Numerical analysis of coal seam spontaneous combustion effects and preventive berm design for composite slope stability in arid open-pit mines

This study investigates the spontaneous combustion of shallowly buried coal seams at the toes of dump–end-wall composite slopes in open-pit mines and its implications for slope stability. An integrated approach combining theoretical analysis, numerical simulations, and field investigations was employed to identify the mechanism of coal-fire initiation, assess its influence on slope stability, and develop a mechanism-informed prevention strategy. The results reveal a mechanism whereby stress redistribution, shear deformation, fracture evolution, and oxygen migration collectively govern coal-fire initiation in composite slopes. The interaction between waste-dump and end-wall slopes induces significant shear stress concentration and deformation within the slope toe, promoting fracture propagation and coalescence. Under hot and arid conditions, the resulting fracture networks provide oxygen pathways that enable spontaneous combustion of shallowly buried coal seams without direct outcrop exposure. Coal burning further reduces slope stability through coupled thermo-mechanical degradation, decreasing the factor of safety from 1.668 to 1.560. A counterweight berm strategy was developed to regulate toe stress conditions, suppress fracture connectivity, and interrupt oxygen transport pathways, increasing the factor of safety from the initial unbermed value of 1.668 to 1.758. The findings provide a geomechanical basis for the assessment and proactive prevention of coal-fire hazards in composite slope systems.