Two types of 13-year-long wave hindcasting data samples in cases where the input wind conditions are taken from the MSM(Meso Scale Model)-based wind data sets provided by JMA(Japan Meteorological Agency) are compared with the measurement data for significant wave heights and wave periods at each of 18 onshore stations deployed along the entire Korean coast. One type of the hindcasting data set is individually obtained at each of the Korean coastal stations by using a backward ray tracing model(BRTM)associated with a high resolution nesting grid put on the Northwestern Pacific Ocean. The other type of wave data set on the entire region is made by SWAN(Version40.91ABC) with a medium-size space resolution grid put on the Northwestern Pacific Ocean. The SWAN-based data is also compared with the measurement data at each of 12 NOWPHAS stations situated along the Japanese Pacific coast. The following results are found: 1) at any of the Korean coastal stations, BRTM yields reasonable estimates; 2) at most stations of not only the Korean coast but also the Japanese Pacific coast, SWAN tends to give an overestimation for wave heights, perhaps due to use of a poorer space resolution grid, and tends to yield an underestimation for wave periods, possibly due to an unsatisfactory formulation of the source term such as the energy dissipation term in the SWAN.

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 It is considered highly that the innermost part of the Ariake Sea will suffer damage from storm surges accompanying typhoons in the future. In addition, there are concerns regarding the increased risk of storm-surge associate with increasing typhoon intensity due to global warming. Hashimoto et al. 2016 suggested that typhoons capable of causing significant storm-surge and inundation disasters could affect the innermost coastal area of the bay even under current climatic conditions by assuming the typhoon T1216 followed a more dangerous route; parallel path that was 2 degrees to the east of its actual route.
 To examine the influence of tide varies, calculation under storm surge condition was performed using WAM by applying the results of the storm surge simulation conducted by Hashimoto et al. 2016. The results showed that wave height reach 2.5m at highest around the innermost coast area of the Ariake Sea. In addition, necessity of considering the time series of tide condition due to storm surge instead of constant value of maximum storm-surge tide was indicated.

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 In Typhoon Lan which came to Japan in 2017, disaster occurred in a wide area on the coast of Japan and long waves were observed in Tokyo bay. In this study, we estimated the wave field generated by the typhoon Lan using three kinds of third generation wave hindcasting models (WAVEWATCH III, SWAN and WAM). Then, the estimation characteristics of three models were clarified by using the contour map, the time series, and the directional spectrum of the wave conditions of the coastal area.

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 In order to accurately predict coastal waves, we built a wave estimation model using WAVEWATCH III on the open ocean and SWAN on the coast. We conducted a simulation on the coast of Tottori prefecture and confirmed that the calculated value reproduces the observation value of NOWPHAS well. Moreover, comparing with the simulation result only with SWAN, we confirmed that the accuracy of the model using WAVEWATCH III in the open ocean is higher. In addition, we examined accuracy according to spatial resolution and showed that it is desirable to finely set the spatial resolution for coastal wave estimation.

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 It is important to understand the wave characteristics because the wave affect to construction precision accuracy in the maritime construction. Especially the installation of floating caisson is always oscillating due to wave action. In this study, the behaviors of floating caisson were calculated, and the results were compared with observed data. Furthermore, the real time wave monitoring was carried out. From these processes, it is possible to grasp to behaviors of floating caisson, and improvement of construction accuracy is expected.

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 In marine construction sites, it is important to obtain long-term wave forecast with sufficiently high accuracy. In this research, one-month weather ensemble provided by the Japan Meteorological Agency is used to forecast one-month wave climate by using WAM to examine applicability of the prediction to maritime construction management. As compared with control run which does not include any perturbation, prediction using ensemble average provides higher accuracy in terms of RMSE and hit rate. In addition, as a result of the evaluation using the Brier skill score, usefulness of the present ensemble prediction is shown as compared with climatological prediction, especially on the Sea of Japan side. Although prediction of high waves induced by a typhoon, which may result in ship evacuation, is less accurate, useful information can be obtained for extratropical cyclone by showing occurrence probability.

