Abstract: To investigate the long-term stability of surrounding rock in cold region tunnels, the gneiss in the Huibai tunnel in Jilin Province was selected for triaxial creep test under freeze-thaw cycles. The mechanism of the freeze-thaw cycle influence on the creep properties of gneiss was analyzed. The experimental results show that with increasing number of freeze-thaw cycles, the creep deformation of gneiss gradually increases, while the creep failure stress, creep duration and long-term strength have a significant decrease trend. Simultaneously, the freeze-thaw cycle temperature has a certain influence on the creep parameters of gneiss. For the same cycle number, the lower the temperature, the larger the initial creep of the rock sample, and the smaller the creep duration and the long-term strength. In addition, based on the experimental results, the parameters of the Burgers model were identified by the 1stOpt optimization software. It performs that the theoretical curve of the model and the experimental curve agree well in the deceleration and stable creep stages. Finally, the influence mechanism of freeze-thaw cycles on the gneiss microscopic structure was analyzed by SEM scanning and energy spectrum EDS. The failure modes of rock samples under long-term load are shear failure. As the number of freeze-thaw cycles increases, the degree of rock rupture becomes more and more serious, and the rock failure block becomes smaller. The research results can provide reference and basis for the support and antifreeze design of rock engineering in cold area.

Key words: gneiss, creep test, damage, long-term strength, freezing-thawing cycles (F-T cycles)