单轴–三轴和渗透水压条件下砂岩应变特性的CT试验研究
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摘要
常规的应力应变试验难以清晰地反映砂岩在不同应力状态下的细观应变特性,然而,砂岩细观应变特性对一些工程的影响是非常巨大的。通过螺旋CT机以及与其配套的实时三轴加载和渗透压力设备对砂岩进行各种应力状态下的应变特性试验,反映出不同应力状态下的砂岩的应变特性有很大不同。结合CT图像和CT数的分析,对砂岩应变过程中的孔隙率的变化能直观地进行计算,以及对CT数方差的分析,能较简单地判断出砂岩的应变特性以及破坏模式。研究结果表明:(1)在单轴和三轴压力作用下,砂岩CT数方差变化剧烈的地方发生脆性变化,而方差比较稳定的地方发生塑性变化;(2)当有渗透水流作用时,砂岩应变特性与干砂岩的应变特性有明显差异,峰值强度显著增大,残余强度也明显增加;(3)砂岩在单轴干燥状态下是发生脆性破坏,而在有渗透压力和围压的情况下发生的是塑性破坏,有围压而没有渗透压作用时的破坏介于两者之间。
Understanding the deformation and fracturing processes is a key problem for rock engineering and earthquake prediction.Experimental rock deformation studies and structural analysis of exhumed fault zones have been used to investigate the mechanism of faulting and to develop models of fault evolution.Through the study which is based on devices including the multislice spiral CT(MSCT) and real-time loading machine and seepage machine,the strain properties of sandstone under uniaxial-triaxial compressive and seepage pressure conditions are found to be different from each other.With integrated analysis of CT images and CT number,the porosity randomly distributed in the stress process is calculated.Through the variant analysis of CT numbers,it is easy to know the strain properties and cracking patterns.When the variance of CT number is increasing rapidly,the strain and cracking pattern of sandstone is brittle.If the variance of CT number is stable or declines linearly slowly,the deformation and failure modes of sandstone are plastic.The strain properties under seepage pressure are different from others.The peak strength and residual strength of a sandstone increases remarkably under seepage pressure conditions.The dry sandstone crack is brittle under uniaxial compressive condition.When the compressive conditions are with seepage pressure and triaxial compression,the crack is on plasticity.With triaxial compressive without seepage pressuret,he crack pattern is between the two patterns above.So,X-ray CT is a useful method for the study of the strain properties of sandstone under uniaxial-triaxial compressive and seepage pressure conditions.
Understanding the deformation and fracturing processes is a key problem for rock engineering and earthquake prediction.Experimental rock deformation studies and structural analysis of exhumed fault zones have been used to investigate the mechanism of faulting and to develop models of fault evolution.Through the study which is based on devices including the multislice spiral CT(MSCT) and real-time loading machine and seepage machine,the strain properties of sandstone under uniaxial-triaxial compressive and seepage pressure conditions are found to be different from each other.With integrated analysis of CT images and CT number,the porosity randomly distributed in the stress process is calculated.Through the variant analysis of CT numbers,it is easy to know the strain properties and cracking patterns.When the variance of CT number is increasing rapidly,the strain and cracking pattern of sandstone is brittle.If the variance of CT number is stable or declines linearly slowly,the deformation and failure modes of sandstone are plastic.The strain properties under seepage pressure are different from others.The peak strength and residual strength of a sandstone increases remarkably under seepage pressure conditions.The dry sandstone crack is brittle under uniaxial compressive condition.When the compressive conditions are with seepage pressure and triaxial compression,the crack is on plasticity.With triaxial compressive without seepage pressuret,he crack pattern is between the two patterns above.So,X-ray CT is a useful method for the study of the strain properties of sandstone under uniaxial-triaxial compressive and seepage pressure conditions.
引文
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[20]丁卫华,仵彦卿,蒲毅彬,等.低应变率下岩石内部裂纹演化的X射线CT方法[J].岩石力学与工程学报,2003,22(11):1 793–1 797.(Ding Weihua,Wu Yanqing,Pu Yibin,et al.X-ray CT approach on rock interior crack evolution under low strain rate[J].Chinese Journal of Rock Mechanics and Engineering,2003,22(11):1 793–1 797.(in Chinese))
[2]刘力强,马胜利,马瑾,等.岩石构造对声发射统计特征的影响[J].地震地质,1999,21(4):377–386.(Liu Liqiang,Ma Shengli,Ma Jin,et al.Effect of rock structure on statistic characteristics of acoustic emission[J].Seismology and Geology,1999,21(4):377–386.(in Chinese))
[3]Ohnaka M,Mogi K.Frequency characteristics of acoustic emission in rocks under uniaxial compression and its relation to the fracturing process to failure[J].J.Geophys.Res.,1982,87:3 873–3 884.
