1. College of Geology Engineering and Geomatics, Chang'an University, Xi'an 710054;
2. Key Laboratory of Western Mineral Resources and Geological Engineering, Ministry of Education, Xi'an 710054;
3. China Railway First Survey and Design Institute Group Ltd., Xi'an 710043
Piedmont fracture of Mount Li that Xi'an metro tunnel pass through was taken as research prototype, and the activity characteristics were analyzed, and the biggest vertical displacement of the ground surface by the fault sticky slip activity was forecast based on the risk analysis results of earthquake in near field. The responsive deformation and failure characteristics of stratum and subway tunnel caused by fracture dislocation were studied by using numerical simulation method, and the critical dislocation amount of section tunnel structure damaged was analyzed and verified; the influence range of fracture activity were calculated, and the main fortification area of the subway tunnel crossing the fault zone was determined. Research result shows that the settlement response of stratum on the hanging wall is more obvious with the increase of the amount of fracture dislocation, differential settlement areas of stratum between the hanging wall and foot wall are concentrate near the fracture zone, which extend to both sides taking on the shape of "inverted triangle" gradually. When the amount of dislocation is greater than 20cm, the differential settlement of metro tunnel between the hanging wall and foot wall is particularly serious; the adjacent sectional tunnels appear tension and dislocation phenomena when the dislocation of hanging wall is 50cm. Based on the changing characteristics of the stratum vertical displacement at the tunnel vault, the least longitudinal fortified lengths of subway tunnel passing through the fault zone are get, which are 40m on the hanging wall and 15m on the footwall. The experimental results are consistent with the field investigation results after contrasting and verifying. Finally, corresponding proposed measures for fortification are put forward.