Abstract: U-shaped crushed-rock embankment (UCRE) is a combination of the crushed-rock sloped embankment and the crushed rock basement embankment applied to the Qinghai-Tibet railway construction. Under a warming climate on the plateau, the effect of long-term cooling in warm permafrost regions needs to be concerned. Based on in-situ measurements for 10 years from the warm permafrost Chuma’er High Plain, the cooling process, cooling mechanism and deformation characteristics of a UCRE were analyzed. Results indicate that the UCRE showed a continual cooling process. Permafrost table beneath the UCRE was elevated significantly and quickly, then maintained in a stable state. Temperatures near artificial permafrost tables decreased significantly, resulting in a great cold energy accumulation. Temperature differences between top and bottom boundaries of crushed rock layers differed with cold and warm seasons, indicating natural convection occurred within the layer for the shady side during January to the early March. while for the sunny side, the convection period was shortened for nearly half a month, due to the high surface temperature of this side. A weak warming for 2 to 3 years caused by thermal disturbances from the initial stage of embankment construction occurred in deep permafrost. However, it was replaced quickly by the subsequent significant cooling process. The small settlement of the UCRE mainly comes from the compression deformation of warm permafrost under the embankment during initial stage after construction. In general, the UCRE shows the long-term effect of decreasing ground temperature, and the relatively weak embankment settlement ensures its stability.

Key words: U-shaped crushed rock embankment, Qinghai-Tibet railway, warm permafrost, cooling effect, embankment deformation