Curtain grouting for dam foundation is one of the most crucial work items in dam construction to secure the impermeability of the foundation rock. Since some decades ago, the Grouting Intensity Number (GIN) Method developed in Europe has been frequently applied to relatively simple geology. On the other hand, the Conventional Method, which requires phased mix proportion and water pressure tests through a sequence of the works, is as yet reliable for inhomogeneous geology, which has complicated hydrogeological structure. This paper presents the development of a sophisticated curtain grouting method to meet with complicated hydrogeological structure, based on application to the Nam Ngiep 1 Hydropower Project in Lao PDR, which has inhomogeneous geology of sedimentary rock with low dip angle weak layers affected by fold movement. The method has been dubbed as “hybrid” because it garners both the economical superiority of the GIN Method in that it enables the use of a single mix proportion, and the technical superiority of the Conventional Method in that the individual design pressure in each stage is set based on critical pressures obtained by water pressure tests.

We conducted NIOM analysis for the earthquake records observed at Yamaguchi regulating reservoir operated by the Japan Water Agency, and examined seismic wave velocity in the dam body. Based on the results, seismic wave velocities in the upper and lower core zones, and the upstream and downstream sides of rock zones were investigated. Then the nonlinear behavior during the relatively strong earthquake motions due to the 2005 Fukuoka-ken seiho-oki earthquake and the 2016 Kumamoto earthquake was discussed. The results revealed that the reduction of the shear rigidity during the Fukuoka-ken seiho-oki earthquake in the upper part of core zone was 35% at a shear strain of 1×10^-4, and those in the rock zones were 25% at a strain of 3 to 5×10^-5.

The Aigawa Dam is located near the urban area. We devised a construction method for the dam so as not to affect the surrounding environment. In a typical rockfill dam, a quarry site is developed near the dam body and materials are procured locally. Large-scale structures such as intake facilities and outlets are basically constructed by placing concrete at the construction site. However, in the Aigawa Dam construction project, the structures are constructed using precast blocks, without having a quarry site or an aggregate plant. I will report on construction examples of urban dams, which are rare in Japan.

Since the global climate change will accelerate sediment yield from watersheds with increasing intensity and frequency of precipitation, many dams will more significantly suffer in future from losing their storage capacities with reservoir sedimentation. In this study, a conceptual model of reservoir sedimentation was proposed, where the sediment yield was estimated from land failures in the catchment and the sediment balance in the channel system was parameterized by a “sediment storage function”. The present model consisting of a couple of concentrated parameters is considerably simplified than so-called physical mechanistic models. Additionally, this has an advantage that reservoir sedimentation is successfully reproduced without using discharge dataset. By using the model, further discussion was made how much reservoir sedimentation will be accelerated in future climate.