Dynamic Damage Evolution and CT Visualization and Characterization of Anthracite from the Southern Part of the Qinshui Basin under Different Confining Pressures.

In order to realize the efficient exploitation of coalbed methane (CBM) in the southern Qinshui basin in China, raw coal specimens with original fractures of the No.3 coal reservoir in the Sihe mine were selected to conduct compression tests with different confining pressures. During this loading process, the synchronous and staged real-time CT scanning tests were carried out by a high-precision X-ray scanner. The mechanical properties, the failure mode, and the evolution of fractures of coal samples due to the increased effective stress were analyzed from the microscopic point of view. The result showed that the original fractures in the coal specimens of the Sihe coal mine are relatively developed. Four mechanical stagescompaction, elastic, yield, and plastic failurewere consistently identified; image-based segmentation allowed real-time, precise quantification of crack initiation and growth. Within the tested confining pressure range, further confirmation through real experiments that compressive strength, peak strain, and elastic modulus rose with confinement, while residual strength was preserved by frictional resistance along fracture surfaces. New fractures tend to start cracking near the original fractures. Crack networks were more intricate under lower confinement (uniaxial tensile failure) and simplified yet more distributed under higher confinement (triaxial shear failure), indicating a transition from brittle to semibrittle/semiductile behavior. Quantitative CT metricsgray value, fracture volume, and fracture porosityproved reliable indicators of damage progression. Porosity is below 1% at the compaction and elasticity stage, twice the size of the original fractures at the initial damage stage. The integrated experimental-visualization workflow elucidates fracture propagation mechanisms in anthracite and offers theoretical guidance for CBM stimulation and ground-control strategies in the Qinshui Basin.