保护层开采过程中卸载煤体损伤及渗透性演化特征研究

发布时间：2018-08-30 07:33

【摘要】：保护层开采及卸压瓦斯抽采是目前首选的区域性瓦斯治理措施。虽然近年来对保护层开采理论的研究取得了很大突破，然而理论研究还存在不足，目前的研究成果多偏重于宏观的现象与规律。本文运用岩石力学、卸荷岩体力学、损伤力学、渗流力学等理论，采用理论研究、实验室实验、数值模拟与工程实践相结合的方法，深入研究了保护层开采过程中被保护层卸载煤体的细观损伤与渗透性演化特征及被保护层渗透率的分布特征，最后，将研究成果应用于淮南矿区潘一矿被保护层瓦斯抽采钻孔的优化。本论文的主要研究结论如下：（1）依据被保护层煤体先经历加载而后三向应力同时被卸载的受力过程，选择固定轴向位移卸围压、固定差应力卸围压作为实验室研究的力学路径，采用离散性小且力学性质与原煤样相近的型煤试样，应用有效应力原理和等效力学路径的方法通过耦合CT实时检测实验与渗透性实验的结果分析了卸载过程中煤体损伤对渗透性的影响，同一卸载力学路径下两不同实验获得的应力-应变曲线特征的一致性验证了把CT实时检测实验与渗透性实验的结果耦合起来分析试样损伤对渗透性的影响的合理性。（2）CT检测实验结果表明，卸载初期损伤发育缓慢，随着损伤的累积，在本论文的实验条件下，从围压卸载至5MPa开始，损伤增长速度加快；试样最终破坏时内部裂纹呈锥形，且试样首先从低密度端发生破坏，进而向高密度端发展；同一试样，密度越小的层位，损伤发展越快，同时，固定差应力卸围压应力路径对试样造成的损伤更大。（3）卸载过程中渗透性实验结果表明，随着初始围压的增大，固定轴向位移卸围压与固定差应力两种卸载力学路径下，差应力减小速率增大处的围压值升高；卸载力学路径下，卸载点前加载阶段，渗透率与轴向应变的关系为k A B11e（A1、B1为拟合系数）；卸载点后卸载阶段，渗透率与轴向应变的关系为k AB2e2（A2、B2为拟合系数）。（4）推导出了用根据CT值表示的损伤变量，获得了卸载过程中损伤变量的变化，结合等效力学路径下渗透性实验的结果，获得了卸载煤体损伤对渗透性的影响，即卸载初期损伤与渗透率增加均较小，随着继续卸载，，在本论文的实验条件下，两种卸载路径下有效围压均卸载至5MPa左右后，损伤和渗透率的增加速度均加快。（5）依据被保护层的膨胀变形情况与实验室获得的渗透率与轴向应变的关系，利用Matlab软件的Surf函数得出了被保护层渗透率的分布特征，即被保护层可分为原始渗透性区、渗透性减小区、渗透性增大区1、渗透性增大区2，基于此，从被保护层切眼和收作线附近区域至工作面内部，瓦斯抽采钻孔的布孔间距依次设计为5m×5m，10m×10m，40m×40m，被保护层工作面掘进、回采期间的瓦斯参数验证了瓦斯抽采钻孔布孔方式优化的合理性。
[Abstract]:Protection layer mining and pressure relief gas drainage is the first choice of regional gas control measures. Although great breakthrough has been made in the research of the mining theory of protective layer in recent years, there are still some deficiencies in the theoretical research, and the current research results are mostly focused on the macroscopic phenomena and laws. In this paper, the theories of rock mechanics, unloading rock mass mechanics, damage mechanics, seepage mechanics and so on are used, and the methods of combining theoretical research, laboratory experiments, numerical simulation and engineering practice are adopted. The evolution characteristics of meso-damage and permeability and the distribution characteristics of permeability of protected layer are studied in detail. The research results are applied to the optimization of gas drainage boreholes in Panyi Mine, Huainan Mining area. The main conclusions of this paper are as follows: (1) according to the loading and unloading process of the coal body in the protected layer, the fixed axial displacement unloading pressure is selected. Fixed differential stress unloading confining pressure is used as the mechanical path of laboratory research. Briquette samples with small dispersion and similar mechanical properties to raw coal samples are used. The effect of coal damage on permeability during unloading is analyzed by using effective stress principle and equivalent mechanical path method through coupled CT real-time detection experiment and permeability experiment. The consistency of stress-strain curves obtained from two different experiments under the same unloading mechanics path verifies the rationality of coupling the results of CT real-time detection experiment and permeability experiment to analyze the effect of specimen damage on permeability. (2) the results of CT test showed that, At the initial stage of unloading, the damage develops slowly, and with the accumulation of damage, the damage growth rate is accelerated from confining pressure to 5MPa under the experimental conditions in this paper, and the internal crack is conical when the specimen is finally destroyed. At the same time, the smaller the density of the sample, the faster the damage development, and at the same time, The damage caused by the confining stress path of fixed differential stress unloading is greater. (3) the experimental results of permeability during unloading show that with the increase of initial confining pressure, Under the two unloading mechanical paths of fixed axial displacement unloading pressure and fixed differential stress, the confining pressure increases at the increase of the decreasing rate of the differential stress, and under the unloading mechanics path, the loading stage of the unloading point before loading, The relationship between permeability and axial strain is k A B 11e (A 1B 1 is the fitting coefficient), the relation between permeability and axial strain is k AB2e2 (A 2 B 2 is fitting coefficient). (4) after unloading point, and the damage variable expressed according to CT value is derived. The change of damage variables during unloading is obtained. Combined with the experimental results of permeability under equivalent mechanical path, the influence of unloading coal damage on permeability is obtained, that is, the damage and permeability increase in the initial stage of unloading are small, and with the further unloading, Under the experimental conditions in this thesis, the effective confining pressures under two unloading paths are unloaded to 5MPa or so. Both damage and permeability increase faster. (5) according to the relationship between the expansion deformation of the protected layer and the permeability obtained in the laboratory and axial strain, the distribution characteristics of the permeability of the protected layer are obtained by using the Surf function of Matlab software. That is, the protected layer can be divided into the original permeability area, the permeability decreasing area, the permeability increasing area 1, the permeability increasing area 2. Based on this, from the area near the protected layer cutting and closing line to the working face, The spacing of the gas drainage boreholes is designed as 5 m 脳 5 m 10 m 40 m 脳 40 m, and the gas parameters during the mining process verify the rationality of the optimization of the distribution mode of the gas drainage boreholes.
【学位授予单位】：中国矿业大学
【学位级别】：博士
【学位授予年份】：2013
【分类号】：TD712

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