Mechanical Damage Characteristics and Energy Evolution Laws of Primary Coal–Rock Combinations with Different Coal–Rock Ratios

To investigate the mechanical damage characteristics and energy evolution laws of primary coal–rock combinations with different coal–rock ratios, uniaxial compression tests were conducted. Combined with acoustic emission monitoring results, a comparative analysis was performed on the yield strength, elastic modulus, acoustic emission signal characteristics, failure characteristics, and energy accumulation–dissipation characteristics of five different coal–rock ratio specimens. The study reveals the following: (1) Defect structures and dimensions of coal bodies influence the strength of specimens, with the peak stress and elastic modulus of specimens showing a decreasing trend with an increasing coal–rock ratio. (2) The transitional zone of primary coal–rock composite exhibits distinct interface effects on coal and rock components. Coal-derived stresses manifest as horizontal tensile stresses, promoting deformation at the interface between coal and rock, whereas rock-derived stresses at the interface manifest as horizontal compressive stresses, restricting deformation at the coal–rock interface. Moreover, positions closer to the interface experience stronger limitations due to the interface effects. (3) Coal–rock interface cracks are more developed in the primary coal–rock composite, with multipoint cracking occurring at the interface during failure, and a feedback mechanism between coal and rock failure exacerbates the damage and dynamic manifestation intensity of coal bodies. (4) The acoustic emission signals from single-rock samples indicate shear failure of the specimens. Conversely, the acoustic emission signals from single-coal samples and combinations suggest that tensile failure is the primary destabilizing factor. Moreover, with an increase in the proportion of coal, specimens transition from tensile failure to tensile–shear composite failure.