煤层群上行开采层间裂隙演化及卸压空间效应

发布时间：2018-05-14 20:41

  本文选题：煤层群 + 采空区　； 参考：《中国矿业大学(北京)》2017年博士论文

【摘要】：煤炭是现今社会最重要的能源之一,长期以来,瓦斯作为一种灾害源,一直威胁着我国煤矿安全生产,矿井瓦斯爆炸事故和煤与瓦斯突出事故时有发生,随着开采深度的增加,这类问题更加严峻。根据大量理论与现场应用实践证明保护层开采及利用保护层开采的卸压作用抽采被保护层卸压瓦斯是最有效的区域性瓦斯治理措施和瓦斯抽采措施。因此,掌握保护层卸压开采机理,卸压范围及其影响因素对精确布置瓦斯抽采钻孔,提高瓦斯抽采浓度、消除瓦斯安全隐患均具有十分重要的意义。本文围绕近距离煤层群上行开采层间裂隙演化规律及卸压空间效应展开研究,综合运用理论分析、数值模拟、相似模拟实验、工程实践等手段对这一问题进行了深入研究。在总结煤岩体中孔隙和裂隙的基础上,运用弹塑性力学、断裂力学等方法从细观和宏观角度分析了含裂隙煤岩体破坏特征和采动裂隙发育拓展机理,得到了覆岩离层裂隙和垂直裂隙发育机理;通过理论分析、相似模拟对长壁工作面采空区应力恢复规律进行了分析,指出了采空区应力分布规律的复杂性及其主要影响因素,推导了采空区应力恢复距离公式;基于采空区应力分布规律,通过卸压系数卸压角得到了不同开采条件下煤层群开采覆岩的应力场和位移场分布规律;通过UDEC数值模拟和相似模拟实验得到了煤层群开采裂隙分布规律,得到了煤层群双重卸压开采与单一煤层开采不同的覆岩裂隙分布和演化规律。主要成果如下:1.采动煤岩体破坏特征及细观裂隙演化机理(1)在成煤过程中及成煤后的地质构造运动使其内部产生了大量的孔隙和裂隙,按照煤体内孔隙直径大小可将其分为微孔、小孔、中孔、大孔、可见孔及裂隙五个级别,按煤岩体中裂隙大小及形态可分为微裂隙、小裂隙、中裂隙和大裂隙四类。(2)根据摩尔-库伦强度准则分析了含单一贯穿裂隙圆柱体的强度及其破坏方式,当β＜φw岩体的抗压强度等于岩块的抗压强度,岩体只能沿岩块发生剪切破坏;当β＞φw,ko＜kw,且σco＞σcw时,裂隙岩体的破坏方式随着围压的不同而不同,随着围压的增大,裂隙岩体由沿裂隙面发生滑移破坏转变为沿岩块发生剪切破坏;当β＞φw,ko＞kw,且σco＞σcw时,裂隙岩体将始终沿裂隙面发生破坏,岩体的强度由裂隙面所决定;当β＞φw,ko＞kw,但σco＜σcw时,若围压σ3＜σ3cr时,岩体裂隙面的抗压强度大于岩石的抗压强度,当轴压增大到一定程度时,裂隙岩体将发生剪切破坏,若围压σ3＞σ3cr时,岩体裂隙面的抗压强度小于岩石的抗压强度,当轴压增大到一定程度时,裂隙岩体将沿裂隙面发生滑移破坏,即在围压增加过程中,裂隙岩体破坏方式由岩块剪切破坏到沿裂隙面发生滑移破坏;当β＞φw,且ko＜kw,但σco＜σcw时,裂隙岩体将会发生剪切破坏,岩体的强度由岩块强度所决定。(3)在增压阶段,煤岩体内原生裂纹经历了剪切滑移-自相似扩展-弯折扩展-剪切扩展的发育过程;在卸压阶段,得到了轴压卸荷过程中裂隙发生反向滑移的应力条件及裂隙尖端的应力强度因子,最大主应力卸荷岩体卸荷过程中,轴压卸荷到围压的过程中,裂隙反向滑移变形必然发生,而张开变形具有应力条件;轴压卸荷到零的过程,裂隙的张开和裂隙扩展都需要一定的应力条件。2.近距离煤层群层间结构及宏观裂隙演化规律(1)基于关键层理论将近距离煤层保护层开采层间结构类型分为:层间无关键层结构,层间含单一亚关键层,层间含两个亚关键层,层间含多个亚关键层。(2)分析了顶板破断形成竖向破断裂隙应满足破断变形强度条件及变形协调条件,得到竖向破断裂隙的张开角度与岩层内部下沉曲线方程的二阶导数有关。基于岩梁的最大应变理论推导出了将岩梁视为简支梁时断裂所满足的跨度条件。(3)层间含多层亚关键层时,亚关键层的位置,层数会影响覆岩裂隙的动态发育和分布规律,亚关键层不会影响裂隙向高处发展,岩性和厚度相同的两亚关键层对其层间裂隙范围增大有抑制作用。3.煤层群上行开采机理及单一煤层开采围岩裂隙演化规律(1)通过比值判别法、三带判别法验证了下部8#煤层作为保护层开采的可行性,通过弹塑性力学推导出了考虑采空区竖向尺度的采场顶板最大损伤高度,进一步验证了上行开采可行性。(2)研究了单一煤层开采围岩裂隙演化规律,工作面煤壁前方应力集中系数随着工作面推进先增大后趋于稳定;在开挖之前,煤岩体垂直主应力大于水平主应力,当煤体开挖后,主应力大小和方向随之变化;工作面煤壁附近顶板主应力以水平应力为主,垂直应力几乎为0,液压支架对顶板的垂直应力分布影响不大;底板的主应力分布分为两个区域,受支架底座影响,在底板1m范围内,主应力以垂直应力为主,水平应力较小,而随着底板深度的增加,主应力方向开始由以垂直应力为主转为以水平应力为主,最后逐渐恢复为垂直应力为主。工作面前方,主应力变化趋势近似“弧形”,从工作面前方煤体中部向顶底板弧度越来越大,最大主应力也由垂直主应力渐渐变为水平主应力;采空区后部垂直主应力较采空区前部要大,逐渐趋于恢复原岩应力状态;采空区围岩应力分布类似“拱形”,拱高随工作面推进先逐渐增大后稍有减小,最终稳定在一定高度。(3)研究了采空区破碎岩体弹性模量对围岩应力场、位移场及裂隙场的影响规律,不同采空区应力行为和不同工作面推进距离展示出了相同的变形特征,顶底板经历了压缩变形、卸压膨胀变形、变形恢复、压缩变形、无变形过程,但不同的采空区应力行为条件下在大小和范围方面有一定的不同,采空区跨落破碎岩体弹性模量越小,其采空区应力恢复距离越大,工作面前方超前支承压力集中系数、煤体破坏范围、顶板垂直位移量及采空区顶板相同位置处围岩膨胀—压缩变形量均越大,越有利于煤岩体释放弹性潜能,使瓦斯赋存状态被激活越有利于覆岩瓦斯的解吸和流动,煤岩体透气性增大,从而有利于瓦斯抽采钻孔的布置和瓦斯抽采。4.采空区应力分布规律及煤层群空间卸压规律(1)研究了采空区应力分布规律。运用采场上覆岩体载荷守恒计算模型、侧向扩展支承载荷模型及基于地表下沉量的采空区应力恢复距离拟合公式,以长平煤矿8#煤层84306工作面为例,当采高为3m时,埋深为530m时,采空区应力恢复距离分别为103,169,140m。采空区应力恢复距离随采高、垮落岩体破碎系数、煤层埋深呈正相关,与采空区顶板岩体单轴抗压强度呈负相关,且与煤层埋深呈非线性关系;采高增大主要影响垮落破碎岩体碎胀系数,其对采空区应力恢复距离的影响较顶板岩性小。(2)得到了下煤层开采后覆岩空间应力及其位移分布规律,根据下煤层保护层顶板垂直应力和垂直位移分布情况,将顶板沿工作面推进方向分为五个区域,自工作面煤壁前方到采空区依次为:原岩应力区、压缩区、膨胀区、应力恢复区、重新压实区,分析了各区域内瓦斯通道的形成和发育特点。(3)下煤层顶板不同位置不同高度的应力分布均不同,距离下煤层越远,垂直应力较原岩应力减小量越小,其三维应力(SXX,SYY,SZZ)两两之间差值越来越小,较大的三维应力梯度和应力不对称性会更容易造成煤岩体内裂隙的产生、扩展及煤岩体破坏,距离保护层工作面越近,煤岩体产生的裂隙越多,且更容易发生破坏。(4)得到了下煤层推进过程中,借助卸压系数和卸压角衡量的上煤层空间卸压效果规律。随着保护层工作面的推进,被保护层的卸压程度和卸压范围逐渐增大,伴随着直接顶和基本顶的垮落,覆岩重力向煤壁方向和切眼转移,使得产生应力集中。随着采空区顶板不断下沉,采空区垮落破碎岩体的压实,对顶板的支撑作用逐渐增大,从而使得在采空区中偏后区域的保护层卸压程度有一定的减小,以采空区中轴线为中线,前后并不对称,保护层最大卸压处位于偏向工作面的方向。距离煤柱不同位置,沿煤层推进方向卸压角不同,切眼侧和煤壁侧卸压角随着靠近煤柱均先增大后减小;距离工作面煤壁不同位置,采空区沿煤层倾向卸压角不同,煤柱侧卸压角随着远离工作面先增大后减小。5.通过实验室相似模拟实验得到以下结论:(1)上煤层开采直接顶初次垮落步距和老顶初次断裂步距均小于下煤层开采,下煤层推进40m时,直接顶大面积垮落,工作面推进到50m时,老顶断裂,形成初次来压,上煤层直接顶初次垮落和老顶初次来压步距分别为30m和45m。