# Study on Rock Damage Mechanism for Lateral Blasting under High In Situ Stresses
## 3 Results and Analysis
### Influence of Biaxial Static Load on the Damage Distribution  
To investigate the characteristic of damage distribution under biaxial loading, \(W\) = 4 cm and P1 = 5 MPa were kept, 11 cases of P2, 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, and 10 MPa, were simulated to investigate the effect of the pressure coefficient \(\lambda=\frac{\text{P2}}{\text{P1}}\) on damage distribution. The borehole is placed on the right side of the cavern, named as case I, or the top side of the cavern, named as case II. Figure 11a shows the shapes of craters for \(W\) = 4 cm under biaxial loads with different \(\lambda\) for case I. With the \(\lambda\) increases, the shapes in the three planes are shrinking in the overall trend. In the XY plane, the shape transforms from a trapezoid to a triangle, and the X-direction dimension reduces much to cause the decrease of the depth of the crater. In the XZ plane, away from the free surface, the Z-direction and X-direction dimensions are both reduced due to the increasing Y-direction compressive stress field. In the YZ plane, two damage zones distribute the leftmost side and the rightmost side along the Z direction for \(\lambda\) = 0, but they disappear for \(\lambda\) = 0.4. For \(\lambda\) = 0, the two damage zones are formed by the combined effect of \(\sigma_{yR}\) and \(\sigma_{yI}\) induced by P1. However, for \(\lambda\) = 0.4, the addition of the new Y-direction compressive stress field (\(\sigma_{y2}\)) induced by P2 will neutralize part of the tensile stress and prevent the formation of the two damage zones. When \(\lambda\) \(\geq\) 0.4, the shape is getting flatter due to the increase of the additional compressive stress field. For case I, the crater volume \(V\) reduces monotonically with the increase of \(\lambda\), as shown in Figure 11c. Figure 10: The craters for \(W\) = 4 cm under different P2: (**a**) perspective view of craters at different planes; (**b**) section A-A. It should be noted that the law only applies to the case of small \(\lambda\). When \(\lambda\) is large enough, the Y-direction compressive stress field induced by lateral pressure P2 will govern the damage distribution around the surface and away from the charge, and the crater volume may be increased with the increase of \(\lambda\), as described in the uniaxial loading case of P2. Figure 11: The shapes and the volumes of craters for \(W\) = 4 cm under biaxial loads with different \(\lambda\) (P1 = 5 MPa): (**a**) case I; (**b**) case II; (**c**) volume with \(\lambda\). Figure 11b shows the shapes of craters for \(W=4\) cm under biaxial loads with different \(\lambda\) for case II. The shape of the explosion crater is the smallest in each plane when \(\lambda=0.4\). In the XY plane, the dimension in the X direction reduces first when \(=0.4\). This is because the X-direction compressive stress field, which is beneficial for the damage development along the X direction, is weakened by the X-direction tensile stress field induced by P2. When \(\lambda=1.0\), the dimension in the X direction increases instead, especially the damage zones on the upside and downside of the borehole. This is because that the damage mechanism has changed, and the damage zones are mainly formed by the combined effect of the X-direction tensile stress, which is caused by the rock rebound, and the Y-direction compressive stress field induced by P2. Compared with the case of \(\lambda=0.4\), the compressive stress field reduces in the X direction but enhances in the Y direction, which is beneficial for the evolution of the damage zones on the upper and lower sides of the borehole. Therefore, the X-direction crater dimension increases at the top of the crater. When \(\lambda=1.6\) and \(2.0\), the crater shape is enlarged further due to the increase of P2. In the YZ plane, the variation characteristics of the crater shape are similar to those in the XY plane, and the shape tends to be a triangle, which is consistent with the characteristics in the uniaxial loading cases of P1.