Poro-elasto-plastic behaviour of dry compacted Fo-Ca clay: experiment and modelling. Application to the resaturation of an engineered clay barrier

Many projects of underground repositories for high level radioactive waste involve an engineered clay barrier, placed between the waste canister and t he surrounding rock. When hydrated, this barrier seals the gap and provides a good watertightness. The natural clay powder, dried and compacted, exhib its hydromechanical couplings during the hydration. Such a coupled behaviou r, interesting for the industrial application, has been clearly demonstrate d by many studies and laboratory experiments. But the modelling of this beh aviour, in order to predict the hydration of the clay barrier, is difficult . A coupled modelling, based, at a macroscopic scale, on the thermodynamics of unsaturated porous media, is proposed. This thermodynamical model found s a general framework for non linear pore-elastic and poro-elasto-plastic c oupled behaviours. The symmetries of this coupling, induced by this thermod ynamical framework, let us take into account the often neglected influence of the mechanical state on the hydraulic problem of the resaturation of the clay. The complete resolution of the flow problem, coupled with the mechan ical behaviour, leads us to study the influence of the rheological behaviou r chosen for the clay (elastic - linear or no linear -, or elastoplastic) o n the evaluation of the duration of the resaturation of the clay barrier.