A new nonlinear rheological damage model for rock

The traditional rheological models for rock consisting of linear components can not describe very well the accelerating creep stage. The closure and expansion of microcracks in the process of rock rheology are analyzed, and the damage mechanics is introduced to construct a new rheological model. The damage law put forward by Kachanov is adopted and the rheological process of rock is divided into the first phase(the initial attenuation creep stage and the steady-state creep stage) and the second phase(the accelerating creep stage), and the corresponding damage evolution equations are deduced. By analyzing the sensitivity of creep parameters, the stress level has a great influence on the damage evolution characteristics. The nonlinear rheological damage model for rock is established based on the effective stress law, and the stress relaxation property is also analyzed. This nonlinear rheological model can describe the complete creep curve very well. Using this model to simulate the whole creep process of mudstone under the confining pressure of 5 MPa and axial deviatoric stress of 43 MPa, it shows, that the nonlinear rheological damage model is right and reasonable. Several calculated damage model curves under different stress levels are shown, which are coincident with practical curves. By comparing the creep test curves with those of Nishihara visco-elastioplastic rheological model, the difference is great between the model curves and the practical ones especially at the accelerating creep stage.