A viscoplastic model including damage for argillaceous rocks

Abstract : Based on numerous studies of laboratory tests and in-situ observations, a macroscopic viscoplastic model which aims to improve the viscoplastic strain prediction within the Excavated Damaged Zone (EDZ) is proposed by introducing a damage variable in Lemaître's model parameters. The mains characteristics of the model are: (a) the short-term behaviour is based on a generalized Hoek-Brown model, damage in the pre-peak phase is described by plasticity theory; (b) the long-term behaviour is based on the modified Lemaître's model, the changes in viscoplastic strain rates due to damage are taken into account by varying the creep activation energy and the strain-hardening parameter as a function of the current damage rate. The proposed model is implemented in the code FLAC3D . Simulations of triaxial compression tests at different levels of confining pressure provide a verification of the implemented model. The influence of damage on the creep behaviour was highlighted by simulating: (a) a multi-stage creep test and by comparing the viscoplastic deformation according to whether the sample remains intact or damaged; (b) a 1-D cylindrical cavity excavated in a viscoplastic medium subjected to an isotropic stress state.