## 3 Numerical Simulation Study
### Comparison and Analysis of Numerical Simulation Results and Actual Monitoring Data  
A GNSS monitoring station on the south slope was installed for displacement monitoring, with its precise location illustrated in Figure 12. Specific monitoring equipment was placed at the center of the slope, as there was less interference from the site. We compared the recorded displacement data from this monitoring device and the simulated displacement data from the equivalent site within the FLAC3D model. The comparison results are as follows.  
Figure 11: Contrasting displacement cloud. (**b**) No-excavation displacement maps. (**a**) Displacement cloud map of the southern mining area of the excavation.  
Figure 10: Numerical simulation of monitoring sites. (**a**) Point A and B maps. (**b**) X direction. (**c**) Y direction. (**d**) Z direction.  
The displacement data from a continuous 1000 h of on-site monitoring were compared with the numerical simulation results, as shown in Figure 13. It was observed that the displacement curves of the monitoring data and numerical simulation results exhibited similar trends. In the initial stage, both sets of displacement curves displayed minimal displacement, indicating a certain degree of lag in the surface subsidence induced by mining activities. This observation was further corroborated by the numerical simulation results at different stages, as illustrated in Figure 7. Both monitoring data and numerical simulation results demonstrated significant displacements in the Y and \(Z\) directions, with relatively more minor displacements in the X direction.  
Figure 12: Location map of on-site monitoring equipment.  
Figure 13: (**a**) Displacement data for 1000 h at monitoring point. (**b**) Displacement data recorded by numerical simulation.  
Based on the monitoring data, the total displacements at the monitoring point within 1000 h were 0.7008 m in the Y direction, 0.1656 m in the X direction, and \(-\)0.6575 m in the Z direction. These correspond to the displacements in the numerical simulation between steps 1600 and 2100. From this, we can infer that the removal at the monitoring point at 1500 h was equivalent to that in the numerical simulation between steps 2400 and 3150. At these moments, the numerical model results showed dy values ranging from 0.884 m to 1.35 m, dx values between 0.42 m and 0.688 m, and dz values from \(-\)1.45 m to \(-\)2.3 m.  
As depicted in Figure 14, the actual monitored displacement results show dy as 1.44 m, dx as 0.20 m, and dz as 1.29 m. There are some differences between the two sets of results, primarily characterized by the overestimation of Z-direction displacement in the numerical simulation and the underestimation of the Y-direction displacement. Additionally, the X-direction displacement in the numerical simulation continued to increase, while the actual monitoring results showed a tendency toward stabilization in the X direction. These differences may be attributed to the fact that, in the natural engineering environment, slope support measures were implemented on both sides of the slope after the excavation of the drainage ditch, limiting the X-direction displacement. The numerical simulation, which did not accurately model this actual situation, resulted in these disparities.  
While the numerical simulation did not precisely predict the actual displacements for this specific monitoring point, this three-dimensional numerical modeling still holds significant value in forecasting surface deformations and providing construction references.