Natural Ca-montmorillonite clay soils or engineered clay barriers in western Canada are often used to contain brine generated from the surface disposal of potash tailings or from drilling activities associated with the oil and gas industry. The performance of these barriers has ranged from excellent to poor. The influence of salt brines on the geotechnical properties of these soils has been recognized as a potentially important factor for some time. It has been well documented in the literature that the behavior of clayey soils is strongly influenced by physicochemical interactions between clay particles and pore-fluid chemistry; consequently, the properties of these soils are sensitive to changes in the electrolyte concentration of the pore fluid. An increase in the concentration of the pore fluid to the levels of a concentrated brine can cause significant changes in the geotechnical properties of the soil. In this paper, the impact of brine contamination on the geotechnical properties of two Ca-montmorillonitic clayey soils of glacial origin from western Canada is reviewed. The influence of clay–brine interactions on the index properties (liquid limit, plastic limit, plastic index, mineralogy, density, grain size, and compaction characteristics), mechanical properties (volume change and shear strength), and hydraulic properties (hydraulic conductivity) is described. A quantitative explanation for the changes that occur in the hydraulic and mechanical properties of these soils as a result of brine permeation is also provided. This explanation relates the changes in pore-fluid chemistry to changes in an effective physicochemical stress state. This approach may be used to predict the changes in hydraulic conductivity, volume, or shear strength of a clayey soil as a result of brine contamination. Key words : clay–brine interactions, diffuse double layer, hydraulic conductivity, soil structure, physicochemical.