Cooling processes and effects of crushed rock embankment along the Qinghai–Tibet Railway in permafrost regions

Crushed rock embankment (CRE) was most prevalent embankment structure with cooling measures along the Qinghai–Tibet Railway in permafrost regions. Ground temperature dataset from embankment construction (in 2002) to 2010 at nine monitoring sites along the railway were compiled to study long term cooling processes and cooling effects of CRE. Monitoring results indicated that the heat stored in filling materials could dissipate out in two cold seasons after embankment construction. Under cooling effect of CRE, permafrost tables beneath CRE moved upwards significantly during the first three years after embankment construction and then maintain almost constant. But underlying permafrost experienced different thermal process in relative warm and cold permafrost regions. In cold regions, underlying permafrost up to 14 m in depth experienced considerable cooling trends during the first five to sixth years after embankment construction. While in warm regions, the uppermost permafrost layer warmed after upwards movement of permafrost table, and underlying deep permafrost had no obvious cooling trends with time. Finally, differences in freezing and thawing seasons of, and differences in ground thermal regimes of cold and warm permafrost regions were investigated based on ground temperature from natural borehole. Then, the different cooling effects of CRE in two regions were interpreted based on these differences.