## 3 Numerical Simulation Analysis and Demonstration of Actual Extraction Sequence in Large Stopes
### Numerical Simulation Analysis of Stepwise Mining in the 60 Line High Mining Face  
To understand the changes in displacement and stress during the stepwise mining process of the high mining face on the 60 line, this study selected the stepwise mining face between 60-3\(\#\) and 60-13\(\#\) for a simulation analysis. From the minimum principal stress cloud map in Figure 6b, it can be observed that, after the completion of the first-step mining, the compressive stress on the second-step pillar is relatively low, generally ranging from 17.5 to 21.0 MPa. This represents a significant reduction in compressive stress compared to the first-step mining, indicating that the stress in the 60 line mining area is largely relieved after the first-step mining is completed. The maximum principal stress cloud map in Figure 6c shows that the second-step mining area and the filling body are generally not subjected to tensile stress. When combined with the distribution of the plastic zone, it can be seen that the second-step pillar is mainly subjected to shear stress, while the filling body experiences compressive stress. For the second-step mining, the extraction is conducted sequentially according to the actual mining sequence of \"mining every third\" at Dongguanshan. Through a numerical simulation, the changes in stress and displacement were analyzed to assess the stability of the mined-out area after the second-step mining. From Figure 7, after the extraction of the 60-3\(\#\) working face, the maximum principal stress cloud diagram (Figure 7a) shows that only the upper part of the void is subjected to tensile stress, with a maximum tensile stress of only 0.21 MPa. The minimum principal stress cloud diagram indicates that the maximum compressive stress in the 60-5\(\#\) working face is 25 MPa, which is an increase from 21 MPa prior to extraction; however, this maximum compressive stress remains relatively low and has minimal impact on the surrounding rock. In terms of the displacement of the void's roof, the roof displacement is significant, reaching a maximum of 13.8 cm, and there is a noticeable displacement in the upper part of the ore body due to the first-stage extraction. Compared to the first stage, the roof displacement in the second stage has significantly increased. On one side of the 60-3\(\#\) working face, there is filling material, while the other side consists of the original rock. The displacement from both sides indicates that the displacement of the filling material is relatively small, with  
Figure 5: Simulation results of the 60-12\(\#\) working face mining. (**a**) Maximum principal stress contour map; (**b**) minimum principal stress contour map; (**c**) displacement contour map; and (**d**) plastic zone contour map. a maximum displacement of 4 cm, while the maximum displacement of the rock mass is 8.59 cm. Figure 6: Stress conditions before two-step mining. (**a**) Simulation range area; (**b**) minimum principal stress cloud map; (**c**) maximum principal stress cloud map; and (**d**) plastic zone distribution. Figure 7: Simulation results after the extraction of the 60-3# working face. (**a**) Maximum principal stress contour map; (**b**) minimum principal stress contour map; (**c**) roof displacement contour map; and (**d**) displacement contour map on both sides. From Figure 8, after the extraction of the 60-7# working face, the maximum principal stress cloud diagram (Figure 8a) shows that the range of tensile stress in the void is small, with the maximum tensile stress value increasing to 1.53 MPa. However, the small range of tensile stress results in an overall minor impact. From the minimum principal stress cloud diagram (Figure 8b), it can be observed that, after the extraction of the 60-7# working face, the maximum compressive stress in the 60-5# working face remains at 25 MPa, which is similar in range and magnitude to that observed after the extraction of the 60-3# working face. The displacement cloud diagram indicates that the maximum displacement reached 16.3 cm.