## 4 Discussion
### Evolution Characteristics of Surrounding Rock Pressure
\begin{table}
\begin{tabular}{c c c c} \hline
**Geological Conditions** & **The Left Line Tunnel** & **The Parallel Pilot Tunnel** & **The Right Line Tunnel** \\ \hline Stratigraphic lithology & \begin{tabular}{c} Gneiss, grayish white, \\ greiss-like structure, mainly \\ composed of quartz, \\ feldspar, mica and so on. \\ \end{tabular} & \begin{tabular}{c} Gneiss, gray-black, \\ greiss-like structure, mainly \\ composed of quartz, \\ feldspar, mica and so on. \\ \end{tabular} & \begin{tabular}{c} Gneiss, cyan-gray mixed \\ with grayish white, \\ greiss-like structure, mainly \\ composed of quartz, \\ feldspar, mica and so on. \\ \end{tabular} & \begin{tabular}{c} Gneiss, gray-black, \\ with grayish white, \\ greiss-like structure, mainly \\ composed of quartz, \\ feldspar, mica and so on. \\ \end{tabular} \\ \hline Rock mass & \begin{tabular}{c} Weak weathering, more \\ developed joint fissure, \\ development of Group 2 \\ developed joints, two \\ groups of main joints \\ developed; the rock mass is \\ relatively intact. \\ \end{tabular} & \begin{tabular}{c} Weak weathering, the joints \\ development of Group 2 \\ main joints; there is a slight \\ kneading and extrusion \\ phenomenon on the palm \\ surface, the rock mass is \\ wedged and blocky, the rock \\ mass is more complete, but \\ there is local fragmentation. \\ \end{tabular} & \begin{tabular}{c} Weak weathering, the joints \\ are more developed, and the \\ palm surface is slightly \\ crumpled. A group of joints \\ runs through the whole \\ palm surface, the rock mass \\ is \\ whole rock mass is \\ \end{tabular} \\ \hline Compressive strength \(\sigma_{\text{c}}\) & 61.4 & 91.4 & 57.8 \\ (MPa) & 2 & 4 & 2 \\ \hline Groundwater seepage rate & \begin{tabular}{c} N39\({}^{\circ}\) E/80\({}^{\circ}\) S \\ \end{tabular} & \begin{tabular}{c} N51\({}^{\circ}\) E/84\({}^{\circ}\) S \\ \end{tabular} & \begin{tabular}{c} N46\({}^{\circ}\) E/82\({}^{\circ}\) N \\ \end{tabular} \\ \hline Joint fissure & \begin{tabular}{c} J1: N32\({}^{\circ}\) E/48\({}^{\circ}\) S, \\ micro-tensile joint, rough \\ joint surface, no filling, joint \\ spacing of 0.6–0.7 m, joint \\ extension of 3.0–4.0 m. \\ J2: N47\({}^{\circ}\) E/34\({}^{\circ}\) N, \\ micro-tensile joint, rough \\ joint surface, no filling, joint \\ spacing 0.7–0.8 m, joint \\ extension 2.0–4.0 m. \\ \end{tabular} & \
\begin{tabular}{c} J1: N38\({}^{\circ}\) E/65\({}^{\circ}\) S, \\ micro-tensile joint, rough \\ joint surface, no filling, joint \\ spacing of 0.8–1.0 m, joint \\ extension 2.0–4.0 m. \\ \end{tabular} &
\begin{tabular}{c} J1: N50\({}^{\circ}\) E/46\({}^{\circ}\) S, \\ micro-tensile joint, rough \\ joint surface, no filling, joint \\ spacing of 0.8–1.0 m, joint \\ extension 5.0–8.0 m. \\ \end{tabular} \\ \hline Buried depth (m) & 837 & 938 & 957 \\ \hline \end{tabular}
\end{table} 
Table 3: Geological conditions of each tunnel. to reach the monitoring section of the parallel pilot tunnel, the surrounding rock pressure enters a change period. During this period of time, the construction of the parallel pilot tunnel was stagnant. There were pieces falling off near the monitoring section, and the data collection process was dangerous, so some data were missing. After the working face of the right line tunnel passes through the monitoring section, the surrounding rock pressure again enters a stable period. As can be seen from Figure 12, in the early growth period, the surrounding rock pressure caused by the deformation of the surrounding rock gradually increased with increase in time after mixing. In the two weeks after the completion of excavation and spraying, the surrounding rock pressure increases gently, and in the third week, the growth rate of the surrounding rock pressure increases. One month after the completion of excavation, the surrounding rock pressure increases to a higher level, and its growth rate slows down, and the surrounding rock pressure remains at a high level. From June 5 to 13, the surrounding rock pressure increased to a greater extent.