Fitting of soil-water characteristic curve and prediction of permeability coefficient model of unsaturated weak expansive soil

Using the weak expansive soil of the high-speed railway in Hami area of Xinjiang as the study object, the impact of compaction on the microscopic pore structure of soil samples was determined by the mercury intrusion test. The soil-water characteristic curves of remodeled soil samples at different dry densities were determined by the pressure plate instrument and filter paper method, and the experimental data were then fitted with Fredlund & Xing models. Based on the soil-water characteristic curve and Childs & Collis-Geroge model, the permeability coefficient of unsaturated weak expansive soil was predicted, and the results were compared and analyzed with Childs & Collis-George model permeability coefficient of the expansive soils in other regions. The results show that compaction has significant effect on the pore distribution and soil-water properties of unsaturated expansive soils, the greater the dry density, the greater the air intake value of the sample, and the more significant reduction in the volume of macropores. The Fredlund & Xing model has the best fitting effect for soil-water characteristic curves. The permeability coefficient of soil decreases with the increase of dry density. The saturated permeability coefficient and dry density can be expressed by an exponential function, and the unsaturated osmosis curves are affected by the combined effects of dry density and expansion potential. © 2022, Central South University Press. All right reserved.