Mechanical behavior and stability control of regenerated roof in long wall stratified mining of thick steeply dipping coal seam

This study focused on the stability control of roof in long wall stratified mining of large dip angle thick coal seam. Taking Panbei Coal Mine in Huainan as an example, the effect mechanism of water content, compression ratio and grain size grading on the compression characteristics of gangue is analyzed by comprehensive application of gangue lateral compression test, 3D imaging borehole detection test, physical simulation and numerical simulation method. In addition, the effect of these factors on the stability of the reclaimed roof were also analyzed, the structural characteristics and stress state of the reclaimed roof were obtained, the dynamic behavior of the reclaimed roof was revealed, the stability control measures of the reclaimed roof were formulated, and the control effect of the reclaimed roof stability was evaluated. The research results indicate that the clay minerals of goaf mudstone and sandy mudstone are beneficial for the secondary cementation of gangue. The contact state and stress state of the gangue during compression under load are constantly adjusted, manifested as the compression and bonding degree of the lower and upper gangue being higher than that of the middle, with the compression and bonding degree of the middle and upper gangue being the smallest, and the regenerated roof being more prone to damage. The particle size distribution of gangue is the main factor affecting the shear strength of recycled roof. As the particle size of the gangue increases, the regenerated roof exhibits ductile failure that slides along the shear line to the staggered and bulging of the gangue particles. That is, the degree of mining fracture in the lower part of the regenerated roof tends to be milder than in the middle and upper parts, and the middle and upper parts are the key prevention and control areas for the stability control of the regenerated roof. The deflection of the main stress can lead to the fracture of the regenerated roof, so a plan for the collapse of the regenerated roof and the grouting.