水力作用下砂岩三轴卸荷试验及破裂特性研究
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摘要
高应力、高水压卸荷条件下岩石的非连续性微缺陷演化过程研究对揭示隧道围岩裂纹的起裂孕育、碎胀裂化和峰值破坏,分析围岩稳定性具有重要意义。利用MTS815型程控伺服刚性试验机开展了砂岩在固定围压、不同水压条件下的水力三轴卸荷试验。试验结果表明:岩石变形在卸荷前以压缩为主,变化微小;卸荷后不久开始快速扩容,直至损伤破裂。水力条件下应力–应变曲线上的各个特征应力值比无水压条件下的饱和试样有不同程度地提高,增加了应变能储备,从初始扩容到峰值强度的历时更短,曲线斜率更陡。随着水压的不断增大,各个特征应力值有所减小,表现在起裂条件降低,压缩极限减小,扩容时间提前,表明了砂岩在高水压条件下的脆性特性进一步增强,抵抗变形破坏的能力逐渐降低。通过扩容特征值与扩容点后的体应变关系,求得初始扩容点后的相对扩容应变与变形模量差,建立了多项式回归关系。研究结论揭示了水力作用下砂岩扩容变形行为的强烈性和突发性,可为水–力双场条件下的围岩变形预测及控制提供参考。
The strong and sudden properties of the bulking and deformation behaviors of the sandstones under the hydro-mechanical(H-M) function are studied. The evolution of micro-defects under high geo-stress and hydraulic coupling conditions are critically important to reveal different stages of the micro-cracks evolving from the initiation to the failure and to evaluate the stability of the surrounding rocks. The MTS815 rock mechanical system is used to test sandstone samples collected from Bamiao Tunnel in Sichuan of China, and the H-M coupling experiment is performed under the fixed confining pressure and varied hydraulic pressure. The findings reveal that the rock deformation is compressive before unloading, though the change is small. However, rapid dilatancy proceeds to the failure stages shortly after the unloading. The stress-strain curves under H-M coupling conditions are generally higher than those without hydraulic pressure, implying that the strain energy is enhanced. In addition, the experienced time lasts shorter from the initial dilatancy point to the peak, and the slope of the curves becomes steeper. Furthermore, with the increase of the hydraulic pressure, the key characteristic stress decreases, which is reflected under lower fracture initiation conditions, reduced compression limits and advanced bulking time. Accordingly, the brittle characteristics of the sandstones are further enhanced while the ability to resist deformation and failure gradually decreases. Finally, a polynomial regression relationship is established by calculating the relative expansion strains after the initial expansion points and their corresponding deformation modulus difference values. In conclusion, the findings of this study may provide advices for the forecast and control of the deformation of the surrounding rocks under multi-conditions.
The strong and sudden properties of the bulking and deformation behaviors of the sandstones under the hydro-mechanical(H-M) function are studied. The evolution of micro-defects under high geo-stress and hydraulic coupling conditions are critically important to reveal different stages of the micro-cracks evolving from the initiation to the failure and to evaluate the stability of the surrounding rocks. The MTS815 rock mechanical system is used to test sandstone samples collected from Bamiao Tunnel in Sichuan of China, and the H-M coupling experiment is performed under the fixed confining pressure and varied hydraulic pressure. The findings reveal that the rock deformation is compressive before unloading, though the change is small. However, rapid dilatancy proceeds to the failure stages shortly after the unloading. The stress-strain curves under H-M coupling conditions are generally higher than those without hydraulic pressure, implying that the strain energy is enhanced. In addition, the experienced time lasts shorter from the initial dilatancy point to the peak, and the slope of the curves becomes steeper. Furthermore, with the increase of the hydraulic pressure, the key characteristic stress decreases, which is reflected under lower fracture initiation conditions, reduced compression limits and advanced bulking time. Accordingly, the brittle characteristics of the sandstones are further enhanced while the ability to resist deformation and failure gradually decreases. Finally, a polynomial regression relationship is established by calculating the relative expansion strains after the initial expansion points and their corresponding deformation modulus difference values. In conclusion, the findings of this study may provide advices for the forecast and control of the deformation of the surrounding rocks under multi-conditions.
引文
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[13]ROBERT L K.Microcracks in rocks:areview[J].Tectonophysics,1983,100(3):449–480.
[14]黄书岭.高应力下脆性岩石的力学模型与工程应用研究[D].武汉:中国科学院武汉岩土力学研究所,2008.(HUANG Shu-ling.Study on mechanical model of brittle rock under high stress condition and its engineering applications[D].Wuhan:Institute of Rock and Soil Mechanics,Chinese Academy of Sciences,2008.(in Chinese))
[15]BRACE W F,PAULDING B,SCHOLZ C.Dilatancy in the fracture of crystalline rocks[J].Geophys Res,1966,71:3939–3953.
