Probabilistic analysis of soil-water characteristic curves

Direct measurement of the soil-water characteristic curve (SWCC) is costly and time consuming. A first-order estimate from statistical generalization of experimental data belonging to soils with similar textural and structural properties is useful. A simple approach is to fit the data with a nonlinear function and to construct an appropriate probability model of the curve-fitting parameters. This approach is illustrated using sandy clay loam, loam, loamy sand, clay, and silty clay data in Unsaturated Soil Database. This paper demonstrates that a lognormal random vector is suitable to model the curve-fitting parameters of the SWCC. Other probability models using normal, gamma, Johnson, and other distributions do not provide better fit than the proposed lognormal model. The engineering impact of adopting a probabilistic SWCC is briefly discussed by studying the uncertainty of unsaturated shear strength due to the uncertainty of SWCC. DOI: 10.1061/(ASCE)GT.1943-5606.0000222 CE Database subject headings: Unsaturated soils; Soil water; Probability; Correlation; Shear strength; Uncertainty principles. Author keywords: Unsaturated soils; Soil-water characteristic curve; Curve fitting; Probability; Translation; Lognormal; Correlation; Random vector.