Analysis of regenerated roof and instability support control countermeasures in a steeply dipping working face

Roof regeneration in coal mining occurs when the remaining bottom slice of thick coal is re-mined. In view of the challenges of roof fall and instability support of a regenerative roof in the mining of steeply dipping coal seams, combined with the geological and engineering conditions of the working face in the Panbei Coal Mine, the mechanism of the instability of the regenerative roof and support is studied, and control countermeasures are proposed. Based on the comprehensive combination of the measurement of the roof structure, physical simulation, numerical simulation, and theoretical analysis, the cementation and compaction degree of the regenerated roof were described. The caving and sliding law of the regenerated roof after bottom slice mining was explored, and the model of support dumping and sliding instability under the roof fall state was established. The results obtained yielded three main findings. Firstly, the compaction degree of the regenerative roof is higher than that of the middle part of the working face, and the compaction degree of the upper part of the working face is the smallest. Secondly, the overburden structure instability of the bottom slice underwent six stages. The fracture of the cantilever beam and the slippage of gangue are the reasons for the enhancement of the acoustic signal at each stage. Finally, the upper part of the stope was identified as the crucial zone in the prevention and control of the support instability. A moving method of metal mesh with pressure and roof scraping was developed, and the support anti-overturning and anti-skid jack was set up to effectively control the stability of the support and roof fall, for safe and efficient mining of a steeply dipping coal seam under a regenerative roof.