Impact of surface irregularities on coal wall stability and support mechanisms: Insights from physical and numerical experiments

Coal wall stability is a critical factor influencing coal mining efficiency and threatens the safety of working faces, where irregular coal wall surfaces significantly affect the contact and support effectiveness of the support plate, thereby impacting stability. Through a combination of theoretical analysis, mechanical testing, and numerical simulations, this study establishes a mechanical model of irregular coal wall surfaces to investigate the effects of the undulation period and undulation height on coal wall failure characteristics. This research reveals the mechanical response mechanisms of irregular coal wall surfaces and proposes an innovative method to enhance coal wall stability by improving the supporting cushion material of the support plate, which was validated through numerical simulations. The results show that the undulation height and undulation period significantly influence the macroscopic mechanical parameters of the samples, with the undulation height exerting a more pronounced effect. The strength of the samples with undulating surfaces is approximately 50%–60% that of the samples with flat surfaces. The failure mode under uniaxial compression is predominantly tensile, resulting in long and slender block fragments with a characteristic “III”-shaped tensile fracture pattern. During the loading process, samples with undulating surfaces dissipate energy at all stages, with a greater proportion of energy dissipation occurring during the early loading stage because of structural damage and the formation of internal cracks. The surface compressive and tensile stresses are correlated with the curvature radius of the convex surface and the elastic modulus of the supporting plate. Reducing the elastic modulus of the supporting plate material can effectively alleviate the stress concentration at convex locations and increase the peak strength. This study provides theoretical foundations and technical references for the prevention and control of coal wall spalling in deep thick coal seam mining.