## 3 The Index System of Risk Assessment for Tunnel Failure
### Evaluation Index  
Three types of evaluation indexes (geological parameters, mining disturbances, and MS data) (Figure 5) were selected for the risk assessment of tunnel failure in the Ashele  
Figure 4: Distribution of tunnel damage with different damage in the Ashele Copper Mine.  
Figure 3: Failure characteristics of different levels of tunnels in the Ashele Copper Mine. (**a**) No damage; (**b**) slight damage; (**c**) moderate damage.  
copper mine by considering the mining engineering, monitoring data, and tunnel damage characteristics. The evaluation indexes of geological parameters were angled between the tunnel and the maximum principal stress, depth, and lithology. The evaluation index of mining disturbances was the distance between the tunnel and its nearest slope. The evaluation indexes of MS data included the accumulative number of MS events, the accumulative released energy, the density of MS events, apparent stress, and displacement. The definitions of these nine evaluation indexes are introduced in Table 2.  
\begin{table}
\begin{tabular}{p{113.8 pt} p{284.5 pt}} \hline \hline
**Evaluation Index** & **Description** \\ \hline Angle & Defined as the angle between the tunnel and the maximum principal stress. The majority of the damage occurred in the strike-drift that, which is oriented perpendicular to the maximum principal stress. \\ \hline Depth & The deeper the tunnels are buried, the greater the vertical stress and the more serious damage that occurs. \\ \hline Lithology & The lithology and the development of joints and fractures have an important influence on the damage of tunnel. \\ \hline Distance & Rock mass is inevitably subjected to changes in stress field after the ore is mined and during blasting disturbances. The closer the tunnel is to the stope, the more the mining disturbances and unloading effects affect the tunnel stability. \\ \hline Accumulated events & Total number of MS events generated within a certain time period and region. The number of accumulated events is used to evaluate the change in regional fracture activities. \\ \hline Accumulated energy & Total energy released by MS events within a certain time period and region. The accumulated energy is used to reflect the degree of energy released by cracks generated inside the rock mass. \\ \hline Event density & Number of MS events per unit volume of rock mass. The event density is used to describe the cluster extent of MS events. \\ \hline Apparent stress \(\sigma_{a}\) & The apparent stress is the ratio of the total radiated seismic energy to the seismic moment. It assesses the amount of energy released per unit of deformation and is defined as: \(\sigma_{a}=\mu/M_{0}\), where \(u\) is the modulus of rigidity of the source and \(M_{0}\) is the seismic moment. \\ \hline Displacement \(\overline{u}\) & It is the average displacement of the source, where \(r_{0}\) is the source radius and is defined as:\(\overline{u}=\frac{M_{0}}{\mu\overline{r_{0}}}\) \\ \hline \hline \end{tabular}
\end{table}
Table 2: Description of the evaluation indexes for tunnel failure in the Ashele copper mine.  
Figure 5: Distribution of MS events within the deep mining area of the Ashele Copper Mine.  
In total, 100 observations between April 2017 to June 2018 were used to populate a risk assessment model for tunnel failure (Table 3). The numbers of no damaged samples, slightly damaged samples, and moderately damaged samples were 24, 44, and 22, respectively. In total, 90 of the observations were randomly selected for modeling, while 10 observations were used for the generalization ability test.