## 4 Simulation Analysis of Overburden Rock under Different Mining Intensity of Fracture
### Simulation Analysis of Damage Characteristics of Overlying Rock Formations  
By observing the range where the overlying rock layer yielded and broke during the advancing process of the working face, the corresponding response characteristics in time and space were analyzed. In order to reflect the deformation law of the overlying rock layer more intuitively, the simulation results of the plastic zone, displacement zone, and stress zone of the overlying rock are used for analysis, the data are extracted and processed for visualization, and the calculation results are reflected in the form of a cloud diagram, as shown in Figure 9.  
Figure 8: FLAC\({}^{\text{3D}}\) numerical calculation coupling model. Figure 9: _Cont_. From the simulation results, it can be seen that when the working face advanced to 30 m, the direct top came to pressure for the first time, which led to the central fracture, but still in the articulation state. The shear stress damage was dominant at both ends of the working face, and the plastic zone range was developed along the coal seam direction, and the broken ring range was about 8 m. Shear and tensile damage occurred in the central area, forming an inverted funnel shape, and the maximum height of the plastic zone was 24.6 m, indicating that the initial collapse of the old top had occurred. The first cycle of the old roof came to pressure and the height of the collapse zone reached 24.6 m.  
When the working face advanced to 90 m, the plastic zone of the working face roof increased, the displacement diagram of the rock layer above the mining area was similar to an \"arch\" shape, and the surrounding rock expanded upward continuously. When the working face was advanced to 300 m, the plastic zone of overburden and pressure relief zone reached the maximum. When the working face advanced to 120 m, the old top fissure developed gradually, the top plate sinkage increased, and was irregularly collapsed. The maximum height of the overburdened plastic zone in the middle of the working face was 92 m, and the maximum height of the top plate plastic zone at the end was 53 m. The height of the collapse zone was 48 m and no longer developed, and the height of the fissure zone was 51 m. When the working face advanced to 180 m, the end of the working face was located at the left border of the dam body, the development of hydraulic fissure was larger, and the overlying rock layer was obviously bending and sinking. The overlying rock plastic zone continued to expand and was more obvious in height, showing a nearly symmetrical saddle shape; the maximum development height was located on the left side of the mining area above the oblique. When the working face advanced to 210 m, it can be seen from the figure that the top plate of the coal seam was still in the state of tensile stress damage, and the width of the damage zone in front and behind the coal wall of the working face did not change much, but the width of the plastic zone in front and behind above the mining void area had increased to 104 m. The scope of the overlying rock damage penetrated the coarse-grained sandstone in the uppermost section of the Zhiluo Group, and a smaller plastic zone appeared on the right side of the reservoir and the dam body, indicating that the mining disturbance had rippled to the reservoir and dam body, the overburden plastic zone range nearly expanded, and the plastic area continued to expand. When the working face was mined at 240 m, it is clear from the figure that the plastic zone on the left side  
Figure 9: Failure characteristics of overlying strata with mining intensity. (**a**) The working face advanced to 90 m. (**b**) The working face advanced to 180 m. (**c**) The working face advanced to 240 m. (**d**) The working face advanced to 300 m.  
continued to develop upward, and the development form on the right side gradually took the shape of an arch.