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考虑应力−瓦斯−温湿度耦合影响下基质损伤破裂煤体渗透率模型

Permeability model of matrix-damaged and fractured coal under coupled effects of effective stress, temperature, and moisture

  • 摘要: 我国煤层渗透率普遍偏低,同时煤层开采过程中渗透率还受到有效应力、温度、水分耦合影响,损破裂伤煤体渗透率模型可以有效预测渗透率的变化,从而指导瓦斯抽采。从煤基质损伤破裂的角度,考虑有效应力、温度与水分对煤体裂隙发育及渗透特性的协同影响,通过引入分形理论量化损伤程度,并结合Langmuir 吸附方程、热膨胀及吸湿应变方程构建了多因素耦合作用下基质损伤破裂煤体渗透率模型并进行了验证。结果表明:构建的多因素耦合作用下基质损伤破裂煤体渗透率模型的拟合曲线与不同瓦斯压力、温度、含水率及应力边界条件的试验数据吻合度较高,这表明构建的多因素耦合作用下渗透率模型在复杂条件下的适用性与准确性。通过对模型参数敏感性分析得出,塑性参数对渗透率的影响明显大于弹性参数对渗透率的影响。弹性阶段温湿度参数通过控制基质膨胀收缩行为改变孔隙闭合程度,实现对渗透率的动态调控,而煤体力学参数和吸附变形主要通过竞争关系调控渗透率。塑性阶段参数通过损伤分形和裂隙贯通尺度效应主导非线性变化,当应力加载至峰值强度时,煤体渗透率急剧增加。构建的模型能够准确描述渗透率随多因素耦合的非线性演化规律,精准预测不同开采条件下煤层渗透率变化,为瓦斯抽采提供理论支持。

     

    Abstract: The permeability of coal seams in China is generally low. Meanwhile, during the coal seam mining process, the permeability is also affected by the coupling of effective stress, temperature and moisture. The permeability model of damaged, cracked and damaged coal bodies can effectively predict the changes in permeability and thereby guide gas drainage. From the perspective of coal matrix damage and fracture, this paper considers the synergistic effects of effective stress, temperature and moisture on the fracture development and permeability characteristics of coal body. By introducing the fractal theory to quantify the degree of damage, and combining the Langmuir adsorption equation, thermal expansion and moisture absorption strain equation, a permeability model of coal body with matrix damage and fracture under the coupling effect of multiple factors is constructed and verified. The results show that the fitting curve of the permeability model of matrix damaged and fractured coal under the multi-factor coupling effect constructed in this paper has a high degree of agreement with the experimental data under different gas pressures, temperatures, moisture contents and stress boundary conditions. This indicates the applicability and accuracy of the permeability model under the multi-factor coupling effect constructed in this paper under complex conditions. Through the sensitivity analysis of model parameters, it is concluded that the influence of plastic parameters on permeability is significantly greater than that of elastic parameters. The temperature and humidity parameters in the elastic stage change the degree of pore closure by controlling the expansion and contraction behavior of the matrix, achieving dynamic regulation of permeability. The mechanical parameters of the coal body and the adsorption deformation mainly regulate the permeability through the competitive relationship. The parameters of the plastic stage dominate the nonlinear changes through the damage fractal and fracture penetration scale effects. When the stress is loaded to the peak strength, the permeability of the coal body surges sharply. The model constructed in this paper can accurately describe the nonlinear evolution law of permeability with the coupling of multiple factors, precisely predict the changes of coal seam permeability under different mining conditions, and provide theoretical support for gas drainage.

     

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