Closed-Form SWCC Functions for Granular Mixtures

Four closed-form water-retention functions (the Gardner, Fredlund – Xing, van Genuchten 4 and 5) were validated using the experimental, ideal water retention curve data of 7 granular fractions (fine gravel, sand and silt) and their 21 mixtures with fractal distribution (being similar to the Fuller curves), composed from 2 to 7 fractions. The measurement was approximate since some sand and kaolinite boxes designated for some fixed suction loads were used being proper for more plastic soils. The homothetic, fractal grading curves with N = 2, 3, ...7 fractions, resp.; resulted in homothetic SWCC-s. A data mining procedure was used to assess the precise shape. Then the discrimination study showed that the 5-parameter model of van Genuchten was the best and the Fredlund-Xing modelwas the secdond best. The results showed some interdependence of the parameters. Discussing the results by considering more complicated grading curve samples, the double Weibull function was found to be better for SWCC-s of gap-graded grading curves.