PREDICTING THE PERMEABILITY FUNCTION FOR UNSATURATED SOILS USING THE SOIL-WATER CHARACTERISTIC CURVE

The coefficient of permeability for an unsaturated soil is primarily d etermined by the pore-size distribution of the soil and can be predict ed from the soil-water characteristic curve. A general equation, which describes the soil-water characteristic curve over the entire suction range (i.e., from 0 to 10(6) kPa), was proposed by the first two auth ors in another paper. This equation is used to predict the coefficient of permeability for unsaturated soils. By using this equation, an eva luation of the residual water content is no longer required in the pre diction of the coefficient of permeability. The proposed permeability function is an integration form of the suction versus water content re lationship. The proposed equation has been best fit with example data from the literature where both the soil-water characteristic curve and the coefficient of permeability were measured. The fit between the da ta acid the theory was excellent. It was found that the integration ca n be done from zero water content to the saturated water content. Ther efore, it is possible to use the normalized water content (volumetric or gravimetric) or the degree of saturation data versus suction in the prediction of the permeability function.