In this study, grain size analysis of sediment were carried out using image processing in order to clarify the distribution of particle diameter and grain sorting quantitatively. The drift sand in the coastal zone is the important problem in the research of beach erosion and sedimentation, and many researchers are trying modeling of this process. Many laboratory experiments of sand transport under oscillatory flow and waves have been carried out in order to clarify the process of sand transport. However, there are a few studies which measured grain size distribution inside the beach. In this study, the grains size distribution is estimated from the computed tomography imaging inside the beach by matching of refractive index.

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It has become known that the existing tsunami breakwaters are insufficient for sheltering harbors and coastal areas as seen in the incidence of destructive tsunami triggered by 2011 great Tohoku earthquake in East Japan, especially in ria bays of Sanriku Area such as Ofunato Bay. Amplification of tsunami heights in a ria bay is one of major causes of the big disaster. In order to mitigate the tsunami disaster, layout of breakwaters at the mouth of the bay has been studied theoretically by numerical simulations. Breakwaters in multi rows, especially double rows of breakwaters, are typical. Focusing on the harbor oscillations for various tsunami period conditions, effectiveness of proposed layouts of the breakwater was examined extensively.

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Transmitted waves through breakwaters due to wave overtopping and their propagation toward quays are sometimes considered in harbor tranquility analysis, because the wave overtopping may occur on breakwaters at harbor entrance in storms. In this study, their effects on cargo handling rate on quays are estimated with considering variations of ratio of wave height due to difference of incident wave height. As a result, it is clear that significant wave transmission cannot occur in case that wave overtopping rate is smaller than 0.02 m³/s/m. Hence, the cargo handling rate which is estimated with such way becomes higher because frequent storm waves are attenuated due to wave breaking instead of generating transmitted waves in harbor inside.

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This study investigates the amplifying characteristic of a wave activated pump through a series of hydraulic experiments. The wave activated pump consists of some vertical columns set in front of a vertical wall. This study confirms that the pump amplifies the wave motion effectively under irregular wave conditions as well as regular wave conditions. The magnitude of a maximum amplification factor depends on a distance between a seabed and the bottom end of the column. A mathematical model is proposed in this study in order to evaluate the amplifying characteristic of the wave activated pump. The model estimates the maximum amplification factor and a resonance period in good accuracy.

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Laboratory experiments were performed to study wave transmission and wave reflection capacity of circular Cylinders as coastal protection from waves. The energy dissipated in circular cylinders may be evaluated by using the drag forces acting on the cylinders and wave particle velocities. A theoretical analysis based on application of the continuity and energy equations to flow through the rows of circular cylinders were made to evaluate wave transmission and wave reflection capacity of mangroves and trees in coastal area. The reflection coefficient K_r is significant for large value of the ratio of the circular cylinders area to the unit bed area in the array of circular cylinders. The theoretical analysis were also made to evaluate wave transmission and wave reflection capacity of mangroves in coastal area. The significant wave reflection from mangroves with large and dense canopy was estimated.

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Artificial reef has been used as a measure to reduce wave energy off to the beach. However, reef body erosion due to return flow on the gap between artificial reefs has been reported. Moreover, most of past studies dealt with sandy beach and permeability of sea bed has not been investigated in depth. Hence, this study aims to investigate characteristics of flow field around artificial reef considering the permeability of sea bed through 2D and 3D numerical simulations. As a result, the permeability affects a return flow, which leads to change in water velocity field. Results of 3D simulation show that the flow field formed around an artificial reef can explain sediment transport around it.

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A series of hydraulic model experiments was performed to clarify the effect of Wave-Dissipating works on wave force reduction of tsunami with soliton fission. First, under the conditions of a wide range of water depth and wave period, the process of tsunami deformation was examined to understand the characteristics of tsunami profiles at the soliton fission including the relation between degree of dispersion and travel distance. Then, the relationship between the pressure of the soliton waves acting on the vertical wall and the degree of dispersion was studied. Finally, the effect of wave-dissipating works on wave force reduction of tsunami was investigated by comparing the wave pressures on a caisson with and without the works under the condition of breaking and non-breaking soliton wave.

