Beach changes along the north shore of the Futtsu cuspate foreland were investigated using aerial photographs and field observation. In this area, sand has been supplied from the south shore of the cuspate foreland, while turning around the Futtsu cuspate foreland, and longshore sand transport with the order of magnitude of 3500 m³/yr occurred in 1980 and 1990. Recently it gradually decreased up to the level of 1500 m³/yr. However, after the 2011 Great Tsunami rapid increase in longshore sand transport was measured owing to the effect of the tsunami.

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 Many cases of structural damage have been reported after Tohoku tsunami earthquake. Among those cases, the failure of breakwater caused by the local scouring on gravel mound due to tsunami overflow can be selected as one of the typical structural damages. This study is intended to clear the characteristics of local scouring on gravel mound under several tsunami overflow conditions. Four cases of discharge and three kinds of gravel diameter were employed to investigate the characteristics of local scouring under tsunami overflow condition. Furthermore, this study proposed a horizontal plate which was introduced to reduce the local scouring. Numerical simulation was also conducted to investigate the flow pattern above the gravel mound and pressure distribution on proposed horizontal plate. This study revealed that the scales of local scouring, its depth and length, depend largely on both overflow discharge and gravel size. Based on the experimental data, this study proposed an equation that can estimate maximum scoured depth under different gravel diameter as well as several overflow conditions. The horizontal plate showed good performance in reducing the scale of local scouring. The length of horizontal plate affects the magnitude of vortices and the maximum scoured depth.

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 The current state of understanding of long-term morphological changes of river mouth deltas is not sufficient to develop physically meaningful models of all processes involved. The objective of this paper is to predict the topography change in the mudflats of Shirakawa river delta due to an abnormal weather phenomenon. In this study, long-term evolutions of Shirakawa River Delta during 1976 to 2013 were investigated using bathymetry, river discharge, wave, and tide data. Moreover, the delta response due to flash flood caused by torrential rainfall on July 12, 2012 in Kumamoto examined using echo soundings. The geomorphological response of Shirakawa River delta indicated that foreset slope and critical bypass depth were advanced to off-shore due to flush flood over 1, 500 m³/hr. The critical bypass depth is controlled by tide and located below mean low water spring. The numerical model was found to be good agreement to explain the phenomena before and after the flood occurred with parameter fitting to the change of cross-shore profile.

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 The Seisho parking area is located in the west part of the Seisho Bypass running along the Seisho coast. This parking lot was protected by a wide sandy beach in the past. Recently, beach was severely eroded, and seawall protecting the parking lot was exposed to waves, and it was damaged owing to storm waves and the scouring. In this study, the causes of the beach erosion and the damage to the parking lot were investigated using aerial photographs and the Narrow Multibeam survey data along with the analysis of the shoreline changes. Future measures were also discussed.

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 Beach erosion has been severe on the Node coast located on northern Kujukuri Beach, and sand dune is being eroded, which has been useful in the protection of the hinterland against tsunami. Despite the importance of the sand dune, sand dune is now disappearing due to erosion. Measures to protect sand dune such as beach nourishment are strictly restricted because of the difficulty in obtaining the permission from the local fishermen, who worry about the impact to the habitat of seashells. There is a conflict between shore protection and maintaining marine environment. Open public discussion is required.

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 When an island or a sand bar is located at the bay mouth, wave field will change due to the wavesheltering effect of the island or the sand bar, resulting in significant beach changes around the bay mouth area. To realize the effect, beach changes were calculated under the conditions that an island is symmetrically or asymmetrically placed at the bay mouth using the BG model (a three-dimensional model for predicting beach changes based on Bagnold's concept).

