Abstract: A case study is conducted on the Heiqia tunnel in the Karakoram alpine region in the northwest of the Qinghai-Xizang plateau to examine the tempo-spatial distribution characteristics and variation rules of the temperature field of the tunnels in extremely high-altitude cold regions. First, a remote automatic monitoring system, including meteorological elements, is established on-site to collect temperature data. Second, a three-dimensional numerical model of the tunnel is proposed, considering the effects of turbulence on heat transfer and conduction, and the accuracy of the model is validated by monitoring the data. Finally, the variational characteristics of the tunnel temperature field before and after laying the insulation layer are analyzed. The results show the following: (1) Freeze-thaw action in the range of 0－270 m from the entrance affects the tunnel, and a linear positive correlation exists between the air temperature in the tunnel and the lining temperature. (2) The influence of air temperature on the radial temperature field of the tunnel is primarily reflected in the lining and shallow surrounding rock. (3) The average temperature of the coldest month in the high-altitude region is the highest, followed by that in the high-latitude region, and that in the extremely high-altitude region is the lowest, whereas the maximum freezing depth presents the inverse order. (4) The thermal insulation layer plays a positive role in insulating the lining and surrounding rock.

Key words: extremely high altitude, tunnels in cold regions, temperature field, numerical model, field monitoring