Permafrost warming under the earthen roadbed of the Qinghai-Tibet Railway

This paper investigates the stability of the earthen roadbed built in the warm and ice-rich permafrost region. The varying thermal regime of the subgrade and the ongoing settlement of the roadbed were observed at field. The temperature data demonstrate that in warm and ice-rich permafrost regions, adoption of earthen roadbed results in warming of the underlying permafrost. It is primarily because the earthen roadbed traps the warm-season absorbed heat in the natural ground. In addition, the carried heat of the earthen roadbed that was constructed in warm season propagates downward to warm the underlying soil. The warming permafrost layer promotes the roadbed settlement, which was mostly linearly developed in the past five service years. A comprehensive analysis for the varying thermal regime and the ongoing settlement shows that the unfrozen water liberated from the warming, undrained layer experiences consolidation. The deformation of the undrained soils is mainly responsible for settlement of the roadbed. In comparison, the temperature variation of this warming permafrost layer is found to be less beneath roadbeds protected by thermosyphons or crushed rock revetments. The installation of thermosyphons into the earthen roadbed is recommended to prevent the further degradation of the underlying permafrost.