VOLUME CHANGE AND PERMEABILITY CHARACTERISTICS OF RED CLAY-BENTONITE MIXTURES UNDER WETTING-DRYING CYCLES AND SALT SOLUTION INFILTRATION

To investigate the performance evolution of red clay-bentonite mixtures concerning wetting-drying cycles and chemical conditions,volume change and permeability tests were conducted on red clay-bentonite mixtures under salt solution infiltration and wetting-drying cycles. The effects of wetting-drying cycles,bentonite contents,and salt solution concentrations on the compacted mixtures were analyzed. The microscopic mechanisms of shrinkage and hydraulic conductivity after different wetting-drying cycles were revealed through mercury intrusion porosimetry(MIP)tests. Experimental results demonstrated that the shrinkage of compacted soil samples increases gradually with an increase in wetting-drying cycles and salt solution concentration. The hydraulic conductivity of the soil samples increases first and then decreases during the wetting-drying cycles. Meanwhile,the addition of bentonite improves the chemical capacity of the soil samples and has the potential to decrease hydraulic conductivity and volume change. MIP test results revealed that the total pore volume and the macro-pore diameter of the soil samples decrease after wetting-drying cycles,and the bimodal characteristics of the pore distribution curves weaken. Furthermore,with an increase in salt solution concentration,the micro-pores remain constant,and the porosity of the soil decreases with a decrease in macro-pores,resulting in greater shrinkage deformation and decreased hydraulic conductivity.