Abstract: The swelling deformation and swelling force of bentonite in contact with water are caused by the repulsive force between particles, and the magnitude of this repulsive force is related to the fixed negative charge density of the soil (represented by the cation exchange capacity, CEC) and the concentration of the pore solution. The previous research on the swelling deformation of bentonite is mainly focused on the pore solution rather than the cation exchange capacity of the soil. In this paper, sodium bentonite is taken as the research object, and Li⁺ fixation method is used to control the fixed negative charge density of bentonite so as to reduce the cation exchange capacity of bentonite. Finally, the free swelling rates of reduced charge bentonite are obtained under different concentrations of LiCl solution. The results show that the free swelling rate of soil samples decreases with the increase of solution concentration; when the concentration is less than 1 mol/L, the decrease is more significant, and then slowly decreases; the free swelling rate of soil samples also decreased as CEC decreases. The physicochemical interaction between the soil particles and pore solution depends on CEC of soil particles and salt solution concentration. Lower CEC and higher salt concentration mean lower repulsive force between soil particles and lower free swelling rate of soil sample. The intergranular stress with the consideration of the physicochemical interaction between particles and pore solution is introduced to describe the experimental results, showing that the swelling deformation and swelling stress under different CECs and different salt solutions are merged on the same curve, which further verifies the effectiveness and applicability of the intergranular stress in simulating expansive soil.

Key words: reduced charge bentonite, Hofmann-Klemen effect, salt solution, free swelling rate, intergranular stress