One of the most important issue concerning underground repositories for nuclear wastes is the long-term behavior of the host rock mass. Degradation of the rock properties may lead to the extension of the Excavation Damage Zone (EDZ) surrounding the opening. In order to predict the evolution of the EDZ with respect to time, a viscoplastic model coupled to damage theory is presented. After outlining the experimental background, a numerical model of an existing tunnel where the EDZ was observed and monitored is presented. The results are discussed in terms of EDZ extension and modification of the stress distribution around the opening. Finally, a more advanced simulation, in which dilatational behavior and damage anisotropy are taken into account is applied to a circular gallery.
Throughout Europe and America, the use of deep underground repositories is considered as a possible solution for the management of High Level Radioactive Wastes. Several Underground Research Laboratories (URL) have been in operation for many years and already provide valuable information for different types of geological formations.
Much is involved in the performance assessment of waste isolation systems. Besides the technological constraints, a comprehensive understanding of the host rock mass is necessary. Phenomena such as coupling between mechanics, hydraulic, thermal and chemical processes need to be considered. The long-term behavior of underground openings is currently the subject of numerous studies in rock mechanics. A better understanding of complex phenomena is required, in order to predict the deformation as a function of time well as the potential development of a damaged zone. The damage zone, known as the EDZ (for Excavation Damage or Disturbed Zone), can develop around the opening wall, thus allowing the possible migration of radionuclide toward the biosphere. In order to avoid such a situation and to ensure safe radioactive waste isolation, the extension and the evolution of the EDZ must be determined over a long period of time (i.e. several millenium). This key issue has been the subject of several conferences during the last few years [1, 2]. Moreover, international organizations such as the Nuclear Energy Agency have published special recommendations regarding the issue [3], and some relevant papers have also been published [4, 5].
