加卸载应力条件下原煤力学与渗透特性研究.pdf

加卸载应力条件下原煤力学与 渗透特性研究* 重庆大学硕士学位论文 （学术学位） 学生姓名魏皑冬 指导教师蒋长宝 教授 学科门类工 学 学科名称矿业工程 研究方向矿井灾害预测及控制 答辩委员会主席许江 教授 授位时间2019 年 6 月 * 国家自然科学基金51674048 万方数据 万方数据 Study on Mechanics and Permeability of Raw Coal under Loading-Unloading Stress† A Thesis ted to Chongqing University in Partial Fulfillment of the Requirement for the Masters Degree of Engineering By Wei Aidong Supervised by Prof. Jiang Changbao June, 2019 † National Natural Science Foundation of China 51674048 万方数据 万方数据 中文摘要 I 摘 要 本论文以取自川煤集团芙蓉公司某煤矿 C1 煤层的原煤煤样为研究对象， 通过 对原煤进行微观孔隙裂隙测试和瓦斯渗透实验、不同轴向加载速率下的原煤力学 与渗透特性实验、不同加卸载应力条件下的原煤力学与渗透特性实验、以及加卸 载应力条件下的煤岩流固耦合数值模拟，以期得出原煤全应力-应变过程中的力学 和渗透特性。具体内容如下 ①原煤的物理性质主要有 煤样的孔直径主要分布在 160nm 以下， 其中 100nm 以下的小孔及微孔占比为 81.5，100nm 以上的中孔占比为 18.5，煤岩颗粒的孔 隙率为 5.65；煤岩颗粒符合 II 型等温线的变化特征，且不存在滞后环现象，BET 比表面积为 0.7192m2/g，平均孔径为 31731.7nm，孔体积为 0.00098cm3/g；扫描 电镜成像中，可见植物组织孔、变质气孔和不平行板状结构下的颗粒间孔三种孔 隙结构；在弹性阶段加载时，原煤渗透率与围压和轴压满足 3 1 eCKAB  的动 态函数关系。 ②不同轴向加载速率下的力学与渗透特性实验中煤岩破坏时应力迅速跌落， 脆性特征较为明显；体积扩容应力、峰值应力、弹性模量和变形模量四种力学指 标，均随轴向加载速率增大而增大；煤样能量耗散在应力峰前阶段绝大部分转化 为可释放弹性应变能，耗散应变能增加的速率较缓，应力峰后阶段弹性应变能急 剧下降，大量释放并转化为耗散应变能，同时应力峰值处的总能量随轴向加载速 率的增大而增大；在原煤静水压力之后的加载阶段，渗透率-轴线应变曲线总体呈 现“V”字形的变化特征，在全应力-应变过程中，煤岩渗透率与轴向应变之间满 足二次多项式函数关系 2 11 KABC，且该函数关系在轴向加载速率较小时更 为适用。 ③不同加卸载应力条件下的力学与渗透特性实验中同一加卸载控制点下， 原煤破坏时的体积应变随加卸载速率比的增大而减小，径向应变和轴向应变随加 卸载速率比的增大而增大，原煤破坏形态随加卸载速率比增大，逐渐向单一宏观 断裂面的破坏形态发展；同一加卸载速率比下，原煤的强度随着加卸载控制点的 增大而增大，原煤破坏后的破坏角随加卸载控制点的增大而降低；随着加卸载速 率比的减小，屈服阶段内的渗透率阶梯状变化特征越发明显，同时屈服阶段内的 渗透率响应变化量和应变响应变化量与加卸载速率比均呈线性关系。 ④流固耦合下的加卸载 RFPA2D-Flow 数值模拟中煤岩的破坏形态为剪切破 坏，随着围压卸载速率的增加，其破坏形态更松散；围压卸载的速率与煤样的峰 值应力之间呈负相关关系；声发射能量为单峰型，峰值点前会出现明显的声发射 万方数据 重庆大学硕士学位论文 II 能量耗散，能够预测各个围压卸载速率下煤岩的破坏前兆，应力峰值点处的声发 射能量表现为随围压卸载速率的增加而增加；压密与弹性阶段渗透率随加载步增 加而逐渐降低，直至趋近于 0，屈服阶段随着围压的持续卸载，煤样内部产生累积 性损伤，导致渗透率小幅升高，破坏与残余变形阶段的渗透率急剧陡增。 关键词关键词原煤；加卸载；力学特性；渗透率；流固耦合 万方数据 英文摘要 III Abstract This paper takes the raw coal sample taken from the C1 coal seam of a coal mine of Furong Company of Sichuan Coal Group as the research object, through the micro-pore crack test and gas permeability test of raw coal, the mechanical and permeability experiments of raw coal under different axial loading rates, the mechanical and permeability experiments of raw coal under different loading-unloading stress conditions, and the fluid-solid coupling numerical simulation of coal under loading-unloading stress conditions. In order to obtain the mechanical and permeability characteristics of the total stress-strain process. The details are as follows ①Pore diameter of raw coal distribute below 160 nm. The proportion of small pores and micropores below 100 nm is 81.5, the proportion of mesopores above 100 nm is 18.5, and the porosity of raw coal is 5.65. The raw coal particles con to the variation characteristics of the type II isotherm and there is no hysteresis loop phenomenon. The coal rock has a BET specific surface area of 0.7192 m2/g, and average pore diameter is 317 31.7 nm, the pore volume is 0.00098 cm3/g. Three pore structures of plant pores, metamorphic pores and intergranular pore. can be found in scanning electron microscopy. When loading in elastic stage, The permeability of raw coal satisfies the functional relationship 3 1 eCKAB   with confining pressure and axial pressure. ②In the experiment of mechanical and permeability characteristics under different axial loading rates The stress drops rapidly when the raw coal failure, and the brittleness characteristic is obvious. Volumetric expansion stress, peak stress, elastic modulus and deation modulus are four mechanical inds, which increase with the increase of axial loading rates. During the pre-stress peak stage, the energy dissipation of coal sample is mostly converted into elastic strain energy, and the rate of dissipation strain energy increases slowly. During the post-stress peak stage, The elastic strain energy drops sharply and is transed into a large amount of dissipative strain energy. The total energy at the peak of the stress increases with the increase of the axial loading rate. During the loading stage after hydrostatic pressure of raw coal, the permeability-strain curve generally presents a “V“ shape. During the whole stress-strain process, the relationship between permeability and axial strain of coal and rock satisfies quadratic polynomial function 2 11 KABC, which is more suitable when the 万方数据 重庆大学硕士学位论文 IV axial loading rate is small. ③In the experiment of mechanical and permeability characteristics under different loading-unloading stress Under the same loading-unloading control point, with the increasement of loading-unloading rate ratio, the volumetric strain decreased, but the axial strain and the radial strain increased, the failure pattern of coal gradually developed from several macroscopic fracture to single macroscopic fracture. Under the same loading-unloading rate ratio, with the increasement of loading-unloading control point, the intensity