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 physical processes involved in developing a failed and damaged zone around an underground opening in crystalline hard racks. Useful and feasible investigation methodology exists for the description of the mechanical response. The effect of drill-and-blast and mechanical excavation on the extent of the damaged zone is also clarified. However, accurate description of the hydrogeological response to the excavation may warrant further studies. The results derived from the experiments are useful to assess the overall impact on the post-closure performance of a geological repository for high-level, long-lived nuclear waste. Whether or not an excavation failed/damaged/disturbed zone exists is not crucial to the overall safety of a geological repository, but excluding the zone may result in nonconservative estimation of maximum 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. Such 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.