Recent experiments in hard rocks to study the excavation response: Implications for the performance of a nuclear waste geological repository

Major excavation response experiments in granitic rocks have recently been finalized in Canada, Japan and Sweden. There is good understanding of the p hysical processes involved in developing a failed and damaged zone around a n underground opening in crystalline hard racks. Useful and feasible invest igation methodology exists for the description of the mechanical response. The effect of drill-and-blast and mechanical excavation on the extent of th e damaged zone is also clarified. However, accurate description of the hydr ogeological response to the excavation may warrant further studies. The res ults derived from the experiments are useful to assess the overall impact o n the post-closure performance of a geological repository for high-level, l ong-lived nuclear waste. Whether or not an excavation failed/damaged/distur bed zone exists is not crucial to the overall safety of a geological reposi tory, but excluding the zone may result in nonconservative estimation of ma ximum radiation dose. The experiments in Canada, Japan and Sweden have not yet dealt explicitly with consequences of the repository being operated for several decades before closure, nor with the thermomechanical effects. Suc h effects may also be of importance for the long-term post-closure function of the repository. (C) 1999 Published by Elsevier Science Ltd. All rights reserved.