# Investigation on Cutting Blasting Efficiency of Hard Rock Tunnels under Different Charge Diameters
## 5 Conclusions  
Through theoretical calculation, numerical simulation, and blasting experiments, the influence of the charge diameter on the cutting blasting efficiency of hard rock tunnels was discussed, and the main conclusions are as follows:  
(1) The theoretical calculations indicated that the radii of the fracture zones under the three different charge diameters from small to large were equal to 288 mm, 396 mm, and 525 mm, respectively. An increase in the charge diameter could expand the destruction range of the cutting holes, and further enhance the destruction degree of the rock far away from the cutting holes in the cutting cavity.  
\begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \multirow{2}{*}{**No.**} & \multicolumn{3}{c}{**Working Condition 1**} & \multicolumn{3}{c}{**Working Condition 2**} & \multicolumn{3}{c}{**Working Condition 3**} \\ \cline{2-7}  & \(D\) **(m)** & \(Q\) **(\%)** & \(D\) **(m)** & \(Q\) **(\%)** & \(D\) **(m)** & \(Q\) **(\%)** \\ \hline
1 & 1.69 & 67.6 & 2.03 & 81.2 & 2.35 & 94.0 \\
2 & 1.78 & 71.2 & 2.08 & 83.2 & 2.31 & 92.4 \\
3 & 1.75 & 70.0 & 2.11 & 84.4 & 2.38 & 95.2 \\
4 & 1.77 & 70.8 & 1.97 & 78.8 & 2.33 & 93.2 \\
5 & 1.81 & 72.4 & 2.06 & 82.4 & 2.29 & 91.6 \\
6 & 1.74 & 69.6 & 2.09 & 83.6 & 2.39 & 95.6 \\
7 & 1.72 & 68.8 & 2.04 & 81.6 & 2.34 & 93.6 \\
8 & 1.80 & 72.0 & 1.99 & 79.6 & 2.40 & 96.0 \\
9 & 1.76 & 70.4 & 2.07 & 82.8 & 2.37 & 94.8 \\
10 & 1.78 & 71.2 & 2.06 & 82.4 & 2.34 & 93.6 \\ Average & 1.76 & 70.4 & 2.05 & 82.0 & 2.35 & 94.0 \\ \hline \hline \end{tabular} Note: \(D\) represents the final cutting depth. \(Q\) represents the hole utilization.  
\end{table}
Table 7: Statistics of cutting blasting results.  
Figure 11: Typical rock fragmentations. (**a**) Working condition 1. (**b**) Wording condition 2. (**c**) Working condition 3.  
(2) The developments of blasting stress waves were visually displayed by numerical simulation. The blasting stress field intensity in the cutting cavity under condition 2 increased by 42-54% on the basis of condition 1, and that under condition 3 increased by 32-44% on the basis of condition 2. The higher stress field intensity was more beneficial to encouraging the rock in the cutting cavity to form small rock fragments that were easy to be discarded.  
(3) The experimental results showed that under the three different charge diameters from small to large, the average final cutting depths were 1.76 m, 2.05 m, and 2.35 m, respectively, and the average hole utilizations of the cutting blasting were 70.4%, 82.0% and 94.0%, respectively. The results powerfully validated that the increase in charge diameter had effectiveness in raising the cutting efficiency of hard rock mine tunnels.  
Conceptualization, P.G. and Q.Z.; methodology, P.G. and B.C.; software, B.C.; validation, P.G., Q.Z. and B.C.; formal analysis, P.G., Q.Z. and B.C.; investigation, P.G., Q.Z., B.C., H.W., Y.X. and B.Z.; data curation, P.G., Q.Z. and B.C.; writing--original draft preparation, P.G. and B.C.; writing--review and editing, P.G. and B.C. All authors have read and agreed to the published version of the manuscript.  
This research was funded by the National Natural Science Foundation of China (nos. 51374012 and 52074009) and the Science Research Project of Zhejiang Province Construction (no. 2021K213).  
Not applicable.  
The data used to support the findings of this study are included within the article.  
The authors declare no conflict of interest.