## 3 Numerical Simulation Analysis and Demonstration of Actual Extraction Sequence in Large Stopes  
Numerical Simulation Analysis of the Actual Step One Extraction Sequence in Large Stopes at the 60 Line  
In the process of gradual extraction in the large stope at the 60 line, issues such as a severe collapse of the mined-out area, concentrated ground stress in the drilling chamber, and damage to support structures have emerged. To gain a deeper understanding of the stress causes behind these problems, this study conducted numerical simulations for all stopes along the 60 line. Following the actual extraction sequence of the mine and based on prior cause analysis, this study investigates the reasons for the collapse of the mined-out areas and the concentration of ground stress. By analyzing the variations in stress, displacement, and plastic zone distribution under different scenarios, the research provides support for optimizing stope structures and extraction sequences. To understand the patterns of displacement and stress during the step one extraction process at the large stope on the 60 line, this study selected the stope sections between 60-4# and 60-12# for the extraction simulations. As shown in Figure 4, after backfilling the 60-4# stope, the simulation results for the extraction of the 60-8# stope indicate that the rock on both sides of the mined-out area is not subjected to tensile stress. The cloud map of the minimum principal stress (Figure 4b) reveals that, after the extraction of the 60-8# stope, the maximum compressive stress occurs in the 60-6# stope, reaching 33.0 MPa, indicating a stress concentration phenomenon. From the displacement cloud map (Figure 4c), the maximum displacement is located at the roof of the 60-8# mined-out area, with a maximum displacement of 6.3 cm. Additionally, the upper region on the side of the 60-8# mined-out area, near the 9# stope, also experiences some displacement, with a maximum displacement of 5 cm, although the affected area is relatively small. The plastic zone cloud map indicates that the rock on both sides of the mined-out area is subjected to shear stress, while the backfill of the 60-4# stope experiences compressive stress. Analyzing the results from the detection of the mined-out areas, it is evident that the 60-4# stope exhibits a minimal collapse, while the 60-8# stope experiences a significant collapse towards the 9# stope. Numerical simulations show that the displacement direction of the 60-8# stope aligns with the actual direction of the collapse; however, the range of displacement is much smaller compared to that of the 60-4# stope, indicating that the primary reason for the collapse is the relatively poor stability of the rock in that region  
According to the simulation results in Figure 5, after the mining of the 60-12# working face, the distribution of the maximum principal stress indicates that the area surrounding the 60-12# void was not subjected to tensile stress. The distribution of the minimum principal stress shows that the maximum compressive stress increased to 33.8 MPa in the 60-6# working face between the 60-4# and 60-8# working faces, with a more pronounced stress concentration. Additionally, the mining of the 60-12# working face exacerbated the stress concentration in the 60-8# working face. In the 60-10# working face, located between the 60-8# and 60-12# faces, the maximum compressive stress reached 33.7 MPa, creating a non-vertical inclined compressive stress range from the top of the 60-12# working face to the bottom of the 60-8# working face. Displacement distribution indicated that due to the significant height of the void in the 60-12# working face, the range of displacement was large, with a maximum displacement of 7.45 cm, primarily located at the upper part of the 60-12# working face near the 60-11# working face. There was also a certain degree of displacement in the lower region near the 60-11# working face, but it was smaller in extent.