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<p>Coal and gas outbursts constitute a critical dynamic hazard in underground coal mining. Gas contributes to structural damage in coal by altering its pore architecture, a process that reflects the macroscale and microscale instability of gas-bearing coal under the combined influence of in situ stress and gas pressure. To clarify the influence of different gas pressures on the residual evolution of pore–fracture structures in coal, this study systematically examines coal specimens saturated at target gas pressures of 0–4&#xa0;MPa using NMRC and site-specific SEM. The results show that, with increasing gas pressure from 0 to 4&#xa0;MPa, the coal specimens exhibit marked residual pore-structure redistribution, the <InlineEquation ID="IEq1"> <EquationSource Format="TEX">\(T_{2}\)</EquationSource> <EquationSource Format="MATHML"><math> <msub> <mi>T</mi> <mn>2</mn> </msub> </math></EquationSource> </InlineEquation> spectra indicate an average decrease of 25.7% in the micropore peak, an increase of 379.3% in the mesopore peak, and the emergence of a macropore peak, suggesting the coexistence of pore-structure redistribution, local pore expansion, and microcrack development. The pore size distribution curve shifts leftward, with the proportion of micropores rising to 72% and that of macropores increasing to 8%, while porosity increases by 493.44%. Fractal dimension analysis reveals that the complexity of micropores and mesopores increases with rising pressure, whereas the macropore-related structure shows a tendency toward reorganization. The micromorphology of the coal surface exhibits stage-wise evolution under different gas pressures: at low pressure, matrix-grain displacement dominates; at medium pressure, pore closure and expansion occur; at high pressure, micro-cracks propagate and coalesce to form macroscopic fractures. This study provides microstructural evidence for understanding pressure-dependent residual damage in coal and offers a reference for interpreting pore–fracture evolution associated with coal and gas outburst processes.</p>

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Multi-scale Microstructure Evolution Characteristics of Gas-Induced Coal Damage: A Study Based on Nuclear Magnetic Resonance Cryoporometry and Site-Specific Scanning Electron Microscopy

  • 期刊论文

  • 发表日期：

    2026年7月14日

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  • Wenqi Zheng,
  • Feng Gao,
  • Hanpeng Wang,
  • Bing Zhang,
  • Yue Niu,
  • Wei Wang,
  • Chunbo Zhou,
  • Zhizhen Zhang,
  • Jiahui Song,
  • Li Ming

摘要

Coal and gas outbursts constitute a critical dynamic hazard in underground coal mining. Gas contributes to structural damage in coal by altering its pore architecture, a process that reflects the macroscale and microscale instability of gas-bearing coal under the combined influence of in situ stress and gas pressure. To clarify the influence of different gas pressures on the residual evolution of pore–fracture structures in coal, this study systematically examines coal specimens saturated at target gas pressures of 0–4 MPa using NMRC and site-specific SEM. The results show that, with increasing gas pressure from 0 to 4 MPa, the coal specimens exhibit marked residual pore-structure redistribution, the \(T_{2}\) T 2 spectra indicate an average decrease of 25.7% in the micropore peak, an increase of 379.3% in the mesopore peak, and the emergence of a macropore peak, suggesting the coexistence of pore-structure redistribution, local pore expansion, and microcrack development. The pore size distribution curve shifts leftward, with the proportion of micropores rising to 72% and that of macropores increasing to 8%, while porosity increases by 493.44%. Fractal dimension analysis reveals that the complexity of micropores and mesopores increases with rising pressure, whereas the macropore-related structure shows a tendency toward reorganization. The micromorphology of the coal surface exhibits stage-wise evolution under different gas pressures: at low pressure, matrix-grain displacement dominates; at medium pressure, pore closure and expansion occur; at high pressure, micro-cracks propagate and coalesce to form macroscopic fractures. This study provides microstructural evidence for understanding pressure-dependent residual damage in coal and offers a reference for interpreting pore–fracture evolution associated with coal and gas outburst processes.