

Moisture content (in percent) at which the soil, when rolled into threads of 3.2
mm (1/8 inch) in diameter, crumbles.
Liquid Limit Test
Liquid Limit Device
 Soil paste is placed in the cup.
 Using the standard grooving tool, a
groove is cut at the center of the soil pat.
Flat Grooving Tool
 The cup is lifted and dropped from a
height of 10 mm.
Wedge Grooving Tool
 Moisture content (%), required to close a
distance of 12.7mm (1/2 inch) along the
bottom of the groove after 25 blows is
defined as the liquid limit.
Soil Pat before Test
Soil Pat after Test
Liquid Limit Test
Before Liquid Limit Test
After Liquid Limit Test
Flow Curve for the Determination of
the Liquid Limit
Flow Curve-Example
Plastic Limit Test
 Defined as Moisture content (%)
at which soil crumbles when
rolled into threads of 3.2 mm
(1/8 inch) in diameter.
 Repeat the rolling of 1/8”
diameter threads of soil until
they lose enough moisture to
break.
Shrinkage Limit
 Shrinkage limit is defined as the moisture content (%) at which the volume
change of the soil mass stops.
 Shrinkage limit test is performed using a porcelain dish about 44 mm in
diameter and about 13 mm high.
 Inside of the dish is coated with petroleum jelly and filled completely with
wet soil.
 Excess soil above the edge of the dish is struck off with a straight edge.
 Mass of the wet soil in the dish is recorded.
 Soil pat is oven dried and then the volume of the dried soil pat is determined.
Shrinkage Limit Test
Soil Pat before Drying
Soil Pat after Drying
Atterberg Limits and Volume Change
Definition of Plasticity Index (PI)
 Plasticity
Index is the numerical difference between the Liquid Limit and
the Plastic Limit.
PI=LL-PL
 It
represents the range in water contents over which a soil behaves in a plastic
manner.
PL
Semi-solid
w%
PI = LL - PL
Plastic (Remoldable)
LL
Liquid
Plasticity Chart
 Casagrande (1932) studied the relationship
between the plasticity index and the liquid limit
of a wide variety of natural soils. On the basis of
the test results, he developed the plasticity chart.
 The A-line separates the inorganic clays from the
inorganic silts. Inorganic clay values lie above the
A-line, and values for inorganic silts lie below the
A-line.
 The information provided in the plasticity chart is
of great value and is the basis for the
classification of fine-grained soils in the Unified
Soil Classification System (USCS).
 The U-line is approximately the upper limit of
the relationship of the plasticity index to the
liquid limit for any currently known soil.
Lining Ponds with Bentonite Clay for Water Retention
Bentonite Clay for Drilling Operations
Liquidity Index (LI)

LI is an indication of the relative consistency of fine-grained soils in its natural state.
LI<0
Semisolid State – high strength, brittle (sudden)
fracture is expected, (Friable)
0<LI<1
Plastic State – intermediate strength, soil deforms like
a plastic material , (Moldable)
LI>1
Liquid State – low strength, soil deforms like a viscous
fluid , (Flowable)
Activity of Fine Grained Soils

Because the plasticity of soil is caused by the adsorbed water that
surrounds the clay particles, we can expect that the type of clay minerals
and their proportional amounts in a soil will affect the liquid and plastic
limits.

Skempton (1953) observed that the plasticity index of a soil increases
linearly with the percentage of clay-size fraction (% finer than 2 mm by
weight) present in the mix.
Plasticity Index ( PI )
Activity 
Percent Clay Size Particles in the Mix (%)
Plasticity Index and Clay Activity
(Skempton, 1953)
Clay Activity, Seed and Woodward
Modification

Seed, Woodward, and Lundgren (1964a) studied the plastic property of
several artificially prepared mixtures of sand and clay. They concluded
that, although the relationship of the plasticity index to the percentage of
clay-size fraction is relatively linear (as observed by Skempton), it may
not always pass through the origin.

Suggested modification to the Skempton’s equation:
Plasticity Index ( PI )
Activity 
Percent Clay Size Particles in the Mix (%)  C '

Based on the experimental results, the C’ value is approximately 9.
Relationship between Plasticity Index (PI)
and Clay-Size Fraction for
Kaolinite/Bentonite Mixtures
Notice that the C’ value ( i.e. the
intersection of the experimental
curves with the x-axis) is
approximately 9.
Influence of the Fines Content on the Density
of the Mixes (Siswosoebrotho, 2005)
Influence of the Fines Content on the Strength of
the Soil Mix (Siswosoebrotho, 2005)
Influence of the Fines Content on the Permeability
of the Soil Mix (Siswosoebrotho, 2005)
Soil Classification
Soil Classification
 Different
soils with similar properties may be classified into
groups and subgroups according to their engineering
behavior.
 Classification
systems provide a common language to
concisely express the general characteristics of soils, which
are infinitely varied, without detailed descriptions.
 Most
of the soil classification systems that have been
developed for engineering purposes are based on simple
index properties such as particle-size distribution and
plasticity.
Role of Classification in Geotechnical Engineering
Unified Soil Classification System
(USCS) Symbols
Unified Soil Classification System (USCS)
Information required for soil classification according to USCS:
Particle Size
1)
 Gravel
(G), Sand (S), silt (M), and Clay (C)
Particle Size Distribution
2)
 Gradation
Parameters (Cc and Cu)
“Atterberg Limits” of the Fine Portion of the Mix
3)

