Given the complexity and diversity of soft rock

the existing constitutive model is difficult to accurately describe the accelerated creep stage of its creep model. To more accurately describe the creep process of the carbonaceous phyllite

this study first summarizes the rheological properties observed in triaxial grading creep experiments. A nonlinear creep model

termed the Snishihara model

is established based on the traditional Nishihara model by incorporating fracture plastic elements and nonlinear damage plasticity. Based on this theoretical model

a three-dimensional finite difference scheme suitable for FLAC3D numerical solutions is derived. Additionally

the yield function

potential function

and three-dimensional stress state of the Snishihara viscoelastic constitutive model are modified. Finally

using the secondary development environment provided by Visual Studio 2015

the custom constitutive model is completed in FLAC3D. The non-accelerating and accelerating creep stages of the Snishihara model are then analyzed to verify the model’s accuracy and reliability. The results show that the numerical simulation aligns well with the indoor creep test results regarding strain increments and creep change curves. This confirms the validity and applicability of the Snishihara creep constitutive model proposed in this study

as well as its secondary development application.