Abstract: JAEA (Japan Atomic Energy Agency) has been conducting geoscientific research and development for geological disposal of high level radioactive waste at underground research laboratory under construction, in crystalline rock at Mizunami, Gifu. Considering water treatment expense, the water inflow should be minimized. Although cement grout has been applied to reduce the inflow at 460 m depth at the MIU (Mizunami Underground Research Laboratory), the water inflow through narrow fractures which cement grout cannot penetrate might be a problem at deeper under-ground. Colloidal silica grout, which is liquid-type grout, has high durability as well as good penetrability and is therefore tested at a depth of 300 m. The experiment consists of two parts: one is an injection test and the other is a water pressure resistance test. In the injection test, a pilot hole is first drilled to examine geological conditions. Then, two series of grouting and permeability tests of the pilot hole were executed. The results indicated that liquid-type grout could sufficiently reduce the hydraulic conduc-tivity of rock mass with less than 1 Lu. In the water pressure resistance test, the ultra-high-pressure packer was set in the pilot hole. The results indicated that liquid-type grout could keep sealing effect even under high water pressures over 9 MPa.
1 INTRODUCTION JAEA (Japan Atomic Energy Agency) has been conducting geoscientific research and development for geological disposal of high level radioactive waste at underground research laboratories under construction, in crystalline rock at Mizunami, Gifu and in sedimentary rock at Horonobe, Hokkaido The ventilation shaft is one of the two shafts completed up to about 500 m as of November 2011. The rock mass consists of hard granite and water inflow occurs when excavating shafts due to perme-able fractures existing in this type of rock.