Study on investigation method of fracture distribution on the basis of data obtained at the Mizunami Underground Research Laboratory, central Japan

Sasao, Eiji   

Fractures in the crystalline rock can act as the pathways for groundwater flow and mass transport. Therefore, understanding of the fracture distribution is an important subject for the disposal of high-level nuclear waste. In this study the author discusses the investigation method to understand fracture distribution effectively. The author drew vertical scan lines on the sketches along the north, south east and west walls of the ventilation shaft of the Mizunami Underground Research Laboratory, and counts number of fractures intersected. Fracture frequencies of four lines were varied even in a few meters distance. Coefficient of variation was reversely correlated with fracture frequency. This imply that coefficient of variation could be improved by intersection of more fractures by borehole investigation. Declined borehole directed to dominant direction of fracture is effective method to understand fracture distribution.