## 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
Therefore, this study compares and analyzes the changes in stress and displacement after the extraction of the 60-7# two-step mining site following the reduction of the middle section dimensions in the 60-6# and 60-8# mining sites. The simulation results are as follows:  
Figure 22 shows the simulation results after completing the two-step mining according to the original mining method, mainly for comparison with this scheme. From the simulation results, it can be seen that only a small portion of the fill material on both sides of the  
Figure 10:4 Simulation results with a 6 m thick pillar left on one side of the central area of the mining site. (**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. void is affected by tensile stress after mining, with a maximum tensile stress of 1.47 MPa, which may lead to some falling of the fill material. From the minimum principal stress cloud map (Figure 22b), it can be observed that there is no stress concentration around the void, and the maximum compressive stress is located in the surrounding areas of the one-step and two-step mining after extraction, which has little impact on the void. The maximum displacement of the roof is 13.6 cm, while the maximum displacement of the fill material on both sides of the void is 5.2 cm. After adopting the scheme of leaving a 4 m thick pillar in the middle of the mining area, the two-step mining area is enlarged, increasing the exposed area of the void, and the simulation results are shown in Figure 10:5 From the maximum principal stress cloud map (Figure 23a), it can be seen that only a small portion of the fill material is subjected to tensile stress, with a maximum tensile stress of 0.45 MPa. The maximum compressive stress is located around the one-step mining area, and the stress in the two-step mining area is basically released. The displacement of the void roof is 12.8 cm, and the displacement of the fill material on both sides of the void is 7.2 cm, but the range is very small, with the general displacement of the fill material being between 2 and 4 cm, which is sufficient to maintain the stability of the fill material. When continuously applying this scheme for extraction in the one-step mining area, compared to the original mining scheme, the tensile stress is reduced, the roof displacement is lowered, and there are no significant changes in the displacement of the fill material, with the only noticeable changes being in the range and magnitude of the maximum compressive stress. Therefore, it is feasible to continue to apply this scheme in the one-step mining area. Figure 10:6 Simulation calculation results of the original two-step 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. In summary, gradually mining from one side of the working area to the other can lead to stress concentration at the opposite end, exacerbating damage to the chamber and rendering it unsuitable for all mining areas. In the mining areas north of line 60 at Dong-guashan, after adopting this mining sequence, some fragmented regions or large mining areas experience severe damage in the void after extraction. Using the method of mining from both sides toward the center, the maximum compressive stress gradually decreases, and the stress concentration is released during the initial extraction, which is beneficial for enhancing the stability of the chamber. However, this scheme requires retaining a 14-18 m thick pillar in the middle of the working area. Due to blasting restrictions and rock fragmentation, it is challenging to blast the pillar all at once, making it prone to collapse and affecting safe operations; therefore, it is not recommended.