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<p>In deep coal seam gas extraction, the coupled effects of cyclic mining-induced stress, repeated blasting disturbances and cumulative plastic damage to coal bodies significantly impact borehole stability and extraction efficiency. To investigate the coupling mechanism of coal damage-permeation under cyclic dynamic disturbance, this study establishes a cyclic loading plastic damage model based on equivalent plastic strain and the model was validated through digital image correlation (DIC) experiments. Combining coal fluid–solid coupling theory with numerical simulation, this study systematically investigates the impacts of cyclic loading intensity, frequency, and path on coal damage evolution and gas extraction efficiency. Results demonstrate: (1) Under constant horizontal stress, an increase in vertical stress leads to the progressive concentration of damage zones around the borehole along the horizontal direction. This is accompanied by horizontal contraction of the borehole. (2) With the peak load increasing from the elastic range to the yield threshold, the coal surrounding the borehole undergoes a transition from elastic deformation to an annular plastic zone. When the peak load significantly exceeds the yield strength, a composite “annular -X-shaped” fracture network develops in the coal. (3) Damage intensifies with cycle numbers, showing linear growth in damage factor within four cycles. Gas pressure decreases with cycles but at diminishing rates. (4) A key finding is that, under equivalent total energy input, the cyclic loading path exerts a decisive influence. Under equivalent energy input, cyclic loading paths significantly influence damage evolution and gas extraction efficiency. The decreasing path results in the most severe damage and the lowest gas pressure. In contrast, the increasing path leads to the widest damage distribution but relatively mild localized damage. The constant path generates the least damage overall. These findings provide theoretical support for maintaining borehole stability and optimizing extraction parameters under cyclic dynamic disturbance.</p>

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Evolution of Plastic Damage in Coal Under Cyclic Disturbance and Its Regulation Mechanism on Gas Extraction Efficiency

  • 期刊论文

  • 发表日期：

    2026年4月15日

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  • Jialiang Bai,
  • Shuangli Du,
  • Huan Zhang,
  • Hongbao Zhao,
  • Wenpu Li,
  • Liancong Wang,
  • Mingji Ding

摘要

In deep coal seam gas extraction, the coupled effects of cyclic mining-induced stress, repeated blasting disturbances and cumulative plastic damage to coal bodies significantly impact borehole stability and extraction efficiency. To investigate the coupling mechanism of coal damage-permeation under cyclic dynamic disturbance, this study establishes a cyclic loading plastic damage model based on equivalent plastic strain and the model was validated through digital image correlation (DIC) experiments. Combining coal fluid–solid coupling theory with numerical simulation, this study systematically investigates the impacts of cyclic loading intensity, frequency, and path on coal damage evolution and gas extraction efficiency. Results demonstrate: (1) Under constant horizontal stress, an increase in vertical stress leads to the progressive concentration of damage zones around the borehole along the horizontal direction. This is accompanied by horizontal contraction of the borehole. (2) With the peak load increasing from the elastic range to the yield threshold, the coal surrounding the borehole undergoes a transition from elastic deformation to an annular plastic zone. When the peak load significantly exceeds the yield strength, a composite “annular -X-shaped” fracture network develops in the coal. (3) Damage intensifies with cycle numbers, showing linear growth in damage factor within four cycles. Gas pressure decreases with cycles but at diminishing rates. (4) A key finding is that, under equivalent total energy input, the cyclic loading path exerts a decisive influence. Under equivalent energy input, cyclic loading paths significantly influence damage evolution and gas extraction efficiency. The decreasing path results in the most severe damage and the lowest gas pressure. In contrast, the increasing path leads to the widest damage distribution but relatively mild localized damage. The constant path generates the least damage overall. These findings provide theoretical support for maintaining borehole stability and optimizing extraction parameters under cyclic dynamic disturbance.