Temperature field characteristics and influencing factors on frost depth of a highway tunnel in a cold region

Frost damage frequently occurs in cold-region tunnels due to temperature changes, posing risks to the structural stability and traffic safety. Therefore, temperature variations and its distribution in tunnels are crucial factors that have to be considered. Temperature measurements were conducted in the Xing'anling tunnel in northeast China from 2016 to 2019 to investigate the spatiotemporal characteristics of the temperature field. An equation to determine frost depth based on the Stephen's method was established to evaluate the influence of different factors on frost depth. The sensitivity of frost depth to different influencing factors was investigated using system stability analysis. The results showed that mean annual temperature inside the Xing'anling tunnel has gradually increased from 2016 to 2019 due to global warming. Freezing front was characterized by three stages based on the freezing rate, i.e., the fast freezing stage, transitional freezing stage, and stable freezing stages. The maximum frost depth ranged from 1.5 to 5.1 m without an insulating layer covering the lining, and a lag of about 2 months was observed with air temperature. Along the length of the entire tunnel, four stages of frost depth were observed, namely, fluctuations and a decrease, a steady decrease, fluctuations and an increase, and a steady increase. Frost depth exhibited an asymmetrical distribution to the length of the entire tunnel. Temperature parameters had the largest influence on frost depth, followed by water parameters and thermal parameter. Density parameters had relatively little influence on frost depth.