Prediction of soil-water characteristic curves using basic soil properties

A model for predicting the soil-water characteristic curve (SWCC) using easy-to-measure basic soil properties has been proposed. The model uses the widely used SWCC function by Fredlund and Xing. This function has three parameters: a, n, and m. a is related to the air-entry value (Psi(aev)) of a soil, n mainly influences the desaturation rate in the transition zone of a SWCC, and m controls the residual moisture content. By analyzing the results of a series of laboratory SWCC tests as well as the results in the literature, explicit empirical equations were established for evaluating the values of a, n, and m using the saturated permeability (k(s)), grain size distribution (GSD), and plasticity index (PI). The basic soil properties were selected based on the conceptual relationship between each SWCC function's parameters and those basic soil properties. The model has been verified by applying it to nine SWCCs in the literature, which were not included in developing the model. The proposed model showed better predictions than the existing prediction models. It is suggested that the model can be used to estimate the preliminary drying SWCC of soils.