## 3 Single-Hole Column Charge Blasting Crater Test for Coal and Rock
### Analysis of Blast Crater Test Results  
#### 3.2.1 Measurement and Statistics of the Blast Crater Volume  
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 results of the statistics are presented in Table 3. Due to the excessive burial depth of explosives in some test holes and the significant confinement effect of the rock, it led to the irregular shape of the crater's bottom, resulting in significant errors in the volume statistics. Therefore, the parabolic method was employed to measure and calculate the statistical volume of each blasting crater. The method is as follows: a plane perpendicular to the borehole axis and aligned with the height of the fractured uplift at the crater perimeter is used as the reference plane. The blasting crater cross-section is divided into a 200 \(\times\) 200 mm grid, and the distance \"\(Y\)\" from each point on the blasting crater's contour to the reference plane is measured, representing the blasting fracture depth at each measurement point. The cross-sectional area is then calculated using Formula (1).  
\[S_{i}=\frac{B}{3}\big{[}(Y_{1}+Y_{\text{m}})+2\big{(}Y_{2}+Y_{4}+\dots+Y_{2j}+ \dots\big{)}+4\big{(}Y_{1}+Y_{3}+\dots+Y_{2j+1}+\dots\big{)}\big{]} \tag{1}\]  
\begin{table}
\begin{tabular}{c c c c c c c c c} \hline \hline
**Bench** & \begin{tabular}{c} **Step** \\ **Height** \\ **\(H\) (m)** \\ \end{tabular} & \begin{tabular}{c} **Berohole** \\ **Diameter** \\ **\(D\) (mm)** \\ \end{tabular} & \begin{tabular}{c} **Cartridge** \\ **Diameter** \\ **\(d\) (mm)** \\ \end{tabular} & \begin{tabular}{c} **Hole** \\ **Pitch** \\ **\(a\) (m)** \\ \end{tabular} & \begin{tabular}{c} **Row** \\ **\(\mathbf{B}\) (mm)** \\ \end{tabular} & \begin{tabular}{c} **Hole Depth** \\ **\(\mathbf{D}\) (mm)** \\ \end{tabular} & \
\begin{tabular}{c} **Charge** \\ **Quantity** \\ **\(\mathbf{Q}\) (kg)** \\ \end{tabular} &
\begin{tabular}{c} **Charge Length** \\ **\(I_{E}\) (m)** \\ \end{tabular} \\ \hline Rock & 14.00 & 70.00 & 70.0 & 5.0 & 7.0 & 1, 12, 1.6, 1.8, 2.0, & 0.36, 0.40, 0.45, \\  & & & & & 1.4, 1.6 & 2.2, 2.4, 2.6 & 0.50, 0.54, 0.58 \\ Coal & 6.00 & 70.00 & 70.0 & 5.0 & 7.0 & 1, 1.2, 0.6, 0.8, 1.0, & 0.13, 0.18, 0.22, \\  & & & & & 1.4, 1.6 & 1.2, 1.4, 1.6 & 0.26, 0.31, 0.35 \\ \hline \hline \end{tabular}
\end{table}
Table 2: Parameters of blasting crater test.  
Figure 3: Operational bench of the experiment.  
Figure 2: Orthogonal test design for blasting crater and parameters.  
where \(S_{i}\) is the area of the \(i\)-th section, \(i\) = 1, 2, 3, \(\ldots\), m\({}^{2}\); \(B\) is the distance between measurement points, \(B\) = 0.2 m; \(Y_{j}\) is the blasting depth at the \(j\)-th point, \(j\) = 1, 2, 3, \(\ldots\), m.  
Then, based on the area of each section, the statistical volume \(V\) (m\({}^{3}\)) of the blasting crater is calculated using the frustum formula, as shown below:  
\[V=\frac{B}{3}\left[(S_{1}+S_{n})+2\left(S_{1}+S_{2}\cdots+S_{i}+\cdots+\sum_{i =1}^{n}(S_{i}\cdot S_{i1})^{1/2}\right)\right] \tag{2}\]  
The statistical results of the coal and rock blasting crater parameters are listed in Table 3.