~Effects of Nanhamageneaus Cementatian...grain contact. They are generally quite difficult to...
Transcript of ~Effects of Nanhamageneaus Cementatian...grain contact. They are generally quite difficult to...
~Effects of Nanhamageneaus Cementatian '·
in Sails
an Resistance ta Earthquake Effects/
by
Barry Scott Milstone ·.~
Thesis submitted to the Faculty of the
Virginia Polytechnic Institute and State University
in partial fulfillment of the requirements for the degree of
Master of Science
in
Civil Engineering
APPROVED:
J. Michael Duncan Thangavelu Kuppusamy
May, 1985
Blacksburg, Virginia
Effects of Nanhamageneaus Cementatian
in Sails
an Resistance ta Earthquake Effects
by
Barry Scott Milstone
G. Wayne Clough, Chairman
Civil Engineering
(ABSTRACT)
Small amounts of cementation in a sand increase its ability to sustain
static and dynamic loads, even in a liquefaction type environment. This
has been shown in previous research examining the behavior of both na-
turally cemented and artificially prepared samples.
Cemented sands are present in many parts of the world and can be caused
by either a variety of cementing agents or by cold welding at points of
grain contact. They are generally quite difficult to sample, but arti-
ficially cemented sands have been shown to aptly model the behavior of
natural materials, and allow for better test controls. Consequently,
artificial samples were used exclusively for the present investigation
which has three major objectives: to investigate the effects of a weakly
cemented lens within a stronger mass; to determine how cementation affects
the volume change characteristics of statically loaded samples; and, to
describe the pore pressure generation of sands subjected to cyclic load-
ing.
Prior to commencing the test program, a number of index tests were per-
formed on the uncemented and cemented sand used during the laboratory
investigation. It was revealed that cementation leads to increased void
ratios which distort relative density calculations used to compare ce-
mented and uncemented samples of similar dry unit weight. The practice
of identifying samples by dry unit weight was adopted for this report.
Static triaxial compression tests were performed on 17 samples. Test
results indicate that although the magnitude of volumetric strain at
failure does not seem to be dictated by the level of cementation, there
is a relationship with cementation and the rate of volume change at
failure. A weak lens was seen to lower the static strength of the
stronger mass. 26 stress controlled cyclic triaxial tests revealed that
a weak lens lowers the liquefaction resistance of the stronger mass. The
cyclic strength of the nonhomogeneous material, however, is higher than
the independent strength of the weak lens. A weak lens has greater in-
fluence at relatively higher levels of cyclic stress. Pore pressure
generation in cemented sands are seen to be controlled by strain. At
shear strain levels below about 1%, cemented sands behave similarly to
uncemented sands with pore pressures increasing more rapidly beyond that
amount of strain. Consequently, pore pressure development during cyclic
loading is described by a broken-back curve which is defined in the early
stages by existing empirical relationships for uncemented sand. Pore
pressure prediction may then be achieved using an equation for cemented
sand, such as that developed in the present work.
ACKNOWLEDGEMENTS
I am humbly grateful to all from whom I have learned during my long and
fortunate journey here.
Special thanks is extended to my advisor, Dr. G. Wayne Clough, for pro-
viding critical insight, encouragement, and a high professional standard.
I would also like to thank committee members, Dr. T. Kuppusamy and Dr. J.
Michael Duncan, for their parts in my education and help during this re-
search.
A grateful acknowledgement is extended to the National Science Foundation
Earthquake Hazard Mitigation Program for their sponsorship of this
reasearch project.
For their important friendship, perspective, and academic and technical
synergy, I thank my fellow students. I shall most fondly remember Al
Sehn, Vern Schaefer and their families, Terese Kwiatkowski, Jotaro
Iwabuchi, Sybil "Hatch, and Phillipe Mayu. The varied help extended to
me during my study in Blacksburg by Civil Engineering staff members,
particularly Vickie Graham and Judy Brown is greatly appreciated.
My greatest thanks goes to my family for their unwavering love and belief
in me, and for their support of any and all of my endeavors.
Acknowledgements iv
TABLE OF CONTENTS
1.0 INTRODUCTION . . . . . . . . . . . . . . . . . . . . . . . .
2.0 BACKGROUND . . . . . . . . . . . . . . . . . . . . . . . . . 2. 1 CEMENTED SOILS
2.2 CEMENTED SAND DEPOSITS
2.3 STATIC BEHAVIOR OF WEAKLY CEMENTED SANDS
2. 4 LIQUEFACTION . . . . • . . • . • . . • . •
2.5 CYCLIC BEHAVIOR OF WEAKLY CEMENTED SAND
2.6 SUMMARY
3.0 EXPERIMENTAL INVESTIGATION
3. 1 INTRODUCTION . . . . . • .
3.2 ARTIFICIALLY PREPARED SAMPLES
3.3 MATERIALS USED
3.4 INDEX TESTING
3.4.1 Specific Gravity
3.4.2 Maximum Index Void Ratio
3.4.3 Minimum Index Void Ratio
3.4.4 Use of Index Properties
3.5 STATIC TESTS
3.6 CYCLIC TESTS
. . . . . . . . . . . .
4.0 SAMPLE PREPARATION . . . . . . . . . . . . . . . . . . . . . Table of Contents
1
3
3
4
5
9
10
13
16
16
17
18
19
22
22
23
25
26
27
29
v
4.1 USE OF THE RAINER
4.2 HOMOGENEOUS SAMPLES
4.3 NONHOMOGENEOUS SAMPLES
4.4 SATURATION •...•
S.O TEST PROGRAM, METHODS, AND EQUIPMENT . . . . . . . . . . 5.1 INTRODUCTION . • • . • • .••.
5.2 STATIC TESTING
5.2. 1 Introduction
5.2.2 Consolidated Drained Triaxial Testing and Equipment
5.3 CYCLIC TESTING ..••..•..•.
5.3.1 Introduction
5.3.2 Method of Loading •••.
5.3.3 Typical Results and Verification of Procedure
6.0 STATIC BEHAVIOR OF CEMENTED SANDS . . . . . . . . 6.1 INTRODUCTION
6.2 HOMOGENEOUS DRAINED BEHAVIOR
6.3 EFFECTS OF NONHOMOGENEITY ON CEMENTED SAND
6.4 VOLUME CHANGE BEHAVIOR
6.4.1 Volumetric Strain Characteristics
6.4.2 Effects of Cementation on Rate of Volume Change
6.4.3 Critical Void Ratio
. . . .
7.0 CYCLIC BEHAVIOR
7.1 INTRODUCTION
. . . . . . . . . . . . . . . . . . . . . . .
Table of Contents
29
32
35
40
45
45
45
45
47
50
50
50
54
62
62
63
74
77
77
78
84
92
92
vi
7.2 EFFECTS OF CEMENTATION ON LIQUEFACTION RESISTANCE 92
7. 3 EFFECT OF CEMENTATION ON DEVELOPMENT OF PORE PRESSURES AND STRAIN 96
7.4 EFFECT OF A WEAK LENS ON LIQUEFACTION RESISTANCE . . . . . 111
a.o SUMMARY and CONCLUSIONS
Appendix A. EQUIPMENT IDENTIFICATION . . . . . . . . . . . . . .
Appendix B. Use of the MTS cyclic Testing Apparatus . . . . . . B. 1 MTS Stress Controlled Cyclic Triaxial Testing Procedure
REFERENCES . . . . . . . . . . . . . . . . . . . . . . . . . . .
Vita . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Table of Contents
119
125
128
128
137
140
vii
LIST OF FIGURES
FIGURE PAGE
2-1 Cyclic Stress Ratio Versus Number of Cycles to 5% Double Amplitude Strain (after Rad And Clough, 1982) ................ 12
2-2 Normalized Plot of Pore Pressure Buildup in Cyclic Triaxial test on 1% Cemented Sand (after Rad and Clough, 1982) .•...... 14
3-1 Monterey #0/30 Grain Size Analysis ............................. 20
4-1 a) Sand Rainer and Mold Used for Cemented Sand Preparation. b) Disassembled Sand Rainer ..............•....•................ 31
4-2 Schematic of Trimmed Samples for Nonhomogeneous Sample Construction . ................................................ 3 7
4-3 Nonhomogeneous Sample Preparation Procedures ................... 38
4-4 Schematic of Vacuum Saturation Apparatus ......•................ 44
5-1 Schematic of Cyclic Testing Apparatus ...•...•.................. 52
5-2 Typical Results of a Cyclic Triaxial Compression Test .......... 55
5-3 Cyclic Shear Resistance Curve for Tamped, Monterey #0 Sand (after Silver, 1976) .........•.............•................. 57
5-4 Cyclic Shear Resistance Curve for Pluviated, Uncemented Sand ... 60
5-5 Peak Results from a Cyclic Triaxial Test on 2% Cemented Sand ... 61
6-1 Stress-Strain and Volume Change Plots for 2% Cemented Samples with Average Dry Density= 15.00 KN/M 3 •••••••••••••••••••••••• 64
6-2 Stress-Strain and Volume Change Plots for 2% Cemented Samples with Average Dry Density= 15.45 KN/M 3 •••••••••••••••••••••••• 65
6-3 Stress-Strain and Volume Change Plots for 2% Cemented Samples with Average Dry Density= 15. 70 KN/M 3 •••••••••••••••••••••••• 66
6-4 Peak Strength Envelopes for 2% Cemented Sand Samples with Average Dry Density= 15.00 KN/M 3 •••••••••••••••••••••••• 70
6-5 Peak Strength Envelopes for 2% Cemented Sand Samples with Average Dry Density= 15.45 KN/M 3 •••••••••••••••••••••••• 71
LIST OF FIGURES viii
6-6 Peak Strength Envelopes for 2% Cemented Sand Samples with Average Dry Density= 15. 70 KN/M 3 •••••••••••••••••••••••• 72
6-7 Stress-Strain and Volume Change Plots for Nonhomogeneously Cemented Sand . ............................................... 7 5
6-8 Peak Strength Envelopes for Nonhomogeneously Cemented Samples .. 76
6-9 Volume Strain at Failure Versus Initial Dry Unit Weight CD Triaxial Test (confining pressure= 103 KN/M2 ) •••••••••••• 79
6-10 Volume Strain at Failure Versus Initial Dry Unit Weight CD Triaxial Test (confining pressure= 207 KN/M 2 ) •••••••••••• 80
6-11 Volume Strain at Failure Versus Initial Dry Unit Weight CD Triaxial Test (confining pressure= 345 KN/M2 ) •••••••••••• 81
6·12 Dilation Angle Versus Initial Dry Unit Weight (Confining pressure = 103 KN/M2 ) ••••••••••••••••••••••••••••• 85
6-13 Dilation Angle Versus Initial Dry Unit Weight (Confining pressure = 207 KN/M2 ) ••••••••••••••••••••••••••••• 86
6-14 Dilation Angle Versus Initial Dry Unit Weight (Confining pressure = 345 KN/M2 ) ••••••••••••••••••••••••••••• 87
6-15 Volume Change at Failure Versus Initial Void Ratio ............. 89
6-16 Critical Void Ratio Versus Confining Pressure .................. 90
6-17 Critical Void Ratio Versus Confining Pressure for Cemented and Uncemented Monterey #0/30 Sand .....•..................... 91
7-1 Cyclic Shear Resistance Curves for Homogeneously Cemented Monterey fl0/30 Sands ......................................... 95
7-2 Pore Pressure Ratio Versus Cyclic Ratio ........................ 97
7-3 Pore Pressure Ratio Versus Cyclic Ratio (2% cemented sand) (after Rad and Clough, 1982) ................................. 99
7-4 Pore Pressure Ratio Versus Cyclic Ratio (uncemented sand) ..... 100
7-5 Pore Pressure Ratio Versus Cyclic Ratio (1% cemented sand) .... 101
7-6 Pore Pressure Ratio Versus Cyclic Ratio (2% cemented sand) .... 102
7-7 Strain Ratio Versus Cyclic Ratio (uncemented sand) ............ 105
7-8 Strain Ratio Versus Cyclic Ratio (1% cemented sand) ........... 106
LIST OF FIGURES ix
7-9 Strain Ratio Versus Cyclic Ratio (2% cemented sand) •.....•..•. 107
7-10 Pore Pressure Ratio Versus Cyclic Ratio Data Compared to Empirically Developed Curves ....•...•••..•...•....•....•.•.. 110
7-11 Cyclic Shear Resistance of Nonhomogeneously Cemented Sand Compared to Various Cementation Configurations .•..••.••••.•. 112
7-12 Unconfined Compressive Strength Versus Cyclic Stress Ratio to Cause Initial Liquefaciton ......•...••................... 116
7-13 Pore Pressure Ratio Versus Cyclic Ratio (nonhomogeneous) ..•.•• 117
7-14 Strain Ratio Versus Cyclic Ratio (nonhomogeneous) ....•........ 118
LIST OF FIGURES x
LIST OF TABLES
TABLE PAGE
2-1 Available Information on Cemented Sands ......................... 7
3-1 Comparison of Monterey #0/30 and Monterey #0 Index Propertes ... 21
3-2 Maximum and Minimum Index Void Ratios for Cemented Monterey #0/30 Sand from This Study and from Muzzy (1983) .... 24
3-3 Summary of Testing Program .•............•....•..•...•.......... 28
6-1 Sample Conditions and Test Results of CD Triaxial Tests on 2% Cemented Sand and Nonhomogeneous Samples .....•............... 67
6-2 Strength Parameters from CD Triaxial Tests on 2% Cemented Sand.73
7-1 Cyclic Triaxial Test Information ............................... 94
a-1 Equipment Information ......................................... 126
LIST OF TABLES xi
1.0 INTRODUCTION
The large amount of damage sustained in the Anchorage, Alaska and Niigata,
Japan earthquakes of 1964 brought to light the need to study earthquake
induced liquefaction of soils. During these and other earthquakes, pore
pressure buildup under undrained conditions resulted in reductions of
shear strength of the soil and led to a large percentage of the documented
failures. Soils most susceptible to liquefaction are medium to loose,
saturated sands in the 6 to 10 meter depth range.
Recent research has shown that small amounts of cementation in a sand
increase its ability to sustain static and dynamic loads, even in a
liquefaction type environment. This means that cementation has a sig-
nificant bearing on the likelyhood of liquefaction failure, and in some
cases might be used as a means to prevent failure. Previous studies have
examined the static and cyclic behavior of both naturally cemented mate-
rials and artificially prepared samples. The present work addresses three
of the questions as yet unanswered by other investigations:
1. What is the effect of nonhomogeneity on the liquefaction re-
sistance of weakly cemented sands?
2. How does cementation affect the volume change characteristics
of statically loaded samples?
INTRODUCTION 1
3. Is it possible to predict the pore pressure generation of un-
drained, weakly cemented sands subjected to cyclic loading?
In this research, a laboratory investigation was performed on arti-
ficially cemented samples of a standard sand. Samples created in this
fashion, by mixing various quantities of Portland cement with sand, have
been shown to appropriately model similar materials that are found in
nature. Initially, the testing program involved performing 14 static
triaxial compression tests on samples cemented with 2% cement, by weight,
and on nonhomogeneous, or layered, samples; performed to determine
strength, stiffness and volume change characteristics. Also, a series
of 26 stress controlled cyclic triaxial tests were performed to develop
cyclic strength curves and to observe the pore pressure generation char-
acteristics. Where possible, published test results were incorporated
to augment the present work.
To establish a basis for the results of this study, background information
is reviewed with regard to liquefaction and cementation in Chapter 2.
Chapter 3 outlines the experimental investigation, including the materi-
als and equipment used, and the testing procedures. Sample preparation
techniques as well as the procedure required to saturate the samples is
discussed in Chapter 4. A detailed description of the testing methods
and the equipment used is included in Chapter 5. The static behavior of
the cemented sands is presented in Chapter 6, and Chapter 7 discusses the
dynamic behavior. Chapter 8 provides a summary of the investigation and
the conclusions of this study.
INTRODUCTION 2
2.0 BACKGROUND
2.1 CEMENTED SOILS
Throughout the world, many natural sand deposits exhibit forms of bonding
between particles. The writer shall refer to this phenomenon as
cementation. One distinguishing characteristic of these materials is
that they are able to stand in steep slopes, approaching vertical. The
bonding, however, is often surprisingly weak, so that these materials can
be crumbled using finger pressure. The major focus of this work deals
with those sands that are only weakly cemented.
Cementation can be caused in nature by a number of different means:
• Welding of sand grains at their contact points. This can occur
due to the internal heat at deposition of such material as
volcanic ash. Prolonged pressure at contact points can also
lead to cold welding as described by Lee (1975).
• The presence of cementing agents. Various materials which are
created as byproducts of nearby weathering, or precipitated out
of groundwater can bond sand particles. These materials in-
clude clays, carbonates, silicates, and iron bearing materials.
BACKGROUND 3
Of particular interest to the present study is that the cementation of
sands is quite often nonhomogeneous. This is evident in e~~posed slopes
as a layering or banding. The resulting static and cyclic responses are
a function of two or more materials that exhibit different independent
behavior. Some of the phenomena that can cause nonhomogeneity include:
• Variable grain size distribution. This occurs in surface-water
borne deposits where seasonal fluctuations in flow can lead to
a vertical grading of grain sizes. The variations in surface
area and intergranular contact area of individual strata lead
to differing degrees of cementation.
• Variations in cementing agents. Inconsistent groundwater com-
position and fluctuation of the groundwater level can also lead
to nonhomogeneous cementation. This is accentuated by periodic
precipitation and leaching of the cementing agents.
