Simplified Relation Model of Soil Saturation Permeability Coefficient and Air-Entry Value and Its Application

Based on the Tao and Kong (TK) model and the fractal model of the soil-water characteristic curve, a simplified model of the relationship between the saturated permeability coefficient and the air-entry value is established in this study: k(s) = k(0)psi(-2)(a). It is shown that the saturated permeability coefficient of soil is determined by its maximum pore size. In order to facilitate the mutual prediction of saturation permeability coefficient and air-entry value, based on the data of five types of soil in the UNSODA database, the comprehensive proportionality constant k(0) of the five types of soil were obtained: sand k(0) = 0.03051; clay k(0) = 0.001878; loam k(0) = 0.001426; sandy loam k(0) = 0.009301; and silty clay loam k(0) = 0.0007055. Based on the obtained comprehensive proportionality constant k(0) and the relationship model between saturated permeability coefficient and air intake value, the air-entry value of five kinds of soils in the existing literature and the SoilVision database were calculated. Comparing the calculated air-entry value with the measured one, the results showed that the model simplifies the traditional air-entry value prediction method to some extent and can effectively predict the air-entry value of different types of soil. On the whole, the model better predicts the air-entry value for sandy, clay, and silty clay loam than loam and sandy loam.