(2)上煤层工作面推进过程中,工作面侧垮落角总体上呈现减小—增大—减小—增大的循环变化过程,顶板周期来压步距为10m,20m,25m等,表现为工作面的大小周期来压现象,伴随着大周期来压剧烈和小周期来压不明显,且基本表现为小周期来压时垮落角减小,大周期来压时垮落角增大的规律,这是由于覆岩关键层的破断使得周期来压步距和来压强度都增大。(3)在下煤层开采过程中,上煤层的卸压程度和卸压范围逐渐增大,工作面前方垂直应力峰值点不断前移,上煤层垂直应力分布形式依次为“V”(基本顶未发生垮落)、“U”(基本顶初次垮落)和“W”(基本顶周期性垮落)型。(4)随着下煤层工作面的推进,顶板周期性垮落和下沉,采空区侧卸压范围和卸压程度先增大后趋于稳定,随着采空区垮落破碎岩体逐渐被压实,采空区底板逐渐恢复原岩应力水平,通过对底板应力监测,底板经历了增压—减压—增压—恢复的过程,采空区应力恢复距离约为120m。(5)下煤层开采过程中,上煤层任一点都经历了压缩,膨胀变形,膨胀变形增大,膨胀变形减小,膨胀变形稳定这几个阶段,待采空区上覆岩层变形稳定后,可将上煤层分为五个区域:压缩变形区,卸压膨胀过渡区,卸压膨胀稳定区,卸压膨胀过渡区,压缩变形区。上煤层裂隙也经历了发育-扩展-压实闭合的动态过程。与数值模拟结果一致。(6)利用Matlab统计得到了下煤层开采过程中覆岩裂隙数量、长度和倾角的统计规律,裂隙总体数目随工作面推进呈“S”型曲线增长,得到了裂隙数目与推进距离的拟合曲线,裂隙倾角以水平和垂直为主,覆岩中水平裂隙数量先增大后减小,获得了随工作面推进不同距离覆岩整体裂隙倾角分布和切眼前方80-140m固定区域内裂隙倾角分布玫瑰图。(7)煤层群双重卸压开采展现出于单一煤层开采不同的覆岩裂隙分布和演化规律,覆岩裂隙经历了生成、扩展、压实、张拉、再压实的复杂动态过程,上煤层的开采使得覆岩裂隙二次发育,卸压范围和程度均增大,上下煤层开采形成的裂隙相互贯通,形成立体瓦斯运移通道。尤其开切眼和工作面煤壁侧竖直破断永久裂隙互相贯通,形成宏观瓦斯通道。
[Abstract]:Coal is one of the most important energy sources in today's society. For a long time, gas is a source of disaster, which has been threatening the safe production of coal mines in our country, mine gas explosion accidents and coal and gas outburst accidents. With the increase of mining depth, this kind of problem is more severe. According to a large number of theories and field application practice, the protection layer has been proved. It is the most effective regional gas control measure and gas extraction measures to extract pressure from the protected layer by mining and using the pressure relief action of protective layer mining. Therefore, mastering the mechanism of pressure relief mining, the range of pressure relief and the influencing factors are all useful for the precise layout of gas extraction drilling, the concentration of high gas extraction and the elimination of the hidden danger of gas safety. It is of great significance. This paper studies the fracture evolution law and the pressure unloading space effect of the upper seam mining in the close range coal seam group, and makes a thorough study of this problem by means of theoretical analysis, numerical simulation, similar simulation experiment and engineering practice. On the basis of the pores and cracks in the total coal rock mass, the use of the bomb is used. Plastic mechanics, fracture mechanics and other methods are used to analyze the fracture characteristics of the rock mass and the development mechanism of the fracture development from the meso and macro angles, and get the development mechanism of the fracture and the vertical fissure of the overlying rock. Through the theoretical analysis, the similar simulation is used to analyze the stress recovery law of the goaf in the long wall working face, and the goaf should be pointed out. The formula of the stress recovery distance in the goaf is derived from the complexity of the force distribution law and the main influencing factors. Based on the distribution law of the stress distribution in the goaf, the distribution law of the stress and displacement fields of the overlying strata is obtained under the different mining conditions by the pressure unloading angle, and the coal is obtained through the UDEC numerical simulation and the similar simulation experiment. The distribution and the evolution law of the cladding fracture of the coal seam group are different from that of the single coal seam mining. The main achievements are as