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真三轴采动应力作用下含瓦斯煤岩损伤演化及渗流特性研究

Experimental study on damage evolution and seepage characteristic of gas-bearing coal rock under true triaxial mining-induced stress

  • 摘要: 为揭示采动应力作用下含瓦斯煤体渗透率演化规律,通过真三轴试验模拟了不同垂直与水平应力升降比(4.75∶1、3.50∶1、2.25∶1)加卸载路径下煤体变形及渗透特性。研究结果表明:水平主应力相对卸载速率减缓可增强煤岩承载能力并提升峰值应力,而较快的相对卸载速率会导致水平应变显著增大造成煤体破坏。渗透率演化呈现3个阶段:初始阶段垂直应力增大促使裂隙闭合,渗透率保持稳定或降低;裂隙扩展阶段伴随垂直应力趋近峰值,渗透率缓慢上升;裂隙贯通阶段因煤样破坏导致渗透率急剧升高,损伤含瓦斯煤体该现象尤为显著。基于气体压力与煤体应变耦合关系,构建了引入损伤因子D和修正因子C的渗透率预测模型,该模型计算结果与试验数据拟合度较高,有效表征了渗透率随应变及气体压力的动态响应机制。

     

    Abstract: In order to reveal the permeability evolution law of gas-bearing coal under mining-induced stress, the deformation and permeability characteristics of coal under loading and unloading paths with different vertical and horizontal stress rise and fall ratios (4.75∶1, 3.50∶1, 2.25∶1) are simulated by true triaxial experiments. The research shows that the reduction of the relative unloading rate of horizontal principal stress can enhance the carrying capacity of coal and rock and increase the peak stress, a faster rate of relative unloading will cause significant changes in the horizontal strain of the coal body, leading to instability and failure of the coal body.The evolution of permeability exhibits three characteristic stages: in the initial stage, the increase of vertical stress causes the fracture to close, and the permeability remains stable or decreases; in the stage of fracture expansion, the vertical stress approaches the peak value and the permeability increases slowly; in the fracture coalescence stage, permeability rises sharply due to coal sample failure, with this phenomenon being particularly pronounced in damaged gas-bearing coal. Based on the coupling relationship between gas pressure and coal strain, a permeability prediction model with damage factor D and correction factor C was constructed.The calculation results of this model are in good agreement with the experimental data, effectively characterizing the dynamic response mechanism of permeability with respect to strain and gas pressure.

     

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