Sihwa tidal plant, located west coast of Korea, is a place to make electricity harnessed tidal variation exceeding 9 m in spring tide. When sea water is abstracted from outside to inside of Sihwa Lake through gates with turbin around high tide, electric power has been generated. And sea water is discharged from inside to outside of Sihwa Lake through sluices and gates of turbin without making electricity around low tide.
 In this study, we introduce that strong current of about 2 m/s were observed at monitoring station located in 2 km away from the sluices of tidal plant. And, we introduce that as a result of reproducing such strong currents by numerical simulation, we identified such strong current was flowing belt-liked toward offshore from sluices, and the location of such belt-like current was moving in corresponding with tide. As a result of sensitivity analysis with the numerical model of reproducing the current, for assessing against current from plants discharging huge quantity of water, we identified that geometrically approximated grid size is necessary, and difference scheme of advection term which increase artificial viscosity are unsuitable.

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 Detection of rip current occurrence is important for safety management of swimming beach. In this study, an X-band radar is employed to observe locations of rip-channels and occurrences of rip current at Uchinada Beach, Kanazawa, Japan. The radar was installed on the back-shore, and the effective coverage of the radar was approximately 1,000 m. In the time averaged radar images, which were processed for every 2 minutes, rip channel locations and rip heads were tracked for 40 days in August and September of 2015. The validity of the results was verified from results of morphological surveys and buoy releases. Rip heads were connected with rip channels, and this was evident when the wave height of the area was more than 0.3 m. Rip channels migrated in a complex manner during the observation.

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 Exceptional long wave called ‘Abiki’ (it's a kind of meteotsunami or seich) has occurred around west coast on Kyushu Island from winter to spring season. Previous studies on Abiki showed initial amplification mechanism called Proudman resonance caused by low crest pressure waves, and secondary amplification mechanism caused by resonance between long wave and bay. However, the nonlinear relationships of tidal variation and Abiki has not been made clear so much. In this study, we tried some simulations of Abiki occurred on Feb., 2009, and basic analysis of interaction between tidal variation and development process of Abiki by using numerical model of nonlinear long wave equation.

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 A survey has been carried out on the characteristics of seiches around Japan using records obtained by Japan Meteorological Agency. Secular variations of frequencies of seiches vary according to stations. Characteristics of two neighboring stations do not necessarily resemble. On the contrary, those of two remote stations may be similar.
 On the other hand, seasonal variations of most stations of the whole country are very similar except some stations situated in Hokkaido, Okinawa and inland sea areas.
 Effects of meteorological disturbances of synoptic scale such as typhoons, low pressures and fronts which are regarded as causes of seiches vary locally every year, but they are very similar all over Japan considering a long period.

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 Characteristics of secondary undulation occurred in Kagoshima Bay during the summer season were examined using the results of observation and numerical simulation. It was clarified that the first-mode oscillation with the 24-minute period and the second mode with the 17-minute period are dominant in the southern and northern regions of the bay, respectively. The first mode has two nodal points at the central part of the southern region and off the bay, while the second mode has a nodal point at the central part of the northern region. Moreover, it was suggested that the two modes in summer occur according to the approach of a typhoon.

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 For a coastal structure constructed on a reef bathymetry, it is important to estimate the surf-beat generation due to wave shoaling and breaking addition to the wave height reduction and the wave set-up. In this study, A series of numerical experiments is conducted by using a Boussinesq model to reveal the characteristics of surf-beat distribution which may have relations to wave height distribution referring some existing experimental formulae. To do this, the wave breaking model based on an one-equation turbulence model is modified with velification to some results of model experiments on wave height distribution on a slope and a reef. In consequence of the results of numerical experiments, the increase of surf-beat height along the penetrating wave direction on a reef is disturbed near a reef-edge in a wave breaking condition.

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 In recent years, MSM(Meso-Scale Model)-based analysis and prediction winds data sets with a high space resolution have been open to public domain by JMA(Japan Meteorological Agency), but validation for accuracy of sea winds in the data sets may not be satisfactory because of the lack of observed sea winds data to be used in the comparison. This study investigates implicitly and explicitly the accuracy of MSM winds data, in cases where not only JMA buoy robot-based winds data and blended winds product based on satellite observation associated with around a 10-year different period but also GPS buoy-based wind speed data during typhoons with 5-day duration are used for the comparison. The main findings are as follows; 1)It may be indirectly deduced that MSM winds data are in rough agreement with JMA buoy winds data on the basis of both the comparison between JMA buoy winds data and blended winds data and the comparison between MSM winds data and blended winds data. 2)MSM wind speed data follows the GPS buoy wind speed data well for its time variation during a typhoon but gives larger values due to a slower decrease at the decaying stage.

