## 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
When using system bolts or locking foot bolts for support, their length should be greater than 3.0 m.  
(2) Analysis of Convergence Deformation in the Surrounding Rock near the Tunnel  
An analysis of the vault settlement (measurement point 1), arch waist (measurement points 2-8), and side wall (measurement points 3-7) horizontal convergence values at the monitoring section (ZK81+445) was conducted. The time-history curves for vault settlement and horizontal convergence deformation around the tunnel are shown in Figure 11. According to Figure 11, The convergence deformation around the tunnel induced by excavation in a water-rich loess tunnel is primarily characterized by vault settlement deformation, with the vault settlement deformation value being larger than the horizontal convergence deformation value. The monitored vault settlement value at the section is 239.2 mm, the arch waist horizontal convergence value is 163.6 mm, and the side wall convergence value is 138.4 mm. The overall convergence deformation value around the tunnel is less than the excavated and reserved deformation value of 400 mm. As the excavated area expands, the convergence deformation of the surrounding rock generally exhibits the following characteristics: linear rapid increase before the inverted arch is closed, nonlinear slow growth after the inverted arch is closed, and stabilization after 14 days of inverted arch  
Figure 10: Radial cumulative displacement distribution inside the rock surrounding the cave (unit: mm). closure. Before the inverted arch is closed, the average vault settlement rate is 16.8 mm/d, accounting for 77.2% of the total settlement. From inverted arch closure to the application of the second lining, the average vault settlement rate is 2.1 mm/d, accounting for 22.8% of the total settlement. Before the inverted arch is closed, the average horizontal convergence rates at the arch waist and side wall are, respectively, 11.5 mm/d and 9.3 mm/d, accounting for 77.3% and 73.7% of the total convergence. From inverted arch closure to the application of the second lining, the average horizontal convergence rates at the arch waist and side wall are, respectively, 1.5 mm/d and 1.4 mm/d, accounting for 22.7% and 26.3% of the total convergence. The monitoring results in this paper significantly differ from the existing literature [9], which indicates that more than 95% of the convergence around the tunnel occurs before the inverted arch is closed. This difference suggests that when the tunnel is excavated through water-rich and soft plastic strata, the convergence deformation of the surrounding rock exhibits variability. Additionally, when the tunnel passes through soft plastic strata, influenced by the low bearing capacity of the soft plastic strata base, there is still a certain degree of nonlinear deformation adjustment in the tunnel after the inverted arch is closed, which should be considered in similar projects. The reason for this is analyzed as follows: After tunnel excavation, moisture in the soft-plastic intercalated rock migrates towards the free surface around the tunnel, increasing the moisture content of the surrounding rock at the arch foot and the bottom of the inverted arch, which further moistens, disturbs, and softens the base. Although the arch foot and base are reinforced with micro steel pipe piles and jet grouting piles, their strength growth still requires some time. To close the inverted arch early, this leads to a certain degree of nonlinear adjustment and deformation. As the bearing capacity of the base gradually increases, its deformation eventually stabilizes. The monitoring results of the internal radial displacement and convergence deformation of the surrounding rock near the tunnel indicate that whether the inverted arch is closed in a timely manner to form a ring and the distance from the inverted arch closure to the excavation face are crucial factors affecting the convergence deformation of the surrounding rock in a soft plastic loess tunnel.