In-situ test study on the cooling effect of two-phase closed thermosyphon in marshy permafrost regions along the Chaidaer–Muli Railway, Qinghai Province, China

More than half of the recently built 142-km long Chaidaer–Muli Railway (CMR) in northern Qinghai Province, China travels across warm (≥−1 °C), ice-rich permafrost in wetlands on the southern flank of the Qilian Mountains. In comparison with the Qinghai–Tibet Railway from Golmud to Lhasa, the CMR traverses mostly across wetlands underlain by more ice-rich permafrost. Warm and ice-rich permafrost is sensitive to human activities and environmental changes, which can result in changes in the active layer thickness and permafrost temperatures, inducing instability and failure of infrastructures in permafrost regions. Thermosyphons were adopted in a quarter of the whole CMR route. For studying the cooling effect of the thermosyphon technique, two monitoring sites with different mean annual ground temperatures were installed since 2007. According to analysis of the ground temperature monitoring results from 2007 to 2010, the thermosyphon technique cooled the underlying permafrost and raised the permafrost table. The CMR has been put in operation since February 2010. The deformation monitoring data from 2008 to 2010 showed that the maximum accumulated settlement was 0.08 m and the minimum was 0.01 m. The settlements mainly happened in the initial months after the embankment construction was finished. In-situ monitoring results indicate that the thermosyphon technique has effect on cooling down the underlying permafrost and keeping the thermal stability of embankment in the unstable, marshy and ice-rich cold regions.