Research For Microstructure Of Hefei Expansive Soil

Hefei area of expansive soils are widely distributed,the structure of expansive soil changes significantly under water,consolidation and other effects,so quantitative analysis of the structure under different conditions,especially the microstructure,is of great significance to solve the problem of expansive soil.With the natural or reconstituted expansive soil in Hefei as the research object,quantitative analysis of the development of microstructure through the soaking test,the consolidation test and shear test.In this paper,choosing undisturbed soil,soaking 3h,soaking 24 h,soaking 72 h samples by the expansibility of expansive soil test are used for Environmental Scanning Electron Microscope(ESEM).The undisturbed soil,remolded soil and lime-modified soil samples were pressed of 200 kPa,400kPa,800 kPa,1600kPa on the base of the previous study.The vertical microstructure of the samples were observed by scanning electron microscopy.At the same time,the pore and particle's microstructure features on the shear fracture surface were quantitative analyzed by the image software.The major achievements and conclusions of the paper:(1)It is found that the microstructure features,such as the grain's contact form and the unit's contact form and arrangement and so on,are one of the important seasons for the expansion through the ESEM images of samples under different soaking time;In a certain consolidation pressure range,there is a linear regression relationship between fractal dimension of the soil particles and the consolidation pressure with the increase of pressure.(2)The microstructure particle and pore of Hefei expansive soil have obvious fractal structure characteristics in the statistical theory.In three-dimensional space,using the gray level of gray image to establish a three-dimensional model,analyzes the fractal dimension of the unit under different conditions,indicate:3D fractal dimension reduces with the increase of wetting time.(3)The quantitative parameters of the microstructure particle and pore have different regularities in different stages of the soaking test,consolidation test and shear test.Such as the directional entropy,circular degree and shape factor of the soil particles increases first and then decreases with the increase of consolidation pressure.Compared with the global threshold to analyze the microstructure in two-dimensional space,the threshold that is back calculated through three-dimensional porosity,is close to the actual value in the paper.