Modeling water flow in an unsaturated compacted soil

A theory for modeling unsaturated flow considering the entrapment of air in a porous medium imbibing liquid is developed. Following the occluded state theory proposed by Schuurman (1966), a theoretical soil-water characteristic function involving discontinuous air phase is derived. The theoretical constitutive relationship is determined using Boyle's law and Henry's law of solubility, and the Kelvin equation for pressure difference across the interface between the air and water phases.; A new testing technique is developed to provide reliable data of the relationship between the pore water pressure and saturation involving discontinuous air phase. Data from these test results are used to validate the proposed occluded state theory. A new method for the measurement of unsaturated hydraulic conductivity, where the air is present in the form of bubbles is described. The method is based on the concept of saturation of the soils by increasing the pore-water back pressure. The developed relationship between the pore water pressure and saturation involving discontinuous air phase is used for determining the increase in saturation due to the increase in the back pressure. An empirical hydraulic conductivity function determined by curve fitting to the experimental measurements leads to the conclusion that the relative hydraulic conductivity increases sharply when the saturation increases from 0.9 to 1.0, and it has a value of 0.1 while the saturation is relatively high (say, > 0.8).; A numerical solution of Richards' equation for one-dimensional transient water flow, which incorporates the experimental findings, is described in this study and its algorithm was coded in a computer program that was used to analyze the experimental results. The approach of determining the unknown parameters of the hydraulic conductivity function by using the transient portion of flow was also investigated. The comparisons between the numerical solutions and the measured transient water flow show that the proposed constitutive relationships are capable of producing simulations of the measurements of the unsaturated flow that are both qualitatively and quantitatively realistic.