Seismic Response Analysis of Tunnel through Fault Considering Dynamic Interaction between Rock Mass and Fault

In order to explore the influences of fault dislocations on tunnel stability under seismic action, a nonlinear dynamic simulation method for the rock–fault contact system is proposed. First, considering the deterioration effect of seismic action on the ultimate bearing load of the contact interface between rock mass and fault, a mathematical model is established reflecting the seismic deterioration laws of the contact interface. Then, based on the traditional point-to-point contact type in a geometric mesh, a point-to-surface contact type is also considered, and an improved dynamic contact force method is established, which considers the large sliding characteristics of the contact interface. According to the proposed method, a dynamic finite element calculation for the flow of the rock–fault contact system is designed, and the accuracy of the method is verified by taking a sliding elastic block as an example. Finally, a three-dimensional (3D) calculation model for a deep tunnel through a normal fault is built, and the nonlinear seismic damage characteristics of the tunnel under horizontal seismic action are studied. The results indicate that the relative dislocation between the rock mass and the fault is the main factor that results in lining damage and destruction. The seismic calculation results for the tunnel considering the dynamic interaction between the rock mass and the fault can more objectively reflect the seismic response characteristics of practical engineering. In addition, the influences of different fault thicknesses and dip angles on the seismic response of the tunnel are discussed. This work provides effective technical support for seismic fortification in a tunnel through fault.