## 5 On-Site Monitoring and Analysis of Surface Deformation Law
### Analysis of Spatiotemporal Evolution Patterns of Ground Settlement  
To analyze the trend of cumulative ground settlement during shield tunneling at the tunnel face and to assess the spatiotemporal distribution characteristics of settlement, numerical simulation data at the same locations as the two monitoring sections were extracted throughout the excavation process and compared with actual monitoring data.  
Figure 11: Comparison of settlement in monitoring sections.  
The results are illustrated in Figure 12, providing a basis for future settlement risk warning and assessment.  
As illustrated in Figure 12, both the monitoring and numerical simulation results at the CDBC719 section indicate a trend of initial increase, followed by a decrease, another increase, and then stabilization. Overall, the settlement is greater directly above the tunnel centerline than on either side. The maximum settlement occurred at the initial excavation stage, with a peak monitored value of \(-5.10\) mm and a simulated value of \(-5.27\) mm. As the shield advanced, settlement gradually decreased. Around \(10\) m of excavation (approximately the \(9\)th segment ring), the shield exited the reinforced zone, resulting in increased surrounding soil settlement. Thereafter, settlement values stabilized and fluctuated around \(-2\) mm in both monitored and simulated data.  
Figure 12 illustrates that at the CDBC709 section, both monitored and simulated settlement initially decreased, then increased, and eventually stabilized. During excavation from \(0\) to \(5\) m, due to the shield being far from the monitoring points, settlement variations were minimal, with both monitored and simulated values around \(-0.5\) mm. Between \(6\) and \(10\) m of excavation, as the shield approached the monitoring points, settlement increased, reaching its peak at \(10\) m, coinciding with the shield leaving the reinforcement zone. In this range, the maximum monitored settlement was \(-4.30\) mm, while the simulated settlement was \(-5.85\) mm. From \(10\) to \(12\) m, as the shield moved away from the monitoring points, settlement began to decrease, and simulation values stabilized. However, monitored settlement continued to increase, reaching a maximum of \(-10.1\) mm. After remedial treatment (as detailed in Section 3.2), settlement gradually decreased and eventually stabilized.  
In summary, the measured and simulated transverse ground settlement curves, as well as the values calculated using the Peck formula, correspond well. All exhibit a symmetric \"V\"-shaped distribution, with maximum settlement at the tunnel centerline and decreasing toward the sides. Cumulative settlement trends from both monitoring and simulation also align: the maximum settlement occurs when the shield is directly beneath the monitoring point, and although settlement fluctuates slightly after the shield exits the reinforcement zone, the overall variation is minimal. Both transverse and longitudinal settlement values remain within control limits, indicating that the reinforcement scheme effectively stabilized the ground in the launching area.