Evolution of Mining-Induced Stress and Fault Slip During Working Face Advance Across Normal Faults in Extra-Thick Coal Seams

During the advance of an extra-thick coal seam working face across a normal fault, tectonic stress and mining-induced stress interact and superimpose, readily inducing stress redistribution in the coal–rock mass, discontinuous movement of the overlying strata, and fault activation and slip, thereby significantly affecting safe extraction of the working face and the control of surrounding rock stability. Taking the extraction of the 2305S working face across the FD8 normal fault in Xinjulong Coal Mine as the engineering background, this study employed a coupled FLAC2D–PFC2D numerical modelling approach to establish normal-fault models with dip angles of 45°, 60°, and 75°. The formation of the normal fault and the subsequent advance of the working face from the footwall to the hanging wall were simulated to investigate the evolution of tectonic and mining-induced stresses, overburden displacement and fracture propagation, and the fault-slip response. The results show that the tectonic stress near the normal fault exhibits a pronounced asymmetric distribution, with a higher degree of stress concentration in the footwall than in the hanging wall. As the fault dip increases from 45° to 75°, the peak stress decreases from 75.6 to 58.8 MPa, while the stress concentration factor decreases from 2.9 to 2.3. Shear cracks dominated the microcracks in the overburden, accounting for 82.63–83.81% of the total. These findings reveal the stage-dependent evolution of stress transfer, overburden movement, and fault slip in normal faults of varying dip, thereby providing guidance for safe working-face advance across faults in extra-thick coal seams and the zoned mitigation of dynamic ground-pressure hazards.