[4]杨更社,谢定义,张长庆,等.岩石损伤特性的CT识别[J].岩石力学与工程学报,1996,15(1):48–54.(Yang Gengshe,Xie Dingyi,Zhang Changqing,et al.CT identification of rock damage properties[J].Chinese Journal of Rock Mechanics and Engineering,1996,15(1):48–54.(in Chinese))
[5]杨更社.岩石细观损伤力学特性及本构关系的CT识别[J].煤炭学报,2000,25(增):102–106.(Yang Gengshe.CT identification on the meso-damage mechanic characters and constitutive relation of rock[J].Journal of China Coal Society,2000,25(Supp.):102–106.(in Chinese))
[6]杨更社.三轴受力状态下岩石损伤扩展力学特性研究[J].西安科技学院学报,2000,20(2):101–104.(Yang Gengshe.On the mechanic characteristics of damage propagation of rock under triaxial stress condition[J].Journal of Xi′an University of Science and Technology,2000,20(2):101–104.(in Chinese))
[7]任建喜,葛修润,蒲毅彬.岩石破坏全过程的CT细观损伤演化机理动态分析[J].西安公路交通大学学报,2000,20(2):12–15.(Ren Jianxi,Ge Xiurun,Pu Yibin.CT real-time analysis of meso-damage propagation law of the whole process of rock failure[J].Journal of Xi′an Highway University,2000,20(2):12–15.(in Chinese))
[8]葛修润,任建喜,蒲毅彬,等.岩石细观损伤扩展规律的CT实时试验[J].中国科学(E辑),2000,30(2):104–111.(Ge Xiurun,Run Jianxi,Pu Yibin,et al.CT real-time test of the propagation law of meso-damage in rock[J].Science in China(Series E),2000,30(2):104–111.(in Chinese))
[9]仵彦卿,丁卫华.单轴条件下砂岩三维破裂过程的CT观测[J].工程地质学报,2002,10(1):93–97.(Wu Yanqing,Ding Weihua.X-ray CT observation on three-dimensional fracturing process of sandstone specimen under uniaxial condition[J].Journal of Engineering Geology,2002,10(1):93–97.(in Chinese))
[10]仵彦卿,丁卫华,蒲毅彬,等.压缩条件下岩石密度损伤增量的CT动态观测[J].自然科学进展,2000,10(9):830–835.(Wu Yanqing,Ding Weihua,Pu Yibin,et al.CT real-time observation on the density damage increment in rock under compressive condition[J].Progress in Natural Science,2000,10(9):830–835.(in Chinese))
[11]丁卫华,仵彦卿,蒲毅彬,等.CT技术应用于岩石实验动态观测的新进展[J].冰川冻土,2000,22(3):218–222.(Ding Weihua,Wu Yanqing,Pu Yibin,et al.New progress in real-time detecting of geotechnical experiment by use of X-ray computed tomography[J].Journal of Glaciology and Geocryology,2000,22(3):218–222.(in Chinese))
[12]Withjack E M.Computerized tomography for rock property determination and fluid flow visualization[J].Society of Petroleum Engineers Formation Evaluation,1988,3(4):696–704.
[13]Klobes P,Riesemier H,Meyer K,et al.Rock porosity determination by combination of X-ray computerized tomography with mercury porosimetry Fresenius[J].Journal of Analytical Chemistry,1997,357:543–547.
[14]Doi N,Kato O,Sakagawa Y,et al.Uchida,T.Characterization of fracture and rock property of the Kakkonda granite by FMI and other loggings[J].Journal of the Geothermal Research Society,1998,20:34–35.
[15]Ohtani T,Nakashima Y,Muraoka H.Three-dimensional miarolitic cavity distribution in the Kakkonda granite from borehole WD–1a using X-ray computerized tomography[J].Engineering Geology,2000,56:1–9.
[16]Wildenschild D,Hopmans J W,Waz C M P,et al.Using X-ray computed tomography in hydrology:systems,resolutions,and limitations[J].Journal of Hydrology,2002,267:285–297.
[17]Goodwin A K,O′Nell M A,Anderson W F.The use of X-ray computer topography to investigate particulate interactions within opencast coal mine backfills[J].Engineering Geology,2003,70:331–341.
[18]International Organization for Standardization.Non-destructive Testing—Radiation Methods—Computed Tomography:Part 1.Principles[M].Geneva,Switzerland:[s.n.],2000.
[19]Hounsfield G N.Computerized transverse axial scanning(tomography):1.description of system[J].British Journal of Radiology,1973,46:1 016–1 022.
[20]丁卫华,仵彦卿,蒲毅彬,等.低应变率下岩石内部裂纹演化的X射线CT方法[J].岩石力学与工程学报,2003,22(11):1 793–1 797.(Ding Weihua,Wu Yanqing,Pu Yibin,et al.X-ray CT approach on rock interior crack evolution under low strain rate[J].Chinese Journal of Rock Mechanics and Engineering,2003,22(11):1 793–1 797.(in Chinese))
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