ABSTRACT ABSTRACT: This paper is devoted to the constitutive modelling of coupled elastoplastic damage in a hard claystone. A summary of experimental data, obtained from triaxial compression tests including unloading cycles, is first presented. These results show an important plastic deformation which is coupled with an induced anisotropic damage. The latter is due to initiation and growth of oriented microcracks that lead to directional deterioration of elastic properties. A constitutive model coupling plastic deformation and induced anisotropic damage is then proposed. The plastic behaviour is described by a typical cohesive-frictional model. Damage is represented by a second rank symmetric tensor. The damage evolution rate is related to tensile strains. The damage effect on plastic flow is also considered. A simple procedure for the determination of model parameters from standards tests is proposed. The validity of the model is checked against experimental data in various loading conditions and water contents.
ABSTRACT ABSTRACT: The argilites from Meuse/Haute-Marne is a material studied by ANDRA, as a potential host rock for radioactive waste disposal. Numerous tests were performed in order to determine the thermo-hydro- mechanical behaviour of this rock. First, physical properties like density, porosity, water content, permeability and mineralogy were determined on all the stratum on core samples (research laboratories) and in boreholes (in-situ). Some uniaxial and triaxial compression tests were performed on samples coming from different depths. Mechanical behaviour is determined as elasto-visco-plastic with an induced anisotropic damage. The material appears stiffer when calcite content increases, and when clay or water content decreases. Biot's coefficient decreases when axial stress increases and the material is able to swell. These phenomena can be explained at the microlevel. Finally, some creep tests were performed under temperature from 20 to 120°C. Viscoplastic strains appear to be very low under hydrostatic stress but increase with deviatoric stress and temperature.