# Study on Rock Damage Mechanism for Lateral Blasting under High In Situ Stresses
## 3 Results and Analysis
### Influence of Span Ratio on the Damage Distribution  
In this section, the span X of 100 mm, \(W=4\) cm, and P1 = 5 MPa were kept, and the span Y = 100, 110, 120 and 130 mm were considered to investigate the characteristic of the damage distribution with different span ratios \(k=\frac{\text{span Y}}{\text{span X}}\). Considering that the static stress field on the top side is less influenced by the variation of span Y, the borehole layout placed on the top side is not considered in this section. Figure 12 shows the Y-direction elastic stress fields with different \(k\) under P1 = P2 = 5 MPa. It can be found that with span Y increases, the \(\sigma_{y}\) on the right side of the rectangle cavern reduces from around 6 MPa to around 2 MPa, but varies little on the top side. The results indicate that the Y-direction compressive stress field on the right side is weakened with the increase of \(k\). Figure 13a shows the explosion crater with different \(k\) under P1 = P2 = 5 MPa. In the XY plane, the crater Y-direction dimensions near the free surface are enlarged with the increase of \(k\), which is similar to the characteristics of case II when \(\lambda\geq 0.4\) in Section 3.2. The expanded damage zones are also induced by the combined effect of the Y-direction rock rebound and the X-direction compressive stress field. When \(k\) increases, the Y-direction  
compressive stress field reduces, and the X-direction compressive stress field increases, which can intensify the combined effect and improve the X-direction damage development. In the XZ plane, the crater shape is enlarged with the increase of \(k\), and the variation characteristic is also consistent with the results of case II when \(\lambda\geq 0.4\) in Section 3.2. In the YZ plane, the crater shape changes from an ellipse to a circle with the increase of \(k\), which is induced by the weakening of the Y-direction compressive field. Figure 13b shows the explosion crater with different \(k\) under P1 = 5 MPa and P2 = 10 MPa. The results show that the shape variation characteristics are similar to those under P1 = P2 = 5 MPa. The crater volumes under different \(k\) are listed in Table 4. It can be found that the crater volume increases with \(k\) increases. The results indicate that in the stressed rock mass, the explosion crater can be improved by increasing the free surface span on the side of the borehole. Especially for the case of unequal biaxial loading, the rock on the side of the maximum principle stress should be excavated first, where the rock breaking efficiency is higher than the other side with the same span, and then the span on the other side can be increased, which is beneficial to improving the explosion crater on this side. In the view of strain energy density, [PERSON] [35] pointed out that the rock mass with a poor strain energy density should be excavated first to release the high strain energy of the adjacent rock, and then the release intensity of strain energy can be effectively controlled and the vibration induced by the instantaneous unloading can be reduced. In our study, the borehole on the side of P2, where the strain energy density is poor (as shown in Figure 14), should also be detonated firstly to improve the crater volume and the critical embedding depth of the charge. Besides, as shown in Figure 14, with the excavation of rock mass on the side of P2, the strain energy density on the other side (P1) will be reduced. The result is beneficial to the control of vibration induced by the instantaneous unloading and the increase of the rock breaking efficiency in the high strain energy zone. \begin{table}
\begin{tabular}{c c c} \hline \hline \multirow{2}{*}{\(k\)} & \multicolumn{2}{c}{V/cm\({}^{3}\)} \\ \cline{2-3}  & **P1 = 5 MPa P2 = 5 MPa** & **P1 = 5 MPa P2 = 10 MPa** \\ \hline
1.0 & 130.2 & 119.0 \\
1.1 & 139.0 & 128.1 \\
1.2 & 141.1 & 135.0 \\
1.3 & 150.0 & 143.2 \\ \hline \hline \end{tabular}
\end{table} 
Table 4: The crater volumes under different \(k\).