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.