## 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
In the early stages of mining, the maximum compressive stress is mainly concentrated within the mining area, distributed near both sides of the mined-out section, as shown in Figure 11b. As mining continues, the compressive stress tends to concentrate toward the center of the mining area; however, there is no significant increase in the maximum compressive stress, which stabilizes around 29.4 MPa. From the displacement cloud map, it is evident that the displacement increases with the widening of the mined area, and the maximum displacement continues to rise. The distribution of the plastic zone shows that there are no significant changes surrounding the mined-out area. In this scheme, the mined-out area is not subjected to tensile stress but is primarily affected by compressive stress. The maximum compressive stress is concentrated in the middle part of the mining area, showing a gradually decreasing trend, indicating that the stress in the mining area is being continuously released. Even after mining to the point where an 8 m thick pillar remains, there is no significant change in the maximum compressive stress. Regarding the displacement of the pillar, as shown in Figure 13, the maximum displacement of the 8 m thick pillar is only 0.84 cm, which is very small. Based on the changes in the maximum compressive stress and the displacement of the pillar in this scheme, the 8 m thick pillar remains in a relatively stable state. However, considering the reasons such as rock fragmentation and the development of joint fissures north of line 60, it is recommended that the thickness of the pillar left for safe extraction be between 14 and 18 m, with the final extraction conducted in one go. Since the blasting charge for each operation in Dongguashan is below 5 tons and the thickness of each blast is limited, achieving a single extraction of a 14-18 m thickness is difficult due to the large height of the mining area north of line 60. Therefore, this scheme is not recommended. Figure 11: Simulation results after four steps of mining. (**a**) Maximum principal stress cloud map; (**b**) minimum principal stress cloud map; (**c**) displacement cloud map; and (**d**) plastic zone distribution. Figure 12: Simulation results after eight steps of mining. (**a**) Maximum principal stress cloud map; (**b**) minimum principal stress cloud map; (**c**) displacement cloud map; and (**d**) plastic zone distribution. From Figure 14, it can be seen that the maximum principal stress cloud (Figure 14a) and the minimum principal stress cloud (Figure 14b) show that, after mining half of the stope, there is basically no tensile stress acting on the area surrounding the empty space, while the unmined material on the other side of the empty space is subjected to significant compressive stress, with a maximum compressive stress of 37.3 MPa. Before mining, the maximum compressive stress is mainly concentrated on both sides of the stope. After adopting this mining scheme, the maximum compressive stress increases. From the displacement of the roof of the empty space (Figure 14c) and the displacement of the pillars on both sides of the empty space (Figure 14d), it can be observed that the maximum displacement of the roof of the empty space is 8.83 cm, while the lateral displacement of the pillar next to the empty space is 3 cm, which is much smaller than the displacement of the roof of the empty space. Compared to the normal stope displacement, the displacement values are all within a reasonable range. After the filling of the empty space, as shown in Figure 15, some regions of the filling body exhibit tensile stress, but both the maximum tensile stress value and its range are relatively small. The maximum compressive stress remains at 37.3 MPa, consistent with the maximum compressive stress before filling, indicating that the filling body does not effectively transmit compressive stress. The maximum displacement of the roof after filling is 8.86 cm, which is nearly the same as the displacement after filling.