Quantitative characterization and three-dimensional reconstruction of bituminous coal fracture development under rock mechanics testing

To examine the development law of a coal fracture structure under uniaxial compression, tension, and shearing, a study involving bituminous coal was conducted. A high-resolution three-dimensional (3D) X-ray microanalyzer (microscale) was used to scan the coal after loading using computed tomography (CT). Finally, a threshold segmentation method was implemented to segment the coal matrix, minerals, and fractures in the CT scanning image of the coal. The scanning volumes of the matrix, minerals, and fractures and their actual volume proportions were calculated. The analysis revealed that the coal sample under tensile stress had the least fractures, and the volume proportion of fracture was significantly smaller than those for the coal samples under uniaxial compression and shear stress. Through the 3D reconstruction of coal and its fractures, the spatial distribution of the matrix, minerals, and fractures in the coal body under different loading conditions was visually and stereoscopically presented. Through a quantitative analysis and comparison of the relevant fracture parameters under different loading conditions, it was concluded that the pore proportion was significantly larger than that of fractures ( > 90%). Classification maps of different coal fractures were obtained, providing a real spatial structure for subsequent numerical simulation. The extension direction, development degree, and connectivity of the main fractures in coal under different load conditions were analyzed from a microscopic viewpoint. Additionally, the length, width, and volume of the veins near the stress loading direction were important factors affecting the coal stress and fracture extension.