## 3 Single-Hole Column Charge Blasting Crater Test for Coal and Rock
### Analysis of Blast Crater Test Results
#### 3.2.2 Analysis of Blasting Crater Test Outcomes  
After the blast, the boundaries of the blast crater are defined, debris inside the crater is cleared, and the crater diameter is measured from different directions (spaced 45\({}^{\circ}\) apart), along with depth measurements of the crater. The typical fragmentation morphology of the coal and rock blast crater test results (partial) is illustrated in Figure 4.  
(1) Analysis of Blast Fragmentation Morphology  
The fragmentation morphology analysis of the coal bench blasting crater test results indicates that under the same borehole depth, an increase in the charge amount led to a gradual increase in the blast crater's fragmentation volume and a reduction in fragment size. As the borehole depth increased, the cast volume gradually decreased. No blast crater was formed when the borehole depth was 1.4 m with charge C1 and 1.6 m with charges C1 and C2. In the rock bench blasting test, blast craters were formed in all cases, and the fragmentation behavior was similar to that of the coal bench. In addition, the test results for coal and rock benches demonstrated that as the explosive mass increased, the large block rate of coal and rock blasting fragmentation improved effectively. With increasing borehole depth, the casting rate of blasting-fragmented coal and rock was controlled, and the large block rate was further optimized. However, as the borehole depth increased further, the upper rock mass of the borehole exhibited a higher \begin{table}
\begin{tabular}{c c c c c c c c c c c c c} \hline \hline
**Stratum** & **Type** & & & & & & & & & & & & \\ \hline \multirow{10}{*}{Coal} & Borehole depth (m) & 1.00 & 1.00 & 1.00 & 1.00 & 1.00 & 1.20 & 1.20 & 1.20 & 1.20 & 1.20 & 1.20 \\  & Charge specifications & C1 & C2 & C3 & C4 & C5 & C6 & C1 & C2 & C3 & C4 & C5 & C6 \\  & Filling height (m) & 0.87 & 0.82 & 0.78 & 0.74 & 0.69 & 0.65 & 1.07 & 1.02 & 0.98 & 0.94 & 0.89 & 0.85 \\  & Statistical volume (m\({}^{3}\)) & 2.54 & 4.28 & 5.55 & 6.36 & 7.32 & 8.11 & 2.32 & 3.79 & 4.38 & 6.52 & 7.73 & 8.77 \\  & Specific charge (kg\(\cdot\)m\({}^{-3}\)) & 0.24 & 0.19 & 0.18 & 0.19 & 0.19 & 0.20 & 0.26 & 0.21 & 0.23 & 0.18 & 0.18 & 0.18 \\  & Borehole depth (m) & 1.40 & 1.40 & 1.40 & 1.40 & 1.40 & 1.40 & 1.60 & 1.60 & 1.60 & 1.60 & 1.60 & 1.60 \\  & Charge specifications & C1 & C2 & C3 & C4 & C5 & C6 & C1 & C2 & C3 & C4 & C5 & C6 \\  & Filling height (m) & 1.27 & 1.22 & 1.18 & 1.14 & 1.09 & 1.05 & 1.47 & 1.42 & 1.38 & 1.34 & 1.29 & 1.25 \\  & Statistical volume (m\({}^{3}\)) & \(\cdots\) & 2.80 & 4.09 & 5.27 & 7.08 & 8.30 & \(\cdots\) & \(\cdots\) & 3.34 & 4.73 & 6.54 & 7.47 \\  & Specific charge (kg\(\cdot\)m\({}^{-3}\)) & \(\cdots\) & 0.29 & 0.24 & 0.23 & 0.20 & 0.19 & \(\cdots\) & \(\cdots\) & 0.30 & 0.25 & 0.21 & 0.21 \\ \hline \multirow{10}{*}{Rock} & Borehole depth (m) & 1.00 & 1.00 & 1.00 & 1.00 & 1.00 & 1.00 & 1.20 & 1.20 & 1.20 & 1.20 & 1.20 & 1.20 \\  & Charge specifications & R1 & R2 & R3 & R4 & R5 & R6 & R1 & R2 & R3 & R4 & R5 & R6 \\  & Filling height (m) & 0.65 & 0.60 & 0.56 & 0.52 & 0.47 & 0.43 & 0.85 & 0.80 & 0.76 & 0.72 & 0.67 & 0.63 \\ \cline{1-1}  & Statistical volume (m\({}^{3}\)) & 3.65 & 4.74 & 5.93 & 6.77 & 7.06 & 6.28 & 4.93 & 5.74 & 6.45 & 7.19 & 7.76 & 8.35 \\ \cline{1-1}  & Specific charge (kg\(\cdot\)m\({}^{-3}\)) & 0.44 & 0.38 & 0.34 & 0.33 & 0.34 & 0.41 & 0.32 & 0.31 & 0.31 & 0.31 & 0.31 & 0.31 \\ \cline{1-1}  & Borehole depth (m) & 1.40 & 1.40 & 1.40 & 1.40 & 1.40 & 1.40 & 1.60 & 1.60 & 1.60 & 1.60 & 1.60 & 1.60 \\ \cline{1-1}  & Charge specifications & R1 & R2 & R3 & R4 & R5 & R6 & R1 & R2 & R3 & R4 & R5 & R6 \\ \cline{1-1}  & Filling height (m) & 1.05 & 1.00 & 0.96 & 0.92 & 0.87 & 0.83 & 1.25 & 1.20 & 1.16 & 1.12 & 1.07 & 1.03 \\ \cline{1-1}  & Statistical volume (m\({}^{3}\)) & 4.58 & 5.51 & 6.00 & 6.56 & 7.10 & 7.85 & 4.22 & 5.45 & 5.82 & 6.97 & 5.84 & 7.04 \\ \cline{1-1}  & Specific charge (kg\(\cdot\)m\({}^{-3}\)) & 0.35 & 0.33 & 0.33 & 0.34 & 0.34 & 0.33 & 0.38 & 0.33 & 0.34 & 0.32 & 0.41 & 0.37 \\ \hline \hline \end{tabular}
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