Abstract: The aim of this research is to explore a new method for evaluating the strength characteristic rapidly of heavy metal-contaminated red clay. Direct shear test and resistivity test were carried out for Cu²⁺ contaminated red clay specimens of varied concentration and dry density. The curves of shear stress and resistivity of Cu²⁺ contaminated red clay varying synchronously with shear displacement were obtained. Meanwhile, the impacts of initial dry density, vertical pressure, and Cu²⁺ concentration on shear strength and resistivity were analyzed. According to the principle of shear strength indexes (C and φ), resistivity indexes (ρ₀ and φ₀) were selected, and the effects of Cu²⁺ concentration on shear strength indexes and resistivity indexes were examined. Furthermore, the quantitative relations between shear strength (indexes) and destructive resistivity (indexes) were discussed. Test results unveiled that the shear stress-displacement curve of Cu²⁺ contaminated red clay displayed typical strain hardening features, while resistivity declined with the increase of shear displacement. Shear strength augmented approximately linearly with the growing of initial dry density and vertical pressure while destructive resistivity showed opposite trend. Both shear strength (indexes C and φ) and resistivity (indexes ρ₀ and φ₀) were in a negative exponential functional relation with Cu²⁺ concentration. In addition, the curve of shear strength vs. resistivity, curve of cohesion vs. initial resistivity, and curve of internal friction angle vs. inclination of resistivity relation curve displayed consistent trend, showing a good positive exponential function relationship.

Key words: red clay, Cu²⁺ contamination, shear strength, cohesion, internal friction, resistivity, heavy metal contamination