正冻土在温度梯度大的情况下，冻结锋面快速移动，孔隙水变成冰，造成原位体积膨胀；而通常在天然条件下，温度梯度都不大，水从未冻区向冻结区迁移，在某一个位置引起冰的累积，形成分凝冰。由于此诱发的冻胀要比原位冻胀大很多，因此，建立一个能够模拟土体水分迁移及分凝冰形成过程的冻胀模型尤其重要。基于第2冻胀理论，建立了饱和土体冻胀模型。在模型中，假设冻结缘中单位时间内水分迁移速度为常数，以计算冻结缘内水压力，再根据克拉方程得到冰压力。根据冰压力的大小作为分凝冰形成判据，研究中假设新的分凝冰形成以后，上一层分凝冰停止生长。模型把水分迁移和冻胀速率当作基本的未知量，模拟了与可天然土体冻胀类似的底部无压补水和顶部加压的冻胀情况。通过数值模拟与试验结果进行对比，初步验证模型的可靠性，其研究结果为实际寒区工程的冻胀预测提供参考。

Under a large temperature gradient, the freezing front moves fast in a freeing soil and pore water transits into ice, resulting in local volumetric expansion. However, because the temperature gradient is generally small in a natural environment, water migrates from unfrozen areas to the freezing area, and crystalizes in some position, where pore ice accumulates and ice segregation occurs. Because the frost heave induced by ice segregation is much more significant than that induced by local volumetric expansion, it is very important to establish a model to simulate the moisture migration and ice segregation formation process. Based on the secondary heave theory, a frost heave model of freezing saturated soil is developed. The proposed model assumes that the flow rate in freezing fringe is constant for each time step. Thus, the water pressure is firstly calculated in freezing fringe, and then ice pressure is obtained based on the Clapeyron equation. The magnitude of the ice pressure is used as a criterion of ice segregation formation, with assuming that when new ice segregation occurs, old ice segregation stops growing. This model also considers the velocity of moisture migration and heave rate as basic unknown quantities, and simulates the heave under similar natural conditions where soil has overburden pressure at the top boundary and nonpressure water supply at the bottom. By comparing the numerical simulations to experimental results, the validity of the model is validated.