RESUL TING FROM EMBANKMENT LOADING OF SOFT CLAY
AND SILT DEPOSITS
for the degree of Doctor of Philosophy in Civil Engineering
in the Graduate College of the
University of Illinois at Urbana-Champaign, 2001
Urbana, Illinois
Fishers, IN 46038
Geotechnical, Environmental and Construction Materials Testing Professionals
www.geotill.com
AND SILT DEPOSITS
MALEK M. SMADI
B.s., Jordan University of Science and Technology, 1988 M.S., Jordan University of Science and Technology, 1991
THESIS
Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy in Civil Engineering
in the Graduate College of the University of Illinois at Urbana-Champaign, 2001
Urbana, Illinois
UNIVERSITY OF ILLINOIS AT URBANA-CHAMPAIGN
GRADUATE COLLEGE
MALEK M. SMADI
RESULTING FROM EMBANKMENT LOADING OF SOFT CLAY AND SILT DEPOSITS
BE ACCEPTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR
THE DEGREE OF DOCTOR OF PHILOSOPHY
~~ Director of Thesis Research
0-517
SILT DEPOSITS
University oflllinois at Urbana Champaign, 2001 Gholamreza Mesri, Advisor
Settlement of structures on soft clay deposits results from flow and
consolidation of soil. In the latter case, water squeezes out from under the
structure, whereas in the former case soil squeezes out. Settlement resulting
from flow of soil depends on the factor of safety against undrained instability.
In construction situations where the factor of safety is small, an accurate
prediction of settlement reSUlting from flow of soil is required. Field
measurements of horizontal deformation of soft clays during and after
construction of embankments and storage facilities have been collected from
throughout the world, covering 180 case histories, to relate lateral deformation
to the factor of safety and to develop a practical procedure for computing
settlements resulting from flow of soil.
The available methods for predicting the undrained settlement and lateral
deformation, including solutions based on elasticity, empirical procedures, and
numerical techniques, were reviewed. The behavior of clay foundations
subjected to embankment loading and empirical methods using lateral
deformation as a measure of undrained stability, were reviewed and discussed.
The 180 case histories of embankments on soft clay and silt deposits with
lateral deformation measurements cover a wide range of subsurface
conditions, including plasticity index Ip from 5 to 340, undrained shear
strength Su from 5 to 80 kPa, Eu/su from 200 to 1000, cr/ plcr/ vo from 1 to 5,
embankment width B from 8.5 m to 630 m, embankment height h from 1 to ill
35m, embankment slope width L from 1.35 to 195 m, and depth of foundation
Lo from 7 to 63 m.
An empirical correlation, based on 58 cases was developed between maximum
lateral deformation Dm or area of lateral deformation profile AD and factor of
safety against undrained failure. Parameters such as Eu, L, B/2 were also
included in the correlation.
A procedure, based on 16 cases with three or more inclinometers at several
distances from the centerline, was developed for determining distribution of
maximum lateral deformation and flow settlement across the embankment as a
function of LoIB and UO.5B. The procedure could be used either with one
inclinometer measurement e.g. near the toe of the embankment, or together
with the empirical correlation between Dm and factor of safety.
A procedure was developed for determining settlement trough resulting from
lateral deformation of soil out from under the embankment. The procedure
could be used together with inclinometer measurements at one location, e.g.
near the toe of the embankment or with Dm or AD determined from the
empirical correlation between lateral deformation and factor of safety.
Using the empirical database and the developed procedures, it was possible to
make successful prediction of lateral deformation and associated settlement for
embankments on soft clay and silt deposits.
IV
ACKNOWLEDGMENTS
This thesis is based on theoretical and empirical studies of field observations
conducted at the University of lllinois. It has been prepared under the direct
supervision of Dr. G. Mesri, Ralph B. Peck Professor of Civil Engineering, to
whom the writer is indebted for his constructive criticism, guidance, and
encouragement in the preparation of the manuscript.
