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| Mechanisms of coal failure modes under the influence of different height-to-diameter ratios and mineral distribution based on in-situ loading CT scanning |
| ZHENG Jiangtao1, 2, BIAN Yufeng1, 2, HUANG Hongtao2, XI Chaodong3, REN Zhangyu4, WAN Changbing4, JU Yang1, 2* |
| (1. State Key Laboratory for Fine Exploration and Intelligent Development of Coal Resources, China University of Mining and Technology-Beijing, Beijing 100083, China; 2. School of Mechanics and Civil Engineering, China University of Mining and Technology-Beijing, Beijing 100083, China; 3. CCTEG Coal Mining Research Institute, Beijing 100013, China; 4. School of Emergency Management and Safety Engineering, China University of Mining and Technology-Beijing, Beijing 100083, China) |
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Abstract To clarify the factors controlling coal failure modes in the end-face region of longwall panels with large mining heights, this study investigates the failure mechanisms of burst-prone coal specimens with different height-to-diameter ratios (?l = 1, 2, 3). Uniaxial compression tests were combined with in situ X-ray computed tomography (CT) scanning to capture the three-dimensional evolution of fractures during loading. Image processing and three-dimensional reconstruction were used to quantitatively analyze fracture propagation, damage evolution, and the effects of mineral distribution. The results show that specimens with ? l= 1 and 3 exhibit greater dispersion in their stress–strain responses, compressive strengths, and elastic energy indices than those with ?l = 2. The uniaxial compressive strength decreases with increasing ?, and all specimens are classified as highly burst-prone according to their elastic energy indices. The failure modes are strongly dependent on l. Specimens with ? l= 1 exhibit peripheral splitting failure caused by strong end restraint, with limited influence from pre-existing internal damage. Specimens with l = 2 exhibit shear failure, with fracture angles consistent with the Mohr-Coulomb criterion. Specimens with l = 3 exhibit a combined shear–splitting failure mode controlled by the initial damage zone as a result of weakened end restraint, leading to the lowest strength. The influence of mineral distribution on fracture propagation increases with ?. For specimens with l = 2 and 3, the principal fractures preferentially propagate along mineral–matrix interfaces, with their azimuth closely corresponding to the mineral distribution. CT-number-based damage variables at 70% of the peak load increase with ?, whereas the post-peak fracture-volume ratio decreases with ?. The fracture networks of specimens with ? l= 2 exhibit the highest fractal dimension, indicating the greatest spatial complexity. These findings clarify the mechanisms by which the height-to-diameter ratio, mineral distribution, and initial damage control coal failure modes and three-dimensional fracture evolution across macro- and mesoscales, thereby providing theoretical support for rockburst prevention in highly burst-prone coal seams with large mining heights.
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2026, Vol. 45 