follows: 1. the failure characteristics of coal rock and rock mass and the evolution mechanism of the meso fracture (1) in the process of coal formation and the tectonic movement of the coal after the formation of coal, a large number of pores are produced inside it. According to the pore diameter of the coal, it can be divided into five levels of micropore, small hole, mesoporous, large hole, visible hole and fissure. According to the size and shape of the crack in the coal rock mass, it can be divided into four kinds: Micro fissure, small fissure, middle fissure and large fissure. (2) the strength and breaking of a single consistent fractured cylinder is analyzed according to the mole Kulun strength criterion. In bad way, when the compressive strength of the rock mass is equal to the compressive strength of the rock mass, the rock mass can only be shear failure along the rock block. When beta > W, Ko < kW, and sigma co > CW, the failure mode of the fractured rock mass varies with the confining pressure. With the increase of confining pressure, the fractured rock changes from slip failure along the crack surface to the rock mass along the rock mass. Shear failure; when beta > W, Ko > kW and sigma co > CW, the fractured rock mass will always be destroyed along the fissure surface, and the strength of rock mass is determined by the crack surface; when beta > W, Ko > kW, but when sigma < 3 < 3cr, the compressive strength of the rock fracture surface is greater than the compressive strength of rock and rock, and when the axial pressure increases to a certain extent, the fracture rock is increased to a certain degree. When the compressive strength of the rock mass is less than 3cr, the compressive strength of the fractured surface of the rock mass is less than the compressive strength of the rock. When the axial pressure increases to a certain extent, the fractured rock mass will slip along the crack surface, that is, during the increase of the confining pressure, the failure mode of the fractured rock mass is broken from the rock mass to the fracture surface. > > W, and Ko < kW, but when sigma CO < CW, the fracture rock will be shear failure, the strength of rock mass is determined by the strength of rock block. (3) in the stage of supercharging, the primary cracks in the coal and rock experienced the development process of shear slip self similar expansion bending expansion shear expansion, and the fracture occurred in the process of unloading in the pressure unloading stage. During the unloading process of the maximum principal stress unloading rock mass, the reverse slip deformation of the crack will inevitably occur during the process of unloading to the confining pressure in the unloading process of the maximum principal stress unloading rock mass, and the opening deformation has the stress condition, and the opening of the fracture and the crack expansion all need certain stress conditions.2.. The interlayer structure and macro fissure evolution law of close range coal seam group (1) based on the key layer theory, the interlayer structure types of close seam protection layer are divided into two layers: there is no key layer structure between layers, the interlayer contains a single key layer, and there are two sub key layers in the layer, and there are multiple sub key layers in the layer. (2) analysis of the roof breaking and