Influence of subway train load on seismic response of twin stacked tunnels using three-directional shaking table test in sand

Abstract

The seismic response of soil and tunnel can be affected by the subway train load in twin stacked tunnel case. However, the existing studies on the seismic response of stacked tunnels do not consider the influence of subway traffic load. Therefore, this study conducted a series of 3-D shaking table tests to investigate the influence of subway train load on seismic response of twin stacked tunnels in sand. The research results indicated that, for the soil-tunnel system, the subway train load reduces the values of both natural frequency and damping ratio. For the soil, the subway train load can inhibit the seismic response, which is manifested in the gradient differences of peak acceleration and peak pore pressure around the upper tunnel significantly decreased, the acceleration amplification effect weakened, and the peak surface settlement obviously reduced. For the tunnel, the subway train load can increase low-frequency amplitude at the crown position of twin tunnels, and decrease low-frequency and high-frequency amplitudes at the inverted arch position of lower tunnel. The peak earth pressure is inversely proportional to the distance from the subway train load application location. The peak strain of the upper tunnel is weakened, and this effect is most obvious at the left sidewall position. The findings in this study will provide reference for seismic design of twin stacked tunnels considering the subway train load.