Ground-temperature controlling effects of duct-ventilated 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.

Full-scale site evaluation of ventilation expressway embankments underlain by warm permafrost along the Gonghe−Yushu Expressway

Ventilation embankments,including those with forced ventilation,natural ventilation,and combination of these,were adopted for the construction of the Gonghe−Yushu Expressway in warm permafrost areas.To evaluate the actual thermal performance of ventilation embankment in the Qinghai−Tibet Plateau,four types of ventilation embankments were selected as objects,and their long-term thermal characteristics were analyzed based on monitoring data.It was found that:1)under the strong scale effect of a wide embankment,the crushed-rock embankment(CRE)was warming up and the permafrost table was declining year by year.Meanwhile,the combined ventilated slab and CRE and ventilated ducts embankment can effectively decrease the ground temperature and raise permafrost table in the year with a colder winter;2)transverse temperature difference caused by the shady–sunny slope effect existed in all the four embankments.However,it was weakened by the combined ventilated slab and CRE and the ventilated ducts embankment due to their stronger cooling effect;and 3)the pre-existing embankment had a remarkable thermal disturbance to the adjacent newly-built embankment,so a reasonable embankment spacing should be considered in practical engineering.These findings would provide a reference for construction of expressway embankments in permafrost regions.