Method of Estimating Air-Liquid Interfacial Area Using Soil Characteristics Curve

Abstract

Air-liquid interfacial area (α_i) is an important parameter in the subsurface hydrology that describes the pore scale distribution of air and liquid inside the porous media. In order to quantify this parameter, a theoretical model using soil characteristics (ψ-θ) curve was developed by introducing a term“hydraulic radius”for the pores inside the medium. This term diminishes the effect of any shape of the pore. The derivation becomes a simple expression which needs only drainage soil characteristics curve. In this study,ψ-θ curves were developed experimentally for three glass beads media (0.25mm,0.50 mm and 0.75mm) and the theoretical method was applied successfully to estimate the parameter, α_i in these different porous media. Results obtained by this method follow the general concept of decreasing α_i with increasing liquid saturation. They also show that the α_i is increasing with decreasing grain size, which supports the frequency distribution of the pore sizes inside the porous media. Estimated air-liquid interfacial area was also compared with the results obtained by an experimental technique using surfactant mass extraction. Comparison of the results shows that the interfacial area determined by this theoretical method provides reasonable estimation. Finally, the method was applied to a sand mixture (d₅₀=0.25mm) to estimate the air-liquid interfacial area and was compared with the experimental results of interfacial tracer technique as described by Kim et al., (1997). Results found by comparing α_i of solid surface area at zero saturation revealed that the theoretical method provides reasonable estimation of α_i than the interfacial tracer technique.