## 4 Results and Analysis
### Results and Analysis of Upper Step Excavation Tests  
According to the design parameters in Table 3, fracturing holes were arranged on the tunnel face to conduct the first upper step excavation test. The comparison before and after rock mass cracking was shown in Figure 11.  
In Figure 11, the left area of the tunnel face basically achieved the ideal rock mass cracking effect after the high-pressure gas expansion rock mass cracking, and the rock mass in the charging area was basically spalling off with a longitudinal depth of about 1.4 m. There was only a small amount of rock mass spalling off in the middle and right area of the tunnel face, but there were fractures distributed around the hole. This was because the two cutting holes in the middle and right cutting areas could not be filled with the \begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline
**Test** & **Cutting Mode** & \begin{tabular}{c} **Quantity of** \\ **Expansion** \\ **Pipe** \\ \end{tabular} & \begin{tabular}{c} **Mass of Gas-** \\ **Generating** \\ **Agent (kg)** \\ \end{tabular} & \begin{tabular}{c} **Depth of** \\ **Cutting** \\ **Cutting** \\ **Space (m)** \\ \end{tabular} & \begin{tabular}{c} **Stripping** \\ **Rock** \\ **Volume (m\({}^{3}\))** \\ \end{tabular} & \
\begin{tabular}{c} **Unit Con-** \\ **sumption** \\ **(kg\(\cdot\)m\({}^{-3}\))** \\ \end{tabular} &
\begin{tabular}{c} **Rock Fragmentation** \\ **(m)** \\ \end{tabular} \\ \hline
1 & Single wedge & 4 & 5.2 & 1.7 & 4.3 & 1.21 & 0.2–0.45 \\ \hline
2 & Double wedge & 6 & 7.8 & 1.8 & 6.7 & 1.16 & 0.2–0.4 \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Results of cutting excavation tests. Figure 11: The comparison before and after rock mass cracking in the test 3. (**a**) Tunnel face before rock mass cracking; (**b**) Tunnel face after rock mass cracking. expansion pipe. The cutting area did not play the role of creating a free surface, resulting in a poor effect. Since there was no hydraulic gun machine further processing the tunnel face, some rock mass of the fractured area was not spalling off. Therefore, the stripping rock volume in test 3 was small and was about 22 m\({}^{3}\). The field noise was moderate as expected in the test. The distribution area of most rock blocks is mainly within 3 m in front of the tunnel face, and the size of most rock blocks ranged from 0.25-0.6 m.  
According to the design parameters in Table 3, fracturing holes were arranged on the tunnel face to conduct the second upper step excavation test. The comparison before and after rock mass cracking was shown in Figure 12.  
In Figure 12, the tunnel face basically achieved the ideal rock mass cracking effect after the high-pressure gas expansion rock mass cracking, and the rock mass in the successful detonation area was basically spalling off with a longitudinal depth of about 1.5 m. There was a punching phenomenon in several holes, and only the 20-40 cm thickness of rock surface was spalling off. Some broken but not spalled rock mass was further processed by the gun machine and excavator. According to the statistics, the stripping rock volume in test 4 was about 39 m\({}^{3}\). The distribution of rock blocks after rock mass cracking at the site was shown in Figure 13.  
In Figure 13, the distribution area of most rock blocks is mainly within 3 m in front of the tunnel face, and the size of most rock blocks ranged from 0.2-0.5 m.  
Comparing the results of the two tests (see Table 5), it is concluded that the rock mass cracking effect of the auxiliary hole network parameter of \"0.8 m \(\times\) 0.7 m\" is better than that of the auxiliary hole network parameter of \"1.0 m \(\times\) 0.9 m\" when the cutting mode of \"central vertical empty hole + double wedge cutting hole\" is chosen for the cutting of the tunnel face. In the successful detonation area, the longitudinal depth of rock mass cracking  
Figure 12: The comparison before and after rock mass cracking in test 4. (**a**) Tunnel face before rock mass cracking. (**b**) Tunnel face after rock mass cracking.