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 Typhoon is one of the most devastating meteorological phenomena causing storm surge disaster. Recently, some researchers reported that typhoons will be stronger and their courses will shift toward the east or/and the north due to global warming. Therefore, it is of great importance to investigate the characteristics of future typhoons. In order to predict the potential storm surge due to the future typhoons, the climate projection data seem to be useful. Based on MRI-AGCM3.2S, it was suggested that the area over which strong typhoons pass through tends to spread in all the directions in the future climate though there is no significant change in the mean typhoon course. In this study, we investigated the changes of typhoon characteristics due to global warming around Japan for several patterns of sea surface temperature distribution by comparing the result of those future climate data and present climate data of MRI-AGCM3.2H. First, we extracted typhoons from the time series of atmospheric pressure data. Next, we counted the number and analyzed the central pressure of all the typhoons every 1 latitude. Then we investigated the characteristics of spatial distribution of number and strength of typhoons. As a result, it is suggested that the characteristics of typhoons seem to change with the sea surface temperature change patterns rather than global warming although the typhoons that hit Japan tends to become stronger in the future for all patterns.

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 Some coastal areas, e.g. the Ariake Sea, the Suo Nada, etc., around Kyushu Island where typhoons often hit have experienced severe storm surges so far. In contrast, the northern coasts of Kyushu facing the Sea of Japan have not met with severe storm surge disasters for a long time. Recently, however, some relatively strong typhoons, e.g. Typhoon 19 in 1991, Typhoon 18 in 2005, etc., hit the northern part of Kyushu. Furthermore, due to global warming, there are growing concerns about possible tremendous storm surge disasters which might be caused by more furious typhoons than ever at the coastal areas around Japan including the northern coasts of Kyushu. In this study, by conducting numerical simulations, the dangerous areas where severe storm surges can occur along the northern coasts of Kyushu were found out first. Next, the basic characteristics of storm surge in Hakata Bay were clarified.

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 In this research, we discussed about the newly ground improvement and countermeasure of liquefaction technology for the seabed based on the microbial functions. This study examined the feasibility of in-situ bio mineralization technologies for the sediment from deep sea area which are located near the surface types of the methane hydrate (depth is the -540m) in Japan sea. Authors used the pre-cultivation which are enhancement of the urease activity from in-situ sediment and the cyclic triaxial test to evaluate the enhancement of the liquefaction strength with three types of microorganisms. The main findings of this research were as follows:(1) the urease activity microorganisms from the deep sea sediment can enhance calcite precipitation during the three weeks cultivation, (2) Surface of the seabed sediment can precipitate the calcite and improvement of liquefaction strength. , (3) The enrichment culture from the deep sea area can enhancement of the liquefaction strength as a solidification of specific microorganisms named Bacillus pasteurii.

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 Local subsidence damage on the airport taxiway right over the ground nearby the underground structure occurred during the 2011 off the Pacific coast of Tohoku Earthquake. Shake table test of a large model in 1g gravitational field was conducted to make clear a mechanism of this subsidence damage. This study focuses on relationship between strain history and subsidence of ground surface in the liquefied ground. As result, the maximum strain and accumulated strain of deviator shear strain around underground structure increased in comparison to other places where far away from the underground structure. Then when subsidence of ground surface increased, distribution of subsidence corresponded to distribution of the maximum strain and accumulated strain in the ground.

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 This study investigates liquefaction resistance of sand under sequenced earthquake motions by cyclic torsional shear tests. Two series of stress-controlled tests, “step loading” and “irregular wave loading”, have been performed. These tests consisted of two different loading phases. In the step loading tests, certain levels of excess pore pressure were first achieved by ordinary, sinusoidal wave loadings. Subsequently, the step loading, which increases cyclic shear stress ratio in steps, was applied. This was done to evaluate the shear stress level at which excess pore pressure restarts to rise in an aftershock. In the irregular wave loading tests, these loading processes were replaced by applying irregular waves based on the record in the 2011 Tohoku Earthquake. The approach in this study effectively evaluates the risk of liquefaction associated with sequenced earthquake motions.

