Abstract
Due to the growing interest in sustainable and environmentally friendly construction materials, biopolymers are increasingly being explored and applied for soil stabilisation in geotechnical engineering. This study evaluates the effectiveness of three commonly used biopolymers—xanthan gum, chitosan, and carboxymethylcellulose—added at concentrations of 1, 2, and 3% by soil weight to improve the physical properties of heavy sandy clay loam. The influence of varying water saturation levels on the stability and performance of treated soils was also investigated. Laboratory tests included determination of soil plasticity, natural water content, consistency limits, and sorption behaviour using the vapour equilibrium technique with saturated sodium chloride and potassium chloride solutions. The results indicate significant improvements in Atterberg limits, particularly plasticity and liquid limits, reflecting enhanced cohesion and structural integrity. Moisture retention characteristics were strongly dependent on environmental humidity and salt solution type. The study confirms that biopolymers are effective, sustainable, and eco-friendly additives for improving soil performance in engineering applications.