采动过程围岩宏细观裂隙场量化模型与演化规律

发布时间：2018-05-19 16:18

本文选题：回采扰动 + 裂隙实测　；参考：《中国矿业大学(北京)》2017年博士论文

【摘要】：本论文的研究依托于国家自然科学基金面上项目(51374216)。瓦斯治理最重要的方法就是瓦斯抽采,而瓦斯抽采最关键的问题就是合理抽采参数的确定。工作面回采过程顶板的裂隙场是采空区瓦斯运移的主要通道,而回采过程又导致顶板裂隙场一直处于动态的变化置中,因此对工作面回采影响下顶板裂隙场的演化规律研究就十分重要,是确定顶板瓦斯抽放钻孔与高位瓦斯抽放巷道等手段布置方式的主要依据。本文以工作面顶板围岩在采动影响下的裂隙场演化规律为研究方向,通过实验室力学实验、分析宏细观裂隙分布、现场钻孔窥视观测、顶板裂隙三维网络重构、真实地质参数条件下数值模拟等研究方法,重点研究了受工作面采动应力影响下,工作面顶板围岩内的裂隙场演化规律。通过研究,本文主要得到了如下结论:(1)采用了最大应力逐渐升高的应力路径下的岩石循环加卸载实验方案,该方案的应力加卸载速度依据现场顶板受力特征确定,同时对实验过程岩石声发射进行监测。发现岩石的循环加卸载实验可以根据声发射信号的特征分为三个阶段,分别是声发射偶发阶段、发展阶段与高峰阶段。以声发射事件数率突然升高为标志的高峰阶段是最主要的阶段,一般始于峰值强度的60%~70%左右。在高峰阶段,高振幅信号出现更多,且声发射定位也明显集中,集中区域与最终的样品破坏位置相对应。岩石整个加载过程90%以上的声发射事件都集中在这个阶段,可以认为岩石内部的裂纹、孔隙等各类损伤都主要是在这个阶段产生的,因此这也是岩石破坏的最主要阶段。(2)声发射信号有明显的Kaiser效应和Felicity效应,通过对Felicity比进行计算,发现Kaiser效应的准确性随着循环加卸载的过程而逐渐降低,声发射越来越多地发生于Kaiser点之前。在对后几个循环的卸载阶段声发射信号进行详细观察后发现,当应力小于上循环的最大值后,会产生明显的声发射信号,但振幅和事件数率都小于本循环加载阶段。经分析,认为当应力小于上循环最大之后,岩石内部产生了一定程度的塑性恢复而产生了声发射信号;而在下一循环的加载阶段,这些塑性恢复在达到本循环最大应力之前就又被破坏而产生声发射信号,表现出了Felicity效应,这个假设很好的解释了Felicity效应产生的原因。由于该现象也是在上一循环应力最大值之后产生,因此定义为后Kaiser效应。(3)在细观尺度上,声发射信号能量与释放的弹性能相关,进而与产生裂隙所需消耗的总能量相关,进而与裂隙的面积相关。根据声发射能量分布可以推断,岩石在破坏过程中,首先是大量小规模裂隙随机出现;随着小裂隙在数量上的增加,它们之间相互连接、贯通,同时产生较大能量的声发射信号;随着裂隙进一步扩展,最终贯穿岩石,导致岩石的破坏,并在这个过程产生大能量的声发射。在宏观尺度上,根据裂隙面大小分布可以进行类似的岩体内的裂隙场演化分析。(4)在细观尺度分析了岩石受载过程的弹性阶段的平衡方程、几何方程、变形控制方程、本构方程等,归纳了以破坏面积占比、摩尔库伦强度准则与抗拉强度准则、声发射累积振铃计数等不同参数为依据的损伤变量定义,最后结合上一章岩石循环加卸载条件下的声发射能量累积的特征,定义了以声发射累积能量为参数的损伤变量D,能够更好的反映岩石在不同时刻的损伤规模。(5)在细观尺度上,对声发射不同振幅值对应的事件总数、和不同能量对应的事件总数之间的关系进行分析,发现小振幅、小能量声发射事件占据绝对的主导,两者呈现为=(6-(7形式的幂函数;在宏观尺度上,对现场地质体宏观裂隙面的尺寸进行统计,发现其在某个尺寸所对应的裂隙面数量之间,在对数图上为一条直线,拟合规律也呈现负幂数关系,与细观尺度岩石声发射振幅、能量分布规律一致,可以认为岩石在细观上的损伤与宏观上的裂隙破坏有一致性,同时验证了岩石材料的自相似性与分形特性。(6)在宏观尺度,分析了前视钻孔窥视仪的工作原理,提出了前视钻孔窥视视频转换为钻孔全景图片的方法,以及从中提取钻孔裂隙产状、位置等信息的原理。利用提出的转换方法将现场的钻孔窥视视频转换为钻孔全景图片,并对图片中的裂隙信息进行提取。进一步地,从这些裂隙信息中提取了裂隙场三维重构模拟所需要的裂隙组强度、产状、大小等参数。(7)利用裂隙的相关参数,基于不连续面三维网络重构原理,使用MoFrac软件,进行了基于现场钻孔观测基础上的工作面顶板裂隙场时空演化三维模拟,并得到以下规律:(1)从空间位置分析,在沿工作面推进方向,裂隙的分布空间主要位于采空区上方范围;在沿工作面走向方向,回采25m及之前,裂隙主要集中在与巷道距离60m范围内,回采达到并超过50m后,在走向方向就变得更平均了;在高度方向,回采6m时裂隙分布在高度10m的范围内,随着工作面的推进,裂隙在高度范围的分布越来越大,例如回采25m时高度在15m左右,回采75m和100m时达到了35m左右,本次现场观测最高距离仅有35m,因此认为裂隙场的真实分布要超过35m;(2)工作面回采6m时,产生的顶板裂隙大小普遍偏小,而随着工作面的回采,顶板内的裂隙面积逐渐增大,老顶的初次与周期来压导致的特大裂隙面会进一步切割、连通之前产生的中、小裂隙面,进而生成复杂的、相互连通的裂隙网络,成为采空区顶板内主要的瓦斯渗流通道;(3)顶板内产生的裂隙的倾角主要以水平方向为主,而裂隙的倾向则没有太明显的特征;关于裂隙面的密度,可以看出也是随着工作面的回采而逐渐增大,并在50m之后逐渐稳定。(8)本构模型的选择与材料参数的赋值在数值模拟中非常重要,是决定数值模拟结果是否合理的关键因素。在FLAC3D中考虑残余强度,将模型的煤、岩体都定义为更加符合实际情况的应变软化模型,同时依据碎涨系数等参数确定了采空区范围,并将采空区定义为双屈服模型;另外,按照Weibull分布对煤层上覆54m顶板岩层的体积模量K和剪切模量G进行随机赋值。(9)通过对回采过程围岩内的垂直应力与塑性破坏区演化进行分析,得出:工作面前方12~14m范围内煤体处于塑性破坏;顶板内的塑性破坏最开始主要出现在采空区上方,回采超过30m后开始在工作面前方煤岩体顶板内产生;工作面回采至72m后再推进,采空区上方出现了一层平面的塑性破坏区域,这是稳定的裂隙带最下层,同时工作面正上方靠前的位置产生大量的塑性破坏,这与顶板的大范围来压或破坏有关,内部可能生成大量的裂隙。顶板的塑性破坏范围可以反映顶板内的裂隙面产生与演化,经过对比与现场观测结果吻合度较高。(10)提出了通过现场顶板钻孔窥视观测来获得顶板裂隙场演化规律,进而确定工作面顶板高效瓦斯钻孔抽采技术关键参数的方法。结合顶板裂隙场的多孔介质特征与瓦斯的主要来源分类,分析了顶板裂隙场的瓦斯渗流规律,进一步结合顶板垮落带与裂隙带高度公式,分析了现场工作面顶板瓦斯抽放钻孔的布置主要参数。考虑钻孔有效抽放长度情况下,对N3-7工作面的钻孔布置方案进行了优化,分别确定了进风巷高位钻孔的布置方案,以及回风巷钻孔组的布置方案。该方案可以为N3-7工作面及其周围的工作面的顶板瓦斯抽放钻孔布置提供参考。
[Abstract]:The research of this paper is based on the project of National Natural Science Foundation (51374216). The most important method of gas control is gas extraction, and the most important problem of gas extraction is the determination of reasonable extraction parameters. The fracture field at the roof of the working face is the main channel of gas migration in the goaf, and the recovery process leads to the roof. The fracture field is always in the dynamic change, so it is very important to study the evolution law of the roof fissure field under the influence of the working face recovery. It is the main basis for determining the layout mode