Saline seepage circulation experiment study on low plastic limit clays combined with microscale tests and the fractal theory

Owing to its high flexibility and low permeability characteristics, clayey soil has been largely used as impermeable material in pollutant burial fillers. Soil permeability is very sensitive and highly pertains to its microstructure. When subjected to the saline environment changes, the changes in soil permeability may increase leakage risk in the burial fillers and endanger the environment. Herein, to facilitate the understanding of the negative correlation between the permeability and ion concentrations in some low plastic limit clays, NaCl solution seepage circulation experiments considering different porosities, sample preparation methods, and ion concentration stages were conducted. Combined with the micro test methods (SEM and MIP) and the fractal theory, the changes in soil permeability at different ion concentrations and the mechanism were studied. The main results showed that compression methods are more suitable than the impact-involved methods for making uniform soil samples; the decrease of the soil’s pore fractal dimension evidenced that the growth of ion concentration would increase the dispersal of soil particles while the morphological change of the dispersal process resembles the blossom of a flower, i.e., the sprout→bud phase→blossom; the dispersed particles are prone to form flocculation in large-size pores (6–8 μm in this paper) and decrease the soil permeability. This dispersal and flocculation effect progressively triggered by the growth of ion concentration can provide new insight into understanding the negative correlation between the permeability and ion concentrations in some low plastic limit clays.