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 On October 23, Typhoon No. 21 hit the coasts in Sagami Bay, and storm waves were incident to the coasts. On the Yanagishima coast immediately east of the Sagami River, severe beach erosion occurred, and foundation stones of the wave dissipating works were scattered by storm waves. On the Chigasaki-naka coast, where beach nourishment has been carried out, damage was minimal compared with that on the Yanagishima coast. Furthermore, on the Hishinuma coast east of Chigasaki-naka coast, the walkway along the costline was severely eroded and destroyed by waves. On October 24, field observation was carried out in the area between the Sagami River mouth and the Hishinuma coast to investigate the field conditions of the eroded coasts after storm waves. In this study, the results of the field observation on the Yanagishima, Chigasaki-naka and Hishinuma coasts were shown.

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 Typhoon 1721 hit the Seisho coast on October 23, 2017, and the seawall of Seisho Bypass extending along the coastline was severely destroyed by storm waves. The damaged area was approximately 600 m east of the previous damaged area of the bypass due to Typhoon 0709, and the bypass was destroyed again after ten years since 2007, similarly to the previous event in 2007. To investigate the cause of the damage, field observation was carried out on October 31 and November 13 around the damaged area. Furthermore, beach changes of the damaged area were investigated using the NMB survey data collected in 2014 and 2016.

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 This paper presented the beach morphological characteristics at Shichiri-mihama Ida coast based on the UAV-SfM/MVS results for 2 years focusing on the volumetric change and the correlation between the run-up height and the morphological change. As a result, erosion predominates in the leeward side between the artificial reefs during high waves and in a wide area during long period waves with a significant period more than 13s. The total volume of Ida coast has increased due to the recently implemented beach nourishment. However, because the foreshore slope of the Ida coast became steep due to the large beach nourishment material, the necessity of sustainable monitoring was suggested. Finally, the possibility to predict the maximum altitude of morphological change in Ida coast foreshores from the calculation of the run-up height by considering the wave direction of the wave after passing through the artificial reef was confirmed.

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 On the Shimoni-ikawa coast facing Toyama Bay, offshore sand discharge into the deep sea through submarine canyons have occurred at several locations. The depth change in grain size of seabed material of this coast with these characteristics has not been investigated. In this study, ten survey lines were set to measure the depth distribution of grain size on the offshore seabed. Seabed sampling was carried out using divers in the depth zone between the shoreline and 20 m depth. The relationship between d₅₀ and local slope determined from the bottom sounding was studied. It was found that d₅₀ correlates well with the local slope independent of the water depth, and that the steeper the local slope, the greater the grain size of seabed material.

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 When artificial alteration is carried out on a coral cay, large topographic changes may be induced because of the imbalance of sand transport around the shoreline of the island. One of the authors considered the impact of the construction of the detached breakwaters to a circular cay as a model case using the BG model (a model for predicting three-dimensional beach changes based on Bagnold's concept). Because such a cay has a closed system for littoral transport, artificial alteration exerted at a location of a cay may affect the entire shoreline of the cay. However, real data concerning this issue was lacking. In this study, taking Minnajima Island offshore of Motobu Peninsula in Okinawa as an example, this issue was considered. It was shown that artificial alteration to enhance the usability of the cay brought the degradation of natural condition of the cay, and influenced to tourism use of the island.

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 Bathymetric survey has been carried out once a year since 1993 around Fukude fishing port facing the Enshu-nada Sea. In the previous studies, these collected field data have not been studied. In this study, these data set were analyzed to investigate the topographic changes around Fukude fishing port, and the rate of longshore sand transport was estimated. In particular, recent sediment budget was made clear. Furthermore, the longshore slope of seabed contour (LSSE) was calculated based on the basic concept of the contour-line-change model, and the longshore change in each contour line was calculated to understand the movement of a specific contour line.

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 On the Imagire-guchi tidal inlet, a jetty was constructed between 1964 and 1974, and an ebb tidal delta has developed due to the interuption of westward longshore sand transport. Such westward longshore sand transport was considered to be kept again with the development of the ebb tidal delta. Although a large topographic changes occurred in this area, it is important to understand the real situation of the beach around this inlet. For this purpose, past aerial photographs were gethered, and the shoreline changes since 1972 were investigated in detail. As a result, westward longshore sand transport is continuously maintained around the marginal area of the ebb tidal delta, and longshore sand transport was estimated to be 1.21×10⁵ m³/yr at the Arai coast west of the inlet.

