Characterization of the granitic rock by meas of the borehole radar; On the result of the measurements at the Kamaishi mine in-situ experiment site

Semba, Takeshi ; Ogata, Nobuhisa ; Hasegawa, Ken; Iwasaki, Hiroshi*; Watanabe, Kunio*

Power Reactor and Nuclear Fuel Development Corporation (PNC) has been developping techniques for evaluation of groundwater flow in the granitic rock as crystalline rock. In a link of this purpose, PNC introduced the borehole radar system (RAMAC) which was developped in Stripa Project by OECD/Nuclear Energy Agency because it is essential to investigate the spatial extent and dimensions of fracture zones. This report describes the results of crosshole measurements which were performed with RAMAC system at the Kamaishi In-situ Experiment Site in the northern part of Honsyu Island, Japan. Crosshole measurements were performed with four boreholes which were drilled at G.L. -260 meters. The tomographic inversion was made using crosshole data and figures of slowness distribution were interpreted. Integrated analysis on the tomogurams was carried out in the combination of the observation of the fracture zones with flowing groundwater. The results are summarized as follows; (1)Spatial extent of some low velocity zones and high velocity zones of electromagnetic waves were delineated. (2)Most of the seeping points identified by borehole TV lies in the low velocity zones. (3)The low velocity zones exactly correspond to the fracture-concentrated zones or fracture zones with flowing groundwater recognized on the walls of the gallery, which was excavated after drilling of the boreholes. (4)This may indicate that low velocity zones obtained by the borehole radar measurements corresponds with fracture-concentrated zones or fracture zones with groundwater in the deep underground.