Numerical investigation on seismic damage of tunnels subjected to fault dislocation using the FDM-DEM approach

Historical earthquake disasters indicate that tunnels crossing active faults (hereinafter to referred as the "crossing-fault tunnel") tend to experience severe damage, making the research on failure mechanisms of tunnels under fault dislocation a critical issue. This paper develops a three-dimensional continuous-discrete coupling model using the FDM-DEM approach to analyze seismic damage of crossing-fault tunnels under fault dislocation. In this model, the host rock and tunnel are modeled as continuous media, while the fault fracture zone is modeled as a discrete medium to capture the effect of its discreteness on tunnel structures. The proposed model is validated through physical model tests and the seismic damage observed from the Daliang tunnel during the 2022 Menyuan earthquake. It is shown that the proposed coupling model provides more accurate simulations than that of traditional continuous model. The simulation results obtained by the proposed model match the experimental phenomena of the physical model tests and the seismic damage of Daliang tunnel, particularly the significant necking phenomena. A parametric analysis based on the Xianglushan tunnel in China is conducted to investigate the effects of fault displacements, fault widths, and dip angles on damage patterns of crossing-fault tunnels. The results indicate that: (1) the tunnel damage is concentrated at the fault fracture zone-host rock interface and the fault plane; (2) the increase in fault displacements and fault widths intensifies and reduces tunnel damage within the fault zone, respectively; (3) fault dip angles affect distribution patterns of additional stress within the fault fracture zone, thereby impacting tunnel damage. This study provides a new insight for simulating crossing-fault tunnel damage, and supports a basis for its seismic design.