多年冻土指天然条件下，冻结状态持续三年或三年以上的土地。多年冻土约占地球陆地面积的26%，主要分布在高纬度或高海拔的寒冷地区。中国多年冻土约有190万平方公里，主要分布在青藏高原、大兴安岭和小兴安岭地区，以及阿尔泰山、天山、祁连山和喜马拉雅山等山地。
多年冻土地区路基病害主要由冻土土体在季节变化条件下的冻融循环造成的。
The disease of subgrade in permafrost region was mainly induced by frost heaving and thawing circulation of frozen soils because of change of seasons.
在多年冻土地区修建铁路，为确保冻土路基的稳定，应使路基长期处于冻结状态。
In permafrost regions, the construction of railway should keep the subgrade frozen permanently so as to maintain the stability of the frozen subgrade.
在多年冻土地区，尤其是高含冰量的多年冻土区，阴阳坡的出现给路基的稳定性带来了极大的危害。
When road water content, the is constructed in permafrost region of long time, especially with rich stability of embankment is dramatically imperiled by the "Yin-Yang" slope.
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