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 Narrow Multi-Beam survey data collected in the area offshore of the Seisho coast in 2014 and 2016 were analyzed. The analysis was carried out, focusing the typical accumulation and erosion pattern which is caused when longshore sand transport was blocked by the offshore reef or groins, and the characteristics that the change in seabed topography decreases seaward and ceases near the depth of closure, instead of simple comparison of the obtained NMB data. Six areas, such as the Sakawa River mouth, Odawara Parking area, the Ninomiya coast where beach nourishment using coarse sediment, and others, were selected, and longshore sand transport and the depth of closure at several locations were evaluated. As a result, it was found that westward longshore sand transport dominated during the observation period, and longshore sand transport was evaluated to be 2.5×10⁴ m³/yr at the Kuzu River mouth.

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 On Hon Chong Beach north of Nha Trang in Vietnam, there existed a natural sandy beach until 2002, similarly to that on Nha Trang Beach. However, land reclamation was carried out along the coastline for the construction of a coastal road in 2003, and sandy beach was buried under the coastal road. In recent years, the recovery of sandy beach of Hon Chong Beach has been discussed to enhance coastal use. For this purpose, bathymetric survey data and satellite images of this beach were collected, and the shoreline changes were investigated together with field observation. Then, numerical simulation using the BG model was carried out to investigate the possibility of the recovery of sandy beach on Hon Chong Beach. It was concluded that if beach nourishment using 6×10⁴ m³ of sand is carried out, a 24-m-wide foreshore could be recovered.

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 Nha Trang is a coastal city and capital of Khanh Hoa Province, on the South Central Coast of Vietnam. The city is on the beautiful Nha Trang Bay, which was chosen in two succeeding years as one of 29 most beautiful bays in the world. It has a long nice sandy beach in the south of Cai River and well known for international and domestic tourists. However, in the northern part of Cai River named as Ba Lang Beach is rather narrowed sandy beach. In addition, there a new reclamation road to the sea was built in the year of 2002 which had changed the shoreline from a concave shape to a straight-line shape of the shoreline. Because of this, serious beach erosion has occurred afterwards, the sandy beach has disappeared at some location on the beach. The objective of this study is to investigate the impact of this artificial bathymetry changes to the wave deformations then causing the beach erosion. The results are clearly indicated that after the road construction, the wave direction is more oblique to the shoreline direction compare to the previous condition. These results are also suggested that in order to recover the sandy beach in this area, the shape of shoreline position has to have a similar concave shape as previous shoreline position.

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 Elongation of a sand spit at Loc An Inlet in the Southern Coast of Vietnam is so remarkable that many resorts and hotels have been built on this newly formed sand spit. The spit elongation is caused by down-drift accumulation of sand introduced by longshore sediment transport. On the other hand, serious erosion of the down-drift sand spit can be observed. In addition, there is a fishing port inside the inlet and the elongation of the up-drift sand spit is causing a problem for navigation of the fishing boats. Due to lacking field data in many coastal zones along the coastline of Vietnam, Landsat and Google earth images from 1988 to 2017 have been utilized for the investigation of the Loc An Inlet's evolution. According to the analysis results, the tip of the up-drift sand spit is shifting with the velocity about 95 m/y while the tip of the down-drift sand spit is retreating at almost the same speed. This indicates that the width of the inlet has remained constant. Longshore sediment transport rate (LSTR) along the up-drift sand spit is calculated as a product of the area change rate of this sand spit and the total depth of closure and berm height. This LSTR shows good agreement with the LSTR calculated by numerical simulation.

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 My Khe Beach is located in Da Nang, the biggest city in Central Vietnam. Coastal erosion occurred in December 2017 has damaged many infrastructures located along this beach. Since there is no well-documented case study about coastal erosion in this area, Google earth images since 2002 were utilized to investigate the deformation of the My Khe Beach. The analysis results indicate that formations of megacusps in this beach were noticeable in the northeast monsoon season and it is clear that beach erosions occurred at the embayments of the megacusps. In addition, these megacusps were smoothed by the calm waves in the southwest monsoon season a few months later. The megacusps observed along the My Khe Beach have the alongshore spacing from 100 m to 300 m and the maximum cross-shore amplitude of 45 m. The local beach resorts have been developed without paying attention to this seasonal fluctuation of the beach. It is necessary to consider the characteristics of shoreline fluctuation clarified in this study for coastal planning and management.

