## 5 Analysis of Numerical Model Results  
### Analysis of the Separate Effects of Blast Load and Water Pressure  
Based on the above model parameters for a rock wall thickness of \(d=1.2\) m, separate models for blast load only (no aquifer) and water pressure only (no blast load) were developed to investigate the separate effects of the blast load and aquifer water pressure on the rock wall. As can be seen from Figure 7, the blast cracks produced by the blast load did not extend to the aquifer location when the original aquifer material was classified as a perimeter rock condition, indicating that the blast load alone did not directly cause a sudden surge of water in the tunnel, although the blast load alone caused cracking damage to the rock wall, the depth of which was \(d=1.18\) m. In addition, the stress cloud under separate water pressure indicates that, although the rock wall is not cracked under water pressure, there is a stress concentration at the shell hole with a pressure of \(P_{\text{S}}=0.32\) MPa, which will produce a stress release under blasting disturbance and is more likely to produce sudden water surges. During karst tunnel drilling and blasting construction, the blasting load is coupled with karst water pressure; therefore, it is necessary that the blasting load \begin{table}
\begin{tabular}{c c c c c c c c c} \hline \hline \(A\) & \(N\) & \(n\) & \(A_{1}\) (GPa) & \(A_{2}\) (GPa) & \(A_{3}\) (GPa) & \(B^{*}\) & \(B_{\text{Q}}\) & \(B_{1}\) \\ \hline
2.50 & 0.85 & 3 & 4.25 & 4.12 & 4.12 & 1.6 & 0.0105 & 1.22 \\ \hline \(B_{2}\) & \(T_{1}\) (GPa) & \(T_{2}\) & \(p_{e}\) (MPa) & \(p_{I}\) (MPa) & \(D_{1}\) & \(D_{2}\) & \(M\) & \(Q_{2.0}\) \\ \hline
1.22 & 4.387 & 0 & 13.3 & 60 & 1 & 0.001 & 0.85 & 0.685 \\ \hline \hline \end{tabular}
\end{table} 
Table 6: Limestone parameters. Figure 6: Numerical analysis geometry and mesh model schematic. and karst water pressure are coupled and included in karst tunnel sudden surge water mechanism research. Based on the above model parameters, for a rock wall thickness of \(d=1.2\) m, separate models for blast load only (no aquifer) and water pressure only (no blast load) were developed to investigate the separate effects of blast load and aquifer water pressure on the rock wall. As can be seen from Figure 7, in the original, aquifer material is dispersed into the surrounding rock conditions, and the blast cracking generated by the blast load on the rock wall caused blast damage with a depth of \(d=1.18\) m. While the width of the rock wall is 1.2 m, the damaged area does not extend to the aquifer location, which indicates that, although the blast load alone caused damage cracking on the rock wall, albeit in the absence of water pressure, it did not directly cause a water inrush in the tunnel. In addition, the stress cloud diagram under separate water pressure shows that the rock wall did not crack under water pressure, although the stress concentration at the bottom of the blast is obvious and there is a high stress area with a peak stress of \(P_{\text{S}}=0.32\) MPa. When the rock wall cracks due to the damage caused by blasting loads, the end of the resulting crack is close to reaching the stress concentration area at the bottom of the blast hole, in which case a stress release is likely to occur. This will likely result in a stress release, causing the damage fissure to penetrate the aquifer and cause water inrush in the tunnel. In the karst tunnel drilling and blasting construction process, the blasting load will be coupled with karst water pressure, and it is necessary to study the blasting load and karst water pressure coupling under the karst tunnel surge water mechanism. Note the stress curve at measurement point #1 under the blast load and water pressure alone (see Figure 6 for an illustration of the measurement point selection). As can be seen from Figure 8a, the peak stress at measurement point #1 reached 51.69 MPa under the blasting load; however, the stress at the measurement point decayed rapidly with time.