forming the vertical break fracture should be analyzed. The opening angle of the vertical breaking fracture is related to the two order derivative of the equation of the inner subsidence curve of the rock stratum. The span conditions for the fracture are derived based on the maximum strain theory of the rock beam. (3) the subcritical layer of the subcritical layer between the layers and the subcritical layers. The position and the number of layers will affect the dynamic development and distribution of the cranny of the overlying rock. The subcritical layers will not affect the development of the fracture to the height. The two subcritical layers with the same lithology and thickness have the inhibition effect on the increase of the interlayer fissure range, and the evolution law of the.3. coal seam group and the single seam mining peri rock fracture evolution (1) through the ratio discrimination method, three The feasibility of mining the lower 8# coal seam as a protective layer is verified with the discriminant method, and the maximum damage height of the stope roof is derived by the elastoplastic mechanics, and the feasibility of the uplink mining is further verified. (2) the fracture evolution law of the surrounding rock in single coal seam mining and the stress concentration coefficient in front of the coal face are studied. As the working face increases first and then tends to be stable, the vertical main stress of the coal and rock mass is greater than the horizontal main stress before the excavation. When the coal is excavated, the size and direction of the main stress change, the main stress of the roof near the coal wall is the horizontal stress, the vertical stress is almost 0, and the hydraulic support has little influence on the vertical stress distribution of the roof. The main stress distribution of the floor is divided into two regions, which is affected by the support base. The main stress is vertical stress and the horizontal stress is small in the 1m range of the floor. With the increase of the depth of the floor, the direction of the main stress begins from the vertical stress mainly to the horizontal stress. Finally, the vertical stress is gradually restored to the vertical stress. The front of the working face is in front, The trend of the main stress change is approximately "arc", and the arc of the coal body is more and more from the middle of the working face to the top and bottom. The maximum principal stress is gradually changed from the vertical main stress to the horizontal main stress. The vertical main stress in the rear of the goaf is larger than the front of the goaf, and gradually tends to restore the stress state of the original rock; the stress distribution of the surrounding rock in the goaf is similar to the "arch" "The height of arch height decreases slightly with the advance of the working face, and then decreases slightly, and finally stable at a certain height. (3) the influence of the elastic modulus of the broken rock mass on the stress field, displacement field and fracture field of the surrounding rock is studied, and the same deformation characteristics are displayed in different goaf stresses and different working faces, and the top and bottom are experienced. Compression deformation, pressure relief expansion deformation, deformation recovery, compression deformation, and no deformation