Characterization of the Excavation Damaged Zone by means of Geological, Geophysical and Hydrogeological Co-interpretation

Over the years and within different R&D projects, SKB, the Swedish Nuclear Fuel and Waste Management Company (SKB), has studied various aspects of a possible generated disturbed or damaged zone around a deposition tunnel for spent nuclear fuel. According to international nomenclature EDZ, the Excavation Damaged Zone, is defined as the blast damaged zone around a tunnel where the damage is not reversible. Knowledge about the EDZ and its possible hydraulic connectivity is essential for underground construction design, underground facility layout, work environment issues and analysis of post-closure safety. This paper will focus on strategies and methodology for determine the hydraulic connectivity of the EDZ for a KBS-3 nuclear waste repository. The integrated use of geological and geophysical methods will also be presented. Due to the hard rock conditions SKB has chosen drill and blast method for excavation of the repository of high level nuclear waste at the suggested site, Forsmark. The requirements of the blast design have been based on theoretical studies and follow up of excavation works under controlled conditions. The results of the excavation works must be verified by methods that provide rapid feedback to the contractor as well as its complete documentation. This documentation has the ambition to describe the initial conditions of the nuclear waste repository by conducting a safety assessment analysis that considers the possibility for migration of radionuclides. However, the final verification of the hydraulic properties of the EDZ has to be verified after completion of a deposition tunnel. SKB has conducted a project aiming at defining and developing standards, strategies and methods needed to design, and gather the sufficient specifications to procure underground construction works of the planned repository for spent nuclear fuel. One part of the project has focused on verifying the extension of the EDZ. The sub-project included geometrical, geological, geophysical and hydrogeological investigations and blasting design documentations. The hydraulic properties of water-saturated conditions in the tunnel floor were evaluated by robust and flexible test method approaches. Based on the proposed investigations it is possible to conduct hydraulic modelling that takes into account a more or less developed EDZ.