of the roof gas drainage drilling and the high gas drainage tunnel. For the research direction, through the laboratory mechanics experiment, we analyze the distribution of macro and micro cracks, the field borehole peep observation, the three-dimensional network reconstruction of the roof fissures, the numerical simulation of the real geological parameters and other research methods, focusing on the evolution law of the fracture field in the wall rock of the working face under the influence of the working face's mining stress. The main conclusions are as follows: (1) the experimental scheme of rock cyclic loading and unloading under the stress path of the maximum stress is adopted. The stress loading and unloading velocity of the scheme is determined by the stress characteristics of the site roof, and the acoustic emission of the rock is monitored at the same time. The cyclic loading and unloading experiments of the present rock can be based on the acoustic emission. The characteristics of the signal are divided into three stages, which are the occasional phase of acoustic emission, the development stage and the peak stage. The peak stage marked by the sudden rise of the number of acoustic emission events is the most important stage, which usually begins at about 60%~70% of the peak intensity. At the peak stage, the high amplitude signal appears more, and the acoustic emission location is also concentrated obviously. The middle area is corresponding to the final damage position of the sample. The acoustic emission events above 90% of the whole rock loading process are concentrated at this stage. It is considered that all kinds of cracks, such as cracks and pores in the rock are mainly produced at this stage, so this is the most important stage of rock failure. (2) the acoustic emission signals have obvious Kaiser Effect and Felicity effect, by calculating the Felicity ratio, it is found that the accuracy of the Kaiser effect gradually decreases with the process of cyclic loading and unloading, and the acoustic emission is more and more occurring before the Kaiser point. After the detailed observation of the acoustic emission signals at the unloading stage of the later cycles, the stress is less than the maximum value of the upper cycle. After that, the amplitude and the number of events are less than the cyclic loading stage. After analysis, it is believed that when the stress is less than the maximum cycle, the interior of the rock produces a certain degree of plastic recovery and produces the acoustic emission signal, and the plastic recovery is the largest in the next cycle. The acoustic emission signal is produced before the stress is destroyed again, showing the Felicity effect. This hypothesis is a good explanation of the cause of the Felicity effect. Since this phenomenon is also produced after the maximum value of the last cycle stress, it is defined as the post Kaiser effect. (3) on the meso scale, the energy of acoustic emission signal and the elastic energy released by the acoustic emission signal. The correlation is related to the total energy consumed by the crevice, which is related to the area of the fissure. According to the distribution of the acoustic emission energy, it is inferred that in the course of the rock failure, the first is a large number of small fractures randomly appearing. With the increase in the number of small fissures, they are connected and connected, and the sound of larger energy is produced. With the further expansion of the crack, the rock eventually runs through the rock, causing rock destruction and producing large energy acoustic emission