Japan Atomic Energy Agency (JAEA) is operating two underground research laboratory projects in order to establish a firm scientific basis for safe geological disposal of high-level radioactive waste (HLW). One of these, the Mizunami Underground Research Laboratory (MIU) project, is focused on crystalline rock. Grouting for reducing water inflow is an essential countermeasure technology utilized during construction of underground facilities. To achieve high quality seals with grouting technology, it is of great importance to select the most appropriate grouting methodology, e.g. injection pressure, pattern of grout holes, as well as grout material, and all taking into consideration the geological conditions. Status of grouting in the Mizunami Underground Research Laboratory is as follows:
Post-excavation grouting test in the Ventilation Shaft at GL.-145m and in the galleries at -300m depths.
Suspension type calcium-silica and solution type water glass were used for post-excavation grouting in the sedimentary rock at Ventilation Shaft. Lugeon values, hydraulic conductivity, water head, and inflow in the zone, assessed pre- and post-injection, were used to evaluate the effectiveness of post-excavation grouting and considered useful. Liquid-type colloidal silica was applied for grouting tests at Ventilation Shaft side of the gallery at GL.-300m. The colloidal silica gel seemed to be stable for water pressures of at least 5 MPa.
Pre-excavation grouting in the Ventilation Shaft at GL.-200m, -420 and -440m depths.
An umbrella type, diverging pattern of injection holes suitable for a shaft were drilled, and Ordinary and super-fine Portland cement were used for grouting. The results suggest that current pre-excavation grouting technology is effective for reduction of groundwater inflow into excavations and that hydraulic conductivity in the surrounding rock mass can be reduced by more than one order of magnitude.
Pre-excavation grouting in the galleries at GL. -300m and -500m depths.
The results suggest that current pre-excavation grouting technology using Ordinary and super-fine Portland cement are effective for reduction of groundwater flow into the galleries.