2.2 CEMENTED SAND DEPOSITS
Cemented soils are widely distributed throughout the world. Some of the
more well known areas as cited by Rad and Clough (1982) are: along most
of the Pacific Coast in California and Oregon, where the common cementing
agents are carbonates, clays, and iron oxides; the deserts of the western
and southwestern United States, where precipitation of calcium carbonate
and other minerals results in a caliche-type soft rock (Hamel, 1973);
loess deposits of the midwestern United States and China (Close and
BACKGROUND 4
McCormick, 1922); large areas of central Guatemala, which are covered by
wind blown volcanic ash deposits (Harp and others, 1978; Sitar, 1979);
some parts of Japan (Yamanouchi and others, 1977) and North Island of New
Zealand (Yamanouchi, 1974), where pumice-flow deposits exist; the Kurkar
deposits along the Mediterranean coastline of Isreal and neighboring Arab
countries which are cemented mainly by calcereous cement (Frydman and
others, 1980); extensive areas of western and central Europe, where the
Keuper sandstone formation is found.
Recent studies have demonstrated that the strength contributions from low
levels of natural cementation are destroyed during sampling and subse-
quently missed in laboratory testing (Frydman et al. , 1980; Beckwith and
Hansen, 1981; Saxena and Lastrico, 1978; Clough and Bachus, 1982). This
suggests that it is possible that many sands are cemented, but not iden-
tified properly because of the disturbance factor in sampling.
2.3 STATIC BEHAVIOR OF WEAKLY CEMENTED SANDS
While there has been limited study of the behavior of cemented soils, the
researchers listed in Table 2-1 have identified important characteristics
of these materials. Some major findings from static tests on naturally
and artificially cemented sands and silts are as follows:
1. There are similarities between artificially and naturally ce-
mented sands.
BACKGROUND 5
2. The friction angle is similar to that of uncemented sands.
3. Cementation manifests itself as a cohesion intercept, with the
cohesion increasing with the level of cementation, amount of
fines, and particle angularity.
4. There is a small, but significant, tensile strength which typ-
ically is about 10% of the unconfined compressive strength.
5. The initial tangent modulus increases with confining pressure
and/or the level of cementation.
6. The brittleness of the sample increases by increasing the
cementation or decreasing the confining pressure.
7. Volumetric increases generally accompany shear failure even for
cemented sands with "loose structures". The volume changes
seem to occur more rapidly than they do in uncemented sands.
The available data base for cemented sands is very limited, particularly
for instances of negligible disturbance and controlled sample properties.
The present study augments work in this regard with a special emphasis
on the effects of nonhomogeneity in the soil, and further investigates
the volume change characteristics of these materials.
BACKGROUND 6
Table 2-la: Available information on cemented sand.
Soil Cementing Reference Tested Agent Sample Type Static Tests Dynamic Tests
Alfi* NCS C and C Hand Trimmed Drained Tx Non (1978)
Bachus et al.* NCS c and c Hand Trimmed (1981) ACS p c Compacted in Mold Drained Tx Non
Beckwith & Hansen NCS Carbonate Non Non Non (1981)
Clough et al.* NCS c and c Hand Trimmed (1981) ACS p c Compacted in Mold Drained Tx Non
Dupas and Pecker ACS p c Compacted in Mold Drained Tx Cyclic Tx (1979)
Frydman et al.** NCS ACS Hand Trimmed Non Cyclic Tx (1980)
Hamel NCS Carbonate Hand Trimmed Direct Shear Non (1973)
Mitchell ACS p c Compacted in Mold Indirect Tension Compression (1976) Flexure Repeated
Poulos NCS Carbonate Different Method Several Types Cyclic Tx (1980) Silicate
Reference
Rad & Clough* (1982)
Salamone et al. (1978)
Saxena & Lastrico (1978)
Sitar* (1979)
Sitar and Clough* (1979)
Sitar et al.* (1980)
Yamanouchi et al. (1977)
00
Table 2-lb: Available information on cemented sand (continued).
Soil Cementing Tested Agent
NCS c and c ACS PC
NCS Carbonate
NCS Carbonate
NCS c and c ACS p c
NCS c and c ACS p c
NCS c and c ACS p c
NCS Thermal Welding
Sample Type
Hand Trimmed Pluviated
76 mm Dension sampler
76 mm Dension sampler
Hand Trimmed Compacted in Mold
Hand Trimmed Compacted in Mold
Hand Trimmed Compacted in Mold
Shirasu Cutter (5 cm dia. tubes)
* Similar Research ** Some insitu tests
Static Tests
Drained Tx
Undrained Tx
Undrained Tx
Drained Tx
Drained Tx
Drained Tx
Several Types
NCS Naturally Cemented Sands ACS = Artificially Cemented Sands Tx Triaxial Test C and C= Carbonate and Clay P C Portland Cement
Dynamic Tests
Cyclic Tx
Cyclic Tx
Non
Simple Shear Cyclic Tx
Simple Shear Cyclic Tx
Simple Shear Cyclic Tx
Non
2,4 LIQUEFACTION
Liquefaction is described by Youd ( 1972) as, "the transformation of a
granular material from a solid into a liquid state as a consequence of
increased pore water pressures." It develops as a consequence of the
propagation of shear stresses due to seismic events, through the soil,
resulting in shear strains in the sand. If the soil is a saturated sand,
and behaves in an undrained mode, the tendency of the soil to strain under
the shear stresses will result in the development of excess pore pres-
sures. The generated pore pressures can be high enough to lower the ef-
fective confining stresses to zero, resulting in drastic strength losses
and possible large strain development, particularly in loose deposits.
This phenomenon has led to catastrophic slope and foundation failures in
recent history.
Conventionally, the term "liquefaction" has several definitations:
• "initial liquefaction" is defined as the point when excess pore
pressures are first equal to the effective confining pressures
that existed just prior to loading.
• Liquefaction can also describe a condition of some predeter-
mined amount of strain, often 5% or 10% for research purposes.
BACKGROUND 9
The reader is referred to The Committee on Soil Dynamics (1978) for a more
complete discussion of related terms. Unless otherwise stated, this re-
port uses the term liquefaction as it relates to initial liquefaction.
Since the mid 1960' s, when liquefaction was recognized as a potential
hazard, a number of methods have been designed for predicting the like-
lihood of its occurrence. These have been important and useful contrib-
utions in light of the heavy development of known seismic areas. At the
present, however, the accepted methods do not directly account for
cementation, which is generally neglected as a conservative assumption;
rather, their influence enters design correlations when they are present
in the field data used as the basis for these methods.
2.5 CYCLIC BEHAVIOR OF WEAKLY CEMENTED SAND
The available data for the cyclic behavior of cemented sands suggests that
cementation increases the cyclic shear resistance of uncemented, but
otherwise similar, sands. This means that cemented sands are better able
to withstand the effects of dynamic loading than are uncemented sands.
It has also been observed that increased levels of cementation will result
in even greater resistance to liquefaction.
In nature, soils may exhibit progressively increased levels of
cementation as a function of age. Lee (1975) has proposed that, even in
the absence of cementing agents, sand particles can become "cold welded"
as a result of prolonged contact under pressure. To simulate these older,
BACKGROUND 10
cemented materials in the laboratory within a reasonable time span, rel·
atively small amounts of cementing agents, often in the form of Portland
cement, are added to sand samples. In fact, while investigating the dy-
namic properties of artificially cemented sands, Dupas and Pecker (1979)
found that cement quantities in excess of 5% of the dry weight of sand
were enough to make the sand totally resistant to liquefaction.
In a study of a weakly cemented natural beach sand, Rad and Clough (1982)
observed that this material required very high stress levels to cause
liquefaction. These researchers also conducted a program of tests on
weakly cemented, artificially prepared sand. They were able to establish
a correlation between level of cementation and liquefaction resistance
for homogeneous cemented sand. This is demonstrated in Figure 2-1 which
plots cyclic shear stress ratio versus the number of cycles to cause 5%
double amplitude axial strain. It is seen here that samples containing
higher levels of cementation require higher stress levels to induce this
amount of strain at the same number of cycles.
Weakly cemented zones within a more strongly cemented sand mass were noted
to lower the liquefaction resistance of a sand (Frydman, et al., 1980).
Clear trends for this effect could not be quantified, however, due to the
variability of the natural materials studied. The present work examines
this issue, using artificially created samples with controlled nonhomo-
geneity.
BACKGROUND 11
~ ~
~ < ~
<J) 00 UJ ~ ~ ~
~ < w :I: ~
u ~
_J u r u
0.6
% CEMENT 0.4
0.2
0.0 10
NUMBER 0F STRESS CYCLES, N
Figure 2-1: Cyclic stress ratio versus the number of cycles to cause 5% double amplitude strain (after Rad and Clough, 1982).
BACKGROUND 12
Rad and Clough (1982) observed that pore pressure development patterns
of cemented sands snbjected to dynamic loading are different than those
of uncemented sands. This is shown in Figure 2-2 which is discussed in
detail in Chapter 7. Basically, this figure is a normalized plot of pore
pressure versus load cycle for cyclic triaxial tests. It can be seen that
the data points for cemented sand fall outside the shaded zone repres-
enting the observed behavior of uncemented sands (Lee and Albeisa, 1975).
Although empirical relationships exist for predicting pore pressure gen-
eration in uncemented sands they appear inappropriate for cemented sands.
The present investigation carries this work further.
2.6 SUMMARY
Weakly cemented sands are found in many parts of the world. They are able
to stand in very steep slopes, but can fail catastrophically when sub-
jected to dynamic loads. The cementation of natural sand deposits is
sometimes nonhomogeneous, containing interbedded strata or isolated
pockets of material that is less cemented than the surrounding mass.
Sample disturbance effects have made it difficult both to identify ce-
mented soils in the field and to characterize them in the laboratory.
Static testing on naturally and artificially cemented sands has shown them
to exhibit a similar frictional response to uncemented sands, while having
a cohesion intercept and stiffer behavior. Field evidence suggests that
cemented sands can be quite resistance to liquefaction. This is sub-
stantiated by cyclic testing of these materials which shows the cemented
BACKGROUND 13
1.0 .. • • • • • • lbu • • • ' 0.8 :::> I :::l ... • • • .. • CS> 0.5 • -~
< a:: • w • a:: ::> 0.4 • (/) (/) • w a:: 0.. w Lee and Albeisa a:: 0.2 (Observed range for CS> uncemented sand) a...
1% CEMENT 0.0
0 0.2 0.4 0.6 0.8
CYCLIC RA TI0,
Figure 2-2: Normalized plot of pore pressure buildup in cyclic triaxial tests on 1% cemented sand (after Rad and Clough, 1982).
1
BACKGROUND 14
sands to be more resistant to seismic loads than uncemented sands, with·
greater differences at higher levels of cementation.
The limited amount of available data needs to be supported in the areas
of: the effects of weak layers on the dynamic behavior of stronger
masses; the effects of cementation on the volume change characteristics
of statically loaded samples; quantifying the behavior of cemented soils
under undrained cyclic loads.
BACKGROUND 15
3.0 EXPERIMENTAL INVESTIGATION
3.1 INTRODUCTION
The major objectives of this testing program are to investigate:
1. the effects of a weak layer on the static and cyclic behavior
of a more strongly cemented mass;
2. the volume change behavior of cemented sands during static
loading;
3. the pore pressure generation characteristics of cemented sands,
subjected to cyclic loads.
Due to difficulties in obtaining undisturbed samples of cemented sand,
artificial samples were used exclusively for this investigation. This
chapter describes the use of artificial samples and the materials used
in their creation. Also included are outlines of the sample preparation
techniques used and the laboratory test program undertaken which includes
index testing as well as static and cyclic triaxial testing.
EXPERIMENTAL INVESTIGATION 16
3.2 ARTIFICIALLY PREPARED SAMPLES
The process of sampling naturally cemented sand deposits by conventional
means, such as driven samplers, often disturbs or destroys the
cementation. Thus, to examine the influences of cementation in the lab-
oratory, it is usually necessary to retrieve undisturbed samples by a time
consuming and difficult hand sampling method. Even with careful attention
to preserving the in-situ qualities of cemented sands, intrasample dis-
continuities and nonuniform cementation as well as variations between
samples are likely to exist. Even a well performed laboratory investi-
gation with such samples can lead to test results that are difficult to
interpret, exhibiting apparently anomalous behavior, as exhibited by
Saxena and Lastrico (1978).
It has been shown (Sitar (1979), Rad and Clough (1982)) that artificially
prepared and cemented samples acceptablly model the behavior of naturally
cemented materials by responding similarly to changes in test controls.
The great benefit of this is that samples with carefully controlled
cementation and density are readily available for laboratory testing.
Samples were created for this investigation with 1 and 2 percent Portland
Type I cement, by weight, at average densities of 15.00, 15.45, and 15.70
KN/M 3 • No higher values were used because stronger and denser samples
are simply not liquefiable under most conditions. The average densities
chosen are consistent with those of previous investigations by Rad and
Clough (1982). Sample preparation is discussed in-depth in Chapter 4.
EXPERIMENTAL INVESTIGATION 17
Basically, a sand-cement mix is rained into molds. The samples are then
saturated by allowing water to slowly petcolate up into the mold through
porous bottom plates. Finally, after a minimum initial curing period of
one day, the samples are transferred to a humid room for additional cur-
ing.
The homogeneous samples were allowed to cure for a total of 14 days in
the saturated environment. This allowed for about a two day window of
possible testing dates with samples of similar strengths after curing.
Nonhomogeneous samples were created by layering partially cured samples
of differing cement contents. Additional information on this procedure
is provided in Chapter 4.
3.3 MATERIALS USED
Monterey #0/30 beach sand was used exclusively for the testing program.
This washed and sieved sand, produced by Lone Star Industries, San Mateo,
California, is predominantly subangular to subrounded quartz silica with
some feldspar. This material, as well as the similar Monterey #0 sand,
is commonly used in investigations of liquefaction problems. A grain size
analysis was performed on the Monterey #0/30 and is presented in Figure
3-1. Since it compares quite closely with that shown by Muzzy (1983),
the minimum and maximum void ratios developed in his study are compared
to values developed by Silver (1976) for Monterey #0 sand (Table 3-1).
A preliminary analysis, described later in this chapter, was performed
during the present investigation and resulted in possible discrepancies
EXPERIMENTAL INVESTIGATION 18
with the values proposed by Muzzy and subsequently discussed by the
American Society of Testing and Materials (ASTM) D18.09.02C Task Group.
The cementing agent used was Portland Type I cement, also produced by Lone
Star Industries. It is relatively easy to use and quantify, and can
provide consistent results. Similar material has been used in previous
studies of artificially cemented sands. The cement was stored in moisture
tight containers while awaiting use to inhibit hydration.
3.4 INDEX TESTING
The maximum and minimum void ratios for uncemented Monterey #0/30 sand
have been determined by Muzzy (1983) as presented in Section 3.3. How-
ever, the characteristics of the sand-cement matrix alter as cement
crystals develop during hydration. To generate index values for the ce-
mented sands, tests were performed following a 14 day curing period so
that the materials would be similar to those used for static and cyclic
testing. As a reference, maximum and minimum index void ratios were also
developed for the uncemented sand.
Sand-cement mixes of 1% and 2% cement content, by weight, were prepared
in molds (as discussed in Chapter 4) and cured in a saturated environment
for 14 days. The samples were then extruded, hand crumbled to individual
particles, and oven dried to cease hydration. The resulting material
EXPERIMENTAL INVESTIGATION 19
trl :><: "'d trl ~ H
~
~ t"'i H
~ C/l t-3 H Ci1
~ H 0 z
N 0
I-:r: (!)
w 3:
>-al
0:::: w z LL
I-z w 0 a::: w Q_
100
90
80
70
60
50
40
30
20
10
0
Gravel Coarse
3"
-
-
-
-
-
"""""
,_
-
,_
I I I I I 0 0 0 0 CXl \0
1.511
I 0 v
I
Sand Fine Coarse Medium Fine
U.S. STANDARD SIEVE SIZE 3 II 3 II /'4 :Is 4
I 0 C\J
II I I I I I
Q CXl \0 v
GRAIN
10 21) 30 40 60 100
~
)
I I 11 I I ;\ "\...J ,,.~
C\J C\J 0
SIZE IN MILLIMETERS
Fines Silt
200
11 I I I I I -: CXl \0 ooq
ci 0
v 0 0
Figure 3-1: Monterey #0/30 grain size analysis.
I C\J 0 0
-
-
-
-
-
-
-
-
-
q 0
100
90
80 I-:r:
70 (!) jjJ 3:
60 >-Cl'.I
50 0:::: w z LL
40 I-z w
30 0 a::: w Q_
20
10
0
Table 3-1: Comparison of Monterey #0/30 and Monterey #0 index properties.
SAND MONTEREY #0 MONTEREY #0/30
STUDY SILVER MUZZY THIS (1976) ( 1983) STUDY
Gs 2.65 2.65 2.65
yd-max 105. 7 105.8 -
Yd-min 89.3 91. 7 -
emax 0.852 0.803 -
emin 0.564 0.563 -
D50 0.36 0.45 0.45
cu 1. 50 1. 60 1. 37
Cc 0.90 1. 00 0.95
EXPERIMENTAL INVESTIGATION 21
exhibited little free cement, suggesting that it was comprised of a mass
of individual sand grains that were coated, in part, with cement crystals.
