冻土地区风的作用分析--以青藏铁路沿线多年冻土为例

在广大的冻土地区，尤其是常年多风的冻土地区，空气与地面之间的热交换不仅仅表现为传导、自然对流和辐射。在风的作用下，地表上部空气的强制对流和表土层中的水分蒸发大大增强，对冻土层的热状况产生重要的影响。对于像青藏高原这样的冻土地区而言，地面上1.5 m处空气的年平均温度要比下附面层底的年平均温度低3～3.5℃以上；同时，对于表土层潮湿的冻土地区而言，水分的蒸发也将会带走土体中的大量热量。从冻土地区风作用的概念——冻土地区的风降低地表温度、促进下伏冻土发育的作用出发，分析了影响冻土地区风降温作用的诸多因素，给出在强风、表土含水量大的条件下，风作用表现得非常显著的结论。然后，通过对比、分析青藏铁路北麓河试验段的2个工程实例，验证了风的作用对冻土温度状况的重要影响。最后，给出了风作用在冻土地区若干基础工程实践中直接或间接的应用，以及利用风的降温作用来保护冻土的工程措施的使用条件和局限性。

WIND'S COOLING EFFECT ON FROZEN SOIL-FOR EXAMPLE OF QINGHAI-TIBET RAILWAY

In wide cold regions, especially frozen soil area with frequent wind, thermal exchange mode between Earth's surface and air does not consist of thermal conduction, natural convection and radiation. Under the action of wind, forced convection of air above ground and water evaporation of top soil layer will be greatly enhanced. They will have important effect on the ground temperature regime. Taking example of frozen soil area in Qinghai Tibet Plateau, annual average air temperature of 1.5m above Earth’s surface is 2.5℃, lower than that of earth’s surface. At the same time, water evaporation brings away a lot of heat stored in moist top soil layer. At first, this paper focused on the concept of wind's cooling effectWTBZ], which suggests that wind in frozen soil area can lower the temperature of earth surface and accelerate the growth of frozen soil. Many factors that affect wind's cooling effect were also analyzed briefly. Then, through comparison and analysis between the two engineering examples in the Beiluhe testing site of Qinghai Tibet Railway, it was proved that wind has significant effect on the thermal status. Finally, this paper presented its direct and indirect application to engineering practice in cold regions, its applicability and limitation in the aspect of protecting permafrost. 