## 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 results show that the maximum tensile stress on both sides of the void is 1.42 MPa, with a small range, which may lead to localized spalling; the maximum compressive stress is concentrated at the four corners of the void, reaching 40.9 MPa. The maximum displacement of the roof is 6.04 cm, while the displacement of the surrounding rock is 5.8 cm. Figure 19 shows the simulation results with 2 m thick pillars left on both sides of the mining area. At this point, the maximum tensile stress on both sides of the void decreases to 1.03 MPa, but the maximum compressive stress increases to 51.9 MPa. The maximum displacement of the roof is 5.0 cm, and the displacement of the surrounding rock increases to 6 cm. Compared to the original mining method, while leaving the pillars reduces tensile stress, it increases displacement and compressive stress, which is not conducive to the stability of the void. Figure 20 shows the simulation results with a 4 m thick pillar left on both sides of the mining site. The results indicate that the maximum tensile stress on both sides of the empty area is 1.03 MPa, which is a decrease; the maximum compressive stress is concentrated on the top and bottom plates, reaching 61.51 MPa, with a small range. The maximum displacement of the top plate decreased to 3.96 cm, and the displacement of the surrounding rock significantly reduced, forming two regions with a maximum displacement of only  
Figure 10:1 Simulation results after the mining area is extracted according to the original mining method. (**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. 1.14 cm, which is a substantial decrease compared to 5.8 cm from the original mining method, indicating a significant improvement in the stability of the pillars. Figure 10:2 Simulation results with 2m thick pillars left on both sides of the mining area. (**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 10:3 Simulation results with 4 m thick pillars left on both sides of the mining area. (**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 21 shows the simulation results with a 6 m thick pillar left on both sides. The results indicate that the maximum tensile stress is 1.46 MPa, which is similar to that of the original mining method, but the range of tensile stress has increased. The maximum compressive stress is mainly located on the top and bottom plates, reaching 49.9 MPa, which is lower than in the previous two scenarios. The maximum displacement of the top plate is 3.2 cm, and the displacement of the surrounding rock on both sides has returned to a single region with a maximum displacement of 6.1 cm, indicating that the apex area is prone to collapse. In summary, leaving a 4 m thick triangular pillar on both sides of the mining site as part of the two-step mining scheme can significantly reduce the displacement of the surrounding rock in the empty area, and the displacement of the top plate is also reduced. Although the maximum compressive stress of this scheme is relatively high, its impact range is small, so a pillar thickness of 4 m is recommended. (2) Simulation Results after Applying This Scheme to Adjacent One-Step High Mining Sites  
As the dimensions of the middle section of the one-step mining site are reduced, the extraction range of the two-step mining site will increase, leading to a larger exposed area of the empty zone. If this scheme is applied to adjacent one-step mining sites, the exposed area of the top plate of the two-step empty zone will increase, and the thickness of the fill on both sides of the empty zone will decrease, which necessitates further verification of the stability of the empty zone.