To investigate mechanism of compressive deformation of red clay contaminated by heavy metal Cu+

CuSO solutions with concentrations of 0

2.5

5.0

and 10.0 g/L were used to prepare the contaminated soil

and consolidation tests

thermal analysis tests

and scanning electron microscopy (SEM) tests were conducted. The results show that the changes of compression coefficient and total compressive deformation of red clay and the changes of pore water (free water

weakly bound water and strongly bound water) content in the clay show the same trend of decreasing first and then increasing with the increase of Cu+ concentration. The structural connection between soil particles in clay soil is mainly based on adsorption water film contact. Cu+ changes the water film thickness of pore water in soil

which leads to the change of pore water content. The water film becomes thinner

the distance between soil particles shortens

the higher the structural strength of soil body

and the greater the ability of soil body to resist compression deformation. With the increase of Cu+ concentration

the microstructure of soil body gradually evolves from loose block-like and flaky units to stacked aggregates with face-to-face contact. When the concentration of Cu+ increases to 10.0 g/L

scale-like units start to appear

the contact mode between units is mainly point-point contact and edge-face contact

the cohesion between soil particles becomes poor

and the structural stability of soil body decreases.