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 High-accuracy bottom surveys by using the RTK-GPS and the ADCP were applied to Nakatsu Intertidal Flat regionally and the sediment discharge from Yamakuni River were estimated by using the data of turbidity meter and the Ashida-Michiue equation. Sediment budget from Yamakuni River to Nakatsu Intertidal Flat was calculated in order to investigate the mechanism of erosion/deposition of the flat. From the long-term data of erosion/deposition of the flat, deposition due to the flood and ordinal erosion could be seen. From the estimation of sediment budget, it was suggested that effects of longshore sediment transport due to mud and sand could not be ignored. From the multivariable analysis of long-term erosion/deposition data, the prediction equation of erosion/deposition of the flat was acquired. It was effected by the precipitation for deposition, the wave height for erosion and the constant value for deposition.

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 After Kumamoto earthquake, about the 0.4m ground subsidence was occurred. That was corresponding to about 140 year’s sea level rise. And then a following-flood has happened two months later after the earthquakes. Therefore, the cross-shore bottom profiles in the intertidal zone could not return to one before the earthquakes. The average grain sizes in 2017 along the clinoform are rougher than them in 2016. A new relationship between amount of sediment discharge and river discharge from Shirakawa River was shown. As a result, it was found that a large amount of sediment flows out even if the river discharge is smaller than that estimated by the past two relational expressions.

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 The construction of breakwaters and other shoreline structures on the part of a coast influences drift sand transport in the bay, and causes comprehensive topographic changes on the beach. This study was designed to investigate and assess sediment dynamics and land use transformation at Shiraragahama Beach in Miiraku where located in the northwestern end of Fukue Island, Nagasaki, Kyushu, Japan. This are is designated as Saikai National Park and has a rich natural environment and a mediaeval historical port. Because of the rapid development of breakwaters for a fishing harbor in recent years, the original shore environments of this sandy beach have changed to tidal sandy flats. First, we evaluated land use patterns in the basin of river flows into the site to fully understand the status of a supply source about deposited sediment. Secondly, we measured the altitude by using RTK-GPS through a year from 2017 and calculated the altitude between traverse lines on Arc-GIS. Finally, we examined the sediment deposit distribution on the site by grain size analysis. The results show, abandoned farmlands in the river basin are increased and it is considered that sediment yield from these grounds is possibly increased as well. The altitude of the site were found not significantly different through a year, but the seasonal changes of rainfall and wind wave were found responsible for the spatial dynamics of sediment in Shiraragahama. Ecosystem, landscape and community use of Shiraragaham are good status which should be conserved.

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 Shirakawa estuary area subsided about 0.4m due to Kumamoto earthquake on April 2016. This ground subsidence is corresponding to a sea level rise rate for a period of about 70 years. Therefore a new long term prediction of delta topography was carried out in consideration of the ground subsidence and the changes of sediment discharge from Shirakawa River with the existing process model. The clinoform will retreat by about 2000m toward the onshore side, and then the subtidal area will be decrease. These calculation results are different from a previous study. Also the amount of sediment discharge has an impact on the change of topography in the future.

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 To determine the beach profile evolution of gravel beach under the irregular waves, the hydraulic experiments were conducted. A gravel beach with a slope of 1/7 was installed and the change of spatiotemporal profile according to the irregular wave was analyzed during 6 hours. Two types of beach profile deformation (reflective/step type) occurred under the accretive wave condition and it can be distinguished using discriminant equation of surf-scaling parameter with the representative wave information of irregular wave (H_5% and T_p). In addition, it was revealed that the similar profile deformation can be reproduced by replacing the irregular wave with the regular wave on the gravel beach, when the regular wave has the same wave information with the representative wave (H_5% and T_p).

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 In this study, laboratory experiments are conducted in a two-dimensional flume with a 1-m-long sandbox in the middle of a slope. Using fluorescent sand tracers and core sample methods, the spatial and temporal variation in the mixing depths in the surf zone are investigated. The core samples are collected from the sand bed where the wave breaking and impinging are observed. The mixing depth is defined as the fluorescent intrusion depth from the bed profile at the time of core sampling with a cut-off value of 10 tracers. In the case of sediment accumulation, the mixing depth is measured from the initial bed profile. Moreover, each case of the experiments is simulated by a numerical model, Large Eddy Simulation (LES), to compare the mixing depths with the velocity field of horizontal bottom eddies. The simulation results of the surface elevations and velocity fields are verified using the measured data. The experiment results indicate that the spatial variation of the mixing depths show different trends depending on the wave breaking style. Moreover, the mixing depth variations are compared with the simulated results of the bottom horizontal eddies. The results indicate that the plunging breaker type of sediment mixing pattern in space within the wave breaking zone correlates with the spatial distribution of the maximum bottom horizontal eddies.