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 Futtsu Point is a cuspate foreland separating Tokyo Bay and the Uraga Strait. On March 11, 2011, a tsunami generated by the Great East Japan Earthquake entered Tokyo Bay with approximately 2 m height, and flowed over this sand bar, dispersing the sand and leaving an isolated protruding sand bar. This resulted in the seawall at the foot of the sand bar being exposed to waves, increasing the potential for damage. After the tsunami, this isolated sand bar was significantly deformed, a sand spit was formed by the action of wind waves, and the seawall was refilled with sand. The subsequent shoreline changes of this protruding sand bar were measured, and the 3-D beach changes were calculated using the BG model.

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 When waves are incident to a sandy beach from two opposite directions, a cuspate foreland or a landtied island may develop. A typical land-tied island can be seen offshore of Shodo Island in the Seto Inland Sea. Another example is Chiringashima Island located in the south part of Satsuma Peninsula, Kyushu. In both cases, the island and land are connected by an extremely slender sand bar that has been stably maintained for a long time, suggesting that it is stable against wave action from both sides of the sand bar. We developed a numerical model for predicting the elongation of a sand bar of a land-tied island using the BG model.

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 Recently, flood shoals have been developed at the entrance of the Tofutsu Lake located along Okhotsk Sea in Hokkaido, and they affect flood control, fisheries in lake, and so forth. In this study, we aimed to reveal the developmental process of flood shoals by observations, which are current observation, water level observation, sediment survey, and video monitoring at the entrance of the Tofutsu Lake. Followings were major accomplishments of this study. (1) The current flow velocity during the flood tide at St. 400 was faster than that during the ebb-tide. (2) The relationship between current speed and friction velocity during the flood tide is different from that during the ebb tide. (3) Flood shoals were developed by not only sea waves, but also adverse tide in the spring-tide.

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 The Kanmon waterway is one of the most important international routes in Japan. Nowadays, the depth in the waterway is maintained at 13m and will be dredged deeper to enable the navigation of larger ships. Some parts of the Kanmon strait are remarkably narrow and curved considerably. Such geographical features induce rapid and complicated tidal currents in the waterway. Consequently, sand waves as well as continuous sediment accumulation occur in the waterway, and the dredging to keep the required water depth has been prerequisite. MLIT (Ministry of Land, Infrastructure, Transport and Tourism) has been continuing the yearly survey of bathymetry in the Kanmon waterway since 1974. Especially, at four areas where the sand waves are formed frequently , the survey has been conducted several times a year.
 In this study, for the purpose of clarifying the characteristics of the sand waves in the Kanmon waterway, bottom topography changes were investigated in detail focusing on Tanoura area where the sand waves are formed remarkably. First, bottom topography in Tanoura area was analyzed by using a GIS, and the motion of sand waves was extracted. Next, the traveling direction of the sand waves was examined by applying PIV(Particle Image Velocimetry). Then, the characteristics of the sand waves, i.e. sizes, moving velocities, occurrence frequencies, etc. were investigated along some cross sections which were set on the basis of the results of PIV analysis. As results, the characteristics of the sand waves were clarified. For example, the moving velocity of the sand waves is about 0.2 to 0.8m/day, and the occurrence frequency is approximately 20 to 45 months.

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 Beach changes on the Hiari-ura coast facing the Pacific Ocean were investigated. This coast is located south of Taito Sea cliff and the sand supply from this coast is considered to be one of the supply sources to Kujukuri Beach, because the sand supply from the Isumi River flowing into this coast can be expected. The shoreline changes were studied using aerial photographs and grain size distribution was measured by sampling of beach materials. It was found that the sand supply from this coast has been exhausted and further sand supply can not be expected.

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 The foreshore slope influencing on the beach profile was considered by using the sounding data at the Tomakomai coast of Hokkaido on the Pacific Ocean. As the result, it was clear that the bar height was influenced by the foreshore slope, the return flow and the incident wave length. Moreover, the relation between the bar height and the return flow was classified by the foreshore slope and the incident wavelength.

