水与微观结构对片岩波速各向异性特征的影响及其机制研究
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摘要
选取3类不同宏观特征的武当群片岩岩样,分别制取不同片理角的标准圆柱试样。采用波速测试获取烘干、浸水处理后的试样的纵波速度,分析不同含水状态下武当群片岩波速各向异性特征,并结合偏光显微镜、扫描电镜下3类岩样的矿物组成与微观结构特征,探讨内外影响因素下的波速各向异性机制。结果显示:武当群片岩主要矿物为硬质粒状石英、长石与软质片状白云母,硬质矿物含量越高、孔隙率越小,则片岩纵波速度越大,反之越小;干燥样的纵波速度表现出显著各向异性,传播方向由垂直片理面向平行片理面变换时,波速逐渐增大,不同方向的波速值可用波速圆公式进行预测;波速各向异性本质上是微裂隙的定向展布、间隔分布的结果,可间接用白云母定向系数δ_2评价各向异性程度k,k~(1/2)与δ_2呈线性正相关,武当群片岩的k值上限为2.90;浸水后试样的纵波速度普遍增大,这是水充填空隙后对片岩等效体积模量的增加起主控作用的结果,片岩吸水后的波速增长效应受其孔隙率与微裂隙分布特征影响,引起不同类片岩间的纵波速度差异,导致同类片岩的波速各向异性程度与浸水时长呈负相关。
Three types of Wudang group schist with different macroscopic characteristics were selected to make the standard cylindrical test specimens possessing different schistosity angles. Firstly, P-wave velocity of the specimens were tested after dried and soaked to investigate the velocity anisotropy of Wudang group schist in different water bearing states. Then, combined with mineral composition and microstructure characteristics of three kinds of schist obtained by polarizing microscope and scanning electron microscopy, he wave velocity anisotropy affected by internal and external factors were further investigated. The results indicate that the major minerals of Wudang group schist are hard granular quartz, feldspar and soft muscovite. The higher content of hard mineral or the smaller porosity of schist, the larger P-wave velocity and vice versa. The P-wave velocity of dry samples shows significant anisotropy. As the angle between the direction of wave propagation and foliation decreases, the wave velocity increases gradually.Wave velocity in different directions can be predicted by the formula expressed as wave velocity circle. The wave velocity anisotropy is essentially caused by the directional and the interval distribution of micro fissures, of which the degree k can be evaluated indirectly through the orientation coefficient δ_2 of muscovite. There is a linear positive correlation between k~(1/2) and δ_2, and the upper limit of the p-wave anisotropy of the Wudang group schist is 2.90. Due to the increase of the equivalent volume modulus of schist after the pores filled by water, the P-wave velocity of the soaking sample is generally increased. And the increasing effect of velocity depends greatly on the porosity and distribution of micro fissures, leading to the difference of P-wave velocity among different kinds of schists and a inverse correlation between the anisotropy degree of wave velocity for the same kind of schist and the soaking time.
Three types of Wudang group schist with different macroscopic characteristics were selected to make the standard cylindrical test specimens possessing different schistosity angles. Firstly, P-wave velocity of the specimens were tested after dried and soaked to investigate the velocity anisotropy of Wudang group schist in different water bearing states. Then, combined with mineral composition and microstructure characteristics of three kinds of schist obtained by polarizing microscope and scanning electron microscopy, he wave velocity anisotropy affected by internal and external factors were further investigated. The results indicate that the major minerals of Wudang group schist are hard granular quartz, feldspar and soft muscovite. The higher content of hard mineral or the smaller porosity of schist, the larger P-wave velocity and vice versa. The P-wave velocity of dry samples shows significant anisotropy. As the angle between the direction of wave propagation and foliation decreases, the wave velocity increases gradually.Wave velocity in different directions can be predicted by the formula expressed as wave velocity circle. The wave velocity anisotropy is essentially caused by the directional and the interval distribution of micro fissures, of which the degree k can be evaluated indirectly through the orientation coefficient δ_2 of muscovite. There is a linear positive correlation between k~(1/2) and δ_2, and the upper limit of the p-wave anisotropy of the Wudang group schist is 2.90. Due to the increase of the equivalent volume modulus of schist after the pores filled by water, the P-wave velocity of the soaking sample is generally increased. And the increasing effect of velocity depends greatly on the porosity and distribution of micro fissures, leading to the difference of P-wave velocity among different kinds of schists and a inverse correlation between the anisotropy degree of wave velocity for the same kind of schist and the soaking time.
