Results of borehole investigation in -500m access/research gallery-north. 13MI38∼13MI44 boreholes

The geological, hydraulic and geochemical data such as rock mass classification, groundwater inflow points and the volume, water pressure, hydraulic conductivity, and results of water analysis were obtained from boreholes (13MI38∼13MI44) in the -500m Access/Research Gallery-North of Mizunami Underground Research Laboratory (MIU). In addition to data acquisition, monitoring systems were installed to observe hydrochemical changes in the groundwater, and rock strain during and after the groundwater recovery experiment. Biotite granite (Toki granite) with medium to coarse-grained equigranular texture is characterized around the -500m Access/Research Gallery-North. Rock mass classification is mostly B class and CH to CM at the fracture zone. Density of fracture in core description is small, and was 2.3 n/m in 13MI38 borehole. Maximum water inflow during drilling borehole was 78 L/min in 13MI38 borehole. Hydraulic conductivity in intact zone ranges from 2.3E-11 to 8.2E-08m/s at low inflow part, and from 1.9E-07 to 9.2E-06m/s at high inflow part, respectively. Groundwater chemistry riches in Na and Cl ion with the concentration ranging from 160 to 220 mg/L, from 280 to 600 mg/L, respectively. The digital data is attached on CD-ROM. (J.P.N.)