## 5 Case Study: \"11.28\" Rockburst in Jinping II Drainage Tunnel
### Simulation Results and Analysis  
A numerical simulation was carried out for the \"11.28\" rockburst case, and the numerical calculation results of the surrounding rock's multivariate catastrophe information after the tunnel excavation are shown in Figure 10. Figure 10a-c, respectively, represents the distribution law of the principal stress difference \(\Delta\sigma\), elastic strain energy \(U^{\mathrm{e}}\), and multi-parameter rockburst energy index \(C_{rs}\) value of surrounding rock. According to Figure 10a, the maximum value of \(\Delta\sigma\) within the surrounding rock is 140 MPa. The \(\Delta\sigma\) value at the upper left of the tunnel is large. The \(\Delta\sigma\) value at both sides and the bottom depth of about 3 m of the tunnel is larger than 60 MPa, and the same is true between the tunnel and structural plane, without any obvious stress concentration above the structural plane. According to Figure 10b, energy is mainly concentrated around the surrounding rock and the region between the tunnel and structural plane, with energy accumulation more obvious at the vault and left spandard of the tunnel. The peak energy value is 1.34 MJ/m\({}^{3}\), while there is no obvious energy accumulation above the structural plane. According to Figure 10c, the peak value of \(C_{rs}\) between the tunnel and structural plane is larger than 40, and the larger value of \(C_{rs}\) shows obvious \"V\" distribution characteristics. According to the judgment standard of rockburst intensity, the rockburst intensity grade of the rock mass within this range is an intense rockburst, and the occurrence range of rockburst is large. The simulated rockburst proneness characteristics are compared with the actual situation of the rockburst pit geometric size, and the results are shown in Figure 11. From the figure, the occurrence range and intensity grade of rockburst reflected by the \(C_{rs}\) index distribution obtained through simulation are basically consistent with the distribution and intensity of the actual rockburst occurrence pit area on site. The rockburst occurrence range between the tunnel and structural plane is approximately in a \"V\" type distribution, and the intensity grades are all above the intense rockburst. The rigid structural plane controls the occurrence boundary of the pit created during the rockburst. Affected by excavation disturbance, the internal stress adjustment, energy dissipation, and release of surrounding rock perpendicular to the structural plane led to the rock's micro-cracks initiating, inoculating, and propagating. The occurrence range of rockburst and fracture \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \(\sigma_{s}\)/MPa & \(\sigma_{y}\)/MPa & \(\sigma_{x}\)/MPa & \(\tau_{xy}\)/MPa & \(\tau_{yx}\)/MPa & \(\tau_{yx}\)/MPa & \(\tau_{xz}\)/MPa \\ \hline \(-\)46.42 & \(-\)51.68 & \(-\)61.48 & \(-\)2.37 & \(-\)0.64 & 3.45 \\ \hline \hline \end{tabular}
\end{table} 
Table 6: Boundary condition of stress [33]. Figure 10: The multivariate information distribution of surrounding rock after tunnel excavation: (**a**) Distribution of stress information; (**b**) Distribution of energy information; (**c**) Distribution of rockburst proneness. \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \begin{tabular}{c} **Density** \\ **(kg/m\({}^{3}\))** \\ \end{tabular} & \begin{tabular}{c} **Shear Modulus** \\ **(GPa)** \\ \end{tabular} & \begin{tabular}{c} **Bulk Modulus** \\ **(GPa)** \\ \end{tabular} & \begin{tabular}{c} **Poisson Ratio** \\ **(GPa)** \\ \end{tabular} & \begin{tabular}{c} **Elastic Modulus** \\ **(GPa)** \\ \end{tabular} & \begin{tabular}{c} **Chesion** \\ **Force (MPa)** \\ \end{tabular} & \
\begin{tabular}{c} **Internal Friction** \\ **angle (\({}^{\circ}\))** \\ \end{tabular} &
\begin{tabular}{c} **Tensile Strength** \\ **(MPa)** \\ \end{tabular} \\ \hline
2780 & 7.68 & 11.66 & 0.23 & 18.90 & 15.60 & 25.80 & 6.50 \\ \hline \hline \end{tabular}
\end{table} 
Table 5: Mechanical parameters of the surrounding rock [33].