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 An opening was produced at a location on the way to the sea of Numakawa-daini floodway to investigate the effect of the set-back type floodway. A field test of the removal of sand deposited inside the conduit of the floodway due to storm waves was carried out. As a result, the excavation of the ground to reduce the ground level in front of the opening up to the level of the floor of the floodway before the flushing and continuous flushing were effective in removing the sand deposited inside the conduit. Furthermore, the side wall of the present floodway and the artificial channel excavated along this side wall were effective in enhancing the berm erosion.

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 On a coast with the predominance of windblown sand, generally the fences for preventing windblown sand are constructed. The effectiveness of such a measure against windblown sand has been confirmed at many coasts. However, practical numerical models for explaining the deposion process of windblown sand around a fence are limitted, in particular, in the practical applications, which restricts the prediction of the effect of the measures against windblown sand. In this study, field observation on topographic changes around fences for preventing windblown sand were carried out at the Shonan coast, and a model for predicting topographic changes were developed using a cellular automaton method.

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 88 temples with a long and distinguished history have been linked by the road in Shikoku Island, Japan. This network is called “Shikoku Henro” and it is well known for one of the pilgrimage route in Japan. In Shikoku region, it is concerned that it will suffer severe damage by Nankai Trough earthquake in near feature. Moreover, this region is attacked by typhoon almost every year and it has much rain throughout the year. Therefore, it may have high risk against natural disaster. Geographically dispersed temples and linked roads may become useful social infrastructures for evacuation. In this study, to clarify the risk against natural disaster in 88 temples and their linked road, questionnaire survey and space in-formation analysis were conducted.

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 A sea fishing raft is a kind of sea floating structure. It is especially difficult for anglers themselves to escape from a sea fishing raft to land under tsunami attack. Owners of sea fishing rafts must have the ability to keep anglers safe. Through an evacuation drill at Minamiise Town, Mie, Japan, we discuss how to smoothly evacuate anglers from the sea fishing raft to the tsunami shelter. Three fishing boats came to the sea fishing raft from their home port, and picked up the participants who acted as anglers. After the participants made a landing, they ran to the tsunami shelter.
 In an analysis of the GPS loggers and the comments of the participants, many participants could not recognize their best evacuation route. In addition, they have the risk of reaching a tsunami before their landing at the port. We point out the significance of considering the integral evacuation route with a best landing point, an evacuation road and a tsunami shelter.

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 On March 11, 2011, about 400 fishing boats stood out to waters off Iwate Prefecture, and some crews fell victims to tsunami caused by the Great East Japan Earthquake. In Taro District, Miyako City, Iwate Prefecture which is a tsunami-prone zone, many fishermen are engaged in aquaculture using small boats with outboard motors which outnumber those in the whole country. We took up Taro-cho Fisheries Cooperative Association as a model of case study, and executed research and analysis on conditions of sea areas of refuge designated by the Fisheries Agency according to the Guidelines for Development of Fishing Areas Resilient to Disasters and fishing boats which took refuge at the time of the Earthquake. In the Guidelines, one of requirements of the sea area of refuge is sufficient depth of water enabling the tsunami flow rate to be lower than one fifth of fishing boats' average speed. However, the result of our study shows the possibility that a sea area which does not meet the requirement can be used as a sea area of refuge. It is also shown that placing a revolving light and a wireless speaker for disaster prevention on the cape head is effective to provide emergency information on tsunami promptly and precisely with crews of a small boat with an outboard motor operating in a coastal aquaculture area, because they enable crews to visually recognize or catch such information even at night.

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 Numerical calculations of storm surge inundation prediction for the attack on the three great bays by the worst course of the largest typhoon have been done so far. The results are used as disaster prevention information such as hazard maps in central and local governments. However, although it is thought that it is offered as disaster information useful for local residents and children, in fact it is difficult to catch the disaster realistically. And we can't intuitively learn the actions to take in the event of a disaster. Therefore, in this research, we utilized VR (Virtual Reality) head mounted display (HMD) to intuitively understand the flooding condition even for people without expertise based on the result of the tidal floodation obtained by numerical calculation. We develop the virtual storm surge immersion experience system using a smartphone and evaluate its usefulness. Since HMD is mounted on a smartphone, it can be implemented at a low price of about 90, 000 yen per set, and operation is very easy.

