Rock engineering design process in ONKALO rock characterisation facility

The ONKALO rock characterisation facility is located in the Olkiluoto area in the west coast of Finland. It aids in collecting the further data needed for the applica-tion of the construction license for the repository of spent nuclear fuel that will be submitted in 2012. It provides an opportunity to develop excavation techniques and final disposal techniques in realistic in situ conditions. The goal of the facility is to provide information for the design of the planned nuclear repository. The ONKALO design method can be considered as a prediction and observation method. Typical rock conditions can be handled using the Observational Method (Peck 1969) approach, and more complex cases (e.g. stress-induced damage, extensively cracked areas, crossings, heat-affected zones, etc.) are handled with numerical and analytical predictions. The design method can be divided into five phases: description of information on existing geology, site investigation and interpretation, obtaining rock mass parameters, calculations, and design. The method has undergone continuous improvement during the different excavation stages and as new rock mechanical challenges have been detected. Examples of Eurocode compatible rock reinforcement design are shown. Finally, the suitability of the current design method for the design of the spent nuclear fuel repository is discussed.