Thawing of permafrost surrounding buried pipelines and a novel powerless air ventilation technique for thawing mitigation

The China-Russia Crude Oil Pipeline (CRCOP) traverses extensive areas of discontinuous permafrost within China, where the challenge of permafrost thaw settlement has emerged as a significant concern. In order to guarantee the pipelines' safe and stable functionality, a monitoring system has been developed in key areas affected by thaw settlement along the CRCOP, providing real-time alerts for pipeline operations and essential data for pipeline studies. It appears that the permafrost around the CRCOP is experiencing localized degradation, with talik persisting around the pipeline in all seasons. In 2022, the seasonal thawing depth (STD) at locations 2 m from the pipeline's center on the CRCOP-I and CRCOP-II reached 11.5 and 9 m, respectively. An innovative W-shaped air ventilation duct (W-AVD) utilizing powerless ventilation technology was developed to address the thaw settlement challenges. A large-scale indoor test platform for pipeline-permafrost interaction was created, enabling the cooling effects and the mechanisms of the W-AVD under on-site measured boundary conditions to be examined. Results demonstrated that the W-AVD can eliminate the closed thaw bulb during cold months and significantly reduce permafrost thaw around the pipelines during warm periods. Such findings offer helpful elements for the CRCOP and analogous permafrost projects in permafrost areas.