Evolution of the Fracture Characteristics in a Rockburst under Different Stress Gradients

The variation in principal stress ratio and principal stress direction deflection caused by the stress gradient distribution of surrounding rock is one of the reasons leading to different types of strain rockbursts. Two typical rockburst failure modes of brittle gypsum debris are discussed based on the study of the macroscopic and microscopic appearance morphologies under different stress gradients. Based on the acoustic emission characteristic parameter analysis of the Gaussian mixture model (GMM), the evolution of internal crack propagation and the fracture mechanism during the rockburst under different stress gradients were explored. The results are as follows: (1) The generation and intensity of rockburst are related to the loading stress gradient. The larger the stress gradient, the more significant the dynamic phenomenon during the rockburst process. (2) There are obvious differences in the morphology and arrangement of crystals on the fracture surface of rockburst debris under different stress loading paths. The brittle fracture of debris can be divided into flake debris dominated by intergranular tensile fracture and massive debris dominated by transgranular shear fracture. (3) The AE characteristic parameter classification method based on the GMM has good applicability in crack classification. With an increase in the loading stress gradient, the proportion of the shear crack increases gradually, which is the main reason for the enhancement of the rockburst intensity.