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 The Compaction grouting (CPG) method is one of the liquefaction countermeasures to increase the density of improved ground by injecting mortar statically into the ground. CPG is often adopted just below or near the existing structures, and accordingly ground upheaval often becomes a problem. In this study, a series of model experiments of CPG methods were conducted for the purpose of developing a method which has more efficiency than the conventional construction's upheaval control. Consequently, the proposed method has proven itself in reducing the ground upheaval quantity by more than 80 %. Furthermore, the results demonstrate that the ground density, K-value and effect of liquefaction countermeasures can be significantly increased by the proposed new Up and Down method (U/D method).

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 This paper presents a concise summary of our recent research advances on wave-induced liquefaction and submarine liquefied sediment flow dynamics. The importance of both mechanisms is illustrated by a latest case study. A quantitative analysis of the event that took place in December 2014 demonstrates that the silty ground formed by repeated pouring of dredged soils underwent liquefaction due to the build-up of residual pore water pressures under sufficiently high wave conditions, and subsequently transformed itself into the form of sediment gravity flows, travelling a long distance and re-deposited. The paper also presents and discusses the analytical basis by which to predict and assess these phenomena for disaster mitigation.

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 In offshore municipal solid waste landfill sites, pile foundations penetrate through natural soils such as clayey soils. The wastes in the landfill may accidentally penetrate into lower part of the pile during the pile installations. In this paper, an experimental study conducted to understand the effects of leakage of wastes during the pile installations is discussed. In the research, the shape of the pile toe was changed. Then, the effects of the shapes of the pile toe on the leakage were discussed. When wastes consist of large-size particles, open-ended piles of a thinned wall at the pile toe are effective to reduce the leakage of wastes. However, thinned wall piles are not effective to reduce the leakage of string-type wastes.

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 Deep embedded and large diameter steel pipe piles have been popularly used in the port facilities nowadays, because of growing size of port facility or changing structural types. Estimation of bearing capacity of large diameter and deep embedded piles is complex problems because of bearing capacity increment by deep embedment and decrement by decrement of plugging effect with using large diameter piles. In this report, pile plugging mechanism was investigated under the sandy ground of different relative density. Open ended model pile penetration experiments were conducted and plugging ratios and incremental filling ratios of each experiment was compared. Finally, coefficient of earth pressure inside of the pile was estimated. Then inner friction force distribution was estimated. As a result, inner friction around the toe of the pile is large and it rapidly decreases along with upward of the pile. And there are very little difference of coefficient of lateral earth pressure observed under different relative densities.

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 Coefficients to correct Hiley's equation were calculated based on the results of dynamic loading tests of piles at the road bridge construction site in Mizushima port. The result shows that the coefficient decided through the bridge had large variability. Therefore, it was concluded that the safety margin should be considered during the calculation of the coefficient. On the other hand, if the coefficient was calculated for each pier, then the variability was small enough for the construction management.

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 To construct an extra-embankment for the disposal pond of dredged clays, the vacuum consolidation method for the reclaimed clay ground was performed. In this paper, the design and construction of vacuum consolidation method for the reclaimed clay ground were outlined. From the results of back-analysis using data of the monitoring and ground survey, the design of vacuum consolidation method for such ground was assessed. It was pointed out that the determination method of model ground for such soft reclaimed clay ground was important. And the determination method using reclamation analysis was proposed. The ground behavior under the construction of extra-embankment was also shown.

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 The vacuum consolidation method with prefabricated vertical drains (PVD) is widely used in Japan for soft ground improvent. Negative pressure is applied to soft ground through PVD in this method. However, the transmission process of the pressure is not clearly explained by the experiments or the numerical analyses. In this paper, the comparison was attempted between the experimental results using the soil tank in which soft clay was applied with negative pressure and numerical analysis results. A soil/water coupled elasto-plastic FEM code, DACSAR-MC was used and the output indicates good correlations with the experimental results up to the degree of consolidation of 70%. It appeares the enfluence of the experimental constraints become innegligible in the late stage of consolidation process.

