Influence and microscopic mechanism of heavy metal invasion on physical and mechanical characteristics of silty clay

Abstract Heavy metal ions significantly alter the physical and mechanical properties of soil following infiltration, thereby jeopardizing the stability of existing structures and constraining the land's comprehensive utilization. As the concentration of heavy metal ions increased, the electrical resistivity of contaminated soils decreased by approximately 90%, the proportion of clay particles reduced, particle size increased, and both the liquid and plastic limits, as well as the plasticity index, decreased by 2%. The thermal conductivity increased by about 17%, and the permeability coefficient remained in the range of 10 −4 cm/s. Heavy metal ions degraded the soil's strength, with unconfined compressive strength of soils contaminated with 2.0% copper, cadmium, and lead decreasing by 34%, 21%, and 28%, respectively. Cohesion decreased by 28%, 38%, and 48%. The intrinsic mechanisms of heavy metal ion infiltration into silty clay were revealed through SEM, XRD, and FITR tests. Microstructural changes correlate strongly with macroscopic test results. This study on the impact of heavy metal infiltration on the engineering properties of soil, and its underlying mechanisms, provides a crucial theoretical basis for assessing soil pollution, remediation efforts, and the effective utilization of contaminated sites.