# Formation Mechanism and Control Technology of an Excavation Damage Zone in Tunnel-Surrounding Rock
## 4 Monitoring the Loose Circle after Two Blasting Tests
In terms of loose range of surrounding rock, the depth of the loose circle caused by the nonelectric detonator was 1.49\(\sim\)2.35 m, and the depth caused by the electronic detonator was 0\(\sim\)1.35 m. The loose range caused by nonelectric detonators is significantly larger than that of electronic detonators in each radial direction, as shown in Figure 8.0 The serious damage depth of 2.35 m is avoided in the L3 direction, and the reduction in other directions is basically above 1 m. Two sections with the same surrounding rock properties cannot be found in the field test, and the random distribution of joint fissures cannot be avoided. There are a large number of joint fissures in the left tunnel wall and the right tunnel spandrel of the test section using electronic detonators after field investigation. The rock is mixed with a weak sand layer, and the water seepage phenomenon is obvious. This leads to the phenomenon of large damage depth at the L1, L2, and R3 positions in the electronic detonator test results. The electronic detonators can reduce the damage depth of more than 1 m, which can significantly reduce the use of supporting bolts, resulting in greater economic benefits, according to the construction experience. At the same time, it also avoids the construction process of post grouting reinforcement. More importantly, it can ensure the safety and stability of the tunnel after blasting. (2) In addition, the use of electronic detonators not only reduces the depth of the damage range but also has a significant effect on retaining the integrity of the surrounding rock. The wave velocity of the rock mass in the loose circle caused by the nonelectric detonator decreases to 13\(\sim\)40%, and that of the rock mass in the loose circle caused by  
Figure 8.1 Schematic diagram of a loose circle during tunneling by nonelectric and electronic detonator blasting. \begin{table}
\begin{tabular}{c c c c c} \hline \hline \multirow{2}{*}{**Test Holes**} & \multirow{2}{*}{**Loosening Range (m)**} & \multicolumn{2}{c}{**Reduction Degree of Longitudinal**} \\  & & & **Wave Velocity of Surrounding** \\  & & & & **Rock** \\ \cline{2-5}  & **Nonelectric** & **Electronic** & **Nonelectric** & **Electronic** \\ \hline R1 & 1.49 & 0 & 22\% & 2\% \\ R2 & 1.75 & 0 & 14\% & 2\% \\ R3 & 1.95 & 1.25 & 13\% & 16\% \\ L1 & 2.15 & 1.15 & 33\% & 17\% \\ L2 & 2.16 & 1.35 & 28\% & 20\% \\ L3 & 2.35 & 0 & 40\% & 2\% \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Property parameters of the tunnel nonelectric and electronic detonator blasting loose circle. the electronic detonator decreases to 16-20%, as shown in Table 3. The use of electronic detonators can significantly weaken the reduction of longitudinal waves in the surrounding rock. It is conducive to giving full play to the supporting role of the original surrounding rock and ensuring the stability of the excavated tunnel. The field tests consume a lot of human and material resources and delay the construction period. It cannot be carried out on a large scale. Therefore, in order to further study the differences between electronic and nonelectric detonators in tunnels surrounding rock damage, it is necessary to use finite element software for further research and analysis.