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 Typhoon Haiyan struck the Philippines in November 2013, causing a severe damage in coastal areas as a result of strong winds and storm surges. Despite the Philippines being a country with a relatively ample experience of typhoon-disaster management, some previous studies have pointed out that evacuations procedures have been delayed due to insufficient perception of storm surges as a life-threatening phenomenon. A survey conducted by the authors in Dec 2015 demonstrated that some residents only started to evacuate after they noticed floodwater that intruded into their houses. The fact of delayed evacuations of some inhabitants, which unavoidably happen in any circumstances, urges the need to further consider optimal evacuation procedure and behaviors under extreme storm surges conditions in order to save more lives. This paper reports findings obtained from the field survey conducted in Tacloban City in pursuance of revealing the evacuation behaviors of residents during Typhoon Haiyan. In addition, this paper includes the presentation of a constructed evacuation simulation model, which aims at investigating optimum evacuation behaviors under storm flooding. The simulation model further questioned the rationale of horizontal evacuation in already flooded condition compared to vertical evacuation inside buildings.

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 Coral reefs well develop offshore of the west coast of Saipan Island. Managaha Island composed of coral sand is located on this reef flat. Large shoreline changes can be observed around the cuspate foreland located at the northwest side of the island. On August 27, 2017, field observation was carried out on this islet together with the investigation of wave climate around Saipan Island and shoreline variation of the island using satellite imageries. The shape of cuspate foreland on the island was classified into four types. The probability of the wave incidence from NE was high during February and April, and October and January, causing leftward longshore sand transport around the cuspate foreland, whereas the wave incidence from SW predominates during July and September, causing rightward longshore sand transport. It was concluded that the shoreline variation around cuspate foreland of this islet was due to these seasonal variations in wave direction.

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 The Pilot Gravel Beach Nourishment was implemented on Fongafale Island in Tuvalu to enhance beach protection and to improve beach use and environment. Community-based beach management is essential to maintain beach with good condition after the implementation; however, no practical examples had been implemented in the Pacific Island Countries. In this research, public relations and environmental education were applied to improve public awareness on beach for realization of community-based beach management. As a result, it was confirmed that public awareness on beach was significantly improved and community voluntarily started beach management activities. In addition, the structure for sustainable beach management was proposed and its effectiveness was examined through implementation.

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 The pilot project of gravel beach nourishment was undertaken in Tuvalu in order to protect the land against coastal erosion and wave overtopping. The community-based adaptive management corresponding to the level of beach use was proposed, and implemented based on the monitoring result for two years. The result shows that the nourished beach can be effectively maintained by the Tuvalu people with low technology and limited equipment.

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 The phenomenon of sedimentation in navigational channel and basin by sand drift or siltation has not been fully elucidated, and many uncertainties are existing when the sedimentation is estimated. Therefore, it is difficult to estimate the sedimentation volume adequately at a time when data availability is limited such as the stage of port development planning in developing countries. In this study, Port “M” was selected as model case for applying the estimation sedimentation in navigational channel and basin in case of limited data availability. The sedimentation volume was estimated by two numerical simulation models, which are commonly used for the sedimentation estimation, based on limited available data such as observed data during short period and validated by comparing with historical bathymetric data. As the result of estimation of sedimentation, although there was a small difference in both results, the reproducibility of sedimentation in navigational channel and basin was ensured.

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 Purposes of the present study are to obtain quantitatively color characteristics of sands which were collected in the mainland beaches in Kagoshima Pref., Japan and to examine relationships between the color characteristics and geological features of the surrounding area of the beaches. Some relationships between the two are clarified, such as that a lot of the beaches have sand colors of medium dark brown under the influence of late Pleistocene non-alkaline pyroclastic flow volcanic rocks, Holocene non-alkaline pyroclastic flow volcanic rocks and non-alkaline pyroclastic mafic volcanic rocks make beach sand color dark gray, and dark blown sands of some east coasts in Osumi Peninsula originate in middle Miocene to late Miocene granodiorite.

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 Since the local scour, which occurs at the foot of the structure for controlling the drift sand and the flow, greatly affect the stability of the structure, the appropriate countermeasure should be taken based on the prediction of scale of the scour. In this study, the flow and sand migration phenomena formed in the vicinity of the vertical flat plate were observed in detail by using a high speed camera and the effect of the height of the vertical plate on the characteristics of the local scour at the foot of the plate was investigated in hydraulic experiment. On the basis of the observation the mechanisms of the occurrence of scour was inferred. Further the countermeasures of penetration of the vertical plate into sand bed and embankment at the foot of the vertical plate were proposed and the effectiveness of them were investigated.

