三轴应力加卸载作用下损伤煤岩渗透率模型研究

Permeability model of damaged coal under triaxial stress loading-unloading

为研究低渗煤岩在应力加卸载作用下损伤破坏过程渗透性变化规律,基于“立方体”结构模型,综合考虑三轴应力加卸载煤岩损伤、有效应力及吸附/解吸作用引起的煤岩割理与基质变形,建立三轴应力加卸载作用下损伤煤岩渗透率模型,并基于试验结果对渗透率模型进行验证。研究结果表明:(1)所构建的渗透率模型,不仅可以较好地反映三轴应力加卸载作用下损伤煤岩渗透率变化规律,而且也可以反映有效应力对损伤煤岩渗透率的影响远大于吸附解吸作用的规律。(2)当煤岩应力水平低于峰值强度时,在恒定围压、持续加轴压应力作用下煤体处于压缩状态,瓦斯渗透率降低;在卸围压、持续加轴压应力作用下,煤体内部开始产生损伤破坏,瓦斯渗透率缓慢上升;使得煤岩在加卸载失稳破坏前,瓦斯渗透率整体呈“V”字型发展趋势。(3)不同初始围压条件下,煤岩加卸载破坏失稳后渗透率增大程度随着初始围压的增大而增大;不同瓦斯压力条件下,煤岩的初始渗透率随着瓦斯压力的增大而增大。研究结果可以为我国采煤工作面瓦斯高效抽采提供理论支撑,具有指导性意义。

In order to study changes in permeability of coal in the process of damage and failure under stress loading and unloading,based on coal“cube”structure model,a triaxial stress loading-unloading damage coal permeability model was established by comprehensively considering the deformation of coal cleats and matrix due to the actions of damage,effective stress and adsorption/desorption under triaxial stress loading-unloading,and the permeability model was verified based on the experimental results. The research results show that the established permeabilitymodel can not only better reflect the change law of the damaged coal permeability under the action of triaxial stressloading and unloading,but also reflect the phenomenon that the effective stress has far greater influence on coalpermeability than adsorption/desorption. When the load on the coal is lower than the peak strength,the coal is in acompressed state under the constant confining pressure and continuous axial compressive loading,and the gaspermeability decreases;while reducing the confining pressure and continuously increasing the axial pressure,damage begins to occur inside the coal,and the gas permeability increases slowly. As a result,the overall gaspermeability of coal exhibits a“V”-shaped development trend before failure. The increase in the permeability ofcoal after failure increases with increasing the initial confining pressure,and the initial permeability of coal increaseswith increasing the gas pressure. The research results can provide theoretical support for the high-efficiencygas drainage and gas disaster prevention and control in my country‘s deep coal mining face,and have guidingsignificance.