AbstractThis study aims to investigate the geotechnical and chemical properties of sand–clay mixtures contaminated with lead and zinc. To prepare the specimens, two kinds of mixtures were studied. Sand–kaolinite and sand–bentonite with different clay fractions were investigated through consistency limits, pH measurement, direct shear test, unconfined compression test, batch adsorption experiment, and electrical resistivity. The heavy metal contaminants were lead nitrate and zinc nitrate hexahydrate, and contaminated specimens were prepared in the laboratory with desired concentrations (i.e., 1.5% and 3% by weight of the dry soil). Based on the obtained results, the presence of kaolinite in specimens decreased the angle of friction. On the other hand, the presence of bentonite in mixtures increased the friction angle. Moreover, sand mixtures including bentonite showed a better capability to adsorb heavy metals than sand–kaolinite mixtures. The electrical resistivity of all the sand–clay mixtures decreased with the increase of concentration. Owing to the acidity feature of heavy metals, the pH of the contaminated soil solutions decreased. Moreover, the adsorption of heavy metals in soils including bentonite was more than that of sand with kaolinite.