3.4.1 Specific Grayitv
Specific gravity determinations were performed on each of the cemented
as well as the uncemented sand, as per ASTM D854. All three materials
showed specific gravities equal to 2.65. This is the same value reported
by Silver (1976) for Monterey #0 and by Muzzy (1983) for Monterey #0/30
sand.
3.4.2 Maximum Index Void Ratio
The maximum void ratios were determined using Method C of the ASTM
D4254-83 Minimum Index Density Test. This test comprises inverting a
stoppered cylinder, partially filled with a known amount of sand, then
tilting it back to the original vertical position. The minimum index
density (maximum index void ratio) is calculated from the resulting
measured volume. The cylinder in this study differs slightly from that
suggested by ASTM. The specification calls for a 2000 ml cylinder about
3 inches in diameter. The actual cylinder used is 3.25 inches in diameter
with a volume of 3153 ml. The height difference between the cylinders
which is a major controlling parameter is 15 cm, or about 30%. This
discrepancy is considered acceptable given that the intent of these tests
is simply to give insight to the sensitivity of maximum index void ratio
to cementation.
EXPERIMENTAL INVESTIGATION 22
The raining apparatus used to create samples for this investigation, and
discussed in ChP.pter 4, can be fitted with a variety of raining plates
that control the density of the constructed samples. To obtain a second
value for comparison, the rainer was fitted with the plate that was
available to produce the loosest possible samples. Sand was rained into
a cylinder of known volume after which the weight was calculated to de-
termine the maximum index void ratio.
The maximum void ratios as determined from both methods are presented in
Table 3.2. These results demonstrate that cementation leads to higher
maximum void ratios. Note that for the uncemented sand, the ASTM method
used in this investigation produced a maximum void ratio in excess of that
reported by Muzzy (1983). Since ASTM procedure was not strictly adhered
to, the higher value may not be accurate. Nevertheless, it would seem
that this void ratio is closer to the 'true' maximum since the ASTM pro-
cedure probably allows for a smaller range of variability than is seen
with these two studies. In light of the similarity between the grain size
properties of Monterey #0 and #0/30, it would also seem that the maximum
void ratios for the two materials should be rather close, as indicated
by the present study.
3.4.3 Minimum Index Void Ratio
The method used to develop minimum index void ratios for the three mate-
rials uses the rainer mentioned previously. In this case the rainer was
fixed with a plate having small holes, resulting in dense packing. The
EXPERIMENTAL INVESTIGATION 23
Table 3-2: Maximum and minumum index void ratios for cemented Monterey #0/30 sand from this study and from Muzzy ( 1983).
MAXIMUM VOID RATIO MINIMUM VOID RATIO CEMENT CONTENT
Muzzy 'ASTM' rainer Muzzy rainer
0% . 803 . 884 . 748 . 563 . 555
1% - . 953 . 852 - . 625
2% - 1. 102 . 903 - . 658
EXPERIMENTAL INVESTIGATION 24
vibratory table recommended by ASTM D4253-83 was not available to the
investigator. Similar apparati were no~ acquired or fabricated because
it was felt that such agitation could disturb the cemented sands by
freeing cement crystals from the sand grains.
The minimum index void ratio data are included in Table 3-2. Again, it
is apparent that increased cementation leads to looser packing as evi-
denced by increasing minimum void ratios. This is the same observation
made from the maximum void ratio data. The minimum value determined for
the uncemented sand by this method is relatively close to but, neverthe-
less, lower than that reported by Muzzy (1983).
3.4.4 Use of Index properties
It is evident from the observed results that there would be problems en-
countered when applying uncemented sand index properties to cemented
sands. It should be pointed out that this observation may only apply to
cemented sands in which cement crystals are present as opposed to cold
welded soils. Relative density calculations based on uncemented index
properties would result in erroneously high values. In any case, the
exact meaning of relative density for cemented sands is not clear since
there are structural differences between the cemented and uncemented
sands. It would seem somewhat confusing to refer to the relative density
of cemented sands as specifically related to uncemented sand properties.
Rather, in the writer's opinion, in order to isolate the structural
characteristics of cementation from index values of the sand samples, it
EXPERIMENTAL INVESTIGATION 25
is preferable to use dry unit weight to distinguish density. Such prac-
tice has been adopted for this report. When applicable, relative densi-
ties reported by other researchers have been converted to dry unit
weights, using index properties provided by the respective researchers.
3.5 STATIC TESTS
It is difficult to meaningfully quantify cementation, due to the great
variety of possible cementing agents. To measure cementation as a percent
of dry weight of the host sand has different meaning for various cementing
agents. Therefore, it is more useful to quantify the effects of
cementation in terms of static strength rather than percent cement in the
soil. To this end, and to investigate the applicability of the critical
void ratio concept to cemented sands, a static testing program was per-
formed. A family of consolidated, drained, triaxial compression tests
was executed on each of the homogeneous materials and on the layered
samples. The procedures followed the general guidelines presented by
Bishop and Henkel (1962). Volume change during the tests was measured
by means of a calibrated burrette in series with sample drainage lines.
A number of unconfined compression tests were also performed on the 2
percent cemented material to observe the sensitivity of the unconfined
compressive strength to testing procedure.
An early concern was that consolidation strains would disrupt the
cementation of samples prior to actual axial loading. Indeed, this pos-
sibility was investigated by Rad and Clough (1982) and found to be non-
EXPERIMENTAL INVESTIGATION 26
existent. Along these lines, however, the writer was curious about the
behavior of samples in which the cementation had been disturbed before
testing. In order to observe the extreme case, a 2% cemented and cured
sample was oven dried and subsequently crumbled by hand. The resulting
sand grains were reconstituted to a similar density as used for the ce-
mented sands, and subjected to drained triaxial compression.
Table 3-3 presents sample and test information for the static testing
program.
3.6 CYCLIC TESTS
Undrained cyclic triaxial tests were performed on uncemented and cemented
samples, using the standard test procedure described by Silver (1976).
A minimum of three tests, at different stress ratios, were performed on
each of the different cemented and uncemented materials to develop the
cyclic shear resistance curves, and to observe the pore pressure gener-
ation behavior of these materials. Table 3-3 includes the numbers of
tests for each catagory of material. 6 cyclic tests were performed on
tamped samples during the development of the testing procedure; a total
of 19 cyclic triaxial tests were subsequently performed on pluviated
samples.
EXPERIMENTAL INVESTIGATION 27
Table 3-3: Summary of testing program.
SAMPLE NUMBER OF NUMBER OF NUMBER OF TYPE, STATIC CYCLIC UNCONFINED
CEMENTATION TESTS TESTS TESTS
0% tamped - 7 -0% pluviated - 4 -
1% - 6 -2% 11 3 2
layered 3 6 -2% crumbled 1 - -
EXPERIMENTAL INVESTIGATION 28
4.0 SAMPLE PREPARATION
4.1 USE OF THE RAINER
The process of preparing a sample by letting sand fall, through air or
liquid, into the sample mold is called pluviation. Pluviation allows a
sample to be prepared in an efficient manner to an established density
with relatively homogeneous properties. Mulilis et al. (1979) describe
the procedure and conclude it is preferable to other methods for research
studies. Rad and Clough (1982) used this procedure for their investi-
gation into the behavior of cemented sands.
In this investigation, an effort was undertaken to optimize the pluviation
technique with regard to simplicity, repeatability, sample homogeneity,
and density control. After attempting a number of different techniques,
a raining method proved the most convenient; whereby the sand-cement mix
is poured through a porous plate at a fixed height above the sample.
Unfortunately, while homogeneous uncemented sand samples could be ob-
tained this way, this was not the case in the initial trials with the
cemented sands.
To check the first samples constructed by this method, they were cured,
air dried and trimmed along both horizontal and vertical planes. The
exposed soil showed vertical columns of darker colored and higher strength
material in locations corresponding to the holes in the rainer plate.
SAMPLE PREPARATION 29
Obviously, the cement had segregated, probably due to different raining
characteristics of the sand and cement, and to the mechanics of imFact
at the rising sample surface. Fortunately, this undesirable effect was
found to be eliminated by adding a diffusing screen approximately 10 mm
below the porous rainer plate. The diffusing screen served to maintain
the sand and cement in a mixture in the completed samples. A number of
samples prepared by the improved technique were inspected by the process
described previously. These samples appeared to have uniform distrib-
ution of cement with no visible color or strength variation.
The sample preparation technique that was finally adopted utilizes a
specially constructed sand rainer (Eid, 1984) that is shown in Figure 4-1.
Two adapter bushings were fabricated for the original rainer, which allow
it to mate with the sample molds and provide a constant cross section
during free fall of the sand-cement mix. Besides allowing for density
control with the use of changeable rainer and diffuser plates, this device
affords homogeneous, consistent, and repeatable sample preparation.
SAMPLE PREPARATION 30
Figure 4-la: Sand rainer and mold used for cemented sand preparation.
Figure 4-lb: Disassembled sand rainer.
SAMPLE PREPARATION 31
4,2 HOMOGENEOUS SAMPLES
All samples were prepared in the laboratory using Monterey #0/30 sand and
Portland Type I cement. It was necessary to first moisten the sand
slightly to insure that the cement was completely and evenly distributed
during mixing. The moisture was kept to 0.35%, by weight, to prevent the
mix from bulking up on the diffuser screen during raining. This quantity
of water was found sufficient to insure that all of the cement was dis-
tributed and bound to the sand grains by capillary tension. After mixing
the moistened sand with the appropriate amount of cement, the mixture was
poured through the rainer into the cylindrical mold shown, both of which
are shown in Figure 4-la. The molds were fabricated from plexiglass
tubing with an inside diameter of approximately 71 mm, cut to a length
of 178 mm with a single longitudinal split. A circular, aluminum plate
with five small diameter drainage holes was fitted to the bottom of the
cylinder which was subsequently secured with two hose clamps. Prior to
preparing the samples, the molds were sprayed with silicon lubricant and
a disk of filter paper was placed in the bottom of each. The sand rainer
was then used to create the samples, with densities being controlled with
properly chosen rainer plate and diffuser screen combinations. The sam-
ples were saturated by allowing the water level to slowly rise through
the porous plate on the bottom of the molds, which had been set on a
pervious bed in a styrofoam box.
The procedure used to prepare the homogeneous samples is as follows:
SAMPLE PREPARATION 32
1. Rainer is assembled with correct porous plate and diffuser
screen combination which is experimentally determined to result
in samples of the desired dry unit weight (relative density).
2. Inside surface of assembled mold is coated with thin coat of
silicon lubricant; filter pa.per is set into bottom of mold.
3. A course sand bed, a.bout 2 centimeters thick, is placed a.t the
bottom of the saturation box to allow free flow of water into
samples. The box is placed a.t a. water source to minimize the
number of times the uncured samples need to be relocated.
4. 1500 grams of a.ir dried sand a.re weighed into mixing bowl.
5. Appropriate a.mount of cement is weighed into a. sepera.te bowl;
this corresponds to 15 grams for the 1 percent mix and 30 grams
for the 2 percent mix. Cement clumps a.re broken up and cement
is discarded if it seems to have begun hydra.ting.
6. 5.2 cc of water (approximately 0.35% of dry weight of sand) is
added to sand which is then mixed thoroughly for a.t lea.st one
minute with spatula. or electric mixer. The same a.mount of
moisture is used for a.11 tests a.s it is a controlling factor
in resultant dry unit weight.
SAMPLE PREPARATION 33
7. Cement is slowly added to moistened sand while it is being
stirred, and mixing is then continued for at least one minute
with spatula or electric mixer.
8. Sand-cement mix is transferred to flask.
9. Rainer is placed on mold and sand is poured through at a con-
stant rate, maintaining a constant 15 to 25 mm head of sand
above the top porous plate. Sand should be added to the mold
until the level rises at least 20 mm above the top of the mold.
Rainer is removed with a vertical motion without disturbance
to mold and excess sand is gently stricken from top of mold.
10. Full mold is transferred to saturation box and slow flow of
water into box is begun, allowing water level to rise through
sample at a rate of approximately 8 centimeters per hour.
11. A small settlement, of approximately 2 mm, may occur at the top
due to the breakdown of capillary tension and particle rear-
rangement.
12. After sample has been allowed to cure in place for at lease 24
hours, it is transferred in saturation box to humid room for
remainder of curing period. The initial curing period helps
to minimize sample densification during transport from the
fabrication area.
SAMPLE PREPARATION 34
13. After 14 days, the top and bottom few centimeters of the sample
are trimmed as a precaution against high cement concentrations.
This is done by prying open the longitudinal split and sliding
the sample to use the mold ends as trimming guides. The sample
is then placed on the triaxial cell bottom platen and filter
paper which have been previously deaired as an aid to sample
saturation. The mold should be.used to provide support to the
sample until it is resting securely on the bottom platen of the
triaxial cell.
Note: It is prudent to prepare at least one spare sample for every
one to two samples that are intended for testing on the same day.
4.3 NONHOMOGENEOUS SAMPLES
A number of different methods were considered for preparing samples to
test the effects of weaker layers of cemented sand within a more strongly
cemented mass. The method adopted and described herein uses cured mate-
rials that are virtually identical to the homogeneous samples. It allows
for control of the relative levels of cementation and the thickness of
the weak layer.
Homogeneous samples of 1 and 2 percent cemented sands that were cured for
seven days are trimmed as shown schematically in Figure 4-2 and layered
to create a nonhomogeneous sample. The newly assembled sample is returned
to a saturated environment for the remainder of the curing period.
SAMPLE PREPARATION 35
The method used is demonstrated in the following photographs, and procedes
as follows:
1. A small batch of 2 percent sand-cement mix is prepared as de-
scribed in the homogeneous sample procedure.
2. 1 and 2 percent samples which have cured for seven days, are
trimmed to the required lengths as shown in Figure 4-2. Samples
should remain confined for the trimming process, and guides
should be used to insure square ends. (A plexiglass sample mold
was trimmed to a variety of lengths to serve both purposes.)
3. After setting the bottom layer vertically (onto a mold end
plate), its top surface is coated with a thin layer of the
sand-cement mix and the central layer is placed upon it. This
procedure is repeated for the top layer.
4. Mold is pried open and carefully lowered around sandwiched
sample until it bears on the edges of the bottom plate. Mold
is secured with hose clamps.
5. Sample is slowly submerged into water bath to cure for an ad-
ditional seven days.
SAMPLE PREPARATION 36
'"'d ~ '"'d s H 0 z
I 0/o
Homogeneous, 1°/o and 2 °/o cemented samples, cured for 7 days.
o• I I
o• Samples are trimmed to proper lengths and ends are made square. Top and bottom few centimeters of 2°/o sample are discarded.
Coot w/ 2°/o mix
D Ends are coated with fresh 2% cement mix as layers are stacked.
T 7cm
_J_ 4m_ 7cm
_L
Layered sample is cured in mold for 7 additional days.
Figure 4-2: Schematic of trimmed samples for nonhomogeneous sample construction.
Figure 4-3a: Bottom layer of 2% sample is trimmed from entire sample, using guide.
Figure 4-3b: Bottom layer is treated with 2% cemented mix.
Figure 4-3c: 1% section, trimmed on bottom, is put in place. Mold is then removed.
SAMPLE PREPARATION 38
Figure 4-3d: Weak layer is trimmed to desired thickness, using guide, and subsequently treated with 2% mix.
Figure 4-3e: Upper 2% section, which was previously trimmed on bottom, is put in place.
Figure4-3f: Mold is pried open, moved to contact bottom platen, and secured with hose clamps.
SAMPLE PREPARATION 39
4.4 SATURATION
To properly measure the volume change behavior and pore pressure gener-
ation of these materials while subjected to static and cyclic loading,
it is essential that they are saturated. In order to saturate a sample,
the voids are filled with deaired water while any entrapped air is usually
driven into solution using increased backpressures (Lowe and Johnson
(1960)). The criteria developed by Skempton (1954) is typically used to
determine the degree of saturation. Herein, the ratio of induced pore
pressure to increased confining pressure, or Skempton's B-parameter, is
monitored between incremental backpressure increases. Ratios in excess
of 0.95 generally indicate a noncompressible pore structure, correspond-
ing to saturated conditions.
With clean sands it is often helpful to percolate the sample with carbon
dioxide prior to flushing with deaired water. The carbon dioxide dis-
solves in water more easily than does air during backpressure saturation
leading to lower backpressures required for complete saturation. This
procedure was considered undesirable for the cemented sands, however, due
to the likelyhood of a deleterious chemical reaction between the carbon
dioxide and the cement.
Due to the presence of cement crystals and to the increased sample
stiffness, it was noticed that high backpressures are required to saturate
the cemented materials. A vacuum saturation technique, described by Rad
and Clough (1984), was developed to mitigate this effect. The reader is
SAMPLE PREPARATION 40
referred to this paper for the theoretical background and experimental
ver:f.fication of the procedure. The apparatus used for the present re-
search is shown schematically in Figure 4-4. The following procedure
represents a slight modifications of the original technique, because the
present apparatus allows for simpler setting and monitoring of the initial
effective confining vacuum, and affords more accurate determination of
the consolidated sample volume for density calculations.
The procedure is as follows:
1. Set sample in membrane onto triaxial cell with valves Tl and
T2 closed, and valves T3 and T4 opened to the flushing tanks.
2. Set regulator R2 to zero. Apply vacuum to regulator Rl which
is then set to 14 KN/M2 ( 4 inches Hg as read on mercury
manometer). Open valve T2 to top of sample, which applies a
negative backpressure condition.
