Effect of coal thickness on mechanical and energy evolution characteristics of coal–rock composite specimen with similar coal–rock strength ratio

Abstract

The stability of coal–rock composite structures is vital to the safety of coal exploitation. To investigate the failure mechanism and energy evolution of coal–rock composite structures of similar strength ratios, uniaxial compression tests based on different coal thicknesses are performed. The results show that both the elastic modulus and peak strain decrease as the coal thickness increases, whereas the peak stress does not exhibit a clear trend owing to the similar strength between coal and rock. The failure mode changes from rock splitting failure to coal–rock failure as the coal thickness increases. The energy evolution of coal–rock composites of different coal thicknesses is similar and can be categorized into three stages based on the dissipated energy variation, i.e., the initial damage, stable damage, and unstable damage stages. Additionally, the ratio of dissipative energy to elastic energy, K, is used to verify and predict the composite specimen failure. A K that fluctuates and increases rapidly implies the failure of the composite specimen. These results can provide a reference for designing support schemes and predicting the failure of coal–rock composite structures.