Disjoining pressure model for the entire soil water retention curve

Abstract

Most models of water retention in soils and other porous media of the lithosphere use concepts of capillary theory or an empirical relationship between the thermodynamic potential (pressure) of water and its content in a porous medium. The study presents an alternative methodological approach based on the equations of the fundamental theory of disjoining pressure of water films and their stability in a polydisperse porous medium with variable water content. Validation of the model using the author’s own and literature WRC data for soils with various texture from sands to clays confirmed its good approximation ability in the complete moisture range from saturation to oven drying with a scatter index 2–20 times lower than in the commonly used van Genuchten model with the same number of parameters. In addition to describing the WRC with calculating pore size distribution, the new model is capable of determining the generalized Hamaker constant for molecular interfacial interactions, the Debye thickness of the electric double layer, and the specific soil surface area alternatively to the standard BET method.