Nonlinear visco-elastic and accelerating creep model for coal under conventional triaxial compression

Abstract

On basis of triaxial creep experimental results of coal with various deviatoric stress levels, a new nonlinear visco-elastic and accelerating creep model is put forward. First, Burgers visco-elastic triaxial creep model is deduced and used to identify the creep parameters by the discrimination criterion of the square of correlation coefficient (R2) and sum of least error square (Q). In Burgers visco-elastic triaxial creep model, the visco-elastic modulus G2 of coal decreases but the visco coefficient η1 and η2 all increase with increasing time, which has distinct time scale effect. The Burgers visco-elastic triaxial creep model fails in predicting long-term deformation characteristics. Then by introducing a time index, a nonlinear visco-elastic triaxial creep model is put forward, which can predict better for long-term deformation behavior of coal. R2 identified by nonlinear visco-elastic triaxial creep model is higher, but Q identified by nonlinear visco-elastic triaxial creep model is smaller 1 order than that by Burgers triaxial creep model. However, Burgers and nonlinear visco-elastic triaxial creep model is very difficult to describe the accelerating creep stage of coal. Therefore in the end, a new nonlinear accelerating creep model is put forward in order to describe the complete creep curve of coal. The nonlinear accelerating creep model has a better agreement with the experimental data.