Failure Behavior and Energy Evolution of Coal-Gangue Composite Structures under Uniaxial Compression

Parting layers, common in coal seams, induce stress redistribution and localized energy accumulation under mining-induced disturbances, significantly affecting the structural stability and fracture behavior of coal masses. To investigate the impact of parting structural parameters on the mechanical response and fracture mechanisms of coal-gangue composites, an orthogonal experimental design was used, varying parting type (yellow mudstone, yellow sandstone, siltstone), thickness ratio (1/5, 1/4, 1/3), and spatial position (upper-middle, middle, lower-middle). A ternary “coal-parting-coal” composite model was constructed, and uniaxial compression tests with acoustic emission monitoring were conducted to assess mechanical behavior, crack evolution, and energy distribution. The results show that gangue strength is the primary factor affecting bearing capacity. High-strength gangue (e.g., siltstone) significantly improves the composite’s peak strength and elastic modulus, with this effect more pronounced at greater gangue thickness and when the parting is positioned centrally or in the lower section. Fracture modes and strain distributions are strongly influenced by parting strength: low-strength partings promote tensile failure, while high-strength partings redistribute stress and inhibit crack coalescence. Digital Image Correlation (DIC) and acoustic emission (AE) analyses reveal that the fracture process evolves in distinct stages, with abrupt transitions. The energy evolution process is divided into four stages: compaction, elasticity, plasticity, and failure. Stronger gangue leads to greater pre-peak elastic energy accumulation, more abrupt post-peak energy release, and enhanced brittleness and impact tendency. These findings provide insights for assessing coal-gangue system stability and preventing rock bursts in deep coal mining. • Orthogonal experiments conducted on coal-gangue composites with different gangue types, thicknesses, and positions. • Mechanical properties mainly controlled by gangue strength; high-strength gangue enhances strength, modulus, and brittleness. • Fracture evolution revealed by AE monitoring and DIC strain fields shows strong dependence on gangue structure. • Energy evolution exhibits four stages; high-strength partings cause greater elastic energy storage, abrupt release, and higher impact risk.