A Study on the Optimal Location for Offset Arrangement of Back- mining Drifts Below a 60-meter-wide Coal Pillar in the Upper Substratum of a Thick Coal Seam

In order to improve the recovery rate of coal resources and address the issue of reasonably positioning staggered mining roadways under thick coal seams, the transportation gallery of working face 52202 in Wulan Setai Coal Mine was taken as the research object. The strength of wide coal pillars in the upper layered section and the loads they bear were calculated and analyzed, resulting in a coal pillar strength of 30.30 MPa, which is greater than the 6.68 MPa load affected by the goaf. Using the limit equilibrium theory, the limit equilibrium zone width of the wide coal pillars in the upper layered section was calculated to be 13.08 m, with the elastic zone located 13.08–39.52 m from the right edge of the coal pillar. Simulate the characteristics of stress and displacement field changes in the surrounding rock when the roadway for layered retreat mining is arranged with different staggered distances using the finite difference numerical simulation software FLAC3D.The results indicate that when the thick coal seam is mined in layers at a staggered distance of 24 meters, the stress on the surrounding rock of the mining roadway tends to be relatively uniform, the deformation is relatively minimal, and the roadway is the easiest to maintain. The proposed design was applied to the 52202 mining roadway in the Wulan Setai Coal Mine. Field practice demonstrates that an externally staggered distance of 24 m for the lower layering mining roadway meets the requirements for safe and efficient production, providing a valuable reference for coal mines under similar geological conditions.