In the advanced use of coastal waste landfill site on the sea, there is a case in which installation of foundation piles through waste layer and the barrier clay layer is necessary to support heavy structures. Associated with this pile driving, there is a concern about that wastes and retained water are taken into the barrier clay layer , and diffuse to the outside. This concern is one of the causes to inhibit the advanced use of the landfill site. In the present study, against these problems, a series of experiments was carried out to clarify the effects of leakage of wastes and polluted water into clay layer during pile driving, and to examine the effect and application range of the measures. As the result of the investigation, it was found that the prevention of the disturbance of the clay layer due to the pile driving is important to reduce the influence of leakage of wastes and polluted water. The methods of driving while drilling inside the pile, of using the pile with an acute angle of end point, and of applying a swellable cut-off of water material to the pile surface were suggested as the measures.

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 An innovative water current energy converter utilizing the flow-induced vibration of a columnar pendulum has been developed. In this study, a new type of converter exploiting the galloping oscillation induced in a semi-circular or a semi-elliptical cylinder pendulum is proposed instead of using the vortex-induced oscillation of a circular cylinder pendulum. This new converter with a semi-circular cylinder pendulum achieved five times higher performance in energy harvesting efficiency than a circular cylinder pendulum. Moreover a semi-elliptical cylinder pendulum achieved twice the performance of the semi-circular cylinder pendulum. Nondimensional power of a semi-elliptical cylinder pendulum increased linearly with nondimensional flow velocity along the one regression line independently of the pendulum length in the low flow velocity range. On the other hand, the nondimensional power of a semi-elliptical cylinder pendulum was approximately constant with nondimensional flow velocity in the high flow velocity range.

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 A structural performance evaluation method for wave-dissipating concrete blocks has not yet been established. In this study, surcharge load acting on the block sitting in the bottom-layer of breakwater covered with wave-dissipating concrete blocks was examined through model experiments against permanent action and variable wave action in order to clarify the characteristics of surcharge load and to investigate the possibility of the formulation of surcharge load. Based on the results of model experiments, surcharge load by permanent action could be approximated by a Gamma distribution. And, surcharge load by wave action was affected by wave overtopping. The formula for estimating surcharge load by permanent action and wave action were proposed.

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 Water level fluctuations resembling long period tsunami waves, which differ from normal wind waves, were observed immediately after the Great East Japan Earthquake of 2011 in multiple locations, such as lakes in Yamanashi Prefecture, the fjords of Norway, and other sites located far away from the epicenter. Very little research on similar abnormal water level fluctuations has been conducted thus far and, in many cases, these studies have treated the phenomena as seiches. However, researchers have not established concrete wave development mechanisms and evaluation methods, and their awareness of this phenomenon and disaster prevention remains low. In this study, we sought to select a quantitative impact assessment method and learn more about this phenomenon. We used previous research and eyewitness accounts to judge that onsite slosh dynamics caused the waves to develop, and we attempted to recreate this phenomenon using a 3-D slosh dynamic analysis. After comparing laboratory results to verify the validity of the analysis, we recreated past examples of waves and also made future predictions. As a result, we were able to recreate abnormal water level fluctuations based on this method. In addition, we identified water damage risks to inland lakes and waterways of inner parts of bays. These are different from risks posed by tsunamis. It is forms immediately after the onset of an earthquake.

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 To utilize coastal waste landfill site on the sea effectively, installation of foundation piles through the waste layer and the natural clay barrier layer will be required to support heavy structures. But when the foundation piles penetrate the clay barrier layer, leakage of polluted water in the waste layer through the ground around the driven piles to the beneath permeable layer is concerned. In this study, a series of experiments was carried out to clarify the effects of the installation of the pile on the performance of impermeability around piles in the clay layer. As the results, it was found that if the gap was caused by the pile installation between the pile and the clay layer, it was closed immediately in the normal consolidation state, and therefore the performance of impermeability around the driven pile was ensured. Moreover, the countermeasure for fail-safe was also suggested.

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 Navigable floodgates such as flap gates and vertical lifting gates are attracting attention as effective countermeasures against tsunamis and storm surges, particularly after the Tohoku tsunami of 2011. A narrow gap between adjacent gate units would inevitably cause an intrusion of seawater into the port basin, which cannot be simply simulated using common tsunami models because the gap is too small to be reproduced in the model. The present study examines the water flow passing through a gate gap by applying a 2D-3D hybrid hydrodynamic model to derive the hydraulic head-to-inflow discharge conversion formula, which is defined as Q = α√(2gh)dW, where Q is the discharge, g is gravitational acceleration, h is the hydraulic head, d is the water depth, and W is the gap width. The coefficient of discharge α can be estimated by a linear regression, which varies with the gap width between the relevant floodgates. For example, the relationship 0.15h + 0.25 was derived for the case where W = 0.3m. The proposed model was verified through case studies in which a time series of hypothetical water levels composed of a Level 1 tsunami and tide or that of a storm surge alone was simulated for a medium-sized port. With this proposed method and given the water level outside the port, the water level rising over a port basin enclosed by floodgates and breakwaters can be calculated using a spreadsheet or other simple computational means that do not require complex models based on computational fluid dynamics.

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