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Proceedings of the 18
th
International Conference on Soil Mechanics and Geotechnical Engineering, Paris 2013
Proceedings of the 18
th
International Conference on Soil Mechanics and Geotechnical Engineering, Paris 2013
4 CONCLUSIONS
Levees are very challenging engineering structures to study, in
part because they are not typically well-engineered structures.
Unfortunately, there is little to no guidance as to how to
evaluate the seismic vulnerability of levees. This study focuses
on systematically studying the dynamic response of levees and
developing a simplified procedure for the evaluation of
seismically induced deviatoric displacements for levees. The
study was based on levee sites representative of select
California Central Valley regions; however, since floodplains
tend to generally have similar depositional environments, it can
be extended to other regions as long as some of the principal
characteristics are still applicable.
Three levee sites, with different underlying soil stratigraphy,
were studied. There were differences in the dynamic response
among the three sites, however these differences were smaller
than the variability in response introduced by the input ground
motions. A wide range of ground motions were used in an effort
to capture not only the average response of levees, but also the
variability and its underlying root causes
.
Four critical sliding surfaces have been selected for the
evaluation of permanent seismic deviatoric type displacements.
The variability of the seismic coefficients for each surface was
found to be related to the degraded site period, indicating that
for earth embankments of small heights (~10 m), the overall site
response is more important than the response of the sliding
mass itself. The seismic displacements were calculated using a
decoupled equivalent-linear, Newmark-type approach. The
variability of the seismic displacements due to the different
ground motions was also significant. It was efficiently reduced
however, by normalizing the displacements with regard to the
peak ground velocity (PGV) of the input ground motion. The
regressions for the normalized displacements showed that PGV
is both efficient and relatively sufficient in capturing the
important characteristics of the ground motion, when computing
seismic slope displacements. The standard deviation of the
regressions is on average equal to 0.3 log units. The graph of
Figure 8 is recommended for estimating normalized
seismically-induced deviatoric displacements for levee sites that
have similar stratigraphy and geometry to the three levees in
Figure 1. This simplified procedure focuses on seismic slope
stability of earthen levees, and is not recommended for other
earth embankments that are vastly different from levees (i.e.
dams, landfills). Since the soil materials were modeled as
equivalent-linear, this procedure should not be extrapolated to
PGA values larger than 0.4g.
5 ACKNOWLEDGMENTS
This study was completed with the financial support provided
by the National Science Foundation Graduate Research Studies
Fellowship (2004-2007) that was awarded to Dr.
Athanasopoulos-Zekkos. The authors would also like to thank
Dr. Shewbridge and Dr. Wu for their help in collecting some of
the soil data used in the analyses and for their useful comments
and insight.
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