Analysis on Stress and Deformation Characteristics of Tunnel Excavation in Loosing Area of Surrounding Rock in Fault Zone

Due to poor conditions of surrounding rock, it will often form loose area or even collapse in the excavation process of tunnel crossing fault zone. In order to explore the stress and deformation variation of surrounding rock with loosing area during tunnel excavation, the ventilation and safety tunnel of Hami Pumped Storage Power Station was taken as an example. And a 3 D numerical calculation model was established and finite difference method was adopted to analyze the variation law of radial stress, deformation and plastic zone during the excavation and support process of surrounding rock with loosing area in fault zone. The calculation results indicate that the radial stress of the top arch is mainly concentrated in the front of the loose area, and the excavation of the lower half layers has little influence on the radial stress of the top arch. The radial deformation of the upper and lower half layers of the tunnel is consistent with that of the arch, which is distributed in a parabolic shape along the excavation depth, and the maximum value is located at the front of the loosing circle. After excavation, the relationship of deformation value at different position on the monitored section is vault＞center of side wall＞arch shoulder. The plastic zone of surrounding rock is mainly distributed around the side wall and the bottom plate, and both of them are shear plastic failure. Therefore, the supporting measures at the side wall and bottom plate should be strengthened in the construction process. This study can provide reasonable suggestions for the support design of loose area tunnel formed by collapse of surrounding rock in fault zone.