Based on triaxial rheological experiment

a nonlinear visco-elastoplastic rheological model is proposed which has creep threshold value

long-term strength

nonlinear viscoplastic body and other components. There are many problems in programming of this complex rheological model

for example

one-dimensional creep threshold value and long-term strength are difficult to express when extended to three-dimensional

and it was difficult to deal with nonlinear viscoplastic part. The yield approach index parameter is used as identification criterions of the creep equation piecewise function

the problems which the creep threshold value and long-term strength in three-dimension are difficult to express

are solved. The expression of viscoplastic part is derived detailedly; and three-dimensional central difference form is given

therefore

the secondary development of this rheological model for FLAC3D is achieved. A case study is given to verify correctness of program compiling. The rheological parameters are identified

the fitting curves are in good agreement with the experimental curves

so as to indicate that the model is correct and reasonable.