Simulation of normal fault rupture and its impact on mountain tunnels

The seismic damage of mountain tunnels is closely associated with the movement of active faults. Seismic design of tunnels crossing active faults is one of the great challenges nowadays. Based on the engineering prototype of the Xianglu mountain tunnel, the water diversion project in central Yunnan Province, a numerical method to simulate the propagation of normal fault rupture is proposed using the finite element method incorporated with the cohesive interface model in fracture mechanics. The proposed method is verified against the post-earthquake reconnaissance and experimental results using the three-dimensional free-field model. It is used to simulate a tunnel crossing a normal fault, and the effects of fault displacement and dip angle on the response of the tunnel linings are discussed. Besides, the damage indices and safety assessment criteria are introduced to preliminarily evaluate the damage of the tunnel linings subjected to fault movement. The results show that the mechanisms of surface rupture exhibit the forms of folding or fault scarps under normal faulting. The axial tensile strain and hoop shear strain of the tunnel linings reach the maximum at the position where they intersect the fault slip surface. The seismic damage state of tunnel along the longitudinal direction is significantly affected by the fault displacement and dip angle. The length of the tunnel linings in a severely damaged and completely damaged state is significantly reduced with the increase of the dip angle. Dip angles of 50° to 70° are more detrimental to structural safety.