of coal increased, but the failure angle of coal decreased. During the yield stage, with the increase of loading-unloading rate ratio, the response variation of permeability decreased with a linear relationship. However, the response variation of strain from loading-unloading control point to permeability transation point increased with a linear relationship. ④ In the numerical simulation of loading-unloading RFPA2D-Flow under fluid-solid coupling the failure mode of coal rock is shear failure, and the failure patterns is looser with the increase of confining pressure unloading rate. A negative relationship between the rate of confining pressure unloading and the final compressive strength has been found. Acoustic emission energy are single peak type, and there will be obvious dissipation of acoustic emission energy before the peak point, which can predict the failure precursors of coal and rock under various confining pressure unloading rates. The acoustic emission energy at the peak stress point increase with the increase of confining pressure unloading rate. The permeability decreases gradually with the increase of loading step until it approaches 0 in compaction and elasticity stages. With the continuous unloading of confining pressure in the yield stage, cumulative damage occurs in the coal sample, resulting in a small increase in permeability. Permeability increases sharply in the stage of failure and residual deation Keywords raw coal; loading-unloading; mechanical properties; permeability; fluid-solid coupling 万方数据 目 录 V 目 录 中文摘要中文摘要 .......................................................................................................................................... I 英文摘要英文摘要 ....................................................................................................................................... III 1 绪绪 论论 ......................................................................................................................................... 1 1.1 引言引言 ........................................................................................................................................... 1 1.2 国内外研究现状国内外研究现状 ....................................................................................................................... 2 1.2.1 加载速率对煤岩力学与渗透性质的影响 ........................................................................ 2 1.2.2 加卸载应力条件对煤岩力学与渗透特性的影响 ............................................................ 4 1.2.3 煤岩流固耦合机理研究现状 ............................................................................................ 6 1.3 论文主要研究内容及技术路线论文主要研究内容及技术路线 ............................................................................................... 7 1.3.1 主要研究内容 .................................................................................................................... 7 1.3.2 技术路线 ............................................................................................................................ 8 2 煤岩孔裂隙物理测试及瓦斯渗透实验煤岩孔裂隙物理测试及瓦斯渗透实验 ................................................................... 9 2.1 实验煤样的取样与制备实验煤样的取样与制备 ........................................................................................................... 9 2.2 概述概述 ......................................................................................................................................... 10 2.3 压汞法煤岩孔裂隙测试压汞法煤岩孔裂隙测试 ......................................................................................................... 10 2.3.1 实验仪器与操作 .............................................................................................................. 10 2.3.2 实验结果与分析 .............................................................................................................. 11 2.4 低温氮法煤岩孔裂隙测试低温氮法煤岩孔裂隙测试 ..................................................................................................... 12 2.4.1 实验仪器与操作 .............................................................................................................. 12 2.4.2 实验结果与分析 .............................................................................................................. 13 2.5 基于扫描电镜的煤岩孔裂隙微观表征基于扫描电镜的煤岩孔裂隙微观表征 ................................................................................. 16 2.5.1 实验仪器与操作 .............................................................................................................. 16 2.5.2 扫描电镜成像结果与分析 .............................................................................................. 16 2.6 不同轴压及围压条件下的原煤渗透率测试不同轴压及围压条件下的原煤渗透率测试 ......................................................................... 19 2.6.1 实验仪器与操作 .............................................................................................................. 19 2.6.2 实验结果与分析 .............................................................................................................. 