多年冻土是指呈冻结状态且持续多年不融的冻土。其上部接近地表部分,往往受季节性影响,冬天冻结,夏天融化,冬冻夏融的部分称为季节融冻层。多年冻土的上部界限,为多年冻土上限,简称上限
结果表明，修筑高路基后，多年冻土上限有所抬升，而下伏土层地温明显升高。
Results indicated that permafrost table was raised, the underlying ground temperature increased after constructing embankment.
多年冻土区修筑沥青路面后，引起了路基下多年冻土上限、多年冻土热状态等变化。
After asphalt pavement having been constructed in permafrost regions, permafrost thermal regime and permafrost table under roadbed will undergo a change.
准确确定多年冻土上限的位置及掌握其变化规律是冻土地区工程勘察的基本工作和重要内容。
It is important work to confirm the position of natural permafrost table and grasp its change law. Introducing the exploring method of natural permafrost table in Qingzang railway.
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