Multiscale numerical analysis of damage in heterogeneous rocks applied to underground works

In the context of underground exploitations, rock behaviour near tunnels and galleries conditions their stability. The excavations generate deformations, damage, and possible fractures in the rock surrounding the underground works. At engineering scale, phenomenological constitutive models are often considered and allow to represent the behaviour of rocks. However, macroscale behaviour takes its origin from small-scale properties. The influence of small-scale characteristics on the materials deformations and damage across scales remains a complex issue. Therefore, the behaviour of a clay rock is modelled at two scales. The excavation with deformation and damaged zones around galleries is reproduced at large-scale. The excavation-induced fractures are reproduced with strain localisation in shear bands. The approach is enriched by including micro- and meso-structuralcharacteristics from the scale of mineral inclusions and clay matrix. The details of the material mesostructure and behaviour (mineralogy, mineral inclusion morphology, mineral spatial arrangement, failure, damage modes, etc.) are embedded in a representative elementary volume. A double-scale numerical framework (FEM×FEM) with computational homogenisation is considered to relate small- and large-scale behaviours, as deformations and failures. The damage and cracking developments at micro- and meso- scales allow to predict macroscale shear banding. The results highlight the possibilities of double-scale computing in the prediction of the behaviour of underground engineering structures.