Geohydromechanical processes in the Excavation Damaged Zone in crystalline rock, rock salt, and indurated and plastic clays - in the context of radioactive waste disposal

The creation of an excavation disturbed zone (EdZ) or excavation damaged zone (EDZ) is expected around all man-made openings in geologic formations. Macro- and micro-fracturing, and in general a redistribution of in situ stresses and rearrangement of rock structures, will occur in this zone, resulting in drastic changes of permeability to flow, mainly through the fractures and cracks induced by excavation. The EDZ may have significant implications for the operation and long-term performance of an underground nuclear waste repository. Various issues of concern need to be evaluated, such as processes creating fractures in the EDZ, the degree of permeability increase, and the potential for sealing or healing (with permeability reduction) in the zone. In recent years, efforts along these lines have been made for a potential repository in four rock types-crystalline rock, salt, indurated clay, and plastic clay-and these efforts have involved field, laboratory, and theoretical studies. The present work involves a synthesis of the ideas and issues that emerged from presentations and discussions on EDZ in these four rock types at a CLUSTER Conference and Workshop held in Luxembourg in November 2003. First, definitions of excavation disturbed and EDZs, that may be applicable to all four rock types, are proposed. Then, an approach is suggested for the synthesis and intercomparison of geohydromechanical processes in the EDZ for crystalline rock, salt, indurated clay, and plastic clay. Comparison tables of relevant processes, associated factors, and modelling and testing techniques are developed. A discussion of the general state-of-the-art and outstanding issues is also presented. A substantial bibliography of relevant papers on the subject is supplied at the end of the paper. (C) 2004 Elsevier Ltd. All rights reserved.