Impact of soil texture on air‐water interfacial areas in unsaturated sandy porous media

Abstract

The gas phase partitioning tracer method was used to measure air‐water interfacial area as a function of water content for eight sandy porous media. The porous media comprised a series of sands with narrow particle size ranges, a sand with a wider particle size distribution, a sandy soil, and a loamy sandy soil. The measurement range was extended to very low water contents in an attempt to determine upper limits for air‐water interfacial areas. The measured values were compared to the normalized surface areas of the porous media. The results of the experiments showed that the magnitude of the air‐water interfacial areas increased with decreasing water saturation and approached that of the normalized surface areas. Generally, air‐water interfacial areas were larger for media with larger specific surface areas. The change in air‐water interfacial area with changing water saturation was less near saturated water contents and greater at smaller values. In addition, the change was greater for the poorly sorted media than the well‐sorted media. An empirical equation was developed to describe the observed relationship between air‐water interfacial area and water saturation. The coefficients of the equation were found to correlate to the porous medium uniformity coefficient. With this equation and associated correlations, only bulk density, specific surface area, and uniformity coefficient are needed to estimate air‐water interfacial area for a given water saturation. The equation was shown to provide a reasonable description of a literature data set.