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 Cement treated soil is used as a countermeasure for poor ground. But, cement treated soil deteriorate by calcium leaching because of exposing seawater. This study considered a technology of reducing deterioration of cement treated soil by using microbial function. This microbial function is urease. The urease is a function to hydrolyze urea. Authors tested seawater exposure tests using 2 types of the urease-producing bacteriums of Sporosarcina aquimarina and Bacillius pasteurii. The purpose of this tests are checking effect of reducing deterioration of cement treated soil by the urease-producing bacteriums.
 In addition, We tested seawater exposure tests 2 types of conditions of temperature 20°C is used for exposure tests, and 30°C is a temperature that is suitable for the growth of bacteriums, the purpose of this tests are checking relation temperature and deterioration speed. The main outcomes are as follows: 1) 2 types of the urease-producing bacteriums have an effect of reducing deterioration 2) 2 types of condition of temperature have relation to deterioration speed.

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 Granulated coal ash is the alternative sea sand. That is manufactured by mixing coal fly ash powder with a small amount of cement and adequate amount of water. GCA consists of particles that ranged from coarse sand to gravel. The mean diameter of GCA is approximately 20mm. Moreover, the particles is a porous material which has a small specific gravity. It is expected that the environmental loads resulting from industrial wastes will be reduced if GCA was used. The purpose of this study is to evaluate of change of chemical composition of GCA utilized alternative sea sand in coastal area. At first, The five kinds of alternative sea sand in different mixing ratio of fly ash and cement were prepared. These materials were cured for 30 months prior to use in the experiments. The changes of the chemical composition of alternative sea sand were analyzed by XRF, XRD, and SEM observation. Moreover, the materials were analyzed to investigate the difference in specific surface by Gas Adsorption. Second, the standard GCA samples were immersed in sea water for three years. And, Divers collected the GCA layer sample which was used for 13 years in bottom sediment of coastal area. These sample materials were evaluated by XRF, XRD. From our findings, it is clarified that the change of the chemical composition of alternative sea sand, which was cured for 30 months and used for long term in coastal area.

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 In order to recycle dredged soil, our research group developed interlocking blocks from dredged soil. Dredged soil interlocking blocks (350 mm in width, 350 mm in depth and 100 mm-150 mm in height) were made from soft clay dredged at the Kanmon Waterway. They were produced with the constant pressure 5 MPa and cement content of 15 %, 20 % and 25 % per the dry weight of clay. On the other hand, Katagiri³⁾ developed dredged and dewatered soil. The unconfined compression test was carried out to investigate material characteristics of dredged soil interlocking blocks and dredged and dewatered soil. The following conclusions are obtained: (1) There was relationship between unconfined compressive strength and dry density about dredged soil interlocking block, but there wasn't much relationship about dredged and dewatered soil. (2) There was relationship between unconfined compressive strength and water content about dredged soil interlocking block, but there was no relationship about dredged and dewatered soil. (3) Inclination of relationship between unconfined compressive strength and water-cement ratio was almost the same about dredged soil interlocking block cement content of 20 % and dredged and dewatered soil cement content of 15 % and 20 %.

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 Fiber-reinforced mixture of dredged soil and steel-making slag (FRMDS) was tested to study its applicability as the sealing geo-material for waste disposal sites in coastal area. In this study, FRMDS was made of Nagoya-port dredged soil with a water content of 160 %, steel-making slag with a diameter of smaller than 9.5 mm and polyester fiber with a shape of 14.8 μm in diameter and 20 ± 5 mm in length. Unconfined compression test was carried out to evaluate the fiber-reinforcing effect on FRMDS, where the stress and strain relationship exhibited strain hardening behavior. Such behavior results from the crack suppression by fiber admixture. Triaxial compression-permeability test was also performed to evaluate the sealing potential of FRMDS. As a result, the permeability of FRMDS was increased with an increase in axial strain, and its increasing trend depended on the effective confining stress before shearing process. Asample of FRMDS, which was composed of 30 vol% steel-making slag and 0.5 vol% polyester fiber, initially possesses a permeability of 2.2×10^-9 m/s. This sample was able to maintain a permeability of less than 1.0×10^-8 m/s, even when an axial strain of 17 % was applied under an effective stress of 50 kN/m².

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 In this study, a series of triaxial compression tests were conducted for basaltic intact rocks sampled in the northeastern onshore and offshore, southeastern offshore and northwestern offshore of Jeju Island, Korea. The strength parameters of Mohr-Coulomb shear failure criterion that represent cohesion and internal friction angle, estimated from the results of the triaxial compression tests were compared and analyzed with porosity(effective porosity), i.e. a parameter representing the vesicular properties of basalts. The results demonstrate that the relation between cohesion and porosity can be classified clearly as two different non-linear regression curves in accordance with two different linear relations in bulk specific gravity and porosity. As the porosity increases, the cohesion decreases exponentially. On the other hand, the internal friction angle decreases with increasing porosity.

