Abstract: To explore the seismic performance of horseshoeshaped tunnel and predict the postearthquake disaster situation of the tunnel, a case study is conducted on the Mopanshan tunnel, a water diversion project in central Yunnan, a finite element model of rocktunnel interaction is established, and structural dynamic analysis is conducted using nonlinear dynamic timehistory method. Considering the uncertainty of site conditions and earthquakes, suitable seismic intensity indices are selected for two different site conditions. Meanwhile, considering the impact of damage parameters on the fragility analysis of the structure, the relative deformation rate of the section and the bending moment bearing capacity ratio are used as damage indices respectively. The results show the following: (1) In the fragility analysis of tunnel structures, peak ground acceleration has a low degree of dispersion and is a more effective seismic intensity index. (2) The trend of tunnel fragility under different damage indices is basically consistent, but when the same damage index is used, the fragility of tunnels in softer sites is higher, and the seismic performance deviates. Therefore, the safety of structures in complex site should be guaranteed. (3) Under fortification conditions, the probability of failure at each performance level of the tunnel is relatively low, meeting the design requirements. In rare earthquakes, the probability of failure at each level is relatively high, and the tunnel damage is relatively severe. 

Key words: horseshoeshaped tunnel, seismic fragility, dynamic timehistory analysis, site conditions, damage index