Evolution of Coal Fractures and Its Influence on Permeability during Progressive Failure Based on In Situ CT Scanning

In the process of deep coal resource extraction, a large number of cracks will be generated in the coal body in front of the working face under mining stress, causing large-scale instability and damage to the coal seam. However, due to limitations in experimental conditions, there is little research on the specific process of crack propagation under mining-induced stress. In response to this situation, this article adopts in situ CT scanning technology to extract the dynamic development process of coal sample fractures under the mining stress path and the traditional triaxial loading path. The damage stages of the coal samples were characterized by analyzing the corresponding stress-strain curves. The reconstruction results of coal sample fractures were quantitatively characterized from four perspectives─fractal dimension, equivalent fracture opening, porosity, and crack volume─and the PNM model. This analysis also elucidated the changes of the internal flow field and permeability during the damage process. Furthermore, the digital volume correlation (DVC) method was utilized to study the evolution of the displacement and strain fields in middling coal samples throughout the loading process. Finally, this study explored the mechanisms of crack propagation by examining the distinct behaviors observed under the two stress paths. The research results of this article have certain reference significance for the study of the coal damage destruction mechanism and fluid transport law under mining stress.