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Sample Report
Edited by BK & CW 12/28/04
Sample Report
EFFECTS OF VOID REDISTRIBUTION
ON LIQUEFACTION FLOW OF LAYERED SOIL
Submitted to US-Japan Cooperative Research in
Urban Earthquake Disaster Mitigation
Principal Investigators:
Bruce L. Kutter and Ross W. Boulanger
University of California at Davis
Principal Collaborator from Japan:
Takeji Kokusho, Chuo University
COVER SHEET FOR PROPOSAL TO THE NATIONAL SCIENCE FOUNDATION
PROGRAM ANNOUNCEMENT/SOLICITATION NO./CLOSING DATE/if not in response to a program announcement/solicitation enter NSF 00-2
NSF9836
FOR NSF USE ONLY
NSF PROPOSAL NUMBER
10/01/99
FOR CONSIDERATION BY NSF ORGANIZATION UNIT(S)
0070111
(Indicate the most specific unit known, i.e. program, division, etc.)
CMS - Division of Civil and Mechanical Systems
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047120084
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IS THIS PROPOSAL BEING SUBMITTED TO ANOTHER FEDERAL
AGENCY?
YES
NO
IF YES, LIST ACRONYMS(S)
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A RENEWAL
AN ACCOMPLISHMENT-BASED RENEWAL
946036494
NAME OF ORGANIZATION TO WHICH AWARD SHOULD BE MADE
ADDRESS OF AWARDEE ORGANIZATION, INCLUDING 9 DIGIT ZIP CODE
University of California-Davis
OVCR/Sponsored Programs
Davis, CA. 956168671
University of California-Davis
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0013136000
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IS AWARDEE ORGANIZATION (Check All That Apply)
(See GPG II.D.1 For Definitions)
FOR-PROFIT ORGANIZATION
TITLE OF PROPOSED PROJECT
REQUESTED AMOUNT
441,631
$
SMALL BUSINESS
MINORITY BUSINESS
WOMAN-OWNED BUSINESS
Effects of Void Redistribution on Liquefaction Flow of Layered Soils
PROPOSED DURATION (1-60 MONTHS)
36
REQUESTED STARTING DATE
SHOW RELATED PREPROPOSAL NO.,
IF APPLICABLE
07/01/00
months
CHECK APPROPRIATE BOX(ES) IF THIS PROPOSAL INCLUDES ANY OF THE ITEMS LISTED BELOW
BEGINNING INVESTIGATOR (GPG 1.A.3)
VERTEBRATE ANIMALS (GPG II.D.12) IACUC App. Date
DISCLOSURE OF LOBBYING ACTIVITIES (GPG II.D.1)
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INTERNATIONAL COOPERATIVE ACTIVITIES: COUNTRY/COUNTRIES
or IRB App. Date
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FACILITATION FOR SCIENTISTS/ENGINEERS WITH DISABILITIES (GPG V.G.)
RESEARCH OPPORTUNITY AWARD (GPG V.H)
PI/PD DEPARTMENT
PI/PD POSTAL ADDRESS
One Shields Avenue, 116 Everson Hall
Civil & Environmental Engr
PI/PD FAX NUMBER
Davis, CA 956168671
United States
530-752-7872
NAMES (TYPED)
High Degree
Yr of Degree
Telephone Number
Electronic Mail Address
PhD
1983
530-752-8099
[email protected]
PhD
1990
530-752-2947
[email protected]
PI/PD NAME
Bruce L Kutter
CO-PI/PD
Ross W Boulanger
CO-PI/PD
CO-PI/PD
CO-PI/PD
NSF Form 1207 (10/99)
Page 1 of 2
EFFECTS OF VOID REDISTRIBUTION ON LIQUEFACTION FLOW OF
LAYERED SOILS
PROJECT SUMMARY
The assessment the post-liquefaction shear resistance behavior of soil is widely
recognized as a controlling factor in many large remediation projects throughout the
country and world. Decisions on whether to proceed with costly ground improvement
projects to mitigate liquefaction hazards often hinge on highly uncertain estimations of
post-liquefaction shear resistance of the soil. The objective of this research project is to
better understand the sources of uncertainty.
One likely source of uncertainty is the lack of procedures to evaluate the effects of void
redistribution on the post-liquefaction shear strength. Void redistribution may be
associated with accumulation of earthquake induced pore pressures near interfaces
between permeable and impermeable soil and by particle intermixing. A program of
dynamic centrifuge modeling tests and laboratory triaxial tests are proposed, in
collaboration with a proposed program of 1-g shaking table tests conducted by Professor
Kokusho at Chuo University, Japan, to study this problem. The centrifuge tests, to be
conducted on the 9 m centrifuge at UC Davis will include models with multiple layers of
contrasting permeability.
In prior research Kokusho has observed flow failures and the formation of water
interlayers beneath impermeable layers even in steeply sloping ground. Water
interlayers, an extreme form of void redistribution raise serious questions regarding
validity of typical stability calculations. Collaboration with Professor Kokusho will
greatly enhance the benefits of this research by allowing comparisons between shaking
table and centrifuge tests over a range of testing conditions. Unless flow failures can be
recreated in both centrifuge and 1-g physical models, the degree to which either modeling
method reproduces an actual liquefaction flow mechanism will remain in question.
A unique feature of this research proposal is to bring together a Board of Consultants,
composed of recognized US and Japanese experts in soil liquefaction, that would
collaborate in the design of the centrifuge experiments and in the back-analysis of the
model results using the same methods used for interpreting case histories. It is hoped that
this collaborative interchange will benefit the profession by bringing different views and
interpretations to bear on the same set of experimental data and help in dissemination of
information and knowledge.
