Monitoring study on the boundary thermal conditions of duct-ventilated embankment in permafrost regions

Duct-ventilated embankment is a roadbed construction method for cooling the underlying soils in permafrost regions. However, numerical simulation methods to predict the long-term permafrost-protecting effectiveness of the roadbed encounter difficulties in selecting boundary conditions, because no monitored data has been collected. In this paper, based on monitored data of field experimental embankments in the Beiluhe section of the Qinghai–Tibet Railway, air temperatures in the ducts and the walls were analyzed and simulated. The results indicated that the annual air temperatures in the ducts were higher than the environmental air temperature by a value of 1.6 to 1.8 °C. This value was less than 1.0 °C in thawing periods and 2.0 °C in freezing periods. On the embankment, the ground temperature at a depth of 0.5 m was higher on south-facing slopes than on north-facing slopes, with a value of 3.5 to 5.5 °C. The monitored data showed that the natural ground surface temperature was about 2.5 °C higher and the embankment surface temperature was 4.0 °C higher than the environmental air temperature, indicating that some values used in previous numerical analyses of surface temperature of the natural ground and embankment were reasonable. To better predict the long-time effect of duct-ventilated embankment on the underlying frozen soils, a physical model and the relative boundary conditions need to be incorporated into numerical analyses.