Research on the types and characteristics of permafrost engineering distress in the China-Nepal Transportation Corridor

The treacherous terrain, complex geology, and frequent natural disasters along the China-Nepal Transportation Corridor posing significant challenges to the maintenance and construction of permafrost engineering within the corridor. This study focuses on the China-Nepal Highway (CNH), and systematically discusses the main types, typical characteristics, distribution patterns, and their interactions with different influencing factors of embankment engineering distress (EH), bridge engineering distress (BH), traffic auxiliary facilities distress (TH), and hydraulic engineering distress (HH) along the route. Field surveys showed that the distress characteristics of the main roads (G318, G216, G219) of the CNH under the freeze-thaw action are as follows: the EH were mainly crack, raveling and differential settlement, accounting for more than 45.0 %, with a higher proportion of crack exceeding 60.0 %; the BH, TH, and HH were mainly dominated by freeze-thaw erosion, accounting for more than 60.0 %, with traffic ancillary facilities being more susceptible to freeze-thaw erosion. According to the statistical results between permafrost engineering distress distribution and permafrost environmental factors, the occurrence of the ED is more prevalent in regions with MAGT below 2.5 °C and MTSFG above 0.3 m, the BD is more likely to emerge in areas with MAGT below 2 °C and MTSFG below 0.9 m, the TD is more prone to occur with MAGT below 2 °C and MTSFG above 1.2 m and the HD tends to be more common when MAGT is below 1.5 °C and MTSFG is range of 0.9–1.5 m. A variety of freeze-thaw disasters (freeze-thaw debris flow, freeze-thaw landslide, thermokarst lake, and freeze-thaw slumping, etc.) were widely distributed along the CNH, directly threatening the road safety. Based on these findings, targeted suggestions were put forward for the proposed China-Nepal Railway from both freeze-thaw disaster prevention measures and freeze-thaw erosion engineering treatment measures. The research results can not only provide basic data for permafrost-related research in the corridor, but also provide scientific references for the prevention and treatment of distress in existing and proposed permafrost engineering within the corridor.