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The estimation method of tsunami wave force acting on a land structure using hydraulic quantities around the structure was newly proposed in this study. Hydraulic experiments were conducted to estimate tsunami wave force acting on the structure. A 2D depth-integrated flow simulation under the installation of a land structure was carried out to examine run-up tsunami deformation. Even though the maximum wave force due to the initial impact of the leading edge on the structure cannot be reproduced by the proposed method, the method could reasonably estimate the tsunami wave force. Tsunami wave forces calculated by CADMAS-SURF/3D were in good agreement with the experimental results on the wave condition that cannot be reproduced by the evaluation method using the 2D simulation results.

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Hydraulic experiments were conducted to estimate tsunami wave pressure acting on a land structure and examine the influence of initial inundation in a land. The experimental results revealed that the runup characteristics of incident tsunami wave are largely different under a dry or wet bed condition. Initial depth in an inundated land has a significant influence on not only inundation pattern at the front of the land structure but also tsunami wave pressure acting on the structure. The vertical distribution of tsunami wave pressure at the time when the maximum wave force occurs was also influenced by the initial inundation. Tanimoto formula for estimating tsunami wave acting on a vertical breakwater was found to be applicable to evaluating tsunami wave pressure acting on a structure in an inundated land.

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The tsunami force acting on a land structure generated by the run-up tsunami was generally evaluated from the maximum inundation depth of the passing run-up tsunami, which is estimated on the supposition that the structure does not exist. However, the maximum depth does not always accompany the maximum tsunami force, e.g., in the case that the inundation depth gradually increase. Therefore the time series evaluation of the tsunami force not with the maximum depth is required. In this study, the physical model experiment to examine the tsunami forces acting on a wall structure in time series was conducted. It is found that the time series of the tsunami force was expressed with the inundation depth and the velocity of the passing tsunami at the same moment.

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After 2011 Tohoku-Oki Earthquake, construction of seawalls with tenacious structure is needed, but there are few studies about change of tsunami force acting on buildings behind the seawalls according to construction of them. So in this study, we looked into the applicability of CADMAS-SURF/3D to calculate tsunami force through reproduction calculation of physical model experiment which was conducted by Arikawa and Oie (2014), and consider about change of tsunami force according to seawalls condition. The results of this study are as follows; 1) The tsunami force acting on buildings behind the seawalls is well reproduced with CADMAS-SURF/3D, 2) Depending on the distance from seawalls, some cases with seawalls have bigger coefficient of pressure α than the cases with no seawalls.

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In this report, the effectiveness of decreasing of tsunami force due to seawall was investigated by physical experiments. The seawall with 30cm height was used in this study, and solitary waves and sin waves were attacking on the building behind the seawall. Three different situations of seawall were tested. One is without seawalls, the other is with seawalls, and those seawalls are falling or rigid. The results show that the relationship between the Froude number and the coefficient of pressure are based on the Bernoulli's principle. When the tsunami height is almost same as the height of seawall, the pressure on the buildings behind seawalls are getting smaller than that without seawalls. The speed of falling of seawall is affected on the pressure on the building. If the speed is getting higher, then the pressure is getting larger.

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Tsunami evacuation buildings are considered as effective countermeasures against tsunami. The openings of buildings may reduce the tsunami force acting them, however, its effect may be influenced by inner configuration of buildings. Moreover, a tsunami direction is another important factor for tsunami forces. In this study, based on hydraulic experiments and numerical calculations, their effects on tsunami forces are investigated. The tsunami force after impact is found to be estimated by hydraulic pressure in different ways according to the size of openings, and for the buildings with large openings, it is confirmed to be considered forces acting on inner walls. In investigation of tsunami direction, the force due to obliquely incident tsunami can be determined by the tsunami acting area and effect of parry the tsunami.

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Numerical experiments on tsunami-induced wave force acting on an inland structure in the presence of nearshore structures are conducted to investigate the effects of the number and arrangement of the nearshore structures. Numerical results show that the water depth coefficient is affected by the presence and arrangement of the nearshore structures, and consequently the evaluation of tsunami force using the interim Japanese national guideline still remains open to question for the presence of nearshore structures. Furthermore, it is revealed that the maximum tsunami force can be evaluated using a formula based on the momentum and drag force.

