Cyclic and monotonic mechanical behavior of heavy metal-contaminated clayey sand stabilized with zeolite

Abstract

Heavy metal contamination in soil presents challenges to geoenvironmental engineering, requiring stabilization to ensure soil performance under various loads. This study investigates the cyclic and monotonic triaxial behavior of heavy metal-contaminated clayey sand, focusing on the influence of clay type (kaolin and bentonite) and zeolite inclusion (5%, 10%, and 15%). A series of laboratory tests were conducted, including consolidated undrained triaxial tests, cyclic triaxial tests, bender element tests, compaction tests, and adsorption tests. In kaolin-based mixtures, contamination decreased peak shear strength by up to 22% and elastic modulus by 28%, due to reduced internal friction despite increased cohesion. In contrast, bentonite-based mixtures showed a 17% increase in shear strength and a 24% rise in elastic modulus with contamination, driven by higher internal friction angles. Zeolite addition improved cohesion and limited strength and stiffness losses, with 10% zeolite inclusion identified as optimal. Under cyclic loading, heavy metal contamination reduced liquefaction resistance, in kaolin mixtures, while 5–10% zeolite addition increased liquefaction resistance by reducing cyclic axial strains by up to 32%. Contamination also lowers small strain shear modulus by 20–30% and raises damping ratio by 15–30%, of which zeolite addition helps stabilize. Atterberg limits, pH measurements, and SEM imaging collectively demonstrate that cation exchange and diffuse double-layer compression govern the observed macroscopic behavior. Zeolite enhances heavy metal adsorption in contaminated soils by up to 70% at 5% content and further by 26% at 10%, with 10% zeolite appearing optimal for adsorption effectiveness.