Assessing Burst Proneness and Seismogenic Process of Anisotropic Coal Via the Realistic Energy Release Rate (RERR) Index

Coal burst hazards seriously restrict the safe mining of deep coal resources. Establishing reasonable indexes from the perspective of inherent material properties is crucial for assessing the risk of coal burst. Coal burst is an issue concerning dynamic fracture, and the generation of kinetic energy is attributed to the mismatch between the energy release rate and the energy demand of dynamic fracture. In view of the above fact, a new realistic energy release rate (RERR) index for assessing the risk of coal burst was proposed in this study. This index considers the contribution of post-peak energy to coal burst and the time effect of failure, and reflects the intensity of energy release during post-peak dynamic fracture. Subsequently, uniaxial compression tests were performed on anisotropic coal specimens with different bedding angles, during which acoustic emission (AE) signals and fracture process images were acquired. Based on the test results, the influence of bedding angle on the mechanical properties and burst behaviors of coal was comprehensively explored. Meanwhile, the reasonableness and effectiveness of the RERR index were verified through a comparison with the actual failure situation (sound, fragment ejection, and AE response) and the results obtained on the basis of the conventional indexes (uniaxial compressive strength USC, elastic strain energy index W_ET, bursting energy index K_E, and duration of dynamic fracture D_T). The comparison reveals that the RERR index is highly linearly correlated with the conventional indexes. Furthermore, the RERR-based classification standard of coal burst proneness grade was given. In addition, the dynamic realistic energy release rate (DRERR) index can effectively characterize the stress drop events during the whole loading (seismogenic) process. The DRERR index exhibits an exponential correlation with the cumulative AE energy during stress drop.