Study on the Mine Pressure Behavior Regularity of Roadways When Passing Through Remaining Coal Pillars in Thick Seam Mining

Abstract

Residual coal pillars retained in the overlying seam represent an important source of stress disturbance that can intensify mine pressure responses in underlying thick coal seam mining. Taking the downward mining of the Carboniferous–Permian dual-system extra-thick coal seam in the Xiao Coal Mine as the engineering context, this study integrates theoretical modeling and numerical simulation to characterize the disturbance extent of the underlying seam, the stress field redistribution in interlayer rock strata induced by the residual coal pillar, the evolution of advanced abutment pressure, and the variation in surrounding rock stress fields as the working face advances underneath the remaining coal pillar. A mechanical model is developed to describe the stress propagation and superposition induced by the coal pillar. Numerical simulation reveals that the vertical stress peak in the interlayer strata reaches 21.79 MPa near the overlying seam floor and 21.71 MPa at the underlying seam roof, and the peak stress in the coal seam roof beneath the pillar reaches 17.0 MPa, approximately 2.2 times the in situ stress, decreasing to 7.8 MPa at 42.5 m from the pillar. As the working face advances from 70 m to 10 m away from the monitoring section, the vertical stress peak on the goaf side increases from 21.19 MPa to 23.69 MPa, and on the solid coal side from 20.73 MPa to 23.46 MPa; the peak position shifts downward by approximately 0.7 m. The high floor stress from the overlying pillar superimposes strongly with the advanced abutment pressure, and the maximum disturbance width occurs at the peak abutment pressure point. Based on these findings, an optimized working face layout is proposed: an internal offset distance of 42.5 m between the mining roadway and the overlying remaining coal pillar. Following implementation of the optimized support scheme and floor grooving measures, field monitoring indicated reductions of 49.5% in roof subsidence and 60% in floor heave, with the maximum floor deformation limited to 256 mm. These results provide a theoretical basis for roadway layout and ground pressure control in downward mining of extra-thick coal seams under similar conditions.