青藏公路多年冻土段沥青路面热量平衡及路基稳定性研究

Study on Thermal Balance of Asphalt Pavement and Roadbed Stability in Permafrost Regions of the Qinghai-Tibetan Highway

为彻底了解和治理青藏公路多年冻土段路基病害 ,选择昆仑山垭口和 6 6道班两种不同冻土类型路段 ,首次在沥青路面上开展路面辐射和热量平衡观测 ,并同时和路旁天然场地自然下垫面进行同项目的对比观测 .通过观测和计算 ,研究了不同冻土类型路段沥青路面下热量收支状况及路基热量年周转 ,找出了致使路基沉陷及产生融化核的根本原因 ,并对路基内融化核形成演化及其稳定性进行分析 ,计算了路基下人为上限达到最大深度及所需时间和融化核的最终稳定厚度 ,为青藏公路整治提出了可行性措施 .

For thoroughly understanding the failure mechanisms of the road in permafrost regions of the Qinghai-TibetanHighway, radiation and thermal balance were observed on the surface of asphalt pavement and two ground surfaces ofdifferent types of permafrost between the Kunlun Pass and Maintenance Squad No. 66(MS-66). Thermal balance of different permafrost sectionsbelow asphalt pavement and annual thermal cycle of the roadbed were calculated based on the observation. There is a part of heat transferredinto the roadbed. Although it only occupies 2%～3% ofthe thermal balance of the road surface, this part of heat has significant influence on the heat regime of the roadbed. This is the main reason responsible for the formation of a thawed core below the roadbed and for the failure of the roadbed in high-temperature permafrost section. Ratio of the total heat absorption to the total heat releasing over the road surface is 1.19∶1for the road surface at the Kunlun Pass, and 4.0∶1 at the MS-66. This means that the heat income and loss below the roadbed is approximately balanced, temperature of permafrost is low and stable, and no thawed core will be formed below the roadbed in the near future at the Kunlun Pass. The heat absorption of the road surface is 4 time of the heat loss at the MS-66. Thawed core began to form 3 years after laying the asphalt pavement, and then gradually thickened. According to a calculation concerning the formation of thawed core below a roadbed, a thawed core will increase during the first ten years with a mean rate of 26 to 27 cm per year. Then the increasing rate will gradually decrease during the second and third ten years, with a decreasing rate very slow since the 40th years. After 30 years the thawed depth will be varying between 6 and 8 m, about 70% of the maximum thaweddepth. After 2010 AC the ice content below the artificial upper limit of the roadbed will gradually decrease, thawing settlement will be small and the roadbed will become to a quasi-stable state. In order to decrease the downward heat transfer from the surface, attempts should be made to change the road surface color, structure and material to decrease and offset a part of heat transferred into roadbed.