花岗岩三轴循环加卸载条件下的气体渗透率
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摘要
为研究花岗岩在三轴循环加卸载条件下气体渗透率的演化规律,利用岩石多场耦合三轴试验仪分别对花岗岩进行三轴恒下限分级循环加卸载试验和气体渗透试验。试验结果表明:加载曲线与上一次循环卸载曲线形成塑性滞回环,随着循环次数的增加,每个循环应力下限的轴向应变也随之增加;前期几个循环试样体积压缩明显,以轴向压缩变形为主,后期轴向应力达到一定数值时体积由压缩转为扩容,裂纹发展方向偏向于轴向方向,均呈剪切脆性破坏;气体渗透率变化分为稳定下降阶段、缓慢增加阶段、急剧上升阶段3个阶段,试样脆性破坏后气体渗透率均上升2～3个数量级;体积应变曲线拐点与横向应变曲线结合起来可以作为研究岩石渗透率变化规律的一个重要参考因素。
To investigate the evolution of gas permeability of granite in triaxial cyclic loading/unloading tests, the cyclic loading/unloading tests and gas permeability tests were carried out on granite specimens under different confining pressures by using a rock T-H-M-C coupled testing system. The test results show that the plastic hysteresis loops are formed by the loading curve and unloading curve of the former cycle. The lower limit of axial strain in each cycle increases with increasing number of cycles. The volume compression of specimens occurs at the first several cycles, and the main deformation is along the axial direction. Afterwards, the specimen volume changes from compression to dilatancy when deviatoric stress increases to a certain value. All specimens are divided into several parts by macroscopic cracks when shear fracture generates, and the orientation of crack is inclined to axial direction. Gas permeability curves are divided into three stages: a stable decline, a slow rise and a sharp rise. The gas permeability increases by 2-3 orders of magnitude after the brittle failure happens. The inflexion point of volume strain curve and the lateral strain curve can be used as an important reference to predict the change of permeability.
To investigate the evolution of gas permeability of granite in triaxial cyclic loading/unloading tests, the cyclic loading/unloading tests and gas permeability tests were carried out on granite specimens under different confining pressures by using a rock T-H-M-C coupled testing system. The test results show that the plastic hysteresis loops are formed by the loading curve and unloading curve of the former cycle. The lower limit of axial strain in each cycle increases with increasing number of cycles. The volume compression of specimens occurs at the first several cycles, and the main deformation is along the axial direction. Afterwards, the specimen volume changes from compression to dilatancy when deviatoric stress increases to a certain value. All specimens are divided into several parts by macroscopic cracks when shear fracture generates, and the orientation of crack is inclined to axial direction. Gas permeability curves are divided into three stages: a stable decline, a slow rise and a sharp rise. The gas permeability increases by 2-3 orders of magnitude after the brittle failure happens. The inflexion point of volume strain curve and the lateral strain curve can be used as an important reference to predict the change of permeability.
引文
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[15]王伟,徐卫亚,王如宾,等.低渗透岩石三轴压缩过程中的渗透性研究[J].岩石力学与工程学报,2015,34(1):40-47.WANG Wei,XU Wei-ya,WANG Ru-bin,et al.Permeability of dense rock under triaxial compression[J].Chinese Journal of Rock Mechanics and Engineering,2015,34(1):40-47.
[16]王环玲,徐卫亚,杨圣奇.岩石变形破坏过程中渗透率演化规律的试验研究[J].岩土力学,2006,27(10):1703-1708.WANG Huan-ling,XU Wei-ya,YANG Sheng-qi.Experimental investigation on permeability evolution law during course of deformation and failure of rock specimen[J].Rock and Soil Mechanics,2006,27(10):1703-1708.
[2]刘松.加卸载条件下花岗岩力学特性研究[D].昆明:昆明理工大学,2016.LIU Song.Research on mechanical properties of granite in cyclic loading tests[D].Kunming:Kunming University of Science and Technology,2016.
[3]EBERHARDT E,STEAD D,STIMPSON B.Quantifying progressive pre-peak brittle fracture damage in rock during uniaxial compression[J].International Journal of Rock Mechanics and Mining Sciences,1999,36(3):361-380.
[4]MARTIN C D,CHANDLER N A.The progressive fracture of lac du bonnet granite[J].International Journal of Rock Mechanics and Mining Sciences&Geomechanical Abstracts,1995,31(6):643-659.
