含瓦斯煤变形破坏特征及渗透行为研究

发布时间：2018-11-20 05:08

【摘要】：瓦斯既是煤与瓦斯突出和瓦斯爆炸等煤矿灾害的主要诱因，同时又是一种不可再生的清洁能源，实现煤与瓦斯共采，不仅能提高煤矿安全生产水平，还将改善我国的能源结构，对保障我国的能源安全有重要意义。而我国煤层普遍具有高瓦斯、低渗透、强吸附的特点，其中煤层渗透率比美国低2～3个数量级，瓦斯抽采难度极大，对煤层进行人工增透成为实现煤与瓦斯共采的有效途径。因此，充分认识含瓦斯煤岩体变形破坏及其渗透性演化规律，定量描述煤层增透效果，对于实现煤与瓦斯共采具有极其重要的意义。本文针对含瓦斯煤变形破坏特征及其渗透行为，开展了实验室试验、理论分析和数值模拟研究。主要研究内容如下：（1）利用MTS815和高压瓦斯渗透试验系统分别对型煤和原煤试样进行了单轴、三轴压缩试验以及瓦斯渗透试验，发现原煤的单轴和三轴抗压强度分别为型煤的10.3倍和3.7倍，单轴和三轴弹性模量分别为型煤的75.1倍和12.7倍，型煤的塑性破坏形式和原煤的脆性破坏形式截然不同。型煤的初始渗透率是原煤的20倍，而破坏后型煤渗透率为原煤的90%。试验研究结果表明目前以型煤试验结果指导煤矿瓦斯抽采设计与施工极易造成重大安全隐患。（2）利用三轴压缩试验研究了不同瓦斯压力下原煤的力学性质，结果表明：随着瓦斯压力的增加，原煤刚度和强度逐渐降低，峰值破坏剧烈程度逐渐减弱，煤样逐渐由脆性劈裂破坏向延性剪切破坏转变。针对不同瓦斯压力下煤岩体损伤破坏特征，，定义了煤岩体双标量损伤模型，同时考虑孔隙瓦斯压力和吸附膨胀应力作用，建立了新的含瓦斯煤弹性损伤本构模型。（3）利用三轴瓦斯渗透试验研究了原煤损伤破坏过程中的渗透特征，结果表明：随着瓦斯压力的增加，原煤渗透率逐渐减小；渗透率与体积应变呈良好的线性关系。基于平板裂隙流动方程建立了煤体渗透率与裂隙体积应变的关系，考虑了瓦斯压力和吸附瓦斯对裂隙体积应变的影响，并首次引入了表征裂隙面粗糙度和裂隙迂曲度对渗透率影响的比例系数，建立了新的渗透率演化模型。（4）基于所建立的损伤本构和渗透率演化模型，自行开发了相应的三维弹性损伤和渗透性耦合分析有限元程序，实现了对采动煤岩体的损伤及渗透率演化的定量描述。并以单一煤层开采为例，对不同瓦斯压力下采动煤岩体损伤和渗透率演化特征进行数值模拟。计算结果表明：随工作面从30m推进到150m，工作面前方煤体损伤范围也由5m增加到30m左右，损伤区内渗透率最大可增加2-3个量级，且相对于煤层瓦斯压力1MPa的计算结果，煤层瓦斯压力6MPa情况下工作面前方煤体损伤度最大增加19%，渗透率比率最大可增加85%。计算结果与工程实际基本吻合，可为煤矿瓦斯抽采设计提供科学指导。
[Abstract]:Gas is not only the main cause of coal and gas outburst and gas explosion, but also a kind of non-renewable clean energy. To realize coal and gas mining together can not only improve the level of coal mine safety production, but also improve the energy structure of our country. To safeguard our country's energy security has the important significance. However, coal seams in our country generally have the characteristics of high gas, low permeability and strong adsorption. The permeability of coal seam is 2 ~ 3 orders of magnitude lower than that of the United States, and it is very difficult to extract gas from coal seam. Artificial antipenetration of coal seam is an effective way to realize coal and gas mining. Therefore, it is of great significance to fully understand the law of deformation, failure and permeability evolution of gas-bearing coal and rock mass, and to describe quantitatively the antireflection effect of coal seam. In this paper, laboratory tests, theoretical analysis and numerical simulation are carried out on the characteristics of deformation and failure and permeability behavior of gas-bearing coal. The main research contents are as follows: (1) uniaxial, triaxial compression and gas permeation tests were carried out on briquette and raw coal samples using MTS815 and high pressure gas permeation test system, respectively. It is found that the uniaxial and triaxial compressive strength of raw coal is 10.3 and 3.7 times of that of briquette, and the uniaxial and triaxial modulus of elasticity is 75.1 and 12.7 times of that of briquette, respectively. The plastic failure form of briquette is different from that of brittleness failure of raw coal. The initial permeability of briquette is 20 times that of raw coal, but the permeability of broken briquette is 90% of that of raw coal. The experimental results show that the design and construction of gas drainage in coal mines are easy to be caused by the results of briquette tests. (2) the mechanical properties of raw coal under different gas pressure are studied by triaxial compression test. The results show that with the increase of gas pressure, the stiffness and strength of raw coal decrease gradually, and the intensity of peak failure decreases gradually. The coal samples gradually changed from brittle splitting failure to ductile shear failure. According to the damage and failure characteristics of coal and rock mass under different gas pressure, the dual scalar damage model of coal and rock mass is defined, and a new elastic damage constitutive model of gas-bearing coal is established considering the effect of pore gas pressure and adsorption expansion stress. (3) the permeability of raw coal during damage and failure is studied by triaxial gas permeation test. The results show that the permeability of raw coal decreases with the increase of gas pressure, and there is a good linear relationship between permeability and volume strain. Based on the plate fracture flow equation, the relationship between coal permeability and fracture volume strain is established, and the influence of gas pressure and gas adsorption on fracture volume strain is considered. A new permeability evolution model is established by introducing the proportional coefficient which represents the influence of fracture surface roughness and fracture roundness on permeability for the first time. (4) based on the damage constitutive model and permeability evolution model, a three dimensional finite element program for coupling analysis of elastic damage and permeability is developed, and the quantitative description of damage and permeability evolution of mining coal and rock mass is realized. Taking single coal seam mining as an example, the characteristics of damage and permeability evolution of mining coal and rock mass under different gas pressure are simulated numerically. The calculation results show that with the coal face advancing from 30 m to 150 m, the damage range of coal body in front of the face also increases from 5 m to 30 m, the maximum permeability in the damaged area can be increased by 2-3 orders of magnitude, and compared with the calculated result of 1MPa of coal seam gas pressure. Under the condition of gas pressure 6MPa in coal seam, the maximum damage degree of coal body in front of working face is increased by 19 percent, and the maximum permeability ratio can be increased by 85 percent. The calculated results are in good agreement with the engineering practice and can provide scientific guidance for the design of coal mine gas drainage.
【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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