Analysis on Pore Evolution and Microscopic Mechanism of Red Clay during Loss Water and Shrinkage

In order to reveal the pore evolution law and shrinkage mechanism of Guiyang red clay in the process of water loss at room temperature, shrinkage test, mercury intrusion porosimetry test and X-ray diffraction test were carried out on the red clay. Crystal layer osmotic pressure theory and capillary theory were adopted to explain its microscopic mechanism. The study results show that: the water content promotes the shrinkage of the red clay, and the shrinkage was anisotropic. The shrinkage goes through three main stages: First, the normal shrinking stage, when the volume of the pores, no matter macro-or meso-, between the aggregates decreases and more and more small pores and micropores appear with the gradual reduction of water content; second, the residual shrinkage stage, when a large number of small pores become micropores within the aggregates; third, the zero shrinkage stage, when all pores remain constant within and between the aggregates. The red clay is high in montmorillonite, and the osmotic pressure difference between the inside and outside of its crystal layer causes the migration of water molecules into the pore, leading to the narrow of the distance between the crystal layers, which macroscopically manifests as soil shrinkage. Through Kelvin capillary theory, we established the relationship between the saturation and the suction of Guiyang red clay at each shrinkage stage, and explained the internal mechanism of controlling of the matrix suction to the shrinkage process.