Dynamic Risk Assessment Method of Collapse in Mountain Tunnels and Application

The collapse is one of the most frequent and harmful geological hazards in the construction process of mountain tunnels. In order to effectively control the occurrence of collapse, a new dynamic risk assessment methodology for collapse based on attribute synthetic evaluation model was established, which includes primary assessment before the excavation and second assessment between excavation and support. According to statistical analysis of many collapse cases, the surrounding rock level I1, rock mass integrity I2, buried depth I3, bias angle I4, groundwater I5, construction factors I6 were selected as assessment indices. Their weights were calculated by using a combination method: subjective weight based on frequency statistic method and objective weight based on analytic hierarchy process. According to the proposed method, the Mountain Tunnel Collapse Risk Assessment System (TCAS) was developed to carry out the real-time assessment for collapse in the mountain tunnel. The TCAS was applied in Hongyansi Tunnel and Shimenya Tunnel. The results were a good agreement with actual excavation situation and the results of other methods.