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Civil-Comp Proceedings
ISSN 1759-3433 CCP: 81
PROCEEDINGS OF THE TENTH INTERNATIONAL CONFERENCE ON CIVIL, STRUCTURAL AND ENVIRONMENTAL ENGINEERING COMPUTING Edited by: B.H.V. Topping
Paper 260
Seismic Safety Evaluation of Liquefiable Embankments under a Strong Earthquake using Finite Element Approaches C. Takahashi+, F. Cai* and K. Ugai*
+Forum8 Co., Ltd., Tokyo, Japan
Full Bibliographic Reference for this paper
C. Takahashi, F. Cai, K. Ugai, "Seismic Safety Evaluation of Liquefiable Embankments under a Strong Earthquake using Finite Element Approaches", in B.H.V. Topping, (Editor), "Proceedings of the Tenth International Conference on Civil, Structural and Environmental Engineering Computing", Civil-Comp Press, Stirlingshire, UK, Paper 260, 2005. doi:10.4203/ccp.81.260
Keywords: embankment, liquefaction, slope stability, finite element method, limit equilibrium method, seismic design.
Summary
The seismic safety evaluation procedure currently used in Japan first calculates the
factor of safety using the
![]() ![]() ![]() The proposed approaches are used to re-analyze the Lower and Upper San Fernando Dams. During the San Fernando earthquake of February 9, 1971 (magnitude 6.6), a major slide occurred in the upstream slope of the Lower San Fernando Dam; slide movements also caused a downstream movement of about 1.5m in the embankment of the Upper San Fernando Dam; however, a major slide did not occur [5]. For the Lower San Fernando Dam, the numerical results can reproduce the major slide with a large residual displacement and a factor of safety after the earthquake is 0.88 when the excess pore water pressure due to the liquefaction was considered. The numerical results show that the excess pore water pressure ratio in the upstream and downstream shell below the phreatic surface was quite high up to about 0.7. This indicates that the hydraulic fill materials in these regions may have either liquefied or been weakened severely. Additionally, the excess pore water pressure ratio in the upstream shell was still high even at 60s after the beginning of the earthquake. For the Upper San Fernando Dam, the calculated lateral displacements were 2.5m at the downstream berm and 1.2m at the downstream toe; they were consistent with the observation of 2.2m at the downstream berm and 1.1m at the downstream toe. The excess pore water pressure ratio in the upstream shell of the Upper San Fernando Dam is about 0.6, and the excess pore water pressure ratio was still high 60s after the beginning of the earthquake. The excess pore water pressure ratio in the Upper San Fernando Dam is about 0.1 lower than that in the Lower San Fernando Dam. Because the Lower San Fernando Dam is 25m higher than the Upper San Fernando Dam, the shear stress before the earthquake in the Lower San Fernando Dam is larger than that in the Upper San Fernando Dam. This is the one of the main reason that a large slide occurred in the upstream of the Lower San Fernando Dam but only some residual displacements occurred in the Upper San Fernando Dam. The factor of safety for the downstream shell is larger than one even when the excess pore water pressure was considered. References
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