in this process. On the macro scale, the fracture field evolution in similar rock mass can be carried out in the same rock mass according to the size distribution of the fracture surface. (4) the equilibrium of the elastic phase of the rock loading process is analyzed in the meso scale. The equation, geometric equation, deformation control equation, constitutive equation, etc. are defined by the definition of damage variables based on different parameters such as damage area occupation ratio, mole Kulun strength criterion and tensile strength criterion, acoustic emission accumulative ringing count and so on. Finally, the characteristics of acoustic emission energy accumulation under the conditions of rock cyclic loading and unloading in the last chapter are defined. The damage variable D with the parameters of the acoustic emission accumulated energy can better reflect the damage scale of the rock at different times. (5) on the meso scale, the total number of events corresponding to the different amplitude values of acoustic emission and the relationship between the total number of events corresponding to different energy are analyzed, and the small amplitude and small energy acoustic emission events are found to be absolute. Leading, the two are presented as = (6- (7 form) power function; on the macroscopic scale, the size of the macroscopic fissure surface of the field geological body is counted, and it is found that it is a straight line between the number of fracture surfaces corresponding to a certain size, and the logarithmic diagram is a negative power relation, the amplitude of the acoustic emission from the meso scale, the energy distribution gauge. According to the law, it can be considered that the damage of the rock in the mesoscopic damage is consistent with the fracture failure in the macro. At the same time, the self similarity and fractal characteristics of the rock material are verified. (6) the working principle of the forward borehole peep is analyzed on the macroscopic scale, and the method of converting the visual frequency of the forward borehole to the borehole panoramic image is put forward and it is proposed from it. Using the proposed transformation method, the borehole peep video is converted into a borehole panoramic picture by using the proposed transformation method, and the fracture information in the picture is extracted. Further, the parameters of the fracture group strength, shape, size and so on are extracted from these fissure information. (7) using the related parameters of the fissure, based on the three-dimensional network reconstruction principle of discontinuities, using the MoFrac software, the three-dimensional simulation of the space-time evolution of the roof crack field on the working face based on the field borehole observation is carried out, and the following rules are obtained: (1) the spatial position analysis, the direction along the working face, the distribution space of the fissure is mainly located in the mining. In the direction of the air area, in the direction of the face along the face, the crack is mainly concentrated in the range of 60m in the range of distance from the roadway. After the recovery reaches and exceeds the 50m, the direction becomes more average in the direction. In the high direction, the crack is distributed in the range of high 10m when the 6m is mined, and the fracture is distributed in the height range with the advancing of the working face. It is getting bigger and bigger, for example, the height of 25m is about 15m, and 75m and 100m have reached about 35m. The maximum distance of the field observation