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 To utilize effectively a soft dredged soil and reduce a construction cost, we contrive new artificial tideland using an improved dredged soil by the steelmaking slag. This artificial tideland be possible to reduction in soil improvement width and increase a dredged soil in quantity. We carried out the centrifuge model tests and verified the stability of this artificial tideland.
 In this paper, we described the characteristics of this artificial tideland and reduction effect in soil improvement, and clarified the result of the centrifuge model test.

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 Temporal variation of soil properties of the reclaimed dredged soil and sand capping at an artificial intertidal flat has been monitored by means of multi-channel analysis of surface waves (MASW). MASW survey has been conducted using geophones during an exposure period; however, it cannot be continued when the survey array submerges even in the period of ebb-tide because of large consolidation settlement. In the present study, MASW survey using hydrophones is applied to the submerged region to continue monitoring the soil properties. The results obtained by MASW survey using hydrophones are similar to those obtained by MASW survey using geophones; however, there is a tendency that the sand capping is evaluated slightly thinner and the bottom boundary of the very soft soil layer is unclear in the MASW survey with hydrophones, because seismic attenuation in the soft soil layers is significant.

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 Granulated coal ash (GCA) has been used to improve the enclosed bay environment as a beach sand alternate material. It has been reported that GCA has water improvement effect. In order to design the GCA shoal in shallow sea area, movement prediction of GCA by numerical simulation is desired. The purpose of this study is to predict the elevation change of GCA beach by numerical model “SBEACH” and to consider the design of GCA in shallow sea area. In this study, some experiments and numerical simulations were carried out. The experiment results of elevation change were simulated by numerical model “SBEACH”.

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 Purposes of the present study are to obtain quantitatively color characteristics of sands which were collected in 41 beaches in Niigata Pref., Japan and to examine relationships between the color characteristics and geological features of river drainage areas which are adjacent to the beaches or of area within 5km distance from the beaches. The geological features drastically changes because of some tectonic lines, the Fossa Magna and so on and accordingly beach sands have a variety of colors. Some relationships between sand colors and geological features are clarified, such as that the beaches in the east side of Agano River have bright color sands owing to felsic plutonic rocks of the late Cretaceous and that those in the Fossa Magna area have dark color sands under the influence of non-alkaline mafic volcanic rocks and sedimentary rocks in the Niigata Oil Field.

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 According to the recent revision of Ports and Harbors Act, seismic strengthening works for privately owned jetties would be required, although their seismic countermeasure correspondence is still quite preliminary. The concept of seismic strengthening method is invented, in which the seismic control damper, utilized as seismic reinforcement for bridges, could be installed to piled pier. In this study, effect of damper is investigated by shaking table test of the experimental model in comparison with conventional pier. It is revealed that the damper absorbs a part of earthquake energy acted on the pier, seismic displacement of the superstructure and bending moment of the steel pipe are substantially reduced.

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 The present technical standard for pier design in Japan employs seismic coefficient method against level 1 earthquake; especially for aseismic reinforced facilities, it adopts dynamic nonlinear effective stress analysis against level 2 earthquake. The simple frame structure analysis for level 1 earthquake covers inertial force on superstructure of pier. However, it cannot precisely deal with forces acting on steel pipe piles under foundation deformation due to intense seismic motion like level 2 earthquake. This fundamental study is to clarify the applicability of elasto-plastic frame analysis for simple seismic performance design of open-type wharf. This paper conducted two-dimensional dynamic effective stress analysis by FLIP model with a white noise seismic ground motion. This study also utilized the elasto-plastic frame analysis for calculation of bending moment along the steel pipe piles of the pier analyzed in the FLIP model.

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 This study aims at discussing the S-wave velocity profile of the ground around Naha port. Both Ryukyu limestone layer and Shimajiri mudstone layer are deposited around the area. N-values obtained by the standard penetration test for Ryukyu limestone layer widely varies because of the variation of degree of consolidation of the layer. However, as the consolidation structures of the soil layer is destroyed in the process of the standard penetration test, it may not be adequate to evaluate the S-wave velocity profile of the ground from the N-values. We conducted microtremor array observation and obtained the S-wave velocity profiles by using the spatial autocorrelation method.