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 The characteristics of spatio-temporal variation of the shoreline location and alongshore variability on the Uchinada Coast, Ishikawa, Japan, have been investigated based on the synthetic examination using a set of aerial photographs between 1947 and 2003, annual field surveys collected from 1998 to 2010, and weekly GNSS field observation conducted over 3 months. The shoreline advanced significantly from 1947 to 1998 in the 1.5km alongshore stretch from the Kanazawa Port. The shoreline location became relatively stable in the recent decades except for the immediate neighborhood of the port. The formation of large cusps is recognized on both of the aerial photograph and GNSS field surveys. Recently, a decreasing trend is observed in the amplitude of the large cusps.

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 Beach changes in the vicinity of Pengambengan fishing port facing Bali Strait in Indonesia were investigated through the comparison of satellite images and field observation. In this area, northward longshore sand transport prevails because of the oblique wave incidence from the Indian Ocean, and this longshore sand transport was blocked by the fishing port breakwater, resulting in severe erosion in downcoast area. As a measure, seawall has been constructed as the case in Oyashirazu fishing port in Japan, instead of sand bypassing as in Santa Barbara in US. The selection of this method causes further downcoast erosion. To stop the erosion, sand bypassing mothod should be taken.

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 The Assessment Rreport No. 5 of IPCC reported that sea level will rise and wave characteristics will change due to the effects of global warming in future climate with very likely. In order to investigate the effects of climate change on beach changes, the numerical model of beach profile change which takes into account of the effects of changes of sea level and waves was proposed in this study, and evaluated shoreline and contour line change of sea bottom around Kaike coast in Tottori prefecture from present to future climate.

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 Beach changes after the gravel nourishment were investigated on the Jinkoji and Akashi coasts in Ibaraki Prefecture. The formation of sand layer on the gravel bed due to shoreward sand transport of medium-size and fine sand under the calm wave conditions was observed and three-dimensional beach changes in response to the change in wave direction were also measured between artificial headland Nos. 6 and 7. Even though the sand layer on the gravel layer disappeared due to offshore sand movement under the storm wave conditions, the gravel layer was stably maintained on the foot of the seawall with a foot protection effect.

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 A natural swimming pool located on a rocky coast behind the Takasu Port breakwater was suddenly burried with sand after the construction of the offshore breakwater of Takasu Port, and the function of the swimming poor was lost. There was a narrow gap with a 0.9 m width in the seawall protecting this swimming pool. Sand was transported through this gap. The mechanism of the deposition of sand was reproduced using the BG model. Predicted results explained the measured results.

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 On the Chigasaki-naka coast, beach nourishment using gravel has been carried out since 2008 and beach changes after beach nourishment were monitored between 2008 and 2012. Although the beach width was widened by the beach nourishment, the diffusion of gravel to the nearby sandy beach, where is a famous bathing spot in this area, was worried. A short floodway No. 6 was located separating the nourishment beach and bathing beach, and this floodway was found to effectively block the movement of gravel to the nearby beach.

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 Irabu Bridge under construction has a causeway at the connecting point to Irabu Island, which formed a wave-shelter zone on the nearby reef and longshore sand transport was induced by the wave-sheltering effect of the causeway. Beach was severely eroded on the south coast of the bridge. Measures using three groins and beach nourishment were taken in 2012. After the completion of the measures, sandy beach was recovered and the spawning of sea turtle was started again. These situations were investigated by field observations along with the comparison of the aerial photographs and the numerical simulation results with the measured.

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 This study show that relationship between the beach environment and caretta caretta egg-laying activities at the Inaka Hama beach of Nagata district a lot of landing most of caretta caretta in Yakushima. Research method, oviposition activity observation of caretta caretta by the infrared camera, beach topography change observation using DifferentialGPS and AMeDAS weather data analysis.
 As the result that Inaka hama bech has the chracteristics of coastal erosion, this beach of topographic change is linked to the seasonal change of wind and qualitative relationship of topographic change and oviposition activity of caretta caretta.

