Specific ion effects on the rheological properties of soils from the Loess Plateau of China

AbstractSpecific ion effects have important impacts on the interaction forces between soil particles, which could strongly affect soil structure, water infiltration and soil erosion. Nevertheless, little is known about how specific ion effects affect soil rheological properties. In this study, the specific ion effects (Na+, K+, and Cs+) on soil rheological properties were systematically investigated using rheometer and quantitatively interpreted through theoretical analysis of soil internal forces. The results showed that specific ion effects pose important effects on soil rheological properties. Specifically, soil rheological parameters such as stress (τ_LVR) and strain (γ_LVR) at the end of the linear viscoelastic region (LVR), as well as shear stress (τ_YP), strain (γ_YP), and storage modulus (G′_YP) corresponding to the yield point (YP) initially remained relatively constant (10−5–10−2 mol L−1), and then increased rapidly (10−2–1 mol L−1) for each cation system, indicating the enhanced soil shear resistance and viscoelasticity. At the same electrolyte concentration, the soil rheological parameters followed the order: Cs+ > K+ > Na+ across all cation systems. The soil rheological parameters for all three cation systems displayed a clear negative exponential relationship with the net force considering cationic non-classical polarization. Strong electric fields surrounding soil particles caused cationic non-classical polarization which significantly reduced electrostatic repulsion between soil particles and finally led to the increase of soil rheological parameters. Additionally, the differences in the ion dispersion forces increased as electrolyte concentration increase at high concentrations (> 10−1 mol L−1), leading to greater discrepancies in the soil rheological parameters among different cation system. This study offers critical insights into the underlying mechanisms governing soil flow and deformation behavior and opens the possibility of improving soil structure by adjusting the soil internal forces.