Evaluation of water retention characteristics in frozen sandy soils using an environmentally controlled column test

Water retention properties in frozen soils, including the soil freezing characteristic curve (SFCC), soil water characteristic curve (SWCC), and hydraulic conductivity, are crucial for understanding water infiltration and climate change in cold regions. In this study, a novel experimental system was developed and conducted to simultaneously investigate the SFCC, SWCC, and hydraulic conductivity of sandy soils during the freezing and thawing phases. SFCC and SWCC were measured during freezing and thawing, while hydraulic conductivity was assessed under unfrozen, frozen, and thawing conditions. The results showed that supercooling effects cause a freezing point suppression of approximately 2 °C, with significant hysteresis observed in SFCC and SWCC, especially at 100 % initial saturation (S_r,i). The ice-entry value (IEV) during freezing was determined to be inversely proportional to S_r,i, with values decreasing by up to 25 % as S_r,i increased from 50 % to 100 %. Hydraulic conductivity during freezing was significantly lower than in thawing or unfrozen states, decreasing by up to 80 % at S_r,i ≥ 30 % due to pore ice formation. Differences in the IEV and air-entry value (AEV) between freezing and thawing phases were attributed to latent heat exchanges during phase transitions. This study highlights the interconnected behaviors of SFCC, SWCC, and hydraulic conductivity under freeze-thaw cycles. These findings enhance our understanding of soil behavior under freeze-thaw cycles and provide critical data for improving water infiltration models in frozen soils.