Quantifying liquid infiltration into unsaturated porous media is essential for many different fields, including environmental engineering. The research in this thesis examined liquid infiltration into an initially dry porous medium, namely soil, with emphasis on examining the influence of sorptivity, wettability, and diffusion on the infiltration process.

Sorptivity (S) quantifies the effect of capillarity on liquid infiltration into porous media. For infiltration into initially dry soil, S depends upon the infiltrating liquid properties, the soil properties, and the maximum liquid content behind the infiltration front, &thetas;_m. Through scaling analyses, it is possible to derive a singular, dimensionless, value of intrinsic sorptivity (S^*), and an accompanying dimensionless Boltzmann transformation (Φ^*), that are independent of these system attributes. This research focused on the validation of ^S* and Φ^* under a range of conditions. In addition, the wetting properties of water and oil during infiltration into dry soil were investigated, and the relationship between liquid diffusivity and liquid content was examined.

Results from 57 horizontal infiltration tests, which employed two liquids and three geometrically similar soils, confirmed a singular value of the intrinsic sorptivity S_av^* = 0.133 ±0.02, where the subscript (av) indicates that &thetas; _m was replaced by &thetas;_av, the average liquid content behind an infiltrating front, in the scaling analyses. Additionally, profiles of normalized liquid content versus Φ _av^* at the end of each test were found to be approximately equivalent for all test conditions, providing confidence in the existence of Φ_av^*.

Test results using water or Soltrol 220 as the infiltrant, demonstrated that water was less wetting than the oil during infiltration events. A surfactant washing method was employed to remove organic ad-layers on the soil grains, which were thought to be responsible for the lower water wettability. Results using the washed soil indicated even lower water wettability during infiltration. This unexpected finding was attributed to loss of fine particles and the increased acidity of the soil pore water, which both arose as a result of the washing method.

Finally, results from eight water infiltration tests, employing moisture probes to monitor water movement, indicated an exponential relationship between soil water diffusivity and water content.