Liquid Limit (LL), Plastic Limit (PL) and Plasticity Index (PI)
Definition of Grain Size in the USCS
Gravel
Boulders Cobbles
Coarse
300 mm
75 mm
19 mm
Sand
Fine
Coarse
Silt and Clay
Medium
Fine
No.4
No.200
4.75 mm
0.075 mm
No.10
No.40
2.0 mm
0.425 mm
Plasticity Chart
Flow chart for
classification of
coarse grained soils.
Flow chart for
classification of
inorganic fine
grained soils.
Flow chart for
classification of
organic fine
grained soils.
USCS Example
Classify the following soil by the Unified Soil Classification
System:
Percent passing No. 4 sieve= 82
Percent passing No. 10 sieve=40
Percent passing No. 40 sieve =64
Percent passing No. 200 sieve=41
Liquid Limit=31
Plasticity Index=12
Solution
 We are given that passing #200 is 41% and LL=31 and PI is 12. Since 59%
of the sample is retained on a No. 200 sieve, the soil is a coarse-grained
material.
 The percentage passing a No. 4 sieve is 82, so 18% is retained on No. 4
sieve (gravel fraction).
 The coarse fraction passing a No. 4 sieve (sand fraction) is 59-18=41%
(which is more than 50% of the total coarse fraction). Hence, the
specimen is a sandy soil.
 Using USCS soil classification flowchart, we identify the group symbol
of the soil as SC.
 Since the gravel fraction is greater than 15%, the group name is:
clayey sand with gravel
AASHTO Soil Classification
 The AASHTO Soil Classification System was originally proposed
by the Highway Research Board’s Committee on Classification of
Materials for Subgrades and Granular Type Roads (1945).
 According to the present form of this system, soils can be classified
according to eight major groups A-1 through A-8, based on their
grain-size distribution, liquid limit, and plasticity indices.
 Soils listed in groups A-1, A-2, and A-3 are coarse-grained
materials, and those in groups A-4, A-5, A-6, and A-7 are finegrained materials.
 Peat, muck, and other highly organic soils are classified under A-8.
AASHTO Soil Classification-General Guideline

8 major groups: A1~ A7 (with several subgroups) and organic soils A8.

The required tests are sieve analysis and Atterberg limits.

The group index, an empirical formula, is used to further evaluate soils within a group
(subgroups).
A1 ~ A3
Granular Materials
Silt-Clay Materials
 35% pass #200 sieve
 36% pass #200 sieve
Using LL and PI separates silty materials from clayey
materials (only for A2 group)

A4 ~ A7
Using LL and PI separates silty materials from clayey
materials
The original purpose of developing the AASHTO classification system was to provide
a systematic method to classify soils for use in highway construction.
Definition of Grain Size in the AASHTO System
Boulders Cobbles
Gravel
Sand
Coarse
305 mm
75 mm
Silt
Clay
Fine
Sieve #10
Sieve #200
0.425 mm
Sieve #40
0.001 mm
0.075 mm
0.002 mm
2 mm
Group Index (GI)
General Equation:
GI  ( F200  35)0.2  0.005( LL  40)  0.01( F200  15)( PI  10)
F200: percentage passing through the No.200 sieve
For Group A-2-6 and A-2-7
GI  0.01( F200  15)( PI  10)
use the second term only
In general, the rating for a pavement subgrade is inversely proportional
to the group index, GI.
AASHTO Classification-Granular Soils
AASHTO Classification-Fine Grained Soils
Range of Liquid Limit and PI for Soils in Groups
A-2, A-4, A-5, A-6 and A-7
Comparison of the Ranges of Particle Sizes
Comparison of USCS and AASHTO Soil
Classification Systems
Comparison of USCS and AASHTO Soil
Classification Systems
Assessment of Soil Properties Based on
the Group Symbol
Assessment of Soil Properties Based on
the Group Symbol, cont.
Classification Summary
 The AASHTO soil classification system is based on sieve analysis (i.e., percent
finer than No. 10, 40, and 200 sieves), liquid limit, and plasticity index. Soils can
be classified under categories:
 A-1, A-2, and A-3 (granular soils)
 A-4, A-5, A-6, and A-7 (silty and clayey soils)
 Group index is added to the soil classification which evaluates the quality of soil
as a subgrade material.
 Unified soil classification is based on sieve analysis (i.e., percent finer than No. 4
and No. 200 sieves), liquid limit, and plasticity index. It uses classification
symbols such as:
 GW, GP, GM, GC, GW-GM, GW-GC, GP-GM, GP-GC, GC-GM, SW, SP, SM,
SC, SW-SM, SW-SC, SP-SM, SP-SC, and SC-SM (for coarse-grained soils).
 CL, ML, CL-ML, OL, CH, MH, and OH (for fine-grained soils).