Study on water migration and microstructure of unsaturated expansive clays

Because of the characteristics of water-swelling and drying shrinkage, the mechanical performances of expansive clay in semi-arid areas deteriorate with the change in humidity and temperature. So investigating the moisture migration in expansive clays is of great significance. Herein, scanning electron microscopy test and water migration tests of unsaturated soil were carried out to address the water variation law and microscopic mechanism in the unsaturated expansive clay. It is found that small and medium-sized pores (2-10μm) are dominated, and these pores are conducive to the rise of water in the soil. The soil with high water content exhibits a flocculent structure, characterized by a small fractal dimension and a high relative hydraulic conductivity. Conversely, the soil with low water content displays a dispersed structure, featuring a large fractal dimension and a low relative hydraulic conductivity. The water migration tests under constant temperature(5, 20, and 40°C) and variable temperature (15-25°C) show that the migration amount at 5°C and 20°C was about 25%-40%, 40%-60% of that at 40°C, respectively. The amount of water migration under constant temperature was obviously lower than that under variable temperature. The research results have provided technical support for effective control of soil change.