Abstract: This paper ascertains the condition of super-cooling of soil with experiments under different freezing conditions. If the environmental temperature is higher than the lowest super-cooling temperature, the super-cooled state of the soil specimen is stable. If the environmental temperature is lower than the lowest super-cooling temperature, the boundary of the specimen shows super-cooled for a short time while the inside of soil specimen is not in super-cooled state. With lowering the temperature step by step, this paper measures the freezing temperatures and lowest super-cooling temperatures of the silty clay and fine sand with different water contents and the silty clay with different NaCl concentrations. The water content has little influence on the freezing temperature of soil when the water content is equal to or greater than the saturated water content. The freezing temperature of soil lowers with reducing the water content if the water content is less than the saturated water content. The lowest super-cooling temperatures for soils with different water contents are nearly the same. The freezing temperature lowers with increasing the NaCl concentration. The coefficient of freezing temperature lowering is very close to that of the ideal dilute solution. A parameter representing the free water content is given along with the use of the factors such as steady time, freezing temperature, environmental temperature or lowest super-cooling temperature.

Key words: frozen soil, freezing temperature, super-cooling temperature, temperature-time curve, experimental study