## 3 Numerical Simulation Analysis and Demonstration of Actual Extraction Sequence in Large Stopes
### Analysis of the Simulation Results of the Two-Step High Mining Area Extraction Process  
During the recovery process in the two-step mining area, significant changes occur in the surrounding rock mass, transforming from high-strength ore rock to lower strength fill material. Additionally, during the recovery process, stress is further released, and the areas where stress is concentrated shift significantly. Therefore, the analysis of the two-step mining area focuses on the following two aspects: first, examining the changes in the maximum compressive stress through cross-sectional diagrams along the mining area, where the patterns of changes in the maximum stress position can be easily identified; second, observing the displacement changes of the fill material on both sides of the void from a direction perpendicular to the mining area. This numerical simulation uses the 60-23# mining area as a case study to conduct numerical calculations on the recovery sequence. From the minimum principal stress cloud map before the recovery of the 60-23# mining area, it can be seen that the maximum compressive stress has shifted to the bottom area of the mining area where it intersects with the cross-cut passage. The compressive stress values within the mining area are relatively low, ranging from 25 MPa to 30 MPa. The maximum principal stress cloud map indicates that, after the initial excavation of the mining area, the internal rock mass is subjected to tensile stress, which is relatively small, and the range of tensile stress is also limited, essentially being insufficient to damage the rock mass. The minimum principal stress cloud map shows that, during the recovery process from one end of the mining area to the other, the bottom of the unmined end of the mining area experiences significant compressive stress, and, as recovery continues, the maximum compressive stress keeps changing. From Figures 24 and 25, the maximum principal stress cloud diagram indicates that, during the process of mining from the center towards both sides, both sides of the empty area experience tensile stress within a certain range. However, the tensile stress is relatively small, and its range is limited. As the mining progresses, the position of the tensile stress gradually changes, and, upon nearing the completion of the mining, the roof of the empty area experiences some tensile stress, albeit at a low level. The minimum principal stress cloud diagram shows that the maximum compressive stress is primarily located at the bottom of both sides of the mining area and at the intersection with the cross-cut tunnel. The maximum compressive stress also varies continuously as the mining advances. From Figure 26, it can be seen that, after half of the mining in the area is completed, the tensile stress is very low, only 0.21 MPa. The maximum compressive stress is located at the junction of the unmined area and the cross-cut passage, reaching 36.4 MPa, but the range is not large. The maximum displacement of the roof in the void is 12.6 cm, while the maximum displacement of the filling material on both sides of the void is 4 cm. From Figure 27, it can be observed that, after the mining area is mined and backfilled and additional mining is conducted, the area surrounding the void is basically not subjected to tensile stress. The maximum compressive stress around the void decreases, with the maximum displacement of the roof reaching 14.1 cm and the displacement of the filling material on both sides being 2 m.  
In the original mining method, the void is essentially not subjected to tensile stress, and the maximum compressive stress decreases, with the maximum displacement of the roof being 14.2 cm and the maximum displacement of the filling material being 2 cm. Compared to this method, there is no significant difference. From the above analysis, it can be concluded that the simulation calculation based on the filling scheme shows no significant differences when compared to the original mining plan for the two-step method.