【作者】 潘荣锟；

【导师】 袁亮； 程远平；

【作者基本信息】 中国矿业大学 ， 安全技术及工程， 2014， 博士

【摘要】 煤层卸压开采是通过应力释放使煤体产生大量的新生裂隙，改变煤体结构特征，促使煤层渗透性发生了根本性的改变，实现煤层增透以促瓦斯抽采。本文以煤层卸压开采为主线，以载荷煤体渗透率演化特性和煤体裂隙扩展机制为重点，以理论分析、实验研究、数值模拟和工程实践为主要手段，研究加卸荷过程中煤体裂隙演化和渗透率变化过程，获得渗透率演化规律和建立相应模型，并将结果应用于卸压开采下被保护层渗透率的分布特性和卸压瓦斯抽采的研究。本论文的主要研究结论如下：（1）制取标准原煤样，采用与卸压开采煤层受力特征相同的力学路径，进行了不同加卸荷下的渗透率实验，得到了不同层理方向上渗透率比达7.5：1，分析卸荷过程渗透率演化差异原因，提出在相同卸荷点应力下试样初始损伤程度越大，卸荷极限承载强度就越低，致使在卸荷过程中试样损伤变形的加剧和大量新裂隙的产生，最终渗透率剧增且大于加荷过程的渗透率。根据渗透实验结果获得了卸荷增透的实验现象和新认识。（2）将损伤力学、卸荷力学和渗流力学相结合，运用RFPA2D–Flow软件模拟了加卸荷作用下不同预置层理试件裂隙起裂、扩展、贯通机制和渗透特性，获得载荷条件下试件裂隙演化过程和渗透变化规律，渗透率的变化与裂隙演化具有一致性。并与渗透实验对比分析，指出卸荷点处试件内部出现的破坏点和损伤微裂隙越多，在卸荷后微裂隙扩展速度就越快，破坏点数量则更多，最终易产发生破断变形，渗透率剧增。（3）根据在载荷条件下试样渗透实验和裂隙演化模拟，得出加荷过程试样渗透率随着有效应力的增大而减小；而卸荷过程试样渗透率随着有效应力的减小而增大，但卸荷过程渗透率并非是加荷过程的简单逆过程，并建立了载荷煤体渗透率与有效应力的关系。对比了试样渗透率演化的整体过程及规律，获得了卸荷过程渗透率演化的三种典型路径的概念模型，提出了与载荷煤体变形特征相对应的弹性渗透率模型、塑性渗透率模型和卸荷增透模型。（4）根据铁法矿区大隆煤矿煤层赋存特点，利用FLAC3D软件对试验矿区被保护层采动变形和应力变化进行模拟研究，得出被保护层采动变形和应力变化规律。结合渗透率演化实验及模型，并利用Matlab中的Surf函数获得了下被保护层渗透率空间分布规律，把卸压采动影响区域的渗透率划分为原始渗透区、弹性渗透区、塑性渗透区和卸荷增透Ⅰ区、卸荷增透Ⅱ区。根据研究结果，选取底抽巷穿层钻孔对被保护层的卸压瓦斯进行抽采，并抽采钻孔的布置方式进行优化。更多还原

【Abstract】 Coal seam mining with the pressure-relief method is to release the stress loaded on thecoal body, resulting in the increase of new fractures, change of the structure and permeabilityof the coal body, and then realization of the gas drainage through permeability increasing. Inthis paper, the fracture evolution and permeability variation of coal during the loading andunloading process were studied by the method of theoretical analysis, laboratory experiments,numerical simulation and engineering research comprehensively, and the fracture evolutionlaw and the corresponding model were obtained and applied to study the permeabilitydistribution and gas drainage in underlying protected coal seam during the pressure-reliefmining. The main conclusions of this paper are as follows:(1) Permeability experiments of the standard cylinders nature coal samples were carriedout under the different unloading stress path similarly as the loaded characteristic ofpressure-relief coal mining. The permeability ratio which reached7.5:1in different beddingdirections were obtained and the cause of the difference of permeability evolution during theunloading process was analysed. The initial damage become bigger and the ultimate bearingstrength reduced at the same unloading point of stress, when the sample has weakcompressive strength induce the damage aggravate increase and the massive generation ofnew fractures in the process of unloading, which induce the permeability increase to greaterthan that in loading process. The experimental phenomena and new knowledge of unloadingincrease permeability mechanism were obtained.(2) Based on the theory of damage mechanics, unloading mechanics and seepagemechanics, the model was built by RFPA2D-Flow to study the characteristics of fractureinitiation, expansion, cut-through and permeability in different pre-fracture direction coalsamples under the action of loaded-unloaded. The fracture evolution law and permeabilityvariation of coal during different unloading are obtained, the fracture evolution andpermeability change were coincident each other. We compared and analyzed the experimentalresults, and discovered that if the sample had many damage micro structure in unloading point,the extension speed of along the bedding plane faster, the number of break-point larger, alarge number of fractures easier produced and breakage deformation, accompanied by thepermeability increasing sharply.(3) According to the permeability experiment and fracture evolution simulation of coalsamples under loading condition, we could conclude that the permeability decrease with theincrease of effective stress during the process of loading; and the permeability increase withthe decrease of effective stress during the process of unloading, but the unloading process is not a simple inverse process of loading. Furthermore, the relationship of the permeability andeffective stress under unloading condition was established. Compared the whole permeabilityevolution process, conceptual models under three different paths of permeability evolution ofcoal under different conditions of stress were proposed, and the elastic permeability model,plastic permeability model and unloading increase permeability model were built, whichcorrespond to the deformation of loaded coal.(4) According to the characteristics of coal seam in Dalong coal mine, the rule of miningdeformation and the variation of stresses on protected coal seam were obtained by the modelconstructed by FLAC3Dsoftware based on testing mining area. Combined with permeabilityevolution experiment and model, and used the Surf function from Matlab, the permeabilityspatial distribution of underlying protected coal seam was obtained. The permeability ofpressure-relief mining influence area could be divided into original permeability area, elasticpermeability area, plastic permeability area, unloading increase permeability Ⅰ area andunloading increase permeability Ⅱ area. On the basis of the research results, we take thebottom lane through coal seam drilling for pressure-relief gas drainage, and optimize thelayout parameters of gas drainage drilling boreholes.更多还原