Effect of Water Chemistry on Soil Hydraulic Properties: An Evaluation with Sand-Clay Mixture and Different Origin Waters

ABSTRACT Understanding how water chemistry influences hydraulic conductivity (k) is crucial for the performance of landfill liners, clay cores of dams, drainage systems, and contaminant transport assessments, where inaccurate permeability estimates may lead to significant engineering and environmental risks. This study investigates the influence of water type, chemical properties, and density on the k of two compacted clay-sand mixtures (70% clay-30 % sand and 30% clay-70 % sand), prepared under the same compaction energy. Falling-head permeability tests were conducted using nine waters with distinct physicochemical characteristics to experimentally evaluate the effects of water chemistry on soil hydraulic behaviour. Results showed that saline and ion-rich waters produced noticeably higher k values, often several times greater than those measured with Distilled Water (DW)—consistent with the strong correlations obtained for EC, salinity, and major ions. The findings also indicated that density, Electrical Conductivity (EC), salinity, and the concentrations of sodium (Na+), potassium (K+), calcium (Ca2+), magnesium (Mg2+), chloride (Cl−), sulphate (SO42−), and bicarbonate (HCO3−) significantly influenced the k value. These trends were strongly supported by statistical analyses, with EC, salinity, Na+, Mg2+, and K+ exhibiting very strong linear correlations with k (r2 = 0.89−0.98), demonstrating that water chemistry exerts a dominant control on permeability. The observed increases are consistent with diffuse double-layer compression and clay particle flocculation under high ionic strength, which enhances pore connectivity and leads to several-fold increases in k relative to DW. Consequently, laboratory tests performed with standard waters may underestimate field permeability in chemically diverse or saline environments, emphasising the necessity of incorporating site-specific water chemistry into geotechnical design and groundwater assessments.