## 4 Results and Discussion
### Damage Effects of Rocks under Different Water Interval Charge Configurations
#### 4.2.2 Length of Water Interval at the Top of the Blast Hole  
Based on the study of Section 4.2.1, the length of the upper water bags for \(CS\#2\) was adjusted using the control variable method. Set 30 cm and 20 cm water bags at the orifice, indicated by \(CS\#4\) and \(CS\#5\). Figures 10 and 11 show the charge structure and the cloud diagram of damage to surrounding rock at 0.6 ms, respectively. The figure shows that as  
Figure 8: Rock damage range around the blast hole at 0.6 ms: (**a**)\(-CS\#1\), (**b**)\(-CS\#2\), (**c**)\(-CS\#3\).  
Figure 9: Variation of \(\sigma_{tmax}\) and \(D_{max}\) with depth of blasthole: (**a**) the variation curve of \(\sigma_{tmax}\), (**b**) the variation curve of \(D_{max}\).  
the water bags at the orifice become shorter, the center of gravity of the explosives shifts upwards, and the damage zone is no longer concentrated in the middle of the blast hole. However, the rock damage at the bottom of the hole tends to decrease because the water bags in the middle become longer and weaken the superposition of stress waves.  
This section covers three charge configurations. The range sizes of PT and PD partitions are different. For comparison, _CS#2_, which has the largest area of PT partition, is taken as a reference. Extract the peak tensile stress \(\sigma\)tmax for 8 units in the PT partition and extract the peak value of the damage variable \(D_{max}\) for all the monitoring units. Figure 12 shows the variation of \(\sigma_{tmax}\) and \(D_{max}\) with the depth of the borehole.  
Figure 12 shows that \(\sigma_{tmax}\) is greater than \(\sigma_{td}\) in PT partition, which reaches the destructive strength of the rock. As the length of the upper water medium changes, the height of the PD partition changes to 1 m, 1.1 m, and 1.2 m. According to Figure 12b, the lengths of the damage variables greater than 0.75 in the PD partition of _CS#2_, _CS#4_, and _CS#5_ are about 70 cm, 80 cm, and 60 cm, which means that the percentage of \(C_{D}\) is 70%,  
Figure 11: Rock damage range around the blast hole at 0.6 ms: (a)—_CS#2_, (b)—_CS#4_, (c)—_CS#5_.  
Figure 12: Variation of \(\sigma_{tmax}\) and \(D_{max}\) with depth of blashhole: (a) the variation curve of \(\sigma_{tmax}\), (b) the variation curve of \(D_{max}\).  
Figure 10: Different water media length at the blast hole orifice.  
72.7%, and 50%, and the variance \(D_{(CD)}\) values are 0.18, 0.15, and 0.21, respectively. It shows that the damage distribution in the PD partition of \(CS\#4\) is more uniform, which is no phenomenon of local damage that is too large or too small. \(D_{\text{max}}\) values at 8 cm below the bottom of the hole is 0.86, the soft rock with developed joints and fissures and poor blastability, avoiding the phenomenon of underbreak while not causing extensive damage to the bottom of the hole. Considering the variation of \(C_{D}\) and \(D_{max}\) values together, \(CS\#4\) can maintain a high level of damage steadily in the PD partition, while having a higher level of tensile stress in the PT partition, resulting in better blasting results.