The proposed work includes funding to support, train, and provide valuable experience to
graduate and undergraduate students. The MESA, MORE, and WIE programs at UC
Davis have agreed to help us recruit from a diverse pool of applicants for the
undergraduate positions. The opportunities for students to design, conduct and analyze
the large scale experiments and to meet renowned experts from the US and Japan will be
an extremely valuable.
TABLE OF CONTENTS
For font size and page formatting specifications, see GPG section II.C.
Section
Total No. of
Pages in Section
Page No.*
(Optional)*
Cover Sheet (NSF Form 1207) (Submit Page 2 with original proposal only)
A
Project Summary
(not to exceed 1 page)
1
B
Table of Contents
(NSF Form 1359)
1
C
Project Description (plus Results from Prior
NSF Support) (not to exceed 15 pages) (Exceed only if allowed by a
specific program announcement/solicitation or if approved in
advance by the appropriate NSF Assistant Director or designee)
17
D
References Cited
2
E
Biographical Sketches
F
Budget
(Not to exceed 2 pages each)
6
8
(NSF Form 1030, plus up to 3 pages of budget justification)
4
G
Current and Pending Support
H
Facilities, Equipment and Other Resources (NSF Form 1363)
1
I
Special Information/Supplementary Documentation
0
J
Appendix (List below. )
(Include only if allowed by a specific program announcement/
solicitation or if approved in advance by the appropriate NSF
Assistant Director or designee)
(NSF Form 1239)
Appendix Items:
*Proposers may select any numbering mechanism for the proposal. The entire proposal however, must be paginated.
Complete both columns only if the proposal is numbered consecutively.
NSF Form 1359 (10/99)
EFFECTS OF VOID REDISTRIBUTION
ON LIQUEFACTION FLOW OF LAYERED SOIL
Submitted to US-Japan Cooperative Research in
Urban Earthquake Disaster Mitigation
Principal Investigators:
Bruce L. Kutter and Ross W. Boulanger
University of California at Davis
Principal Collaborator from Japan:
Takeji Kokusho, Chuo University
BACKGROUND AND STATE OF KNOWLEDGE
The uncertainty in assessing the post-liquefaction shear resistance behavior of soil is
widely recognized as a controlling factor in many large remediation projects throughout
the country and world. Decisions on whether to proceed with costly ground improvement
projects to mitigate liquefaction hazards often hinge on uncertain estimates of postliquefaction shear resistance of the soil. The objective of this research project is to
investigate the role of void redistribution, which may be associated with impeded
drainage or particle intermixing, on the post-liquefaction shear resistance behavior of
sand. A program of dynamic centrifuge modeling tests and laboratory triaxial tests are
proposed, in collaboration with a proposed program of 1-g shaking table tests at Chuo
University, Japan, to study this problem. Background information and the state of
knowledge related to this problem are discussed below.
Evaluating potential instability in liquefying soils, or estimating the residual shear
strength (Sr) of a liquefied soil, is a difficult task. Recent experimental studies have
contributed to an improved understanding of factors affecting Sr, and helped to reduce
large differences between Sr values back-calculated from case histories and Sr values
obtained from laboratory testing of field samples (with appropriate corrections for
disturbance per the steady state approach). Laboratory testing by several investigators has
shown that Sr, or the shear resistance over a large range of strains, is affected by stress
path (extension vs. simple shear vs. compression), fabric, consolidation stress, fines
content, and strain level. For example, Vaid et al. (1995) showed a factor of 5 difference
in the deviator stress at 8% shear strain for a sand tested along different stress paths in a
hollow cylinder testing device. A basic question remains, however, whether or not
laboratory testing fully captures the mechanisms of instability that act in situ.
In this regard, void redistribution due to earthquake loading has been identified as
potentially having an important influence on the in situ residual shear strength, or steady
state strength, of saturated sands (e.g., NRC 1985). The process of void redistribution
within a globally undrained sand mass was termed Mechanism B by NRC (1985), and a
potential situation where it might occur was illustrated by the schematic in Figure 1. Of
related interest is Mechanism C (NRC 1985) where the outward flow of pore water due to
Figure 1. Mechanism B by NRC (1985) Example of potential void redistribution
within a globally undrained sand layer.
Figure 2. Mechanism C by NRC (1985) –
Example of potential failure by spreading of
excess pore pressures with global volume
changes.
excess pore pressures in a sand mass, such as illustrated in Figure 2, could spread into
overlying soils and/or cause a loosening of the upper portion of the sand. In this case, the
sand is neither globally nor locally undrained, since there is drainage from the sand.
Terzaghi and Peck (1967) pointed out the potential importance of redistribution of
pore pressures in horizontal seams of permeable soil on the stability of a slope, as shown
in Figure 3. The higher permeability sand seam would allow high consolidation-induced
pore pressures in the clay stratum below the embankment to be redistributed towards the
toe of the embankment. The resulting additional increase in pore pressures (and hence
piezometric line as shown in their figure) in the sand seam beneath the toe would reduce
the shear strength along the seam and reduce the stability of the embankment. A similar
mechanism could occur if layers of high permeability transfer earthquake-induced excess
pore pressures from a distance to shear zones in a slope.
