钻孔瓦斯预抽作为高瓦斯矿井瓦斯防治的最主要技术手段，能够有效降低煤层瓦斯含量，从根本上防治煤与瓦斯突出等相关灾害。钻孔施工导致孔周煤体应力重分布，造成煤体破裂，形成特殊的“环状”损伤破坏区域。预抽钻孔破裂区煤体是瓦斯向钻孔内运移的必经通道，运移过程是Darcy渗流和Fick扩散相结合的混合运动，但目前对于此类煤体的孔隙结构认识不清，孔周破裂煤体渗透率演化规律不准确。因此，本文以理论推导和室内试验及工程验证相结合的方法，分析钻孔孔周破裂煤体的孔隙结构特征，测定其渗透特征参数，建立预抽钻孔孔周煤体孔隙-渗透率演化模型，研究孔周破裂煤体渗透率演化规律，进而指导煤层瓦斯高效抽采，达到资源开发利用，煤矿安全生产的目的。主要得到了以下结论：

预抽钻孔孔周裂隙网络的发育状态是决定瓦斯汇流速率和煤体渗透率的关键因素。为了研究这类孔隙和裂隙网络对孔周瓦斯汇流特性的影响，根据应变软化特性Mohr-Coulomb准则，应用三段式应力-应变软化模型，推导了钻孔弹粘性区煤体变形破坏的应力解，分析了时间效应下塑性软化区强度，进一步给出钻孔弹性区、塑性区、破碎区煤岩体的应力及位移表达式。得到了孔周破碎区和裂隙区煤体结构的等效物理模型。

结合预抽钻孔孔周破裂煤体的结构特征，采用自主设计的负压抽采模拟渗透试验系统，对不同应力状态下孔周煤体的渗透参数进行了测定，基于KC方程的计算原理，得到孔隙率与渗透率关系式。分析得到孔周煤体表观渗透率关于负压的敏感性与级配系数n有着密切的关系。最后，结合上述试验煤体的渗透参数特征，掌握了孔周破裂煤体的渗透特性演化特征。同时，通过自主研发的全自动三轴渗流试验系统，研究有效应力对渗透率演化机制的影响，引入Ergun方程，通过对渗透参数进行推导计算，得到了仅与孔隙率相关的计算式，分析有效应力与孔周煤体孔隙结构的演化的规律。

在前面试验的基础上，从孔隙率基本定义角度，综合运用有效应力理论和模型渗透率方程，考虑瓦斯吸附解吸、煤体基质膨胀理论、气体压缩变形等内容，通过对钻孔周围煤体弹塑性力学表达式推导，构建了预抽钻孔孔周煤体孔隙-渗透率演化模型，通过现场工程试验得出，验证了预抽钻孔孔周煤体孔隙-渗透率数学模型具有可靠性，因此该模型可为实际工程中瓦斯抽采提供理论参考。

通过以上研究，从结构上揭示了预抽钻孔孔周煤体的孔隙结构特征，分析了钻孔孔周煤体的渗透特征，建立了预抽钻孔孔周煤体孔隙-渗透率计算模型，并根据大佛寺煤矿40103工作面预抽钻孔孔周煤体渗透参数计算并验证了模型的准确性，对于预抽钻孔瓦斯抽采效率提高提供了理论依据，具有重要的现实意义。

As the main technical means of gas prevention and control in high gas mines, borehole gas pre-pumping can effectively reduce the gas content of coal seams and fundamentally prevent coal and gas protrusion and other related disasters. Borehole construction results in a redistribution of stresses around the perimeter of the borehole, causing the coal body to rupture, forming a special 'ring' of damage and destruction. The coal body in the fracture zone of the pre-drilled borehole is a necessary channel for gas transport into the borehole, and the transport process is a mixture of Darcy seepage and Fick diffusion, but the pore structure of this type of coal body is not well understood, and the permeability evolution of the fractured coal body around the borehole is not accurate. Therefore, this paper combines theoretical derivation with indoor tests and engineering verification to analyse the pore structure characteristics of perforated coal bodies, determine their permeability parameters, establish a pore-permeability evolution model of perforated coal bodies in pre-smoking boreholes, and study the permeability evolution law of perforated coal bodies, so as to guide the efficient extraction of coal seam gas and achieve the purpose of resource exploitation and coal mine safety production. The following conclusions were mainly obtained:

(1) The development of peripore fracture networks in pre-sumping boreholes is a key factor in determining gas sink rates and coal permeability. In order to study the influence of such pores and fracture networks on the gas sink characteristics around the borehole, a three-stage stress-strain softening model is applied according to the Mohr-Coulomb criterion for strain softening characteristics, and the stress solution for deformation and damage of the coal body in the elastic-viscous zone of the borehole is derived, and the strength of the plastic softening zone under the time effect is analysed, and further expressions for the stress and displacement of the coal body in the elastic, plastic and fracture zones of the borehole are given . The equivalent physical model of the structure of the coal body in the fracture zone and fracture zone around the hole is obtained.

(2) Combined with the structural characteristics of the fractured coal body around the pre-pumping borehole, the permeability parameters of the coal body around the borehole under different stress states were measured using the self-designed negative pressure pumping simulation permeability test system, and the relationship between porosity and permeability was obtained based on the calculation principle of KC equation. The sensitivity of the apparent permeability of the perforated coal body with respect to negative pressure is closely related to the grading factor n. Finally, by combining the characteristics of the permeability parameters of the above-mentioned test coal bodies, the evolution characteristics of permeability properties of perforated fractured coal bodies are grasped. At the same time, the effect of effective stress on the evolution mechanism of permeability is investigated through the self-developed fully automatic triaxial percolation test system, and the Ergun equation is introduced to obtain the calculation equation related to the porosity only by deriving the permeability parameters and analysing the law of effective stress and the evolution of the pore structure of the perforated coal body.

(3) On the basis of the previous tests, from the perspective of the basic definition of porosity, the effective stress theory and the model permeability equation are integrated, taking into account gas adsorption and desorption, coal matrix expansion theory, gas compression and deformation, etc. Through the derivation of the elastic-plastic mechanical expressions for the coal body around the borehole, a pore-permeability evolution model for the coal body around the borehole of the pre-sumping borehole is constructed, which is derived through field engineering tests and verifies the reliability of the pore-permeability mathematical model for the coal body around the borehole of the pre-sumping borehole, so the model can provide theoretical reference for gas extraction in practical engineering.

Through Through the above research, the pore structure characteristics of the perimeter coal body of the pre-pumping borehole were revealed structurally, the permeability characteristics of the perimeter coal body were analysed, a pore-permeability calculation model for the perimeter coal body of the pre-pumping borehole was established, and the accuracy of the model was calculated and verified based on the permeability parameters of the perimeter coal body of the borehole in Dafosi coal mine, which provides a theoretical basis for the improvement of the gas extraction efficiency of the pre-pumping borehole and is of great practical significance.