通过不同降温条件的冻结试验，明确了土中出现过冷的条件。当环境温度高于土的最低过冷温度时，土表现出稳定的过冷状态；当环境温度低于最低过冷温度时，边界出现短暂过冷，而土样内部不出现过冷。通过分级降温的方法测定了不同含水率的粉质黏土和细砂以及不同NaCl浓度的粉质黏土的冻结温度和最低过冷温度。当含水率等于或高于饱和含水率时，含水率对冻结温度影响不大；当含水率低于饱和含水率时，冻结温度随含水率减小而降低；不同含水率土样的最低过冷温度相差不大；冻结温度降低随NaCl浓度增大的比例系数与理想稀溶液中水的凝固点降低系数非常接近。结合稳定冻结时间、冻结温度、环境温度或最低过冷温度引入了能间接反映自由水含量的指标。

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.