A fractional-order viscoelastoplastic creep constitutive model for intensely altered rock accounting for moisture content

Abstract

Moisture content significantly impacts the time-dependent deformation and long-term stability of intensely altered rocks. To investigate their complex creep behavior, a fractional-order viscoelastoplastic constitutive model was developed using fractional calculus. The model employs Abel dashpots to characterize both viscoelastic and viscoelastoplastic behaviors. Large-scale triaxial creep tests under varying moisture contents and confining pressures validated the model and elucidated parameter variations. Theoretical results agreed well with the experimental data, verifying the model’s ability to capture attenuation, steady, and accelerated creep stages. The shear modulus, bulk modulus, and viscosity coefficients exhibited decreasing trends with increasing moisture content but increasing trends with increasing confining pressure. In contrast, the fractional order increased with both moisture content and confining pressure. Higher moisture thus enhances the rocks’ instantaneous elastic deformation and viscous behavior. Parameter evolutionary laws directly corresponded with macroscopic creep curves and specimen failure modes. This study provides a solid theoretical basis for predicting long-term deformation of moisture-affected altered rocks in engineering practice.