Freezing point of sodium sulfate loess in check dams after freeze-thaw

When evaluating the range of salt weathering of loess check dams during freeze-thaw, the freezing point and its relationship to suction should be considered. Field surveys on the salinity of loess slopes of check dams in Shenmu county of northern Shaanxi were conducted in spring from 2019 to 2021. Marked salt concentration was observed in the slope surface, approaching the threshold of saline soil of 0.3% and sodium sulfate was the main component. Freezing point, suction and microstructure of sodium sulfate loess after freeze-thaw were studied. Results show that soil freezing point decays with freeze-thaw cycles, which is linked to pore structure and particle morphology, as revealed from quantitative indexes of soil microstructure. The matric suction of sodium sulfate loess declines with freeze-thaw, while the osmotic suction that depends mainly on solute concentration is less correlated. The Mizoguchi model was found to be valid for estimating the freezing point of salt-free loess, but it deviates significantly for sodium sulfate loess. To address the above limitation, a modified model that considers the correlation between soil freezing point and suction under freeze-thaw conditions was suggested and verified by test data.