Grouting has practical importance for the reduction of groundwater inflow into excavations for the construction of underground facilities. Considering the performance assessment aspects of a radioactive waste repository, the performance of engineered barrier system could be adversely affected by high pH plume generated from grout using material such as ordinary Portland cement. Therefore, a quantitative estimation of the effectiveness of grouting and grout material is essential. Study of grouting performance has been carried out in Mizunami URL excavated in crystalline rock. The target volume for the investigation is the rock surrounding a refuge niche where the pre-excavation grouting was performed. After excavation of the refuge niche, ten investigtion boreholes were drilled and inflow and water pressure measurement was monitored during drilling. Core observations included observation of grout penetration into fractures, Borehole TV, resisitivity logging and hydraulic tests was carried out. Resisivity tomography was also applied between the boreholes to estimate the penetration and distribution of grout in two/three dimensionally. The groundwater flow analysis was performed to estimate the effect of grouting quantitatively. The results suggest that the existing grouting technology is effective to reduce groundwater inflow into drift and the hydraulic conductivity in surrounding rock may decrease more than one order of magnitude before grouting.
The crystalline basement rocks in Japan generally have relatively abundant fractures and high permeability. Therefore, grouting is very commonly used and is one of the important techniques for construction of underground structures in Japan. However, conventional grout, such as ordinary Portland cement, may affect the performance of the engineered barrier system in geological disposal of high-level radioactive waste.
Considering this possibility, METI (Ministry of Economy, Trade and Industry) initiated a study, The project for Grouting Technology Development!, to develop the methodology needed for grouting in deep geological environments and to provide an evaluation of the influence of grout on the geological disposal system. Japan Atomic Energy Agency (JAEA) has been conducting the study for METI since FY2007.
In this paper, studies on grouting performance done for the METI study, are described. Field investigations of grouting performance were done in the Mizunami Underground Research Laboratory (MIU), Gifu Prefecture, Japan. The MIU facility (Fig. 1) is a generic URL, intended for geoscientific research and development in crystalline, granitic rock (Hanamuro," 2004). The field investigations were carried out around a refuge niche excavated in the granite where pre-excavation grouting was performed. In the MIU project, excavation is progressing using pre-excavation grouting to reduce groundwater influx thus control the cost for treatment of large inflow volumes.
(Figure in full paper)
The following information is needed to estimate the influence of grouting for inclusion in the safety assessment for geological disposal:
Amount of injected grout and its chemical effect on natural barrier.
Actual grout distribution and penetration into fractures and the change in rock mass properties of the grouted rock volume.
This main aim of the study is to establish the methodology to assess quantitatively the above information.
