Effect of physicochemical characterisation on water retention–soil shrinkage behaviour of compacted Regina clay

Expansive soils exhibit high plasticity and significant volume change, posing challenges to geotechnical design. This research investigates the influence of physicochemical characterisation on the water retention–soil shrinkage behaviour of compacted Regina clay, a highly expansive glaciolacustrine deposit in southern Saskatchewan. Mineralogical, chemical, and suction-imposed test results were integrated to evaluate how clay composition and pore-fluid chemistry influence coupled flow through and volumetric response during drying. The soil was found to be smectite-dominated, silica–alumina rich, and characterised by high cation exchange capacity, moderately saline pore fluid, and a Ca–Mg dominated exchange complex. The water-retention curve exhibited bimodal behaviour, indicating distinct inter-aggregate and intra-aggregate drainage domains, while the soil shrinkage curve showed a well-defined s-shaped response. Coupling the two relationships through a common gravimetric water-content axis showed that capillary-controlled drainage governs the main shrinkage response, whereas high-suction behaviour converges towards an adsorption-controlled regime. These results demonstrate that the physicochemical properties of compacted smectite-rich expansive clay directly influence both water retention and shrinkage behaviour by controlling the transition from capillary to adsorption-dominated processes.