Dynamic process of the thermal regime of a permafrost tunnel on Tibetan Plateau

- Long-term on-site observation is used to study the thermal regime of permafrost tunnel.
- The dynamic process of thermal regime is analyzed from the construction to the operation of trains.
- The overcooling phenomena of the surrounding rock is found.

The thermal status of the rock surrounding tunnel will change during construction and operation periods in cold regions, thereby affecting the stability of tunnel. Field observations of thermal regime of a permafrost tunnel were conducted on Tibetan Plateau. The results show that during the past 12 years, the surrounding rock experienced a warming that subsequently returned to the natural thermal regime, and that was followed by a cooling process. The thermal disturbance distance of the surrounding rock was approximately 30.5 m after the construction. Compared with the air temperature outside the tunnel, heat source of the construction has a great influence on the temperature of the permafrost surrounding the tunnel. The temperature of the permafrost is sinusoidally varying, which achieves a steady state after twelve freeze-thaw cycles. The mean annual ground temperature of the permafrost, and the maximum and minimum temperature amplitudes decreased with time. The heat convection between the air in the tunnel and the surrounding rock during the operation of trains needs to be considered for the design of the permafrost tunnel that could gradually reduce the temperature of the permafrost. The permafrost tunnel could occur to freeze-thaw damage for the sections that lack laid insulation material.