The potential significance of in situ void redistribution, particularly with regard to
mechanism B (Fig. 1), remains controversial (e.g., Seed 1986, McRoberts & Sladen
1992, Castro 1995). Void redistribution was first observed to occur within laboratory
sand specimens (Casagrande & Rendon 1978, Gilbert 1984). Casagrande (1980)
subsequently suggested that void (or water content) redistribution was a phenomenon
Figure 3. Effect of horizontal layering on slope instability in presence of
consolidation-induced pore pressure. (Terzaghi and Peck, 1967)
associated with cyclic laboratory tests and may not reflect in situ behavior. More
extensive void redistribution resulting in the formation of water inter-layers between
stratified soil layers was observed in shaking table models by Liu & Qiao (1984).
Arulanandan et al. (1993) reported redistribution of densities within a globally-undrained
sand layer, confined by clay layers, within a model embankment tested in a centrifuge,
but there are several limitations in the interpretation of these results as noted by Castro
(1995). Centrifuge tests of gentle slopes by Fiegel & Kutter (1994) showed that the
presence of a lower permeability soil layer affected the distribution of deformations with
the slope; A concentration of deformations developed at the interface of a liquefying sand
layer and an overlying silt layer, whereas deformations were more uniformly distributed
in homogenous slopes of sand.
More recently, the introduction of thin silt layers into otherwise homogenous sand
models on a shaking table, was shown by Kokusho (1999) and Kokusho et al. (1998) to
lead to the formation of water interlayers or void redistribution, both during and after
shaking. Kokusho’s dramatic video recordings of failure mechanisms show that large
delayed flow failures occur when silt layering is present. Without silt layers, the
deformations stop at the end of shaking. One of Kokusho’s experiments, shown in Figure
4, involved an arc of silt within the slope. Shaking was perpendicular to the slope so
inertial forces did not drive slope deformations. Soil above the silt continued to deform
after the end of shaking, while soil below the silt arc did not (Figure 5). Video recordings
showed that a water interlayer formed along a limited portion of the silt arc. The postshaking deformation above the silt arc was roughly equal to the shaking-induced
deformations. A second test was performed for the identical homogenous slope of sand
but without any silt arc. In this test, the deformations ceased at the end of shaking as
shown in Figure 6. The shaking table results in Figures 5 and 6 illustrate that impeded
drainage can have a major role in timing and mechanism of liquefaction-induced
deformations. Kokusho’s observation of water interlayers in steeply sloping ground has
significant implications; it is an extreme form of void redistribution. The occurrence of
water interlayers in the shaking table test may be biased by low effective stress levels and
transverse direction of shaking. If these interlayers could also be observed in centrifuge
model tests, the possibility of their occurrence in the field will be further substantiated.
Disagreement in the profession regarding the potential for void redistribution in the
field and its implications for design would seem to have two main aspects. First, field
observations only reflect the consequences of any void redistribution, and hence its
occurrence or nonoccurrence can only be inferred rather than conclusively demonstrated.
Secondly, physical mechanisms for void redistribution as derived from soil mechanics
principles are not well developed, and the unanswered theoretical questions can lead to
doubts as to the significance of such a mechanism.
Boulanger (1998) described a quantitative mechanism for void redistribution in sand
following earthquake shaking for the simplest case of an infinite slope. The analysis
results suggest that void redistribution is not just an artifact of laboratory testing, but
rather may be more pronounced in the field due to the in situ gradients of stress and pore
pressure that are not recreated in laboratory element tests (e.g, triaxial, simple shear). The
implication is that the in situ Sr of liquefied soil depends on the in situ boundary and
Figure 4. Shaking Table Test with a Silt Arc to Study Effect of Water Film (Kokusho 1999)
Figure 5. Deformation of Points Above Silt
Arc Continued After Shaking
(Kokusho 1999)
Figure 6. Deformation of Points in the
Homogenous Slope Without a Silt Arc
Stopped After Shaking (Kokusho 1999)
loading conditions (stratigraphy, permeabilities, earthquake characteristics, stress path) as
well as on the pre-earthquake soil properties and state.
A NSF-sponsored workshop entitled “Post-Liquefaction Shear Strength of Granular
Soils”, was held at the University of Illinois, in April 1997. In his keynote lecture at the
workshop, Martin (1997) stated “It has been observed in past earthquakes that, in some
instances, large slope displacements have been initiated sometime after the earthquake
ground shaking ceased. This suggests that pore pressure redistribution may be affecting
the overall shearing resistance of the soil mass.” In his keynote lecture, Castro (1997)
discusses the possibility of void redistribution, and states that “The [redistribution] issue
is far from clear.” Castro also points out that if there is redistribution, the redistribution
“will in no way be reflected in the results of SPT or CPT index tests.” In another keynote
lecture at the workshop, Byrne and Beaty (1977) point out that granular material is
generally nonhomogeneous comprising loose, dense, fine and coarse zones. They
introduce the idea that intermixing of a coarse uniform soil with a fine uniform soil will
produce a mixture with greatly reduced residual strength which can result in a flow
failure. Such intermixing of particles could be viewed as another form of void
redistribution. Byrne and Beaty (1997) cite a case history where this mixing caused a
flow failure at a mine in Zambia, and they posed the question: “Was mixing a factor at
the Lower San Fernando Dam?”
From the three keynote lectures discussed above, basic questions about the
importance of nonhomogeneities and layering are raised. The applicability of centrifuge
testing to estimate the shear strength of liquefied soil, the evaluation of the effects of
drainage and mixing during flow, the re-evaluation of field case histories and the
augmentation of case histories of flow slides using physical models were all cited in the
workshop summary and recommendations. Our proposal is to investigate influences of
layering and inhomogeneity on void redistribution associated with flow slide phenomena.
