Abstract: Relative permeability coefficient is an important content in the study of seepage characteristics of unsaturated soils. In consideration of the hysteresis effect of unsaturated soil seepage caused by the non-uniformity of soil pores, a soil-water characteristic curve (SWCC) model reflecting the hysteresis effect of unsaturated flow is constructed by using the fractal theory and the Buckingham-Darcy law. On such basis, a model of relative permeability coefficient of unsaturated flow is derived. The proposed model is simple in form and contains only one parameter. The rationality of the model proposed in this paper is verified by five representative sets of test data of relative permeability coefficient. Compared with the Assouline model, the proposed model has superior fitting results.

Key words: unsaturated soil, capillary system, relative permeability coefficient, fractal theory, Buckingham-Darcy law