2021 年 17 巻 1 号 p. 1-4
The geology of the Nam Ngiep 1 Hydropower Project (NNP1) in Lao PDR (hereinafter “Laos”) consists of alternating layers of sandstone and mudstone with a gentle downward gradient and has an anticline on the right bank due to fold movement. Furthermore, during excavation of the dam foundation rock, weak layers, which are relatively thin and low-angled, appeared in the riverbed. In order to efficiently implement curtain grouting for the dam foundation with complicated geology without any delay and cost overrun from the originally planned construction schedule and budget, a new grouting method named Hybrid Method was developed, which is incorporating the advantages of the Grout Intensity Number (GIN) Method advantageous in simplicity itself and the Conventional Method advantageous in quality assurance regarding impermeability. As a result of implementation of the Hybrid Method, the curtain grouting work was completed with keeping the original construction schedule and satisfying the necessary criteria regarding impermeability. The grout performance was verified by the image analysis using X-ray computed tomography (CT). Since it is expected that the number of dam constructions with complicated geological conditions will increase all over the world, it is anticipated that further sophistication of the Hybrid Method will improve its qualitative and economical attractiveness.