Study of the hydro-mechanical behavior of argilites. Application to the Tournemire site.
Nirina RAMAMBASOA, thesis of the Ecole Polytechnique, speciality mechanics, defended on the 10th January 2001.
In order to fulfil its mission of research and expertise about deep nuclear waste disposals, the French Institute for Nuclear Protection and Safety has selected the Tournemire site to study the confining properties of argillaceous media. This study is mainly motivated by the apparition of cracks that after the excavation of two galleries perpendicularly to an old tunnel. These cracks are not of mechanical or tectonic origin. They are regularly spaced and follow the rock subhorizontal stratification. Their aperture is very sensitive to the hygrometry in the galleries. These cracks are supposed to result of the rock desaturation, which is in contact with an unsaturated atmosphere.
In order to validate this hypothesis, an hydromechanical constitutive law for Tournemire shale is proposed. In order to take account of the shale desaturation and of microscopic interactions specific of argillaceous media, chemical potential is used as an hydric variable instead of interstitial pressure, which is classically used in poromechanics. This constitutive law differs from classical elastic law by the dependence of elastic parameters with the water chemical potential and by the adding of shrinkage strains and mechanical strains to get total strains. The numerical simulation of the Tournernire galleries desaturation shows the existence of high tractions around the excavation that certainly lead to material failure. The propagation of the cracks at the front faces is modeled by taking account of the interactions between the cracks in order to predict their depth and to explain their almost periodical distribution on the site.