During graduate study, the writer was employed part time in the office of
Minority Student Affairs. Special acknowledgement is due Mr. Otis Williams,
Associate Director of Minority Student Affairs at University of lllinois for his
valuable help.
Special thanks are extended to Professors E. J. Cording, J. H. Long, T. D.
Stark, and Dr. G. Fernandez for their encouragement during writer's graduate
study at the University of lllinois.
The writer wishes to thank his office mates Dr. H. Eid and Mr. B
Vardhanabhuti, and Dr. M. Shahain, M. Al-zoubi, M. Ajlouni, V. Schifano,
and M. Maniaci, graduate students at the University of lllinois, for discussions
and constructive criticism during the preparation of this thesis.
The author wishes to express his gratitude to the Department of Civil
Engineering and the National Science Foundation (NSF) for their continued
support during writer's graduate study at the University of lllinois at Urbana
Champaign.
Finally the writer gratefully appreciates the continued encouragement, support
and patience of his parents, brothers, and sisters throughout his education.
v
1.3 Scope .............................................................................. " .... 4
LATERAL DEFORMATIONS .......................................... 6
2.1 Introduction ...................................................................... 6
Lateral Deformation Using Theory of Elasticity .............. 6
2.2.1 Flow Settlement.. ......................................................... 6
2.2.2 Lateral Defolmation .................................................... 9
Using Constitutive Models .............................................. 11
2.3.1 Constitutive Models .................................................. 11
Case Histories ............................................................ 12
Finite Element Method ............................................. 16
Empirical procedures ....................................................... 17
2.4.5 Effect of Vertical Drains on Lateral Deformation .... 24
2.4.6 Field Deformation Analysis (FDA) ......................... 25
2.4.6.1 Loading Stage ...................................................... 25
2.4.6.2 Post-Loading Stage ............................................. 30
TO E:MBANKMENT LOADING ........................................ 67
Embankment Loading ...... " ................................................. 67
3.1.2 Yielding of Clay Foundation under Embankments ..... 68
3.1.3 Foundation Behavior Described Using Effective
Stress Path ..................................................................... 69
under Embankments ........................................................... 72
Stage Embankment Construction ................................. 72
Construction .................................................................. 75
3.3.1 Effect of Soil Type on the Distribution
of Lateral Deformation ................................................. 81
V11
Distribution of Lateral Deformation ............................ 81
3.3.4 Effect of Time on the Distribution of
Lateral Deformation ..................................................... 84
Deformation Profile ...................................................... 84
Clay Foundations ................................................................ 85
3.4.1.1 Vane Tests ............................................................... 86
3.4.2 The Value of Factor of Safety that Triggers
an Abrupt Increase in Rate of Lateral Deformation .... 88
3.5 Shear Stress Level and Undrained Shear Deformations .... 89
3.6 Undrained Modulus of Soft Clay and Silt Deposits ........... 92
3.7 Lateral Deformation under Reinforced Embankments ...... 94
CHAPTER 4 CONTROL OF El\fBANKMENTS CONSTRUCTION
BY OBSERVING LATERAL DEFORMATION .......... 131
4.1 Measurement of Dm and St .............................................. 131
4.2 Evaluation of AD and As ................................................. 132
4.3 Using Horizontal Displacement,
4.4 Horizontal Displacement at the Surface
and the Factor of Safety .................................................. 133
4.5 Dm/St and St ..................................................................... 134
viii
Total Load (~q/M)m and q) ) ......................................... 136
4.7 Other Methods ............................................................. · .... 137
CHAPTER 5 CASE mSTORIES .............................................................. 193
CHAPTER 6 PREDICTING SETTLEMENT RESULTING FROM
LAT~RAL DEFORMATION ... , ....................................... 330
6.3 Lateral Displacement Volume of Soil and Associate
Settlements ...................................................................... 333
