Seismic motion input methods of viscous-elastic boundary and numerical simulation of seismic response on large diameter tunnels

To determine the selection of input wave field at the bottom of the viscous-elastic boundary, and study the seismic response of two parallel large-diameter shield tunnels, corresponding numerical models were established for analysis. First, through the study of wave method for seismic motion input of viscous-elastic boundary, several different wave fields selection methods for calculating the equivalent nodal forces at the bottom of the model were compared using free field and scattering field models. Then, using viscous-elastic boundary and the previous seismic motion input method, established soil-tunnels system finite element models with different interval between two large-diameter tunnels and input seismic waves with different spectral characteristics analyzed the dynamic response of the soil-tunnels system. The results show that the simulation accuracy is highest when calculating the equivalent nodal loads by the free wave field, and the seismic input method based on the substructure of artificial boundaries also has high accuracy; spectral characteristics of seismic motion has a significant impact on the dynamic response of tunnels, while the influence of two tunnels interval is relatively small; the influence of tunnels interval on the bending moment and axial force of tunnels lining is different. The research results can provide reference for accurately seismic motion input of viscous-elastic boundary and seismic design of large-diameter shield tunnels.