The full-stage creep model based on fractional differentiation and Perzyna overstress function for deeply buried soft rock

Aim: ing at the problem that the traditional rock creep constitutive model cannot accurately describe the full-stage creep characteristics of rock, this paper proposes the FBNVP model that can describe the creep characteristics of deeply buried soft rocks in full-stage. Based on fractional differential theory, this model improves the viscosity element and can accurately describe the nonlinear growth process in the stable creep stage. The nonlinear viscoplastic element is constructed based on fractional exponential equation, which can accurately describe the accelerated growth process of creep stage III. The model accurately expresses the three-dimensional constitutive equation under viscoplastic conditions based on the Perzyna overstress function. The indoor uniaxial and triaxial creep test results of chlorite schist in Jinping II hydropower station verify the correctness of the one-dimensional and three-dimensional analytical solutions of the FBNVP model. The results show that compared with the traditional creep model the FBNVP model can accurately describe the creep characteristics of deeply buried soft rock in the full-stage. The model has the characteristics of accurate description, few parameters, clear physical significance and wide application range. It can provide reliable theoretical support for creep analysis of deeply buried soft rock.