Quantitative Evaluation Methods of Brittle Failure Characteristics of Coal: A Case Study of Hard Coal in China

Coal brittleness is one of the important indexes to characterize the post-peak characteristics of coal, which is closely related to the efficiency of underground coal mining and the degree of coal disaster. In this paper, the compression characteristics of coal are studied by laboratory experiment, which is characterized by relatively long nonlinear elastic stage, smaller plastic stage and stress drops in post-peak stage. On this basis, the existing brittleness evaluation methods are summarized, and the applicability of 11 indexes of 6 physical parameters to the quantitative evaluation methods of coal brittleness are analyzed and discussed. The results show that: (1) for the coal is a complexity heterogeneous medium with hole and fracture, there are different degrees of limitation on the methods of coal brittleness quantitative evaluation,which can be used to roughly estimate the brittleness of coal, but it can not accurately characterize its brittle characteristics. (2) Based on the whole process stress–strain curve, the brittleness degree index B5 is more suitable for the brittleness characterization of coal by quantitatively considering the relative size and absolute rate of post-peak stress drop.