Study on the fracture evolution mechanism of overlying strata in gently inclined coal seam mining based on numerical simulation and microseismic monitoring

The mining-induced movement and fracture development of overlying strata in gently inclined coal seams are more complex than those in horizontal seams and directly affect surface subsidence and roof water hazard prevention and control. Taking the 1632(3) gently inclined working face of Dingji Mine as the engineering background,this study combines UDEC discrete element numerical simulation with an underground microseismic monitoring system to reveal the asymmetric evolution mechanism of mining-induced overlying strata fractures. The key findings are as follows:The roof strata form an asymmetric stress equilibrium arch,whose formation-fracture-reformation cycle corresponds in real time to the periodic caving movement of the overlying strata. Fractures evolve through “initiation-propagation-interconnection” stages,with microseismic events showing alternating spatiotemporal clusters of high-frequency-high-connectivity and low-frequency-low-connectivity zones. Fracture distribution exhibits distinct asymmetry:along the dip direction,it is denser on the updip side and sparser on the downdip side; vertically,the fracture density decreases from bottom to top,being sparser in the upper strata and denser in the lower strata. The height of the water-conducting fracture zone obtained by numerical simulation (55. 35 m) agrees well with the microseismic monitoring result (49±1. 8 m) (error<8. 2%),and the deviation from the theoretical prediction remains within 13. 5%,verifying the reliability of the combined analysis method. These results provide a theoretical basis and engineering reference for surface subsidence control and roof water hazard prevention in gently inclined coal seam mining.