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 It is difficult to evaluate site amplification factor analytically because site amplification factor is affected by several factors such as three dimensional deep subsurface profile. Site amplification factors have been evaluated by spectral inversion using strong motion record in the previous study. Therefore, site amplification factor has not been evaluated precisely at sites without strong motion observation.
 This study aims at discussing a simple estimation method of site amplification factors at ports in Kinki and Kyushu regions by use of deep subsurface profile. Amplification factors at low frequencies and peak amplification factors were estimated by the stochastic analysis. Estimated amplification spectra were obtained by modifying the amplification spectra assuming horizontally layered deep subsurface profile. Applicability of the proposed method was discussed.

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 Since the Great East Japan Earthquake, tenacity has been required for structures against Tsunami. Especially for the tsunami with extraordinary power, it is more realistic to adopt the multifaceted protection rather than a single structure. In this context, pile-type porous vertical barrier is expected to be effective. In this paper, a simple theoretical explanation on its tsunami mitigation effect was provided, and the model experiments were conducted to examine the influence of the porosity ratio and the material of the barrier. The results showed that the wave force on the barrier and the height of the tsunami behind the barrier in the trade-off relationship and are the functions of the loss coefficient, which is expressed by the friction factor and the porosity ratio. It was demonstrated that the effective barrier can be designed by choosing the adequate value of the loss coefficient. Finally, a case study of designing the barrier was introduced, by applying the experimental results to the full-scale case based on the Froude law.

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 Many structures near shoreline were destroyed severely by The Great East Japan Earthquake Tsunami of 2011. In this study, to discuss tsunami pressure acting on concrete bridge on the Rikuzentakata City, calculation of tsunami transformation and pressure was carried out with nonlinear shallow water equations and CADMAS-SURF/3D. In those results, the horizontal and vertical pressures of the tsunami acting on concrete bridge were showed by the calculation results. The calculation data showed that the tsunami pressure is influenced from the topographical condition of before and after the earthquake.

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 During a scenario earthquake with M_W9.0 along the Nankai Trough, not only strong motion but also huge tsunami is predicted in Hirokawa Town, Wakayama Prefecture, Japan. Seismic waveforms in the Tsunami attack area were already predicted with very high density based on the SMGA models considering local site effects. In this paper, walking times from the evaluation sites of local site effect to designated refuge places were measured. Using the non-evacuation time based on the time history of instrumental seismic intensity and the measured time based on results of the walking experiment, we evaluated the difficult area for tsunami evacuation in Hirokawa Town.

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 During the 1993 Southwest Hokkaido Earthquake, not only strong motion but also huge tsunami is attacked in Aonae District, Okushiri Island, Japan. Seismic waveforms in the tsunami strike area were already estimated based on the SMGA models considering local site effects. In this paper, walking times from the sites of interest to original refuge places were measured. Using non-evacuation time during the 1993 main shock and evacuation time after the 1993 main shock, we evaluated the difficult area for tsunami evacuation in Aonae District taking into account tsunami travel time. The evaluated difficult area agree well with the actual area of human casualty observed after the 1993 main shock.

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 In the Great East Japan Earthquake, the amount of fishing ports' damage resulted 815,059 million yen in 319 fishing ports in Japan. In particular, in Iwate Prefecture, Miyagi Prefecture and Fukushima Prefecture, each amount of damage is respectively 278,488 million yen in 108 fishing ports, 423,780 million yen in 142 fishing ports, and 61,953 million yen in 10 fishing ports. Fishing port disaster is to be restored by public work, ordering party is Fishery Agency, prefecture and municipality. Contractor is fishing port construction company that belongs to All Japan Fishing Port Construction Association. Many fishing port construction companies from all over the country since the disaster restoration work is large, took part in ordering the construction of three prefectures. This paper describes following to research and study. For construction of smooth disaster restoration fishing port work, the measurements are investigated and analyzed at the ordering parties and the constructors. For the contractors, A questionnaire survey was conducted in order to understand the challenges of disaster restoration work. This study is useful in order to prepare for the huge fishing port disasters such as the Nankai Trough huge earthquake.

