# Formation Mechanism and Control Technology of an Excavation Damage Zone in Tunnel-Surrounding Rock
## 5 Finite Element Analysis and Removal of Stress Redistribution Factors
The finite element simulation can ensure that the material properties of surrounding rock are the same in two times of blasting. The surrounding rock is assumed to be a homogeneous material without joint fissure. Therefore, the calculated results of nonelectric and electronic detonators are smaller than those of field tests, which is reasonable. This further validates the irregularity of the damage profile in Figure 11 in Section 4. It shows that in the area where the electronic detonator test is used, the joint fissures at the left wall and right spandrel positions of the tunnel have a great influence on the test results. It significantly reduces the blast resistance of surrounding rock. The field blasting tests can only monitor the final damage range of surrounding rock because of the instantaneity of explosion. In fact, the loose circle of surrounding rock is generated by the double effects of stratum stress redistribution caused by excavation and blasting load impact. Here, the finite element simulation method is used to analyze these two factors in depth. The numerical simulation consists of two cases. One was to simulate the blasting effect without applying a dynamic load, and the other was to simulate the blasting effect while applying a dynamic load. The two simulation results are shown in Table 5.  
From Table 5, the following conclusions can be drawn:  
(1) The thickness of the loose ring was approximately 1.32 m without considering the blasting load when the tunnel was excavated by conventional nonelectric detonator blasting. The thickness of the loose ring generated by the blasting load was approximately 0.66 m. The final thickness of the loose ring was 1.98 m. It can be considered that the extent of the loose circle generated by the redistribution of surrounding rock stress accounts for 67% of the final loose circle. The range of the loose circle produced by the blasting load accounts for 33% of the final loose circle range. Although the thickness of the rock loose \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Computational Model** & **Excavation Footage (m)** & **Yield Volume (m\({}^{3}\))** & **Average Thickness (m)** \\ \hline Nonelectronic detonator & 3 & 137.33 & 1.980 \\ Electronic detonator & 3 & 104.86 & 1.514 \\ \hline \hline \end{tabular}
\end{table} 
Table 4: The average thickness of the loose ring calculated by simulation. \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Computational Model** & **Loading Situation** & **Yield Unit Volume (m\({}^{3}\))** & **Loose Ring** & **Thickness of Love Ring** & **Influence of Blasting** \\  & **Situation** & **Volume (m\({}^{3}\))** & **Thickness (m)** & **Due to Blasting** & **Action on** \\  & & & **(m)** & **Load (m)** & **Loose Ring** \\ \hline Nonelectronic & Yes & 137.33 & 1.98 & 0.66 & 33\% \\ detonator & No & 91.34 & 1.32 & 0.20 & 13\% \\ \hline Electronic & Yes & 104.86 & 1.51 & 0.20 & 13\% \\ detonator & No & 91.34 & 1.32 & 0.20 & 13\% \\ \hline \hline \end{tabular}
\end{table} 
Table 5: The average thickness of the loose ring in the comparative test. circle caused by surrounding rock excavation accounts for the main part, the influence of the blasting load is also significant. (2) The thickness of the loose ring was approximately 1.32 m without considering the blasting load when the tunnel was excavated by electronic detonator blasting. The thickness of the loose ring produced by the blasting load was approximately 0.20 m. The final thickness of the loose circle was 1.51 m. It could be considered that the range of the looseness circle generated by the stress redistribution of the surrounding rock accounts for 87% of the final loose circle. The range of the loose circle produced by the blasting load accounts for 13% of the final loose range. The damage proportion of electronic detonator blasting load to surrounding rock loose circles is much lower than that of nonelectric detonators.