Constitutive Equations With Internal State Variables for the Inelastic Behavior of Soft Rocks

The mechanical behavior of soft rocks is quite complex as it may involve a variety of deformation mechanisms. When loaded under compressive stresses at intermediate temperature, such rocks often show a semi-brittle response controlled by dislocations motion and microcracking. Because these two types of physical processes are acting simultaneously, the constitutive equations should involve a coupled approach. In this paper, the authors extend an existing unified model with internal state variables, developed for the ductile regime, to accommodate semi-brittle behavior of low porosity rocks. To do so, a damage variable Dv is introduced into the model. This requires a modification of the kinetic law and the addition of an evolution law for Dv. After presenting some of the main features of soft rocks behavior, the main equations are introduced together with a few attributes of this new model.