Climate change effects have become global concern through decades due to its emerging hazards. Sea Level Rise (SLR) is one of the effects which may cause harm to the coastal communities due to the risk of damages, such as shoreline retreat and beach erosion. There are many previous studies regarding the effect of SLR on sandy beaches. However, the study regarding gravel beach response under SLR is still rare. Therefore, this study is conducted to investigate the effect of SLR on the past shoreline change by using Bruun rule on currently eroded gravel beach, Ida beach in Shichiri-mihama coast, Mie Prefecture. By comparing the calculation result with the past shoreline change data obtained from network camera system, the proportion of SLR contribution in shoreline change can be assessed. Results shows that SLR contribution is ranging between 5.1 – 8.7% of the actual shoreline retreat from November 2017 to November 2019. This indicates that there are other factors such as extreme waves playing more dominant role in the shoreline change compared to SLR in this gravel beach.

 An opening was built in channel No. 1 out of three channels of Numakawa-daini floodway to transform the shape of the channel into a set-back type and the capability of flood discharge through the opening was investigated by a field test. Field investigation was carried out on December 8, 2020 and imageries were taken using a UAV before and after the flooding. Three-dimensional topography was measured using the UAV imageries as well as the measurement of water levels in the water tank, from which flood water is discharged, and the opening using a pressure-type water level gages. A flood water with a maximum discharge of 5.5 m³ /s flowed down over the berm, when the water level inside the water tank was +2.74 m above MSL and the water head between the opening and surface of water tank was 2.1 m.

 We collected data on drift ice (Sea of Okhotsk, total drift ice area; Abashiri Coast, total ice cover), waves (Monbetsu NOWPHAS), and shoreline positions along the Okhotsk coast, and conducted a preliminary study on the effect of drift ice on shoreline variation. The shoreline position of the sandy beach of Kitami coast (about 140 km long) at every 10 m was read from satellite images taken during 1990-2020. The relationship between the total ice cover and the significant wave height along the Abashiri Coast indicates that the ice floes suppress the waves reaching the coast. The shoreline position of the target area tended to move forward in general. The relationship between the amount of ice and the shoreline variation suggests that the shoreline position may have shifted landward in the years when the amount of ice was low.

 Selecting Komaka Island 3 km offshore of Chinen Peninsula in Okinawa and surrounded by coral reef was selected as a study site, field observation on the shoreline changes of a cay was carried out on July 13, 2019, and the shoreline changes were investigated using satellite images. The shape of cuspate foreland behind the island was classified into three types (circular, slender oval, and elongated oval). Then, numerical simulation on change in cuspate foreland was carried out using the modified BG model. In this model, wave height distribution changes in response to the wave-sheltering effect by the island is assumed, although waves are incident from the direction normal to the circular shoreline. Longshore sand transport is assumed to be induced owing to the spatial distribution of the wave height. The results of numerical simulation explains well the deformation of Komaka Island given a K_d value.

 On the Inage coast, beach nourishment was carried out in 2019 using white sand imported from western Australia for the reproduction of "white sandy beach". After the renewal work, white sand nourished on the beach surface was carried to the backshore by high waves associated with a typhoon and windblown sand due to strong wind, and the scenery of the beach became different from the originally-intended white sandy beach. In this study, topographic changes after beach nourishment of the Inage coast were investigated by field survey, and topographic changes due to the windblown sand was reproduced using a model for predicting topographic changes considering the effects due to both waves and windblown sand.

 Miyazaki Sun Marina has been suffering from a sedimentation problem at the entrance of its navigation channel. One of the reasons of this problem is assumed a sediment transport from the north side of the marina. In this study, two sets of data are used to investigate the sedimentation problem. One is a set of long-term depth data that has been measured inside the Miyazaki Port annually from 2008 to 2018. The other is also a set of short-term depth data that has been measured along the marina navigation channel every day from 2018 to 2020. Characteristics of depth change obtained from those data are investigated based on a linear regression analysis. This study suggests an area that causes the sedimentation problem in the marina navigation channel.

