The cold accumulative effect of expressway embankment with a combined cooling measure in permafrost zones

Abstract

The thermal performance of an experimentally built expressway embankment with a combined cooling measure at Beiluhe Basin in the Qinghai-Tibet Plateau was investigated based on long-term field monitoring. Six-year records of soil temperatures showed that the embankment cooled by a measure combining hollow concrete bricks and ventilation ducts had a significant cooling effect on the subgrade soil. Over the investigated time period, the permafrost table beneath the embankment moved upward to the natural ground surface, and the subgrade soil layers down to a depth of −15 m underwent a considerable cooling. Then, the long-term thermal performance of this kind of cooled embankment with different surface widths (13 and 26 m) is comparatively studied using numerical simulations. The simulated results show that both embankments perform well in cooling the subgrade soil. However, the annual heat loss of the subgrade soil beneath the wider cooled embankment is greater than that of the narrow ones. Via the wider cooled embankment, more cold accumulates in the subgrade soil after the embankment's construction, which we term as the “cold accumulative” effect. This cold accumulative effect can ensure the underlying permafrost thermal stability better in the context of climate warming and strength the long-term embankment stability.