## 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
moisture content of the surrounding rock at the vault and arch waist exhibits a four-stage change characteristic: linear increase \(\rightarrow\) sharp decrease \(\rightarrow\) slow increase \(\rightarrow\) stabilization. The moisture content of the surrounding rock at the side wall, arch foot, and inverted arch shows a three-stage change characteristic: linear increase \(\rightarrow\) slow decrease \(\rightarrow\) stabilization. Due to the influence of excavation disturbance and support boundary conditions, the stress field and seepage field of the surrounding rock redistribute, causing moisture migration from the vault to the arch foot and inverted arch. After the initial support is closed into a ring, the moisture content of the surrounding rock slowly decreases and stabilizes. Therefore, strengthening waterproofing and drainage measures, enhancing the support capacity of the arch foot, and promptly closing the excavation into a ring during the excavation and construction period are of great significance for ensuring the stability of the surrounding rock. 3.2 Analysis of Radial Displacement and Horizontal Convergence Deformation in the Surrounding Rock near the Tunnel  
Monitoring and analysis of radial displacement and convergence deformation in the surrounding rock near the tunnel are crucial for determining the scope of excavation-induced disturbance and loosening, reasonably predicting excavation deformation, and ensuring the stability of the tunnel's surrounding rock and construction safety. Therefore, monitoring radial displacement and convergence deformation in the surrounding rock can effectively guide and optimize the length of excavation benches, determine the timing of lining support, reasonably predict the reserved deformation of the surrounding rock, and provide important guidance for controlling over-excavation and achieving engineering economy and safety. (1) Analysis of Radial Displacement in the Surrounding Rock near the Tunnel  
Due to the influence of excavation procedures and the different installation times of multi-point displacement meters at various monitoring points, the vault monitoring point is installed after the excavation of the upper bench, while the arch waist and side wall monitoring points are installed after the excavation of the middle bench. At the time of installation, the stress and deformation of the surrounding rock have already been  
Figure 9: Distribution pattern of rock moisture content around the cave before and after precipitation (red lines indicate before precipitation, green lines indicate after precipitation). partially released. Therefore, only the final deformation of the radial displacement within the surrounding rock is statistically analyzed. Figure 10 shows the distribution of cumulative radial displacement within the surrounding rock measured by multi-point (four-point) displacement meters at the vault, right arch waist, and right-side wall of the monitoring section. Figure 8 indicates that the radial displacement within the surrounding rock of the soft plastic section exhibits the following characteristics: larger displacement at shallow depths close to the tunnel wall, smaller displacement at deeper depths, larger displacement at the vault, smaller displacement at the side wall, and displacement at the arch waist falling between the two. At a position 1 m away from the tunnel perimeter, the radial displacements at the vault, arch waist, and side wall are, respectively, 31.6 mm, 22.3 mm, and 15.6 mm. As the excavated area increases, the scope of disturbance, damage, and loosening of the surrounding rock also expands, leading to a reduction in rock stability. Therefore, to control the scope of damage and loosening in soft plastic surrounding rock and reduce the release of stress and displacement, it is advisable to adopt excavation and support techniques that facilitate early dewatering, use of micro-benches, short excavation lengths, and rapid closure.