# Study on Rock Damage Mechanism for Lateral Blasting under High In Situ Stresses
## 3 Results and Analysis
### Influence of Uniaxial Static Load on the Damage Distribution under Different Burdens
It should be noted that there is still a large low-level damage zone (\(D\) < 0.7) between the blasting cavity and the free surface for \(W\) = 6 cm, as a result, the explosion crater cannot be formed. In order to evaluate the explosion crater clearly, the crater volume \(V\) is measured by counting the high-level damage elements (\(D\geq\) 0.7) and summing their volumes. The crater volumes for each burden under different static loads are shown in Figure 5. It can be found that with P1 increases, the volume of explosion crater tends to increase. When P1 is less than 8 MPa, the \(V\) for \(W\) = 2 cm is the smallest (no crater for \(W\) = 5 and 6 cm, as shown in Figure 4) due to excessive dissipation of the explosion energy into the atmosphere and the \(V\) for \(W\) = 3 cm is the largest, which indicates that the optimal burden is 3 cm. However, when P1 is more than 8 MPa, the burden of 4 cm is optimal because its corresponding crater volume is the largest. It can be clearly seen that the \(V\) for \(W\) = 2 cm is not sensitive to the static load, but the others vary greatly with changing P1, especially for \(W\) = 4 cm, \(W\) = 5 cm and \(W\) = 6 cm when P1 \(\geq\) 5 MPa. The above results are due to the rapid expansion of the damage zone near the free surface for \(W\) = 5 cm and \(W\) = 6 cm (as shown in Figure 4). It should be noted that the \(V\) for \(W\) = 6 cm is the volume sum of the blasting cavity and the  
Figure 3: Y-direction elastic stress fields (\(\sigma_{y}\)) under different static loads (\(W\) = 4 cm): (a) P1 = 5 MPa; (b) P2 = 5 MPa; (c) P1 = P2 = 5 MPa. damage zone near the free surface, but not the crater volume (as shown in Figure 4). It can be concluded that the P1 can change the optimal burden of charge and increase the critical embedding depth of the charge. In order to investigate the variation in the shape of the explosion crater, the craters (formed by the elements with \(D\geq\) 0.7) for \(W\) = 4 cm under different P1 are plotted in Figure 6. In the XY plane, the shape of the explosion craters is similar to a triangle and expands with the increase of P1. The diameter of the crater in the Y direction also becomes larger with the increase of P1 at different depths (X direction), especially in the top of the crater, where a new damage zone is generated. The above results are induced by the combined effect of the Y-direction tensile component of the stress wave and the Y-direction tensile stress field (as shown in Figure 3a). In the XZ plane, there is a clear trend that with the increase of P1, the diameter in the Z direction becomes larger, especially when  
Figure 4: Damage contours for each burden under different static loads (P1) at cut Z1. Figure 5: Crater volumes for each burden under different static loads (P1). P1 = 8 MPa. This is because with the increase of Y-direction stress field (\(\sigma_{y1}\)) induced by P1, the combined effect of the Y-direction tensile component of incident stress wave (\(\sigma_{y1}\)) and Y-direction stress field (\(\sigma_{y1}\)) is intensified and promotes the initiation and propagation of radial tensile fracture at point A, as shown in Figure 7a. Besides, some damage zones appear in the left side of the borehole due to the stress concentration, but they expand little in the Y direction, as shown in the YZ plane. In the YZ plane, when P1 = 5 MPa, the long axis of the bottom circle of the crater is in the Y direction. This is because the superposition of the Y-direction component of reflected tensile stress (\(\sigma_{yR}\)) and Y-direction stress field (\(\sigma_{y1}\)) at point B (as shown in Figure 7b) increases the Y-direction dimension of reflected tensile damage zone around the free surface, which is also shown in the XY plane. However, with the increase of P1, the long axis of the bottom circle of the crater transfers from Y direction to Z direction due to the faster growth of the diameter in the Z direction, which is consistent with the results in the XZ plane and can be illustrated by Figure 7a.