Given the potential for dynamic load-induced support crushing that may occur during mining under an interval goaf through an isolated coal pillar (ICP) in shallow closely spaced coal seams, this paper systematically explored this issue through a case study of the 30,103 working face at the Nanliang Coal Mine. We employed a combined approach of similarity simulations, theoretical analyses, numerical simulations, and field measurements to investigate the catastrophic failure mechanisms and prevention strategies for dynamic pressure-related hazards encountered when mining a lower coal seam that passes through an ICP. The findings indicated that the synchronous cutting instability of the interlayer effective bearing stratum (IEBS) and double-arch bridge structure of the ICP roof were the primary causes of dynamic load-induced support crushing at the working face. A mechanical model was developed to characterize the IEBS instability during mining under an interval goaf. The sources and transmission pathways of dynamic mining pressure during mining passing through the ICP were clarified. The linked instability of the double-arch bridge structure of the ICP roof was induced by IEBS failure. The UDEC numerical model was utilized to elucidate the instability of the IEBS during mining in the lower coal seam and to analyze the vertical stress distribution patterns in the floor rock strata of the interval goaf. A comprehensive prevention and control strategy for roof dynamic pressure, which includes pre-releasing concentrated stress in the ICP, strengthening the support strength of the working face, and accelerating the advancement speed was proposed. The effectiveness of this prevention and control strategy was validated through actually monitoring the characteristics of mining pressure data from the 30,103 working face following pressure relief. The findings provide valuable insights for rock stratum control of shallow and closely spaced coal seam mining under similar conditions.

This paper aims to address the issue of hydraulic support crushing accidents or support failures in the retracement roadway (RR) that frequently occurs when a fully mechanized mining face is retraced during the end-mining stage. The deformation and instability mechanism of surrounding rock in the RR during the end mining of a fully mechanized mining face at the Hanjiawan Coal Mine located in the northern Shaanxi mining area is explored through field measurement, theoretical analysis, similar simulation, and numerical simulation. The results reveal that the stability of the remaining coal pillar (RCP) and the fracture position of the main roof are the main factors contributing to large-scale dynamic load pressure in the RR during the end-mining stage. The plastic zone width limit of the RCP is identified to be 5.5 m. Furthermore, the stress distribution within the RCP during the end-mining stage is determined, and the linear relationship between the load borne by the RCP and the strength of the coal pillar is quantified. A similar simulation experiment is conducted to examine the collapse and instability characteristics of the overlying rock structure during the end-mining stage. UDEC (v.5.0) software is utilized to optimize the roof support parameters of the RR. A surrounding rock control technology that integrates the anchor net cable and hydraulic chock is proposed to ensure RR stability. Meanwhile, a method involving ceasing mining operations and waiting pressure is adopted to ensure a safe and smooth connection between the working face and the RR. This study provides a reference for the surrounding rock control of the RR during end mining in shallow, closely-spaced coal seams under similar conditions.

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.