3. Measure the height of the sample at four locations and measure
the diameter at three locations with a pi-tape.
4. Secure outer cylinder on triaxial cell and fill with water,
leaving at least 1 inch air space at top of cell. (Insure that
cell is vented during the filling process. ) Connect vacuum from
R2 to top of cell.
SAMPLE PREPARATION 41
S. Increase total vacuum at Rl at an increment of about 14 KN/M2 ,
adjusting R2 simultaneously to maintain 14 KN/M2 (4 inches Hg)
14 KN/M2 effective confinment. When air seems to have stopped
flowing from top of sample, increase vacuum at Rl again. Repeat
this procedure until maximum available vacuum is achieved.
6. Open valve Tl, allowing flow of desired water through sample
from upper flushing tank. This water must be desired just prior
to sample saturation as flushing tank is not airtight.
7. When sample appears saturated and bubbles have stopped flowing,
close valve Tl and reduce vacuum at valve Rl to the initial
total vacuum, while simultaneously adjusting regulator R2 until
it is zeroed. Open valve Tl.
8. Remove vacuum line from cell and replace it with cell pressure
line. Connect a low pressure guage to monitor cell pressure.
9. Simultaneously increase cell pressure and reduce vacuum, main-
taining effective confinement, until vacuum is completely re-
placed with cell pressure.
10. Backpressure saturate sample while checking Skempton's B-
parameter.
SAMPLE PREPARATION 42
B values in excess of 0.96 were achieved for all tests, at backpressures
on the order of 350 KN/M2 •
SAMPLE PREPARATION 43
AIR COMPRESSOR
VACUUM PUMP
AIR COMPRESSOR
l
.. : : ...
·:· .· : .
TRIAXIAL CELL
UPPER FLUSHING TANK
a:: UJ 0 0 <( ....J CD
a:: <(
R2i-----------------------
MERCURY MANOMETER
LOWER FLUSHING TANK
Figure 4-4: Schematic of vacuum saturation apparatus.
SAMPLE PREPARATION 44
S.O TEST PROGRAM, METHODS, AND EQUIPMENT
S.1 INTRODUCTION
This chapter discusses the testing program undertaken for this thesis,
which can be divided into three distinct phases. The first involves ma-
terial identification and index testing, as described in Chapter 3. The
two other aspects concern static and cyclic testing. The work was per-
formed both to augment previous efforts and to expand the understanding
of the behavior of weakly cemented sands in seismic environments.
S.2 STATIC TESTING
S.2.1 Introduction
Chapter 3 outlines the known research dealing with the static behavior
of lightly cemented sands. Most of the work in this area is concerned
with natural soils; materials which generally exhibit an appreciable de-
gree of variability. The properties of artificially created samples,
however, can be controlled in the laboratory. The effects of cementation
on static behavior can thus be more accurately isolated and quantified
if prepared samples are used.
Rad and Clough (1982) have done extensive static testing on artificially
prepared samples of cemented sand, and have documented many of their
TEST PROGRAM, METHODS, AND EQUIPMENT 45
specific characteristics. Their testing procedures were used as a general
guideline for the present study; their data were also used where possible
for comparative purposes and to enlarge the available data base for this
investigation.
The major portion of the static testing program involved 11 strain con-
t,rolled, consolidated, drained, cyclic triaxial tests on 2% cemented
samples, by weight, as well as similar tests on 3 layered, or nonhomoge-
neous, samples. Two unconfined compression tests were also performed on
the 2% cemented sand. Finally, one consolidated, drained triaxial test
was performed on a sample of the 2% cemented material that was cured,
crumbled, and subsequently reconstituted prior to testing. Of interest
here was the difference in strength and volume change behavior between
the crumbled sample and those which were intact prior to loading.
The intent of the test program on the 2% material was to develop strength
parameters, and observe volume change behavior. The strengths are im-
portant both as a measure of cementation and as a basis of comparison for
the effects of a weak lens on the static behavior of a stronger mass.
Volume change behavior is of interest as it relates to liquefaction re-
sistance. The nonhomogeneous samples were tested in static compression
to determine whether a reduction in liquefaction resistance, owing to the
presence of a weak lens, would be evident in static behavior.
TEST PROGRAM, METHODS, AND EQUIPMENT 46
S.2.2 Consolidated Drained Triaxial Testing and Equipment
Both the homogeneous and layered samples were tested in an identical
manner, and using the same equipment. The single crumbled and reconsti-
tuted sample was also subjected to this type of loading. Following sample
preparation and curing, which is described in Chapter 4, 7 cm diameter
samples were trimmed to approximately 15.3 cm in length and placed on the
triaxial cell. The triaxial cell and pressure/volume change panel was
purchased from Geotechnical Equipment Corporation in Highland Park,
Illinois. Latex membranes with a wall thickness of approximately 0.3 mm
were used to isolate the samples from the cell pressures. The top and
bottom platens are flush fit with porous brass material to allow free
drainage. A disk of Whatman #1 filter paper was placed at each end of
the sample to minimize transport of cement through the drainage lines.
The drainage lines consist of rigid Saran tubing with a wall thickness
of about 0.6 mm, providing for a drainage system with negligible flexi-
bility.
With a 4 inch mercury vacuum applied to the sample, the height was meas-
ured at four locations with a scale accurate to 0.4 mm. The diameter was
measured at the one-third points with a pi-tape accurate to 0.03 mm. The
triaxial chamber was then assembled around the sample and filled with
water, following which the sample vacuum was replaced with an equivalent
cell pressure.
TEST PROGRAM, METHODS, AND EQUIPMENT 47
Sample saturation, as discussed in Chapter 4, requires that cell pressure
and backpressure be monitored in order to check Skempton's B-parameter.
This was done with Entran pressure transducers that were calibrated prior
to the start of this test program. One transducer was connected directly
to the triaxial chamber and the other was connected to both the top and
bottom sample drainage lines by means of a t-fitting.
Samples were consolidated once the B-parameter was found to be in excess
of 0.96, whence the samples were assumed to be saturated. Volume change
during both consolidation and axial compression was calculated by meas-
uring the amount of water expelled from or drawn into the sample. This
was done with a graduated burette, calibrated to 1.325 cc per centimeter
of height, that was connected directly to the drainage lines. A burette
with a 55 cc capacity was found necessary to accommodate the volumetric
expansion of the cemented samples. Consolidation was generally allowed
to continue for about thirty minutes before the samples were axially
loaded. Each of the samples was trimmed, saturated, consolidated, and
failed in axial compression within a period of 5 hours after removal from
the curing bath.
Constant rate of strain axial loading was provided by a load frame pur-
chased from Research Engineering of San Pablo, California. The loading
component consists of a hydraulic piston that is pneumatically pressured.
Vernier needle valves allow control of oil flow to the piston resulting
in controlled rates of axial strain. The loads were transmitted to the
samples through a load rod with a hemispherical tip contacting a conical
TEST PROGRAM, METHODS, AND EQUIPMENT 48
seat on the sample top platen. The load rod was supported at the triaxial
cell by a Thompson linear bushing assembly that maintained cell pressure
with a close tolerance air bushing. Residual load rod friction at the
bushing was examined and found to be negligible.
Before loading the samples, the strain rate was set to 15 percent per
hour. Variation in sample stiffness," as a function of strain, required
that the rate be monitored and periodically adjusted during loading.
Samples were taken to 15 percent axial strain.
Data readings included axial deformations from a dial gauge accurate to
2.5*10 3 mm, axial loads from ans-type load cell with a maximum capacity
of 4.5 KN, and volume change with the graduated burette mentioned previ-
ously. The data was recorded by hand and subsequently stored on an Apple
IIe microcomputer diskette. Data reduction was executed with a modified
Basic language program, originally developed by Allen Sehn at Virginia
Tech that includes: area corrections, stress and strain calculations,
density determination, maximum deviatoric stress, axial and volumetric
strain at failure, and initial tangent modulus. General sample deforma-
tion was qualitatively noted at failure and at the end of each test.
TEST PROGRAM, METHODS, AND EQUIPMENT 49
5.3 CYCLIC TESTING
5.3.1 Introduction
The goals of the cyclic testing program are to provide an indication of
the effects of nonhomogeneous cementation on liquefaction resistance and,
if possible, to quantify the cyclic behavior of cemented sands in general.
The laboratory procedures used are described by Silver (1976) and Silver
et al. (1976). Since all samples are artificially created it is possible
to control both the level of cementation as well as the sample density.
In order to compare the effects of three different levels of cementation
and one layered, or· nonhomogeneous, material an attempt was made to
maintain constant densities of approximately 15. 70 KN/M 3 throughout the
testing program. Liquefaction resistance curves were generated for sam-
ples with 0%, 1%, and 2% cementation, and for 2% cemented samples with a
one centimeter middle layer at 1% cementation.
5.3.2 Method of Loading
A variety of laboratory methods are available for the evaluation of
liquefaction resistance of sands. These include the cyclic triaxial,
simple shear, and torsional shear, as well as cubical shear devices. Of
these, the cyclic triaxial test is the most widely performed due to its
relative simplicity and availability. Consequently, this is the best
TEST PROGRAM, METHODS, AND EQUIPMENT 50
understood and most standardized test (Silver, 1976).
effort, only the cyclic triaxial test was utilized.
In the present
The testing technique that was followed, for the isotropically consol-
idated, undrained, cyclic triaxial tests, is described by Silver {1976)
and will not be repeated here. Appendix B, however, includes a procedural
outline, highlighting some specific considerations for the particular
equipment used in these tests. The basic test arrangement is shown in
Figure 5-1. The axial loads applied to the samples in the stress con-
trolled tests were sinusoidal in nature and provided by a closed loop MTS
servo-hydraulic system.
The axial loads were monitored with an s-type load cell, conditioned to
give a full scale output of ±100 pounds. For accurate excess pore pres-
sure measurements, a differential pressure transducer with a range of 0
- 50 psi was placed between the cell pressure and the sample. Axial
displacements were monitored with an LVDT (linear variable differential
transducer) mounted above the load frame actuator. The loads were con-
trolled with the MTS 445 controller and 410 digital function generator,
and verified with a Tektronics 502A oscilloscope. A multi-channel
Honeywell light beam recorder provided a permanent record of the loads,
axial deformations, and pore pressures during testing.
TEST PROGRAM, METHODS, AND EQUIPMENT 51
V1 N
HONEYWELL VISICORDER
MTS SYSTEM 410 FUNCTION
GENERATOR
445 CONTROLLER
406 CONTROL UNIT
DIFFERENTIAL PRESSURE TRANSDUCER
·1· I I I
I I I I I I I I LVDT
r ..L-L-, I
:HYDRAULIC 1 ACTUATOR I
I
Figure 5-1: Schematic of cyclic testing equipment.
At the outset of this research project, state-of-the-art loading and
monitoring components, including the MTS controller and the Honeywell
Visicorder Oscillograph, were newly purchased. The controller, coupled
to an existing 10 kip load frame, replaces an earlier model used in this
investigation to help develop a test procedure. The initial effort was
directed at assembly and calibration of the test system shown schemat-
ically in Figure 5-1. A user's guide, describing the equipment and its
use in performing liquefaction tests, was developed to aid in procedural
continuity at the VPI Geotechnical Laboratory (Milstone, 1985).
Prior to testing, samples were saturated and consolidated to 103 KN/M2 ,
to be consistent with previous work. To insure isotropic consolidation,
a static axial compression load was applied to the sample to compensate
for the reduction in this stress direction due to the upward action of
cell pressure on the loading rod. Samples were allowed to drain at the
top and bottom during consolidation. The resultant volume change and
axial strain were recorded following a 30 minute consolidation period,
for determination of sample density and area at the time of cyclic load-
ing. Consolidation volume change was monitored with a graduated burette
connected to the drainage lines, while axial strain was measured with the
MTS lvdt.
The samples were subjected to cyclic loads of a sinusoidal nature with a
frequency of 1 cycle per second, as is standard practice. The amplitude
TEST PROGRAM, METHODS, AND EQUIPMENT 53
of the loading function is calculated from the chosen stress ratio, S , r
which is defined as:
S = !:io / 2o ' r c (5. 1)
where: !:io = maximum deviatoric stress
o ' = consolidation stress c
For each stress ratio, cyclic loads were continued until liquefaction was
achieved and cyclic strains appeared to have stabilized. Testing was
halted if liquefaction had not occurred within five hundred cycles. Ad-
ditional tests were performed on similar samples at a range of stress
ratios until a complete liquefaction resistance curve could be developed.
Analysis of the cyclic t~st data also includes an investigation of the
rate of pore pressure buildup in the various materials. This is discussed
more extensively in Chapter 7 along with the other cyclic test results.
S.3.3 Typical Results and Verification of Procedure
During the cyclic triaxial tests, axial loads, axial deformation, and
generated pore pressures are continuously recorded with the Honeywell
Oscillograph. A typical set of results from such a test, performed on
cemented sand at a stress ratio of 0.35, is presented in Figure 5-2. The
measured loads and deformations are converted to represent axial stress
and strain, respectively.
TEST PROGRAM, METHODS, AND EQUIPMENT 54
_l_.----
=:? I :t 1~ :. · . %-d q =2 2, . c ~·--<-,, --------- Ii_ l - ---t-
I;: I.
' ; "'F'
~
~--=---=- -_;_:-·:-·· I'•
t==
===·:;;::::§== -_ -· -· _.::_ --
! i ! ! . I, i I r,,
1 I I I i I ~ I It I I
I i I I I I 11 '
I ! ii ! i- l 1 I I I i ' ! I
'·
! ! I I ii i I : I l ~ I i ! I I f?i I I! i Ir i I i i :
I I I 11 ' i ~~' ' Ii I P: I I i ' ' I ' : I I I I i 11 p ! I I I [. I ' ! 11 i I
I ! I I :~ I I I I I 11 I I .. ~1 I I i l
11 i I I Ii I I ! I I I i I , i: i I 1 1 .i.. i I 11
I 'I : I i I! i .> ii I i 11 I I I I i I I 1..,µ.. ~! i l !
i I i Ii : i I) I I i Ii : i; i ! Ii I: I I ~i Ii I Iii ' I I i I' ! !~ i I': i, i I 11 i 11 I I
I i : ' ' IT i ! di 11 i.;; i I : . I i. ! I 111 I i : • ; 111 I i i ! l I : ! I I ; I 1-
l l i i i I I
' i i ' : l I i I i i I i I I I I I·~ I ~ I i i I i I I I I I ! i I I i i I
1 ~ : I i 1 1 : 1 1 111 11 1 1 .1 ;j ~ 1 1 1 :-n 1 1 1 i 1 ··1 1 1 1 1 1 r.: II\. I I il'li I . ; i 1: '.t\11 i• i :.,1 I j i'"t ! * 1 r I I I! If! I 111 i ! ! : , i
rt01 S~'3'1W \i.aO') . c-.01s!'GJ,lr.!! 1 r I i j F; ! ,: ! I I : i I I I ! ! ! I I J,1' 1 I I i : i ; I
' Figure 5-2: Typical results of a cyclic tria.xial compression test.
TEST PROGRAM, METIIODS, AND EQUIPMENT 55
The cyclic shear stress ratio can be verified from these plots by first
dividing the peak double amplitude cyclic load by two times the consol-
idated sample area, to determine the maximum deviatoric axial stress.
This value is then divided by two times the effective confining pressure
to evaluate the shear stress ratio.
The standard method of presentation for liquefaction studies is referred
to as the cyclic shear resistance curve and is a plot of the stress ratio
versus the number of cycles to liquefaction. An example of this, after
Silver (1976), is shown in Figure 5-3. This curve represents initial
liquefaction for Monterey #0 sand samples prepared by a tamping method.
The figure presents results of essentially identical liquefaction tests
on similar material, performed by eight independent laboratories.
Prior to the purchase of the more advanced MTS system, an older MTS 406
control unit was available to the researcher. Since sand samples had not
previously been successfully liquefied at Virginia Tech, it was necessary
to develop and verify a proper test procedure. This effort yielded re-
sults from a family of six tests on tamped Monterey #0/30 sand samples
which are included on Figure 5-3. It is observed that the data generated
by the early procedure falls in the general range of the 'standard'
Monterey #0 curve developed by Silver and others (1976), plotting somewhat
lower than the results presented by Muzzy (1983) for Monterey #0/30 sand.
TEST PROGRAM, METHODS, AND EQUIPMENT 56
SUMMARY CURVE
MONTEREY SAND NO. 0 O.BL-~~~~~~~~+-~~~~~~~~~
WET TAMPING COMPACTION t),,t) <1 N
11 a: '11 0.6 0 I-<( a: (/) (/) w a: I-C/)
INITIAL LIQUEFACTION
10 100
NUMBER OF CYCLES
LABORATORY
1.000
DENSITY (KN/M3)
0 15.49
2 6 15.54
3 0 15.59
4 • 15.32
5 0 15.46
6 • 15.53
7 & 15.60
8 'i;) 15.59
MILSTONE ¢ 15.54 MUZZY EB 15.46
10.000
Figure 5-3: Cyclic shear resistance curve for uncemented Monterey #0 sand (after Silver, 1976).
Monterey #0/30 sand is used in this project because it is similar to the
Monterey #0 sand used in previous investigations but no longer available
from Lone Star Industries. Comparisons of the two materials are presented
in Chapter 3.
