Experiments on the initial freezing point of dispersive saline soil

In this study, the characteristic of the initial freezing point (IFP) of a dispersive saline soil (lean clay) with different contents of water and salt was investigated, and ten freeze-thaw cycles were conducted to investigate their impacts on the IFP. The soil freezing characteristic curves (cooling curves) for this soil under different experimental combinations did not all exhibit the supercooling phenomenon, and some curves did not display equilibrium stages. A method was therefore proposed to determine the IFP by reading the subzero temperature corresponding to the inflection point on a cooling curve without an equilibrium stage. It was interesting to note that increasing the water content lowered the IFP of the dispersive saline soil, and the IFPs subjected to different numbers of freeze-thaw cycles had the same values when the water content was between the optimum water content and the plastic limit, but when the water content exceeded the plastic limit, the IFP dropped considerably. The IFP of bicarbonate dispersive saline soil first dropped monotonically and then remained unchanged regardless of the number of freeze-thaw cycles. The IFP of sulfate dispersive saline soil was evidently affected by the freeze-thaw cycles, and its variation trend could be divided into 3 stages. HCO3− had a greater influence on the IFP than SO42−. Correlation analysis indicated that the freeze-thaw cycle had no significant effect on the IFP of dispersive saline soil with changing water content. However, more than 10 freeze-thaw cycles might cause a statistically significant impact on the IFP of bicarbonate dispersive saline soil, whereas 5 and 7 cycles had significant (p < 0.05) and strongly significant (p < 0.01) impacts on the IFP of sulfate dispersive saline soil, respectively. The findings can provide rational and experimental references for the research on the IFP of dispersive saline soil.