A 3D Discrete-Continuum Coupling Approach for Investigating the Deformation and Failure Mechanism of Tunnels across an Active Fault: A Case Study of Xianglushan Tunnel

For water transmission tunnels constructed in high-risk seismic regions of western China, active faults pose threats of serious ruptures to the tunnels. To overcome this issue, a 3D discrete-continuum coupling approach is introduced into the study. By this approach, spherical discrete-element-method (DEM) particles are used to represent the surrounding rock mass, and the tunnel is considered to be the continuous finite-difference-method (FDM) zone. In this way, a 3D coupling model was established to study the longitudinal displacement profile and stress response of the tunnel lining under various fault dislocations. The failure pattern of the surrounding rock mass was investigated from a micro perspective. Meanwhile, the design strategy of flexible joint was investigated with the present numerical model. The results from a parametric study show that the smaller segment length, wider width and weaker strength of the flexible joints are beneficial to the anti-dislocation performance of the tunnel. Moreover, an orthogonal array test technique was utilized to investigate the influence level of the main design parameters of the flexible joint on the lining internal stress. With the obtained knowledge, the optimal combination for flexible joint design was presented. Findings may provide references for the anti-dislocation issue of tunnels across active faults.