| Frost heave severely damages revetments of rivers, canals, lakes, and reservoirs in cold northern China. Soil replacement with low-frost-susceptibility sand is a common countermeasure. However, significant frost heave deformation and cracking still occur in concrete-lined channels with sand fill and low groundwater, defying classical hydro-thermo-mechanical theory. This study establishes a frost heave model for revetments based on water-heat-vapor-structure coupling theory, specifically accounting for vapor migration. The model couples temperature, moisture (liquid/vapor), and stress-strain fields, focusing on the impervious concrete slab's "canopy effect." Applied to the sand-filled North Main Canal (Kaidu River, South Xinjiang), the model reveals: while sand's low water retention inhibits liquid water migration and replenishment, its large pores facilitate vapor migration towards the cold slab under thermal and vapor pressure gradients. Vapor condenses under the slab, forming ice lenses with a volume far exceeding the soil's porosity. During the thawing period, these ice lenses melt rapidly, causing supersaturation of the base soil, loss of matric suction and shear strength, drastically increasing slope failure risk. This vapor-driven "canopy effect" is the key mechanism behind frost damage in low-susceptibility sand fills. The model reveals the intrinsic mechanism and deformation patterns of lining structures that lead to significant frost heave damage in practical engineering even after backfilling with non-frost-susceptible materials. It provides a theoretical basis for predicting frost damage and designing anti-frost heave measures in water conveyance channels in cold regions. |