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We made model experiments on run-up tsunami inunduation flow with sea ice floes in an urban area. After the collision force of ice acts on structures, flow is dammed up due to the formation of Ice-jam between the structures, and large static force also acts on the structures because of water level rise and water pressure between the structures due to the jamming. The steady state is kept for a while. While we developed a simple mechanical model for estimation of the water depth and the tsunami force at the steady state, we compared calculated values by this model with experimental ones to verify the validity of the model. Further, in the design of facilities with openings such as windows and pilotis, we proposed that the design force by tsunami current acting on such parts should not be reduced because of the jamming.

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Large-scale model experiments on tsunami hydrodynamic load on a vertical tide wall were carried out, in order to investigate characteristics and scale effects of tsunami hydrodynamic load. Experimental results showed that impact pressures with very short duration were measured, which were highly localized in space and time, just after the tsunami fronts with air-water mixing conditions impacted the tide wall. After that, complicated vertical pressure profiles were observed, in which there were subatmospheric pressure and local maximum pressures. The vertical pressure profiles became hydrostatic profiles in a few seconds after the tsunamis impacted the tide wall, and the inundation depths estimated from the pressure profiles agreed with those measured upward side of the tide wall.

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Hydraulic experiments using scale building models were conducted in order to investigate tsunami loads acting on buildings with apertures. In the case of the buildings with apertures only on the front side, the maximum tsunami loads in the horizontal direction can be equal to or higher than those acting on buildings without apertures. It was also found that the water entered through apertures into the buildings impinges on the internal ceiling, and the upward loads can be caused which are different from buoyancy effects. Numerical simulations by the 3D VOF method could reproduce these phenomena and the variation of tsunami loads in both horizontal and vertical direction with high accuracy.

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Impact tsunami wave pressure acting on near the bottom of a land structure was measured with high speed video images of fluid motion in front of the structure. The value of the maximum impact pressure reached 10 times that of the hydrostatic pressure. The impact pressure changed with some patterns of the fluid motion. The patterns also changed with Fr number. Under low Fr number conditions, the gauge pressure is composed of the dynamic pressure by the maximum of the fluid velocity and the hydrostatic pressure which depends on the height of fluid raising along the front wall. However, Fr number becomes higher, the gauge pressure is getting equal to the dynamic pressure only. The maximum value of the impact pressure can be fit into the function of 0.5 times square of the velocity.

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A laboratory experiment is conducted to make clear fundamental characteristics of fluid force and collision force due to tsunami-driven shipping container acting on a porous onshore tsunami barrier. Fluid force becomes large as the porosity of the barrier decreases, and then the reduction of inundation depth behind the barrier is significant. The correlation between fluid forces on the barriers and reduction of inundation flow can be characterized by the relative incident bore height to barrier height. A tsunami-driven container slows down in front of the barrier due to the interaction between the container and reflection wave from the barrier, so that the reduction of collision force is much significant in the case of the barrier with low porosity. The collision force for high porous barrier is much larger than the fluid force.

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In this research, hydrodynamic force of Tsunami acting on bridge was studied both numerically and experimentally. At first, hydrodynamic force acting on PCT girder in steady flow was calculated by CFD. Numerical results cleared that lift is negative in steady flow. Therefore, high velocity is required if girder resists hydrodynamic force by frictional resistance. Scale model test was carried out to verify numerical results. Test results were similar to numerical results qualitatively. Because actual flow of run-upped Tsunami is somewhat different from steady flow, hydrodynamic force in the process of elevation of water surface was studied as next step. In this case, lift was positive and depended on water level and the rate of elevation.

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In the event of a winter tsunami, there is the concern that floating ice sheets originating from sea ice might impact structures if the ice is carried by tsunami run-up. Accordingly, we conducted hydraulic model tests that reproduced the vertical and longitudinal behaviors of floating ice sheets carried by tsunami run-up. We clarified the characteristics of wave force for tsunamis that contain sea ice sheets and the impact of such tsunamis against bridge girders. In this test we reproduced a flow that contained solid substances and liquid substances. We confirmed that the wave force of a tsunami whose ice cover rate is 80% is about 2.5 times the wave force of a tsunami that contains no ice. We succeeded in showing the wave force characteristics of tsunami waves containing water and ice running up rivers in winter for bridge girder structures.

