A new time-dependent constitutive model and its application in underground construction

Based on the classic visco-elastic Burgers model, a new visco-elastoplastic creep model is proposed in this paper, introducing a viscoplastic unit accounting the irreversible creep strain. The viscoplastic unit consists of a dashpot element and the Mohr-Coulomb slider element, which are connected in parallel. By connecting the viscoplastic unit and the viscoelastic Burgers unit in series, the new model can compute the elastic and plastic creep deformation of rock. The governing equation of the proposed model is implemented in the numerical finite difference code (FLAC(2D)) using its built-in FISH language for constitutive models, and then applied on a real tunnel accounting for the delayed deformation of rock mass around tunnel. A discussion is presented comparing the numerical results and the monitoring data of the time-dependent convergence developed in the tunnel.