is only 35m. Therefore, the true distribution of the crack field is more than 35m; (2) the size of the roof crack is generally small when the face is recovered to 6m, and the area of the crack in the roof is gradual with the mining of the working face. In addition, the large fissure surface caused by the initial and periodic pressure of the old top will further cut, and the small fissure surface which is generated before connecting, then generates complex and interconnected fracture networks, and becomes the main gas seepage channel in the roof of the goaf, and (3) the inclination of the fissure produced in the roof is mainly in the horizontal direction and the fracture is tilted. There is no obvious characteristic in direction; on the density of the fracture surface, it can be seen that it is gradually increasing with the recovery of the working face, and gradually stabilizes after 50m. (8) the selection of the constitutive model and the assignment of material parameters are very important in the numerical simulation, which is the key factor determining the rationality of the numerical simulation results. In the case of FLAC3D, the residue is considered to be residual. In addition, the coal and rock mass of the model are defined as the strain softening model which is more consistent with the actual situation. At the same time, the goaf range is determined according to the parameters such as the coefficient of fragmentation. The goaf is defined as a double yield model. In addition, the volume modulus K and the shear modulus G of the overlying 54m top slate are randomly assigned according to the Weibull distribution. (9) Through the analysis of the vertical stress in the surrounding rock and the evolution of the plastic failure zone in the surrounding rock, it is concluded that the coal body is in plastic damage in the range of 12~14m in front of the work, and the plastic failure in the roof is mostly above the goaf. After the recovery exceeds 30m, the roof of the coal rock mass is produced in front of the working face, and the working face is recovered to 72m. In addition, a plastic failure area of the plane appears above the goaf, which is the lower layer of the stable fracture zone, and a large number of plastic damage is produced at the top of the working face, which is related to the large pressure or failure of the roof. The interior of the roof may produce a large number of cracks. The plastic failure range of the roof can reflect the roof. The formation and evolution of the fracture surface are in good agreement with the field observation results. (10) the evolution law of the roof fissure field is obtained through the field roof drilling peep observation, and then the key parameters of the high efficient gas drilling technology are determined. The porous media characteristics of the joint roof fracture field and the main gas are main. According to the classification of the source, the gas seepage law of the roof fissures field is analyzed, and the main parameters of the gas drainage drilling in the roof are analyzed by combining the height formula of the roof caving zone and the fracture zone. Considering the effective drainage length of the drilling hole, the drilling layout scheme of the N3-7 working face is optimized. The layout of the high hole drilling in the wind tunnel and the layout of the drilling group in the return air lane can provide reference for the layout of the roof of the working face of the N3-7 and the roof of the working face.
【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】：TD712.61;TD31

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