The back-calculation of shear resistance from case histories can not distinguish
between mechanisms. For example, a significant issue is how to distinguish between
deformations that are due to cyclically-induced stresses that never exceed the soil’s full
undrained shear resistance, versus deformations due to cyclic stresses temporarily
exceeding the soils full undrained shear resistance. In many cases, herein referred to as
“lateral spreads” deformations are caused by seismically induced cyclic loads
superimposed on gravity loads. In other cases, herein referred to as “flow failures”, large
deformations occurred after shaking under the influence of monotonic gravity loads. Both
cases may be potential affected by void redistribution (whether through impeded drainage
or particle intermixing). The appropriate “strengths” to use for the prediction of
deformations cause by lateral spreads and for assessment of flow failures are likely to be
completely different.
These complications are illustrated by the shaking table results of Kokusho (1999)
shown in Figures 4 to 6. Significant differences in displacements occurred between the
two models, with the only difference being the presence of a thin silt interlayer (the rest
of the sand slope was at the same initial density). If Sr values for the sand were backcalculated based on the observed deformations, as has been largely done for past case
histories, then the Sr values would be different for these two models. This illustrates how
the back-calculated Sr from case histories are more likely a macro response (as
recognized by Seed 1986).
OBJECTIVES AND SIGNIFICANCE
One of the objectives of this research project is to better understand the factors
that affect the uncertainty in the post-liquefaction shear resistance of soil. The emphasis
will be on understanding the mechanisms and significance of void redistribution on the
development of liquefaction-induced deformations, including its effects on the backcalculation of apparent (or residual) shear resistance using the same procedures that have
been used to interpret case histories. The apparent or residual shear resistance of liquefied
soil (Sr) back-calculated from observed deformation is a macro-response that may
strongly depend on numerous factors like drainage boundary conditions. These
complications may limit the conditions where Sr may reasonably be correlated to initial
conditions as represented by SPT and CPT penetration resistances alone.
Current design procedures used in practice do not explicitly acknowledge that pore
pressure or void redistribution can strongly affect the apparent “residual” strength of
liquefied soil. Methods derived from laboratory element tests, such as the steady state
approach using field samples or suggested normalized strengths (Sr/σv′) derived from
tests on reconstituted specimens, implicitly ignore the effects of pore pressure or void
redistribution. These approaches may prove to be unconservative under certain adverse
drainage or layering conditions. When it comes to back-calculation of Sr from case
histories, the question is whether or not the lowest Sr values already reflect adverse void
redistribution effects or not. Identifying these limitations in current design procedures can
lead to better designs that mitigate the effects of impeded drainage in a rational way.
Collaboration with Professor Kokusho will greatly enhance the benefits of this
research by allowing comparisons between shaking table and centrifuge tests over a range
of testing conditions. Kokusho (1999) has already completed a series of tests
investigating the role of impeded drainage, some of which have not yet been published,
and is submitting a proposal to perform additional shaking table studies over a broader
range of conditions. A letter from Professor Kokusho describing his intent to collaborate
on these studies is attached.
The mechanisms associated with void redistribution [or water film formation
(Kokusho 1999)] should be identifiable in both shaking table (1-g) and centrifuge
modeling studies. Unless the mechanisms can be recreated in both methods of physical
modeling, the degree to which either modeling method reproduces an actual field
mechanism will remain in question. It would be reasonably questioned whether the
limitations of scaling (at 1-g or in a centrifuge) were affecting the magnitude of the
observed effects of void redistribution. Questions regarding scaling effects would include
not only the scale of any loosening zone (or bifurcating interface) but also the rate of pore
pressure migration which would affect the rate of void redistribution or water film
formation. Thus, there is a strong benefit to a coordinated modeling effort using 1-g and
centrifuge models to increase confidence that the physical models are capturing a
mechanism that can develop in the field.
Most numerical modeling methods for capturing liquefaction-induced
deformations do not attempt to accurately capture the effects of pore pressure
redistribution and the potential for water film interlayer formation or loosening of thin
zones of sand near impeded drainage boundaries. Again, the first step is to identify the
mechanisms and the range of conditions where their effects are important. The need to
numerically model these behaviors with refined constitutive models or numerical
schemes will be clarified by the proposed experiments.
Another objective of this research proposal is to bring together a Board of
Consultants, composed of recognized experts in soil liquefaction, who would collaborate
in the design of the centrifuge experiments and in the back-analysis of the model results
using the same methods used for interpreting case histories. It is hoped that this
collaborative interchange will benefit the profession by bringing different views and
interpretations to bear on the same set of experimental data.
BROADER IMPLICATIONS
Engineering undergraduates will be employed throughout this project to provide
an integrated educational and research experience. Both PI’s have consistently involved
undergraduates in geotechnical research projects; this past year alone they have employed
Amy Smith, Sam Shiotani, and Pongphan Chauvapun, and have guided other
undergraduates through independent research studies.
For the proposed work we plan to hire two undergraduate students to work part
time throughout the duration of the project. One of these students will be an advanced
undergraduate that has completed undergraduate courses in geotechnical and earthquake
engineering. This undergraduate will be expected to fully contribute to the project as a
“researcher”. The second undergraduate will be recruited as a starting freshman Civil
Engineering Major to assist the graduate students and to learn what is involved in
research and to begin considering pursuit of education beyond a Bachelors Degree. We
will directly contact the MESA Engineering Program (MEP), Mentorships and
Opportunities for Research in Engineering Program (MORE) and the Center for Women
in Engineering at UC Davis to connect with traditionally underrepresented groups of
students for these positions. The MESA program at Davis has already agreed to refer
promising freshman to us for this endeavor.
