Seismic fragility analysis method for evaluation of dislocation resistance of tunnels crossing active fault zones

As the dislocation of active fault is the main factor leading to the failure of the tunnels crossing the fault, it is essential for the seismic design to evaluate the dislocation resistance performance of the tunnels crossing active fault zones. However, the relevant methods are still lacking. A seismic fragility analysis method is proposed for evaluating the dislocation resistance performance of the tunnels crossing active fault zones. Firstly, the formula for calculating the exceedance probability of fault displacement at the tunnel site is derived based on the probabilistic fault displacement hazard analysis (PFDHA). Secondly, a three-dimensional elastic-plastic finite element analysis model for the rock-fault-tunnel interaction system is established. The seismic fragility analysis indexes are selected, and the quantitative relationship between tunnel damage and fault displacement is obtained using the pseudo-static pushover analysis method. Finally, the seismic fragility of the tunnels crossing active fault zones under any given ground motion levels is calculated using the formula for the exceedance probability of fault displacement in the tunnel site area. Taking a tunnel through an active strike-slip fault as an example, based on the established fragility analysis method, the influence law of fault dip angle on the dislocation resistance performance of tunnel structure is explored. It is shown that a smaller fault dip angle is associated with lower fragility of the tunnel structure, and the fragility of the tunnel lining in the hanging wall is significantly higher than that in the footwall. The fragility of the tunnel is more sensitive to variations in the moment magnitude scale of 5~8. The damage probability of tunnel structure can be significantly reduced by choosing the tunnel line to pass near the end of the fracture zone. The proposed method can quantitatively describe the fragility of the tunnel at different cross sections under given ground motion intensities and provide a scientific basis and analytical method for the seismic design and the evaluation of the dislocation resistance performance of the tunnels crossing active fault zones.