# Research on Excavation Method for Soft Rock Tunnel Based on Stress Release Rate
## 4 Conclusions  
Based on the typical soft rock tunnel project of the Dongmachang No. 1 Tunnel, this paper studies the excavation method of a soft rock tunnel based on stress release by combining field measurements with model tests, and we obtain the following main conclusions:  
1. Tunnel excavation is essentially an accumulation process of stress release and displacement release. The two have a very close internal relationship. Combined with the field-measured data, the assumption that the stress release rate is approximately equal to the displacement release rate under certain conditions is verified. 2. A model test method for simulating tunnel excavation based on stress release is proposed: the confining pressure is loaded step by step from 0 to be consistent with the initial stress, which corresponds to the change process of the stress release rate in the surrounding rock. Combined with the field measurement results, the reliability of the test method is verified. 3. Model tests were carried out on tunnels with different excavation methods. The three-bench seven-step method had the best control effect on the deformation of surrounding rock, followed by the three-bench core soil method. The deformation of surrounding rock caused by the two excavation methods was reduced by 11.8-12.4% and 6.7-6.9%, respectively. 4. Through the monitoring of the contact pressure, steel arch, and the calculation of safety factor, it is shown that the pressure of the first layer of the three-bench seven \begin{table}
\begin{tabular}{c c c c c c c c c c c} \hline \hline  & & & \multicolumn{3}{c}{**Three-Bench with Reserved**} & \multicolumn{3}{c}{**Three-Bench Seven-Step**} \\ \cline{3-11}
**Supporting** & **Monitoring** & & & & & & **Core Soil** & & & \\
**Structure** & **Position** & **Force** & **Moment** & **Safety** & **Force** & **Moment** & **Safety** & **Force** & **Moment** & **Safety** \\  & & **(kN)** & **(kN-m)** & **Factor** & **(kN)** & **(kN-m)** & **Factor** & **(kN)** & **(kN-m)** & **Factor** \\ \hline  & Vault & 286.7 & 23.7 & 1.99 & 311.9 & 33.4 & 1.49 & 351.1 & 34.6 & 1.42 \\ The first & Spandrel & 236.8 & 24.6 & 2.01 & 325.8 & 27 & 1.75 & 461.4 & 39.5 & 1.20 \\ primary & Hance & 268.9 & 25.1 & 1.93 & 341.6 & 27.8 & 1.69 & 455.5 & 34.4 & 1.34 \\ support & Arch foot & 189.5 & 12.6 & 3.54 & 233.7 & 19.5 & 2.42 & 283.3 & 22.5 & 2.08 \\  & Arch bottom & 187.3 & 14.9 & 3.14 & 219.9 & 18.4 & 2.57 & 233.6 & 21.9 & 2.22 \\ \hline  & Vault & 298 & 30.2 & 1.77 & 278 & 26.2 & 2.03 & 270.2 & 16.6 & 2.78 \\ The second & Spandrel & 267.5 & 28.6 & 1.89 & 238 & 20.4 & 2.51 & 187.6 & 29.4 & 2.19 \\ primary & Hance & 289.1 & 29.1 & 1.83 & 239.1 & 16.9 & 2.86 & 201.3 & 20.1 & 2.65 \\ support & Arch foot & 207.4 & 18.5 & 2.80 & 187.1 & 14.1 & 3.50 & 152.8 & 11.8 & 4.21 \\  & Arch bottom & 184.4 & 16.2 & 3.18 & 134.4 & 12.9 & 4.09 & 87.4 & 10.3 & 5.37 \\ \hline \hline \end{tabular}
\end{table} 
Table 10: Comparison of the internal force and safety factor for the primary support with different middle bench lengths. step method is 11.5% and 14.6% higher than that of the three-bench core soil method and the three-bench method, respectively, and the pressure of the second layer is reduced by 12.75% and 2.7%, respectively. The more excavation steps in the construction method, the more sufficient the stress release of the surrounding rock, which can give full play to the supporting role of the primary support and improve the safety of the secondary support. Based on the actual engineering and test results, it is recommended that the three-bench core soil method is more reasonable for the construction of a high-stress soft rock tunnel through an active fault zone. Conceptualization, C.H. ; Methodology, H.K. ; Software, J.N. and F.L. ; Validation, J.N., H.K. and F.L. ; Formal analysis, C.H. ; Resources, C.H. and W.Y. ; Data curation, J.N. and F.L. ; Writing--original draft, J.N. ; Writing--review & editing, H.K. and W.Y. ; Supervision, W.Y. ; Funding acquisition, C.H. All authors have read and agreed to the published version of the manuscript.