Study on pressure-relief effect and protection scope of long-distance lower protective seam mining based on similar...

This study investigates the long-distance pressure-relief protection effect of mining the Wu 8 coal seam on the overlying Ding 5.6 coal seam in Pingmei No. 6 Coal Mine using similar physical simulation and PFC^3D numerical modeling. The spatiotemporal evolution laws of the overlying strata stress field, fracture field, and displacement field were systematically analyzed. Results show that the overlying strata fracture field presents a trapezoidal distribution and undergoes three stages: initiation, propagation, and compaction. The vertical stress peak is 3.6-4.4 times that of the horizontal stress peak, and the pressure-relief zone of the protected coal seam is inwardly staggered by 35-40 m along the strike and 11-14 m along the dip. The displacement field of the protected coal seam evolves into a bowl-shaped structure with a slow-fast-stable subsidence trend. Based on an expansion deformation rate of ≥ 3‰ and a critical stress of 16.9 MPa, the effective pressure-relief protection scope was determined, with corresponding pressure-relief angles of 60.9°-62.2° along the strike and 80.5°-81.3° along the dip. The conclusions provide a theoretical basis for outburst prevention and pressure-relief gas extraction in long-distance protective seam mining.