■ Tono Geoscience Center

Development of Experimental Techniques / Facilities at JAEA R&D Centers13-12 Shafts Excavated to -500 m Depth=Construction of Shafts and Research Tunnels and Confirmation of Reduced
Groundwater Inflow at the Mizunami Underground Research Laboratory=Borehole
Large volume ofgroundwater inflow
50 m

2500

-200 m Measurement
Niche off Ventilation
Shaft

Prediction: A/R Gallery (Without grouting)-200 m Measurement Niche
off main Shaft

Prediction: A/R Gallery (Grouting)Groundwater inflow (ℓ/min)

Sub Stage(Every 100 m deep)-300 m Access/Research
Gallery-300 m Stage-300 m Measurement
Niche off Ventilation
Shaft

Measured: A/R Gallery (Grouting)

2000

Measured: Borehole

1690 ℓ/min
2.4 MPa

1500

1000

400 ℓ/min
500-500 m Stage

100 ℓ/min
00102030

40

5060

70

8090

100

Distance from Main Shaft (m)Ventilation Shaft:-500.2 m (Ǿ4.5 m)

Main Shaft:-500.4 m (Ǿ6.5 m)

Fig.13-26 Layout of the Mizunami
Underground Research Laboratory
Depth of the shafts as of March 31, 2012.

Fig.13-27 Predicted and measured groundwater inflow during
excavation of A/R Gallery and drilling borehole
Upper panel is the -300 m A/R Gallery and borehole, and location of
the large volume of groundwater inflow. Lower panel shows predicted
and measured groundwater inflow during excavation of -300 m A/R
Gallery and drilling borehole.

The Mizunami Underground Research Laboratory iscurrently under construction in Mizunami City. As of March
2012, the Main and Ventilation Shafts have been excavated toGL -500 m (meters below ground level, Fig.13-26).
To mitigate potential excess groundwater inflow, preexcavation grouting was conducted before the excavation of
the shafts and tunnels. Grouting refers to the injection ofmaterial such as cement into open fractures in a rock mass tostabilize and seal the rock. In planning the construction, it
was necessary to obtain reliable preliminary information on
the bedrock conditions in terms of the rock mass stability andhydrogeology. Therefore, site characterization borehole
investigations were conducted before excavation began.
These investigations indicated that large groundwater inflow
could be expected during excavation.
Fig.13-27 shows the results of grouting around the -300 m
Access/Research (A/R) Gallery. In this area, maximumgroundwater inflows in excess of 1000 /min were expected
at several locations during borehole drilling. This area also
has relatively high groundwater pressure (2.4 MPa). Grouting
using ordinary Portland cement was performed in thisgeological environment, and the measured total groundwater
inflow after excavation of the -300 m A/R Gallery wasactually about 100 /min. Consequently, we conclude thatexisting grouting technology is applicable in deep undergroundenvironments and under high groundwater pressure conditions.
The grouting technology was improved and optimized
through several grouting trials during excavation, and themethod can be applied to rock masses with a wide
conductivity range under relatively high groundwaterpressure conditions. Existing grouting technology using
ordinary Portland cement and super-fine cement wasdemonstrated to reduce the conductivity of a rock mass in therange of 10-7 m/s. Furthermore, grouting methodology using
liquid-type grout material was also tested in the -300 m
Measurement Niche. The methodology will be applied forgrouting rock masses under 10-7 m/s. The excavations haveshown that the pre-excavation grouting was successful andthe targeted reduction in inflow was achieved. Thus, theresults indicate that this methodology is effective in reducing
water inflow.

Reference
Mikake, S., Ikeda, K. et al., Studies on Planning and Conducting for Reducing Water Inflow due to Underground Construction in Crystalline Rock, JAEATechnology 2010-026, 2010, 146p. (in Japanese).
JAEA R&D Review 2012121