[16]黄伟,沈明荣,张清照.高围压下岩石卸荷的扩容性质及其本构模型研究[J].岩石力学与工程学报,2010,29(增刊2):3475–3481.(HUANG Wei,SHEN Ming-rong,ZHANG Qing-zhao.Study of unloading dilatancy property of rock and its constitutive model under high confining pressure[J].Chinese Journal of Rock Mechanics and Engineering,2010,29(S2):3475–3481.(in Chinese))
[2]李根,唐春安,李连崇.水岩耦合变形破坏过程及机理研究进展[J].力学进展,2012,42(5):593–619.(LI Gen,TANG Chun-an,LI Lian-chong.Advances in rock deformation and failure process under water-rock coupling[J].Advances in Mechanics,2012,42(5):593–619.(in Chinese))
[3]刘冬梅,蔡美峰,周玉斌,等.岩石裂纹扩展过程的动态监测研究[J].岩石力学与工程学报,2006,25(3):467–472.(LIU Dong-mei,CAI Mei-feng,ZHOU Yu-bin,et al.Dynamic monitoring on developing process of rock cracks[J].Chinese Journal of Rock Mechanics and Engineering,2006,25(3):467–472.(in Chinese))
[4]卢兴利,刘泉声,苏培芳.考虑扩容碎胀特性的岩石本构模型研究与验证[J].岩石力学与工程学报,2013,32(9):1886–1893.(LU Xing-li,LIU Quan-sheng,SU Pei-fang.Constitutive model of rocks considering dilatancy–bulking behavior and its calibration[J].Chinese Journal of Rock Mechanics and Engineering,2013,32(9):1886–1893.(in Chinese))
[5]李海波,赵坚,李俊如,等.基于裂纹扩展能量平衡的花岗岩动态本构模型研究[J].岩石力学与工程学报,2003,22(10):1683–1688.(LI Hai-bo,ZHAO Jian,LI Jun-ru,et al.Study on constitutive relation of rock under dynamic compression based on energy balance during crack growth[J].Chinese Journal of Rock Mechanics and Engineering,2003,22(10):1683–1688.(in Chinese))
[6]李海波,赵坚,李俊如,等.三轴情况下花岗岩动态力学特性的实验研究[J].爆炸与冲击,2004,24(5):470–474.(LI Hai-bo,ZHAO Jian,LI Jun-ru,et al.Triaxial compression tests of a granite[J].Explosion and Shock Waves,2004,24(5):470–474.(in Chinese))
[7]陈国庆,冯夏庭,江权,等.考虑岩体劣化的大型地下厂房围岩变形动态监测预警方法研究[J].岩土力学,2010,31(9):3012–3018.(CHEN Guo-qing,FENG Xia-ting,JIANG Quan,et al.Study of dynamic early warning method of surrounding rock deformation monitoring for large underground powerhouse considering rock degradation[J].Rock and Soil Mechanics,2010,31(9):3012–3018.(in Chinese))
[8]GRIFFITH A A.The phenomena of rupture and flow in solids[J].Philos Trans R Soc Lond,1921,221A:163–198.
[9]GRIFFITH A A.Theory of rupture[C]//Proceedings of the 1st International Congress on Applied Mechanics.Delft:Technology Boekhandelen Drukkerij,1924:55–63.
[10]吴刚,孙钧.卸荷应力状态下裂隙岩体的变形和强度特性[J].岩石力学与工程学报,1998,17(6):615–621.(WU Gang,SUN Jun.Deformation and strength characters of jointed rock mass under unloading stress states[J].Chinese Journal of Rock Mechanics and Engineering,1998,17(6):615–621.(in Chinese))
[11]李天斌.汶川特大地震中山岭隧道变形破坏特征及影响因素分析[J].工程地质学报,2008,16(6):742–750.(LI Tian-bin.Failure characteristics and influence factor analysis of mountain tunnel at epicenter zones of great Wenchuan Earthquake[J].Journal of Engineering Geology,2008,16(6):742–750.(in Chinese))
[12]吉小明,杨春和,白世伟.岩体结构与岩体水力耦合计算模型[J].岩土力学,2006,27(5):763–768.(JI Xiao-ming,YANG Chun-he,BAI Shi-wei.Structure and hydromechanical coupled calculation model for rock mass[J].Rock and Soil Mechanics,2006,27(5):763–768.(in Chinese))
[13]ROBERT L K.Microcracks in rocks:areview[J].Tectonophysics,1983,100(3):449–480.
[14]黄书岭.高应力下脆性岩石的力学模型与工程应用研究[D].武汉:中国科学院武汉岩土力学研究所,2008.(HUANG Shu-ling.Study on mechanical model of brittle rock under high stress condition and its engineering applications[D].Wuhan:Institute of Rock and Soil Mechanics,Chinese Academy of Sciences,2008.(in Chinese))
[15]BRACE W F,PAULDING B,SCHOLZ C.Dilatancy in the fracture of crystalline rocks[J].Geophys Res,1966,71:3939–3953.
[16]黄伟,沈明荣,张清照.高围压下岩石卸荷的扩容性质及其本构模型研究[J].岩石力学与工程学报,2010,29(增刊2):3475–3481.(HUANG Wei,SHEN Ming-rong,ZHANG Qing-zhao.Study of unloading dilatancy property of rock and its constitutive model under high confining pressure[J].Chinese Journal of Rock Mechanics and Engineering,2010,29(S2):3475–3481.(in Chinese))
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