Morphology-driven saturated hydraulic conductivity in hydrophobised sands

Saturated soil hydraulic conductivity is known to be influenced by soil wettability. However, results on the relation between soil hydrophobicity and saturated hydraulic conductivity are often contradictory, with both negative and positive relationships reported. Contrasts are associated with changes to the soil particle morphology after treatment to induce hydrophobicity, from particle size and shape to surface roughness. Here, constant-head tests on hydrophobised sands with known physicochemical properties and particle attributes were conducted and supported using interferometry and a dynamic image analyser. Results show a selective effect on the saturated hydraulic conductivity depending on the type of hydrophobising agent used. At high concentration (e.g. 3·5%), samples treated with dimethyldichlorosilane show an increase in the saturated hydraulic conductivity, which can be attributed to the smoothening of the surface of the grains. Samples treated with wax and tung oil have a reduction in saturated hydraulic conductivity, which is attributed to a non-negligible increase in particle size and reduced pore space.