## 3 Deformation Characteristics of Yuntunpu Tunnel  
With the excavation of multiple sections of the Yuntunpu Tunnel, the deformation of the surrounding rock continues to increase, with the most severe deformation reaching 50 cm/d. The damage to the support structure caused by large deformation includes the distortion and deformation of the steel arch frame, cracking, peeling, and local peeling of the lining concrete at the arch crown and side walls, seriously affecting construction safety and efficiency. The on-site monitoring data and construction records of the research section are summarized, and the major deformation characteristics of the severely deformed area are analyzed. They are mainly manifested in the following aspects:  
1. The initial deformation rate of excavation is high, and the self-stabilization time of surrounding rock is short. The deformation rate of the surrounding rock at section D6K234 + 205 is shown in Figure 4. From Figure 4, the rate of change of the arch settlement and horizontal convergence shows a trend of the first surge and then a slight decrease. The change rates of arch settlement and horizontal convergence peaked on the seventh day, and the maximum deformation change rates reached 27.3 mm/d and 30.7 mm/d, respectively. On the 28 th day, the deformation rate decreased to the lowest and remained stable at around 5 mm/d. The initial deformation rate of the surrounding rock is high, and the deformation increases rapidly, making it difficult to control. The main reason is that the surrounding \begin{table}
\begin{tabular}{c c c c c c c c c c c} \hline \hline \multirow{2}{*}{**Serial**} & **Test Section** & \multicolumn{4}{c}{**Fracturing Parameter/(MPa)**} & \multicolumn{4}{c}{**Stress Value/(MPa)**} & \multirow{2}{*}{**St Direction (\({}^{\circ}\))**} \\ \cline{3-3} \cline{5-10}  & **Depth/(m)** & & & & & & & & & \\ \hline
1 & 274.8–275.8 & & 10.69 & 7.69 & 2.69 & 2.43 & / & 9.95 & 7.69 & 7.27 & \\
2 & 320.3–321.3 & 15.63 & 9.63 & 8.13 & 3.13 & 2.88 & 6 & 11.88 & 8.13 & 8.65 & N52\({}^{\circ}\) W \\
3 & 356.8–357.8 & 13.99 & 8.99 & 8.49 & 3.49 & 3.24 & 5 & 13.24 & 8.49 & 9.44 & \\
4 & 384.0–3850 & 18.76 & 9.26 & 8.76 & 3.76 & 3.5 & 9.5 & 13.52 & 8.76 & 10.16 & N38\({}^{\circ}\) W \\
5 & 392.4–493.4 & 17.84 & 11.94 & 9.84 & 3.84 & 3.59 & 5.9 & 13.99 & 9.84 & 10.38 & \\
6 & 432.6–433.6 & 15.73 & 12.23 & 10.23 & 4.23 & 3.98 & 3 & 14.48 & 10.23 & 11.44 & N31\({}^{\circ}\) W \\
7 & 445.1–446.1 & & 11.86 & 10.36 & 4.36 & 4.1 & / & 15.12 & 10.36 & 11.77 & \\ \hline \hline \end{tabular}
\end{table} 
Table 2: PDZ-Yuntunpu-04 hydraulic fracturing in situ stress measurement results. rock is weak, the crustal stress is high, and the deformation process is accompanied by strain softening. The self-stability ability of the surrounding rock is extremely poor, and the self-stability time is only ten hours at most. Large total deformation  
The deformation of the Yuntunpu Tunnel is mainly caused by inward extrusion deformation, with significant deformation occurring at mileage 7#, mileage 6#, and mileage 5#. The deformation time history curve of section D6K234 + 210 surrounding rock is shown in Figure 5. It can be seen from Figure 5 that the deformation monitoring time of surrounding rock at this section is 101 days in total, and the initial deformation of the surrounding rock is large. The vault settlement and horizontal convergence reach 543.1 mm and 501.5 mm on the 20 th day. The deformation growth slows, and the final cumulative monitoring deformation reaches 815.2 mm and 874.0 mm, respectively. The monitoring of the arch settlement and horizontal convergence values are close to 1 m, indicating that the deformation of the surrounding rock is uniform and the overall deformation is large. The deformation time history curve of the surrounding rock of section D5K231 + 990 is shown in Figure 6. From Figure 6, the settlement and horizontal convergence of the arch crown in this section have a long time, which continues to increase after 60 days. After 120 days, the deformation reaches stability.