Abstract: Triaxial loading and unloading creep tests were carried out on RLW-2000 rheological testing machine to study the creep mechanical properties of sandstone. The instantaneous elastic, instantaneous plastic, viscoelastic and viscoplastic strains of sandstone under different deviatoric stress levels were obtained via viscoelastic plastic strain separation, and the variation rules of viscoelastic plastic strain and elastic modulus were examined. The experimental results demonstrate that: 1) the creep of rock is a viscoelastic plastic deformation process consisting stages of instantaneous deformation, decaying creep and stable creep during loading, as well as instantaneous and lagged deformation recovery during unloading. (2) The difference between initial creep rate and steady creep rate of sandstone could reach two orders of magnitude, both growing with the climb of deviatoric stress level. (3) The isochronal deviatoric stress-strain relation of sandstone shows obvious nonlinear characteristics, and the curve gradually deviates from the strain axis. The creep deformation of rock has both linear and nonlinear characteristics. The research findings could offer reference for the study of long-term stability of underground engineering.

Key words: sandstone, loading and unloading creep, viscoelastic plasticity, strain separation, elastic modulus, tunnelling