In addition to direct mechanical perturbations, an excavation influences rock conditions (mechanical, hydraulic and chemical properties). The internal fluids could be drastically modified and, in particular, the presence of water in the rock with regard to hydration and desiccation. The aim of the present study is to investigate the influence between the degree of saturation and the physical/mechanical properties for Tournemire shale rock. Anisotropy effects are also studied to identify hydromechanical behaviour. The different degrees of saturation are imposed by controlled suctions with continuous measurement of physical parameters such as weight and deformations. The volume variations (swelling or shrinkage behaviour) would result principally from the opening or closing of the inter-layers space. Uniaxial and triaxial compressive tests are carried out in order to attempt to establish a relationship between different mechanical parameters (elastic and failure data) and the sample saturation. The mechanical behaviour is sensitive to the saturation state of the shale with an important part of the stratification and its relative orientation to the mechanical stress.

International audienceDigital image correlation techniques (DIC) are applied to sequences of optical images of argillaceous rock samples submitted to uniaxial compression at various saturation states at both the global centimetric scale of the samples and the local scale of their composite microstructure, made of a water-sensitive clay matrix and other mineral inclusions with a typical size of 50 μm. Various scales of heterogeneities are revealed by the optical technique. Not only is it confirmed that the clay matrix deforms much more than the other mineral inclusions, but it also appears that the deformation is very inhomogeneous in the matrix, with some areas almost not deformed, while others exhibit deformation twice the average overall strain (for a gauge length of 45 μm), depending on the local distribution of the inclusions. In almost-saturated rocks, overall heterogeneities are also linked to the presence of a network of cracks, induced by the preliminary hydric load. On such wet samples, DIC analysis shows that the overall strain results both from the bulk deformation of the sound rock, with deformation levels similar to those in dry samples, and the closing or opening of these mesoscopic cracks

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