A fundamental model of water retention based on the theory of disjoining pressure of soil water

The article presents a new methodological approach to modeling the soil water retention curve (WRC), based entirely on the Deryagin phenomenon of wedging pressure of water films in relation to the soil physical system. It operates with a variable mass fraction of the liquid phase (soil solution) with the parameters of the concentration and charge of electrolyte ions, the specific surface area of the solid phase, as well as limitations by porosity and the standard potential of a conditionally zero water content in the soil. The new model, validated according to the author’s and independent literature data for soils of various genesis and granulometric composition from sands to clays, showed good agreement with experimental data and a more adequate description of water retention with normalized root-mean-square errors 5-10 times smaller compared with the most common empirical van Genuchten model for describing the WRC. Along with an adequate description of WRC in the entire range from the state of water saturation to conditionally zero water content, the new model makes it possible to analytically calculate pore size distributions, estimate the generalized Hammaker constant for interphase molecular interactions of liquid and solid phases of soil, the Debye thickness of the double electric layer and the specific surface area of the solid phase of soil, alternatively to the standard BET method.