Research on creep characteristics and variable parameter-based creep damage constitutive model of gneiss subjected to freeze–thaw cycles

To investigate the long-term stability of surrounding rock in tunnels in cold regions, the gneiss in the Huibai tunnel of Jilin Province in China was selected for the triaxial creep test after subjecting it to freeze–thaw (F–T) cycles. Furthermore, the influence of F–T cycles on the creep properties of saturated gneiss was analyzed and discussed. The experimental results showed that the increase in the number of F–T cycles increased the creep deformation of gneiss gradually, while the creep failure stress, creep duration, and long-term strength decreased significantly. Additionally, based on the experimental results, a variable-parameter creep damage model was proposed considering the effect of F–T cycles on gneiss. The creep damage model was composed of three components: a Hooke body, a Kelvin body (parallel viscoelastic components), and a new nonlinear viscoplastic damage component. The creep damage model can not only describe the three typical creep stages (primary creep, secondary creep, and tertiary creep), but also reflect the effect of F–T damage on the creep failure stress. The comparison between the creep test curve and fitting curve of the theoretical model verified the accuracy and applicability of the model. The result of this study can provide a reference value for the support design and anti-freeze damage design for geotechnical engineering in cold areas.