Nonlinear Response of Firm Ground Identified from Vertical Array Records and Its Simulation Using Multiple Mechanism Model

Abstract eng:
In the design procedure of port structures including quay walls in Japan, the residual deformation of structures subject to strong ground motions is often evaluated by finite element analysis. For this analysis, the material parameters should be, in principle, determined based on in-situ geotechnical investigations and laboratory tests. The application of laboratory tests for a firm ground with a shear wave velocity over 300 m/s, however, is quite debatable because, due to a possible disturbance during sampling from the firm ground, the shear strength of the soil, for example, might be significantly underestimated. So far we have no reliable way to determine the model parameters for the firm ground in such analysis, although the results of such analysis are often dependent on how we model the firm ground. During the 2007 Off Mid Niigata Prefecture, Japan, earthquake (MJ6.8), very important data was obtained at a vertical array site KSH in the near-source region operated by the Tokyo Electric Power Company, Inc. (TEPCO). The layers spanned by the vertical array mostly consist of a firm ground with shear wave velocity larger than 300m/s. In this article, the authors try to simulate the response of the vertical array site using a computer program FLIP, which is a finite element code equipped with the multiple mechanism model. The simulation results suggest that use of a typical value of shear resistance angle may lead to underestimation of the shear strength of a firm ground subject to a very strong ground motion.

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