Abstract: Dispersive soil is prone to erosion when subjected to significant hydraulic gradients, also referred to as piping failure. In the case of earth dams, such failure can cause a grave threat to residents surrounding. This creates a pressing need for a systematic study on the dispersive mechanism of cohesive soils. In this work, we evaluate the dispersivity of loess specimens taken from Jingyang, Shaanxi, through combining pinhole test, pore water salts test, and empirical formula, focusing on the key factors of dispersivity and the underlying mechanism for loess changing from agglomeration to dispersion structure. The results show that the soil is prone to disperse when its pH value is alkaline and its cation content and exchangeable sodium ion content meet the conditions of CNa+ > 1 mmol/L and ESP > 7%, respectively. Comparison with similar problematic soils in other countries reveals that for the Jingyang loess, its electric potential ξ is mainly influenced by the pH value rather than the clay content or liquid limit; Its relatively low dielectric constant is due to a low liquid limit. Its soil salt content or moisture content can affect the change in the soil-water mixture dielectric constant in the imaginary part, i.e., the change in dielectric loss, but its dispersivity remains significant.

Key words: loess, dispersivity, pinhole test, dispersive mechanism