土冻结过程中水热变化特性的模型试验研究

为研究正冻土水热变化特征及它们之间联系，对非饱和黏土进行单向冻结模型实验，结果表明：土在冻结温度附近降温速率最小，持续时间较长；靠近表面土降温快，较其下部土提前进入冻结，且冻结历时短；靠近顶面的测点温度曲线重合度不如其下层，可能因为受外界次要因素干扰时深层土壤受影响小；正冻土温度分布大致分为两段，冻结区线段斜率大于未冻区，随冻结时间增加，非冻结险段线段斜率会先增大后减小，最终两段线变为一段线，此时温度沿土柱高度线形分布；未冻水含量变化拐点大致在冻结锋面处，距冻结锋面越近，吸力越大，水分迁移量越大，随冻结时间的增加，非冻结区水分迁移速度变大；未冻区土水势梯度最小，正冻区及冻结区土水势梯度大小关系并不明确；未冻水含量变化与温度变化一致，未冻水含量变化分为三个阶段：缓慢下降阶段、快速下降阶段、指数下降阶段。

Model Experimental Study on the Change Characteristics of Hydrothermal in Soil During Freezing

In order to study the characteristics of water and heat changes of the normal frozen soil and the relationship between them, the unidirectional frozen model experiment of unsaturated clay was carried out. The results showed that the cooling rate of soil near the freezing temperature is the smallest and lasts longer; Near the top surface of soil cool faster and enters into the freezing earlier than lower part of the soil, and its freezing period lasts for a short time; the coincidence degree of the temperature curve near the measuring point of the top surface is not as good as that of the lower part, which may be due to the smaller influence of the deep soil caused by the secondary factors; the temperature distribution of the freezing soil can be roughly divided into two sections, the slope of the frozen section is larger than that in the unfrozen section. As the freezing time increases, the slope of the non-frozen section firstly increases and then decreases, and finally the two sections become a section of line.And the temperature is linearly distributed along the height of the soil column. The inflection point of unfrozen water content change roughly is at the frost front, and the closer the frost front is, the larger the suction is and the greater water migration is; With the increase of freezing time, the water migration rate becomes larger; the gradient of soil water potential is the smallest in unfrozen area, and the relationship between the gradient of soil water potential in the freezing and the frozen area is not clear; Unfrozen water content changes consistently with the temperature, change of unfrozen water content is divided into three stages: slowly decline stage, rapidly decline stage, Exponentially decline stage.