Doctoral and Masters students will be employed under this project. Research on
the large centrifuge provides a broad background and training to graduate students,
preparing them for practice or research careers. They learn experimental techniques for
soils, advanced instrumentation and control systems, large data set management skills,
and visualization techniques in addition to their primary research on the geotechnical
aspects of their research topic.
Participation of underrepresented groups has been a consistent goal of the PI’s. At
present, they together support six female students (5 graduate and 1 undergraduate: Berna
Sunman, Tara Hutchinson, Christina Curras, Maria Hollister, Key Rosebrook, and Amy
Nelson). Other supported students are ethnically and internationally diverse.
The large centrifuge facilities at the Center for Geotechnical Modeling are used in
laboratory sessions for three courses: the freshman course on Introduction to Civil and
Environmental Engineering (ECI-3) and the upper division courses Soil Mechanics (ECI171L) and Data Acquisition, Visualization and Control (ECI-121). These visiting
sessions are often planned to coincide with ongoing experiments and thus may coincide
with some of the tests proposed herein. The instrumentation facilities and control systems
are used in the ECI-121 laboratory session.
All centrifuge test results will be documented in data reports, including all raw
electronic test data. The Center for Geotechnical Modeling has openly distributed data
reports for tests over the past three years, and provided this data over the internet or on
disk to numerous other researchers. Data reports are fully contained documents that allow
other researchers to analyze the data. Data reports and their availability are described at
http://cgm.engr.ucdavis.edu/. An eventual goal of the Center is to be able to transmit live
video of the test preparation, testing, and test dissection over a network, such as
envisioned through the NEES program. For the present project copies of video of flow
failures will be posted on the internet after the experiments.
The basic physics involved in post-liquefaction behavior include a complex
system of two-phase coupled mechanical/hydraulic behavior that may include localized
bifurcation and water interlayer formation. Understanding these basic physical
mechanisms has the broadest implications for the scientific and technological
advancement of engineering procedures used to design structures subject to such
behavior.
WORK PLAN
The research will involve the following major tasks:
1. Model tests on the centrifuge.
2. Comparison with model tests on 1-g shaking table.
3. Back-calculation of the relevant strength by different proposed procedures, and
evaluation of post-shaking deformations or other observations that indicate
that pore pressure redistribution is or is not significant for each model.
4. Triaxial testing in compression and extension to measure the undrained stressstrain behavior of the soil.
5. Integration of results and summary of findings including reconciling backcalculated strengths with laboratory test results.
A unique feature of this proposal is the establishment of a Board of Consultants that will:
1. Carefully review the planned centrifuge experiments before the tests to ensure
that sufficient data will be retrieved to enable accurate back-calculation of the
relevant strength by existing procedures.
2. To check the back-calculation procedures to ensure proper implementation of
different methods of evaluating the post-liquefaction shear strength.
3. To review the plan for conducting laboratory triaxial compression and extension
testing.
4. Compare the strengths of liquefied soil calculated and measured by the various
tests and procedures.
The following individuals have been contacted and have already agreed to serve on this
Board:
Takeji Kokusho, Chuo University
Gonzalo Castro, GEI Consultants
Ricardo Dobry, Rensselaer Polytechnic Institute
Steven Kramer, University of Washington
Professor Kokusho will be a key collaborator in coordinating experimental studies
between the proposed 1-g shaking table studies at Chuo University and the centrifuge
studies proposed herein. Contingent upon Professor Kokusho’s input and available
funding, we plan to add at least one additional Japanese researcher to the Board of
Consultants. Getting other influential researchers and engineers together to discuss the
test results and analysis will have the added benefit of helping to build a consensus on the
controversial topic of the “strength” of liquefied soil.
SCHEDULE
The research will be carried out in three phases:
I. Planning and conducting the first four centrifuge experiments, studying existing and
new data generated by Professor Kokusho, and planning of triaxial tests.
II. Back calculations from centrifuge tests and shaking table tests, conducting two
additional centrifuge tests, and conducting triaxial tests.
III. Summary, comparison, analysis and reporting.
PHASE I. Duration 18 months.
The first meeting of the Board of Consultants, the PI’s, and research students will
be about three months after the project is funded, before the centrifuge tests are
conducted. At this meeting a detailed plan for centrifuge testing will be presented by the
PI’s and the Board will provide criticism and advice. The members of the Board will each
be asked to make a presentation on how they think the experiments should be
instrumented and to make a detailed description of the desired back analysis procedures.
The advice of the Board will be incorporated in the experimental plan, and the
centrifuge model tests will be conducted. The first four tests will be conducted using the
large shaker on the large centrifuge, at a centrifugal acceleration of 40 g. In these tests, it
is anticipated that at least 2 flow failures will be produced. The details of the experiments
are described later in this proposal. The data from each of these experiments will be
published in separate data reports and distributed to the Board and made available to the
public via pdf files at http://cgm.engr.ucdavis.edu/.
PHASE II. (12 months)
Phase II will begin with the second meeting of the Board of Consultants, the PI’s
and research students. Centrifuge results and preliminary back analysis of the
experiments (to determine the appropriate post-liquefaction shear strength) will also be
reported to the Board. In addition, the plan for laboratory element testing will be
presented and discussed. The Board will critique and review the planned and completed
centrifuge tests, proposed laboratory element testing and the preliminary back analysis
procedures.
Element tests will be conducted to investigate the peak strength, and monotonic
strength of the soil using triaxial compression and extension testing. The intention is to
determine the location of the steady state line in e-lnp′ space and determine the effect of
these stress paths on the stress-strain response.