As noted cyclic data on tamped Monterey #0/30 sand tested by Muzzy (1983)
has been plotted on Figure 5-3. His work concludes that this sand has a
higher cyclic shear resistance than does Monterey #0, as demonstrated by
this curve. The relatively lower liquefaction curve initially developed
in the present investigation for Monterey #0/30 sand suggested that re-
finements to the testing procedure were necessary.
Cyclic testing was improved with the arrival of the more advanced MTS
loading system, use of pluviated samples, and modified testing methods
that strictly comply with the requirements of the standard cyclic testing
procedure described by Silver et al. (1976). These include attention to
the sample uniformity and saturation, loading equipment, and to load and
pore pressure measurement devices. To insure that the present procedure
is compatible with the standard practice, a comparison was made with
documented results of pluviated Monterey #0 sand samples tested by Mulilis
et al. (1977).
Figure 5-4 presents a plot of cyclic stress ratio, S , versus the number r
of cycles to initial liquefaction, N1 . , for the results of Mulilis et iq
al. (1977) and this investigation. The data in this figure represent the
condition of initial liquefaction, where the induced excess pore pressure
TEST PROGRAM, METHODS, AND EQUIPMENT 58
is first equal to the effective confining pressure. It is noteworthy that
the curves have similar shape. As expected, the Monterey #0/30 sand from
this investigation is more resistant to liquefaction than the Monterey
#0 sand due to higher density and the slight, inherently higher resistance
shown by Muzzy (1983).
Peak values of stress ratio, strain and pore pressure for a test on 2%
cemented sand are given in Figure 5-5. This method of presentation shows
that deformation remains minimal until the onset of liquefaction. This
behavior was exhibited in all of the tests, and is investigated more
closely in Chapter 7.
The stress ratio can be seen to remain relatively constant throughout most
of the test. It is observed, however, that as axial strains become ap-
preciable, the stress ratio begins to drop off. While the cyclic testing
device is operating in a stress controlled mode, it is unable to keep up
with the large deformations. This is typical of many dynamic testing
devices. The concern is minimized, though, since the stress ratios gen-
erally remain constant through the onset and initial development of
liquefaction. The phenomena described above and shown in Figure 5-5 were
compared to, and found to be consistant with, peak result trends presented
by others (Silver, et al., 1976; Rad and Clough, 1982). It is felt that
this serves as additional verification of the cyclic testing procedures
adopted for the present investigation.
TEST PROGRAM, METIIODS, AND EQUIPMENT 59
0.55
0.50
~ 0.45
0 0. 40 !-CI a: 0.35 (j') (f)
~ 0. 30 t-(f)
a: 0.25 CI l..LJ
~ 0. 20 u ~
u >-
0. 15
u 0. 10
0.05
0.00 2 5
I I
I I
I I
AVG. DENSITY = 15.40 KN/M 3
UNCEMENTED INITIAL LIQUEFACTION
M!LSrnNE M~NT.•0/30-('.)
MULl LIS M~NT. •O
15.58
! I I I
10 20 50 100 200 500 1000 NUMBER QF STRESS CICLES, N
Figure 5-4: Cyclic shear resistance curves for uncemented sand.
TEST PROGRAM, METIIODS, AND EQUIPMENT 60
(f)
~ ~ 'a:: .28 - - minimum allowable stress = 0.8 SR - - -a:: <( (f) f- 0:: I (f)
_J 2 ~<(~ x a:: -<( 1-
(f)
w Oz ::::>-I- <( - a:: ci I- -~ (f) ~ <( -_J
<(
~~ CD
i5 c
.25
c 0 ·c;; ., Q) ... Q.
~ (.)
5
0
-5 10
5
0
100 - - - - - ~ - - - - - -·
"-Initial Liquefaction I
~ ;:JO)
0• 0.. WC\J
a:: :E 0 2 ....... 50 w ,,, z (.) ~ ::.::: ::::::>a:: -0 a.. ~
-----0 2 3 4 5 6 7 8 9 10 20 30 40 50 70
NUMBER OF STRESS CYCLES, N
Figure 5-5: Peak results from a cyclic triaxial test on 2% cemented sand.
TEST PROGRAM, METHODS, AND EQUIPMENT
100
61
6.0 STATIC BEHAVIOR OF CEMENTED SANDS
6.1 INTRODUCTION
There are three primary goals of the static testing phase of this study:
1. To gain insight into the effects of cementation on volume
change. This allows investigation of the critical void ratio
concept as it applies to cemented sand. The information can
also be used to seek correlations with liquefaction resistance.
2. To observe the effects of a weak lens on the static strength
properties and volume change characteristics of more strongly
cemented sand.
3. To add to the existing data base of controlled cemented sand
triaxial tests, and to provide a quantitative measure of the
cementation. This provides some basis of comparison with which
to evaluate the effects of weak lenses.
Eleven consolidated drained triaxial were performed on a family of 2%
cemented sand at densities of 15.00, 15.45, and 15. 70 KN/M 3 , and on a
second group of 2% cemented samples at a density of 15. 70 KN/M 3 • The
second set of 2% samples included a weaker, 1%, layer formed at midheight.
The creation of the samples is discussed in Chapter 4, and the testing
STATIC BEHAVIOR OF CEMENTED SANDS 62
procedures are detailed in Chapter 5. A limited number of unconfined
co~pression tests were performed on the homogeneous material for cali-
bration purposes.
6.2 HOMOGENEOUS DRAINED BEHAVIOR
The 2% cemented samples at average densities of 15.00, 15.45, and 15. 70
KN/M 3 were tested at confining pressures of 69, 207, and 345 KN/M2 •
Stress, axial strain, and volume change were monitored with a load cell,
dial guage and graduated burette respectively. Stress-strain and volume
change plots from the three sets of tests are presented in Figures 6-1
to 6-3. Note that compression failure, which is taken as peak deviatoric
stress, generally occurs at axial strain levels of approximately 6% to
7%. All samples show volumetric contraction up to axial strains of 1%
to 2%, whence they begin to dilate. The information derived from these
tests is also organized in tabular form (Table 6-1).
It can be seen that both stiffness (initial tangent modulus) and peak
stress increase with increasing density and confining pressure, as is the
case for uncemented sands. Peak strength envelopes for these materials
are defined from p-q diagrams shown in Figure 6-4 to 6-6. Unconfined
compressive strengths were calculated from the resulting friction and
cohesion parameters. A summary of this information is shown in Table 6-2,
which includes strengths generated from Mohr's envelopes and from the
unconfined compression tests. Trends are consistent with those noted by
STATIC BEHAVIOR OF CEMENTED SANDS 63
15 I
1 Ll >--
13 -
12 -
1 I -C't 10 -0 --' C't 9 ~ ~ ..... . . . z ~ 8 -
('I) 7 -0
6 -... 0 5 -
Li - .. . 3 -. "
I I
2 3 I
5
I I
. . .. . .
! AVG. DENSITY • IS.OOKN1M> 1 27. CEMENTED SYMBOL 0 c Y,l,M':
! I I
0
• 0 0
'59 2C~
'3"-:CS
0 0 0
-
-
-
-
-
-
-
-
6 7 8 9 10 11 12 13 1 Ll 15 16 AXIAL STRAIN (%1
0 1 2 3 4 s 6 7 8 9 10 11 12 13 14 15 16 5 ..---.-~.....--.-~...----...~...----.-~...---.-~~--.-~....---....~-.---.~....,......,
N ll
z 3
~ 2 ..... en
EXTENSrnN
o"'
l!J
"' " 0
"' 0 0 0
• 0 0
(!) • 6 • .. .. ... 0 0 0 " 0 0 0 0 0
. . . LU ""•"' ~ 0 'IE"~+-~-+-~--r.,.,..."'-"'+0 ---;;:-"-!7~--r--'+-~-+~--+~--,r--~t--~+-~-+-~-'+-~-t-~--t~~r--1
000 l!l 0 ~ ~ .a
...J ~"""'~l!lc""" o o • r""\. •a;"~OOC!IC!HJO O a • > -1 ................. .
CONTRACT 1 ON
Figure 6-1: Stress-strain and volume change plots for 2% cemented samples with average dry density= 15.00 KN/M 3 •
STATIC BEHAVIOR OF CEMENTED SANDS 64
15
14 >--
13 >--
12 I-
11 >--
Cll 10 a --' Cll 9 :r:
' z 8 ~ ,_
C'll 7 I-
b 6 I-...
b 5
00
50
N 4
z 3 -a: 2 a: I-U"l 1 IL.I %: 0 ::::> ...J 0 -1 >
.·
. .
1 2
1 2 EXTENSlON
. . • . . .
.. · .· .··
' 3 4
3 4
5
5
olll 11i"~ .,,,.
~"' °""'"' o'ln"'1~
:i,,'b•
CONTRACTION
.. .,,, .,,, .... ... . .
6 7 8 9 10 AXIAL STRAIN (%)
6 7 8· 9 10 • 0.
~o (Jo 0
oP d!l
"" ""' "" "" 00 ... ,.,ec
..
I AVG. DENSITY • 15.llSKNtH3
I 27. CEHENTEO
1 1
I
1 1
1 1 0 0 c
SlMBClL [!] I!)
I
12 13
12 13 o1 o ~I 0
.
!1 e 9<NtM2J
69 69 207 345
. . .
14 15
14 15 ::;ii O
. . . 0 • .
-
-
-
16
16
Figure 6-2: Stress-strain and volume change plots for 2% cemented samples with average dry density= 15.45 KN/M 3 •
STATIC BEHAVIOR OF CEMENTED SANDS 65
15 ..-~-..-..-..-..-.....,..... ........ _I ................................................................................................................................................................. ~
Ji AVG. DENSITY • 15. 70KN1M, 2X CEMENTED
14 >--
12
1 1
0
·• 0
"" 0 "'
I I I
1 207 345
! 4> C!I c:i !!I., o C!:I :a e o o ~ o ~I!) o o .'!l l!l o--L---1-----------l
~ 0 ~ ~ c
-
-" 0
(I) 7 0 "
c •• • l!I .-
" • 6 -5 - 0
"
0 " 3 1-- l!I
" " • 2 -"
" l!I
1 " I
1
"'
l!I l!I
" "'
I
2 3 I ;
4 s 6 7 8 9 10 11 AXIAL STRAIN l%l
12 13 14 15
-
-
-
-
16
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 s------....----.---......----.-------------------------------------
z cc a: I-C()
3
2
EXTENSJON
rnNTAACT rnN
• • l!I " . "
Figure 6-3: Stress-strain and volume change plots for 2% cemented samples with average dry density= 15. 70 KN/M 3 •
STATIC BEHAVIOR OF CEMENTED SANDS 66
Table 6-1: Sample conditions and test results of CD triaxial tests on 2% cemented sand and nonhomogeneous samples(l2-14).
INITIAL DENSITY CJ3 I PEAK sif EVf TANGENT
TEST STRE§S MODULUS (KN/M3) (KN/M2) (KN/M ) (%) (%) (KN/M2)
1 14.96 69 279 5. 7 1. 62 44750
2 15. 10 69 305 5.3 1. 05 40210
3 15.04 207 640 6. 1 0.66 69140
4 15.05 345 997 6.8 0.60 76738
5 15. 40 69 330 4.8 1. 70 66004
6 15.39 69 314 4.5 1. 58 59416
7 15.53 207 837 6.9 1. 39 79418
8 15.48 345 1220 7. 1 0. 73 98179
9 15.67 207 876 7. 2 1. 48 71740
10 15. 71 207 976 o.9 1. 54 80797
11 15. 73 345 1245 6.8 0. 74 114115
12 15. 26 69 297 5.6 1. 86 41840
13 15. 33 207 757 7. 1 . 65 74508
14 15. 47 345 1149 7.3 .91 110320
STATIC BEHAVIOR OF CEMENTED SANDS 67
Rad and Clough (1982). Specifically, the cementation manifests itself
as an apparent cnhesion that increases with increasing density. Conse-
quently, unconfined compressive strengths are also seen to rise.
Table 6-2 includes test results from cemented sands that have been studied
by other researchers. For the most part, friction angles are quite sim-
ilar for all the investigations. However, there are differences in ap-
parent cohesion and unconfined compressive strength. It is suspected,
for similarly prepared artificially cemented soils, that relatively minor
differences in sample preparation technique, cement quality, distribution
throughout sample, and curing time are major contributors to the strength
differences.
Figure 6-2 and Table 6-1 also include test data from the crumbled and
reconstituted, 2% cemented sample. Notice that both the stress-strain
and the volume change behavior of this disturbed material are similar to
that of the undisturbed cemented sample at a similar density. It is ex-
pected that additional testing would bear out previous results; namely,
that disturbance of the cementation lowers the static strength, but has
a relatively small effect on volume change characteristics. This possi-
bility is supported by the observation that most of the volumetric ex-
pansion takes place after 2% axial strain; a point where much of the
cementation has been destroyed even in initially intact samples.
While liquefaction potential has been related to the density of uncemented
sands, it has been shown that this is not the only controlling parameter
STATIC BEHAVIOR OF CEMENTED SANDS 68
in cemented soils. Volume change seems to be a better index of the cyclic
behavior of cemented sands. This material property can be assessed by
in-situ means such as the self-boring pressuremeter, and is preferable
to measurements of cementation which are difficult at best.
STATIC BEHAVIOR OF CEMENTED SANDS 69
800
600
Milstone - Yd=lS.00, ¢=34, C=40 II
C" 400
200 P=34, C=26
'( d= 14. 61' ·:P=34' C=l2
0 0 200 400 600 800 1000
p = ( 0"'1 + O"~) 2
Figure 6-4: p-q Diagram (average dry density= 15.00 KN/M 3 ).
STATIC BEHAVIOR OF CEMENTED SANDS 70
c
800
]N 600
~ Milstone - Yd=lS.45, ¢=36, C=60 ~
?" II
~ C" 400
- Yd=lS.34, ¢=36, C=40
200
Rad - Yd=lS.23, ~=36, C=20
0 --~~~~ ...... ~~~~--~~~~--~~~~--~~~--0 200 400 600 800 1000
Figure 6-5: p-q_Diagram (average dry density= 15.45 KN/M 3 ).
STATIC BEHAVIOR OF CEMENTED SANDS 71
II
O"
800
600
400
200
~ilstone - ~d=lS.70, P=JS, C=85
t,=J7, C=58
Rad - ~d=L6.07, ~=39, C=30
0 --~~~-----~~~---i~~~~--a..~~~~.....i..~~~~~ 0 200 400 600 800 1000
Figure 6-6: p-q Diagram (average dry density = 15. 70 KN/M 3 ).
STATIC BEHAVIOR OF CEMENTED SANDS 72
Table 6-2: Results of CD triaxial tests on 2% cemented sand.
MOHR'S p-q RESEARCHER, DENSITY e) c ucs ucs
SAMPLE (KN/M3) (DEG!{EES) (KN/M2) (KN/M2) (KN/M2)
RAD 14. 61 32 20 73 72 1% CEMENT 15.23 35 26 95 94
(PLUVIATED) 16.07 39 20 83 80
REYES 14.62 31 11 46 42 1% CEMENT 14.89 33 8 29 26
(PLUVIATED) 15. 32 36 22 86 66
MILSTONE 15. 46 37 30 120 104 LAYERED
MILSTONE 15.00 34 40 150 141 2% CEMENT 15. 45 36 60 236 167 *
(PLUVIATED) 15. 70 35 85 327 331/95
RAD 14.61 34 12 45 64 2% CEMENT 15.23 36 20 79 95
(PLUVIATED) 16.07 39 30 129 111
SITAR 15. 51 34 46 173 (2% TAMPED)
* 95 KN/M2 from unconfined compression tests.
STATIC BEHAVIOR OF CEMENTED SANDS 73
6.3 EFFECTS OF NONHOHOGENEITY ON CEMENTED SAND
Nonhomogeneous samples prepared for this investigation were subjected to
consolidated-drained triaxial tests, performed at confining pressures of
69, 207, and 345 KN/M2 • The samples were comprised of a 15 cm tall sample
at 2% cement content with a one centimeter thick, weaker, 1% lens at
midpoint. Sample preparation is discussed in Chapter 4.
The stress-strain and volume change data are plotted in Figure 6-7, and
key results are included in Table 6-2 along with those for homogeneous
samples.
The weak lens is seen to lower both the peak stress and the stiffness of
the stronger mass. By plotting the peak test data in p-q space (Figure
6-8), it can be seen that the friction angle of the layered material is
not significantly changed from that of the 2% homogeneous material.
However, the cohesion intercept definitely decreases as a result of the
weaker cementation at the sample centers. The reduction of the apparent
cohesion is to approximately half that of the homogeneous 2% mass. There
is an associated drop in unconfined compressive strength due to the weak
lens to a value of approximately half that of the homogeneous material.
While all of the cemented samples exhibited bulging deformations at the
time of failure, the nonhomogeneous samples had a more exaggerated bulge
toward midheight, in the vicinity of the weak lens.
STATIC BEHAVIOR OF CEMENTED SANDS 74
15
14 -
13 -
12 -
11 f-
('<
10 0 ...... ...I
('<
9 L ' z 8 f-~
(I) 7 b
6 -b~
5 ij
50
~ 4
z 3 -a: 2 a: I-fJ') 1 LU 2: 0 :::> _J 0 -1 >
-2
. 0
•
1
1
" 0
I
2
2
. .