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Some bridges have been failed by Tsunami and river flood in Japan. One of the reasons of the damage was the lack of useful method for evaluating the action of the bridges subjected to the water flow. This means that there was no verification of the bridges caused by Tsunami. The authors have conducted experiments and numerical analysis in order to understand the effect of bridge properties: the cross-section shape of beam, velocity of water, height under the beam, and the existing of gird wall, on the force applied to the beam by water flow. This paper focused on the railway bridges having large depth of beam compared with the road bridges, and uniformed flow of water.

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Some bridges were failed by Tsunami at Great East Japan Earthquake. One of the reasons of the accident was the lack of useful method for evaluating the action of the bridges subjected to Tsunami. This means that there was no verification of the bridges caused by Tsunami. The authors have conducted experiments and numerical analysis in order to understand the Tsunami force applied to the prestressed concrete viaducts. This paper focused on the railway bridges having a large depth of beam compared with the road bridges, and also focused on the shape of Tsunami by controlling the wave period.

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This paper examines the tsunami hydraulic loads on I girder bridge using a three dimensional (3D) two-phase (water and air) flow analysis. The effect of the air and water in the hydraulic loads on I girder bridge is examined by comparing with the results from a hydraulics experiment. It is found that a larger amount of air is trapped in the I girder and the experimental results can be simulated by the two-phase flow analysis. Next, the 3D two-phase flow analysis is used to examine the effect of the 3D topography on the hydraulic loads of the Koizumi bridge with I girder damaged by the 2011 Tohoku earthquake tsunami. The numerical example reveals that the hydraulic loads on the Koizumi bridge vary largely with the position of the bridge because the tsunami velocity and height change in apace due to the 3D surrounding topography.

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In the Tohoku-Pacific Ocean Earthquake, many bridges were washed away by the tsunami, the wave height of which exceeded the conventional assumption. In the future, countermeasure for tsunami disaster will be needed, and the evaluation of tsunami wave force acting on bridges will be very important. In this study, hydraulic model experiments and numerical analyses using VOF method were carried out for a bridge superstructure model to clarify the influence of tsunami wave shapes to tsunami wave force acting on it. As a result, it was confirmed that maximum wave force can be expressed as a function of the wave front slope of tsunami incident wave.

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From the videos recording tsunami caused by the Great East Japan Earthquake, it was observed that tsunami waves attacking coastal area mainly showed steady flow form, with a 1~2m bore wave happening at surge front. And most of damaged bridge girders were swept away by steady flow. Thus, the experiment simulating steady flow, was conducted to evaluate wave force on bridge girder. As a result, it was found that wave force of steady flow could be estimated with the use of the drag coefficient C_d proposed by the Specifications for Highway Bridges and when Reynolds number Re of steady flow changed from 10⁶, the drag coefficient C_d for bridge girder in steady flow only changed 10%. Lastly, due to steady flow became turbulent condition gradually with increase of flow velocity, besides the wave force on bridge front surface, the wave force on girders became bigger, which caused a little increase of drag coefficient.

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A large number of breast type seawalls behind the fishing ports were damaged due to the Great East Japan Earthquake on March 11 in 2011. The collapse of seawalls without tsunami overflows was confirmed in many fishing ports, so we needed to reconsider the present calculation methods of tsunami induced forces on seawalls. In this research, physical model tests were conducted in a wave flume to investigate the tsunami induced forces on breast type seawalls under non-overflow condition. As a result of the tests, we propose the calculation formula of hydrodynamic pressure exerted on seawalls composed of both of as a function of the Froude number and maximum incident tsunami wave height and as a function of inundation depth in front of seawalls.

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This paper proposes a determination method of earthquake and tsunami damage to the storage facility at the production facility in the coastal areas. Earthquake and tsunami damage determination was performed combining three dimensional tsunami analysis and structural analysis. First of all, the pressure applied to the structure is calculated by three dimensional tsunami analysis. Next, the structural analysis model which can express a damage situation was created, and seismic response analysis and tsunami response analysis were conducted. Finally, damage judgment was determined by stress and the amount of deformation of the plate. From this result, analysis of the proposed method showed the usefulness by damage simulation of the earthquake and tsunami that apply to the structure.

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Tsunami force acting on tanks was discussed based on the experimental results ranging from subcritical flow to supercritical flow. The water level around the tank and the tsunami pressure were also measured. The comparison between the pressure profile and the water level around the tank shows that the pressure is lower than the hydrostatic pressure under the supercritical flow while that under the subcritical flow is close to the hydrostatic pressure. The mechanism on the pressure fields was discussed. The tsunami force acting on multiple tanks was also measured and effects of the tank disposition on the force were discussed.

