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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. [Copyright &y& Elsevier]

Abstract: Hydromechanical behavior of argillaceous rocks is currently studied in order to predict the perturbations around ventilated galleries of a nuclear waste storage. This paper presents the results of desaturation–resaturation experiments performed on mudstone samples bored at 500m depth at Bure (France) where an underground research laboratory is under construction. We characterize the mass transfer process in the Bure mudstone, in terms of moisture diffusivity as a function of the relative humidity. A diffusivity identification method based on the measured mass evolution during transfer is proposed for the cases of uniaxial and radial diffusions. A significant non-linearity of moisture diffusivity has been observed. The retention curve, the diffusivity evolution, the ultrasonic velocity and the hydric strains have been investigated during the desaturation–resaturation process without mechanical loading. Hydric strains are anisotropic and non-linear with respect to relative humidity. A hysteresis has been observed on the ultrasonic velocity evolution, on the hydric strain variation and on the retention curve. Moisture diffusivity evolution is not the same along the desaturation path than along the resaturation path; this could be explained by the difference in moisture capacity on these two paths. The effect of desaturation–resaturation on mechanical behavior of the Bure mudstone is analysed by carrying out uniaxial compressive tests on samples with different water contents. Elastic parameters and compressive strength depend clearly on the suction. The mechanical behavior seems to be sensitive to the hydric path but further testing is needed to confirm these preliminary results. [Copyright &y& Elsevier]