Comparison of grouting with silica sol in the Äspö Hard Rock Laboratory in Sweden and Mizunami underground research laboratory in Japan

Paper in proceeding, 2014

Silica sol is a material that seems to fulfill the non-hazardous requirement of final repository and capable of penetrating into narrow fractures. The rock grouting strategy with silica sol has been studied and applied for some recent projects in Sweden. The design methodology is based on the determination of the distribution of fracture transmissivity and the theoretical penetration length. In 2008, grouting with silica sol was applied in the construction of a short tunnel at 450 m depth in the Äspö Hard Rock Laboratory (Äspö HRL), the TASS-tunnel. In 2010, a grouting experiment with silica sol was performed at a niche of 300 m depth in the Mizunami Underground Research Laboratory, the MIU-300-niche. Despite the fact that silica sol has been used for a couple of decades for soil consolidation or sealing of fractures, it has seldom been applied as a material for rock grouting during tunneling. The purposes of this study are: • Comparing the grouting work with silica sol in TASS-tunnel and MIU-300m-niche. • Investigating the applicability of the design method used in TASS-tunnel to the grouting experiment performed in MIU-300m-niche. • Suggesting further development of grouting techniques. It was found that although there was quite a difference in the geological conditions and grouting methods, both sites had good sealing quality results. In addition, the Swedish design method seems to be applicable to MIU-300m-niche even with the difference in the fracture aperture distribution in each site. Furthermore, the water inflow in a borehole at MIU-300m-niche has gradually decreased during the three years. One explanation for this good durability of silica sol can be that the grout penetration created a larger overlap between the boreholes than that achieved in TASS-tunnel. A large penetration length of grout minimizes the risk of erosion and/or dilution of grout, thus creating a durable sealing. It can be suggested that the Swedish method can be applied to the design and evaluation of the grouting works in Japanese rock with high intensity of fractures. Moreover, the use of Japanese silica sol or an additional overlap and pumping time might improve the grouting quality in Sweden.