Nonlinear Snishihara creep constitutive model and its development and application

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.