Structural damage assessment of mountain tunnels in fault fracture zone subjected to multiple strike-slip fault movement

Fault fracture zones are adverse geological conditions often encountered in the constructions of mountain tunnels. Extensive structural damage to the mountain tunnels in adjacent to the fault fracture zones has been documented in the past earthquakes. In current work, three-dimensional numerical model of a water conveyance tunnel crossing multiple active strike-slip faults was established to assess the structural damage with consideration of four primary influence factors: the magnitude of fault movement, the distance between adjacent fault planes, the tunnel-fault intersection angle and the mechanical properties of the rock mass in the fault fracture zone. Two quantitative damage indices, namely, the overall structural damage index and the concrete lining crack width, are proposed in this study to investigate the structural integraty and the serviceability of the water conveyance tunnel subjected to fault movements. The numerical results indicate that the cross-sectional damage of the tunnels primarily concentrated in the vicinities of the fault planes, and the boundaries between the fault and the competent rock. With the increase of the distance between adjacent fault planes, the structural damage of the tunnel in the region near the center of the fault fracture zone rapidly decreases. The tunnel-fault intersection angle also significantly affects the performance of the tunnel under fault movement. Moreover, the increase of surrounding rock mass stiffness in the fault fracture zone reduces the extension but increases the severity of damage to the tunnel lining. Overall, the numerical results of this study provide a better understanding of the response of mountain tunnels under multiple strike-slip fault movement.