Study on permeability characteristics of Yili loess under freeze-thaw cycles

The fundamental mechanism underlying freeze-thaw-induced loess landslides is closely associated with changes in soil structure and permeability during repeated freezing and thawing. This study systematically investigated the effects of different moisture contents (7%, 14%, 21%, 28%) and freeze-thaw cycles (0–40 cycles) on the permeability characteristics of Ili loess through triaxial permeability tests and scanning electron microscopy (SEM) analysis. Results demonstrate that under freeze-thaw cycles: Low moisture content samples (7%, 14%) present a “decline–rise” trend in permeability coefficient, reaching minimum values at 5 cycles; high moisture content samples (21%, 28%) show a three-stage “increase–decrease–increase” fluctuation pattern, stabilizing after 20 cycles. Freeze-thaw cycling alters the soil structure through a progressive damage sequence involving pore development during freezing, crack initiation and coalescence, and the formation of interconnected preferential flow channels. Porosity and permeability coefficients change synchronously, displaying an overall “stable-unstable-stable” evolution. Low moisture groups (7%, 14%) reach minimum porosity values of 42.3% and 30.5%, respectively, at 5 cycles, while high moisture groups (21%, 28%) peak at 39.6% and 41.9% after 3 cycles, both stabilizing post 20 cycles. SEM observations reveal distinct particle boundaries and a compact structure in unfrozen samples, developing surface irregularities and particle fragmentation after 3 cycles, with re-emerging clearer contours but a looser structure after 20 cycles. The study demonstrates that moisture content regulates pore reorganization through ice crystal distribution, while cumulative structural damage from freeze-thaw cycles drives nonlinear permeability evolution. These findings provide theoretical support for seepage field modeling and early warning of freeze-thaw loess landslides.