# Study on Surface Damage Induced by High Heavy Layer Movement and Mining-Induced Earthquakes
## 4 Discussion  
### Engineering Practice  
During the advancing of the initial working face in the No.7 mining district, a full-basin strike monitoring line was established on the ground directly above the starting cut  
Figure 12: Comparison of subsidence whether induced with mining-induced earthquakes: (**a**) comparison of top stratum during 600–650 m excavation; (**b**) comparison of heavy layer during 600–650 m excavation; (**c**) comparison of top stratum during 650–700 m excavation; (**d**) comparison of heavy layer during 650–700 m excavation; (**e**) comparison of top stratum during 700–750 m excavation; (**f**) comparison of heavy layer during 700–750 m excavation; (**g**) comparison of maximum subsidence under different excavation plans.  
of the 7202 working face, as shown in Figure 13. From 5 July 2021 to 15 February 2023, the working face underwent 11 elevation observations and 1 plane observation over a 21-month period. The monitoring results are presented in Figure 14.  
As shown in Figure 14, monitoring data from 10 May 2020 indicated only slight land subsidence. However, data from 11 July 2020, revealed significant land subsidence, with a substantial increase in the subsidence magnitude. This aligns with the timing of the high-energy mining-induced earthquakes on 24 May 2022, confirming the bending subsidence of the heavy layer and necessitating mitigation measures for the working face.  
Monitoring results show that during the actual mining process, the frequency of high-energy microseismic events increased significantly when the working face advanced to approximately 450 m from the open cut. To address this, deep-hole roof pre-splitting blasting techniques was applied to the overlying rock layer. Drilling and blasting operations were conducted on the lower layer of the heavy layer to create the space required for its fracture and subsidence. The design and implementation of the blasting holes are illustrated in Figure 15. By blasting the multi-layered sandstone and mudstone between  
Figure 14: Accumulative subsidence curve of land subsidence monitoring strike.  
Figure 13: Land subsidence strike monitoring line.  
the heavy conglomerate layer and the working face, their bulking coefficient was significantly increased, ensuring sufficient subsidence to fill the goal, as shown in Figure 16. This approach aims to reduce the length of the separation space and control its height, minimize the accumulated bending elastic energy within the heavy conglomerate layer, and ultimately decrease the frequency and intensity of mining-induced earthquakes caused by the fracture and bending subsidence of the heavy layer. This mitigates the negative impact of the heavy layer and mining-induced earthquakes on surface damage.  
As shown in Figure 17, the maximum cumulative subsidence point is B21A, with a total subsidence of 233 mm, and regional subsidence is observed at surface monitoring points B20-B28. This indicates that the Jurassic heavy conglomerate layer directly above the goal has fractured. After implementing deep-hole roof pre-blasting, the lower rock layer deformed and fractured. Due to the bulking effect of the broken rocks, their expanded volume filled the separation space, reducing its size and mitigating the fracture and movement of the heavy layer. Microseismic monitoring results show that after blasting, mining tremor energy was mostly concentrated in the range of 10\({}^{2}\)\(\sim\)10\({}^{3}\) J, with no further occurrence of high-energy mining-induced earthquakes. The land subsidence rate slowed significantly, effectively reducing the frequency and intensity of heavy layer-type mining  
Figure 15: Schematic diagram of blasting broken roof drilling section: (**a**) strike direction locations diagram; (**b**) cross-section along strike diagram; (**c**) boreholes cross-section along dip diagram.  
induced earthquakes. This achieved the goal of mitigating surface damage induced by mining-induced earthquakes.