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 The Tohoku-Pacific Ocean Earthquake and tsunami gave serious damages to many breakwaters in Tohoku region, Japan. The major cause of failure is the tsunami wave force. However, a new type of failure is confirmed: caused by scouring of the harbor side mound by overflow and seepage flow. In fact, the cause of failure of 9 among the 22 destroyed breakwaters was scouring of the mound and any effective measurement against that cause has not been invented. Therefore, in the previous research we developed a new method to calculate the stable weight of an armor block in consideration of the overflow and seepage flow from the view point of the geotechnical engineering. In this paper, using this method, the most effective shape of the armor block will be described. Furthermore, some sort of hydraulic model experiments with Kamaishi bay breakwater as a subject have been done in order to see the difference of damage in terms of different 3 height ratio (given by height divided by radius of blocks) shapes of blocks and 2 ways of laying blocks. Thorough this methodology the optimum proportion of the block which has a hole like annulus was found. The hydraulic model experiments also revealed that the most effective height ratio was 1/2 out of 1/4, 1/2 and 3/4. In conclusion, it can be reasonable to use this methodology to determine the optimum shape of armor blocks only under the situation of overflow, however when it comes to the time of only seepage flow, more investigation must be done.

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 This study aims to evaluate the stability of steal gabion mattress against tsunami-induced strong flow through hydraulic model tests. Performed tests are to observe the scaled mattresses on the mound under steady flow condition. The flow velocity was increased step by step and the relationship between number of damaged mattresses and the velocity was observed. A series of tests were performed to investigate the effect of mattress layout condition and the Isbash coefficient was determined from the critical velocity observed in each test case. Their coefficients are almost same as one of precast concrete armor units or embedded stone. This study shows high performance of the gabion mattress.

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 The study aims at confirming the effect of widening works for caisson type breakwaters against tsunami-induced seepage flow in the rubble mound. The study compares the calculated baring force of rubble mound by the Geotechnical Finite Element Analysis (GeoFem) and that by the Simplified Bishop Method stipulated by the Technical Standard for Port and Harbor Facilities. The result shows a strong correlation between the two.

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 After the Tohoku earthquake in 2011, coastal dikes are required to be improved their tenacity against tsunami disaster. And it is reported that scours of coastal dikes caused by tsunami overflow were mainly occured at the toe of the slolpe. In this study, the fixed-bed hydraulic physical experiment and numerical simulation were conducted to understand the distribution of local pressure on a dike under tsunami overflow. Moreover, some countermeasures to improve the tenacity of dikes were proposed and examined in the experiments. It was comfirmed that the distribution of pressure on the dike changed at the top and the toe of the slope, and large negative pressure occured at the top of the slope. To reduce the negative pressure is considered to be an effective way for improvement of its tenacity, so that small weir type countermeasures were set on the top and the toe of the slope and tested in the experiment. The negative pressure at the top of the slope and the large velocity at the toe of the slope were significantly reduced by the suggested countermeasures. It is successfully confirmed from the experiment that suggested countermeasures can contribute to improve the tenacity of dikes. Moreover, the numerical simulation using OpenFOAM simulation code was conducted and showed good agreement with the experiment results.

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 In this study, tsunami resistance performance for a tsunami coastal dike of air bag structural type which can be stood with air expansion has been inspected through some experiments. Relatively small tsunami when flooding on the land is targeted, whereas full-scale experiments have been executed in an underground tank. The tank is separated by a wall on a reveal part of which test dike material is installed and water is poured in the front side of the test dike surface to exert the hydrodynamic pressure imitating the tsunami design pressure distribution and to measure strain, displacement and inner pressure change of the membrane surface.
 It is necessary to remark that air compression and inner pressure raise on tsunami may cause material deformation and back side membrane surface movement intermediated by air pressure change, and membrane strain variation with initial inner air pressure also cause material distortion. On the other hands, pressure raise inside the air bag mitigates membrane distortion in the front surface of the structure which will improve tsunami resistance performance of the proposed dike.

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 Sihwa tidal plant, located west coast of Korea, has been in operation since August, 2011. In front of the tidal plant, strong current which reaches a maximum speed of 2.5m/s is occurred due to drainage from the Sihwa lake. The strong current has significantly changed the morphology of muddy bed in front of the plant.
 In this study, morphology change rapidly occurred after the plant operation has been examined based on analyzing field survey data. It is confirmed that both bed erosion and granulation of sediment have occurred under the strong current of drainage. It is also estimated the changes in depth and sediment in the future by using relation between critical depth of sediment movement and grain size.

