Laboratory study of strength, leaching, and electrical resistivity characteristics of heavy-metal contaminated soil

In this work, geotechnical properties of heavy-metal contaminated soil consist of basic properties, strength, leaching, electrical resistivity and microstructural characteristics were investigated. The results showed that the clay content, specific surface area and cation exchange capacity of the soil decreased as heavy-metal concentrations increased. The decrease in basic properties was more significant in Zn-contaminated soil than that in Pb-contaminated soil. The unconfined compressive strength (UCS) decreased as heavy-metal concentrations increased. The effect of Zn2+ on UCS was confirmed to be greater than that of Pb2+. The leached heavy-metal concentration increased with higher initial heavy-metal concentrations. A greater leaching capacity was observed in Zn-contaminated soil compared to Pb-contaminated soil. With increasing pore fluid resistivity, UCS values gradually increased and leached ion concentrations dramatically decreased before becoming stable. Zn-contaminated soil was found to have a lower strength and higher leached-ion concentration than Pb-contaminated soil. A set of equations was proposed to successfully predict the engineering properties of contaminated soil using pore fluid resistivity. Microstructural analysis presented that, as heavy-metal concentrations increased, clay particles aggregated, the flocculation structure and the inter-aggregate pores became enlarged. Zn-contaminated soil had larger aggregate and inter-aggregate pores, compared to Pb-contaminated soil. In general, significant effects of heavy metal ions on geotechnical properties of the contaminated soil have been revealed and analyzed in the present work, which could be predicted using the pore fluid resistivity in a more effective way.