Abstract :
[en] The disposal of radioactive wastes in deep underground repositories has been studied for some years (OECD/NEA, 1995). Argillaceous rocks are good candidates to host the repositories mainly because of their low permeability. In the case of France the Callovo-Oxfordian argillite (COX) has been chosen by the national agency ANDRA to be the host rock to store the radioactive waste.
During the previous years, the problem of gallery excavations in the COX host rock has been deeply studied in Université de Liège; especially the simulation of the damaged zone (EDZ) created in the surrounding of the galleries during their excavation (Blümling et al. 2007). The problem, involving strain localization, is not well posed when modelled using classical mechanics; to overcome this, a microstructured model is used: local Second Gradient (Collin et al. 2006), this avoids the pathological mesh dependency by introducing a regularizing internal length.
At the moment, the constitutive models for the COX take into account several transverse anisotropies: in situ stress state, elastic moduli, saturated permeability and plastic, this is achieved by the use of a fabric tensor that influences the cohesion (Pietruszczak et al. 2002). Classic elasto-plastic models like Drucker Prager and Van Eekelen, with cohesion softening, are appropriate to model the evolution of the EDZ, but they fail at reproducing the long term convergence of the gallery. To solve that, a visco-plastic model, independent from the plastic model, has been added.
The object of this researchis to study, by means of numerical simulations using Lagamine, the evolution of the GED and GCS galleries after the excavation and during a period of 100 years. The value of 100 years is retained because of the necessity to keep the stability of the underground repository and allow an eventual manipulation of the waste with newly developed technologies in the future.
