Constitutive Model for Shear Creep Behavior of Bolted Jointed Rock Mass Based On the Thermodynamics of Internal Variables Theory

To investigate the evolution of creep characteristics, in bolted rock discontinuities under long-term loading conditions, a three-dimensional viscoelastic-viscoplastic constitutive model was developed within Rice's thermodynamic framework of irreversible internal variables, which incorporates the inhibitory effect of bolts on the creep behavior of rock discontinuities. This study introduces three sets of internal variables associated with viscoelasticity, viscoplasticity, and damage evolution, respectively. The variations of free energy and energy dissipation during creep deformation were analyzed through the thermodynamic potential function, enabling the segmentation of the entire creep process into distinct viscoelastic and viscoplastic stages for detailed examination. The validity of the proposed model was verified through multi-stage shear creep tests conducted on samples of bolted rock discontinuity collected and prepared from the Wudongde Hydropower Station. The results demonstrate that the model accurately characterizes the creep deformation behavior of the bolted rock discontinuity. The model, developed within an internal variable thermodynamic framework, provides a more realistic and reliable prediction of long-term creep deformation, strength degradation, and ultimate failure risk of the bolted rock discontinuity under sustained loading conditions. These insights offer a solid theoretical foundation for the long-term stability analysis of high-slope and underground engineering projects.