为研究砂土换填路基的水热特性，通过室内冻融循环试验的方法研究了换填不同级配砂土试样的不同深度处水热变化，以及对比分析换填粗砂、细砂对下层粉质黏土产生的影响。结果表明：冻结过程中，距离冷端位置较近的土体会发生“增水现象”，粉质黏土较砂土更容易发生水分迁移；换填细砂和换填粗砂都能够抑制下部粉质黏土降温和减小冻结深度，从而避免路基冻胀融沉灾害；换填细砂较换填粗砂对于抑制顶端负温向下传递的效果更好，换填细砂更利于维持温度稳定；换填细砂较换填粗砂的冻深更小，更有利于抑制路基土体冻胀和维持内部水稳定；土壤的冻结特征曲线与融化特征曲线是不重合的，在换填的交界面处，换填细砂的冻融特征曲线受温度影响最小。可见换填砂土可有效避免路基冻胀现象发生，且换填细砂的效果优于粗砂。

In order to study the hydrothermal characteristics of the sand soil replacement subgrade, the method of indoor freeze-thaw cycle test was used to investigate the hydrothermal changes at different depths of the sand samples with different gradations, and to compare and analyze the effects of coarse sand and fine sand on the silty clay in the lower layer. The results show that during the freezing process, the soil close to the cold end will have a "water increase phenomenon", and the silty clay is more prone to water migration than the sandy soil. Both the replacement of fine sand and the replacement of coarse sand can inhibit the cooling of the lower silty clay and reduce the freezing depth, so as to avoid the frost heave and thawing of the subgrade. Compared with coarse sand, the replacement of fine sand has a better effect on inhibiting the downward transmission of negative temperature at the top, and the replacement of fine sand is more conducive to maintaining temperature stability. The freezing depth of the replacement of fine sand is smaller than that of the replacement of coarse sand, which is more conducive to inhibiting the frost heave of the subgrade soil and maintaining the internal water stability. The freezing characteristic curve of soil and the thawing characteristic curve of soil do not coincide, and the freeze-thaw characteristic curve of replacement fine sand is least affected by temperature at the interface of replacement. It is concluded that the replacement of sand can effectively avoid the occurrence of frost heave phenomenon of subgrade, and the effect of replacing fine sand is better than that of coarse sand.