Experimental Study on the Engineering Properties and Resistivity of Clay Contaminated by Alkali and Heavy Metal Ions

The enrichment of metal ions on the surface of clay particles significantly leads to the loosening of the particle surface structure, thereby weakening the macroscopic engineering properties of the clay. In this study, sodium ions (Na⁺) and potassium ions (K⁺) as monovalent metal ions, along with lead ions (Pb²⁺) and zinc ions (Zn²⁺) as divalent metal ions, were selected as metal ion contaminants. The focus was to investigate their effects on the microstructural morphology, macroscopic engineering properties, and electrical properties of the clays. The aim of the study is to clarify the relationship between the valence state and concentration of these four types of metal ions and the engineering properties of clay, and to predict the engineering properties of metal-ion-contaminated clay using resistivity parameters. The results indicate that the incorporation of metal ions reduces the average particle size, transforming the soil structure from flaky to a honeycomb form. Under the same loading conditions, metal-ion-contaminated clay exhibits a lower void ratio. As the concentration of metal ions increases, pore volume decreases, thereby enhancing soil compressibility. Alkali metal ions primarily influence the soil structure through a dispersive effect, while heavy metal ions exert a cohesive effect. Monovalent alkali metal-ion-contaminated clay demonstrates larger compression coefficients across all load levels, whereas heavy metal-contaminated soils exhibit higher compression coefficients under low loads. Furthermore, the shear strength and cohesion of metal-ion-contaminated clay are lower than those of field-state clay. At lower concentrations, the internal friction angle may exceed that of field-state clay; however, as the concentration of metal ions increases, the shear strength, internal friction angle, and cohesion significantly decrease. The presence of metal ions also reduces soil resistivity, which declines at a diminishing rate with increasing concentration. At lower ion concentrations, monovalent alkali metal ions have a slightly stronger effect on reducing resistivity compared to divalent heavy metal ions. Resistivity parameters effectively reflect the compressibility and shear characteristics of metal-ion-contaminated clay, revealing a negative linear correlation between resistivity and compression ratio under uniaxial loading, while a positive linear correlation exists with shear strength, internal friction angle, and cohesion. These insights provide a basis for the rapid evaluation of engineering characteristics in metal-ion-contaminated clay.