Thermal regime of conventional embankments along the Qinghai–Tibet Railway in permafrost regions

Thermal regime of conventional embankments (CEs) was investigated by compiling ground temperature data from 13 monitoring sites along the Qinghai–Tibet Railway in permafrost regions. The investigation included shallow ground temperatures within embankment, variations of permafrost table and dynamic changes of deep permafrost temperature beneath embankment. The results indicated that the shallow ground temperatures within two embankment shoulders differed from each other; the difference at depth of 50 cm was less than 1 °C in warm seasons but more than 2.7 °C in cold seasons. Statistic analyses of permafrost table variations beneath CEs confirmed existence of a reasonable height range of CE in regions with mean annual ground temperature (MAGT) < − 0.6 to − 0.7 °C. When the height of CE lay in the range, underlying permafrost tables all had obvious upward movements and could be maintained well with time. By contrast, in regions with MAGT > − 0.6 °C, permafrost tables either declined (beneath sunny shoulders) or maintained near original level (beneath shady shoulders) at majority sites no matter what the height of CE was. As these permafrost tables were not stable; ground temperatures near them increased slowly with time. Analyses of ground temperature profiles indicated that the deep permafrost beneath CEs all warmed in the contexts of climate warming and construction activities, and this warming trend was more pronounced in warm permafrost regions. Supra-permafrost talik developed and/or permafrost degraded from both permafrost table and permafrost base beneath embankment at some sites with MAGT > − 0.5 °C.