Thickness on Consolidation ..................................... 336
6.4.1 Lateral Deformation Distribution Across
Embankment Width .................................................. 338
Embankment Width .................................................. 339
1X
1-95 Sec 246 Using the Proposed Method ...................... 351
6.7.1 The Influence of the Inclinometer Location on
the Predicted Undrained Settlement for Embankment
1-95 Sec 246 Using the Proposed Method ................. 352
6.7.2 Undrained Settlement Prediction for Embankment
1-95 Sec 246 Using the Proposed Method
and the Giroud (1973) Method ................................. 352
6.7.3 Undrained Settlement Prediction for Embankment
. 1-95 Sec 246 Using the Proposed Method
and Poulos (1972b) Method ..................................... 353
6.7.4 Maximum Lateral Deformation Profile Across
the Embankment Width for 1-95 Sec 246 using
the proposed method and MIT-E3 .......................... 353
6.7.5 Maximum Lateral Deformation Profile Across
the Embankment Width for Rio de Janeiro Trial
Embankment Using the Proposed Method and
CRISP ........................................................................ 354
Sec 246 using ILL1CON for Consolidation Settlement
and the Proposed Method for the Undrained
Settlement ........................................................................... 355
Embankment 1-95 Sec 246 Using ILLICON ............. 356
x
7.1 Summary ......................................................................... 546
7.2 Conclusions ..................................................................... 551
Volume of soil per unit length of embankment that displaces
laterally, measured at the toe.
Pore pressure parameter A at (crl - cr3)max
Total volume of soil per unit length of embankment and B/2
that displaces vertically.
Volume of soil per unit length of embankment and B/2
that displaces vertically due to lateral flow of soil = AD
Coefficient of compressibility
The ratio of incremental excess porewater pressure to the
incremental mean effective stress
Swelling index
Maximum lateral deformation
width
Undrained Young's modulus
Threshold height or critical height
Influence value, depending on the shape of the loaded area and
the depth of the elastic layer
Isotropic (equal all-round pressure) consolidated drained
compression test
Liquidity index
Plasticity index
compression test
Permeability
Non-dimensional Deformation Method
X111
Nz
NZsum
pi
Su
deformation (= DlDm)
Depth of certain point at depth z 1 Whole depth of the lateral
deformation profile (= z/ZD
Depth of Maximum lateral deformation 1 Whole depth of the
lateral deformation profile (= Zrr/ZI = 0.26 ± 0.14)
Depth of minimum undrained shear strength 1 Total depth of
the lateral deformation profile
(d 1 - d 3)12, (d y - d h)12
Net foundation pressure.
the voids
The undrained shear settlement resulting from lateral
deformation of the foundation soil
Maximum undrained settlement across the embankment width
Undrained shear strength
Mobilized undrained shear strength
Undrained vane shear strength
Undrained Strength Stability Analysis
woN atural water content
ZI Depth of influence of lateral deformation
Zm Depth of maximum lateral deformation
a Deformability factor
mm Increment of maximum lateral deformation near the toe per
increment of time
of time
Volume change
Radial strain
Volumetric strain
Unit weight
Final effective vertical stress
Vertical consolidation stress
Drained friction angle
1.1 Statement of the Problem
When an embankment load is rapidly applied to a deposit of saturated clay, the
clay deforms at constant volume to accommodate the imposed shear stresses. The
settlement associated with these deformations, which occurs without significant
dissipation of excess porewater pressures, is called undrained settlement.
Evaluation of the undrained settlement of structures on clay is important for a
number of reasons. First, Undrained settlement may constitute a large portion of the total
final settlement, depending on the nature of the soil, the loading geometry, and the
thickness of the compressible layer. Second, analysis of undrained settlement is an
integral part of the analysis of the overall settlement-time behavior of foundations. Third,
undrained settlement is closely related to the undrained stability of a foundation.
Excessive undrained settlement may be a warning of impending failure.
The two basic components in the theoretical analysis of undrained settlement are:
an analysis to relate settlement to the loading geometry and the soil properties; and the
determination of the appropriate stress-strain and strength properties of the soil to input to
the theoretical solutions.