 Serizawa et al. predicted deformation of a circular island composed of sand using the BG model, taking the development of longshore sand transport owing to longshore variation in breaker height into account, after the calculation of the wave field using the energy balance equation. In this calculation, the calculation of wave field and beach changes were repeatedly carried out. In this study, a simple method to predict beach changes of a circular island was developed using the BG model without recurrent calculations. Assuming that waves are incident to the direction normal to the shoreline of an island with changing K_d value, longshore sand transport was taken into account by the analogy to the Ozasa and Brampton’s method. Calculation results were in good agreement with the results shown by Serizawa et al.

 This study describes an efficient ultra-high-resolution topographic measurement method to obtain hydraulic experimental data that should serve as a benchmark for the numerical fluid dynamics analysis of local scouring. In this study, small-scale model experiments were conducted to measure a scour hole's topography around a monopile of an offshore wind turbine foundation in combined waves and current, a current-alone, and a waves-alone. Using two types of synchronized laser displacements mounted on a self-propelled cart, we could quickly measure the scour holes with the ultra-high resolution with a grid spacing of less than 1/20 of the diameter of the monopile.

 Sediment samples and beach edges were collected and measured at several locations in Sesoko Island and Ada Beach in Okinawa known as coral reef beaches. The sediments were classified into coral fragments, foraminifera, shell fragments, minerals and sea urchin spines, while foraminifera were classified into Baculogypsina spaerulata, Calcarina gaudichaudii and others. In addition to the grain size and circularity, high-dimensional information obtained by Fourier analysis was newly used as sediment characteristics. The direction of movement of the sediment was investigated based on these physical characteristics.

 Results of the foraminifera shape evaluation indicates that the high harmonic number component decreases with the progress of star sand abrasion, the spectral intensity also decreases, and the grain size becomes smaller. The NE direction of the sediment transport was predominant in using the whole sediment, while the SW direction was principal in using the star sand, which was consistent with previous aerial photographs and existing reports, respectively. By quantitatively evaluating foraminiferal shape changes, it is possible to discuss the direction of the sediment transport in coral reef beaches.

 In the present study, numerical simulations on morphological changes at river mouth sandbar were performed at the Arakawa estuary in Niigata during Spring season of 2018. The results of numerical simulations by using XBeach were in qualitatively agreement with the aerial pictures. Furthermore, in order to indicate the flushing mechanism of the river mouth sandbar, the numerical simulations of morphological changes were quantitatively assessed. The Brier Skill Score (BSS) were employed as a quantitative index for the evaluation of lateral lines for the result of numerical simulations. As a result, BSS exceeds 0.5 in lateral lines closest to rivers and in trench excavation, indicating that the morphological changes are calculated with high precision. In addition, the numerical reproducibility of morphological changes near sea are highly dependent on the accuracy of simulated wave height. Finally, from the result of quantitatively assessment, it can be said that the opening mechanism of river mouth sandbar were associated with rapid changes in bed shear stress caused by a rapid increase in flow rate.

 As for the monopile foundation for offshore wind turbine, stone-based scour protection is commonly used in Europe. A filter layer of crushed stone to prevent suction of sand ground is covered by an armor layer using large stones to prevent scattering of the filter layer. In Japan, it is difficult to obtain good quality stones especially for the armor layer, so we propose a scour protection using Filter Units (FU), the rock bags, for the armor layer.

 In this study, hydraulic model tests using a sandy movable bed were conducted to confirm the stability of the scour protection in high waves and to investigate the effect of varying the planar extent of FU installation area. The scour protection did not settle and scour around FU was not significant when the area of FU was reduced to three times the diameter of the monopile under the conditions studied.

 The Kochi coast facing the Pacific Ocean has a beach process characteristics in which the beach collapse due to abnormal typhoon waves and the beach reforming due to normal wave power are balanced in the erosion-deposition phase changes. In this paper, we focus on the erosion phase of the beach changes in the Nangoku construction area of Kochi coast due to abnormal wind and waves. A numerical analysis was conducted to reproduce the coastal erosion mechanism for the 24 major storms from 2011 to 2019. The beach change process is simulated with a sediment transport model formed by wave-current coexisting model in shallow water where the offshore sediment transport caused by undertow can’t be neglected. The developed sediment transport model is tuned from the results of topographical changes in multi-narrow beam depth sounding surveys. The effects of beach protection measures of the Nangoku construction area was evaluated from the point of view of sediment control by the coastal structures scheduled.

