Abstract: Notable rheological behavior has been observed in the surrounding rock of tunnel in water-rich environment. The expression of creep damage in consideration of water content is established through triaxial compression creep test on sandstone at saturated state. The rheological behavior of sandstone is visco-viscoelastic-viscoplastic. The structure of creep model is determined as H-N-H｜N-N｜S by the unified rheological mechanics model theory. On such basis, the creep damage model is obtained through damage evolution and is extended to three-dimensional case. By three-dimensional difference computation of the constitutive model, secondary development is completed in FLAC^3D by C++ and FISH languages. The secondary development is proved successful and the parameters of the model are correct via numerical verification. The present creep damage model is also verified feasible by three-dimensional computation of the tunnel under varied creep time. The research results offer reference for establishing and developing similar constitutive models and analyzing the safety of long-term tunnel operation.

Key words: sandstone, creep damage, constitutive model, secondary development, numerical simulation, displacement monitoring