Studies of grouting performace in the Mizunami Underground Research Laboratory

Matsui, Hiroya ; Takeuchi, Shinji; Sugihara, Kozo; Yui, Mikazu

Grouting has practical importance for the reduction of groundwater inflow 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 was 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. Ten investigation boreholes were drilled and several kinds of investigations were carried out. The groundwater flow analysis was performed to estimate the effect of grouting quantitatively. The results suggested 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.