Study on mechanisms of strain variation at great depth

Horiuchi, Yasuharu; Hirano, Toru*; Ikeda, Koki; Matsui, Hiroya

Dai-40-Kai Gamban Rikigaku Ni Kansuru Shimpojiumu Koen Rombunshu (CD-ROM), p.242 - 247, 2011/01

Japan Atomic Energy Agency (JAEA) installed the intelligent type strain meters, at G.L-500m depth in pilot boreholes drilled from the 200m level in the ventilation and main shafts of the Mizunami Underground Research Laboratory (MIU). Strain variations due to several events including the excavation itself were monitored and analyzed. Monitoring results indicate that the intelligent type strain meter is able to measure very small fluctuations and detect rock deformation from blasting with 300m vertical separation from the measurement section. The strain meter can detect conditions in the rock mass such as differences in deformability.

Evaluation of applicability of a new quantitative rock mass classfication method at the Mizunami Underground Research Laboratory

Asai, Hideaki; Kuji, Masayoshi*; Horiuchi, Yasuharu; Matsui, Hiroya

Dai-40-Kai Gamban Rikigaku Ni Kansuru Shimpojiumu Koen Rombunshu (CD-ROM), p.13 - 18, 2011/01

Considering the design, construction and safe operation of large underground facilities such as for the geological disposal of high-level radioactive waste, an important requirement is to utilize a rock mass classification method that can estimate site specific rock mechanical properties based on surface-based investigations and geological observations during excavation. For this study, a new quantitative rock mass classification method based on the Japanese Geotechnical Society standard was proposed and applied to the sedimentary formations and the granite at the Mizunami Underground Research Laboratory. The results were compared with the rock mass classification system developed by the Central Research Institute of Electric Power Industry and commonly used in Japan. Then the applicability of the new rock mass classification could be evaluated.

Pre-excavation grouting with micro-fine cement below four hundreds meter depth

Ishii, Yoji; Mikake, Shinichiro; Kamiya, Akira; Watanabe, Kazuhiko; Nobuto, Jun*; Kusano, Takashi*

Dai-40-Kai Gamban Rikigaku Ni Kansuru Shimpojiumu Koen Rombunshu (CD-ROM), p.185 - 190, 2011/01

The "Mizunami Underground Research Laboratory" has been carrying out scientific research in granite to establish the technological basis for high-level radioactive waste disposal. To get reliable information on the rock mass geology and hydrogeology and on the bedrock conditions, a pilot borehole investigation was carried out before sinking the Ventilation Shaft. A region with high hydraulic head and low hydraulic conductivity was intersected by the pilot borehole at around GL-400m during these investigations. To reduce water inflow during excavation, pre-excavation grouting with micro-fine cement was done in this region before sinking the ventilation shaft. Despite the high hydraulic head and the low hydraulic conductivity, effective reduction of water-inflow was achieved.

Test execution of liquid-type grout at depth of 300m of Mizunami Underground Research Laboratory

Nobuto, Jun*; Tsuji, Masakuni*; Kusano, Takashi*; Mikake, Shinichiro; Kamiya, Akira; Ishii, Yoji

Dai-40-Kai Gamban Rikigaku Ni Kansuru Shimpojiumu Koen Rombunshu (CD-ROM), p.179 - 184, 2011/01

At Mizunami Underground Research Laboratory, the water inflow should be minimized, considering water treatment expense. Although cement grout has been applied to reduce water inflow up to 460 m depth, water inflow through small fractures which cement grout cannot penetrate can not be neglected at deeper underground. Liquid-type grout which has high durability as well as good penetrability was therefore tested at the depth of 300 m. Test results indicated that liquid-type grout could sufficiently reduce hydraulic conductivity of rock mass with less than 1Lu, and could keep improvement effect even after applied water pressure of more than 9 MPa was applied.

Application of seismic tomography survey for monitoring EDZ development

Sugita, Yutaka; Nakamura, Takahiro; Sanada, Hiroyuki

Dai-40-Kai Gamban Rikigaku Ni Kansuru Shimpojiumu Koen Rombunshu (CD-ROM), p.230 - 235, 2011/01

JP, 2010-116655   Patent publication (In Japanese)

Excavation disturbed zones (EDZ) will usually develop around excavations when underground facilities are constructed. Consequently, the mechanical, hydraulic and geochemical properties of the rock mass will change as an EDZ develops. Estimation of the extent, variation in properties and their evolution in the EDZ area is important for assessing critical migration pathways of radionuclides in the disposal of high level radioactive waste. The authors examined the applicability of seismic tomography and borehole expansion tests for monitoring the changes in mechanical properties of an EDZ using a Mine-by experiment (horizontal drift, diatomaceous mudstone) in the Horonobe Underground Research Laboratory project. Simple seismic tomography surveys may be used for monitoring the EDZ.

Fracture hydraulic characterization based on aperture data measured by 50 cm scale rock sample

Sawada, Atsushi; Tetsu, Keiichi*; Sakamoto, Kazuhiko*

Dai-40-Kai Gamban Rikigaku Ni Kansuru Shimpojiumu Koen Rombunshu (CD-ROM), p.236 - 241, 2011/01

The homogeneous one-dimensional parallel plate model is usually applied for nuclide migration model in a single fracture. An actual fracture in the natural geological environment has complex rough surface. It is one of issues for developing the methodology how to define the representative parameters used for the parallel plate model, such as transmissivity and aperture. In this study, we conducted the fracture geometrical characterization by grinding 50 cm scale of rock block including a single natural fracture, and we obtained fracture aperture distribution. The relationship between fracture aperture distribution and hydraulic characterization was examined by comparing numerical simulation with hydraulic test results.