Transversely isotropic creep characteristics and damage mechanism of layered phyllite under uniaxial compression creep test and its application

The layered surrounding rocks of tunnels undergo large creep deformation due to the presence of planes of weakness, thereby the deformation severely endangers the safety of tunnels. This study conducts uniaxial compression creep tests to experimentally investigate the transversely isotropic creep characteristics and the damage mechanism of layered phyllite samples having bedding angles of 0, 22.5, 45, 67.5, and 90°. The results indicate that the creep deformation of the specimens takes place in four stages: the instantaneous elastic deformation stage, the deceleration creep stage, the steady-state creep stage, and the accelerated creep stage. The cumulative creep deformation and the creep time during the steady-state creep stage of the specimens initially decrease and then increase as the bedding angle changes from 0 to 90°, thereby, corresponding to the initial increase and subsequent decrease in creep rate during the deceleration creep stage. Based on the existing viscoelastic-plastic damage creep model, the creep parameters E 1 , E 2 , η 2 , and η 3 are observed to initially decrease and then increase with the increase in bedding angle, hence demonstrating that the creep characteristics and damage mechanism of the layered rock mass are controlled by the effect of the natural weakness planes and show significant transversely isotropic characteristics. Then, the damage creep model was embedded into FLAC 3D numerical analysis software to analyze the displacement change of surrounding rock and its supporting structures of the tunnel with different bedding angles. The results of the calculation accurately reflected creep deformation characteristics of the layered surrounding rocks of tunnels induced by excavation.