In situ experimental study on thermal protection effects of the insulation method on warm permafrost

To evaluate the thermal protection effects of the insulation treatment, a 307 m long railway test section was constructed on the Qinghai–Tibetan plateau in 2001. Over 5 years observation data were collected and analyzed. The results showed that there was an obvious temperature difference between the top and the bottom of the insulation. The temperature of the deep permafrost rose for both the expanded polystyrene (EPS) and polyurethane foam (PU) sections due to the embankment construction. Because the soil temperature at the depth of 0.5 m below the south facing slope was much higher than that of the north facing slope and was a few degrees higher than that of the embankment surface, the permafrost temperature under the south facing slope rose, and the permafrost temperature under the centre of the embankment remained unchanged, and the permafrost temperature under the north facing slope dropped. Accordingly, the artificial permafrost table under the center of the embankment did not change, while the artificial permafrost table under the northern slope rose, and the artificial permafrost table under the southern slope declined. The experiment indicated that the insulation method was suitable for permafrost regions with low embankment surface temperature and it was not suitable for warm permafrost regions with high embankment surface temperature.