Study on 3D nonlinear visco-elastic -plastic creep constitutive model with parameter unsteady of soft rock based on improved Bingham model

The characteristics of the nonlinear accelerated creep stage of rock cannot be represented by the traditional model combined by the linear element, which brings great challenges to engineering applications. We proposed a new nonlinear viscous dashpot element with a strain trigger which was further connected with the Bingham model to form a new one-dimensional (1D) constitutive model. The newly established model can represent the constant and accelerated creep characteristics of rock, and the corresponding 3D constitutive equation was deduced in detail. Then, the attenuation law of the elastic modulus during the triaxial compression process was introduced into the 3D creep constitutive equation to obtain 1D nonlinear creep constitutive model which can reflect the whole process curve of rock creep. The model parameters were identified by the triaxial compression creep experimental data of mudstone. From the comparison of results calculated by this model and experiments, it can be concluded that the improved Bingham model not only can describe preciously the three creep phases including deceleration creep, stable creep and acceleration creep of soft rock, but also has the advantages of few components and simple combination form. This study provides a new study reference for the nonlinear creep constitutive model of soft rock.