影响锅盖效应因素的研究

Influence factors for “pot-cover effect”

锅盖效应是指非饱和土中由于上覆结构密闭导致水分不能排出而引起的浅层土体含水率增加的现象。分析认为初始含水率、边界低温以及土体中的密闭隔断层对锅盖效应有着重要影响,选取边界低温作用下由气态水迁移补水而产生的锅盖效应进行研究,建立数值模型开展大量数值试验,探究初始含水率、边界低温以及隔断层对锅盖效应的影响规律。研究发现：土体初始含水率处于塑限附近时,低温作用周期内浅层土体最大液态水含量达到峰值,峰值大小约在液限附近;当土体初始含水率处于液限附近时,浅层土体液态水增加现象消失,此时锅盖效应处于一个消失临界点;边界低温降低,因冻结锋面下移,浅层土体低温期可达最大液态水含量先升高后降低;铺设隔断层会使土体中产生双锅盖效应,将隔断层铺设在0℃附近（正温）的土层处,可有效减少锅盖效应引起的增水。

When the surface of the unsaturated soils is covered by a water and air proof layer, the water content of the shallow soils will increase with time. This phenomenon is considered as the ＂pot-cover effect＂. The analysis shows that the initial water content, boundary temperature and insulating layer have an important influence on the ＂pot-cover effect＂. Here one type of the ＂pot-cover effect＂ is studied, in which the water supplement of the shallow soil depends on the water vapor transfer. A large number of numerical experiments are carried out to explore the influence laws of the initial water content, boundary temperature and insulating layer on the ＂pot-cover effect＂. The research shows that when the initial water content of soils is close to the plastic limit, the maximum value of the liquid water content in the shallow soils during the low-temperature period is higher than that of other samples with different initial water contents, which is near the liquid limit. When the initial water content of soils is near the liquid limit, the increasing phenomenon of water caused by the ＂pot-cover effect＂ will disappear. This point corresponds to the vanishing critical point. With the decrease of the boundary temperature, the maximum value of the liquid water content in shallow soils during the low-temperature period increases at first and then decreases because of the moving down of the freezing front. The insulating layer in soils can cause ＂double pot-cover effect＂ and the water increment caused by the ＂pot-cover effect＂ can be significantly reduced by laying the insulating layer at the position where the soil temperature is around 0℃（above zero）.