It is anticipated that the results and the preliminary back analysis will raise some
questions as well as answers. In Phase II, two more centrifuge tests will be planned and
conducted at either UC Davis or another centrifuge depending on the advice of the Board
of Consultants. The potential benefits of performing tests at another centrifuge could be,
for example, to evaluate the repeatability of any observed phenomena at a higher
centrifugal acceleration on a smaller centrifuge.
During Phase II, back analysis of the results will be carried out in detail according
to the recommendations of the Board.
PHASE III. Duration: 6 months
The results of all element tests, centrifuge tests, and back analyses will be
summarized and compared and presented in a draft final report, which will be distributed
to the Board of Consultants for their review and comments. One last meeting of the
Board will be held near the end of PHASE III to help establish a consensus on the topic
of void redistribution on flow failures. If the project is as successful as we anticipate, it
may be appropriate to expand the final Board meeting into a small workshop to include
more practicing engineers and researchers.
CENTRIFUGE AND LABORATORY TEST PROGRAM
The details of the centrifuge and laboratory testing program may change in
response to the recommendations of the Board of Consultants, as described in the above.
Figure 7 shows three different centrifuge model configurations that will be the basis of
the proposal put to the Board for discussion at the first meeting.
Proposed Centrifuge Tests
A total of six centrifuge tests are proposed. One pair of of centrifuge tests will
provide direct comparison against a pair of shaking table tests to be performed at Chuo
University under a pending proposal by Professor Kokusho. The design of these two tests
will be finalized upon funding of our individual proposals, but is expected to be a
variation on the tests described above (Figures 4-6). One test will likely incorporate
horizontal silt interlayers Figure 7(a) and another test will be homogenous fine sand
throughout. The sand will be placed at a relative density of about 40% using dry
pluviation and vacuum saturation. About 75 instruments will be used to monitor each
experiment (about 30 accelerometers, 30 pore pressure transducers and 15 displacement
transducers).
silt layer
(a)
silt layer
fine sand embankment
(b)
silt layer
silt layer
fine sand
embankment
gravel layer
(c)
finely stratified-hydraulic
fill embankment
Figure 7. Schematic plans for 6 model tests; Two variations will be tested for each of the
three configurations.
We will use Nevada sand, which is the same sand used in VELACS and most of
our past model studies. The silt will be nonplastic. A mixture of water and methyl
cellulose will be used for the pore fluid, thereby providing improved scaling of the
consolidation behavior. It is expected that the tests will be performed in our rigid
container with polycarbonate walls that allow observation of slope deformations using
side-mounted cameras. All tests will be performed at a centrifugal acceleration of about
40 g.
Shaking motions for these models will be along the long-axis of the model and
hence coincide with the dip of the slope. Therefore, the inertial loads associated with
shaking will contribute to slope deformations, which is one aspect that will be different
from the tests performed by Kokusho (see Figure 4 – shaking is along the strike of the
slope). The proposed shaking will consist of a very short duration motion, perhaps just a
single cycle of shaking. If no failure occurs in a few seconds, a larger pulse will be
applied, and a few seconds later an even larger pulse will be applied until a failure occurs.
If a flow failure still does not occur, a longer duration earthquake will be applied. All of
these shakes will follow each other within a few seconds, to minimize the strengthening
of the soil due to consolidation between shaking events.
Another pair of tests (Figure 7(b)) will be designed to combine the deleterious
effects of discontinuous layers of more permeable soil in addition to silt layers. The
overall geometry and sand properties of the models shown in 7(b) will be very similar to
those depicted in 7(a) to provide cross-comparisons. Large pore pressures will be
generated by earthquake shaking of these models. The gravel layer across the model
below the level of the toe of the slope is expected to rapidly conduct pore water from a
region of high overburden (high excess pore pressure) toward the toe of the slope. This is
analogous to the effect of the permeable layer in the problem (Figure 3) posed by
Terzaghi and Peck (1967). Arrows in figure 7(b) indicate the expected flow of water into
the gravel under deep backfill and exit of water near the toe of the slope. It is suggested
in Figure 7(b) that silt layers could also be used to restrict the dissipation of pore
pressure, but the value of the additional complexity of the silt layers will be discussed
with the Board of Consultants.
The last pair of centrifuge tests are tentatively planned to represent an
embankment constructed with hydraulic silty sand fill. The most well documented
example of an earthquake-induced flow failure is probably the collapse of the Lower San
Fernando Dam in 1971. This failure produced very large deformations that were
obviously driven by gravity loads acting on a soil mass weakened by an earthquake; the
flow occurred 20 to 30 seconds after the shaking stopped (Seed et al. 1989). In some
respects, the proposed centrifuge tests will attempt to represent conditions similar to
those in the Lower San Fernando Dam. A model embankment will be constructed of
uniform, hydraulically placed slurry of silty sand. The slurry will be placed in thin lifts,
and will be expected to naturally segregate to produce a layered structure similar to that
obtained during construction of the San Fernando Dam. The model will be constructed
with as slow a sedimentation rate as possible to produce the loosest possible structure.
The proposed shaking sequence will be similar to that described for the other sets of tests.
The finely stratified hydraulic fill will (1) allow high pore pressures from the core to flow
toward the slope face, (2) produce interfaces where water interlayers may form, and (3)
provide a large interface surface area for intermixing of stratified deposits.
