Description of time-dependent deformation in sedimentary rocks

This paper deals with formulation of constitutive relations describing the time-dependent deformation in sedimentary rocks. In contrast to classical viscoplasticity, the creep effects are attributed here to a progressive evolution of material microstructure. First, an internal variable monitoring the degradation process is introduced followed by presentation of a general framework of chemo-plasticity. The formulation is applied to two typical types of sedimentary rocks, viz. anisotropic shale and isotropic chalk. Two different mechanisms of microstructure evolution are considered which affect the kinetics of the deformation process, i.e. progressive rearrangement of fabric associated with formation of microcracks and the intergranular pressure solution. Numerical examples are provided and the results are compared with the available experimental data.