# 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
The result is also consistent with the law that the long axis of blast-induced damage is parallel to the max principal compressive stress (Z direction). It can be concluded that the crater shape is governed by the reflected tensile fractures when P1 \(\leq\) 5 MPa, but governed by the radial tensile fractures when P1 \(\geq\) 8 MPa. Another five cases of uniaxial static loads, P2 = 0 MPa, P2 = 2 MPa, P2 = 5 MPa, P2 = 8 MPa and P2 = 10 MPa, were simulated to investigate the effect of load direction on damage distribution. Figure 8 shows the damage contours at cut Z1 and the crater volumes for different burdens under different P2. In the case of P2 = 2 MPa, the crater volumes are enlarged for \(W\) = 2 cm, 3 cm, and 4 cm, but shrunk for \(W\) = 5 and 6 cm, as shown in Figure 8b. There is still no crater formed by the blasting for \(W\) = 5 and 6 cm. as shown in Figure 8a. The increase of the crater volumes for \(W\) = 2, 3, and 4 cm is mainly induced by the increase of reflected tensile fractures around the free surface, where the combined effect of the X-direction component (\(\sigma_{xR}\)) of reflected tensile wave and the compressive stress field (\(\sigma_{y2}\)) induced by P2 promotes the damage development at point C and D, and the increase of radial tensile damage zone, where the combined effect of the Z-direction tensile component (\(\sigma_{zL}\)) of incident wave and \(\sigma_{y2}\) promotes the damage development at point B, as shown in Figure 9. However, the reductions of the crater volumes for \(W\) = 5 cm and 6 cm are induced by the reduction of radial damage zones distributed around the charge, where the volumes of blasting cavities are mainly restrained by \(\sigma_{y2}\), especially at point A, as shown in Figure 9. In the case of P2 = 5 MPa, the crater volumes are increased when \(W\) = 2 cm, 4 cm, 5 cm, and 6 cm but reduced when \(W\) = 3 cm. For \(W\) = 3 cm, this may be because the increase of reflected tensile fractures around the free surface is smaller than the reduction of the radial tensile damage zone around the charge. There is a clear increase of the damage zones for \(W\) = 4, 5, and 6 cm, which is induced by the great increase of fractures around the free surface. Especially for \(W\) = 5 cm, the fractures around the free surface are clearly enlarged and begin to connect with the blasting cavity formed by the damage zone around the charge. For \(W\) = 6 cm, the combined effect of \(\sigma_{xR}\) and \(\sigma_{y2}\) is enhanced due to the intensification of the latter, and some damage zones extend from the free surface to the borehole. However, the damage zones only distribute along the Y direction but expand little in the Z direction, so the crater is hard to form. In the case of P2 = 8 MPa and 10 MPa, with the increase of static load, the damage zones become larger, except for \(W\) = 3 cm, where the damage zone distribution along the Z direction is reduced, as shown in Figure 8a. It should be noted that the crater is still not formed for \(W\) = 6 cm. For each W, the fractures tend to extend along the Y direction with P2 increases, which is consistent with the law that the long axis of the blast-induced damage zone is parallel to the max principal stress (Y direction). Figure 6: The craters for \(W=4\) cm under different P1. Figure 7: Schematics of superposition of original stress field (P1) and stress wave and its influence on the crater shape: (**a**) radial tensile fracture induced by incident compressive stress wave; (**b**) reflected tensile fracture induced by reflected tensile stress wave. With the increase of P1 or P2, the crater volume can be enlarged. However, the increase of \(V\) with P1 is more than that with P2. For example, when \(W=4\) cm, the \(V\) for P1 increases by 17.1, 25.8, 26.8 and 60.3 cm\({}^{3}\) compared with that for P2 when the stress level is 2, 5, 8 and 10 MPa, respectively. In other words, when the static load values are the same, the \(V\) is increased by 15-31% for P1 compared with P2.