Preliminary study on development of a methodology for evaluating the performance of host rock for geological disposal based on surface-based investigations

Inagaki, Manabu*; Tanaka, Tatsuya*; Hashimoto, Shuji*; Maekawa, Keisuke  ; Shibata, Masahiro 

In Japan, a step-wise approach is applied in the site selection process for the geologic disposal site. Preliminary surface-based investigations will be followed by detailed investigations. The basic repository concept, including underground design and layout, will be discussed at the end of surface-based investigations. The repository concept will depend on the spatial extent of the candidate rock formation(s) and their barrier performance. However, information obtained from the surface is limited and includes uncertainties. It is thus important to assess host rock performance considering uncertainties. In this study, methodology for evaluation of geological conditions has been developed that focuses on determining the usable volume of host rock with specific performance characteristics. Initially, multiple performance indices have been discussed and defined from the viewpoint of barrier performance. Then the evaluation procedure is illustrated by using the dataset obtained from the Horonobe Underground Research Laboratory Project. Finally the proposed procedure is reviewed and future challenges are extracted.