Ground-temperature controlling effects of ductventilated railway embankment in permafrost regions

Based on observed data from field-testing embankment of the Qinghai-Tibet Railway, ground-temperature controlling effect of duct-ventilated embankment is studied in this paper. The results show that ventilation ducts can effectively cool the soils surrounding the ducts of the embankment, and the heat budget of the ambient soils in a year shows as heat release. Temperature status of the permafrost below the embankment with ducts buried in the relatively high position is similar to that of the common embankment. The permafrost processes warming all along in the two freezing-thawing cycles when the embankment was constructed. However, the temperature of the frozen soils below the embankment, in which the ducts buried in the relatively low position, rises a little in the initial stage. After that, it cools down gradually. At the same time, ventilation ducts can effectively reduce the thermal disturbance caused by the filled soils. The frozen soils below the common embankment and that with high-posited ducts absorb heat all along in the initial two cycles. While the soils below the embankment with low-posited ducts begin to release heat in the second cycle. This phenomenon proves that the ventilation embankment with low-posited ducts shows efficient temperature-controlling effect. Such embankment can actively cool the subgrade soils and therefore keeps the roadbed thermally stable.