Stress-strain behavior of heavy metal-contaminated sand-clay mixtures stabilized with carbonate

The leakage of heavy metals from pipelines, chemical storage, and industrial waste in response to industrialization and suburban development is a significant environmental concern. These heavy metals can profoundly impact the geotechnical properties of clayey soils, notably shear strength and soil microstructure, which play a crucial role in the design of landfills and buffer liners. Due to the susceptibility of clay liners to shrinkage cracks, compacted sand-clay mixtures (SCM) are preferred in landfills. Thus, this research aims to investigate the unconfined compressive strength characteristics of various SCM contaminated with three lead concentrations (0.1, 0.2, 0.5 mol/l). Three types of clay including bentonite, kaolinite, and zeolite were used to study the shear behavior of SCM for liners. Additionally, the impact of sodium carbonate additives as a remediation technique for the contaminated soil was assessed. Results indicate that sodium carbonate enhances the shear strength of heavy metal-contaminated sand-kaolinite mixtures (SKM), while it reduces the shear strength of contaminated sand-bentonite mixtures (SBM). The differential behavior of SKM and SBM is attributed to the respective changes in diffuse double layers. Despite bentonite having a larger specific surface area, the primary characteristic of sand-kaolinite-bentonite mixtures (SKBM) is governed by bentonite. Consequently, the addition of sodium carbonate to contaminated SKBM results in a slight reduction in peak axial stress. Furthermore, although the compressive strength of contaminated SKM is significantly reduced with the introduction of 5% zeolite, the incorporation of sodium carbonate in the mixture restores its strength. From a practical standpoint, while carbonate treatment improves the performance of buffer liners against heavy metal contamination, the remediated soil may not be suitable for load-bearing purposes.