Mechanism of generating hydrodynamic pressure due to the motion of gate and dam body has never been elucidated, and the hydrodynamic pressure on crest gate of concrete gravity dam during earthquake has never been observed. For this reason, we observed hydrodynamic pressure on crest gate during earthquake and analyzed them. In this study, we first carried out a 3D finite element model analysis and reproduced the seismic response of the hydrodynamic pressure on the gate. Secondly, we changed specifications of 3D finite element model to evaluate a sensitivity of response of hydrodynamic pressure. As a result, we elucidated the following two points. The first is that the generation of hydrodynamic pressure on the gate is mainly due to gate vibration, at many common gates. The other is the relationship between gate setback ratio, gate span ratio and the hydrodynamic pressure on gate generated by gate vibration.

In the Senbon Dam, the PS anchors have been reinforced to satisfy the stability of seismic resistance against static seismic forces. Based on the case study of reinforcement by PS anchors in Senbon Dam using FEM analysis, the effects of rock stiffness, anchoring method, fixing position, and dam height were analyzed on the stresses that occur in the dam. As a result, the normal stress at the bottom of the dam tends to be tensile at the upstream end if the rock stiffness is large, but there is little influence on the fixing position or anchor type. It was also confirmed that the large dam height would make it difficult to cause tension.

Continuous control of the operation of compaction machine by GNSS or another has developed in ordinary fill compaction. However, it seems that its application to the area control of impermeable performance of water-impermeable fills, such as fill dam core zones, has not been challenged. In this study, based on the results of laboratory and full-scale field tests, a method to area-control the impermeable performance of compacted soil was developed. This method was applied to the field using CCV obtained from the response acceleration of vibratory compactor as the soil stiffness index. It was confirmed by various quality control tests that appropriate quality was ensured for the areas constructed by the introduced management method.

Seismic response analyses for an ideal earth dam model were conducted by equivalent linearizing method in order to investigate the effects of evaluation method for shear modulus of unsaturated area to the response acceleration. The G-γ (correlationship between shear modulus and shear strain) for the analyses were obtained from soil tests at saturated and unsaturated conditions. Input waves with maximum acceleration of 0.5 m/s² and 5.0 m/s² derived from the observed data at Kawanishi Dam were applied. Today's standard method, which calculated the shear modulus at unsaturated condition by multiplying the shear modulus at saturated one for every shear strain by the ratio of the initial shear modulus at unsaturated condition to that at saturated one, tended to estimate the shear modulus at unsaturated condition to be larger in the specific range of shear strain and the response acceleration to be smaller in most part of the unsaturated area than the method which reproduced the G-γ obtained from soil tests.

GPS displacement monitoring system can automatically and continuously provide the three-dimensional displacements at multiple points on dam body surface with high accuracy. Monitoring results over the years has the great potential to assess the safety and the health of embankment of dam. This study presents a method to evaluate the deformability characteristics of dam body utilizing the relationship between the horizontal displacement data and the water level of the reservoir over the years. Based on the evaluation results, in the case of Taiho-waki Dam, 66.0-m-height-rockfill dam with central soil core, the deformability characteristics of the dam body has been improving year by year since the first impoundment. In the case of Ishibuchi Dam, which was affected with the Great East Japan Earthquake in 2011, the post-quake deformation characteristics of dam body recovered its pre-quake level, although it showed temporary large deformation just after the earthquake.

Central Nepal was jolted by the M_w 7.8 Gorkha earthquake on 25 April 2015. The tremor affected 32 administrative districts of the country and killed over 8,790 people. It also caused enormous damage to physical infrastructures, including residential buildings, schools, colleges, hospitals, industries, hydropower projects, roads, and highways. Based on a post-disaster need assessment, the Government of Nepal estimated the rehabilitation and reconstruction cost at NPR 669 billion or US$ 6.7 billion. This paper provides an overview of geological setting and seismicity of the country followed by a brief discussion on impact of the earthquake on hydropower projects. The quake severely damaged surface structures like powerhouse, settling basin, penstock pipe, and access road of many operating and under-construction projects. The earthquake-induced landslide debris accumulated on hillslopes is being gradually transported each year by rainwater into the nearby river. This excess sediment load to the river further reduces the lifespan of turbines and storage capacity of reservoirs. Hence, hydropower projects are under the risk of seismic and sediment disasters for which preparedness, including policy measures, are of utmost importance. Taking lessons from the Gorkha earthquake, this paper recommends carrying out sediment-control measures in the hilly areas, install accelerometers in major hydropower projects for recording strong ground motion from future earthquakes, and revise the existing operating guidelines and seismic codes.

During construction of the Roller Compacted Concrete (RCC) dam at the Nam Ngiep 1 hydropower project (NNP1) in Lao PDR, cracks in the direction of the dam axis emerged on the RCC placing surface at the left bank side where RCC placing suspended in order to install the penstock to be embedded in the dam body. The NNP1 conducted the crack investigation and thermal stress analysis by inputting the observed ambient temperature and development of RCC strength into the analysis and it was found that the main cause was the difference of the concrete temperature between inner and surface portions of the RCC according to the sudden larger drop of the ambient temperature compared in the mid December than that of the average year. This report presents the process of the above investigation and analysis for seeking the cause, check of the dam stability, and measures based on hearing from RCC experts.

Kawamata Dam is an arch-type dam with the height of 117m which was completed in 1966 as part of the Kinugawa hydraulic control of the Tone River system. After 50 years since the construction of dam, the requirement for reinforcement of rock foundation and construction of rock foundation PS anchor near the downstream of the dam increases. The installation of a large-scale anchor gantry was implemented in the steep topography during limited annual operation days while maintaining a dam including the discharge running. This study explains the technical features, issues and countermeasures to ensure the drilling quality and tension fixing of the large and long anchors in Japan.