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 Beach changes along a 7-km-coastline between the Minato River in Kazusaminato and Isone Point facing Uraga Strait were investigated using aerial photographs and by field observations. The relation between beach changes and the collaption of sea cliffs extending along the coastline were investigated. In particular, after the 2011 Great Earthquake, sea cliffs were newly collapsed owing to heavy rainfalls and additional earthquakes, and a large amount of sand was supplied to the coast. Also beach erosion was further intensified by the decrease in sand supply from upcoast.

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 On a coast with a predominant longshore sand transport, the content of coarser sand increases upcoast, resulting in the formation of steep foreshore slope, whereas the content of fine sand increases downcoast, because the movement velosity of fine sand is larger than that of coarse sand. This phenomenon is important in considerating beach nourishment using sand with different grain sizes. However, such data have not yet been obtained. In this study, sampling of foreshore materials as well as the measurement of the foreshore slope was carried out at 79 points along the 30-km-long shoreline of northern Kujukuri Beach in 2011. Longshore sorting of sand was analyzed using such data.

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 Fly ash beads has been utilized for sludge to the enclosed bay as a beach sand alternate material and the water improvement effect is obserbed. In order to design the shoal by fly ash beads, it is necessary to understand the moving characteristic of the fly ash beads by flow and waves. However, the detailed moving characteristic in the shoal is not clear. So the moving characteristic at the time of installing fly ash beads in a shoal is clarified by a hydraulic model experiment. This paper reports the experimental result about moving characteristic of fly ash beads by the flow and wave.

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 This paper describes the results of experimental investigations of sediment transport and topographic change in mixed soil conditions exposed to steady flow in an open channel and regular waves in a wave flume with a tidal flat structure to understand the influence of cohesive sediments on sediment transport in cohesive and non-cohesive sediment mixtures. In the open channel experiments, the sediment transport rate q was investigated with the influence of clay and steel slag increasing resistance force by cohesive effects and surface roughness adding to sand on sediment transport under the same hydrodynamic condition. From the results, both the steel slag and clay mixtures decreased q and the effects of a decrease in q for steel slag mixtures were larger than that for clay mixtures in the same content ratio p_f. The wave flume experiments showed the opposite crown migration between sandy and sand-clay tidal flats. In the sandy tidal flat, an increase in wave height led to increasing shoreline retrogression and broadening eroded area in the early stage expanded with ripple formation during experimental time. However, in the sand-clay tidal flat, the topographic change was characterized by the little topographic change without ripple formation in the early stage, the advanced crown in the final profile, and the loss of clay on the surface layer of the tidal flat with time. Since a modified critical Shields parameter considering cohesive force showed better performance to evaluate sediment transport in sand-clay mixtures, it was required to take into account cohesive effects when discussing the sediment dynamics in mixed soil conditions.

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 Pressure injection of slurry dredged soil into the ground is one of the restoration methods for the artificial tidal flat causing the ground subsidence. To improve the injection effect, the authors invent the new type of the artificial tidal flat by using the mixed soil of the dredged soil and the converter slag between the filling soil and the covering sand.
 In this paper, through the field experiment test, we proved that the new type of the artificial tidal flat is effective for the injection of slurry dredged soil compared with the usual type. And we indicated the reproduction of this method by FEM analysis.

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 Longshore sediment transport environment is not readily improved for the coastal erosion. The structure which has low crested crown in the upper side as much as possible while developing the gently effect in the lower side of the countermeasure establishment is demanded for this by longshore sediment transport balance. By this research, we evaluated a characteristic of the low levee crown jetty by hydraulic pysical model test from deepwater jetty, comparison with the normal scale jetty.

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 On Sanur Beach in Bali, the restoration of sandy beach has been carried out by the extensive beach nourishment with the construction of a Y-shaped groin shoreward of a reef gap. After the construction of this groin, sand was deposited offshore of the Y-shaped groin due to the shoreward sand transport on the reef flat under waves. The meachnism of sand deposition was numerically reproduced using the contourline-change model. Predicted results well explained the measured beach changes.