process, but there are certain differences in the size and range of different goaf stress and behavior conditions, the smaller the elastic modulus of the broken rock mass in the goaf, the greater the recovery distance of the stress in the goaf, the pressure concentration coefficient of the front supporting pressure and the coal body breaking in the front of the work. The larger the expansion of surrounding rock expansion and compression deformation at the same position of the roof at the top of the goaf, the more it is beneficial to the release of elastic potential of coal and rock mass, and the activation of gas is more conducive to the desorption and flow of the overlying rock gas, and the permeability of coal and rock mass is increased, which is beneficial to the layout of gas extraction drilling and gas extraction. The stress distribution law of.4. goaf and the law of pressure unloading in the space of coal seam group (1) studied the stress distribution in the goaf, using the load conservation calculation model of the overlying rock mass, the lateral extended support load model and the fitting formula of the recovery distance of the goaf based on the surface subsidence, taking the 84306 working face of the Changping Coal Mine as an example, when the height of the coal seam is high. For 3M, when the buried depth is 530m, the stress recovery distance of the goaf is respectively the height of the stress recovery distance in the 103169140m. goaf, the broken coefficient of the rock mass, the buried depth of the coal seam is positively correlated, and the uniaxial compressive strength of the roof rock mass in the goaf is negatively related, and it has a non linear relationship with the buried depth of the coal seam, and the height increase mainly affects the broken rock broken rock mass. The influence of expansion coefficient on the stress recovery distance of the goaf is smaller than that of the top slate. (2) the spatial stress and displacement distribution of the overlying rock after the mining of the lower coal seam is obtained. According to the vertical stress and vertical displacement distribution of the roof of the lower coal seam, the roof is divided into five regions along the surface of the working face, from the front of the coal face to the goaf. The region in turn is the original rock stress area, compression area, expansion area, stress recovery area, recompacting area, and analyzed the formation and development characteristics of the gas channel in each region. (3) the stress distribution of the different height of the roof of the lower coal seam is different, the farther the coal seam is, the smaller the vertical stress is smaller than the original rock stress, and its three-dimensional stress (SXX, SYY, SZZ) The difference between 22 is getting smaller and smaller, the larger three-dimensional stress gradient and stress asymmetry will lead to the formation of cracks in the coal and rock, the expansion and the destruction of coal and rock, the closer to the working face of the protective layer, the more cracks produced by the coal and rock mass, and more prone to damage. (4) in the process of the coal seam propulsion, the pressure unloading coefficient and unloading are used. With the advancing of the working face of the protective layer, the pressure relief degree and the pressure relief range of the protected layer