Thermal performance of a novel crushed-rock embankment structure for expressway in permafrost regions

The current crushed-rock interlayer structure, which was successfully adopted in construction of the Qinghai-Tibet Railway, cannot maintain the foundation stability of expressways in permafrost regions because of the strong heat absorption of the wide and dark-colored asphalt pavement surface. To satisfy the higher cooling requirement of expressways, a novel crushed-rock interlayer structure, which especially focuses on enhancing the cooling performance on the embankment core, is presented. A heat transfer model, which includes air convection in the crushed-rock interlayer and the heat conduction with a phase change in the soil layers, was developed to simulate the temperature evolution of a full-scale testing expressway embankment section built in Huashixia, the Qinghai-Tibet Plateau. The numerical results indicated that the new structure has a significant cooling performance and especially plays an effective role in lowering the permafrost temperature beneath the centerline of the expressway. Moreover, the new structure has the benefit of maintaining symmetry of the embankment temperature distribution. Therefore, it can be concluded that the new structure is an effective method to prevent permafrost degradation under expressways and can ensure the long-term thermal stability of embankments under the climate warming. The study provides reference and guidance for expressway design and construction in permafrost regions, such as the planned Qinghai-Tibet Expressway.