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In order to find out the mechanism of tsunami bore wave on bridge girder, the bore wave experiment was carried out with a bridge girder model. As a result, the measured maximum horizontal force on bridge girder by force transducer was found close to the calculated maximum force by the integration from the wave pressures on girder front surface. Thus, the horizontal force is dominant to the wave pressure on girder front surface. Besides, from the parameter study of wave height, it is noted that both horizontal force and the wave velocity of girder location are proportional to wave height. Thus, it is concluded that bore wave horizontal force has a high correlation with wave height.

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A floating-type evacuation shelter from tsunami is the facility which is swepted in tsunami. Therefore, for establishment of the shelter on site, it is an important task to predict motion of the shelter with accuracy in terms of strength for tsunami fluid force and safety of evacuees. In this study, a numerical model for prediction of translational and rotational motion of the shelter is presented. According to comparison with laboratory experimental results, calculated results on translational and rotational motion reasonably agree with experimental ones with accuracy.

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In this paper, responses of a pontoon in tsunami were studied. As an example, a pontoon by the mooring pile system of Izushima fishing port in Miyagi Pref. was treated. The pile of the pontoon was pulled out of the tsunami which was derived from the Great East Japan Earthquake. Model tests in a solitary wave was carried out and tsunami simulation was also carried out. The pontoon was capsized in fast elevating cases of water surface. In order to suppress the capsizing, it is effective to place the roller fender lower than the gravity center to increase restoring moment. According to the tsunami simulation for Izushima fishing port, tsunami height was small enough compared to the wave length and elevation speed was slow. Thus, the pullout force of the pile is estimated mainly from surplus buoyancy, and capsizing should not be occurred.

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Numerical simulation of nonlinear interaction between floating thin-plates and surface waves has been performed to study the reduction of tsunami height due to propagation of tsunamis through very large floating structures (VLFS). When a solitary wave propagates through a floating thin-plate, wave disintegration occurs, resulting in generation of short floating-body waves, such that the wave height of the main wave is decreased. While the main wave is combined with the short waves after progressing through the thin-plates, the wave height of the main wave is increased. Once the main wave passes the short waves, its wave height decreases, which indicates that a VLFS is applicable to reduce tsunami height. The reduction effect depends on both the length of floating structures and the interval of the structures.

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The 2011 Tohoku earthquake and tsunami at 14:46 JST on 11 March 2011 affected large areas of the eastern and northern part of Japan, and many sea disasters of vessels moored in harbors occurred. We conducted surveys on two large tankers with mooring line breakage. During the surveys, the mooring line breakage happened due to not only the tsunami impact but also oscillations of dolphins by the seismic vibration. In this paper, we have composed a time domain model to estimate moored ship behavior due to oscillations of dolphins during earthquake, and investigated into the actual mooring line breakage of the VLCC at S-port, using the simulation model and the observed ship motion by GPS.

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Tsunami overflowing a breakwater is reproduced by a numerical model to evaluate the stability of armor units covering the harbor-side of the rubble mound. This model solves the overflow jet above the water surface and the harbor-side flow field separately to avoid entrainment of excessive bubbles. Using this model, the applicability of the Isbash formula for the stability of armor stones and concrete blocks against tsunami overflow is examined. The relationship between the Isbash number and the degree of movement of armor stones is clarified. In the case of concrete blocks, the Isbash number of the stability limitation varied with the thickness of the overflow jet. The Isbash formula by C.E.R.C. (1977) tends to overestimate the effect of slope angle, when applied to concrete blocks. A stability prediction method for armor blocks based on fluid forces acting on each armor block is presented as well.

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Many breakwaters were damaged by the Great East Japan Earthquake of March 11, 2011. Many of these were destroyed under tsunami overflow. Some results of researches indicated that in the case where scouring of the foundation had occurred, the safety factors for bearing capacity failure declined to less than in a case where the foundation part was not scoured. But, the relation between the overflow and scouring depth had not been clarified. In this study, the scouring depth due to tsunami overflow was investigated by using the physical model tests. Results pointed out that the scouring depth can be evaluated by the scale of vortex due to overflow.

