Description of brittle-ductile behaviour of rocks using a dilatancy damage model

The progressive degradation of the mechanical properties of rocks due to the evolution of microcracks is described by a Continuous Damage Mechanics (CDM) based constitutive model. The initiation and subsequent propagation of microcracks are governed by special damage and yield criteria based on dilatancy concepts. Hence, damage parameters and associated evolution equations are expressed in terms of internal state variables such as macroscopic plastic shear strain and dilatancy. A series of damage and yield surfaces in the stress space describe damage and plastic yielding evolutions respectively. Salient brittle-ductile behaviours of rocks in compression (both monotonic and cyclic) are captured by the model.