## 4 On-Site Monitoring of Disaster Prevention and Response Measures for Water-Rich Loess Tunnels
### Result Analysis  
#### 4.3.1 Analysis of Changes in Moisture Content of Surrounding Rock Around the Tunnel  
Due to the tunnel passing through soft-plastic strata, a construction plan was adopted where deep hole precipitation was carried out on the surface before excavation. After excavation, changes in the moisture content of the surrounding rock were influenced by the excavation process, and there is a certain correlation between them. Figure 8 shows the variation curves of the moisture content at each measurement point on the monitoring section with monitoring time and excavation space. \begin{table}
\begin{tabular}{c c c c} \hline \hline \multicolumn{2}{c}{**Displacement Rate of Surrounding Rock**} & \multicolumn{2}{c}{**Distance From Excavation Face**} \\ \multicolumn{2}{c}{**(B is the Tunnel Excavation Span)**} \\ \hline
**Displacement Rate** & **Measurement** & **Monitoring the Distance Between the** & **Measurement** \\
**(mm/d)** & **Frequency** & **Cross-Section and the Excavation Surface (m)** & **Frequency** \\ \hline \(\geq\)5 & 2 times/d & (0–1) B & 2 times/d \\
1–5 & 1 time/d & (1–2) B & 1 time/d \\
0.5–1 & 1 times/2–3 d & (2–5) B & 1 time/2–3 d \\
0.2–0.5 & 1 time/3 d & \(>\)5 B & 1 time/7 d \\ \hline \hline \end{tabular}
\end{table} 
Table 5: Monitoring frequency of monitoring sections. Figure 8 indicates that due to the influence of surface precipitation and excavation steps, the moisture content of the surrounding rock at different measurement points exhibits significant temporal and spatial variations over time. The changes in moisture content of the surrounding rock mainly occur from the excavation of the upper bench to before the construction of the secondary lining, and it generally stabilizes after the construction of the secondary lining. Across the entire monitoring section, the moisture content of the surrounding rock at the inverted arch and arch foot is significantly higher than that at the vault and side wall, which is consistent with the observed mud flow and seepage at the arch foot. After 30 days of precipitation, the average moisture content of the surrounding rock decreased from 28.8% to 22.3%, transforming the rock from soft-plastic to plastic, slowing down water seepage, and significantly improving the self-stabilizing ability of the surrounding rock. The variation in moisture content in the surrounding rock of the monitoring section with the excavation steps is as follows: after the excavation and support of the upper bench, the moisture content of the surrounding soil and rock at the vault and arch waist increases linearly and rapidly; after the excavation of the middle bench, the moisture content of the surrounding soil and rock at the vault decreases linearly, while the moisture content at the arch waist and side wall continues to increase; after the excavation of the lower bench and inverted arch, the moisture content of the surrounding soil and rock at the vault continues to decrease, then slowly increases and stabilizes, the moisture content at the arch waist and side wall decreases first and then stabilizes, and the moisture content at the inverted arch increases slowly and then stabilizes; with the spatial changes in monitoring time and the tunnel face, the moisture content of the surrounding soil and rock in the monitoring section undergoes uniform migration, and the moisture content at each measurement point stabilizes after the completion of the secondary lining construction. The average moisture content of the surrounding rock at the vault is 21.4%, at the arch foot is 23.2%, and at the inverted arch is 24.5%. The distribution pattern of moisture content in the surrounding rock after stabilization is shown in Figure 9. The variation pattern of moisture content in the surrounding rock with monitoring time and excavation space in the monitoring section indicates the following: The  
Figure 8: The variation curve of moisture content at measuring points with monitoring time and excavation space.