三轴应力作用下煤体渗透率演化特征试验研究

    Experimental study on evolution characteristics of coal permeability under triaxial stress conditions

    • 摘要: 在复杂加载条件下,开采应力扰动使受扰煤体孔隙和裂隙结构发生动态演化,引起渗透率非线性变化,显著影响瓦斯抽采效率。为此,依托三轴试验设备,以刘庄矿150804工作面煤样为研究对象,采用煤岩心渗透率自动测量仪,开展了不同轴压、围压、气体压力条件下煤体渗透率的演变特征及破坏行为试验,并分析了渗透率的变化规律。结果表明:在轴压 3~9 MPa、围压 1~3 MPa、气体压力 0.2~1.0 MPa 范围内,轴压和围压与煤体渗透率总体呈负相关关系,气体压力高会促使煤体裂隙闭合,导致渗透率降低,但在高应力组合条件下渗透率的变化幅度趋于减小;围压增大压缩了煤体孔隙结构,渗透率随围压升高而持续下降,当轴压为3 MPa、围压从1 MPa增至3 MPa时,渗透率降低了0.52×10−17 m2;轴压对渗透率的影响呈现先增强后减弱的趋势,初始阶段(轴压3~5 MPa)因煤体压实导致渗透率下降,超过屈服极限后(轴压5~9 MPa),内部裂隙与孔洞增多,渗透率上升。

       

      Abstract: Mining stress disturbance causes dynamic evolution of the pore and fracture structures of disturbed coal under complex loading conditions, leading to nonlinear changes in permeability, which significantly affects gas drainage efficiency. To address this issue, relying on triaxial test equipment, taking coal samples from the 150804 working face of Liuzhuang Coal Mine as the research object, and using an automatic coal core permeability measuring instrument, this study investigates the evolution characteristics and failure behaviors of coal permeability under different axial pressure, confining pressure, and gas pressure conditions, and analyzes the variation laws of permeability. The results show that within the range of axial pressure of 3 to 9 MPa, confining pressure of 1 to 3 MPa, and gas pressure of 0.2 to 1.0 MPa, the axial pressure and confining pressure are generally negatively correlated with the permeability of the coal body. High gas pressure will cause the coal body fractures to close, resulting in a decrease in permeability. However, under high stress combinations, the variation range of permeability tends to decrease. The confining pressure compresses the pore structure of the coal body, and the permeability continuously decreases with the increase of confining pressure. When the axial pressure is 3 MPa and the confining pressure increases from 1 MPa to 3 MPa, the permeability decreases by 0.52×10−17 m2. The influence of axial pressure on permeability shows a trend of first increasing and then decreasing. In the initial stage (axial pressure of 3 to 5 MPa), due to coal body compaction, the permeability decreases. After exceeding the yield limit (axial pressure of 5 to 9 MPa), the internal fractures and cavities increase, and the permeability increases.

       

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