摘要

Thermal state of permafrost under high embankment along Qinghai-Tibet Railway is monitored and studied. Three monitoring profiles with different embankment heights (3.0, 4.2 and 5.0 m) in the Beiluhe test site are chosen to analyze the characters of ground temperature under the embankment. The in-situ monitoring results show that the reasonable embankment height has positive effects on frozen soil protection and can promote the rise of permafrost table under the embankment. The permafrost tables under the three embankments have 0.3-0.7 m rise after two freezing-thawing circles. But the engineering effect does not increase linearly with the embankment height. The embankment with a height of 3.0 m has better engineering effects that those with heights of 4.2 m and 5.0 m according to the analysis. To ensure the thermal stability of the roadbed, the reasonable embankment height must be met. The analytical results also indicate that the high embankment has potential disadvantages. The thawing process of the embankment surface is longer while the freezing process is shorter than that of the natural surface. The embankment surface temperature, which is similar with that of natural surface in freezing process, is higher in thawing process. The consequence is that the thawing exponential of embankment surface is greater while the freezing exponential is smaller than that of the natural surface. At the same time, the conduction of cold energy in cold semi-year as well as heat energy in warm semi-year is held back because of temperature resistance of embankment material, which causes the ground temperature below the permafrost table to increase for sustaining the rise of the permafrost table. These disadvantages may affect the long-term stability of the permafrost under the embankment. Analysis of the observation data indicates that the engineering thermal disturbance depth of high embankment to the permafrost is about 10.0 m.

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