Masahiro TOMOBUCHI
Investigation on long-term subsidence of clayey ground after Chuetsu-Oki earthquake in 2007
Satoru OHTSUKA
In 2007 Niigata Prefecture Chuetsu-Oki Earthquake, the principal ground disasters are liquefaction of sandy ground and slope failure. On the other hand, no distinct disaster has been found at clayey ground immediately after the earthquake. Long-term subsidence of ground after earthquake is, however, observed at Shinbashi in Kashiwazaki city.
This study conduct boring survey and indoor element tests for sampled soil for investigate the long-term subsidence mechanism. As the results, the sampled soils were found relatively highly-structured. In the second process, the subsidence behavior of ground was simulated by soil-water coupling elasto-plastic FEM analysis. In the simulation, Cyclic Mobility model by Zhang et al. (2007) is used for the constitutive model. Its parameters were determined based on element test results. Based on the simulation results, the factors for long-term subsidence were discussed and the successive subsidence was predicted forward.The followings are concluded in this study.
1) Subsidence of ground observed before 2007 Niigata Prefecture Chuetsu-Oki Earthquake is due to pumping up ground water and Subsidence part is the shallow soft clay layer.
2) Long-term subsidence observed after 2007 Niigata Prefecture Chuetsu-Oki Earthquake was explained as rise of excess pore water pressure due to hard shaking. The behavior was found to continue for a long time because its permeability is very low. In particular, subsidence is outstanding in the area where clayey layer is thick.
3) Subsidence is expected to continue over the long term future from the results of the simulation.
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