Triaxial Testing Program
A series of triaxial tests will be performed on specimens of Nevada sand. The data
obtained will augment an existing database including cyclic, monotonic, drained,
undrained, simple shear, triaxial, torsional hollow cylinder tests at a variety of densities
(Chen 1995 & Arulmoli et al. 1992) as well as other ongoing work that we are aware of.
A limited program of laboratory testing is proposed to obtain data from specimens
reconstituted in the same manner and at the same relative density as used in the
centrifuge tests.
Isotropically-consolidated undrained tests will be performed at three different
confining stresses representing the range of stresses produced in the models. Both
compression and extension tests will be performed. A series of cyclic triaxial tests will be
performed at the intermediate value of confining stress used in the monotonic loading
tests described above. Select tests will also be repeated using specimens prepared at
slightly higher and slightly lower relative densities. These test results will allow
consideration of how uncertainties in model density might affect the results of centrifuge
and laboratory tests.
REFERENCES CITED
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Arulmoli, K., K.K. Muraleetharan, M.M. Hossain, and L.S. Fruth 1992. VELACS
Verification of Liquefaction Analyses by Centrifuge Studies Laboratory Testing
Program Soil Data Report, Prepared for NSF, Earth Technology Proj. No. 90-0562,
March.
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tests, Geotechnical Testing Journal, GTJODJ, ASTM, 21(2): 120-131.
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measurements in model tests, Geotechnical Testing Journal, GTJODJ, ASTM,
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Arulnathan, R. 1999. Dynamic properties and site response characteristics of organic
fine-grained soils, Ph.D. thesis, University of California, Davis.
Boulanger, R. W., Arulnathan, R., Harder, L. F., Jr., Torres, R. A., and Driller, M. W.
1998, Dynamic properties of Sherman Island peat, Journal of Geotechnical and
Geoenvironmental Engineering, ASCE, 124(1): 12-20.
Boulanger, R.W., R. B. Seed, & C. K. Chan 1991. Liquefaction behavior of saturated
sands under uni-directional and bi-directional monotonic and cyclic simple shear
loading. Report UCB/GT-90-08, Univ. of California, Berkeley, 521 pp.
Boulanger, R. W. and S. P. Truman 1996. Void redistribution in sand under postearthquake loading. Canadian Geotechnical J., 33:829-833.
Byrne, P.M. and M. Beaty 1997. Post-Liquefaction Shear Strength of Granular Soils:
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the Society in November, 1972, and published in 1984.
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Castro, G. 1995. Discussion. J. Geotechnical Engineering, ASCE 121(7):572-273.
Castro, G. 1997. Post-Liquefaction Shear Strength from Case Histories. Shear Strength of
Liquefied Soils. (Stark, Olson, Kramer and Youd, eds.) Proceedings of April 17-18
Workshop at Urbana, Illinois.
Chen, Y.-R. 1995. Behavior of a Fine Sand in Triaxial, Torsional and Rotational Shear
Tests, PhD Thesis, Department of Civil and Environmental Engr., University of
California, Davis.
Fiegel, G. L. and B. L. Kutter 1994. Liquefaction-induced lateral spreading of mildly
sloping ground. J. Geotechnical Engrg, ASCE 120(12):2236-2243.
Gilbert, P.A. 1984. Investigation of density variation in triaxial test specimens of
cohesionless soil subjected to cyclic and monotonic loading, Report No. GL-84-10,
Corps of Engineers Waterways Experiment Station, Vicksburg, MS.
Howard, R.W.A, B.L. Kutter, and R. Siddharthan 1998. Seismic Deformation of
Reinforced Soil Centrifuge Models, Geotechnical Earthquake Engineering and Soil
Dynamics III, Geotechnical Special Publication No. 75, ASCE, Vol. 1, pp.446-457.
Ishihara, K. & H. Nagase 1980. Closure to Ishihara & Yamazaki (1980), Soils and
Foundations, JSSMFE, 20(1).
Kokusho, T. 1999, Formation of water film in liquefied sand its effect on lateral spread,
ASCE J. Geotechnical and Geoenvironmental Engineering, Vol. 125 No. 10, pp. 817826.
Kokusho, T., Watanabe, K., and Sawano, T. 1998. Effect of water film on lateral flow
failure of liquefied sand. 11th European Conference on Earthquake Engineering,
Balkema, Rotterdam, 1-8.
Kutter, B.L. and A. Balakrishnan 1998. Dynamic model test data from electronics to
knowledge, Centrifuge 98, Kimura, Kusakabe, Takemura (eds.), Balkema, Rotterdam,
Volume 2, in press.
Kulasingam, R., Boulanger, R. W., and Idriss, I. M. 1999. Evaluation of CPT liquefaction
analysis methods against inclinometer data from Moss Landing.” Proceedings, 7th
US-Japan Workshop, MCEER (in press).
Liu, Huishan & Taiping Qiao 1984. Liquefaction potential of saturated sand deposits
underlying foundation of structure. Proc. Eighth World Conf. Earthquake
Engineering, Vol. III, San Francisco.
Martin, G.R. 1997. Post-Liquefaction Shear Strength from Laboratory and Field Tests.
Shear Strength of Liquefied Soils. (Stark, Olson, Kramer and Youd, eds.) Proceedings
of April 17-18 Workshop at Urbana, Illinois.
McRoberts, E. C. & J. A. Sladen 1992. Observations on static and cyclic sandliquefaction methodologies. Canadian Geot. J., 29(4):650-665.
NRC, National Research Council 1985. Liquefaction of soils during earthquakes.
National Academy Press, Washington, D.C.
Romero, S. 1998. The behavior of silt as clay content is increased, Masters thesis,
University of California, Davis, 108 pp.
