Abstract: Relative permeability coefficient and soil-water characteristic curve(SWCC) are important parameters in the study of unsaturated flow, and the capillary system has become one of the important methods to study relative permeability coefficient. On the assumption of using capillary system instead of soil pore, traditional water content model of capillary system was improved based on the Young-Laplace equation and fractal theory. A model predicting the relative permeability coefficient of unsaturated soil in consideration of the water content of unsaturated pore was proposed. Four groups of experimental data were used to verify the proposed model, and the root mean square deviation (RMSD) was used to evaluate the error between experimental data and predicted data. Results manifested that the RMSD values of all the four groups of data were smaller than 0.025, indicating that the model is of practical significance for predicting the relative permeability coefficient of unsaturated soil.

Key words: unsaturated soil, relative permeability coefficient, soil-water characteristic curve(SWCC), capillary system, water retention