The impact of water repellency on soil mechanics

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Contrary to a prevalling assumption in geotechnical engineering, soils can exhibit low wettability. Water repellent behaviour has been identified in contaminated, engineered and natural soils, and waste. These include oil contaminated soils (e.g. oil spills in refineries), carbon rich waste (e.g. lignitic mine waste), carbon engineered soils (e.g. soils amended with biochar), soils subjected to wildfires and some agricultural and forest soils, and sulphur blocks in mineral exploration. Despite research on the hydrological implications (reduced infiltration, enhancement of soil erodibility by wind and water, post fire debris flows), very little is known on the influence of water repellency on soil engineering properties. This proposal will address this knowledge gap by investigating the relationship between wettability and the engineering properties of unsaturated soils (with air and water in the pores). It will test the hypothesis that soils with a lower affinity for water exhibit poorer performance in terms of their engineering behaviour (higher compressibility and lower shear strength). This will be achieved by combining experimental techniques from Soil Science, Chemistry and Soil Mechanics. The results will provide a first insight into the influence of wettability on the engineering behaviour of soils.