Normalized Input-Output Minimization (NIOM) analysis was conducted for the earthquake records observed at Agigawa Dam in Gifu prefecture, Japan, operated by the Japan Water Agency, and the propagation velocities of the seismic waves in the dam body were closely investigated. The results revealed that (1) the S-wave velocity in the upper and the lower parts of the core zone were 420-450 m/s and 520-540 m/s, respectively, (2) the S-wave velocity in the rock zone on the upstream side was 480-500 m/s, and S-wave polarization anisotropy was found in these results, whereas (3) the S-wave velocity in the rock zone on the downstream side showed larger value (580 m/s), and the polarization anisotropy was not seen, and (4) the distributions of the P- and S-wave velocities obtained in this study were consistent with those observed by the PS logging held in 1999.

A variety of resources have being applied to Roller Compacted Concrete (RCC) dams in the world, in order to secure the water tightness of the dam body. Treatment of concrete block joints, upstream portion and concrete placing joint as well as design of concrete mix proportion are important factors for the above purpose. In addition, usually vertical drainage holes are arranged in the dam body to drain the leakage water properly for reducing uplift pressure acting on concrete placing joints. The practice of the works for enhancing water tightness of the dam body in the Nam Nigep Hydropower Project in Lao PDR, which has a 167 m RCC dam, is introduced and its effectiveness is discussed through 2 dimensional finite element permeability analysis and proved through in-situ permeability test and observation of concrete placing joint by CT scanning.