引文
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[15]邓涛,韩文峰,保翰璋.饱水大理岩的波速变化特性研究[J].岩石力学与工程学报,2000,19(6):762-765.DENG Tao,HAN Wen-feng,BAO Han-zhang.The characteristics of wave velocity variations for marbles saturated in water[J].Chinese Journal of Rock Mechanics and Engineering,2000,19(6):762-765.
[16]李楠,张新,王达轩,等.煤样吸水全过程纵波波速变化规律及波形特征实验研究[J].岩石力学与工程学报,2017,36(8):1921-1929.LI Nan,ZHANG Xin,WANG Da-xuan,et al.Experimental study on the variation of P-wave velocity and waveform characteristics during the whole process of water absorption of coal samples[J].Chinese Journal of Rock Mechanics and Engineering,2017,36(8):1921-1929.
[17]尹晓萌.武当群片岩的各向异性研究及其在隧道支护中的应用[D].武汉:中国地质大学,2017.YIN Xiao-meng.The anisotropy of Wudang group schist and its application in tunnel support[D].Wuhan:China University of Geosciences,2017.
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[20]卜靖.不同含水率红砂岩单轴受压状态下超声波参数变化规律研究[D].徐州:中国矿业大学,2016.BO Jing.Study on the variation of ultrasonic parameters of red sandstone with different water content under uniaxial compression[D].Xuzhou:China University of Mining and Technology,2016.
[2]席道瑛,陈林,张涛.砂岩的变形各向异性[J].岩石力学与工程学报,1995,14(1):49-58.XI Dao-ying,CHEN Lin,ZHANG Tao.Anisotropic deformation of sandstone[J].Chinese Journal of Rock Mechanics and Engineering,1995,14(1):49-58.
[3]席道瑛,陈林.岩石各向异性参数研究[J].物探化探计算技术,1994,16(1):16-21.XI Dao-ying,CHEN Lin.On anisotropism of rock in geophysics[J].Computing Techniques for Geophysical and Geochemical Exploration,1994,16(1):16-21.
[4]姚增,丁梧秀,王俊杰.黄河上游某坝基岩体弹性波速的各向异性与归一化研究[J].地质灾害与环境保护,1996,7(2):38-43.YAO Zeng,DING Wu-xiu,WANG Jun-iie.A study on anisotropy and normalization of the rockmass elastic wave velocity in a dam foundation at the upper reach of Yellow River[J].Journal of Geological Hazards and Environment Preservation,1996,7(2):38-43.
[5]邓涛,杨林德.各向异性岩石纵、横波的波速比特性研究[J].岩石力学与工程学报,2006,25(10):2023-2029.DENG Tao,YANG Lin-de.Characteristics of velocity ratio of P-wave and S-wave for anisotropic rocks[J].Chinese Journal of Rock Mechanics and Engineering,2006,25(10):2023-2029.
[6]RAI C S,HANSON K E.Shear-wave velocity anisotropy in sedimentary rocks:a laboratory study[J].Geophysics,1988,53(6):800-812.
[7]尹志恒,狄帮让,魏建新,等.裂缝参数对纵波能量衰减影响的物理模型研究[J].石油地球物理勘探,2012,47(5):728-734.YIN Zhi-heng,DI Bang-rang,WEI Jian-xin,et al.Study on the physical model of the effect of crack parameters on the energy attenuation of P-wave[J].Oil Geophysical Prospecting,2012,47(5):728-734.
