## 4 Results and Discussion
### Damage Effect of Rock under Different Explosive Quantities  
In smooth blasting, the hole spacing is small, with stress waves between neighboring holes conducted in the direction of each other along the connecting lines of the holes, which strengthens the superimposed interference effect and makes it easier to form through fissures. When studying the impact of the explosive charge on the destructive effects, considering the interaction of stress waves between blast holes due to changes in the charge can lead to more accurate results. Therefore, double blast holes with different plosive quantities are established to evaluate the variation of stress wave interactions on the rock damage effect. According to \(CS\#4\), the length of the upper explosive is reduced by 10 cm, while the length of the lower explosive is reduced by 10 cm and 20 cm, as indicated by \(CS\#7\) and \(CS\#8\). Figures 13 and 14 show the charge structure and the cloud diagram of damage to surrounding rock at 0.6 ms, respectively. Figure 14 illustrates that the damage between the holes is more severe than on both sides of the holes due to the superposition of stress waves. The degree of damage decreases with the reduction of plosive quantity. When the quantity reduces to a critical value, the damage falls below the threshold value. As a result, the stress waves cannot produce numerous through-cracks between adjacent blast holes, nor can they form a flat profile surface. Extract the peak tensile stress \(\sigma\)max for 8 units in the PT partition and extract the peak value of the damage variable \(D_{max}\) for all the monitoring units. Figure 15 shows the variation of \(\sigma_{tmax}\) and \(D_{max}\) with the depth of the borehole. Figure 15 shows that all four charging structures can damage the rock in the PT partition. \(CS\#6\) reduces the charge by 16.7% compared with \(CS\#4\), and the distance of the upper explosive from the free surface increases by 10 cm, while the \(\sigma\)max at the orifice increases by about 33.9%. \(CS\#7\) reduces the charge by 20% compared with \(CS\#6\), and the distance of the lower explosive from the free surface increases by 10 cm, but the \(\sigma_{tmax}\) at the orifice is about the same for both. The track at the orifice is approximately equal. Under the same change condition, \(\sigma\)tmax at the orifice of \(CS\#8\) is 25% lower than that of \(CS\#7\). Therefore, \(CS\#8\) is the best, while \(CS\#7\) is the second best. For the preferred charge structure, it is necessary to evaluate the rock damage effect of the PD partition as well. Figure 15b shows that the \(C_{D}\) values of the four charge structures are 90.9%, 100%, 100%, and 80%. Among them, the \(D_{\text{max}}\) values of \(CS\#4\) and \(CS\#8\) did not reach the damage threshold at \(\pm 10\) cm from the bottom of the hole, which increased the risk of the residual hole phenomenon. The \(D_{\text{max}}\) values of \(CS\#7\) and \(CS\#8\) showed similar trends, with a decrease in \(D_{\text{max}}\) values at 1.5 m of the middle water medium. The longer the length of the mid-water medium, the smaller the \(D_{\text{max}}\) value is, and when the length of the water medium exceeds 40 cm, the \(D_{\text{max}}\) value decreases to less than 0.75. \(CS\#6\) and \(CS\#7\) show  
Figure 13: Different plosive quantity structure. better effects in the PT and PD partitions, although the \(D_{(CD)}\) value of \(CS\#7\) is slightly larger, but the explosive quantity is less. Comprehensive analysis of the previous, preferred \(CS\#7\) for the best charging structure, the upper and lower charge ratio of 1:3, and water media volume ratio of 2:2:1. Compared with the air interval, the plosive quantity of \(CS\#7\) is reduced by about 33.3%, the explosive energy distribution is more uniform, and the utilization rate is higher. The study of literature [2] shows that when replacing 20 cm of explosives at the bottom of the hole with air, the excavation efficiency is reduced by 4.3%.