EXTENSrnN
3
3
CCINTRACTl(]N
4
4
5
5
" "
6 7 8 9 AXIAL STRAIN
6 7 8 9
" " l!I
l!I
I AVG.DENSITY• 15.70KN1H' NONH0110GENEOUS
-
. . .
l!I 0
1 0 11 (%)
1 0 1 1 I
l!I l!I l!I 0
S'(M80L <Jc iKN;M'I
I
12 13
12 13 I
l!I l!I
I
14
14
69 207 345
I
15
15
I
-
-
-
-
-
-
-
16
16
Figure 6-7: Stress-strain and volume change plots for nonhomogeneously cemented samples.
STATIC BEHAVIOR OF CEMENTED SANDS 75
800
]N 600
Yd 15.46,¢ 37° c 30 '
II
er 400
200 -
0 .__~~~....L...~~~--IL--~~~....L-~~~---'-~~~---J 0 200 400 600
Figure 6-8: Peak strength envelope for nonhomogeneously cemented samples.
STATIC BEHAVIOR OF CEMENTED SANDS
800 1000
76
6.4 VOLUME CHANGE BEHAVIOR
6.4.1 Volumetric Strain Characteristics
When a sand is sheared in drained conditions there is typically a tendency
for volume change. For example, looser samples densify. In undrained
conditions with a saturated, loose sand, this leads to increasing pore
pressures that can cause liquefaction in cyclic loading. Denser materials
can dilate during drained shear; in undrained loading pore pressures are
reduced, minimizing strains and the likelyhood of liquefaction. Theore-
tically, then, if cementation serves to alter volumetric response, the
result could indicate changes in liquefaction resistance.
The drained static compression test results from this and other research
(Singh, 1984; Reyes, 1983; Rad and Clough, 1982) can be used to examine
this issue. Included in the data set are results from tests performed
on uncemented Monterey #0 and #0/30 sand, as well as the same sands ce-
mented with 1% and 2% Portland cement, by weight. For a variety of den-
sities, tests were executed at a range of confining pressures. Volume
strain at failure (peak stress) is plotted versus initial dry unit weight
for tests at similar confining pressures (Figures 6-9 to 6-11).
Analysis of the resulting plots reveals no clear trends of volume change
at failure as a function of cementation. Volumetric strain at failure
does not appear to differ to any significant degree for different levels
of cementation; any apparent differences are inconsistent. The basic
STATIC BEHAVIOR OF CEMENTED SANDS 77
conclusion from these figures is that the absolute magnitude of volume
strain is independent of cementation. Thus, there appears to be no basis
to believe that cementation has a major effect on liquefaction resistance
through the volume changes, per se, of the soil.
6.4.2 Effects of Cementation on Rate of Volume Change
The rate of volumetric expansion during shear has been proposed as a pa-
rameter that can be related to liquefaction resistance (Vaid, et al.,
1981). The expansion rate, or dilation rate, is characterized by the
dilation angle, v, which is the inverse sine of the slope of the volume
expansion curve. This is expressed as:
sin v = oV / oo ( 6. 1)
where: av = change in volume
oo = change in shear strain
Vaid and others have shown dilation angle to be linearly related to rel-
ative density of uncemented Ottawa test sand, demonstrating that materi-
als of higher relative density are characterized by higher angles of
dilation. Dilation angles, as measured from a drained laboratory or
in-situ test, can then be related to liquefaction resistance as a function
STATIC BEHAVIOR OF CEMENTED SANDS 78
~
;;-..:
> ~
. z a: a: I-(/)
i.J :::c ~ ....I 0 >
3 <J = c 103 KN/SM (!) iJNCEMENTEO m '--'
2 ~
Q]
.<!>. 0
-1 lY.5
l i: 2%
!'.!)
CEMnJT CEMENT
C) ~
.<!I. Q]
8
(:'.)
15.0 15.5 16.0 DRY UN I T WE I G HT , 14 IK N ;M 3l
16.5
Figure 6-9: Volume strain at failure for CD triaxial test versYs initial dry unit weight (confining pressure= 103 KN/M 2 ).
STATIC BEHAVIOR OF CEMENTED SANDS 79
3 (5 = c 207 KN/SM Q) UNCEMENTED
;;--.: ¢ NONHOMOGENEOUS 2 12] Ii'. CEMENT
> 6 2i'. CEMENT '4) ['] 6
6 ['] z (')
a: cc CJ I-(/)
(') w 6 L!'.
,!',
::::E ~ :::::) _J 0 ['] 0 > 6
-1 14. 5 15.0 15.5 16. 0 16.5
DAY UN IT WE I GHT, dd o<N1M 3l
Figure 6-10: Volume strain at failure for CD triaxial test versus initial dry unit weight (confining pressure= 207 KN/M 2 ).
STATIC BEHAVIOR OF CEMENTED SANDS 80
3 <5 = 3 L! 5 KN/SM c ~ UNCEMENTEO
~ ¢' NC ~J HOM 0 GEN EO US 2 ['] 1 i'. CEMENT
> A 2% CEMUJT ~ ['.]
C) z a:
['.]
CL I-<J)
(')
w ~ ::::> _J 0 0 >
['.]
-1 14. 5 1 5. 0 15.5 16. 0 16.5
ORY UNIT WEIGHT, rd IKN1M 3 l
Figure 6-11: Volume strain at failure for CD triaxial test versus initial dry unit weight (confining pressure= 345 KN/M 2 ).
STATIC BEHAVIOR OF CEMENTED SANDS 81
of rela~ive densi~y. For this research project it ~as desired co knc~
whether dilation angle is affected by cementation.
All the dilation angles reportP-d herein were determined from consolidated
drained triaxial test data where volume change was measured directly from
s3mple drainage lines. Dilation angles were calculated from the =esulting
volume change curves (as shown in Figures 6-1 to 6-3) and from estimated
shear strains. Shear strain estimates are necessary because only axial
strains were monitored during the reported tests. By assuming right
circular cylinder deformation, shear strains may be calculated thusly:
knowing: 0 = (6.2)
( 6. 3a)
= z.l(A /TT) c (6. 3b)
(6.3c)
Substituting:
o = e L + 1 - ( 1. 12 8 ID . ) ( ./V . Cl - e V) I ( L . (1- e L) ) ) l. l. l.
( 6. 4)
Where: o = shear strain
e1 = axial strain
eH = horizontal strain
STATIC BEHAVIOR OF CEMENTED SANDS 82
,,. = volumetric strain ~v
D. = initial sample diameter l
Df = final sample diameter
L. = initial sample height 1
V. = initial consolidated sample volume l
A = corrected sample following strain c
Equation 6.4 was applied to test data and found to give results close to
This is consistent with the elastic theory assumption of
Poisson's ratio equal to 0.5 for a saturated, incompressible sample.
Dilation angles were determined for the portion of the volume expansion
curves that is representative of sample failure. This analysis was exe-
cuted on uncemented sand data as well as data from samples containing 1%
and 2°0 cement by weiglit. These data are plotted in Figures 6-12 to 6-14
for respective confining pressures of 69, 207, and 345 KN/M 2 • Al thongh
there are a limited number of points, cemented sands appear to display a
linear rel3tionship between density and dilation angle. There is also a
consistent trend of increased dilation angle with increasing levels of
cementation. Tims, while absolute volume change v;as not affected by
cementation, the data in this section show that cemented sands reach a
given level of volume change at a rate faster than their uncemented
cousins. The difference between the two increases as cementation in-
creases.
STATIC BEHAVIOR OF CE~E~TED SANDS 83
As mentioned previously, it has been difficult to sample or test most
cemented materials in the field without first disturbing the cementation.
Consequently, liquefaction resistance of these natural deposits may be
underestimated. The self boring pressuremeter has the capability of
measuring the rate of volume change, or the dilation angle. With no other
indication of cementation, increased dilation angles are likely to be
interpreted as higher density uncemented sand. Nevertheless, it is pos-
sible that the cyclic strength determined from the apparently higher
density will adequately reflect the cyclic strength of the actually
looser, but cemented, deposit. Repeated tests, at the same location, may
also give an indication of the presence of cementation by yielding lower
dilation angles on subsequent, disturbed, tests.
6.4.3 Critical Void Ratio
As one of the objectives of this research, it was intended to investigate
the application of Casagrande' s critical void ratio concept ( 1936) to
cemented sands. For this purpose, volume change at failure from drained
compression testing is plotted versus initial void ratio (Figure 6-15).
For each confining pressure, graphical interpolation of the data provides
an initial void ratio at which, theoretically, there would be zero net
volume change at the point of maximum shear stress. These values are
plotted versus the respective confining pressures to develop the critical
void ratio curve. An example of this is shown in Figure 6-16. A similar
STATIC BEHAVIOR OF CEMENTED SANDS 84
40 (j) <5 = 103 KN/SM w c w C) UNCEMEIHEO cc
CJ 1% CEMrnT c...:i w 30 <!; 2% CEMENT 0
~
w _J 20 (..,:) z a: z El
t- 10 a: _J ..... Cl
0 14. 5 15.0 15. 5 16. 0
DR Y UN I T W E I G HT , 1 d IK N 1M 3)
Figure 6-12: Dilation angle versus initial dry density (consolidation pressure = 103 KN/M 2 ).
STATIC BEHAVIOR OF CEMENTED SANDS
16.5
85
Cf) w w a: (.!)
40
~- 30
-~ . w _J 20 (.!) z a: z 0
..... 10 a:: _J
Cl
0
(J = 207 KN/SM c (!) UNCEMENTEO CJ ! ".' CEMENT .<!> 2% CEMENT
14. 5 15. 0 15.5 16.0 DRY UNIT WEIGHT, 1• IKNtM 3)
Figure 6-13: Dilation angle versus initial dry density (consolidation pressure = 207 KN/M 2 ).
STATIC BEHAVIOR OF CEMENTED SANDS
16.5
86
Cf) w w a: L') w a
~
w _J L') z a: z El ..... I-a: _J ..... a
40 (J = c 31.!5 KN/SM Q) UNCEMENTED ~ 1 i:: CEMENT
30 a 21. CEMENT ~ NCJNHCJMCJGENECJUS
20
10
0 14.5 15.0 15.5 16.0
DRY UN IT WE I G HT , "{ 4 tK N !M 3l
Figure 6-14: Dilation angle versus initial dry density (consolidation pressure = 345 KN/M2 ).
STATIC BEHAVIOR OF CEMENTED SANDS
16.5
87
relationship may also be developed by using residual, or steady state,
volume strain rather than that at failure.
A previous study in this area (Reyes, 1983) noted that cementation appears
to lower the critical void ratio of sands. Reyes tested sands with 1%
cementation. For comparative purposes, the present work produced data
for 2% cemented sands. Test results from other researchers (Rad & Clough,
1982; Singh, 1984) were also reduced in the appropriate manner to enlarge
the data base for this study.
All available data are plotted in Figure 6-17 as critical void ratio
versus confining stress. Both the 1% and 2% cemented sands appear to have
lower critical void ratios than the uncemented sand. The reasons for this
finding are not clear. It may be that the conventional critical void
ratio concept is simply not applicable to cemented sands, since the volume
change values used in developing the diagram are those at large strains,
where cementation bonds have already broken down. The maximum influence
of the cementation lies at low strains; a level where uncemented sands
have yet to mobilize their shear resistance. In addition, it is likely
that the zone of failure in the cemented samples is confined to a smaller
area; that relatively less sample is involved in dilatent behavior than
in the uncemented samples. Density calculations, which average the volume
strain in the failure zone over the entire sample, would result in ap-
parently low void ratios leading to the behavior shown in Figure 6-17.
STATIC BEHAVIOR OF CEMENTED SANDS 88
c: 0 (/)
w c: a:: g_ ::::::> x .....J Q)
~ ~
w ~ c: ::::::> 0 .....J '.;: 0 (.) >c .... -c:
0 (.)
e init.
Figure 6-15: Volume change at failure from CD triaxial tests versus initial void ratio.
STATIC BEHAVIOR OF CEMENTED SANDS 89
ea
0 I j::: <t a::
I a 0 > ___ l ...J <t eb j:::
I I ~·
-t -1-ec I I
0-a (j"b 0-c
EFFECTIVE CONFINING PRESSURE
Figure 6-16: Critical void ratio versus confining pressure.
STATIC BEHAVIOR OF CEMENTED SANDS 90
.86
• . 84
.82
....: ·;:: () .80 Q.)
• 0 . 78 f- • <t: a:::
.76 a 0 >
.74 _J <t: . (.)
i='. .72 ii:
(.)
.70 • - Uncemented • - 1°/o Cemented
.68 • - 2°/o Cemented
.64 -----------------------------------------------0 100 200 300 400 500 600 700 800
EFFECTIVE CONFINING STRESS, 0-3' (KN/M2)
Figure 6-17: Critical void ratio versus confining stress for cemented and uncemented Monterey #0/30 sand.
STATIC BEHAVIOR OF CEMENTED SANDS 91
7,0 CYCLIC BEHAVIOR
7.1 INTRODUCTION
This chapter presents the results of the cyclic testing program outlined
in Chapter 4. Observations as to the effects of cementation on
liquefaction resistance, in general, are provided and compared to those
of Rad and Clough ( 1982). The test results also provided enough data with
which to examine the effects of cementation on rate of pore pressure
generation and to relate this to strain development during cyclic loading.
Finally, cyclic tests performed on the nonhomogeneous samples revealed
some of the effects that a weak lens has on a more strongly cemented mass.
7.2 EFFECTS OF CEHENTATION ON LIQUEFACTION RESISTANCE
Liquefaction tests were performed on uncemented sand and homogeneous ce-
mented samples with cementation levels at 1% and 2%. To allow comparison,
the average densities are all approximately 15.70 KN/M 3 • Pertinent in-
formation is provided in Table 7-1. The test results are plotted in
Figure 7-1 as the stress ratio versus the number of cycles to initial
liquefaction. Referred to as the cyclic shear resistance, or liquefaction
resistance, curves, each of the curves in Figure 7-1 represent a family
of tests on samples at a different level of cementation. A higher curve
indicates that a greater number of cycles are required for liquefaction,
at a given stress ratio. As expected, cementation has the effect of in-
CYCLIC BEHAVIOR 92
creasing the liquefaction resistance of sands. This trend is also dem-
onstrated when liquefaction is defined as eithe~ 5% or 10% double
amplitude axial strain. It should be noted that the previous work in this
area by Rad and Clough (1982) demonstrates the same tendency.
Taken together, Figure 7-1 and Figure 2-1, which is a similar presentation
of the Rad and Clough (1982) test results, point to another phenomenon.
These plots demonstrate that for samples which liquefied below about 30
cycles, the cyclic shear resistance curves increase rapidly as the number
of cycles decrease. While this behavior is evident for uncemented sand,
it is observably more prominent for the cemented materials. It appears
that cementation, while consistently increasing the liquefaction resist-
ance of sands, has its greatest effect at cyclic loads that are within
the range of duration of probable seismic events. This substantiates the
practical import of continued research efforts concerning the effects of
cementation on liquefaction resistance.
CYCLIC BEHAVIOR 93
Table 7-1: Cyclic triaxial test information.
TEST PERCENT DENS!~ STRESS SKEMPTON NUMBER CEMENT (KN/M ) RATIO B-factor NS% Nl0% Nl. iq
19 0 15.68 . 26 . 96 11 - 10
18 0 15.44 . 25 1. 00 23 - 20
17 0 15.63 . 22 1. 00 101 - 95
16 0 16.07 . 20 . 96 427 - 421
1 1 15. 66 . 40 . 98 - - 7
11 1 15. 75 . 3.5 . 99 20 - 14
2 1 15. 76 • 30 . 98 26 - 19
4 1 15.67 . 25 . 99 45 - 33
5 1 15. 59 . 23 . 99 208 - 200
3 1 15.68 . 20 . 99 - - * 9 2-1-2 15.35 . 45 . 99 6 19 8
7 2-1-2 15. 41 . 40 .99 7 30 10
8 2-1-2 15.35 . 35 . 99 17 59 13
10 2-1-2 15.33 . 325 . 99 17 - 19
12 2-1-2 15.23 . 31 1. 00 39 - 32
6 2-1-2 15.33 . 30 . 98 142 - 120
15 2 15.67 . 55 . 98 25 - 19
14 2 15. 70 . 45 . 98 - - 35
13 2 15. 79 . 33 . 99 221 - 210
* Sample did not liquefy in 560 cycles.
CYCLIC BEHAVIOR 94
0.60 '' I I I AVG. DENSITY • 15.70 KN/M 3
0.55 CEMENT CONTENT VARIED INITIAL LIQUEFRCTION
0.50 2% CEMEN7 CONTE~~~ c:: cc (.{) l % CE~ENT CONTENT 6
0. lJ 5 1;~ OJO N(n ~JGlUEFi ::c: 0 IJNCEHENTEO CJ
I- 0.40 a: cc (.{) 0.35 en lJ..j cc I- 0.30 en cc a: 0.25 lJ..j :r: (.{)
u 0.20 _J u 0. 15 >-u
0. 10
0.05
0. C10 2 5 10 20 50 100 200 500 1000
NUMBER OF STRESS CYCLES, N
Figure 7-1: Cyclic shear resistance curves for cemented sand.
CYCLIC BEHAVIOR 95
7.3 EFFECT OF CEMENTATION ON DEVELOPMENT OF PORE PRESSURES AND STRAIN
Presently, pore pressure and strain development during cyclic loading of
cemented sands are not well understood. It is important to resolve this
issue since if pore pressure generation in cemented sands can be predicted
empirically, effects due to an~icipated seismic events can be predicted.