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 A new method to improve the function of an artificial reef was investigated by a numerical simulation using the BG model. On ordinary artificial reef, strong shoreward currents are induced, causing erosion in shoreline area. As a new method, another submerged reef was proposed to be built in the shoreward zone of the already constructed aritificial reef to block shoreward currents. The results of this study show that the application of the ordinary-type artificial reef on a coast composed of fine sand should be restricted.

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 In many coasts of Thailand, serious coastal erosion has occurred by human development action and breakwaters for preventing it have been constructed. Especially since many coasts in the gulf of Thailand consist of very fine bed materials, wave dissipation breakwaters made of bamboo piles and detached breakwaters made of geotextile bags which were packed bed materials have been constructed instead of concrete block breakwaters. However, since these countermeasures aren't durable facilities, the reconstruction of lost manrove forests is wanted.
 In this research, the specification of an effective mangrove forest for preventing coastal erosion is found from field surveys in the Gulf of Thailand. Moreover, an evaluation method of the wave dissipation effect by the mangrove forest is found from the research of existing papers. Then, the prevention effects of the coastal erosion by the mongrove forest, the bamboo pile breakwater, and the geotextile-bag detached breakwater are compared and examined using the prediction model of Ca et al.'s with the high reproducibility of sea bottom change.

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 A new countermeasure for erosion of the artificial bed materials made of fly ash beads was developed based on the principle of straw checked-board. The developed countermeasure has a permeable structure around which large eddies cannot be generated and should be placed with a suitable distance apart each other. The hydraulic physical model test was conducted to determine the suitable distance and to investigate the wave conditions under which the countermeasure is effective. The suitable distance was found to be less than excursion length of water particle at the bed. The field test was conducted to confirm the performance of the developed counter measure in Hiroshima Port, Japan.

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 Sliding wear test between metal material and artificial ice with interposed sand was carried out to clarify the deterioration mechanism of steel structures due to abrasive wear caused by solid matter such as sand in sea ice. The amount of wear of the metal sample (stainless steel) increased bi-linearly with increase in sliding distance. While the wear rate (amount per distance) did not depend on the sand amount or sand particle size, even a tiny amount of small sand particles had a certain cutting ability, in which case the wear state immediately shifted to steady wear. Tests using natural sea ice samples confirmed that solid matter in the natural sea ice actually caused abrasive wear. The steady wear rate caused by the natural sea ice agreed with that rate by artificial ice with artificially interposed sand in this test method. As a result of an exposure test of steel plates in ice covered areas, the wear/corrosion rate in those areas was confirmed to be higher than in the case of normal sea areas.

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 Sea ice always moves in the up-and-down direction continuously under the influence of a tide. The sliding wear test in a low-temperature chamber was carried out to examine the condtions of removing rust layers, using corroded steel specimen with rust layers in contact with saline ice. The contact pressure and amount of sand at the interface were taken as paramaters here to understand corrosive wear in the ice-infested sea. Since the obtained conditions, that could remove rust layers, are as usual in the field, larger wear of steel in ice-infested sea compared to ice-free sea must be considered in the design of steel structures. Also, it is possible to predict the deterioration of steel in ice-infested sea using the relationship between corroded amount of steel and elapsed year.

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 Recently, wave overtopping due to heavy storms increase in ice-infested sea area in winter. However, sufficient examination has not been carried out on the wave runup characteristics in ice-covered area. In this study, hydraulic model experiments and simulation by the coupling of the two model(SWAN - CADMAS SURF) is carried out to investigate wave runup characteristics. The proposed simulation method gives a good agreement with the observed wave data and experimental results. Furthermore, the results of the experiments show that reduction in wave runup heights due to block mound breakwater.

