Field investigation on thermal characteristics of a slope-cooling structure for permafrost embankment in the Qinghai-Tibet Plateau

A poor cooling effect on warm permafrost (> −1.0 °C) was observed in the crushed-rock revetment embankment (CRRE), which is widely used in the Qinghai-Tibet Railway. The filling of the porous rock layers caused by wind-blown sand and rock-weathering in the Qinghai-Tibet Plateau can further weaken the cooling capacity of the CRRE and may cause instability of the railway vehicles. This study describes a novel slope-cooling structure (NSCS), which combines a CRRE and a slope-warming prevention measure. A full-scale embankment was built using the new design in a warm permafrost region of the plateau. Ground temperatures and air speeds in the pore space of rock layer of the slopes were monitored. The thermal characteristics of the NSCS were evaluated along with its cooling performance. The results indicated that the new slope structure produced an effective cooling process on the side-slopes and the subgrade permafrost. The permafrost table was elevated and the ground temperatures at the embankment shoulders showed a decreasing trend after construction, particularly under the shady side. Asymmetrical convection process, which exhibits a significantly higher air speed and frequency in winters than those in summers, was observed to occur in the rock layers of the new structure. The NSCS decreases the heat absorption during summers and thus is beneficial for the heat-dissipating of the side-slopes. Moreover, the NSCS can reduce the sunny-shady slope temperature difference, which is induced by embankment orientation; therefore, the symmetry of the embankment temperature distribution is maintained. In general, these cooling characteristics contribute to the enhancement of thermal stability of the embankment and confirm the application of the NSCS as an effective method for the design and maintenance of embankments formed on warm permafrost. •A novel slope-cooling structure (NSCS) for permafrost embankment was presented.•The thermal characteristics and cooling performance of the NSCS were evaluated.•The NSCS effectively cooled the side-slopes and underlying subgrade permafrost.•The NSCS reduced the sunny-shady slope temperature difference.•The NSCS maintained the symmetry of the embankment temperature distribution.