Identification and comparisons of crack stress threshold for raw coal and briquette under triaxial compression

The reasonable determination of the coal rock stress threshold holds significant importance for the objective description of coal rock deformation stages and fine-scale crack evolution during failure. This study aims to accurately identify the stress threshold for raw coal and briquette crack propagation under triaxial compression and to determine suitable identification methods. The stress thresholds were determined via triaxial compression experiments, coupled with the monitoring of stress, strain, and acoustic emission (AE) signals. This was achieved by employing the crack axial strain method, the moving point regression technique, and the AE response method. The results indicate that the crack closing stress (σcc), crack initiation stress (σci), and crack failure stress (σcd) of raw coal were consistently and accurately identified using all three methods. However, in the context of triaxial compression experiments on raw coal, the AE response method proves inadequate for delineating the stress threshold associated with crack propagation, necessitating precise identification via alternative methods. These findings contribute to a deeper understanding of the progressive failure process and the macroscopic failure mechanisms of coal samples, with significant theoretical implications for evaluating the stability of deep coal mining operations.