21 2.7 本章小结本章小结 ................................................................................................................................. 23 3 轴向加载速率对原煤力学和渗透特性的影响轴向加载速率对原煤力学和渗透特性的影响 ................................................. 25 3.1 概述概述 ......................................................................................................................................... 25 3.2 实验准备及方案实验准备及方案 ..................................................................................................................... 25 3.3 实验结果与分析实验结果与分析 ..................................................................................................................... 27 万方数据 重庆大学硕士学位论文 VI 3.3.1 原煤应力-应变曲线 ......................................................................................................... 27 3.3.2 加载速率对原煤力学指标的影响 .................................................................................. 28 3.3.3 加载过程原煤能量耗散特征 .......................................................................................... 31 3.3.4 加载过程原煤渗透特性 .................................................................................................. 33 3.4 本章小结本章小结 ................................................................................................................................. 35 4 加卸载状态对原煤力学和渗透特性的影响加卸载状态对原煤力学和渗透特性的影响....................................................... 37 4.1 概述概述 ......................................................................................................................................... 37 4.2 实验准实验准备及方案备及方案 ..................................................................................................................... 37 4.3 实验结果与分析实验结果与分析 ..................................................................................................................... 40 4.3.1 加卸载状态下原煤力学特性 .......................................................................................... 40 4.3.2 加卸载状态对原煤破坏形态的影响 .............................................................................. 45 4.3.3 加卸载状态下原煤渗透特性 .......................................................................................... 46 4.4 本章小结本章小结 ................................................................................................................................. 48 5 加卸载状态下煤岩流固耦合数值模拟加卸载状态下煤岩流固耦合数值模拟 ................................................................. 51 5.1 概述概述 ......................................................................................................................................... 51 5.2 煤岩破裂过程流固耦合模煤岩破裂过程流固耦合模型型 ................................................................................................. 51 5.3 加卸载状态下煤岩破裂过程流固耦合数值模拟加卸载状态下煤岩破裂过程流固耦合数值模拟 ................................................................. 52 5.3.1 几何模型及数值模拟参数 .............................................................................................. 52 5.3.2 加卸载状态下煤岩损伤特征 .......................................................................................... 54 5.3.3 加卸载状态下煤岩强度与声发射能量特征 .................................................................. 55 5.3.4 加卸载状态下煤岩渗透特性 .......................................................................................... 58 5.4 本章小结本章小结 ................................................................................................................................. 60 6 结论与展望结论与展望 ............................................................................................................................ 63 6.1 本文的研究成果及结论本文的研究成果及结论 ......................................................................................................... 63 6.2 主要创新点主要创新点 ............................................................................................................................. 64 6.3 后续工作展望后续工作展望 ......................................................................................................................... 64 参考文献参考文献 ...................................................................................................................................... 65 附附 录录 ...................................................................................................................................... 71 A. 作者在攻读硕士学位期间发表的论文作者在攻读硕士学位期间发表的论文 .................................................................................. 71 B. 作者在攻读硕士学位期间参加的科研项目作者在攻读硕士学位期间参加的科研项目........................................................................... 71 C. 作者在攻读硕士学位期间获得的奖励作者在攻读硕士学位期间获得的奖励 .................................................................................. 71 D. 学位论文数据集学位论文数据集 ...................................................................................................................... 72 致致 谢谢 ...............................................................................................................