基于数字图像技术的砂土液化可视化动三轴试验研究
摘要
常规动三轴试验不能实现试样细观结构的观测,对原有CKC型振动三轴仪实施可视化改进,开发用于试验过程试样细观结构观测的试验系统。在砂土振动液化试验中,利用显微数码摄录技术全程动态摄录整个试验过程砂土细观结构的变化,从摄录录像中提取特征时刻的数字图像照片,导入自主开发的数字图像细观结构分析软件DeoDIP,对比分析液化前后砂土细观结构(颗粒定向性、接触法向、接触数)的演化规律,追踪标志砂颗粒的运动轨迹。结果表明:液化时,颗粒长轴没有明显的优选方向,制样引起的初始各向异性被消除;接触法向呈现各向异性特征,其主方向在整个试验过程中一直偏于竖直方向;平均接触数发生了损失,液化排水后得到恢复,说明试样振动密实。液化前,各标志颗粒具有基本相同的运动轨迹,颗粒运动以平动为主,旋转作用很小,颗粒运动与试样变形保持较好的整体性;颗粒之间相对运动加剧,颗粒之间不断接触分离,部分颗粒出现悬浮现象,且颗粒旋转明显。可视化三轴试验结果不仅有助于研究砂土液化的细观力学机理,并能为液化细观数值模拟提供试验基础。
A modified CKC cyclic triaxial apparatus is used to monitor the evolution of granular soil microstructures during cyclic triaxial tests.Micro digital screening techniques are used to capture the change of microstructures of sand samples during liquefaction induced by cyclic loading.Digital images at certain stages of the tests are cut from the videos and further processed by self-developed software named GeoDIP.The microfabric evolutions including particle orientation,contact normal and number of contacts are analyzed.Labeled particles are traced to study the micro mechanism of soil deformation.It is found that there is no preferred orientation of the long axes of particles in liquefied samples.The main direction of contact normal between particles orients vertically whether the sample is liquefied or not.The samples experience a significant loss of contact number during liquefaction,but the number regains a lot after post-liquefaction drainage.Soil particles exhibit obvious translational motion before liquefaction,but start to move relatively and rotate when liquefaction occurs.The results of this study can not only explore the micro mechanism of sand liquefaction,but also provide an experimental basis for numerical modeling of sand liquefaction.
A modified CKC cyclic triaxial apparatus is used to monitor the evolution of granular soil microstructures during cyclic triaxial tests.Micro digital screening techniques are used to capture the change of microstructures of sand samples during liquefaction induced by cyclic loading.Digital images at certain stages of the tests are cut from the videos and further processed by self-developed software named GeoDIP.The microfabric evolutions including particle orientation,contact normal and number of contacts are analyzed.Labeled particles are traced to study the micro mechanism of soil deformation.It is found that there is no preferred orientation of the long axes of particles in liquefied samples.The main direction of contact normal between particles orients vertically whether the sample is liquefied or not.The samples experience a significant loss of contact number during liquefaction,but the number regains a lot after post-liquefaction drainage.Soil particles exhibit obvious translational motion before liquefaction,but start to move relatively and rotate when liquefaction occurs.The results of this study can not only explore the micro mechanism of sand liquefaction,but also provide an experimental basis for numerical modeling of sand liquefaction.
引文
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[2]ODA M.Initial fabrics and their relations to mechanical properties of granular materials[J].Soils and Foundations,1972,12(1):17–36.
[3]沈珠江.土体结构性的数学模型-21世纪土力学的核心问题[J].岩土工程学报,1996,18(1):95–97.(SHEN Zhu-jiang.Mathematical modeling of structured soil-the key problem of soil mechanics in new century[J].Chinese Journal of Geotechnical Engineering.1996,18(1):95–97.(in Chinese))
[4]IBRAHIM A A,KAGAWA I.Microscopic measurement of sand fabric from cyclic tests causing liquefaction[J].Geotechnical Testing Journal,1991,14(4):371–382.
[5]孟祥跃,张均锋,谈庆明,等.冲击载荷下饱和砂土中流动和破坏的X光观测[J].岩石力学与工程学报,2002,21(6):803–807.(MENG Xiang-yue,ZHANG Jun-feng,TAN Qing-ming,et al.X-ray observation on flow and failure of saturated sand under impact loading[J].Chinese Journal of Rock Mechanics and Engineering,2002,21(6):803–807.(in Chinese))
[6]王庶懋,高玉峰.砂土与EPS颗粒混合的轻质土(LSES)细观结构的CT研究[J].岩土力学,2006,27(12):2137–2142.(WANG Shu-mao,GAO Yu-feng.Research on meso-structure of lightweight sand-EPS beads soil(LSES)using CT[J].Rock and Soil Mechanics,2006,27(12):2137–2142.(in Chinese))
[7]NG T T,WANG C M.Comparison of a 3-D DEM simulation with MRI data[J].International Journal for Numerical and Analytical Methods in Geomechanics,2001,25(5):497–507.
[8]WHITE D J,TAKE W A,BOLTON M D.Measuring soil deformation in geotechnical models using digital images and PIV analysis[C]//10th International Conference on Computer Methods and Advances in Geotechanics.Tucson,2001:997–1002.
[9]ALSHIBLI K A,STURE S.Sand shear band thickness measurements by digital imaging techniques[J].Journal of Computing in Civil Engineering,1999,13(2):103–109.
[10]张连卫,张建民,张嘎.基于数字图像的粒状材料细观组构特征分析技术[J].岩土工程学报,2008,30(10):1555–1559.(ZHANG Lian-wei,ZHANG Jian-min,ZHANG ga.Microfabric analysis technique for granular materials based on digital images[J].Chinese Journal of Geotechnical Engineering,2008,30(10):1555–1559.(in Chinese))
[11]李元海,靖洪文,曾庆有.岩土工程数字照相量测软件系统研发与应用[J].岩石力学与工程学报,2006,25(增刊2):3859–3866.(LI Yuan-hai,JING Hong-wen,ZENG Qing-you.Development and application of digital photogrammetry software package for geotechnical engineering[J].Chinese Journal of Rock Mechanics and Engineering,2006,25(S2):3859–3866.(in Chinese))
[12]洪宝宁,胡昕,周宇泉,等.三轴应力下黏性土微细结构试验[J].水利水电科技进展,2006,26(6):47–50.(HONG Bao-ning,HU Xin,ZHOU Yu-quan,et al.Experimental study on microstructure of cohesive soil under triaxial stress[J].Advances in Science and Technology of Water Resources,2006,26(6):47–50.(in Chinese))
[13]邵龙潭,孙益振,王助贫,等.数字图像测量技术在土工三轴试验中的应用研究[J].岩土力学,2006,27(1):29–34.(SHAO Long-tan,SUN Yi-zhen,WANG Zhu-pin,et al.Application of digital image processing technique to triaxial test in soil mechanics[J].Rock and Soil Mechanics,2006,27(1):29–34.(in Chinese))
[14]周健,余荣传,贾敏才.基于数字图像技术的砂土模型试验细观结构参数测量[J].岩土工程学报,2006,28(12):2047–2052.(ZHOU Jian,YU Rong-chuan,JIA Min-cai.Measurement of microstructure parameters for granular soil model using digital image technology[J].Chinese Journal of Geotechnical Engineering,2006,28(12):2047–2052.(in Chinese))
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