Cooling performance enhancement of a new expressway embankment in the Tibetan Plateau permafrost zone

The crushed-rock interlayer (CRI), as typical cooling technique used in the Qinghai-Tibet Railway, cannot be directly applied in expressways traversing permafrost areas because of the intense heat-absorption asphalt pavement. Sufficient cooling of permafrost foundation to meet the demand of engineering stability is an important issue. In this study, a CRI embankment combined with vertical ventilation ducts (VVDs) was designed to strengthen the convective cooling of wide expressways. To assess the performance of the combination design, a field experiment was conducted in the Tibet Plateau by building a full-scale expressway section. A numerical model was then developed and validated to analyze the heat transfer process and to predict its long-term thermal regimes considering climate warming. Results show that the new structure can produce an obviously increased convection cooling on permafrost foundation by enhancing the winter cold-energy utilization. The VVDs at the centerline play an effective role in dissipating heat accumulation in embankment center and can eliminate thermal asymmetry caused by plateau's prevalent wind direction. The combination of CRI and VVDs is effective to control ground temperature to improve expressway embankment stability. This new design could be considered for application in expressways built on permafrost stratum.