This aspect of cemented sands is studied here.
One manner of viewing the pore pressure development is given by Lee and
Albeisa (1974). In this normalized presentation, the pore pressure, at
a given stress cycle, divided by the initial confining pressure, is
plotted against the same number of cycles divided by the number of cycles
to liquefaction. Seed and others (197.5,1976) have used this scheme to
develop an empirical method of predicting pore pressure development in
uncemcnted sands, given as:
where: pore pressure
rN' cyclic ratio
( 7. 1)
ratio = U / o ' e c
= N I ~ 1 . iq.
a = exponential factor
This curve has been plotted on Figure 7-3 for a= 0.70. The range of
observed values for uncemented sand as documented by Lee and Albeisa
(1974) is also shown on this diagram.
CYCLIC BEHAVIOR 96
u
b ""' QJ ::::J
::::>
'--
0
t-a: a: w a: ::::) CJ) CJ)
w a: 0....
LU a: 0 0....
1. 0
0.8
0.6
0.4
0.2
0.0 0.0
RANGE OF VALUES FOR UNCEMENTED SAND fLEE 8. ALBEISA, 1975)
0.2 0.4 0.6 0.8
CYCLIC RATIO,
Figure 7-3: Pore pressure ratio versus cyclic ratio.
1. 0
CYCLIC BEHAVIOR 97
Rad and Clough (1982) have shown (Figures 2·2 and 7-4) that weakly ce-
mented sands have a different pore pressure response during cyclic loading
than do uncemented sands. The plot of normalized points for the cemented
materials generally falls above the ranges noted by Lee and Albeisa (1974)
and De Alba et al. (1975) for uncemented materials. The scatter of these
points, which is an artifact of combining results from different tests,
makes further analysis difficult.
The cyclic test data from this investigation is presented in similar
fashion as Figures 7-5 through 7-7. The data from individual tests are
considered in terms of stress ratio level. Only homogeneous samples are
considered; uncemented in Figure 7-5, 1% samples in 7-6 and 2% samples
in 7-7.
Figure 7-5, which describes the behavior of the uncemented sands tested
for this investigation, shows agreement with values documented by Lee and
Albeisa (1974) for typical uncemented sands. This is believed to rein-
force the validity of the procedures used during the present investi-
gation. In Figures 7-6 and 7-7, as mentioned previously, pore pressure
ratio curves from the cemented sands are compared with the Lee and Albeisa
range. As was the case with the data of Rad and Clough (1982), the data
points for the cemented materials plot higher than the uncemented range,
indicating a more rapid pore pressure development than for the uncemented
sands. However, since the curves are classified according to stress ra-
CYCLIC BEHAVIOR 98
lb(J
' ::> I :::J
l.i
.. (S) -r-< c::: w c:::
. :J (f) (f) w 0:: a.. w c::: (S) 0..
1.0 • • • • • I • • • • • 0.8 • • • • • 0.6 • •
• • • • • • 0.4 •• • • Lee and Albeisa
(Observed range for 0.2 uncemented sand)
2% CEMENT 0.00 0.2 0.4 0.6 0.8
CYCLIC RA TI0, r0-N/N1
Figure 7·4: Pore pressure ratio vs. cyclic ratio (2% cement) (after Rad and Clough, 1982).
•
1
CYCLIC BEHAVIOR 99
u
b ........
Q)
::J
L
I--er: a:
::I
UJ a: ::::> (f) (f) UJ a: a.. UJ a: 0 a..
1. 0
0.8
0.6
0.4
0.2
0.0 0.0
KE I STRESS RAT IO 0.200 0.220 0.250 0.260
UNCEMENTED
0.2 0.4
CICLIC AATrn,
SYMBOL
~
x .<!:>
['.]
~ RANGE OF VALUES FOR UNCEMENTEO SANO !LEE ~ ALBEISA, 197Sl
0.6 0.8
Figure 7-5: Pore pressure ratio vs. cyclic ratio (uncemented).
1. 0
CYCLIC BEHAVIOR 100
1. 0
u
b 0. 8 ........
CV :::::l
t-a: a: w
0.6
~ ·O. 4 If) If) w a:: CL
UJ a: 0 a.. 0.2
0.0 0.0
KE I STRESS ART iO 0.230 0.250 0.300 0.350 0.400
1 i: CEMENTED
0.2 0.4
CYCLIC RATIO,
SYMBOL ~
x L!:.
l2J C>
RANGE OF VALUES FO~ UNCEMENTED SAND !LEE lo ALBE 1 SA, 1975!
0.6 0.8
Figure 7-6: Pore pressure ratio vs. cyclic ratio (1% cement).
1. 0
CYCLIC BEHAVIOR 101
1. 0
u
b o. 8 ' Cl) ::J
J-a:: c:c LU
0.6
~ 0. 4 U1 U1 LU c:c a..
0.2
0.0 0.0
KEI STRESS I
RRT!CJ 0.330 0.450 0.550
2i.'. CEMENTED
0.2 0.4
CICLIC RATrn,
51MBCJL
L!>
~
~
RANGE CF VALUES FCA UNCEMENTEO SANO CLEE ~ ALBEISA, 19751
0.6 0.8
Figure 7-7: Pore pressure ratio vs. cyclic ratio ( 2% cement).
1. 0
CYCLIC BEHAVIOR 102
tio, it can be seen that the points outside the uncemented range are as-
sociated exclusively with high stress ratio loading. This is consistent
with the fact that cementation was shown in Chapter 6 to increase the rate
of volume strain under drained, static loading. Higher dilation angles,
as measured in the field, would suggest the earlier and more rapid pore
pressure buildup characteristics of cemented sands.
Further examination reveals another consistent trend. Namely, cemented
sands under low stress ratio loading yield a pore pressure response con-
sistent with that of the uncemented sands. This implies a relationship
to sample deformation which is quantified in these tests as axial strain.
While it is known that axial strain and pore pressure development are
linked, as evidenced by parallel plots of the two (Figure 5·4), the re-
lationship warrants further investigation.
Since the absolute value of axial strain varies with changes in sample
and test conditions, the strains for each test must be normalized before
common trends can be evaluated. Figures 7·8, 7-9 and 7-10, show the axial
strains for the tests of this investigation in a normalized fashion,
similar to the pore pressure generation curves discussed previously. The
strain ratio is defined as the axial strain at a given cycle, divided by
the axial strain at liquefaction. This is plotted versus the cyclic ra-
tio, or cycle number divided by the number of cycles to initial
liquefacton. In all cases, the strains develop slowly until a point where
the rate increases rather rapidly. It is suspected that near the time
that this inflection occurs, the most highly stressed portion of the
CYCLIC BEHAVIOR 103
sample is transformed from a cemented, monolithic mass to a granular ma-
terial consisting of sand grains c~ated with cement crystals.
CYCLIC BEHAVIOR 104
KEY STRESS SYMBCIL AATICI
0.200 e:i 0.220 x 0.250 A
0.260 [!]
·1. 0
UNCEMENTED
a. a .,. -
t.V .........
c· t.V
II a.6 .... '-
. c -I-c:: 0.4 cc z ..... c:: a:. 1:-U'l
a.2
a.a ·· a. a 0.2 O.Y a.6 0~8 1. 0
CYCLIC RATI(j,
Figure 7.-8: Strain ratio vs. cyclic ratio (uncemented).
CYCLIC BEHAVIOR 105
.,.. -w
.......... c:: w
II
. .., '-
. 0 ...... I-a: a: z ...... a: a: I-U'l
1. 0
0.8
0.6
0.4
0.2
0.0 0.0
KEI STRESS RAT !CJ
0.230 0.250 0.300 0.350
11. CEMENTED
0.2 0.4
CICLIC RATIO,
SYMBCJL
C9 x ~
c:J
0.6 0.8
Figure 7·9: Strain ratio vs. cyclic ratio (1% cement).
1. 0
CYCLIC BEHAVIOR 106
-t.J.)
" c: t.J.)
"' L
0
t-a: a: z a: a: t-(.{)
1. 0
0.8
0.6
0.4
0.2
0.0 0.0
KE I STRESS RAT IO
0.330 0.450 0.550
2% CEMENTED
0.2 0.4
CYCLIC RATIO,
SYMBOL
L!'>
(')
[']
0.6 0.8
Figure 7-10: Strain ratio vs. cyclic ratio (2% cement).
1. 0
CYCLIC BEHAVIOR 107
Comparison of the strain development plots with their respective pore
pressure development plots, shows that the marked change in rate of dtrain
precedes the tendency for the pore pressures to develop in a manner dif-
ferent from that of uncemented sands. At low strain ratios, the pore
pressure development of the cemented sands is similar to that of the un-
cemented sands and may be described by Equation 7. 1. Beyond some limiting
strain ratio, on the order of 0.20, the cemented sand pore pressure de-
velopment curves differ significantly from those of uncemented materials.
This limiting strain ratio corresponds to single amplitude axial strains
on the order of 0.7% and shear strains on the order of of about 1.0%, as
estimated by elastic theory. Wissa and Ladd (1964) observed in static
tests that, at this general range of strain, the cementation breaks and
the strength contribution from friction becomes dominant. This behavior
was also noticed by Saxena and Lastrico (1978) who state that, "beyond
certain strain levels there is a gradual breakdown in cementation."
This suggests that, for this type of cemented sand, the cementation does
not affect the trace of pore pressure generation until a certain amount
of strain has destroyed some of the sand-cement bonds. This is substan-
tiated by visual observation of the samples during cyclic loading.
Once this transformation has taken place, the pore pressure generation
curves adopt a different shape than that for uncemented sand. The char·
acter of these cemented sand pore pressure generation curves is then more
closely described by the equation:
CYCLIC BEHAVIOR 108
where: ru, pore pressure ratio
rN' cyclic ratio
B = factor
= u I 0 I e c
= N I N1 . iq.
(7. 2)
Given the cyclic ratio, the pore pressure ratio can be estimated from the
inverse of Equation 7.2:
(7. 3)
Figure 7-11 shows a variety of these curves along with some of the test
data. It is observed that the B-factor increases with increasing stress
ratio. It appears that pore pressure generation for cemented sands cycled
at higher stress ratios, requiring relatively few cycles to liquefaction,
may be predicted by Equation 7.2. At lower stress ratios, pore pressure
generation is described by Equation 7.1 up to a point where the shear
strains exceed about l~. The remainder of the curve can then be approx-
imated by E~uation 7.2, developed for cemented sand behavior. This is
demonstrated in Figure 7-11 by the curves representing data from tests
performed at stress ratios of 0.25 and 0.30.
Prior to developing this concept further, it will be necessary to gain a
better understanding ~f both the mode and the effects of strain in cy-
clically loaded, cemented sands.
CYCLIC BEHAVIOR 109
u
b ' v =>
:::> L
t-a: a: u.J a: ::::i U"J U"J u.J a: a.. u.J a: 0 a..
1. 0
0.8
0.6
0.4
0.2
0.0 0.0
KEI STRESS I SYMBCJL RAT !Cl
0.250 x 0.300 ~
0.350 12:1
0.400 <'>
1 i.: CEMENTED - - - Equation 7 .1 --Equation 7.2
,:;,:······.::···!;:/""\__RANGE OF VALUES FCTR - UNCEMENTEO SANO
!LEE t. ALBEISA, 19751
0.2 0.4 0.6 0.8 1. 0
CYCLIC RATIO,
Figure 7-11: Pore pressure ratio vs. cyclic ratio data for cemented sand compared to empirically developed curves.
CYCLIC BEHAVIOR 110
7.4 EFFECT OF A WEAK LENS ON LIQUEFACTION RESISTANCE
The liquefaction resistance curve for the layered sample is compared in
Figure 7-12 to the curves for the other materials of this investigation.
As discussed in Chapter 4, the nonhomogeneous samples were created by
layering homogeneous materials of the same density as used in the homo-
geneous static and cyclic tests. In this case, a 1 centimeter layer of
a 1 percent cement mix is sandwiched between two, 7 centimeter layers of
2 percent mix sand.
There are two features of the liquefaction curve for nonhomogeneous
cementation (Figure 7-12) that warrant special attention. First, and not
surprisingly, the curve for this material falls between the curves for
the homogeneous, 1% and 2% samples. This is significant in that the
nonhomogeneous samples constitute a layering of those two materials. This
demonstrates that weak lenses certainly lower the liquefaction resistance
of stronger masses, but do not necessarily constitute a limiting condition
"weak link" that fully determines the cyclic shear resistance of the de-
posit. Secondly, it is interesting to note that the liquefaction re-
sistance curve for the layered samples lies closest to the 1% curve at
higher stress ratios, while at lower stress ratios the curve seems to veer
toward the 2% curve. This suggests that the weak lens has less influence
on the total mass at low shear stress levels, but, shows the reverse trend
at high shear stress levels.
CYCLIC BEHAVIOR 111
0.60
0.55
0.50 a: Cf)
• 0.45 0
~ 0. 40 a: ~ o. 35 I.LI a: ~ 0. 30 a: ~ 0. 25 :c Cf)
u 0. 20 ..... .....I u o. 15 >-u
0. 10.
a.as 0.00
1 2 5 10 20 so
AVG. DENSITY • JS. 70 KN/M3
LAYERED SAMPLES INllIRL LIQUEFRClJON
21. CEMENT CDNTENT CJ NDNHDMDGENEDUS + 1 'l. CEMENT CDNTENT ~
ND LICUEFRCTIDN. l'l. )::(
UNCEMENTEO
I 1
100 200 500 1000 NUMBER ~F STRESS CICLES, N
Figure 7·12: Cyclic shear resistance curves for nonhomogeneous samples compared to various cementation configurations.
CYCLIC BEHAVIOR 112
This may be a function of strain as indicated in Section 7.5, where high
strains were seen to cnntrol the rate of pore pressure generation in cy-
clically loaded samples. This can be interpreted as the cementstion ex-
erting its character more strongly st increased strains.
During cyclic testing st low stress ratios, the stronger masses were no-
ticed to develop appreciable strains st a proportionately earlier stage
of loading than st higher stress ratios. At higher stress ratios, greater
strains were noted in the central, weaker lens than in the stronger mass,
even up to the point of initial liquefaction. This would result in the
weak lens exhibiting more of its cemented characteristics than the
stronger material, leading to greater control over pore pressure gener-
ation. Ultimately, this means that the weak lenses have a stronger in-
fluence upon liquef sction resistance st higher stress ratios.
It is significant to note from Figure 7-12 that the weak lens consistently
predominates the liquefaction resistance st events lasting up to 20 cy-
cles, which constitutes the range of duration for most reported seismic
events (Silver and Park, 1975). It is not known whether these observa-
tions hold true for variations in the relative levels of cementstion
within the samples, and the relative thicknesses of the layers.
Since there are a wide variety of natural cementing agents, it is diffi-
cult to quantify this in terms of percent cement as can be done for the
artificially cemented sands. It is more appropriate to refer to levels
of cementstion in terms of unconfined compressive strengths. Recalling
CYCLIC BEHAVIOR 113
that it was shown, during the static testing phase of this research, that
the presence of a weak lens in a stronger mass is also reflected in this
static strength measurement, the unconfined compressive strength may be
used to compare homogeneously cemented samples to those with inconsist-
encies. Figure 7-13 plots the unconfined compressive strength versus the
cyclic shear stress ratio necessary to induce liquefaction in a given
number of cycles (10, 50, and 100).
The unconfined compressive strengths presented in Table 6-2 are
representitive of the effective cementation levels and determine the
abscissae of the data points in Figure 7-13. The cyclic shear resistance
curves shown in Figure 7-12 provide the basis for the ordinates. For
instance, the 2% cemented sand has an unconfined compressive strength of
327 KN/M1 • Examination of the proper curve in Figure 7-12, which was
developed for initial liquefaction, shows that a stress ratio of 0.375
is required to cause liquefaction in exactly 100 cycles. Similar points
are plotted for the uncemented and nonhomogeneous samples to develop the
100 cycle resistance curve.
The trend of the curves in Figure 7-13, which is asymptotic with respect
to stress ratio, is inconsistent with observed behavior; high levels of
cementation, or unconfined compressive strength, have been shown to pre-
clude liquefaction in laboratory testing (Dupas and Pecker, 1979). In a
qualitative sense, however, Figure 7-13 demonstrates that the cyclic re-
sponse of undrained, nonhomogeneously cemented soils may be distinguished
by static strength properties.
CYCLIC BEHAVIOR 114
It is apparent that static tests, particularly carefully performed in-
situ procedures on undisturbed soils, can provide enough information to
reflect the liquefaction resistance of nonhomogeneously cemented soils.
The controlling factor in these situations would seem to be compitability
between the testing device and the discontinuities in the soil.
Insofar as pore pressure development is concerned, it is evident form
Figures 7-14 and 7-15 that observations made about cemented sands, gen-
erally hold true for nonhomogeneously cemented soils. These pore pressure
ratio and strain ratio plots demonstrate the same stress ratio and axial
strain relationships seen with the homogeneous samples; at low stress
ratios and low strain levels, the cemented sand behaves similarly to un-
cemented sand. Consequently, generated pore pressures in
nonhomogeneously cemented sands may be predicted by judicious use of
Equations 7.1 through 7.3.
