A Fundamental Water-Retention Model Based on the Theory of Disjoining Pressure of Soil Water

A new methodological approach to modeling the water retention curve (WRC) as the soil basic hydrologic and physical property based entirely on the Deryagin’s concept of water film disjoining pressure phenomenon with respect to the soil physical system has been proposed. It operates with a variable mass fraction in the liquid phase (soil solution) with the electrolyte ion concentration and charge parameters, the specific surface area in the solid phase, and limitations induced by the soil porosity and conditionally zero water potential standard state. The new model was validated based on the author’s and independent literature data on soils of various geneses and granulometric compositions ranging from sands to clays. It showed a reasonably good correspondence with the experimental data and more appropriate water retention characteristics with the use of normalized root-mean-square errors five to ten times lower than that in the most common van Genuchten empirical model for WRC characteristics. In addition to the appropriate description WRC characteristics in the full range from the saturated soil status to the conditionally zero water content, the new model makes it possible to estimate the pore size distribution analytically and to calculate the generalized Hamaker constant for interphase molecular interactions between liquid and solid soil phases and the Debye electric double layer thickness. Moreover, the model allows us to determine the soil specific surface area in the solid phase as an alternative to the standard Brunauer–Emmett–Teller method.