Fracture propagation in gas-bearing coal under triaxial compression using computed tomography scanning techniques

To explore the evolution of characteristics and trends of fractures in gas-bearing coal, in situ computed tomography scanning experiments were performed on coal samples under different gas pressures and applied loads. The spatial distribution of fractures in computed tomography images of coal samples was visualized by using image analysis and processing software. Furthermore, the internal fracture structure of gas-bearing coal was analyzed qualitatively and quantitatively using grayscale statistical theory and fractal theory, respectively. The results of this study indicated that during the whole stress–strain process of gas-bearing coal, the pixel ratios of two-dimensional and three-dimensional fractures showed three stages: slow decline, slow growth, and rapid growth. For the statistical characteristics of computed tomography scan gray images, the contrast first decreased and then increased, while the correlation, energy, and homogeneity first increased and then decreased. In addition, in the whole loading stage, the fractal dimension of coal samples decreased first and then increased with the increase in strain value, while the Euler number was just the opposite. Significantly, after the failure of gas-bearing coal, the peak strength, elastic modulus, and Euler number decreased linearly with increasing gas pressure, and the intricacy and interconnection of the fracture network improved. The results furnish a vital understanding of gas drainage from coal seams and safe operation of coal mines.