Study on Dynamic Response of Soil Layer at the Bottom of Subway Shield Tunnel Under Seismic Action

The dynamic response characteristics of the soil layer at the bottom of the subway shield tunnel under seismic loads are related to the seismic performance and seismic safety evaluation of the subway shield tunnel structure. It is of great significance to reveal the dynamic response and seismic failure mechanism of the subway shield tunnel structure and its surrounding soil layer under seismic action. With the shield tunnel of Xiamen Metro Line 6 (from Maluan Center to Jimei Island) as an engineering case, the dynamic response characteristics of the bottom soil layer of shield tunnel with different structural stiffness under different seismic loads are systematically studied using the finite difference method. The results show that (1) under seismic loads, with the increase of the distance from the bottom of shield tunnel, the vertical stress of each monitoring point increases and its vertical displacement decreases, and the change rate of both increases; (2) with the increase of seismic wave peak acceleration, the vertical stress and displacement of the soil layer at the same distance from the bottom of the shield tunnel show an increasing trend. Specifically, the farther the soil layer is from the bottom of the tunnel, the greater the increase rate is; (3) as the concrete strength grade of shield tunnel segment increases, the vertical stress of soil layer at the bottom of shield tunnel increases and the vertical displacement decreases, while the overall change is within a slight range.