Modification of Clay with Sodium and Potassium Chloride Brines: Insights from Laboratory-Sedimented Samples of High-Plasticity Clay

In engineering practice, the need for evaluating and controlling deformations that occur upon unloading of clays is met in several applications, including land reclamation, excavations, tunneling, and well stability. Cation exchange has proven a useful means to stabilizing sensitive soft clays by increasing their residual strength properties. Testing on artificial clay mixtures indicates that this method could also have a potential for improving deformation properties, but the scale of these effects in natural clays is unknown, making in-situ application unfeasible. The aim of this study is to investigate the potential of chemical modification to control the deformations that develop upon unloading of natural clays. This paper evaluates the modified deformation indices as well as consolidation and permeability coefficients of a natural high-plasticity clay when resedimented in four different brines, based on sodium (Na+) and potassium (K+) at two charge concentrations. In addition, the ability to modify the deformation behavior in swelling is investigated through subsequent exposure to brines of different concentrations or dominating cation ahead of unloading. The tests display a clear effect on the deformation properties from the resedimentation environments, with potassium domination increasing the void ratio in compression and inhibiting swelling. Additionally, potassium domination leads to a higher coefficient of consolidation mainly from an increased permeability. Subsequent exposure to different brines induced a systematic change in the swelling index mainly when changing the dominating cation, while increasing concentration had negligible impact. The results of this study are presented along with the relevant data from the literature, thus providing guidance on the application range of chemical modification of clays with different mineralogy.