## 6 Conclusions  
In this paper, the range of the surrounding rock loose zone was theoretically analyzed by using the stress method and work-energy relationship method. The theoretical formula  
Figure 14: Schematic diagram of the stress loose zone range: (**a**) Schematic diagram of loose zone range under working condition 1; (**b**) schematic diagram of loose zone range under working condition 2; (**c**) schematic diagram of loose zone range under working condition 3. \begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline
**Working Condition** & \(L_{bl}\) **(m)** & \(m\) & \(L_{b2}\) **(m)** & \(n\) & \(m_{r}\), \(n\) & \(L_{b}\) & **Measured Value (m)** \\ \hline
1 & 0.106 & 1.0–3.6 & 1.026 & 1.0–1.3 & \(\begin{array}{c}m=1.2\\ n=1.2\\ m=1.2\end{array}\) & 1.36 & 1.2–1.4 \\
2 & 0.326 & 1.0–3.0 & 1.599 & 1.0–1.4 & \(\begin{array}{c}m=1.2\\ n=1.3\end{array}\) & 2.47 & 1.8–2.6 \\
3 & 0.254 & 1.0–1.2 & 0.913 & 1.0–1.2 & \(\begin{array}{c}m=1.0\\ n=1.0\end{array}\) & 1.17 & 0.6–1.5 \\ \hline \hline \end{tabular}
\end{table} 
Table 5: Calculation results of the loose zone of each part and value of the coupling coefficient. for the loose zone thickness was given, and the formula was modified through the coupling coefficient. Based on an example of the Qingdao Metro single-track tunnel project, the applicability of the formulas of the two theoretical methods was analyzed. The final calculation results showed that the stress method was more applicable, while the calculation results of the work-energy relationship method were more conservative. Through this study, we drew the following conclusions:  
1. The study of this paper shows that the scope of the loose zone of surrounding rock is affected by the original rock stress, surrounding rock conditions, burial depth, and blasting parameters. In the case of the same tunnel section, the worse the surrounding rock conditions, the greater the original rock stress, the larger the scope of the loose zone, and the greater the difference between the scope of the loose zone at the arch crown and the arch shoulder. 2. The formation of the surrounding rock loose zone can be divided into two parts. One part is the stress loose zone formed under the action of in situ stress due to the stress release after chamber excavation, and the second part is the blasting-expansion loose zone formed by the crack propagation under the action of a blasting load. 3. When using the Finner solution to calculate the range of the surrounding rock loose zone under low ground stress, only the stress loose zone underground stress is considered, and the blasting expansion loose zone under the blasting load is ignored, resulting in a large difference between the calculated value of the surrounding rock loose zone and the measured value. The stress loose zone only accounts for a small part of the surrounding rock loose zone, and the blasting expansion loose zone is the main part of the surrounding rock loose zone. 4. In the process of actual chamber excavation, the formation of a loose zone under the action of in situ stress and the expansion of the blasting stress wave were not simple and independent but rather had a coupling effect. Although the range of the loose zone under the influence of the in situ stress was small after chamber excavation, the influence of the in situ stress on the formation of the final loose zone was large. Conceptualization, [PERSON], G.W. and J.L. ; methodology, G.L., J.L. and G.W. ; software, G.W. ; validation, G.L., J.L. and G.W. ; formal analysis, G.L., F.H. and X.G. ; investigation, G.L. and G.W. ; resources, G.L., F.H., X.G. and J.L. ; data curation, G.W. and J.L. ; writing--original draft preparation, G.L. and G.W. ; writing--review and editing, [PERSON], J.L. and G.W. ; visualization, [PERSON]; supervision, [PERSON], J.L., F.H. and X.G. ; project administration, G.L., F.H., X.G. and J.L. ; funding acquisition, G.L., F.H. and X.G. All authors have read and agreed to the published version of the manuscript. This research received no external funding. Not applicable.