[5]刘亚运,苗胜军,魏晓,等.三轴循环加卸载下花岗岩损伤的声发射特征及能量机制演化[J].矿业研究与开发,2016,36(6):68-72.LIU Ya-yun,MIAO Sheng-jun,WEI Xiao,et al.Acoustic emission characteristics and energy mechanism evolution of granite damage under triaxial cyclic loading and unloading[J].Mining Research and Development,2016,36(6):68-72.
[6]赵星光,李鹏飞,马利科,等.循环加、卸载条件下北山深部花岗岩损伤与扩容特性[J].岩石力学与工程学报,2014,33(9):1740-1748.ZHAO Xing-guang,LI Peng-fei,MA Li-ke,et al.Damage and dilation characteristics of deep granite at Beishan under cyclic loading-unloading conditions[J].Chinese Journal of Rock Mechanics and Engineering,2014,33(9):1740-1748.
[7]SOULEY M,HOMAND F,PEPA S,et al.Damageinduced permeability changes in granite:A case example at the URL in Canada[J].International Journal of Rock Mechanics and Mining Sciences,2001,38(2):297-310.
[8]陈亮,刘建锋,王春萍,等.压缩应力条件下花岗岩损伤演化特征及其对渗透性影响研究[J].岩石力学与工程学报,2014,33(2):287-295.CHEN Liang,LIU Jian-feng,WANG Chun-ping,et al.Investigation on damage evolution characteristic of granite under compressive stress condition and its impact on permeability[J].Chinese Journal of Rock Mechanics and Engineering,2014,33(2):287-295.
[9]胡少华,陈益峰,周创兵.北山花岗岩渗透特性试验研究与细观力学分析[J].岩石力学与工程学报,2014,33(11):2200-2209.HU Shao-hua,CHEN Yi-feng,ZHOU Chuang-bing.Laboratory test and mesomechanical analysis of permeability variation of Beishan granite[J].Chinese Journal of Rock Mechanics and Engineering,2014,33(11):2200-2209.
[10]BRACE W F,WALSH J B,FRANGOS W T,et al.Permeability of granite under high pressure[J].Journal of Geophysical Research,1968,73(6):2225-2236.
[11]许江,王维忠,杨秀贵,等.细粒砂岩在循环加、卸载条件下变形实验[J].重庆大学学报(自然科学版),2004,27(3):18-21.XU Jiang,WANG Wei-zhong,YANG Xiu-gui,et al.Experimental study on the deformation characteristic of fine-sandstone under the loading and unloading condition[J].Journal of Chongqing University(Natural Science Edition),2004,27(3):18-21.
[12]肖福坤,申志亮,刘刚,等.循环加卸载中滞回环与弹塑性应变能关系研究[J].岩石力学与工程学报,2014,33(9):1791-1797.XIAO Fu-kun,SHEN Zhi-liang,LIU Gang,et al.Relationship between hysteresis loop and elastoplastic strain energy during cyclic loading and unloading[J].Chinese Journal of Rock Mechanics and Engineering,2014,33(9):1791-1797.
[13]孔祥言.高等渗流力学[M].合肥:中国科学技术大学出版社,1999.KONG Xiang-yan.Advanced seepage mechanics[M].Hefei:University of Science and Technology of China Press,1999.
[14]胡大伟,朱其志,周辉,等.脆性岩石各向异性损伤和渗透率演化规律研究[J].岩石力学与工程学报,2008,27(9):1822-1827.HU Da-wei,ZHU Qi-zhi,ZHOU Hui,et al.Research on anisotropic damage and permeability evolutionary law for brittle rocks[J].Chinese Journal of Rock Mechanics and Engineering,2008,27(9):1822-1827.
[15]王伟,徐卫亚,王如宾,等.低渗透岩石三轴压缩过程中的渗透性研究[J].岩石力学与工程学报,2015,34(1):40-47.WANG Wei,XU Wei-ya,WANG Ru-bin,et al.Permeability of dense rock under triaxial compression[J].Chinese Journal of Rock Mechanics and Engineering,2015,34(1):40-47.
[16]王环玲,徐卫亚,杨圣奇.岩石变形破坏过程中渗透率演化规律的试验研究[J].岩土力学,2006,27(10):1703-1708.WANG Huan-ling,XU Wei-ya,YANG Sheng-qi.Experimental investigation on permeability evolution law during course of deformation and failure of rock specimen[J].Rock and Soil Mechanics,2006,27(10):1703-1708.