PREDICTION MODEL FOR UNSATURATED WATER RETENTION AND PERMEABILITY FUNCTION IN THE FULL SUCTION RANGE

The water retention function and permeability function of unsaturated soils are fundamental parameters for characterizing the water retention capacity and water transportation of unsaturated soils. They exhibit distinct features in the capillary stage and adsorption stage due to different physical mechanisms. However, most traditional functions only consider the water retention and permeability properties of capillary water within the capillary stage and cannot adequately characterize the adsorbed water within the adsorption stage. To address this limitation, we modified the traditional VG model, based on the traditional VG water retention function and VG-M permeability function, by correcting it with a modified parameter C(ψ). This modification allows the traditional VG model to determine the residual suction value ψ_r for unsaturated soils, distinguishing between capillary flow in the capillary stage and thin film flow in the adsorption stage. Additionally, considering the characteristics of thin film flow, we proposed a parameter Γ(ψ)to improve the issue wherein the traditional VG-M permeability function often underestimates the unsaturated permeability coefficient in the adsorption stage. This led to the establishment of a permeability function model for the full suction range. Finally, we verified the rationality of the modified VG and VG-M models using three sets of measured water retention and permeability data. The results demonstrate that the prediction outcomes of the modified water retention model and permeability function model are more consistent with the measured data in the adsorption zone compared to the traditional models.