Abstract: In order to study the influence of heavy metal ions intrusion on the soil engineering properties, the typical clay layer in Jingjiang City of Jiangsu Province was selected. Soil samples with five concentrations of CuSO₄ solutions (0%, 0.5%, 1%, 2% and 3%) were prepared. Direct shear test, triaxial test, unconfined compressive strength test and compression test were used to investigate the difference of mechanical properties before and after CuSO₄  contaminated soil samples, and the corresponding environmental tests and X-Ray powder Diffraction (XRD) tests were used to compare the results The results show that the minimum shear strength of the soil sample appears at the concentration of 0.5% CuSO₄  in direct shear test and triaxial test, and the minimum value of unconfined compressive strength appears in the concentration range of 0.5%~1% CuSO₄ . The cohesion and unconfined compressive strength of the two tests decrease first and then increase, showing a “concave” type change. The extreme value of the cohesion change appears at 0.5%. The results of triaxial test show that the internal friction angle decreases, while the direct shear test value oscillates. The acidic CuSO₄  solution would dissolve the cementitious substances in soil samples, and Cu²⁺ would destroy the original electric double layer structure, resulting in the thinning of the bound water film and the reduction of the strength. The CuSO₄  solution with high concentration had a single electric layer structure and produces colloidal substances.

Key words: CuSO₄ ,  , pollution, clay, cohesion, environmental properties