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 This study carried out laboratory experiments to obtain data sets for estimation of the scour around the mono-pile constructed for offshore wind power especially when the water depth is relatively large and KC number is relatively small. The experiment investigated the influence of several factors on observed scour depth, such as the diameter of the mono-pile, incident wave heights and periods, and grain size of the bottom sediment. While obtained results showed the similar relationship of KC number and scour depth to that of the empirical formula presented by the existing studies, obtained scour depth tended to be larger than the ones obtained through the empirical formula.

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 In the case where an incident plane wave meets a liner structure in perpendicular direction, the overlapped wave forms a classical stationary wave, which induces characteristic sediment flow on seabed. In more general situations, however, the incident wave meets linear structures in not perpendicular but diagonal directions. In these cases overlapped waves would behave in three-dimensional manner; the effectiveness of two-dimensional analyses and/or experiments would be limited. Present study aims to analyze the sediment flow induced by the diagonally incident and reflected waves, and evaluate quantitatively the erosion-deposition behavior, taking the response of seabed effective stress response to wave loading into account. We used an analysis method comprised with linear wave theory, pore-elasticity for seabed medium, and empirical sediment flow model mobilized by sea wave traction.

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 At Chirihama beach, the sand-pack as the beach sand erosion control method was installed at sea water line in the sand beach, and the sand-pack effectiveness was examined with the hinterland erosion protection. The crest height by the beach sand erosion control method was arranged as two different types , and monitored how effective such two different crest height are against the hinterland. As a result, T.P.+0.1 m had a better effectiveness as beach sand erosion control method from the point of view of sand beach recovery and the landscape characteristics. Regarding the place arranged by the crest height T.P.+0.5 m, the height target can be easily adjusted to T.P.+0.1 m through discharging the filling material. Since the sand-pack method can adjust the crest height through discharging the filling material, it should be suggested to be effective method in executing the countermeasure for beach sand erosion in which effective target crest height is difficult to forecast while planning, but adjustable during the installation.

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 The liquefaction resistance and N-value of silty/clayey sand with varying fine content and plasticity were investigated by laboratory testing. The liquefaction resistance of silty/clayey-sands decreased with the increment of fine content as opposed to the assumption of the current liquefaction assessment method. Meanwhile, the N-values of the silty/clayey-sands decreased with the fine contents. It was found that the current liquefaction assessment method overestimates the liquefaction resistance of the materials used in this study.

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 In recent years, dynamic numerical analyses are often used to design harbor structures subjected to earthquakes. In the analyses, the ground improved by the sand-compaction-pile method (SCP method) causes excessive deformation. On the other hand, the SCP-improved ground has not been reported on damage in the past earthquake, and it demonstrates the improvement effectiveness. The reason for the difference between this calculation and the real phenomenon would be that the stress state of the SCP-improved ground, which was a composite ground of sand piles and ground, was complicated and difficult to evaluate. It is difficult to properly model the state in analyses. Especially, the increase of the static earth pressure coefficient K-value, which was confirmed on the actual modified ground, is not considered in the current analyses. In this study, the K-value increase was reproduced in the ground behind the caisson in centrifuge model tests, and the improvement effectiveness was examined. As a result, high improvement effectiveness could be confirmed by taking into consideration the K-value increase in addition to density increase.

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 In the gravity-type quay wall supporting the earth pressure behind the structure by the self-weight, an increase of the horizontal earth pressure due to liquefaction result in damage of the caisson. It is predicted that further damage will be occurred due to the tsunami acting on the quay wall damaged by the preceding earthquake. As a countermeasure against the quay damage, a method of solidifying the back-filling layer behind the caisson has been proposed. In this research, the seismic response of gravity-type quay wall with improved backfill has been investigated by experimental simulation using geotechnical centrifuge. As a result, it was confirmed that the displacement of the caisson can be reduced by solidifying the backfill and a further effect can be expected by combining the improved backfill and the caisson.

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 This paper discusses the experimental findings pertaining to the instability of the offshore monopile foundations due to wave-induced liquefaction in sand beds. The emphasis of the experiments was placed on investigating the relation between the occurrence/propagation of liquefaction and the increase in the displacement of the monopile, leading to collapse under the action of severe traveling fluid waves. A range of wave tests using a drum centrifuge was performed under a centrifugal acceleration of 70 gravities. It was found that the monopile put on the bed base started moving significantly upon the progress of liquefaction to the soil depth corresponding to the 1/3 of embedment depth of the monopile. The experimental results also show the effects of embedment to the dense layer and the significance of rotation of principal stress axes.

