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A Multi-mechanism Coupled Framework for Thermal Spalling in Coal: Thermal Fracture Mechanisms and Physicochemical–Structural–Mechanical Interactions
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DOI：10.1007/s00603-026-05821-4.png)
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Abstract
En 中文
Coal thermal spalling poses significant risks to cavity stability and gasification efficiency during underground coal gasification (UCG) and other high-temperature coal engineering processes, yet its underlying mechanisms remain poorly understood due to strong thermo-hydro-chemo-mechanical coupling. In this study, anthracite from the Jincheng mining area (Shanxi, China) was subjected to staged thermal treatments from 25 to 600 °C. A multi-scale experimental approach integrating Fourier-transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), nuclear magnetic resonance (NMR), scanning electron microscopy (SEM), permeability measurements, and mechanical testing was employed to systematically characterize the coupled evolution of physicochemical properties, pore-fracture structures, and mechanical behavior. Results reveal a pronounced stage-dependent thermal response: below 200 °C, moisture loss and gas desorption induce pore contraction, matrix densification, and temporary strength enhancement; between 200 and 500 °C, organic pyrolysis and mineral dehydration or decomposition dominate, promoting volatile release, pore expansion, fracture development, permeability increase, and mechanical degradation; above 500 °C, the combined effects of gas-pressure buildup, mineral transformations, and heterogeneous thermal expansion promote fracture coalescence, coal skeleton collapse, and layered thermal spalling. Thermal stress analysis further demonstrates that thermal spalling is controlled by coupled microcrack initiation and instability driven by four primary mechanisms: (i) surface thermal stress induced by temperature gradients, (ii) differential thermal expansion between minerals and the coal matrix, (iii) lamination-induced stress mismatch, and (iv) internal pore pressure from volatile release. These mechanisms collectively govern fracture networks propagation, interconnection, and ultimate material detachment. Based on these findings, a multi-mechanism coupled evolution framework is proposed to link thermal stress-fracture mechanics, physicochemical transformations, pore-fracture structure evolution, and mechanical degradation, providing a mechanistic basis for evaluating thermal-spalling behavior in UCG and other high-temperature coal-related engineering environments.
Keywords:
Anthracite
Thermal spalling
Pore-fracture evolution
Physicochemical transformations
Mechanical degradation
Underground coal gasification
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