Seed, H.B. 1986. Design problems in soil liquefaction. J. Geotechnical Engrg., ASCE,
113(8):827-845.
Seed, H.B., R.B. Seed, L.F. Harder & H.-L. Jong 1989. Re-Evaluation of the Lower San
Fernando Dam, Report 2, prepared for Dept of Army, US Army Corps of Engineers,
Washington, DC, contract No. DACW39-85-C-0048, September, 265p.
Siddharthan, R.V., Ganeshwara, V., and Kutter, B.L. 1999. Development of a Seismic
Deformation Model for Mechanically Stabilized Earth (MSE) Walls, , Proc., 8th
Canadian Conference on Earthquake Engineering, pp. 353-359.
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Sons, New York.
BUDGET JUSTIFICATION
One month of summer support per year is requested for the Principal Investigator (Bruce Kutter), one-half
month per year for the co-PI (Ross Boulanger), and one month per year is requested for the UC Davis
Centrifuge Facility Manager (Dan Wilson). The PI will be responsible for overall project coordination of
meetings, laboratory and centrifuge tests. The co-PI, will play an advisory role for all phases of the project
and will be in charge of planning and conducting the triaxial tests. The facility manager will help in details
of meetings with the Board of Consultants and in day to day supervision of the graduate and undergraduate
students while they are conducting the centrifuge tests. The budget includes one month of support per year
for a technician (Dennis O’Brien) who will help in small machining tasks, and to train new students in the
use of equipment, machines, and forklift. Department technical support funds will be used to get Computer
Support and from a Department Development Engineer (regarding Apparatus machining or design).
One graduate student (Ph.D. candidate), with help from two undergraduate students will conduct
the six centrifuge model tests and the triaxial tests. Based upon our experience, one full time graduate
student (50% academic year, 100% summer) with help of the technicians and undergraduate student
assistants can in one year conduct two or three large scale centrifuge model tests. This includes planning
the experiments, constructing the models, dissecting the models, keeping photographic records and
logbook, preparation of a complete data reports for each test, and preparing a conference paper. In
addition, the student should be able to co-author at least one conference or journal article in each year. For
the graduate student, we include fees and tuition expenses.
Consumables includes photography, tons of soil for the models, methyl cellulose to adjust pore fluid
viscosity and a few new instruments to replace those lost to attrition. Travel includes the cost of meetings
of the Board of Consultants (one from Japan, one from the West Coast, two from the East Coast) at UC
Davis. In the first year we have a somewhat larger travel budget which will allow the PI’s to travel to
Japan to observe the shaking table tests by Prof. Kokusho and coordinate the research. We plan to meet
with Prof. Kokusho at least once per year either in the US or Japan. We plan to schedule some of these
meetings around international conferences to economize. Centrifuge time is charged at $8000 per test,
which is based upon our established rate of $800/day and our experience that each test will occupy the
centrifuge, instruments, and/or model containers for ten days per test.
FACILITIES, EQUIPMENT, AND OTHER RESOURCES
Work will be performed at the centrifuge site of the Center for Geotechnical Modeling at
UC Davis. The Center operates a small (1-m radius) and a large (9-m radius) geotechnical
centrifuge, both of which are equipped with servo-hydraulic shakers for simulating earthquake
type motions. Prof. Bruce Kutter, the current Director of the Center, was involved in bringing the
large centrifuge to UC Davis and has helped develop the UC Davis facility from the beginning.
Mr. Tom Kohnke, the Center's head technician, has over eight years of experience working with
and developing the geotechnical centrifuges at UC Davis. Dr. Dan Wilson, the Center's facility
manager, has over eight years experience with centrifuge modeling, both in performing research
experiments and in developing equipment for use on the centrifuges at UC Davis.
The UC Davis centrifuge has the largest radius and by far the largest model containers
(1.7 x 0.7 x 0.7 m3 inside volume) available on any centrifuge shaker in the US. Two new
centrifuges in Japan have comparable dimensions. The shaker on the UC Davis centrifuge has a
servo-hydraulic actuator capable of producing base motions that simulate realistic earthquakes,
sine sweeps, or single small spikes of acceleration. Peak base accelerations as high as 40 g,
velocities up to 0.8 m/s, and peak to peak displacements of 25 mm can and have been produced
by the shaker. For a 40 g centrifuge tests, these motions correspond to prototype earthquake base
motions with 1 g acceleration, 0.8 m/s, and 1 m displacement. More details regarding the
centrifuge facilities may be found at http://cgm.engr.ucdavis.edu.
The Center facilities include a large soil mixer, a large consolidation press, three model
containers for the large centrifuge and several containers for the small centrifuge. Also a bank of
about 100 instruments (accelerometers, pore pressure transducers, displacement transducers, etc.)
is available for users of the Center’s facilities. The centrifuge facilities at UC Davis are available
to researchers outside UC Davis for independent or collaborative research (see
http://cgm.engr.ucdavis.edu). Most of the data generated using the centrifuge is made available
to interested researchers on the web, CD or Zip disk.
In addition to conventional equipment such as direct shear, consolidation, compaction
equipment, the Department of Civil Engineering Soil Mechanics laboratories include computer
controlled triaxial and torsional hollow cylinder apparatus, equipment and electronics for
measurement of shear wave velocities using bender elements, and graduate student computer
laboratories.
The Center has access to an active fully functional machine shop run by the College of
Engineering, and the professional staff of Facility Services, who can assist in development and
design of mechanical and electrical apparatus that might be required for this project.