Han Zhicheng

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.

Based on the idea of harmonic extraction, the problem of reducing the damage of the coal seam waiting for upward mining. Using the theoretical analysis method, a schematic diagram of coordinated mining along the dip direction of coal seam is established, and the calculation method of reasonable layout parameters of coal seam working face early mining is given. Based on the upward mining problem of the No.1 coal seam in the fifth panel of Zaoquan Coal Mine, the influence parameters of the No.2 coal seam, No.6 coal seam and No.7 coal seam mining on the No.1 coal seam were determined by similar simulation test. Then, the layout parameters of working face were determined. The research method of numerical calculation was used to evaluate the degree and uniformity of movement and deformation of the No.1 coal seam, combining five indicators: subsidence, horizontal movement, inclined deformation, curvature deformation, and horizontal deformation. The results indicate that when the working face is arranged using the layout parameters provided in this article, it can promote the further subsidence of the No.1 coal seam at the position of the remaining coal pillar. The movement and deformation indicators of the No.1 coal seam all reach the most uniform degree of the geological mining conditions, which can effectively offset the uneven deformation problem of the No.1 coal seam caused by the influence of the remaining coal pillars, making multiple mining operations a favorable condition for upward mining and achieving the goal of reducing the damage of the No.1 coal seam.