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To investigate influence of nappes induced by tsunamis flowing over breakwaters, a single-phase flow model, CADMAS-SURF/3D and a two-phase flow model, FSSM are applied to existing hydraulic experiments. From comparison, the single-phase flow model can predict the hydraulic experiments with sufficient accuracy in terms of water surface elevation and the shape of a nappe. In contrast, the two-phase flow model underestimates water surface elevation at the seaward edge of the breakwater in the presence of a parapet because a decrease in pressure due to flow separation causes an increase in flow velocity on the breakwater. Furthermore, both models give different distributions of pressure acting on the landward side of the breakwater probably because nappe-induced vortices are not computed with sufficient resolution.

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Leaning revetment is a common type of seawall structure. In common cases, armor blocks and foot protections are placed in front of their lower part. Main purpose of the blocks is to prevent rubble foundation sucking away in high wave condition. However, previous study indicates that these blocks prevent sudden displacement of leaning revetments. In this study, experiments were conducted to measure effect of the blocks to prevent leaning revetments' displacement. The result of the experiments indicated that these blocks have functions: they help to increase stability of leaning revetment's structure including rubble backing if the blocks have abundant weights, they could be evaluated in calculation of stability of leaning revetments, offshore direction force which they receive by a leaning revetment may change under their placed condition.

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One of the possible basic structural countermeasures taken for a breakwater to protect foundation mound and seabed against scouring caused by overflow is widening work for increasing the height of the foundation mound behind the breakwater. The widening work behind the caissons is topped with scour prevention work and a revetment to provide scour resistance to the structure. But the stability of armour blocks on the widening works is not cleared. In this report, the physical experiments were conducted to make clear the mechanism of failure of armour blocks under overflow of tsunami, and to consider the estimation methodology of stability of armour blocks. The results indicated that the stability of blocks related with the porosity of blocks and was estimated by using Isbash equations.

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Obtaining knowledge of characteristics of splash generated by wave impact on a concrete construction in ports and harbors is one of significant research topics for highly effective protection of the structure from salt damage. In this study, the generation process of splash by wave impact on vertical wall was captured by high-speed cameras in a laboratory flume with pure water. Using PIV and PTV techniques, spatial location, diameter, and velocity of each splash particle were measured. Further, it was shown that distribution of splash diameters was formulated by the Gompertz curve with two parameters as the Weibull and the logarithmic function of splash diameter. Moreover, mean velocity and mean direction of each diameter of splash were also presented.

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This study aim to evaluate the fundamental performance of the Hydroplane Tsunami Barrier by using the 1/200 scale hydraulic model. The Hydroplane Tsunami Barrier is a kind of movable breakwater. The main body is fixed to the pedestal by the special rubber belt, and it rises by hydraulic force due to tsunami and storm surge. The effectiveness of this breakwater for tsunami countermeasures is indicated through experiments of response characteristics for hydraulic force, wave force acting on the main body and the damping effect for wave height. As a result, it is revealed that water pressure acting by the maximum wave height is larger than the impact force due to the rotation of the main body. It was confirmed that the damping effect increases with the height of the tsunami.

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The effectiveness of countermeasures to improve the tenacity of coastal dikes against tsunami overflow is investigated numerically in terms of local scouring at its landward toe and wave force acting on armor blocks. Numerical results show that protection blocks and filter units covering the foundation around the landward toe of the dike move the scouring area landward and reduce its maximum depth, suggesting that these countermeasures would be effective to extend the time before beginning the damage of the body of the dike. It is also revealed that air vents created at the armor blocks reduce an increase in air pressure inside the dike, improving the stability of the armor blocks. Furthermore, it is found that there is no effect of a sheet pile against liquefaction during an earthquake on the local scouring and wave force.

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This study aims to investigate collision forces of drifted objects due to tsunami acting on cylindrical structures. The hydraulic experiments were conducted to investigate the characteristics of collision forces to columns. Through hydraulic experiments, it is clearly confirmed that the peak values of collision forces depend on the rigidity of drifted objects. This result suggests that when the drifted object has low rigidity such as cars or boats, the collision forces acting on structures are relatively small. The numerical simulation of collision forces of a drifted car to column structures were also conducted by using a 3-D simulation model based on SPH method. The simulation results show that the behavior of the drifted car and collision forces are simulated qualitatively well.

