基于SEM和MIP试验结构性黏土压缩过程中微观孔隙的变化规律

 为探求土体在变形过程中微结构形态的演化规律，对湛江结构性黏土进行室内压缩试验，通过真空冷冻升华干燥法对天然土和压缩后土制样，进行扫描电子显微镜扫描试验和压汞试验，基于灰度计算土的三维孔隙率，分析压缩过程中微观孔隙的变化规律。结果表明，较二值化处理获得的二维孔隙率，三维孔隙率物理意义明确，求取方法简单，有较高准确性。湛江天然黏土孔径为1.0～0.1 μm的小孔隙组占优，其孔隙体积占总孔隙体积的73%。压缩过程中，P＞?k前，各孔径组分变化甚微。P＞?k后，随压力的增大，小孔隙含量表现为先增加后降低。各孔隙组对外力的敏感度与孔隙体积含量正相关。由于压汞过程存在“瓶颈”效应，其结果可能会夸大小孔隙的分布密度而低估大孔隙的分布密度。结构性黏土压缩过程中微观结构形态的演化可分为结构微调、结构破损、结构固化3个阶段。该研究有助于深入了解土的变形机制，为结构性土的工程设计提供科学的依据。

EVOLUTION OF MICROSCOPIC PORE OF STRUCTURED CLAY IN COMPRESSION PROCESS BASED ON SEM AND MIP TEST

Compression tests for structured clay in Zhanjiang were conducted to obtain the evolution of soil microstructure in deformation process.Natural soil samples and soil samples after compression tests were prepared for SEM and MIP tests by lyophilization.Three-dimensional porosity was calculated based on gray scale,the evolution of microscopic pores in compression process was qualitatively and quantitatively analyzed.The results show that,compared with two-dimensional porosity based on binary image,the three-dimensional porosity has advantages of explicit physical significance,simple calculation method and high accuracy.Pores with diameters of 1.0-0.1 μm were dominant in natural clay,whose volume took up 73% of total pore volume.When P< k,each pore size changed little.When P> k,fine pore content firstly increased,subsequently decreased with the increase of the pressure.In the compression process,a positive correlation between the sensitivity of each pore size to external forces and pore volume content was found.The distribution density of the fine pores might be exaggerated while the one of macro-pores might be underestimated in MIP for the bottleneck effect during MIP test.The evolution of microstructure of structured clay in the compression process might be divided into three stages:fine tuning stage,damage stage and solidification stage.The study is helpful for good understanding of deformation mechanism of soil,and provides a scientific basis for engineering design of structured clay.