The thermal effect of strengthening measures in an insulated embankment in a permafrost region

Abstract

An embankment with heat insulation can only retard a rise in temperature or the thawing of permafrost, and the thermal stability of the embankment cannot be maintained under global warming conditions. Therefore, strengthening measures are required to ensure embankment stability. Based on in-situ observational data from the Qinghai–Xizang Railway in Beiluhe, variations in the thermal regime under a thermally insulated embankment after the implementation of strengthening measures were analysed. The results show that the strengthening measure of thermosyphon installation can play an effective role in the embankment cooling process; however, no protective effect of the spall rock revetment was observed. The shallow mean annual maximum temperature in the upper 0.5m of soil decreased from 2.2 to 0°C with an average of 1.8°C, appearing as a striking “cold energy accumulation” process which predominantly results from thermosyphons and heat insulation material, after the strengthening measures were implemented. Meanwhile, the permafrost table under the embankment appeared as a “second rising process”, ranging from 0.90m for DK1139+670 to 2.56m for DK1139+780, with an average of 1.66m. The “sunny–shady slope effect” was not well controlled after the implementation of the strengthening measures under the embankment with thermal insulation. However, the difference in temperature between the ground and underlying permafrost table, under the left and right shoulder of the embankment, gradually decreased. Besides, thermal influence of the embankment to the surrounding permafrost in the deep layer is observed to be eliminated after the implementation of the strengthening measures.