A microcracks-induced damage model for initially anisotropic rocks accounting for microcracks closure

We formulate a new micromechanical damage model for anisotropic rocks. This model accounts not only for the coupling between material initial anisotropy and the damage-induced one, but also for the opening/closure status (the so-called unilateral effects) of evolving microcracks. A closed-form expression of the overall free energy of the microcracked medium is implemented in an appropriate thermodynamics framework to derive a complete damage model for initially anisotropic rocks. The salient features of this model are fully illustrated. Then, its capabilities are demonstrated through an application to a Taiwan argillite subjected to direct tensile loading (including off-axis ones) for which the damage model well captures experimental data (mechanical response, growing damage rocks strength). Finally, the response of the studied rock along a tensile loading followed by an unloading and a reloading in compression is provided in order to illustrate the so-called unilateral damage effects due to microcracks closure.