In the process of gas extraction, fracture-pore structure significantly influences the macroscopic permeability of coal seam. However, under the multi-field coupling, the mechanism of coal seam fracture-pore evolution remains to be clarified. In this paper, considering the effect of adsorption expansion, the fractal theory for porous media coupled with the multi-field model for coal seam is considered, and a multi-field coupling mechanical model is constructed by considering the influence of fracture-pore structure. Furthermore, the evolution mechanism of fractal dimension with physical and mechanical parameters of coal seam is studied. It is found that the fractal dimension for coal seam is inversely proportional to mining time and in situ stress, proportional to elastic modulus, Langmuir volume constant and Langmuir volume strain constant, and inversely proportional to Langmuir pressure constant. Compared with other factors, Langmuir pressure constant and Langmuir volume strain constant have the significance influence on the fractal dimension for the fracture length.

中文翻译：

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多场耦合下压裂煤层分形维数演化研究

在瓦斯抽采过程中，裂缝—孔隙结构对煤层宏观渗透率有显着影响。但在多场耦合下，煤层裂缝-孔隙演化机制仍有待阐明。本文考虑吸附膨胀效应，将多孔介质分形理论与煤层多场模型相结合，考虑裂缝-孔隙结构的影响，构建多场耦合力学模型。进一步研究了分形维数随煤层物理力学参数的演化机理。发现煤层分形维数与开采时间和地应力成反比，与弹性模量、朗缪尔体积常数和朗缪尔体积应变常数成正比，并且与朗缪尔压力常数成反比。与其他因素相比，朗缪尔压力常数和朗缪尔体积应变常数对裂缝长度的分形维数有显着影响。