Abstract:
To investigate the crack evolution of gas-bearing coal under the influence of interburden, this study focuses on gas-bearing coal as the research object. Using an industrial CT scanning system for coal-rock under load, a series of experiments were designed and conducted under constant confining pressure, with different gas pressures and varying interburden thickness and number of layers. These experiments were used to scan the cracks in gas-bearing coal under load, obtaining original CT images of the cracks in gas-bearing coal. Three-dimensional reconstruction techniques were employed to create digital models of the gas-bearing coal, allowing for visualization of the internal crack structure. The structural parameters were then calculated using Avizo software for quantitative analysis of the crack evolution characteristics in gas-bearing coal. The results indicate that the failure mode of gas-bearing coal samples under triaxial loading is shear failure. The cracks in pure coal samples exhibit composite forms such as parallel and intersecting cracks. In interburden coal samples, cracks mainly concentrate in the coal body, with only one or two major cracks extending into the rock mass and penetrating the interburden layer, which shows little damage. In the case of double-layer interburden samples, damage is primarily concentrated in the coal body between the two interburden layers, and the macro-cracks after failure typically exhibit a characteristic "A"-shaped pattern. Under the influence of interburden, the crack ratio, three-dimensional fractal dimension, and average coordination number in gas-bearing coal increase with the increase in gas pressure, while these parameters decrease as the interburden thickness and number of interburden layers increase. The increase in gas pressure causes the Coulomb failure line and the Mohr stress circle to approach each other. Gradually, the conditions for sample failure are approximated, facilitating the development of fractures more easily. The increase in interburden thickness reduces the energy release rate of crack propagation, increases the critical crack length, and makes crack propagation more difficult.