Assessing the Fracturing Process of Rocks Based on Burst–Brittleness Ratio (BBR) Governed by Point Load Testing

Brittleness is an intrinsic mechanical property of rock materials that has attracted significant attention to be properly quantified as it plays an important role in characterization of brittle fracturing. Endeavors have led to the establishment of many Brittleness Indices (BIs) for various rock types and widespread engineering applications. Among them, assessing burst proneness as a serious challenge in underground mining has received considerable attention. Parallel to BIs' development, various Bursting Liability Indices (BLIs) have been proposed to specifically assess coal bursting phenomenon. Despite having different names, both BI and BLI in principle have aimed at evaluating the burst–brittleness level of different rocks for different applications. In this study, the principles of burst and brittleness were discussed followed by the development of a novel so-called burst–brittleness ratio (BBR) to assess the relative burst–brittleness of rock types irrespective of their applications. To do so, the proposed BBR was governed by point load testing (PLT) which has significant advantages over the other rock testing methods used in BI estimation such as direct or indirect tensile testing. To examine the suitability of the proposed ratio, three different rock types from various geological origins including coal, granite and sandstone were selected and tested under uniaxial compressive, indirect tensile Brazilian and point loadings. The high-speed imaging technique and Acoustic Emission (AE) were utilized to characterize the cracking process (e.g., failure under shear or tension) and to monitor the real-time failure behavior of samples under different loading conditions. The resulting data revealed that the severity of strength loss in coal samples was significantly higher than that observed in other rock types particularly under uniaxial compression endorsing the validity of the proposed BBR.