Comparative Study on Ground Motion Input Methods for Tunnels under Viscoelastic Boundary

At present, the viscoelastic artificial boundary is used as the dynamic boundary for seismic response analysis of tunnels, but there is no detail comparison on the seismic input method. Using ABAQUS finite element analysis software, a three-dimensional model of tunnel-soil layer is established to verify the accuracy of viscoelastic artificial boundary and the reflection and transmission of ground motion at different interfaces. Taking a railway tunnel in Qingdao as an example, the displacement input method, the acceleration input method and the equivalent nodal force input method are respectively used to study the dynamic response characteristics of the tunnel under different input methods. The results illustrate that the input method has a significant effect on the seismic response of the tunnel. The results of displacement input and acceleration input are equivalent. The minimum displacement response of the tunnel is 0.12 times that of the node force input, and the maximum stress response is 2.45 times that of the node force input. The results of tunnel response displacement with the nodal force input method are more consistent with the analytical solution and the calculation accuracy is much higher. Therefore, the equivalent node force input should be given priority in the seismic response analysis of tunnels.