Abstract: To assess the impact of wetting-drying cycles on the hydraulic properties of undisturbed loess, we performed saturated permeability tests and soil-water characteristic tests on Q₃ loess from Gansu Province under four different wetting-drying cycle paths. The aim is to examine the changes in permeability and soil-water characteristic curves (SWCC) with the number of cycles, cycle amplitude, and lower bound water content. Results revealed that the deterioration of saturated permeability coefficients can be modeled using a hyperbolic function with respect to wetting-drying cycles. After six cycles, the deterioration tends to stabilize. As cycle amplitude increases, the deterioration of saturated permeability coefficients exhibits a linear increase, while a linear decrease with the rise in lower bound water content. The SWCC of loess can be represented by the V-G model; parameters θ_s, α, and n remain relatively unaffected, whereas the parameter θ_r declines exponentially with an increase in the number of cycles. Deterioration models for saturated permeability coefficients and SWCC models considering the above three parameters of wetting-drying cycles are established, enabling the prediction of unsaturated permeability coefficients of loess.

Key words: undisturbed loess, wetting-drying cycles, permeability coefficient, soil-water characteristic curve, deterioration model