Results of pilot borehole investigation in -500m access/research gallery-north (12MI27 and 12MI33 boreholes)

Tsuyuguchi, Koji; Kuroiwa, Hiroshi; Kawamoto, Koji; Yamada, Nobuto; Onuki, Kenji; Iwatsuki, Teruki  ; Takeuchi, Ryuji  ; Ogata, Nobuhisa ; Suto, Masahiro; Mikake, Shinichiro 

This document summarizes the data of pilot boreholes (12MI27, 12MI33) in the -500m Access/Research Gallery-North. The geological, hydraulic and geochemical data were obtained. In addition, groundwater monitoring system was installed in closure test gallery for the flooding test in phase III research. The results of investigation, biotite granite with medium to coarse-grained equigranular texture are characterized. Rock mass classification is B from CH class. Minor fault with fault gouge that was not presumed by an original model are observed in 12MI33. Density of fracture in 12MI27 near the Main-shaft fault tends to be compared to 12MI33. Water inflow in both boreholes is less. Permeability ranges from 4.8E-10 to 6.1E-09m/sec at the zone without alteration and with low inflow, from 1.1E-07 to 2.7E-07m/sec at the zone without alteration and with high inflow, respectively. Groundwater chemistry is rich in Na and Cl ion.