<p>Increased coal mining depths in China increase coal and gas outburst risks, necessitating the study of deep gas-bearing coal mechanics. In this research, triaxial seepage‒compression tests with acoustic emission (AE) monitoring and numerical simulation are employed to analyze coal degradation, crack deformation, and failure under gas/confining pressures, including fragment size distribution and fractal analysis. The results reveal a competitive mechanism: gas pressure nonlinearly degrades coal strength, whereas confining pressure counteracts this effect. Increasing the gas pressure (0 to 4 MPa) increased the crack initiation strain proportion by 113.69% but decreased the crack damage strain proportion by 26.15%. Conversely, increasing the confining pressure (5 to 25 MPa) suppressed crack initiation (55.89% decrease in the initiation strain proportion) but enhanced damage strain accumulation (44.31% increase) through lateral constraint. Elevated gas pressure reduced the cumulative energy of the AE by 65.88% and increased the fractal dimension <InlineEquation ID="IEq1"> <EquationSource Format="TEX">$D_{f}$</EquationSource> <EquationSource Format="MATHML"><math> <msub> <mi>D</mi> <mi>f</mi> </msub> </math></EquationSource> </InlineEquation> from 1.70 to 2.13, indicating that earlier consumption of elastic energy by gas-induced damage promoted crack branching. In contrast, a higher confining pressure increased the peak AE energy by 42% and decreased <InlineEquation ID="IEq2"> <EquationSource Format="TEX">$D_{f}$</EquationSource> <EquationSource Format="MATHML"><math> <msub> <mi>D</mi> <mi>f</mi> </msub> </math></EquationSource> </InlineEquation> to 1.27, demonstrating concentrated energy release through dominant crack propagation by suppressing crack bifurcation. Numerical simulation results revealed that gas pressure and confining pressure influence the mechanical characteristics of cracks by controlling their deformation capability. High gas pressure increases crack propagation complexity and results in more branch cracks, whereas high confining pressure leads input energy to prioritize crack widening and propagation, reducing branch cracks. These findings clarify the mechanical mechanisms of outbursts under deep high-stress and high-gas conditions, providing theoretical support for predicting dynamic hazards in deep mining.</p>

Competitive Effects of Gas Pressure and Confining Pressure on Crack Deformation and Failure Characteristics in Gas-Bearing Coal

期刊论文
发表日期：

2025年11月20日

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Wenqi Zheng,
Feng Gao,
Hanpeng Wang,
Chunbo Zhou,
Zhizhen Zhang,
Li Ming

摘要

Increased coal mining depths in China increase coal and gas outburst risks, necessitating the study of deep gas-bearing coal mechanics. In this research, triaxial seepage‒compression tests with acoustic emission (AE) monitoring and numerical simulation are employed to analyze coal degradation, crack deformation, and failure under gas/confining pressures, including fragment size distribution and fractal analysis. The results reveal a competitive mechanism: gas pressure nonlinearly degrades coal strength, whereas confining pressure counteracts this effect. Increasing the gas pressure (0 to 4 MPa) increased the crack initiation strain proportion by 113.69% but decreased the crack damage strain proportion by 26.15%. Conversely, increasing the confining pressure (5 to 25 MPa) suppressed crack initiation (55.89% decrease in the initiation strain proportion) but enhanced damage strain accumulation (44.31% increase) through lateral constraint. Elevated gas pressure reduced the cumulative energy of the AE by 65.88% and increased the fractal dimension $D_{f}$ $D_{f}$ from 1.70 to 2.13, indicating that earlier consumption of elastic energy by gas-induced damage promoted crack branching. In contrast, a higher confining pressure increased the peak AE energy by 42% and decreased $D_{f}$ $D_{f}$ to 1.27, demonstrating concentrated energy release through dominant crack propagation by suppressing crack bifurcation. Numerical simulation results revealed that gas pressure and confining pressure influence the mechanical characteristics of cracks by controlling their deformation capability. High gas pressure increases crack propagation complexity and results in more branch cracks, whereas high confining pressure leads input energy to prioritize crack widening and propagation, reducing branch cracks. These findings clarify the mechanical mechanisms of outbursts under deep high-stress and high-gas conditions, providing theoretical support for predicting dynamic hazards in deep mining.