Seismic response of subway station subjected to mainshock-aftershock sequences by centrifuge shaking table tests

Abstract

During the 1995 Kobe earthquake, the Daikai Station suffered a severe collapse, drawing more attention to the earthquake damage response of underground structures. However, the performance of underground structures under the mainshock-aftershock sequences has yet to receive much attention. In this paper, the dynamic response and damage development process of the subway station under the mainshock-aftershock sequence were studied and explored through a series of centrifuge shaking table tests. The Selection-Adjustment-Generation method of artificial main aftershock sequence construction was introduced. Steel grits were mixed into the overlying soil to simulate the vertical inertia force. It is found that the Selection-Adjustment-Generation method is easily implemented, maintaining the local time-frequency characteristics of the original seismic waves as much as possible. The failure mechanism of the subway station subjected to mainshock-aftershock sequences can be summarized into two main aspects. One is the reduction of the horizontal deformation capacity of the columns due to the vertical inertial force induced by the overlying soil under the vertical seismic load. Sudden brittle failure will happen to the columns with higher axial pressure under horizontal earthquakes, which weakens their vertical support capacity. The other is the damage accumulation under mainshock-aftershock sequences. The station in the dry sand site is more susceptible to damage for the amplification effect. Both ends of the columns of the subway station experience crack with a strain exceeding 500 με during the mainshock. During the second aftershock, the bottom of the outer columns was crushed. In the liquefiable site, the liquefied layer weakens the upward propagation of horizontal seismic load and protects the structure to a certain extent. This series of tests illustrate the damage development process of underground structures under the main-aftershock and provides valuable experimental data for further study of the earthquake damage response of underground structures.