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 Recently, as production of farmed shellfish such as a scallop is increasing, a large amount of shells are produced as a by-product. Recently, these shells are reused in various fields. As one of them, the shells have been used at final disposal waste sites using the effect of capillary barrier.
 In this paper, the experiments have been carried out over movable bed with constant water level and changing one. The experimental results showed that the shells can reduce the rate of erosion under constant water level and promote the effect of deposition.

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 This study discusses the effect on the change in cross sections of bodies of artificial reefs when artificial reefs are subjected to irregular waves, caused by the difference in the particle size of filling works constituting bodies and whether or not armor materials are installed. Wave height distribution has a dominant influence on the change in cross-sections of bodies constructed only from mixed crushed stones; the stones around the top of the slope are eroded and the eroded stones are deposited on the top of the crest in a convex shape. For a body with an armor material installed, the material around the top of the slope topples and filling works flow. The erosion area due to the leakage of filling works is expanded with increasing number of waves. For a given wave, wave energy dissipation by a body constructed from mixed crushed stones is larger than that by a body made of a single crushed stone.

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 The mechanism of sand deposition inside the Numakawa-Daini Floodway on the Fuji coast was investigated using the BG model (a model for predicting three-dimensional beach changes based on Bagnold's concept). The shape of the floodway was selected to be the one with two or three openings, the point depth of the floodway to be 3 or 5 m, and the floor depth to be 3 or 5 m below MSL. Moreover, the redeposition mechanism of sand was also investigated after the removal of all deposited sand. Sand deposition was induced by landward sand transport due to ongoing waves, and sand deposition on down-coast opening was the largest, resulting in the deposition length of 30 m inside the floodway. Even if sand is removed, quick redeposition occurred.

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 A holding device with a chain net was used to automate the removal of wave-dissipating blocks, thereby reducing labor.
 Shape of wave-dissipating blocks are more than 40. The most difficult block to be removed was shaped like a combination of two anchors. The author tried to remove a pile of the blocks in the model experiment using the holding device with a chain net. It was possible to remove the blocks successively through adequate observation of the situation, taking into account the posture change of each block during lifting to eliminate entanglement with the surrounding blocks. As a result of the trial calculation of time efficiency based on the model experiment, the removal method for anchor-shaped blocks using a holding device was more efficient than standard time efficiency for general blocks.

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 Hydraulic model experiment and on-site measurement of an actual construction site were carried out focusing on the type and method of operation of the bucket in the grab dredging. The characteristics of the flow field at the time bucket lowering-hoisting is revealed. And it was further investigated bucket operation method for inhibiting diffusion and turbidity occurs. As a result, rather than operating the bucket at a uniform lowering speed, by decelerating the lowering speed on the way, it was confirmed that can inhibit the flow velocity generated in the bottom surface. For normal bucket as compared to a sealed bucket was revealed that flow generated during lowering is small. Further, even when the hoisting operation, when the hoisting speed of the bucket is slow, it was confirmed that it can inhibit the flow generated around. Such an effect of the reduction of the lowering-the hoisting speed of the bucket was also confirmed in the field measurement.

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 Declining workers and technical skills to the next generation have been problems in the offshore construction sites. Until now, investigations of construction works have been done. However, there is more space to consider this matter. In this study, we focusing on instructions of an operation leader, and considered the correlations between the instructions, wave and weather conditions, and caisson behavior. During the installation of the caissons, based on the instructions, construction processes can divide into two stages; a moving stage, and a settlement stage. The caisson was easily affected by waves during the moving stage. Also, in the settlement stage, spectrum peak appeared in the high-frequency region. Moreover, from the interview with the operation leader, we realized the timing of the instructions and the meanings of each behavior.

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 If sea ice can remove rust layers from steel surfaces of steel structure in the winter time, larger wear rate of steel structure in ice-infested sea compared to ice-free sea must be considered in the design of steel structures. In fact, serious damage has occurred to training levees made of steel-sheet-pile-type seawalls on the Sea of Okhotsk. Sliding wear tests were conducted in a cold room to evaluate the effect of some factors (sand inclusion, contact pressure and ice temperature) on wear rate of rust layers, using two types of steel specimen with rust layers which were made both at indoor (type-1) and inside of harbor (type-2). Larger effect of sand inclusion on wear rate at the mild wear region, and larger scatter of its wear rate were obtained. And, it was obtained that wear rate of (type-1) at the mild wear region was approximately the same as that of type-2 under the conditions of no sand inclusion. Also, the applicability of Holm's equation to the evaluation of wear amount was indicated.

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