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Most geomaterials exhibit localized modes of failure, which appear in the form of shear bands or cracks. This appearance could be gradual or very abrupt, depending on the type of materials and also loading conditions. In particular, failure of rocks or concrete is very abrupt in tension and indicates the brittle nature of these materials under such conditions, while in compression regime and under increasing confining conditions, their failure gradually becomes more ductile with the onset and propagation of shear bands. The orientation and size of shear bands and/or fracture process zones in localized failure vary with the loading and materials. As a consequence, a correct description of geomaterial behavior must take into account all these characteristics of failure. This is however not always the case in constitutive modelling of geomaterials, and while working well under homogeneous condition, most (if not all) existing models do not possess details on the size and orientation of localization zones when localized failure takes place. This prevents them from capturing correctly the failure behavior of the materials, the most important characteristic of which is size effect. We present in this study a new approach to incorporate both size and orientation of localization zone in constitutive models for geomaterials. The proposed approach is however generic to cope with localized failure in any kind of materials. The concepts together with technical details behind them, and numerical results are presented to show the potentials of the new approach.

Localisation, Size effects, Geomaterials, Constitutive Modelling