The Temporal Effect of Distress Developments of Frozen Embankments in the Permafrost Regions along the Qinghai-Tibet Highway

The distress development of highway embankments in permafrost regions presents accumulative and abrupt characteristics according to the survey data of the Qinghai-Tibet Highway (QTH). In view of this problem, this study proposes the concept of a temporal effect of embankments in permafrost regions. The concept represents the service life of an embankment by analyzing its distress history under different geological conditions, embankment scales, and structures. The maintenance history, reconstruction material, and distress data of the QTH over the past 60 years were collected in this article. The relations between highway distress and mean annual ground temperature (MAGT), permafrost degradation rate, and ice content were studied based on the survey data. The service life was determined by considering the previously mentioned factors. Besides, the newly developed distresses and their temporal effects were analyzed by using the treatment measure. The results showed that the MAGT and service life was negatively correlated. With MAGT increasing from -3.0 degrees C to -0.5 degrees C, mean annual service life decreased from >40 to <10 annum (a). As the permafrost degradation rate increased, the time of embankment distress occurrence was increasingly shortened. Secondly, when the permafrost degradation rate exceeded 15 cm/a, no section with a service life of >40 a existed. When the permafrost degradation rate exceeded 20 cm/a, the embankment was found to be in need of reconstruction in 10 a. Thirdly, the higher the ice content, the earlier the distress occurred and the higher the distress grade. Especially in warm and high degrading-rate permafrost regions, the embankment on an ice layer with soil inclusions showed severe distresses 2-3 a after pavement construction, and was in need of maintenance or reconstruction in 5-10 a. Finally, installing the special treatment measures could effectively delay the development process of embankment distress. The survey results indicated that the cooling efficiency of thermosyphon embankment, crushed-rock embankment, ventilation duct embankment, and thermal insulation-layer embankment could reach 95, 55, 90, and 90 %, respectively, and their distress prevention efficiencies were 70, 80, 60, and 70 %, respectively.