The finite element method of analysis facilitates the solution of a broad range of
boundary loading problems involving inhomogeneous, anisotropic and nonlinear soil
properties. However, even though improved analytical capabilities have been developed,
accurate determination of stress-strain properties in undrained shear for in situ clay
deposits remains a major obstacle to the successful analytical prediction of undrained
1
settlement. Therefore, the principal aim herein is to present an empirical method for
estimating undrained settlement using the in situ measurements of lateral deformations.
When an embankment, storage facility, or a footing is constructed, that is of
limited size in comparison with the thickness of the compressible ground, there are two
components of deformation; one is the volumetric compression due to consolidation and
the other is the shear distortion. An example of the latter is the immediate lateral
deformation and associated settlement under undrained conditions. Shear deformation or
flow causes horizontal displacement of soil. The undrained shear deformation depends
on soil profile, nature of the soil deposits, type of structure, and rate and method of
construction. Shear deformation can cause large initial and post construction settlements.
Experience with the construction of embankments on soft ground has shown that
there have been many instances of base failure of embankments. However, evaluating
and comparing entire ground deformations may allow a prediction of ground failure
during embankment construction.
The lateral deformation of soft clay due to embankment loading is becoming more
of interest because lateral deformation has detrimental effect on the behavior of adjacent
structures such as pile foundations, movement of bridge abutments, and movement of
water and gas pipelines.
In this study current empirical, numerical, and elastic-theory methods for the
prediction of undrained lateral deformation, and settlement of clay foundations subjected
to embankment loading are reviewed. Field measurements of lateral deformation for 180
embankments on soft clay and silt deposits were used in the present investigation. The
distribution of lateral displacement with depth is used to calculate the settlement resulting
from lateral deformation.
In general, finite element methods have not been very successful in predicting
lateral deformation. Accuracy of predictions however has increased for the finite element
methods which properly model constitutive equations of soil, the loading procedure, and
time dependent creep. Empirical methods for estimating lateral deformation are
2
presented predicting settlement resulting from lateral flow for undrained and drained
conditions.
1.2 Objectives of the Study
The objectives of this research are to develop, using field observation of lateral
deformation, empirical procedures for: (a) determining distribution of lateral deformation
across an embankment, based on a limited number of inclinometers measurements, (b)
predicting settlement resulting from lateral deformation, (c) relating lateral deformation to
factor of safety against undrained failure, (d) using lateral deformation as a measure of
undrained stability, (e) examining time-dependant deformation of soil subjected to
embankment loading and different drainage boundary conditions, (f) superimposing
undrained deformation and drained one-dimensional consolidation settlement.
Field measurements of horizontal deformation of soft clay and silt deposits during
and after construction of embankments and storage facilities have been collected from
throughout the world, covering 180 case histories. These probably represent 95% of
cases with lateral deformation measurements reported in the literature. The undrained
settlement resulting from the lateral deformation of the foundation soil is computed from
an integration of the lateral deformation profile obtained at various locations across the
embankment width.
Lateral deformation of the ground resulting from embankment loading has been
the subject of numerous studies for years. There has been an interest in predicting lateral
deformation because of the observed detrimental effect of lateral deformation on adjacent
structures and also because plastic flow that produces lateral deformation may lead to
ground failure. However, even in the absence of a ground failure and adjacent structures,
lateral deformation is important because it contributes to settlement of the embankments,
storage facilities, and structures on soft ground. In some situations, part of lateral
deformation results from multidimensional consolidation. A procedure has been
3
lateral deformation and factor of safety against undrained failure. The correlation
includes influence of ground condition as well as the geometry of the embankment.
1.3 Scope
In Chapter 2, the available methods for predicting the undrained settlement and
lateral deformation are reviewed. They are divided into three categories: solutions based
on elasticity, numerical techniques, and empirical procedures.
In Chapter 3, behavior of clay foundations subjected to embankment loading is
reviewed and discussed. The behavior includes, yielding of clay structure, porewater
pressures produced by embankment loading, lateral deformation with depth, stability
analysis and choosing the mobilized undrained shear strength, the value of factor of safety
that triggers an abrupt increase in rate of lateral deformation, shear stress level and
undrained shear deformations, and the undrained modulus of soft clay and silt deposits.