[8]李维新,史謌,王红,等.岩石物理弹性参数规律研究[J].地球物理学进展,2007,22(5):1380-1385.LI Wei-xin,SHI Ge,WANG Hong,et al.The study on the relationships of elastic properties of rock physics[J].Progress in Geophysics,2007,22(5):1380-1385.
[9]刘洪文.济阳坳陷岩石密度与纵波速度的关系[J].油气地质与采收率,2008,15(6):26-28.LIU Hong-wen.The relationship between the rock density and the longitudinal wave velocity in the Jiyang depression[J].Petroleum Geology and Recovery Efficiency,2008,15(6):26-28.
[10]唐杰,郭渊,孙成禹,等.碳酸盐岩波速与弹性模量变化规律试验研究[J].中国石油大学学报(自然科学版),2012,36(5):62-66.TANG Jie,GUO Yuan,SUN Cheng-yu,et al.Experiment study of wave velocity and elastic modules variation characteristics for carbonates[J].Journal of China University of Petroleum(Edition of Natural Science),2012,36(5):62-66.
[11]WYLLIE M R J,GREGORY A R,GARDNER L W.Elastic wave velocities in heterogeneous and porous media[J].Geophysics,1956,21(1):41-70.
[12]KAHRAMAN S.The correlations between the saturated and dry P-wave velocity of rocks[J].Ultrasonics,2007,46(4):341-348.
[13]邓华锋,原先凡,李建林,等.饱水度对砂岩纵波波速及强度影响的试验研究[J].岩石力学与工程学报,2013,32(8):1625-1631.DENG Hua-feng,YUAN Xian-fan,LI Jian-lin,et al.Experimental research on influence of saturation degree on sandstone longitudinal wave velocity and strength[J].Chinese Journal of Rock Mechanics and Engineering,2013,32(8):1625-1631.
[14]孟召平,刘常青,贺小黑,等.煤系岩石声波速度及其影响因素实验分析[J].采矿与安全工程学报,2008,25(4):389-393.MENG Zhao-ping,LIU Chang-qing,HE Xiao-hei,et al.Experimental research on acoustic wave velocity of coal measures rocks and its influencing factors[J].Journal of Mining&Safety Engineering,2008,25(4):389-393.
[15]邓涛,韩文峰,保翰璋.饱水大理岩的波速变化特性研究[J].岩石力学与工程学报,2000,19(6):762-765.DENG Tao,HAN Wen-feng,BAO Han-zhang.The characteristics of wave velocity variations for marbles saturated in water[J].Chinese Journal of Rock Mechanics and Engineering,2000,19(6):762-765.
[16]李楠,张新,王达轩,等.煤样吸水全过程纵波波速变化规律及波形特征实验研究[J].岩石力学与工程学报,2017,36(8):1921-1929.LI Nan,ZHANG Xin,WANG Da-xuan,et al.Experimental study on the variation of P-wave velocity and waveform characteristics during the whole process of water absorption of coal samples[J].Chinese Journal of Rock Mechanics and Engineering,2017,36(8):1921-1929.
[17]尹晓萌.武当群片岩的各向异性研究及其在隧道支护中的应用[D].武汉:中国地质大学,2017.YIN Xiao-meng.The anisotropy of Wudang group schist and its application in tunnel support[D].Wuhan:China University of Geosciences,2017.
[18]VOIGT W.Lehrbuch der Kristallphysik[M].Leipzig:Teubner-Verlag,1910.
[19]陈超,楼章华,金爱民.饱和水与干燥碳酸盐岩声波各向异性研究[J].岩性油气藏,2017,29(4):131-137.CHEN Chao,LOU Zhang-hua,JIN Ai-min.Acoustic anisotropy of water-saturated and desiccated carbonate rocks[J].Lithologic Reservoirs,2017,29(4):131-137.
[20]卜靖.不同含水率红砂岩单轴受压状态下超声波参数变化规律研究[D].徐州:中国矿业大学,2016.BO Jing.Study on the variation of ultrasonic parameters of red sandstone with different water content under uniaxial compression[D].Xuzhou:China University of Mining and Technology,2016.