Evolution of Frost Penetration and Ablation in the Surrounding Rock of Cold Region Tunnels

Taking Jiangluling tunnel as an example, a numerical model for investigating the evolution of the frost penetration and ablation in the surrounding rock of cold region tunnels is presented based on the governing equations of the coupling problem of temperature and air flow fields in cold region tunnels. As the tunnel starts to operate and cold air flows in, frost penetration starts. The thawed permafrost section near the entrance and exit freezes again after 5 years of operation, and the unfrozen surrounding rock section in the middle part starts to transform to permafrost gradually in the 6th to 10th year of operation. Thereafter, the frozen circle becomes thicker slowly. From the 20th year to the 40th year, the temperature of surrounding rock maintains stable approximately. Thereafter, the temperature of surrounding rock starts to increase, and the entrance and exit part starts to re-melt due to the climate warming. Frost ablation starts. After the 80th year, the frozen surrounding rock in the range of 500 m from the entrance and 150 m from the exit approximately re-melts. To the 100th year, the surrounding rock in the whole tunnel re-melts as the result of frost ablation. Moreover, frost penetration and frost ablation develop much faster from the entrance along the wind direction than those from exit.