## 3 Numerical Simulation Analysis and Demonstration of Actual Extraction Sequence in Large Stopes
### Simulation Result Analysis of the One-Step High-Profile Working Face Extraction Process
The maximum displacement of the pillars on both sides of the filling body is 2.5 cm, a reduction of 0.5 cm compared to before filling. From Figure 16, after half of the stope is filled, mining is conducted on the other half of the stope. The results show that there is no tensile stress acting on the empty space, and the maximum compressive stress around the empty space decreases to 30 MPa. The roof displacement of the empty space is 10.4 cm, with the maximum displacement of the filling body in the empty space being 2 cm, and the maximum displacement of the rock mass being 3 cm. Compared to full mining (10 cm), there is not a significant change in the roof displacement of the empty space. From the above analysis, it can be concluded that, after recovering half of the mining area, the surrounding rock in the empty area is not affected by tensile stress, and the displacement on both sides of the empty area is small, indicating good stability. After filling and recovering the other half of the mining area, the displacement of the roof, the rock on both sides, and the filling body are all within a reasonable range, and the maximum compressive stress decreased. In summary, this method has been proven feasible through a numerical simulation; however, the process on-site is complex and the pressure on mining production tasks is significant, so it cannot be widely promoted, although it may be considered for application in certain mining areas. Figure 13: Displacement cloud map of the 8 m thick pillar. Figure 14: Simulation results after half of the extraction. (**a**) Maximum principal stress cloud map; (**b**) minimum principal stress cloud map; (**c**) displacement cloud map of the roof; and (**d**) displacement cloud map of the pillars. Figure 15: Simulation results after half of the filling. (**a**) Maximum principal stress cloud map; (**b**) minimum principal stress cloud map; (**c**) displacement cloud map of the roof; and (**d**) displacement cloud map of the pillars. From the previous simulation results, it is known that, after the two-step mining, the filling body is relatively stable, and the stability of the filling body is an important foundation for this plan. After reducing the dimensions in the middle of the one-step mining area, the thickness of the filling body in the central area of the one-step mining needs further numerical simulation calculations to determine whether it can meet the stability requirements. Due to the change in the mining area dimensions, this numerical simulation requires redesigning and recalculating for the model, as shown in Figure 17. This simulation takes the 62 line mining area as a reference and focuses on the concentrated high mining areas for the numerical simulation calculations, covering the range from the 62-1# to the 62-12# mining areas. The height of the model from the 60-4# to the 60-12# mining areas is set at 125 m.  
Figure 16: Simulation results after the recovery of the other half. (**a**) Maximum principal stress cloud map; (**b**) minimum principal stress cloud map; (**c**) displacement cloud map of the roof; and (**d**) displacement cloud map of the pillars. Figure 10:0 Model of the 62-2# to 62-12# mining areas. Determine the thickness of the retained rock mass on both sides of the middle section of the mining area. In this scheme, a certain thickness of rock mass is retained on both sides of the middle section of the one-step mining area for the two-step mining. The thickness of the retained rock mass needs to be confirmed through simulation calculations. This simulation involves a numerical analysis of the triangular rock columns with thicknesses of 2 m, 4 m, and 6 m retained on both sides of the mining area. The simulation results are as follows. Figure 18 presents the simulation results of a single void after complete extraction using the original mining method, compared with the new scheme.