Study on pressure-relief effect and protection scope of long-distance lower protective seam mining based on similar physical simulation and PFC3D

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.