This study examines the effect of water salinity levels on the mechanical geotechnical properties of clay-rich soil. Laboratory tests were conducted on a set of soil samples with varying salinity levels, including unconfined compressive strength (UCS), Atterberg limits, oedometer, and direct shear tests. The conducted test results are further used to evaluate alterations in soil properties resulting from exposure to sodium chloride (NaCl) concentrations ranging from 0 mM (pure water) to 600 mM (seawater). The findings show a progressive decrease in liquid limit, plastic limit, and plasticity index with increasing salt concentration, indicating reduced water affinity and significant physicochemical alterations to the soil structure. These trends are consistent across all experimental observations and have been confirmed by zeta potential measurements and mineralogical analyses using X-ray diffraction (XRD). However, maximum dry density increased in parallel with a decrease in optimum moisture content. The increase in salinity led to a decrease in compressive strength, indicating a weakening of the soil structure. The shear strength parameters (cohesion and Internal friction angles) experience a decrease due to the presence of saline water. Therefore, soils with high salinity will also exhibit lower shear strengths. The results of this study provide reliable information to support road construction activities in coastal environments.
