## 3 Application of the New Charging Structure
### Results and Discussion  
To verify the availability of the new charging structure, three full-section tests were performed in the excavation face. The three tests used 34, 28, and 33 peripheral holes, respectively. The test blastholes were charged using the new charging structure mentioned above and paint was marked on the rock surrounding the corresponding test blastholes. The blasting effect was confirmed and the blasting traces were observed after blasting was completed. After blasting, the test blastholes were identified using the marks. The three experiments show that the new charging structure meets smooth blasting requirements. There are visible half-hole traces on the tunnel wall, the explosive exhibits a good detonation propagation effect, and misfire does not occur. The rock surrounding the blastholes drops out and the outline contour forming effect is good. Thus, there is no need to refine. Figure 8 shows the smooth blasting results of the left, right side walls, and the arch crown of the tunnel cross-section after the first test. Since there are obvious half-hole traces and there is no explosive residue, sympathetic detonation of explosives occurs in the new charging structure. According to the statistics of recent cyclical footage in tunnel excavation, the cyclical footage of three tests was 3.5 m, 3.6 m, and 3.3 m, respectively. Figure 9 shows that the cyclical footage of the three full-section tests is at a normal level. Thus, the application of the new charging structure does not affect the normal tunnel excavation cyclical footage. Figure 10 shows tunnel profile scanning photos after conventional blasting and full-section tests. Upon comparing tunnel profile scans, one can see that the tunnel profile control improves, the actual excavation profile is in good agreement with the theoretical one, the overbreak and underbreak volumes are normal, and blasting smoothness meets requirements. Figure 10 shows that reasonable amounts of overbreak and underbreak occur in some parts of the tunnel, regardless of whether the new charging  
Figure 8: Smooth blasting results from the first test. (**a**) blasthole traces on the left side wall, (**b**) blasthole traces on the arch crown, (**c**) blasthole traces on the right side wall. Figure 9: Tunnel excavation cyclical footage. structure is used. This can be dealt with in the planning section process and does not affect normal tunnel construction. Figure 10 were the tunnel profile scanning photos at the bottom of blastholes after blasting. Because the blastholes have a certain extrapolation angle, the overbreak/underbreak volumes at the at the bottom of the hole is the largest. The two-dimensional tunnel profile scanning at the bottom of blastholes can provide a reference for the overbreak/underbreak volumes of one excavation round to a certain extent. With the advancement of technology, compared with two-dimensional tunnel profile scanning, laser scanning or photogrammetry could better reflect overbreak/underbreak volumes of one excavation round. As demonstrated by [PERSON] et al. [31], the use of laser scanning or photogrammetry could clearly record the rock surface geometry. Through photogrammetric reconstruction, a three-dimensional model is established and compared with the real tunnel environment, the rock excavation conditions on each cross-sectional profile can be extracted. Therefore, in the future, the tunnel profile would be scanned after each blasting round and the volume after blasting would be compared against the ideal, designed tunnel profile in three dimensions, rather than on the two-dimensional section. Theoretically, the number of test blastholes should be 36, 31, and 41 in the three full-section blasting tests. However, we actually use 34, 28, and 33 test holes, respectively. Thus, the distance between blastholes is sometimes too large and underbreak occurs. Moreover, the average tunnel  
Figure 10: Scanning photos of tunnel profiles.