Evaluation of the relationship between freezing point and suction of sodium sulfate loess near 0°C

Correlation between freezing point and suction of sodium sulfate loess upon phase change is fundamental for understanding the mechanism of salt weathering of check dams in Loess Plateau of China. Given the ongoing controversies over frozen soil suction measurement, soil suction test near 0°C was employed as a compromise to link with freezing point. The test data from vapor equilibrium technique (VET) and the TEROS-21 Gen 2 soil water potential sensor were combined with the reported data to derive a temperature-dependent calibration model from the correspondence between the suction and the equilibrium water content of Whatman No. 42 filter paper. This model holds the merits of robust accuracy, simple structure with merely two parameters to be calibrated, and the capacity to capture the temperature effect on the calibration curve. The freezing point of sodium sulfate loess is closely linked to the suction at 0.5°C. Both matric and osmotic suctions do not linearly superimpose on the freezing point but exhibit a coupling effect. A modified Mizoguchi model was accordingly developed and verified for five types of saline loess. The results will throw light on the nature of salt weathering of check dams and are also encouraging for targeted treatments.