南京粉砂三轴压缩过程中的三维孔隙结构演化特征
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摘要
砂土三轴剪切过程中细观孔隙结构演化与其宏观力学性质之间存在着紧密联系。基于南京大学自主研发的微型三轴仪,对南京粉砂试样进行了三轴剪切试验,利用显微CT扫描,获得了加载过程中试样的三维孔隙结构演化特征。结果表明:试样表现出应变软化-硬化型的应力-应变关系曲线;端部摩擦阻碍试样体积膨胀,发生鼓形区状破坏;试样整体体孔隙率从初始的46.3%减小到40.9%,后增大到43.0%附近,且试样破坏区孔隙率显著增大;统计区状破坏区表征单元体孔隙参数,发现破坏前孔隙被压密消失,孔隙数量减少32.4%,平均孔隙半径减小48.8%,导致孔隙半径分布趋于集中,破坏后破坏区域内出现大量大半径的孔隙;颗粒间错动导致颗粒棱角破碎,使孔隙形状趋于规则。
A close relationship exists between the evolution of micro pore structure and macro mechanical properties of sand during the triaxial shear test.The micro-triaxial shear apparatus developed by Nanjing University was used to perform the triaxial shear test on Nanjing silty sand;micro-CT scanning was used to obtain the evolution features of 3D pore structure of the specimen during the loading.The results show that the specimen exhibits strain softeninghardening-type characteristic of stress-strain curve;the friction at both ends of the sample impedes the specimen's volume expansion,causing the drum type zone destruction occurring in the specimen;the porosity of specimen decreases from 46.3% to 40.9%,then increases to about43.0%,and the porosity of failure zone increases obviously;according to the pore parameters of representative elementary volume of zone destruction area,the pores are compressed before failure,causing a decrease of the pore number by 32.4%and a decrease of the average pore radius by 48.8%,so that there are a concentration of the distribution of pore radius,and a good amountof pores with large pore radius occur in the post-failure zone;the dislocation of particles makes the edges of the particles broken,causing the pore shape tends to be regular.
A close relationship exists between the evolution of micro pore structure and macro mechanical properties of sand during the triaxial shear test.The micro-triaxial shear apparatus developed by Nanjing University was used to perform the triaxial shear test on Nanjing silty sand;micro-CT scanning was used to obtain the evolution features of 3D pore structure of the specimen during the loading.The results show that the specimen exhibits strain softeninghardening-type characteristic of stress-strain curve;the friction at both ends of the sample impedes the specimen's volume expansion,causing the drum type zone destruction occurring in the specimen;the porosity of specimen decreases from 46.3% to 40.9%,then increases to about43.0%,and the porosity of failure zone increases obviously;according to the pore parameters of representative elementary volume of zone destruction area,the pores are compressed before failure,causing a decrease of the pore number by 32.4%and a decrease of the average pore radius by 48.8%,so that there are a concentration of the distribution of pore radius,and a good amountof pores with large pore radius occur in the post-failure zone;the dislocation of particles makes the edges of the particles broken,causing the pore shape tends to be regular.
引文
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[6]史琳,许然,许强辉,等.基于显微CT技术的结焦砂三维孔隙结构精细表征[J].清华大学学报:自然科学版,2016,56(10):1079-1084.SHI Lin,XU Ran,XU Qiang-hui,et al.Advanced Characterization of Three-dimensional Pores in Coking Sand by Micro-CT[J].Journal of Tsinghua University:Science and Technology,2016,56(10):1079-1084.
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[8]刘治清,宋晶,杨玉双,等.饱和细粒土固结过程的三维孔隙演化特征[J].工程地质学报,2016,24(5):931-940.LIU Zhi-qing,SONG Jing,YANG Yu-shuang,et al.Three-dimensional Pores Evolution Characteristics During Consolidation Process of Saturated Fine-grained Soil[J].Journal of Engineering Geology,2016,24(5):931-940.
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[11]刘向君,熊健,梁利喜,等.基于微CT技术的致密砂岩孔隙结构特征及其对流体流动的影响[J].地球物理学进展,2017,32(3):1019-1028.LIU Xiang-jun,XIONG Jian,LIANG Li-xi,et al.Study on the Characteristics of Pore Structure of Tight Sand Based on Micro-CT Scanning and Its Influence on Fluid Flow[J].Progress in Geophysics,2017,32(3):1019-1028.
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[16]CHARALAMPIDOU E M,HALL S A,STANCHITS S,et al.Characterization of Shear and Compaction Bands in a Porous Sandstone Deformed Under Triaxial Compression[J].Tectonophysics,2011,503(1/2):8-17.
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[18]李小春,曾志姣,石露,等.岩石微焦CT扫描的三轴仪及其初步应用[J].岩石力学与工程学报,2015,34(6):1128-1134.LI Xiao-chun,ZENG Zhi-jiao,SHI Lu,et al.Triaxial Apparatus for Micro-focus CT Scan of Rock and Its Preliminary Application[J].Chinese Journal of Rock Mechanics and Engineering,2015,34(6):1128-1134.
[19]朱宝龙,巫锡勇,李晓宁,等.合肥地区重塑黏性土细观结构演化三轴CT试验[J].西南交通大学学报,2015,50(1):144-149.ZHU Bao-long,WU Xi-yong,LI Xiao-ning,et al.Triaxial CT Tests of Meso-structure Evolution of Remodeled Cohesive Soil in Hefei[J].Journal of Southwest Jiaotong University,2015,50(1):144-149.
[20]朱建群.含细粒砂土的强度特征与稳态性状研究[D].北京:中国科学院研究生院,2007.ZHU Jian-qun.Strength Properties and Steady-state Behavior of Sandy Soil[D].Beijing:Graduate University of Chinese Academy of Science,2007.
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[23]王继庄.粗粒料的变形特性和缩尺效应[J].岩土工程学报,1994,16(4):89-95.WANG Ji-zhuang.Deformation and Scale Effect of Coarse-grained Material[J].Chinese Journal of Geotechnical Engineering,1994,16(4):89-95.
[24]朱俊高,刘忠,翁厚洋,等.试样尺寸对粗粒土强度及变形试验影响研究[J].四川大学学报:工程科学版,2012,44(6):92-96.ZHU Jun-gao,LIU Zhong,WENG Hou-yang,et al.Study on Effect of Specimen Size upon Strength and Deformation Behaviour of Coarse-grained Soil in Triaxial Test[J].Journal of Sichuan University:Engineering Science Edition,2012,44(6):92-96.
[25]朱逢斌,陈甦,孙雷江,等.自制砂雨装置填砂装样质量分析[J].地下空间与工程学报,2013,9(增2):2076-2078,2092.ZHU Feng-bin,CHEN Su,SUN Lei-jiang,et al.Quality Analysis of Sand Filling by the Self-made Pluviation Device[J].Chinese Journal of Underground Space and Engineering,2013,9(S2):2076-2078,2092.
[26]程朋,王勇,李雄威,等.砂雨法制备三轴砂样的影响因素及均匀性研究[J].长江科学院院报,2016,33(10):79-83,92.CHENG Peng,WANG Yong,LI Xiong-wei,et al.Factors and Homogeneity of Triaxial Sand Specimens Preparation with Air Pluviation[J].Journal of Yangtze River Scientific Research Institute,2016,33(10):79-83,92.
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