CYCLIC BEHAVIOR 115
0.6
::<J z er.. 0 ;::> 1-1 < E-< 0.4 u C,.) N=SO < c ~ N=lOO E-< ~
:::i c O" H 1-1
~ ..J IX. ....:i < Cl.) H 0.2 Cl.) ~ ::<J ,_.; i::r:: z E-< H :n
I 0.0 LO----.l..----1~00 ____ .i.._ ___ 20~0----"'-----30~0----"-----400
UNCONFINED COHPRESSIVE S'i'REHGTH (KN/H2)
Figure 7-13: UCS vs. stress ratio to liquefaction.
CYCLIC BEHAVIOR 116
u
b .......
Q) :::J
::I L
...... t-a: a: IJ.J a: ::::> (J') (J') IJ.J a: a.. IJ.J a: 0 a..
1. a
a.8
a.6
a.4
a.2
a.a a.a
KEY STRESS SYMBCIL RRT !Cl 0.300 C)
0.325 x 0.350 .:!>
0.400 ~
0.450 ~
NCJNHCJMCJGENECJUS
.::·· .:::ii''".,/';!ii'''l\__ RANGE CIF VALUES FCIR
. UNCEMENTED SAND !LEE ~ ALBE I SA, 19751
a.2 a.4 a.6 a.8 C'YCL IC RAT rn,
Figure 7-14: Pore pressure ratio vs. cyclic ratio (nonhomogeneous).
i. a
CYCLIC BEHAVIOR 117
.,. -w
......... c: w
II
"" L
. 0 ...... I-a: cc z ...... a: cc I-U')
1. 0
0.8
0.6
0.4
0.2
0.0 0.0
KE I STRESS SYMBCIL RAT!CI
0.300 C)
0.400 ~
0.450 ~
NONHOMCJGENECIUS
0.2 0. Lj 0.6 0.8
CICL IC RAT rn,
. Figure 7·15: Strain ratio vs. cyclic ratio (nonhomogeneous).
1. 0
CYCLIC BEHAVIOR 118 .
8.0 SUMMARY AND CONCLUSIONS
Cemented sands are prevalent throughout the world. While they are often
able to stand in slopes approaching vertical, failure of saturated de-
posits as a result of seismic activity can be catastrophic. Cementation
has been shown to increase the peak strength, stiffness and liquefaction
resistance of sands. Much of the work in this area has been done with
natural materials wherein it is difficult to isolate the parameters con-
tributing to static and cyclic strength. The present work serves to al-
leviate this condition by providing static and cyclic test data from 35
tests on carefully controlled, artificially prepared samples.
The focus of this work centered on three areas that had yet to be ad-
dressed satisfactorally by previous research:
1. What is the effect of nonhomogeneity on the liquefaction re-
sistance of lightly cemented sands?
2. How does cementation affect the volume change characteristics
of statically loaded samples?
3. Is it possible to predict the pore pressure generation of un-
drained, weakly cemented sands subjected to cyclic loading?
SUMMARY and CONCLUSIONS 119
A degree of preliminary work was necessary prior to beginning the actual
tests. An efficient sample preparation technique was developed, based
on improvement of a method devised by Rad and Clough (1982). The new
method is made possible by a mated sand rainer and mold device which is
easy to use and allows construction of homogeneous samples at controlled,
consistent, densities. It was also necessary to develop a means of
preparing layered samples to simulate cemented sand deposits with weak
lenses. This was done by stacking partially cured, homogeneous, samples
of cemented sand at two levels of cementation; essentially, a one cen-
timeter 'lens' of 1% cemented sand was embedded into a 15 centimeter
tall, 2% cemented sample. The method insures accurate control of rela-
tive thickness and degree of cementation of the respective layers.
To achieve complete saturation of the cemented material, a vacuum satu-
ration device was constructed, primarily based on the original version
described by Rad and Clough (1984).
A state-of-the-art cyclic triaxial testing apparatus was assembled
around a new MTS 445 controller. All controller components were tested
and calibrated, and the Honeywell Oscillograph , used for data retrieval,
was made compatible with the ranges of load, deformation, and pore
pressure expected from the respective transducers during normal testing.
For the consolidated, drained, static triaxial tests, 2% cemented sam-
ples were constructed to densities of 15. 00, 15. 45, and 15. 70 KN/Ml.
Layered samples at a density of 15. 70 KN/Ml were tested in the same
SUMMARY and CONCLUSIONS 120
manner. Undrained cyclic triaxial tests with pore pressure measurement
were performed on uncemented sand, 1% and 2% cemented sand, 1L.1d layered,
or nonhomogeneous, samples. The average density of all the samples
tested in cyclic fashion was 15.70 KN/M 3 •
The static testing program yielded the following observations:
1. The addition of different quantities of Portland cement to sand
samples introduces structural differences upon curing. Conse-
quently, the use of the relative density concept does not seem
applicable to these materials. For this investigation, the
writer has chosen to distinguish density by dry unit weight.
2. A weak lens is seen to lower both peak strength and stiffness
of a stronger mass. This is due primarily to a reduction in
the apparent cohesion of the composite material.
3. The absolute magnitude of volumetric strain developed at fail-
ure seems to be independent of the level of cementation.
4. The rate of volumetric expansion is related to the amount of
cementation.
5. Casagrande's critical void ratio concept, in its present form,
is not applicable to cemented sands.
SUMMARY and CONCLUSIONS 121
The undrained cyclic triaxial compression data lead to the following
conclusions:
1. Monterey #0/30 sand has a higher liquefaction resistance than
does Monterey #0 sand.
2. At low stress ratios, when a large number of cycles to
liquefaction are required, the pore pressure generation of ce-
mented sands is similar to that of uncemented sands.
3. As the stress ratio increases, the shape of the cemented pore
pressure development curve exhibits characteristics different
than that of uncemented sand. The shape of this curve has been
described and can be used in prediction for pore pressure de-
velopment in cemented sands.
4. The rate of pore pressure development seems to be controlled,
in part, by the magnitude of cyclic axial strain. Similarly,
the effects of cementation on pore pressure generation actually
becomes more evident after sample strain has destroyed some of
the sand-cement bonds.
5. A weak lens serves to lower the ability of a stronger mass to
sustain dynamic loads. This effect is seen to decrease with
decreasing stress ratio.
SUMMARY and CONCLUSIONS 122
6. If appropriate static in-situ tests are carefully performed,
the results are likely to reflect increased liquefaction re-
sistance due to cementation.
The writer suggests that future research efforts in the area of lightly
cemented sands include:
1. Testing of nonhomogeneous samples constructed by other methods,
such as continuous raining, without the possible discontinui-
ties introduced at the layer boundaries by the present tech-
nique.
2. A parametric study of layered samples focusing on the effects
of relative layer size and cementation level. This should in-
clude samples with an uncemented lens.
3. Tests on samples with different types of cementation, ideally
with cementing agents with less tendency to crystalize than
Portland cement.
4. Additional testing of reconstituted, cemented samples to de-
termine whether these materials are useful as indicators of
in-situ liquefaction resistance.
S. Further investigation into the concept of using field tests,
such as the self boring pressuremeter, to measure behavior
SUMMARY and CONCLUSIONS 123
characteristics of cemented sand, that can be related to
liquefaction resistance.
SUMMARY and CONCLUSIONS 124
APPENDIX A. EQUIPMENT IDENTIFICATION
Appendix A. EQUIPMENT IDENTIFICATION 125
Item
Load Frame
Pore Pressure Panel and Triaxial Cell
Load Cell
Pressure Transducer
Differential Pressure Transducer
Table A-la: Equipment Information
Model
RE-SS-2400E
SM-1000
EPX-lOU-100
DP15-50
Serial Number
VPI83941
VPI85879
A36761
2R3R-Dl3-l
648 59
Operating Range
1000 lbs.
0-100 psi
0-50 psi
Manufacturer/Supplier
Budd Riley Research Engineering 2640 Dundee Road San Pablo, CA 94806 (415) 223- 4798
Marshall Silver Geotechnical Equipment Corporation 151 Belle Avenue Highland Park, Illinois 60035 (312) 433-0014
Interface, Inc. 7401 E. Butherus Dr. Scottsdale, Arizona 85260 (602) 948-5555
Entran Devices, Inc. 10 Washington Avenue Fairfield, New Jersey 07006 (201) 227-1002
Validyne Engineering Company 8626 Wilber Avenue Northridge, California 91324 (800) 423-5851
Item
MTS System:
controller
valve driver
auto mode switching servo
D.C. conditioner
A.C. conditioner
limit detector
control unit
digital function generator
Visicorder
Table A-lb: Equipment Information (continued)
Serial Model Number
810R 959.93
445 .11 251
440.14 2918
440.17 264
440.21 5787
440.22 2520
440.41 672
436 .11 596
410.31 2643
1508C 0806A684
Operating Range Manufacturer/Supplier
MTS Systems Corporation Box 24012 Minneapolis, Minnesota 55424 (612) 937-4000
Honeywell Test Instruments P.O. Box 5227 4800 E. Dry Creek Denver, Colorado (303) 773-4584
Division
Road 80217
APPENDIX B. USE OF THE HTS CYCLIC TESTING APPARATUS
This appendix describes the procedure used to perform stress controlled
cyclic triaxial tests with the equipment available to the researcher
during the experimental phase of this research project. A list of all
equipment components, with pertinent information, is included in Appen-
dix A. It is suggested that the reader become adequately familiar with
the appropriate manufacturer 1 s literature before operating equipment.
Damage to the more sensitive apparati or bodily injury may otherwise
result.
The following procedure assumes that the triaxial cell, with sample, is
prepared for testing; and that the MTS 445 controller, Honeywell
Visicorder, and differential pressure transducer have been calibrated.
The reader is referred to the VP! MTS User's Guide (Milstone, 1985) for
calibration procedures.
B.1 MTS STRESS CONTROLLED CYCLIC !BIAXIAL TESTING PROCEDURE
1. Hydraulics off. Clear D/A on 440.17 auto mode switching servo mod-
ule.
(This resets error count to zero.)
Enter STROKE mode on 445 front panel, activating channel 1 (and its
indicator light on the 440.37 processor controller module).
Appendix B. Use of the MTS Cyclic Testing Apparatus 128
processor controller. Pressing the STROKE button successively will
switch the active c~annel.
2. On 440.37 processor controller: Select set point, span 1 for channel
1. Select set point, span 2 for channel 2.
(LOAD mode will be controlled by channel 2. This procedure commits
the span control dials on the 445 front panel to the respective
program modes, and activates the set point control dial for both
modes.)
3. Exercise the servo valves and the actuator:
a. On 440. 17 switching servo module: Select set point on readout
select.
b. On 445 front panel: Monitor set point on meter board by
switching to SERVO. It is more accurate to monitor settings with
a voltmeter. This can be done by patching to a voltmeter from
the output jacks that are directly below the sweep meter.
c. Adjust set point to 0.000 using set point knob at COMMAND area
of 445 controller. Apply low pressure while simultaneously
pressing interlock reset button. Hold interlock reset button
until piston has stabilized in neutral position. Both + and -
balance indicator lights will be out at this point.
Appendix B. Use of the MTS Cyclic Testing Apparatus 129
d. Adjust span 1 to approximately 2 volts to control stroke length.
e. Apply high pressure hydraulics.
f. On 410 function generator: Choose invert-sine wave; set fre-
quency of RATEl to 1 cycle per second.
g. Begin program by pressing RUN button on 436 control unit. This
will commence the piston to cycling the chosen distance (span)
about the set point.
h. Span may be adjusted, if desired, while program is running.
4. This warmup time (1/2 to 1 hr.) may be used to saturate sample which
has not yet been placed in load frame.
Stop program by pressing STOP button on 436 control unit.
5. Switch to LOAD mode:
a. Set range of load cell conditioner and apply limit detect to
protect load cell from overload:
• Choose range 1 - 4 on 440.21 load cell conditioner module.
This will effectively increase the sensitivity of load cell
output by factors of 1, 2, 5, and 10 respectively. (ex.:
Appendix B. Use of the MTS Cyclic Testing Apparatus 130
For 100 lb. load cell at range setting 3, lOV output re-
presents 20 lbs.)
• Set upper and lower (tension and compression) limit detect
values for XDCRl on 440.41B module. Limits are chosen based
on load cell capacity, XDCRl calibration range, and antic-
ipated maximum loads.
• Flip XDCRl toggle switch on 440.41B module to INTLK. This
will cause system to interlock (shut down) if chosen limit
is exceeded, protecting load cell from overload. Look at
COMMAND area of 445 front panel. XDCRl limit detect lights
will glow green if interlocking limit option has been prop-
erly activated.
b. Turn hydraulics off with 436 control unit. Switch to LOAD mode
and channel 2 by pressing LOAD button on 445 front panel.
c. Zero the load cell feed back:
• Monitor XDCRl (load cell feedback) with voltmeter patched
to output jacks below sweep meter.
• While there is no load applied to the load cell, zero the
feedback by adjusting the balance (ZERO dial) of the load
cell 440.21 D.C. conditioner. (Rightmost module behind 445
front panel.)
Appendix B. Use of the MTS Cyclic Testing Apparatus 131
6. Fit triaxial cell onto MTS load frame:
a. Apply low pressure hydraulics. Interlock should not have been
activated since there is no error between the load cell feedback
and the set point which are both 0.000.
b. Applying a compression load to the load cell, by hand, will force
the piston to move down as the feedback system attempts to return
the measured load to 0.000.
c. Set triaxial cell on piston platen, screwing wing-bolts in
place. The bolts should be left loose until step-g, after the
cell has been moved into its final position.
d. Applying a tension load to the load cell, by hand, will raise
the piston with the cell into contact with the threaded rod at
the load cell. Keep fingers out of dangerous places.
e. Tap cell into concentric position with load rod in contact with
coupling barrel. Contact is maintained by the tensile force
applied to the load cell.
f. When triaxial cell is concentric with load cell, screw coupling
barrel a distance of about 4 threads onto threaded portion of
load rod (maintaining tension force until threads are engaged.)
Secure top and bottom of coupling barrel with lock nuts.
Appendix B. Use of the MTS Cyclic Testing Apparatus 132
g. Tighten wing-bolts to secure triaxial cell to MTS piston.
7. Isotropically consolidate sample:
a. Set compensating axial load to affect isotropic stress condi·
tions:
1) Loading rod remains locked in position.
2) Load has been determined experimentally for each consol·
idation pressure, or it is calculated as:
(cell press.*load rod area) - wgt.of(rod+platen)
3) While monitoring XDCRl, adjust set point to apply compen-
sating load. (Counterclockwise adjustment induces com·
pression; clockwise adjustment induces tension.)
b. Consolidate sample:
1) Record initial burette reading.
2) Monitor XDCR3 (LVDT feedback) and record initial sample
height.
3) Close valve to burette such that sample is undrained.
Appendix B. Use of the MTS Cyclic Testing Apparatus 133
4) Increase cell pressure to chosen consolidation pressure.
5) Unlock piston to apply compensating axial load.
6) Open valve to commence consolidation.
7) Following consolidation, record final burette reading and
final XDCR3 reading. Volume change and axial strain due to
consolidation can then be calculated by applying the appro-
priate calibration factors.
8. Prepare Honeywell Visicorder:
• Aim galvanometers to appropriate zero locations.
• Set time gap and paper speed.
(Time gap of 1.0 seconds and paper speed of Smm/second are con-
venient.)
9. Set amplitude of loading program (deviatoric load):
a. Amplitude of deviatoric load is calculated from chosen stress
ratio:
Dev.Str.=SR*2*init.eff.consol.press.*sample area
where: sample area has been corrected for consolidation.
b. Set deviatoric load by adjusting span 2 to proper dial setting.
Appendix B. Use of the MTS Cyclic Testing Apparatus 134
10. Verify deviatoric load:
a. Lock load rod to the triaxial cell.
b. Monitor XDCRl by connecting an oscillocope to the output jacks
on the meter board.
Start paper advance of Honeywell Visicorder for additional mon-
itoring source. This output is convenient as the hard copy is
easily scaled for higher accuracy.
c. Begin program by hitting RUN button on the 436 controller. This
will generate feedback from the load cell that can be monitored
at the oscilloscope and Visicorder, while adjusting the span to
obtain the correct deviatoric load. This procedure also warms
up the feedback system and allows the loading system to seat
itself, without disturbing the sample.
d. Stop program.
11. Liquefy sample:
a. Unlock load rod.
b. Close valve to burette such that sample is undrained.
c. Start paper advance of Honeywell Visicorder.
Appendix B. Use of the MTS Cyclic Testing Apparatus 135
d. Hit RUN. Watch sample and Visicorder for signs of liqeufaction.
e. After sample has liquefied:
• Stop program.
• Open valve to burette allowing excess pore pressures to
dissipate. (This will indicate if there was any zero shift
at the Visicorder.)
• Stop Visicorder paper advance.
12. Remove sample from load frame:
a. Close valves to drain lines at pressure panel and at sample; then
remove cell pressure line and drainage lines from triaxial cell.
b. Monitor XDCRl and return to zero by adjusting set point clock-
wise.
c. Loosen lock nuts and back off coupling barrel from load rod.
d. Apply compression load to load cell, by hand, forcing actuator
to lower the cell.
e. Switch hydraulics off. Remove anchor bolts and remove cell from
load frame. (If convenient, it is helpful to empty the cell of
water before lifting it from MTS frame. )
Appendix B. Use of the MTS Cyclic Testing Apparatus 136
REFERENCES
Bishop, A. W. and Henkel D. J. , Measurement of Soil Pr2perties in the Triaxial Test. Second Edition, Edward Arnold Publishers, Ltd. , London, England, 1962.
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