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 After the Great Hanshin-Awaji earthquake, Some drums drifted from the Kobe-city coasts to the Izumiohtsu-Izumisano coasts. Based on hints of the drifintg drum accident, we perfromed the tracking simulation of drifting drum size objects considering leeway effects in the Osaka Bay. Some of empty drums have arrived in 12 hours at the Izumiohtsu-Izumisano coasts. All objects have arrived within 24 hours. The trajectories of the empty drums show toward the sourheast from the departure point. Nonleeway objects can hardly arrive at coasts in 48 hours. The empty drum experiment shows the same tendency as the drifting drum accident. There are some possibilities that leeway effects make the empty drums arrive at the Izumiohtsu and Izumisano coasts in 12 hours crossing the Osaka bay. Therefore we suggest that the quick measure to collect drifting objects need depending on their size.

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 In orde to determine the turbulent diffusivity of spilled oil, experimental measurements of dyamic response of floating thin objects to wind were conducted. Using a small wind tunnel with water channel, transient movements of C-heavy oil droplets and thin rubber mats floating on the water were measured in the stepwise wind change. It was found that the movements of the objcects can be approximated with a 1st order delay model. The delay time and gain were correlated with the wind velocity. Movements of the rubber mats on more viscous fluid than water were also measured to investigate the viscosity effect. It was found that the molecular viscosity has important effect to the delay time and wind-induced surface flow is confined within very thin water layer of several millimeters.

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 In regard to quaywall on shallow water at fishing port, the seismic coefficient method has been applied to a design against level-one earthquake ground motion. However, Improved design technique which realizes adequate seismic performance is required to cope well with the performance regulations for fishing port facilities in the near future. Therefore, in this paper, based on seismic design technique of commercial and industrial port, design parameters for quaywall on shallow water are examined. First, Two-dimensional dynamic finite element analyses on typical cross section of gravity-type quaywall are conducted against various sine waves. These analyses show the accerelation values which bring prescribed displacement by frequency of sine waves. These values bring the design parameters to reflect frequency characteristic of gravity-type quaywall on shallow water, duration time of ground motion and allowable displacement during in-service period. The improved coefficient for seismic design can be calculated from these parameters. Finally, the analyses are carried out on a cross section of quaywall designed upon these parameters against various level-one seismic waveforms. These indicate the validity of parameters.

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 Design of pile supported wharf is conducted based on the assumption that load is not transmitted to the framed structure from the earth retaining and bending moment of the pile becomes maximum at pile head. However, validity of the assumption has not been examined thus far.
 In this study, two dimensional finite element earthquake response analysis modeling pile supported wharf is conducted. As pile head rigidity, both fixed condition and hinged condition were considered. As boundary condition between framed structure and earth retaining, three conditions were considered as follows: independent, load is transmitted when the distance between the framed structure and the earth retaining becomes smaller than a certain value and fixed condition. In addition, three ground condition, three pile rigidity and two seismic wave was considered. The result of the analysis showed that it is not necessarily advantageous to apply the fixed pile head and independent boundary condition.

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 In this paper, earthquake and tsunami damage determination method of the storage tank is proposed. Earthquake and tsunami damage determination was performed combining three-dimensional tsunami analysis and structural analysis. First of all, the pressure applied to the tank is calculated by three-dimensional analysis Tsunami. 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 on the storage tank.

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 In breakwaters covered with wave-dissipating blocks, outer walls of the caisson may show local failure in repeated collision of the blocks. Local failure induces drainage of the filling in the caisson so that the self-weight of the caisson would be reduced. This failure of the outer wall decreases stability of the caisson against sliding and harbor calmness. The design and verification method of the caisson and the preventive measures against such accidental impact loads are necessary to be developed while they have not been established so far. When the preventive measures are implemented, it is important that the life-cycle cost (LCC) would be considered. This paper investigated the advantageous conditions of the preventive measures from the viewpoint of LCC reduction considering the ratio of failed caisson to total ones, by comparing the cost for the preventive measures and the cost for post-failure repair.

