Enhancement of leachate-contaminated clay soils with silver nanoparticles: Physical, mechanical, and microstructural effects

Landfill leachate is a chemically aggressive effluent that can migrate into surrounding ground and degrade the engineering performance of fine-grained soils by modifying pore water chemistry, weakening interparticle bonding, and increasing fabric heterogeneity. These processes can reduce strength and stiffness and promote localized deformation in geotechnical systems near waste disposal facilities. This study evaluates an aqueous silver nanoparticle additive (AgNPs) for improving clay under municipal landfill leachate contamination by integrating mechanical testing, nondestructive ultrasonic pulse velocity (UPV), and microstructural observations. Natural clay and fully leachate-contaminated clay were treated with AgNPs dosages of 0%, 0.005%, 0.01%, and 0.015% by dry soil mass. Unconfined compressive strength (UCS) and the secant stiffness modulus at 50% of peak stress (E50) were derived from stress-strain responses. Leachate contamination weakened the clay skeleton, whereas AgNPs increased strength and stiffness. UCS rose from 179 kPa to 245 kPa in the natural series and from 88 kPa to 114 kPa in the contaminated series at 0.01% AgNPs. E50 increased from about 1950 kPa to about 3350 kPa for natural clay and from about 1050 kPa to about 2150 kPa for contaminated clay, while UPV increased from 889 m/s to 1095 m/s and from 511 m/s to 741 m/s, respectively. Microstructural evidence confirmed matrix densification and reduced pore connectivity, although pore size heterogeneity remained more pronounced under contaminated conditions. Overall, the results demonstrate the practical potential of low-dosage AgNPs to enhance mechanical performance and internal integrity in leachate-affected clays.