Canals are essential for water transfer in cold and arid regions. However, they are vulnerable to damage under drying-wetting and freezing-thawing cycles, with wetting during freezing–thawing periods significantly intensifying frost damage. Yet, the underlying mechanisms involving heat-water-deformation interactions remain insufficiently quantified. This study employs field monitoring to investigate temperature, water content, and deformation behaviors in canals. Then, a coupled water-heat numerical model incorporating seepage effects was developed and applied to analyze how leakage increases soil moisture and exacerbates frost damage. Results show that canal temperatures are controlled by water temperature and leakage during water supply, and by air temperature and solar radiation during water cut-off, with freeze–thaw transitions further modulating thermal behavior. Shady slopes freeze more readily, whereas sunny slopes experience greater evaporative loss. Spring irrigation sharply lowers the 0 °C isotherm below water level, triggering peak frost heave at its onset, followed by rapid thawing. Frost heave is lowest on sunny slopes and greatest at mid-shady slopes, with maximum differences exceeding sixfold. After thawing, minor slippage occurs on shady slopes, while sunny slopes remain stable. Canal frost damage is driven by elevated soil water from leakage and winter irrigation, as well as sharp thermal imbalances induced by spring irrigation and solar radiation disparities between slopes. Preserving the integrity of anti-seepage systems proves more effective in mitigating frost damage than early termination of winter irrigation. This study provides the first integrated field-based and modeling evidence on frost damage mechanisms in cold-arid canals, establishing a scientific foundation for mitigation strategies.
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