Permafrost thawing along the China-Russia Crude Oil Pipeline and countermeasures: A case study in Jiagedaqi, Northeast China

The China-Russia Crude Oil Pipeline (CRCOP) traverses 441-km-long permafrost zones in northeastern China. Since the pipeline operation in 2011, significant ground surface subsidence occurred within the trench of the pipeline in warm and ice-rich permafrost zones. Oil temperatures from three pump stations were obtained and the soil temperatures around the pipe at two cross sections along the CRCOP in Jiagedaqi, northeast China were monitored during the period from 2011 to 2017. With the date records, permafrost thawing and thaw bulb development around the pipe were investigated in this study, as well as the cooling effect of thermosyphons experimentally installed around the pipe. Results showed that the mean monthly oil temperature ranged from 0.4 to 17.9 °C and increased slowly with operation time increase. Due to thermal effect of the warm oil, the artificial permafrost table near the pipe was approximately 5.9 m greater than that in the natural ground 5 years after pipeline operation. A thaw bulb developed around the pipe and expanded at a rate of more than 1.0 m/a in depth. Following the permafrost thawing, ground subsidence around the pipe was significant. The buried depth of the pipe declined with a rate of approximately 0.35 m/a during the study period. To mitigate the permafrost thawing and the pipe settlement, a pair of thermosyphons were experimentally installed at the two sides of the pipe in March 2015. After 2 years of installation, the shallow foundation soils were cooled down and the thaw bulb was partially re-frozen. However, there was still a thawed layer beneath the pipe. Long-term thermal regime of foundation soils under the cooling effect of the thermosyphons needs further investigation.