<p>随着煤矿开采深度不断增加，深部煤层采场应力增大，且空间分布不均匀，煤体裂隙呈现非线性发展，煤层渗透性发生变化，导致采掘工作面瓦斯异常涌出，瓦斯浓度超限频发，严重影响了瓦斯的高效抽采，矿井瓦斯灾害防治成为煤与瓦斯安全共采的关键问题之一。煤体的裂隙扩展是由应力引起的微观结构变化向细观结构发展的过程，是一个多尺度孔裂隙演化过程，瓦斯在不同尺度孔裂隙中的渗流模式具有本质区别。因此明确煤体微细观孔裂隙演化及瓦斯渗流规律研究，对科学合理防治瓦斯灾害具有一定指导意义。</p> <p>通过开展压汞实验、核磁共振实验和X-ray CT扫描实验，获得煤体孔隙特征参数，得出实验煤体整体孔隙结构发育，其中微小孔较为发育，而微小孔与中大孔间的连通性较差；运用分形理论，通过分孔径段对煤体孔隙结构进行量化表征，分析煤体中孔隙结构复杂性，表明煤体孔隙分形维数均在2.7以上，孔隙结构总体复杂程度高，非均质性强。结合压汞实验、核磁共振实验和X-ray CT扫描实验，建立了煤体孔隙全孔径分布曲线，表明煤体中孔隙微小孔和大孔发育，有利于瓦斯的渗流。</p> <p>利用光学散斑技术和声发射技术分析煤体试件加载过程中表面裂隙演化和内部损伤演化特征，得出煤体试件表面位移和变形随加载速率的增大而减小，其破坏模式由拉张、剪切破坏向拉张剪切复合破坏转变；声发射计数、能量随加载速率的增大而增大，声发射事件空间分布能较好反映出煤体内部裂隙演化特征。</p> <p>通过X-ray CT对破裂前后的煤体试件进行扫描，借助AVIZO软件定量表征煤体内部的孔裂隙结构特征，重构煤体破裂前后的三维可视化模型，提取等效孔隙网络模型，统计等效孔隙半径、孔喉半径，配位数、面孔隙度等参数，分析煤体破坏前后孔裂隙结构的变化特征。利用AVIZO软件中的绝对渗透率模型进行瓦斯渗流模拟，得出煤体中孔裂隙渗流的流速越大，渗流压力小，则煤体的孔裂隙越发育，渗透性也就越好，反之渗流的流速越小，渗流的压力大，则煤体的孔裂隙不发育，渗透性差。煤体破裂前后的孔裂隙渗流相比，煤体破裂后孔裂隙渗流流速更大，渗透性更好，煤体中的孔裂隙更发育，有利于瓦斯的渗流。研究结果为探讨煤层瓦斯渗流规律、防治煤与瓦斯开采事故方案的制定措施提供了一定理论依据。</p>

<p>With the continuous increase of coal mining depth, the stope stress of deep coal seam increases, and the spatial distribution is not uniform. The fracture of coal body presents a nonlinear development, and the permeability of coal seam changes, which leads to abnormal gas emission in the mining face and frequent gas concentration overrun, seriously affecting the efficient extraction of gas. The prevention and control of mine gas disaster accidents has become one of the key issues of coal and gas safety co-mining. The fracture propagation of coal body is a process from the microscopic structure change caused by stress to the microscopic structure development. It is a multi-scale pore fracture evolution process. The seepage mode of gas in different scale pore fractures is essentially different. Therefore, it is of certain guiding significance for scientific and reasonable prevention and control of gas disasters to clarify the evolution of micro-pore cracks in coal and the law of gas seepage.</p> <p>Through the mercury intrusion experiment, nuclear magnetic resonance experiment and X-ray CT scanning experiment, the pore characteristic parameters of coal body were obtained. It is concluded that the overall pore structure of the experimental coal body is developed, in which the micro pores are more developed, and the connectivity between the micro pores and the large pores is poor. Using fractal theory, the pore structure of coal is quantitatively characterized by the pore size section, and the complexity of pore structure in coal is analyzed. It is shown that the fractal dimension of coal pores is more than 2.7, and the overall complexity of pore structure is high and the heterogeneity is strong. Combined with mercury injection experiment, nuclear magnetic resonance experiment and X-ray CT scanning experiment, the full pore size distribution curve of coal pores was established, indicating that the development of micropores and macropores in coal pores is conducive to gas seepage.</p> <p>The evolution characteristics of surface cracks and internal damage during the loading process of coal samples were analyzed by optical speckle technology and acoustic emission technology. It is concluded that the surface displacement and deformation of coal samples decrease with the increase of loading rate, and the failure mode changes from tensile and shear failure to tensile and shear composite failure. The acoustic emission count and energy increase with the increase of loading rate. The spatial distribution of acoustic emission events can better reflect the evolution characteristics of cracks in coal body.</p> <p>X-ray CT was used to scan the coal specimen before and after fracture. The pore-fracture structure characteristics inside the coal were quantitatively characterized by AVIZO software. The three-dimensional visualization model before and after the fracture of the coal was reconstructed, and the equivalent pore network model was extracted. The equivalent pore radius, pore throat radius, coordination number, surface porosity and other parameters were counted, and the change characteristics of pore-fracture structure before and after the fracture of the coal were analyzed. The absolute permeability model in AVIZO software is used to simulate gas seepage. It is concluded that the greater the flow velocity of the seepage of the pore and fissure in the coal body, the smaller the seepage pressure, the more developed the pore and fissure of the coal body, and the better the permeability. On the contrary, the smaller the flow velocity of the seepage, the greater the seepage pressure, the pore and fissure of the coal body is not developed and the permeability is poor. Compared with the seepage of pores and fissures before and after coal fracture, the seepage velocity of pores and fissures after coal fracture is larger, the permeability is better, and the pores and fissures in coal are more developed, which is conducive to the seepage of gas. The research results provide a theoretical basis for exploring the law of coal seam gas seepage and formulating measures for preventing coal and gas mining accidents.</p>

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