# 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  
In this section, a span X of 100 mm and a span Y of 100 mm are applied to the numerical model, and then the simulations of uniaxial loading of P1, uniaxial loading of P2, and biaxial loading were conducted. The damage contours of cut Z1 at 100 us were extracted from the numerical results. The variation characteristics of damage distribution, the volume \(V\) and the shape of the crater were studied in detail in this section. According to the elastic mechanics, on the right side of the rectangle cavern, the X-direction stress is small, and the stress field is governed by the Y-direction stress, especially near the free surface. Therefore, the blast-induced damage is mainly affected by the original Y-direction stress field. Figure 3 shows the Y-direction elastic stress fields (\(\sigma_{y}\)) under different static loads (\(W\) = 4 cm). For the stress \(\sigma_{y}\), its sign is positive in tension and negative in compression. As seen from the Y-direction stress contours, the rectangle cavern induces stress concentration near the free surface. For P1 = 5 MPa, as shown in Figure 3a, there is a large tensile stress zone on the left side of the borehole, especially near the free surface, and a small tensile stress zone on the right side of the borehole. The maximum tensile stress is 6.6 MPa near the free surface and \(\sigma_{y}\) decreases to around 2 MPa on the left side of the borehole. For P2 = 5 MPa, as shown in Figure 3b, the excavation zone is in a compressive stress field. The \(\sigma_{y}\) is maximum around the free surface (around 12 MPa), and it decreases to around 7 MPa on the left side of the borehole. For P1 = P2 = 5 MPa, as shown in Figure 3c, the excavation zone is also in a compressive stress field, but the compressive stress field is weakened, and the distribution changes a lot. The maximum \(\sigma_{y}\) transfers from the free surface, where the \(\sigma_{y}\) decreases to around 4 MPa, to the four corners of the cavern. The above static stress field analysis is beneficial to understanding the coupling mechanism of static load and blasting stress wave load on the rock damage characteristics in the subsequent dynamic analysis. To evaluate the influence of P1 on the damage distribution due to blasting, five cases of uniaxial static loads, P1 = 0, 2, 5, 8, and 10 MPa, were first conducted in this section. Figure 4 shows the damage contours for different P1 with different burdens at cut Z1. As mentioned in Section 2.2, the elements with a damage level above 0.7 are regarded as severe damage zone and form the explosion crater. In the case of P1 = 0 MPa, blast-induced severe damage zones (\(D\geq 0.7\)) are widely distributed and can form craters from the charge center to the free surface when the burden \(W\) is no more than 4 cm. When \(W\) is more than 5 cm, the blast-induced severe rock damage (\(D\geq 0.7\)) mainly distributes around the explosive and little severe damage zone covers the free surface, but the two zones are not connected. Thus, in the cases of \(W\) = 5 cm and \(W\) = 6 cm, only blasting cavities are formed around the  
Figure 2: Numerical model of single hole blasting with a lateral free surface. charge but no crater is formed by the blasting. Therefore, the burden should be no more than 4 cm to form an explosion crater in the case of P1 = 0 MPa. In the case of P1 = 2 MPa, the damage zones are enlarged for each burden, but the severe damage zone (\(D\geq\) 0.7) around the charge and the damage zone near the free surface are still separated when \(W\) = 5 cm and \(W\) = 6 cm, which indicates no crater is formed. When P1 increases to 5 MPa, the damage zones are further enlarged, and the two zones begin to connect for \(W\) = 5 cm but not for \(W\) = 6 cm. In the case of P1 = 8 MPa and 10 MPa, with the increase of static load, the damage zones become larger. Especially for \(W\) = 5 cm, the severe damage zone is clearly enlarged near the free surface, thus a crater is formed.