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 In this paper, the authors have developed a new protective covering system which can ensure the anticorrosion of steel piles and strengthening of joint parts between steel pile and beams of the concrete superstructure by applying the Ultra High Performance-Strain Hardening Cementations composites, UHP-SHCC, which is one of the fiber reinforcement mortars using the synthetic short fibers. The authors evaluate the effect of the improvement of flexural capacity of the steel piles and joint parts between a steel pile and a beam of a superstructure. The large scale flexural loading tests of tested steel piles, to which the UHP-SHCC protective covering system was applied, were performed in the laboratory.
 From the loading test and discussions, the authors confirmed that the UHP-SHCC protective covering system efficiently contributed to improvement the flexural capacity.

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 The high rigidity steel pipe sheet pile(490N/mm² grade) has been used in deep water quay walls. When it comes to high rigidity, the maximum bending moment of steel pipe sheet pile increases. If the stress of steel pipe sheet pile is greater than the design value, it is necessary to increase the cross section(diameter or thickness). Therefore, the rigidity increases further, the maximum bending moment also increases. On the other hand, if increasing the strength of the steel pipe sheet pile, it is possible to design it without increasing the cross section. Therefore, a design method of high-strength steel pipe sheet pile(570N/mm² grade) corresponding to the current standard has been proposed. It is feared that stiffness reduction due to the application of high-strength steel pipe sheet pile would adversely affect the seismic performance. As results of dynamic analysis, the deformation of top of the high strength steel pipe sheet pile quay wall(570N/mm² grade) in earthquake is equivalent to the conventional steel pipe sheet pile (490N/mm² grade). The reason is because it is determined by the earthquake resistance of anchorage work.

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 A large amount of waste contaminated by radioactive cesium was released from Fukushima daiichi nuclear power plant due to the great east japan earthquake. The objectives of this study were to examine the permeability characteristics and water adsorption properties of a geo-material . In this study, Tokuyama clay was mixed with different proportions of bentonite and steel slag. Results revealed that the coefficient of permeability decreases with the increase of bentonite and that increases with the adding of steel slag. The adsorption performance was found to be decreased with the adding of bentonite. In contrast, the adsorption performance was comparatively increased with the adding of steel slag.

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 Suction anchors have advantages over drag or pile anchors, in precise placement and installation feasibility at deep water locations, and have been employed in mooring systems of floating platforms for offshore gas/oil production in e.g. Gulf of Mexico. Growing attention has recently been given in Japan to offshore wind power generation utilizing floating structures, whereas sandy deposits are widely formed at seabed surfaces around the country. Centrifuge model tests have been carried out to study the holding behavior of suction anchors in saturated loose sandy ground with viscous scaling taken into consideration, focusing on effects of drawing speed, direction of the mooring line, and location of the connecting point between anchor and the line. There observed increase in peak tension force in mooring lines in both vertical and inclined rapid pullout cases, associated with negative fluid pressures developed inside the anchor and at the anchor tip, even installed in sandy deposits.

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 It has been shown already that the pile driven by the vibratory pile driving with water jetting and constructed soil cement block on the tip can reduce sound and ground vibration, and perform high bearing capacity. However, the construction process of the soil cement block on the pile tip hasn't been relieved. Because of this situation, the authors have tried to clarify the mechanism of that by the centrifuge model test and model tank test. As a result, it is shown that the length which water jet excavates can be analyzed quantitatively by the previous research about jet grouting. And, in the case of multiple water jet, it is presumed that the soil strength of the gap between the excavation area decrease and the excavation progresses more efficiently. Finally, the authors have made a design about the suitable specification for the large diameter pipe pile, and confirmed that this can construct the soil cement block for the large diameter pipe pile by the model field test.

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 Recently, there is a tendency that piles diameters of the foundation for the port structure is getting larger, because the scale of the port structures is bigger, the water depth of quays is deeper, and the structure system is getting rationalized. On the other hand, the large diameter pile which is driven by the traditional impact hammer or vibratory pile driving with cement milk jetting is difficult to perform high bearing capacity. In addition, the vibratory pile driving with water jetting and constructed soil cement block on the pile tip , which the authors have confirmed the performance in smaller than 1000 mm diameter, has not been confirmed that it is possible to construct the soil cement plug for the large diameter pipe piles. In this situation, the authors have studied the constructing process of soil cement block by water and cement milk jetting, and developed the more suitable method for large diameter pipe piles. In this paper, the validation test for the piles driven by this method is shown. Its test is consisted of boring, unconfined test and X-ray computed tomography test for the soil cement block. As a result, it is confirmed that this method is effective for the large diameter pipe piles.

