Abstract:

The authors investigate the longitudinal temperature characteristics and anti-freezing design methods for a highway tunnel in the western Sichuan plateau, China, through field temperature measurements and numerical simulations conducted during the operational period. The findings are as follows: (1) The longitudinal temperature in short tunnels in the western Sichuan plateau shows negative temperature penetration in winter, while long and extra-long tunnels exhibit weakly symmetric and asymmetric temperature distributions. (2) The temperature distribution at the tunnel portal and the occurrence of negative temperatures inside the tunnel are influenced by the surrounding environment in winter, particularly the terrain features and the height differences at both tunnel ends. (3) The freezing index and the annual number of freezing days at the tunnel portal decrease with increasing distance from the portal. This decrease is slower in tunnels where one-way natural wind prevails. (4) The antifreezing design of tunnel lining structures in the western Sichuan plateau should be based on the frost-heave sensitivity of the surrounding rock. A freezing index of 180 ℃·d is recommended as the critical value. The insulation length for the ditches on both sides of the tunnel can be determined by the monthly average zero-degree temperature. For lining sections with a freezing index exceeding 180 ℃·d and a monthly average temperature below 0 ℃, short-term freeze-thaw cycles frequently occur. Thus, the concrete durability index should be enhanced to ensure the long-term stability of the tunnel lining structure.

Key words:  , high-altitude tunnel, longitudinal temperature field, anti-freezing design, on-site monitoring, numerical simulation, freezing index, freezing depth