## 4 Stability Analysis
### Analysis of the Development Morphology of the Caved Zone  
Based on the numerical calculation results, the morphology of the development of the caved zone is analyzed in conjunction with the orebody fugacity. The morphology of the caved zone was fitted with a smooth surface. The morphology of the caved zone in the Beiyi quarry mined to \(-\)60 m, \(-\)120 m, \(-\)180 m, \(-\)240 m, and \(-\)360 m is shown in Figure 8.  
There is a mining site north with \(-\)60 m level mining and a caved area mainly in the area west of E9 development. This is because the ore body west of E9 is lower, the \(-\)60 m ore body is mostly in the west mining area range, open-pit bottom area, and the southeast end of the gang below the ore rock cave. In the E9 profile, near the boundary, the bubbling area is not developed to reach the surface, as seen in Figure 8a. The lower part of the side gang rock cave will cause the foot of the slope sink and the upper part of the rock fissure to sprout and expand, which will lead to the problem of a landslide in the east gang of the open pit. With the mining to the \(-120\) m level, the caved zone develops to the southeast, and then the caved zone in the E9 profile develops to the surface, as seen in Figure 8b. However, the general extent of the caved zone in the open pit did not experience a large change. The rock layer in the Beiyi quarry is a diagonal structure and the ore body below \(0\) m extends to the north, so the south gang of the open pit is represented by the lower plate. In addition, a \(40\) m thick cover layer is laid at the bottom of the open pit, and the ore body in this area has a large interlayer, which can be crumbled and filled with debris during the mining process, all of which can effectively prevent the development of an open pit. This can be seen from the direction of surface material movement at one point, as shown in Figure 9.  
Figure 8: _Cont._  
Figure 7: Distribution characteristics of stress field around the mined-out area at the level of \(-240\) m in Beiyi mining area (maximum principal stress, unit: Pa).  
Figure 8: The northern mining area is mined to the boundary of the subsidence area at different levels (green represents the boundary of the subsidence area). (**a**) is the \(-60\) m level, (**b**) is the \(-120\) m level, (**c**) is the \(-180\) m level, (**d**) is the \(-240\) m level, and (**e**) is the \(-360\) m level.  
Figure 9: Direction of movement at a certain moment when mining to \(-60\) m surface in Beiyi mining area.  
From \(-120\) m onwards, the ore body deposit in the Beiyi west zone decreases, while the ore volume in the Beiyi east zone gradually increases. At this time, the development of the caved zone is mainly located in the northeast zone. Since the ore body in the east zone is buried at a greater depth and is gently dipping, the caved zone gradually emerges upward. However, by the end of mining (\(-360\) m), the caved zone did not develop to the surface either. By measuring the vertical distance between the boundary of the caved zone and the surface, it was found that at the end of mining, the top of the caved zone near the E11 profile was still \(220\) m away from the surface, and the moving mining void in the E13 profile was \(539\) m away from the surface. In addition, since mining, the caved zone has not developed towards the west gang of the open pit. Because the underground ore body is far away from the west gang, it is beneficial to the stability of this gang.