Soil water retention of a compacted sandy clay with sub-critical water repellency

Soil water retention curves are usually obtained on the assumption that soils are wettable. While this is true at high water contents, where pores are filled by water or a film of water covers the particles, it is less likely for drier states, where the adhesion of water menisci to the surface of the particles is controlled by the material chemistry and surface roughness, the presence of organic matter and the soil water content. Here, we present suction, water content and wettability measurements for model samples following drying paths. A comparison is done for a model material (sandy clay) in an initially wettable and sub-critical water repellent state (<90 degrees). Wettability was manipulated by treatment with organic acids which mimic the chemistry of natural water repellent substances. Suction was measured with a high suction tensiometer and wettability via contact angles by the sessile droplet method. The results revealed lower water retention and greater contact angles for the water repellent samples.