Dynamic Evolution of Fractures in Overlying Rocks Caused by Coal Mining Based on Discrete Element Method

Mining-induced fractures and overlying rock movement change rock layer porosity and permeability, raising water intrusion risks in the working face. This study explores fracture development in working face 31123-1 at Dongxia Coal Mine using UDEC 7.0 software and theoretical analysis. The overlying rock movement is a dynamic, spatially evolving process. As the working face advances, the water-conducting fracture zone height (WFZH) increases stepwise, and their relationship follows an S-shaped curve. Numerical simulations give a WFZH of about 112 m and a fracture–mining ratio of 14.93. Empirical formulas suggest a WFZH of 85.43 to 106.3 m and a ratio of 11.39 to 14.17. Key stratum theory calculations show that mining-induced fractures reach the 16th coarse-sandstone layer, with a WFZH of 97 to 113 m and a ratio of 12.93 to 15.07. Simulations confirm trapezoidal fractures with bottom angles of 48° and 50°, consistent with rock mechanics theories. A fractal permeability model for the mined overburden, based on the K-C equation, shows that fracture permeability positively correlates with the fractal dimension. These results verify the reliability of simulations and analyses, guiding mining and water control in this and similar working faces.