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 In the aftermath of the 2011 Tohoku earthquake and tsunami, there has been a growing recognition of the need to reinforce caisson-type breakwaters against tsunamis. To enhance the strength of breakwaters, the method of putting rubble stone or concrete blocks behind caissons has been proposed. However, the resistance mechanisms and reinforcement properties of breakwaters have not yet been identified. Therefore, in this study, these mechanisms and properties were investigated by performing horizontal-loading tests using a breakwater model, and by observing rubble stone or concrete blocks subjected to centrifugal acceleration. Test results showed that large reinforcements could increase the resistance and bearing capacity of breakwaters. Furthermore, it was found that the mound did not reach the critical-limit state although the allowable structural-displacement magnitude would have been exceeded; such mound behaviour should be considered while assessing structural resistance.

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 The large-scale unique and box-shaped sand-bag (the soil box) with permeable material such as gravel or sand can hold its shape even on the soft ground.The strong internal friction is occurred by one-point lifting and binding force with truss-band inside the soil box , and it causes stabilization and solidification of the soil particles, sand/ gravel, in the soil box . Effectiveness of the soil box to the countermeasure against liquefaction and soft ground that have been identified through its successful achievements with relatively small buildings on land; such as private housing, prefectural road, and private residential development. However, the mechanism of liquefaction control and soft ground control of the soil box has not been clear yet. Thus, we conducted small-scale vibration test, with 1/10 scale for liquefaction examination , to identify the mechanism. As the result, we found that the soil box foundation wrapped in excess pore water pressure and kept the bearing capacity just under the foundation, and also the soil box reduced the ground acceleration of the soil box foundation on the liquefaction ground.

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 The caisson-type quay wall is one of the major types used in Japan. In recent years, it is desirable that this type quay wall have more front-water depth to better accommodate the larger and larger vessels coming alongside. The authors have been studying the new construction method of the front-water-depth enlargement. In the new method, a rubble mound beneath a caisson is solidified then cut to increase the front-water-depth of the caisson. Several series of model tests and numerical analyses related to the design and construction of the new method were conducted. The results declared the feasibility of the new method. This paper presents the results of the studies for the new construction method.

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 We reclaimed artificial ground made of dredged soil and converter slag. And we were confirmed that the mass construction is possible by using pipe mixing method and using drop mixing method.
 From the result of survey, features of both method revealed. We also obtained a coefficient values that are necessary for establishing the foundation strength.

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 This paper investigates the effectiveness of slag and lime-mixing and mechanical dehydration method (called “SLMD” in this paper) as one of new recycling technique for dredged soils. Steel slag has been used in geotechnical field to improve soil property because it induces chemical reaction to solidify between soil particles. In the SLMD procedure, soft clay mixed with slag and slaked lime and dehydrated with a high pressure to increase the strength. In order to evaluate the effective of mixing slag and lime instead of cement, the strength property of clay produced by the SLMD (called “SLMD clay”) was investigated and the factors that make up the SLMD clay was investigated by principal component analysis. Soft clays dredged at the Hakata port was used to prepare slag and lime-mixed specimen. The main conclusions obtained from this study are as follows: 1) The highest strength for the specimen is 23MPa, when the SLMD clay includes slag content 45%, lime content 10% and 10MPa of dehydration pressure. 2) The unconfined compressive strength tends to increase sharply with decreasing water-slag and lime ratio, which decreases with the increasing slag content. 3) A new design of the SLMD clay was proposed by focusing on physical properties of Hakata clay, contents of slag and lime, dehydration pressure.

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