1634
Proceedings of the 18
th
International Conference on Soil Mechanics and Geotechnical Engineering, Paris 2013
(a)
(b)
0
20
40
60
80
-20
-10
0
Depth (m)
NewFill,
=34
OldFill,
=34
ML/CL,PI=10,Su=25 kN/m 2
SM, PI=11,
=32
CH, PI=37, Su=35 kN/m 2
A
B
C
D
E
FS=3.0 (pre earthquake)
FS=1.3 (during earthquake, no strength reduction)
FS=1.0 (during earthquake, 15% strength reduction)
Distance (m)
Figure 6 (a) Subsurface condition at Carrefour Shopping Center (b) Extensometer measurements at Carrefour Shopping Center (Martin et al., 2004)
Table 2. Summary of input parameters and estimated strength loss of two case histories
Case
Seismological information
Site/ soil condition
Estimated results
Mw R
PGA
Vs
OCR
PI
Nc
eff
Strength loss
-
(km)
(g)
m/sec
-
-
(-)
(%)
-
(%)
Berryman
7.0
0.2
0.72
240
3-5
15-30
29
1-3
0.75
25-30
Carrefour
7.4
5
0.24
120
1
10-37
28
0.3
0.88
10-15
Bearing-capacity was evaluated using a slope stability
approach before the earthquake and during the earthquake with
a pseudo-static type analyses. The failure surface was
constrained to a depth of 10 m below the ground surface
because extensometer measurements indicate that large
deformation occurred at this depth. As shown in Figure 6, the
FS for slope stability is 3.0 pre-earthquake and becomes 1.0
with a 15% estimated strength reduction (as listed in Table 2),
compared to 1.3 without considering strength loss during the
earthquake. The result suggests that the soil layer exhibited
strength loss and that the amount of strength loss simply
estimated by the proposed procedure leads to an analysis
outcome consistent with the field observations.
7 CONCLUSION
In this paper we present an analysis procedure to estimate
cyclic softening of saturated clays under seismic loading.
Unlike common liquefaction potential analysis procedures that
use a stress-based approach, the procedure uses a strain-based
approach to estimate cyclic softening and associated strength
loss. The procedure has two main components: (1) estimation of
the shear strain amplitude and the equivalent number of uniform
strain cycles within the soil mass induced by an earthquake
event; and (2) estimation of the softening and associated
strength loss within the soil given the effective shear strain
amplitude and the equivalent number of uniform strain cycles.
The procedure is successfully implemented in pseudo-static
analysis for analyzing one design case and one field case
history and is found to generally provide reasonable, first-order
estimates of cyclic softening consistent with the field
observations.
8 ACKNOWLEDGEMENTS
This study was mainly performed by the first author during his
employment with URS Corporation. The authors acknowledge
URS’ support. The authors also would like to acknowledge Mr.
Fidèle Nikiema in translating the abstract into French.
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