水对煤样力学性质与破坏形式的影响

发布时间：2018-11-06 20:28

【摘要】：中国煤炭资源开采70%左右的产能集中在中西部干旱半干旱区域,而水资源是制约该区域煤炭资源大规模开采的关键因素之一。当前,保水开采和采空区地下水库储水已成为缓解该区域水资源日趋紧张的关键技术。通过研究水对煤样裂隙发育和破坏形式的影响规律,对采空区地下水库储水煤柱坝体尺寸设计、保水开采导水裂隙带高度计算等具有重要意义。为探究水对煤样力学性质的影响,利用自制无损浸水实验装置控制煤样(西沙河煤矿,长方体试样;新桥煤矿,标准圆柱体试样)含水率并结合煤样吸水变化规律,确定了西沙河煤样含水率选择分别为0、2.37%、3.78%和5.29%,新桥煤矿标准圆柱型煤样含水率选择为0、4.98%、9.92%和12.33%。通过单轴压缩实验研究发现:煤样含水率随着浸水时间呈现快速增长期、缓慢增长期和稳定期。煤样的峰值应力、强度软化系数、弹性模量、应变软化模量、后峰值模量均随着含水率增加而呈现不同程度的减小,而峰值应变随着含水率的增加而增加,表明了水对煤样力学性质具有明显弱化作用。通过声发射(AE)、X射线衍射(XRD)、电镜扫描(SEM)和压汞实验(MIP)等方法研究了水对煤岩裂隙扩展规律和煤样破坏形式的内在机理。研究表明:具有很高亲水性的伊利石是影响煤样吸水性的主要粘土矿物;结合刚度-应力和声发射累计计数-应力关系曲线,不同含水率煤样的裂隙发育阶段可利用累计计数-应力关系划分5个阶段,即压密,弹性,裂隙稳定发育,不稳定发育和峰后阶段;煤样声发射活动集中出现在D点(裂隙损伤阈值)之后。同时,研究发现煤样的裂隙压密应力阈值,初始发育阈值和损伤阈值随着含水率增大而减小,但其值占峰值强度的比值不变,分别为14.80%,29.93%和72.71%;随着含水率增大,煤样声发射活性减弱,声发射累计振铃计数减小,同时弱化了煤样内部颗粒连接,增加了煤样滑动破坏的可能性。通过对比分析声发射的RA和AF值发现:所有煤样裂隙呈现张剪复合型裂隙,无单一拉伸或者剪切裂隙出现。但随着含水率增大,煤样的总裂隙和张裂隙数目均减少,但剪切裂隙比例却明显增大。水作用下煤样RA-AF值核心区域向低AF高RA区域靠拢,煤样的宏观裂隙形态主要表现为裂隙充分发育,剪切裂隙集聚甚至贯穿,最后煤样破坏表现为以剪切破坏为主的可能性大大增加。
[Abstract]:About 70 percent of China's coal production capacity is concentrated in arid and semi-arid areas in the central and western regions, and water resources are one of the key factors restricting large-scale exploitation of coal resources in this region. At present, water conservation and water storage in underground reservoirs in goaf have become the key technology to alleviate the increasing shortage of water resources in this area. By studying the influence of water on the development and failure form of coal fracture, it is of great significance to design the size of coal pillar dam of underground reservoir in goaf and to calculate the height of water-conducting fissure zone in water-retaining mining. In order to investigate the influence of water on the mechanical properties of coal samples, coal samples were controlled by self-made non-destructive soaking device (Xishahe coal mine, cuboid sample); In Xinqiao Coal Mine, standard cylinder sample) moisture content, combined with water absorption law of coal sample, determined that the selection of water cut in Xishahe coal sample was 0.2.373.78% and 5.29%, respectively. The water content of standard cylindrical briquette in Xinqiao Coal Mine was chosen to be 0 ~ 4.98% and 12.33% respectively. Through uniaxial compression experiments, it is found that the moisture content of coal samples increases rapidly, slowly and steadily with the soaking time. The peak stress, strength softening coefficient, elastic modulus, strain softening modulus and post-peak modulus of coal samples all decreased with the increase of moisture content, but the peak strain increased with the increase of water content. It is shown that water has an obvious weakening effect on the mechanical properties of coal samples. By means of acoustic emission (AE), X ray diffraction (XRD), electron microscope scanning (SEM) and mercury injection experiment (MIP) the law of water crack propagation and the internal mechanism of coal sample failure were studied. The results show that Illite with high hydrophilicity is the main clay mineral affecting the water absorption of coal samples. According to the curve of the relationship between stiffness and stress and acoustical emission accumulative counting and stress, the fracture development stage of coal samples with different moisture content can be divided into five stages by accumulative counting and stress relationship, that is, compaction, elasticity and stable development of fractures. Unstable development and postpeak stage; The acoustic emission activity of coal samples occurs after D point (crack damage threshold). At the same time, it is found that the compressive stress threshold, initial development threshold and damage threshold of coal samples decrease with the increase of water content, but the ratio of the values to the peak strength of coal samples is 14.800.93% and 72.71%, respectively. With the increase of water content, the acoustic emission activity of coal sample decreases, and the accumulative ring number of acoustic emission decreases, at the same time, the internal particle connection of coal sample is weakened, and the possibility of slippage failure of coal sample is increased. By comparing the RA and AF values of acoustic emission, it is found that all the fractures in coal samples show tension-shear composite fractures, and no single tensile or shear fractures appear. However, with the increase of water content, the number of total fractures and tensile fractures of coal samples decreases, but the ratio of shear fractures increases obviously. Under the action of water, the core area of RA-AF value of coal sample is closer to the area with low AF and high RA. The macroscopic fracture morphology of coal sample mainly shows that the fracture is fully developed, and the shear fracture accumulates and even runs through. Finally, the possibility of shear failure is greatly increased.
【学位授予单位】：中国矿业大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TD821

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