自然界中不同粒径土颗粒的随机组合造成土体中孔隙分布的随机性。土体冻结时，由于不同孔径中水分势能的差异，导致孔隙水冻结在时间上的有序性，即在相同温度下，粗大孔隙中水分首先冻结，然后逐渐向细小孔隙发展。水分冻结体积膨胀，从而引起粗颗粒土向上抬升，称为热筛效应。同时土体冻结过程中，伴随水分向冻结锋面迁移，土中＜０．００１ｍｍ的微粒将随水分产生对流迁移。本成果对揭示冷生土壤形成规律、若干冰缘现象形成机理及冻结锋面的不平整性具有重要意义 The random distribution of pores in soil caused by the random combination of particles with different grain sizes in nature. When the soil is frozen, due to the difference of the potential energy of water in different pore diameters, the temporal orderliness of pore water freezing results in that the water in the coarse pores is frozen first and then gradually develops into the fine pores at the same temperature. Water freezing volume expansion, causing the coarse grained soil uplift, known as the heat screen effect. At the same time, during the soil freezing process, with the migration of moisture to the frost front, particles of <0.001 mm in the soil will migrate with the water. This result is of great significance to reveal the formation of cool-sown soils, the formation mechanism of some ice-rimmed phenomena and the frost-front unevenness