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Coastal dikes in Iwate, Miyagi, and Fukushima prefectures in Japan were seriously damaged caused by the tsunami by 2011 off the Pacific coast of Tohoku Earthquake. One of the main factors of damage was landward bed scouring due to tsunami overflow. We focused on the effect of shape of landward slope protection and toe protection works on landward bed scouring, and carried out small scale tests to clarify the effect of these works. The experimental results show that a large scouring hole was formed around the landward toe area in any shape of slope protection works without bed protection works condition. Landward bed protection works have an effect to reduce the size of scouring hole and surface protuberance of landward toe protection works have more effect to reduce the max scoring depth and the scoring area.

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Two-phase flow simulation was performed to estimate pressure in trapezoid-shaped coastal dike armored with concrete during tsunami overflow. The results of the simulation were verified with pressure on the bottom of coastal dike armor measured in large-scale model experiments on infiltration to the embankment soil covered with cast-in-place concrete or concrete blocks. The simulation showed that pressure in the dike body increased with the overflow depth at the seaward slope toe of the dike, and that sheet piles at the seaward slope toe mitigated pressure rising in the dike body.

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Embankment reinforcement with steel sheet piles is presented as a countermeasure against tsunami overflow, which is known as a main cause of failures of coastal embankments due to the 2011 tsunami. In the presenting structure, one or two vertical sheet piles are put inside the embankment and they are expected to keep total height of the embankment after severe erosion of landward slope. The effect of the sheet pile structures was discussed through hydraulic experiments in a horizontal open-channel with a 1/50 embankment model. Deformation of the embankment and the sheet pile structure was recorded by a video camera and strain gauges. Embankment height after overflow was about 70% and 95% of the initial height respectively for one and two sheet pile structure while it was only 17% for non-pile structure.

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The tsunami generated by the 2011 off the pacific coast of tohoku earthquake caused massive damage to coastal dikes. It is required for coastal dikes to increase the resistance of tsunami. Although some coastal dikes resistant to tsunami are proposed, embankment materials which can enhance the resistance of coastal dikes are not identified clearly. In this study, embankment materials of a coastal dike which can enhance its resistance are investigated by conducting hydraulic physical model tests. The results of hydraulic tests showed that embankment mixed by cement or clay could enhance the resistance of tsunami. The numerical simulation was also conducted to clarify the erosion process of lean cement mixed soil.

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Conventional type of costal dike covered with concrete-blocks is designed to resist against wave forces relying on its self-weight while dissipating the uplifting water pressure via a pervious underlying layer. However, continuous waves, like tsunami bore, generate dynamic wave pressure in the previous layer, and uplift the concrete-blocks. In addition, the shoulder-blocks on the downstream slope are lifted up and dragged away by negative water pressure. In order to alleviate these structural defects, a new type coastal dike is proposed, which integrates concrete-blocks using geotextile to an underlying low-permeable soil-cement layer. The results of hydraulic tests indicate that the new type dike has a high stability against tsunami bore by restraining the generation of dynamic wave pressure inside the backfill, while resisting against uplift force by anchoring the concrete-blocks with geotextile to stable backfill and connecting each other via a joint structure.

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Coastal dikes were seriously damaged by tsunami of The 2011 off the Pacific coast of Tohoku Earthquake. The main cause of the damage was supposed to be scouring at the back slope toe. In this study, in order to estimate scouring landward of coastal dikes induced by tsunami overflow, a numerical model which introduced a geomorphological process into CADMAS-SURF/2D was developed. Then, the model was verified by comparison with experimental results. As a result, while numerical results may lead to underestimate width of scouring, the calculated maximum scour depth showed good agreement with experimental results. Thus, it was indicated that this model could be applied to estimate scouring at the back slope toe of coastal dikes.

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The earthquake that occurred three years ago generated huge tsunamis, and it caused serious damage to Japan. To create stronger embankments in case of future tsunamis, so many studies have been conducted. In renovating coastal dikes, we must consider not only function, but also landscape conservation and depletion of limited natural resources. Based on these considerations, we apply a rehabilitation technique for fill-type dam embankments to strengthen coastal dikes. It uses muddy soil (for example dredged soil from port) mixed with cement, which provides excellent resistance against earthquakes and tsunamis. In this paper, we have developed a new soil-improvement technique for coastal dikes.

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