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 In view of the need to utilize ocean space and develop seabed resources, the assessment of the stability of deep seabed soil has emerged as an important challenge in the field of geomechanics. To study seabed stability, the consolidation characteristics and strength of the natural ground must be ascertained. However, soils sampled from the ocean bottom are subject to effects that differ from those exerted from sampling on earth. More specifically, non-negligible effects of disturbance are expected. Therefore, we conducted numerical simulations to investigate the effects of vaporizing dissolved gases on the mechanical behaviors of soil specimens during sampling and on the consolidation characteristics and undrained shear strength as determined by laboratory tests. The analyses revealed that the interaction between decreasing effective stress caused by sampling, overconsolidation and desaturation causes the difference between the soil strength ascertained by laboratory testing and in-situ soil strength.

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 When using the core sample retrieved from deep seabed, to evaluate the strength of deep seabed ground where shallow type methane hydrates existed, the core samples are subjected to a large stress relief during sampling. As a result, gas dissolved in the pore water will come out of solution and cause disturbance to the soil structure. Consequently, it is difficult to obtain the accuracy in-situ strength.
 Therefore, in this study, gravity type cone penetration test (CPT) was conducted off the coast of Eastern Hokkaido in the Sea of Okhotsk, where shallow methane hydrates existed, and tried a direct measurement of the sea ground strength. In addition, the influence of sample disturbance of core sample was evaluated in comparison with the onboard test results. As a result, it is found that the onboard test result is underestimated in the sample with high concentration of dissolved gas and with much sand content. On the other hand, the in-situ strength can be evaluated by the simple gravity type CPT.

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 The decontamination work implemented after the Fukushima Daiichi Nuclear Power Plant accident generated the removed soil containing radioactive cesium. This study assumed that the removed soil would be disposed of in a coastal disposal facility, and the geomaterial used for the sealing layer of the coastal disposal facility was developed. The necessary sealing performance of the geomaterial was examined, and the effects of mixing of bentonite, sand, and zeolite on marine clay were studied. Bentonite was added for improving the sealing performance. Sand was added for improving the low compressibility of the sealing material and the workability by increasing the coefficient of consolidation. Zeolite was added for improving the adsorption of cesium. The effective porosity obtained by the column test in consideration of the flow velocity in pore space was the same as the porosity obtained by the consolidation and seepage test. The hydraulic conductivity for flow in pore was increased by the addition of sand but not by the addition of zeolite.

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 Deep embedded and large diameter steel pipe piles have been popularly used in the port facilities nowadays for supporting large vertical load, because of growing size of port facility or changing structural types. Estimation of bearing capacity of large diameter and deep embedded piles is a complex problem such that bearing capacity is increased because of deep embedment and bearing capacity is decreased because of decrement of plugging effect by using large diameter piles. In this paper, factors which influence the method of estimating the inner frictional force of the open-ended pile were investigated. As a result, it was found that inner foil height greatly influenced the estimation of the inner frictional force.

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 The CPG method is a method of increasing the soil density by injecting mortar, and it is applied as a liquefaction countermeasure under the existing structure of the ports and airports. However, ground upheaval often becomes a problem. The “up and down method (U/D method),” a new CPG method, was developed in our previous small-scale model tests and field tests. This new method greatly improved upheaval control and the efficacy of liquefaction mitigation compared with the conventional CPG method. The purpose of this research was (1) to increase construction efficiency (2) verify upheaval control mechanism. Consequently, it was found that the workability can be improved by using an injection pipe with a tip end tapered shape. The upheaval control mechanism was found to be explained by the cyclic elastoplastic contraction of the ground due to the up and down of the new CPG method.

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 To investigate the geotechnical characteristics of embankment mounted with the dewatered clay lumps at seven years ago, the surface wave exploration, cone penetration tests and the consolidated constant pressure direct box shear tests on the block samples obtained from the embankment were performed.
 As a result, the densities of embankment without a part of ground surface were kept the value at the construction. The rupture envelopes obtained from the direct box shear tests were located above the fail criterion of dewatered clay lumps at the design, it was therefore confirmed that the embankment at the present maintained its stability.

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