gradually increase, with the collapse of the direct top and the basic top, the gravity of the overlying rock is transferred to the direction of the coal wall and the cut of the eye, so that the stress concentration is produced. With the continuous subsidence of the roof of the goaf, the collapse area is broken down. The compaction of crushed rock mass increases the supporting effect of the roof gradually, thus reducing the pressure relief degree of the protective layer in the rear area of the goaf, taking the axis of the goaf as the middle line, before and after and unsymmetrical, and the maximum pressure unloading place of the protective layer is located in the direction of the working face. On the other hand, the pressure angle of the cutting side and the side of the coal wall increases with the coal pillar first increasing, and then decreases with the coal wall in different positions. The pressure angle of the goaf along the coal seam is different, and the side pressure angle of the coal pillar decreases with the increase of the working face and then the.5. through laboratory similar simulation experiment. (1) the direct roof collapse of the upper coal seam mining is first broken. The step distance and the first break distance of the old roof are less than the lower coal seam mining. When the lower coal seam pushes into 40m, it directly tops the large area, and the working face is pushed to 50m, the old roof is broken and the initial pressure is formed. The first fall of the top coal seam and the initial pressure step of the old roof are respectively 30m and 45m. (2) coal seam advancing process, and the side fall angle of the working face side. On the whole, the cyclic variation process of decreasing - enlarging - decreasing - increasing, the pressure step distance of the roof period is 10m, 20m, 25m, etc., which is characterized by the periodic pressure phenomenon of the working face, which is not obvious with the large period pressure and the small period, and the fall angle decreases with the small cycle pressure, and the fall angle increases when the large period pressure is pressed. The large rule, this is due to the breakage of the key strata of the overlying rock, which makes the periodic pressure step and the pressure strength increase. (3) during the mining of the lower coal seam, the pressure relief degree and the pressure relief range of the upper coal seam gradually increase, the vertical stress peak point in front of the working face is moving forward continuously, and the vertical stress distribution in the upper coal seam is in turn "V" (the basic top has not occurred. "U"), "U" (primary roof fall) and "W" (basic top periodic collapse) type. (4) with the advancing of the coal seam working face, the cyclical collapse and subsidence of the roof, the lateral pressure relief range and pressure relief level of the goaf first increased and then tended to stabilize, with the collapse of the goaf crushed rock mass gradually compacted and the bottom floor of the goaf gradually restored the original rock stress. Level, through the stress monitoring of the floor, the floor has undergone the process of pressurization, decompression, pressurization and recovery, and the stress recovery distance of the goaf.

【学位授予单位】：中国矿业大学(北京)
【学位级别】：博士
【学位授予年份】：2017
【分类号】：TD712.6
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本文编号：1889387