In Chapter 4, methods using lateral deformation as a measure of undrained
stabiltty are reviewed and discussed. In addition, a method to control embankment
construction by observing lateral deformation is developed through relating lateral
deformation to factor of safety against undrained failure. The same empirical correlation
could be used to estimate the maximum lateral deformation at the toe or the area of lateral
deformation profile with depth, given the factor of safety against undrained failure.
In Chapter 5, the collected database covering 180 case histories is presented.
These probably represent 95% of cases with lateral deformation measurements reported
in the literature. All the parameters that are believed to affect the undrained deformations
are identified for the cases and are included in Table 5.1. The references for the cases are
tabulated in Table 5.2. These cases are sorted by case name in Table 5.3 and they are
sorted by case ID in Table 5.4. In addition, the general parameters whenever available for
the case that were used in the present empirical analyses are tabulated in Table 5.5. The
4
behavior of the lateral deformation with depth is strongly dependant on the soil type.
Therefore, normalized lateral deformation measurements are presented together with the
soil profile and soil properties.
In Chapter 6, displacement volume of soil and associate settlements is discussed.
Two types of correlations have been examined for each case history. In the first
correlation, the lateral deformation near the toe has been compared with the total
settlement at the embankment center during and after construction. In the second
correlation, the area of lateral deformation has been compared with the area of total
settlement during and after construction. From these correlations the values of the
deformability factor RDS for different cases have been computed and the averages are
tabulated in Table 6.1 for different periods during and after construction. Two empirical
procedures are presented and discussed: (1) predicting distribution of lateral deformation
across embankment, (2) predicting settlement resulting from lateral deformation. Then
the two proposed methods are verified by implementing them on several case histories.
Finally, in Chapter 7, the summary and conclusions are presented.
5
DEFORMATIONS
2.1 Introduction
Loading the soft clay and silt deposits by embankments or storage facilities
creates vertical settlement and lateral deformation. In some cases, the undrained shear
distortion, which is included in the undrained settlement and lateral deformation, causes
stability problems for the embankment or storage facilities and adjacent structures.
Therefore, a prediction of lateral deformations prior to construction would allow (a) an
estimate of settlements resulting from flow of soil for stable situations and (b) soil
improvement measures and construction procedures to prevent excessive deformations or
unstable conditions.
The available methods for predicting the undrained settlement and lateral
deformation can be divided into three categories: solutions based on elasticity, numerical
techniques (e.g. using FEM), and empirical procedures.
2.2 Prediction of Undrained Settlement and Lateral Deformation Using Theory of
Elasticity
The theory of elasticity has been previously used to predict undrained settlement
and lateral deformation.
2.2.1 Flow Settlement
The settlement resulting from lateral deformation or flow of saturated soils has
6
settlement, and undrained settlement. In this thesis settlement resulting from lateral
deformation of soil is termed flow settlement to distinguish it from consolidation
settlement. Flow settlement results from time-independent as well as time-dependent
flow of soil from under the structure, whereas consolidation settlement in saturated soils
results from time-dependent flow of water from under the structure.
Terzaghi (1943), using the solution by Steinbrenner (1934), expressed elastic settlement
for a flexible load on a circular area in terms of values of surface load q, thickness of
elastic layer La, modulus of elasticity of the layer, E, and Poisson's ratio v, Fig. 2.1. In
Figs. 2.1 band 2.1c the base of the elastic layer is rigid and elastic layer adheres perfectly
to the rigid base. Figure 2.1 shows that the ground surface under and outside the loaded
area settle and the magnitude of settlement at the edge of loaded area is about 50 to 70%
of the settlement at the center. In Fig. 2.1 c where the depth ratio LaIR is smaller than 2/3
and Poisson's ratio is close to 0.5, the settlement is maximum at a distance of two third of
the radius from the center of the loaded area, it…