SWC-150 Fredlund soil water characteristic cell is used to test the soil-water characteristic curve (SWCC) of gravelly soils with different densities under different vertical stresses. The influence of the vertical stress and dry density on the SWCCs is investigated. The SWCCs are fitted based on Fredlund & Xing tri-parameter model using least-square method. The parameters of the model are determined and discussed. With the increase in the vertical stress and dry density

the model parameter n increases while m decreases. Except that the parameter a slightly decreases with the increase in the dry density during wetting process

it increases with the increase in the vertical stress and dry density. Based on the fitting results

the influence of the vertical stress and dry density on the air or water entry value and the slope of the SWCC are studied. The quantitative relationships between the air or water entry value

the slope of transition segment of the SWCC and the vertical stress

dry density are proposed. The results show that the air or water entry value has a positive linear relationship with the vertical stress and dry density. Nevertheless

the water entry value has little change with the change in the dry density. The slope of transition segment of the SWCC presents hyperbolic relationship with the vertical stress

while the relationship between the slope and the dry density is linear.