The cyclic resistance of predominantly fine-grained soils has received considerable
attention following ground and foundation failures at sites underlain by silt-rich
soils during recent earthquakes. In several cases substantial ground deformation
and reduced bearing capacity of silt soils has been attributed to excess pore
pressure generation during cyclic loading. These field case studies are significant
due to the occurrence of liquefaction related phenomena in soils that would be
characterized as not susceptible to liquefaction using current geotechnical screening
criteria. The most widely used of these criteria, the "Chinese Criteria" and its
derivatives, are based solely on soil composition and they are essentially diagnostic
tools that categorize the soil in a binary fashion as either liquefiable or non-liquefiable.
The most significant limitations of these screening tools are that they
fail to account for the characteristics of the cyclic loading. This investigation was
undertaken to elucidate the potential for strain development in silts during cyclic
loading, and to develop a practice-oriented procedure for evaluating the seismic
performance of silts as a function of material properties, in situ stresses, and the
characteristics of the cyclic loading.
This dissertation presents the results of a multi-faceted investigation of the potential
for seismically induced pore pressures and large strain development in silt soils.
The primary focus of the research was on the synthesis of laboratory testing results
on fine grained soils. Laboratory data from cyclic tests performed at Oregon State
University and other universities formed the basis for enhanced screening criteria
for potentially liquefiable silts. This data was supplemented with field data from
sites at which excess pore pressure generation, liquefaction, and/or ground failures
were observed during recent earthquakes. This investigation specifically addressed
the behavior of silts during loading in cyclic triaxial tests due to the relative
abundance of data obtained for this test. The data was used in conjunction with
standard geotechnical index tests to enhance an existing energy based procedure for
estimating excess pore pressure generation in silts. This pore pressure model can
be used with the uncoupled, stress-based methods for estimating the post-cyclic
loading volumetric strain developed in this investigation.
The energy-based excess pore pressure model and empirical volumetric strain
relationship were used to calibrate for applications involving silt soils a nonlinear,
effective stress model for dynamic soil response (SUMDES). The SUMDES model
was employed, along with the equivalent linear total stress model SHAKE, to
estimate excess pore pressures generated at un-instrumented field sites that have
exhibited evidence of liquefaction during recent earthquakes. A comparison of the
SUMDES and SHAKE results highlighted the limitations of the latter model for
simulating dynamic soil response at various levels of shaking and pore pressure
response. The results of the SUMDES modeling at several well documented case
study sites are presented in this dissertation. These comparisons are valuable for
demonstrating the uncertainties associated with modeling of the effective stress
behavior of silt during seismic loading. / Graduation date: 2005
| Identifer | oai:union.ndltd.org:ORGSU/oai:ir.library.oregonstate.edu:1957/29005 |
| Date | 22 September 2004 |
| Creators | Sunitsakul, Jutha |
| Contributors | Dickenson, Stephen E. |
| Source Sets | Oregon State University |
| Language | en_US |
| Detected Language | English |
| Type | Thesis/Dissertation |
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