Zedex - an in-situ study of the importance of the excavation disturbed zone to repository performance

The excavation of shafts and tunnels in a waste repository will cause a disturbance to the surrounding rock mass with possible alterations to rock mass stability and hydraulic properties. The properties and extent of the disturbed zone must be considered in the design of a repository and in the assessment of its long-term safety. In addition, the data collected in drifts, which will be used for detailed characterization of the repository, will be affected by excavation effects. ANDRA, UK Nirex, and SKB have jointly set up the ZEDEX Project at the Aespoe Hard Rock Laboratory, Sweden, in order to improve understanding of the properties and extent the Excavation Disturbed Zone (EDZ). The main objective is to study the mechanical behavior of the EDZ with respect to its origin, character, magnitude of property change, extent, and its dependence of excavation method. The project will also provide a test of equipment and methodology for quantifying the EDZ. The ZEDEX Project includes tests of open-quote normal close-quote excavation by drill and blast, a smooth blasting procedure based on low shock explosives, and excavation by tunnel boring. The ZEDEX Project is still in progress and results have not been fully analyzed. The preliminary analysis of the results indicates that the measurable changes in properties induced by tunnel excavation are comparatively small