Effects of chemical treatments on the swelling behaviour of clay-bearing geomaterials

Abstract Clay swelling causes volumetric expansion and compromises the stability of underground excavations. Chemical treatment serves as an essential approach for swelling control by affecting osmotic and intra-crystalline swelling mechanisms. This study assesses the swelling behaviour of compacted clays and intact rocks subjected to chloride salt solutions. Compacted clay specimens soaked in concentrated and dilute saline solutions behave differently due to the interplay between osmotic pressure and cation exchange reactions. At 1 mol/L, potassium chloride (KCl) more efficiently reduces clay swelling than sodium chloride (NaCl) and calcium chloride (CaCl 2 ), whereas at 0.1 mol/L, all salts slightly increase swelling deformation due to enhanced osmotic swelling. Spraying KCl is applied as a treatment step during wetting and drying cycles. Experimental results show that KCl-treated clays develop fewer surface cracks and exhibit reduced water retention during re-saturation, accounting for the limited expansion. KCl solution is also used to stabilise rock swelling and to provide a comparison with deionised water. The swelling potential of the rock is constrained by its strengthened rock matrix and further suppressed by the KCl treatment. Microscopic analyses are conducted on dry-state and post-treatment rocks. Both deionised water and salt solutions alter the surface morphology, as quantified by surface roughness parameters. KCl crystals are identified in high-contrast regions of microscopic images, while some crystalline phases may precipitate due to water evaporation. Enhancement of rock durability and assessment of groundwater chemistry are addressed to implement chemical treatment under field conditions, offering insights into optimising swelling control measures.