Comparative analysis of cooling effect of crushed rock embankment along the Qinghai-Tibet Railway

Based on the in-situ monitoring data of ground temperature along the Qinghai-Tibet Railway, the cooling effects of crushed rock embankments (crushed rock revetment embankment and U-shaped crushed rock embankment) positioned in different permafrost regions with diverse mean annual ground temperatures were analyzed. The comparative analysis showed that either in basically stable low temperature permafrost regions (mean annual ground temperature -2.0.= TCP<-1.0.) or in badly unstable warm permafrost regions (mean annual ground temperature TCP>-0.5.), the crushed rock embankment had uplift the permafrost table beneath the embankment effectively; but the two kinds of crushed rock embankment performed different in providing cooling effect. The latter produced more cooling effects than the former; it could keep the deep permafrost thermal stable while raising the permafrost table and cooling the shallow permafrost. Whereas the rising of permafrost table beneath the crushed rock revetment somewhat consumed the cold energy of deep permafrost and consequently made the deep permafrost warmer. The analysis also indicated that the lower the mean annual ground temperature, the stronger the cooling effect of air-convection crushed rock embankment. It should be noted that in badly unstable warm permafrost regions, the crushed rock revetment hadn't produced enough cooling effect and the underlying deep permafrost warmed considerably; so some enhancement measures are needed to ensure the long-term stability of the embankment.