Predicting chemical influence on soil water retention curves with models established based on pore structure evolution of compacted clay

The mechanism of the effect of salt solution on the water retention capacity of compacted clay is studied from the microscopic perspective. Based on the fractal theory and the double-porosity characteristic of compacted clay, the fractal model and dual-porosity model for predicting the soil-water retention curve of compacted clay are established. And the gravimetric water content and matric suction calculated from the pore size distribution data in the relevant literature are fitted by the established models. Results show that there is a "flat section" caused by the dual-porosity structure of compacted clay in the soil-water retention curve, which tends to be lower with the increase of salt solution concentration. In this case, the dual-porosity model fits the data better than the fractal model. The soil-water retention curve shows no "flat section" for the compacted clay with inconspicuous dualporosity structure. Due to the inhibition of the formation of the diffusion double layer, the reduction of macropore volume is prevented during hydration. The chemical correction equation for the fitting parameters is also established, which well reflects the change of the fitting parameters with the concentration of solution by using the two models to predict the soil-water retention curves of compacted BES (rho d = 1.5 Mg/m3) and compacted FEBEX bentonite (rho d = 1.65 Mg/m3). The modified parametric equation is substituted into two models, and subsequently the modified soil-water retention model considering the effect of pore structure and chemical solution is obtained.