## 4 Results and Analysis  
### Results and Analysis of Cutting Excavation Tests  
According to the design parameters in Table 2, cutting holes and empty holes were arranged on the tunnel face to conduct the first cutting excavation test. The comparison before and after cutting rock mass cracking was shown in Figure 8.  
In Figure 8, the rock mass near cutting holes #1, #2 and #3 was basically spalling off after the high-pressure gas expansion rock mass cracking. There was a punching phenomenon in cutting hole #4, so the rock mass around the hole was not spalling off, but there was a small amount of fracture distributed around the hole. The section formed by rock mass cracking had an irregular shape, with a maximum width of 2.5 m, a maximum height of 4.0 m and an area of about 6.7 m\({}^{2}\). The deepest depth of cutting space could reach  
Figure 7: Plane arrangement of fracturing holes in the upper step excavation tests. (**a**) Test 3; (**b**) Test 4.  
1.7 m. Some broken but not spalled rock mass were further processed by the gun machine and excavator. According to the statistics, the stripping rock volume in test 1 was about 4.3 m\({}^{3}\). The field noise was slightly larger than expected due to the punching phenomenon in the test. The distribution of rock blocks after rock mass cracking at the site was shown in Figure 9.  
In Figure 9, the distribution of the rock blocks was relatively scattered in the test, and the rock fragmentation ranged from 0.2-0.45 m. The farthest distance of the rock blocks from the tunnel face reached 20 m.  
According to the design parameters in Table 2, cutting holes and empty holes were arranged on the tunnel face to conduct the second cutting excavation test. The comparison before and after cutting rock mass cracking was shown in Figure 10.  
Figure 8: The comparison before and after cutting rock mass cracking in test 1. (**a**) Tunnel face before cutting rock mass cracking; (**b**) Tunnel face after cutting rock mass cracking.  
Figure 10: The comparison before and after cutting rock mass cracking in test 2. (**a**) Tunnel face before cutting rock mass cracking; (**b**) Tunnel face after cutting rock mass cracking.  
Figure 9: The distribution of rock blocks after rock mass cracking in the test 1.  
In Figure 10, the rock mass near cutting holes was basically spalling off after high-pressure gas expansion rock mass cracking. The section formed by rock mass cracking had an irregular shape, with a maximum width of 3.9 m, a maximum height of 2.8 m and an area of about 7.5 m\({}^{2}\). The deepest depth of cutting space could reach 1.8 m. 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 2 was about 6.7 m\({}^{3}\). The field noise was moderate as expected in the test. The distribution area of large rock blocks is mainly within 3 m in front of the tunnel face, and occasionally small pieces of rock fragment flew 50 m away. The rock fragmentation ranged from 0.2-0.4 m.  
Comparing the results of the two tests (see Table 4), it is concluded that the rock mass cracking effect of the cutting mode of \"central vertical empty hole + double wedge cutting hole\" is better than that of the cutting mode of \"central vertical empty hole + single wedge cutting hole\". With the cutting mode of \"central vertical empty hole + double wedge cutting hole\", the maximum depth of the cutting space is deeper, and the unit consumption is smaller, and the distribution of the rock blocks is relatively concentrated, and the rock fragmentation is relatively uniform. Therefore, in the upper step excavation tests, the cutting mode of \"central vertical empty hole + double wedge cutting hole\" was uniformly chosen for the cutting of the tunnel face.