Mechanism of Fracture Evolution and the Mechanical Response of Coal Rock Composites

Understanding the mechanism of fracture evolution in underground stacked coal–rock composite structures is crucial for the accurate prediction and prevention of mine disasters. In this study, the fracture evolution characteristics of a coal–rock–coal (CRC) composite structure under uniaxial compression were monitored and studied using three-dimensional digital image correlation and an RA-AF method based on acoustic emission (AE) parameters. The fracture mechanisms of the CRC composites were revealed based on experimental results and theoretical analyses. The results indicate that the compressive strength and elastic modulus of CRC composites increase with the thickness of the rock layer and the strength of the coal and rock. Owing to the differences in the thickness and strength characteristics of coal and rock in CRC composites, three fracture modes were identified. The fracture of the CRC composite structure is determined by the stress redistribution and energy release, which are dominated by the mechanical and size effects of coal and rock.