Effects of chemical solutions on the hydromechanical behavior of a laterite/bentonite mixture used as an engineered barrier

Abstract

Compacted laterite and bentonite, as well as a mixture of the two, are strongly impermeable and can effectively prevent the migration and diffusion of contaminants. This study explored the feasibility of employing a laterite/bentonite mixture as a vertical barrier in landfills, tailings ponds, or sites contaminated by heavy metals. Permeability tests using chemical solutions of different concentrations and compression tests were performed on mixed bentonite/laterite samples with different dry densities and mixing ratios. The permeability and consolidation characteristics were verified using scanning electron microscopy. The hydraulic conductivity of the laterite samples decreased with increased dry density, and the hydraulic conductivity of the mixed-soil samples decreased with increased bentonite content. Adding bentonite significantly improved seepage control performance. The hydraulic conductivity of the pure laterite was 4.7 × 10−7 cm/s, whereas that of the laterite sample mixed with 20% bentonite was 1.6 × 10−8 cm/s. The compacted laterite with a dry density of 1.5 g/cm3 was demonstrated to satisfy the permeability specifications to serve as a landfill seepage control system. When the concentration of the heavy metal or salt solutions increased, the laterite flocculation increased, and the hydraulic conductivity decreased. The laterite in the mixed soil samples substantially affected these characteristics, particularly decreasing the hydraulic conductivity. As the concentration of the chemical solutions increased, the yield stress of the compacted samples and the compression index decreased, and the compression performance improved. These findings indicate that chemical solutions significantly affect the hydromechanical behavior of a laterite/bentonite mixture used as an engineered barrier.