Coupled effects of interface parameters on mechanical behaviours and mesoscopic failure of coal-rock composite structures using DEM

Interface slip triggers dynamic disasters in steeply inclined coal seams, yet coupled effects of inclination θ and modulus ratio n remain poorly understood. Numerical models with θ = 0°–60° and n = 0.5–2.0 were established to investigate mesoscopic evolution mechanisms of coal–rock composites. Increasing θ markedly reduces strength, with a maximum drop of 28.41% at n = 0.5 and 30° as the inflection point. Higher n suppresses interface slip, lowering the critical reversal angle from 47.5° to 42.7°. Increasing θ drives energy towards rock, whereas higher n enhances overall energy storage, offering guidance for disaster prevention in steeply inclined seams.