Modelling the role of pore water salinity on the water retention behaviour of compacted active clays

Compacted active clays are used as construction material for engineering barriers in many geotechnical and geo-environmental applications. Their very low permeability makes them particularly suitable as liners for the containment of both municipal and radioactive waste, since it allows very limited fluxes of contaminants. Experimental data show that the water retention behaviour of active clays is very dependent on pore water chemistry, since for a given matric suction the mass of stored water decreases with water salinity. This issue can have relevant effects on the performance of clay liners, considering that active clays are usually cast in place in unsaturated conditions and that the chemical composition of their pore water after compaction may be different from the one of the surrounding environment. In this paper, the effects of water content and water salinity on compacted clay fabric are firstly reviewed, through existing formulations which consider them separately. An enhancement of the existing formulations is then proposed, by merging both contributions. The model is finally validated against experimental water retention data from the literature, showing good prediction capabilities. In the case of the active clays considered, at given water ratios, the model predicts that the matric suction can vary between one and two orders of magnitude with salt concentration. As a counter fact, at a given matric suction and initial dry density, the model predicts that the water retained by samples inundated with distilled water is more than twice with respect to the water retained by samples saturated with a concentrated solution.