单向冻结时土颗粒位移的热筛效应及对流迁移

Thermal Sieve Effect and Convectional Migration of Soil Particles During Unidirectional Freezing

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。

Pore distribution of soil composed of different sizes of particles is random in the nature. The probability of forming large pores in coarse grained soil is larger than that in fine grained soil. When soil is freezing, water in large pores is first frozen and the coarse particles will be first up lifted and up lifted again by water in small pores freezing. Therefore, freezing point can be considered as a vibration sieve caused by temperature fluctuation which leaves coarse particles on the sieve and fine grain particles beneath. This phenomenon of soil particles moving vertically is so called the effect of thermal sieve. At the same time, the soil particles will move together with water and result in clay nuclear in ice lenses. This phenomenon is so called conventional migration of soil particles. This study is of great significance on explanation of formation of cryogenic structure and periglacial phenomenon and unevenity of freezing front.