Abstract: Soil-Water Characteristic Curve (SWCC) is a fundamental concept for the studying of the mechanical properties and hydraulic characteristics of unsaturated soils. In this paper, a granitic residual soil in Guangzhou area was used in the laboratory study. The soil-water characteristics and infiltration characteristics of unsaturated residual soils at low saturation (high suction) were investigated by using the salt solution vapor balance method and the filter paper method to obtain the SWCC of residual soils at the full suction stage. The results show that the moisture content of the SWCC curve decreases sharply with the increase suction in the early stage and then decreases slowly in the later stage. In addition, the existing SWCC models were compared with the experimental data to characterize the soil-water characteristics of the residual granite soils in Guangzhou, and the Fredlund-Xing model was found to be suitable for describing the soil-water characteristics of these unsaturated soils. Finally, the soil-water characteristics obtained from the Fredlund-Xing model are combined with the Mualem infiltration model to propose a suitable model for predicting the infiltration coefficient of unsaturated granitic residual soils in Guangzhou. The research results of this project provide an important basis for the further research on the mechanical and hydraulic properties of unsaturated granitic residual soils in Guangzhou.

Key words: granitic residual soils, matrix suction, soilwater characteristic curve, hydraulic conductivity