Geotechnical properties of sandy clayey soil contaminated with lead and zinc

Abstract

Previous studies have shown that pore fluid influences the geotechnical properties of soils. The aim of this paper is to investigate the effects of various concentrations of lead nitrate and zinc nitrate hexahydrate heavy metals in pore fluid on geotechnical properties of kaolinite–sand mixtures based on laboratory tests. Remolded samples of kaolinite–sand mixed with 5 and 25 cmol/kg-soil concentrations of $${\text{Pb}}\left( {{\text{NO}}_{3} } \right)_{2}$$ and $${\text{Zn}}\left( {{\text{NO}}_{3} } \right)_{2} \cdot 6{\text{H}}_{2} {\text{O}}$$ solutions were prepared. One-dimensional consolidation tests, direct shear tests, unconfined compression tests, consistency tests, sediment tests, adsorption tests, and X-ray diffraction tests were conducted on samples to investigate the changes in geotechnical properties of samples in the presence of heavy metals in pore fluid. The results indicate that the presence of Pb(II) and Zn(II) would decrease the initial void ratio and sedimentation of samples which is attributed to the noticeable changes in soil microstructure. With increasing Pb(II) concentration from 0 to 25 cmol/kg-soil, the void ratio of kaolinite containing 10, 25 and 40% sand decreased 18, 24 and 32% respectively. In addition, the reduction rates in similar samples containing Zn(II) were 14, 19 and 23%. The liquid limit of samples also decreased when the concentration of heavy metals increased to 25 cmol/kg-soil. The reduction in liquid limit was 21%, 15% and 14% for Pb(II) and 16, 12 and 7% in the presence of Z(II) for samples with 10, 25 and 40% of sand respectively. Significant decrease in the amount of cohesion also observed according to the test results. In the ratio of 40% sand the cohesion decreases 51% and 24% for Pb(II) and Zn(II) when the concentration of heavy metal increased from 0 to 25 cmol/kg-soil. The results of unconfined compression tests show that there is noticeable reduction up to 52% due to Pb(II) with the concentration of 25 cmol/kg-soil in the ration of 60% kaolinite and 40% sand.