 Recently, the number of the breached river levees, mainly due to overtopping, has naturally risen along with the increase in heavy rainfall. It is logically expected that water disasters will typically continue to occur and intensify frequently in the future. Therefore, having a “resilient river levee”, that prolongs the time until the river levee is breached, is necessary. For this, suppressing erosion and suction of the back slope of the river levee against overtopping is important. On the other hand, many scallop shells piled up around fishing ports like Hokkaido, cause environmental problems like a stench. This specific study clarifies experimentally that the crushed shell particles layer established on the back slope of the river levee is effective in suppressing erosion and suction against overtopping.

 On March 11, 2011, the 2011 off the Pacific coast of Tohoku Earthquake occurred and strong motion records were obtained on the D-Runway of Haneda Airport. The behavior of the D-Runway during the earthquake was investigated using the observation records and the validity of its seismic design was verified. FLIP simulation was performed using the model and parameters used for the design of the connecting structure between the landfill and pier sections by inputting the observed ground acceleration. As a result, the response of the landfill and the pier simulated by FLIP were in good agreement with the observed records. Regarding the connection structure, although the lateral displacement obtained by FLIP exceeded the observed value, it was confirmed that the seismic design using FLIP resulted in a conservative design.

 Recently, precast concrete structures have been highly demanded for the purpose of labor reduction at construction sites. Superstructure with precast concrete member has many advantages because it can reduce the time of field work affected by many factors such as ocean wave. The authors have proposed a pre-stressed joint construction method for port pier superstructure by using post-tensioning prestress to assemble the superstructure members which are transported from factory to construction site. This method is expected to save labor and improve construction efficiency because it does not require cast-in-place concrete of the superstructure. However, the shear capacity of pre-stressed joints has not been studied yet. In this study, loading experiments are conducted to evaluate the performance of this method. As a result, it was confirmed that the shear capacity of pre-stressed joints was higher than the frictional force assumed in the existing evaluation formula.

 In this study, we focus on developing an economical seismic retrofit method for pile supported wharf and piled pier by retrofitting damping member between all the piles through the comparison on the shaking table test. The targeted wharf type had depth of 7.5 meters with three rows of steel pipe pile with L-shape block revetment and backfill soil case and without cases as piled pier type. The effect of the retrofitting damping member was to reduce the maximum displacement of the superstructure, bending moment of pile head and increase the damping constant. The improvement of the displacement reduction and damping constant was assumed that the energy absorption in damping member was larger for the piled pier, while the damping constant of pile supported wharf was increased by the relatively large overall displacement due to the displacement of the revetment.

 To increase the passive resistance of earth retaining structure, such as a quay wall, the quantitative evaluation of the improvement effect is important in the practical design. In particular, when the front of the steel pipe sheet pile is improved in the normally consolidated clayey ground to increase the passive resistance to earth pressure from the ground behind the quay wall, there are many unclear points about the mechanism of passive resistance and the relationship between the improvement range and the improvement effect. A simple design method using a beam-spring model can be used. However, this method is designed for sandy soil, and its applicability to viscous soil is not yet confirmed. In this study, the applicability of the design method using the beam-spring model to the solidification and improvement of an existing gravity-type quay wall using steel pipe sheet piles is examined using centrifuge model experiments.

 When developing harbor facilities and artificial reclamation island in soft clayey ground, finite element analysis using an elasto-viscoplastic constitutive model is generally used. However, the predictive precision of the finite element analysis is rarely inspected, and the knowledge about its reliability and validity of the soil parameter set is still lacking. It's often pointed out that the predicted value of lateral displacement is more excessive than the actual measurement and that the transformation state by the analysis is different from actual phenomenon. From the background like this, the authors proposed the elasto-viscoplastic constitutive model, which it was aimed for to improve predictive precision of the lateral displacement. In this paper, we apply this model for five construction examples adopting the different ground improvement method and show the precision inspection of the predicted value of vertical and lateral displacement. As a result of inspection, we show that predictive precision of the lateral displacement improved than a conventional model.

 A series of injection experiments and shaking table experiments were conducted with the aim of verifying the "equivalent improvement rate (a_se)" especially the correction coefficient α, which indicates the degree of contribution of the improvement effect to the "cyclic volume rate (CVR)" used in a new CPG method (U/D method).

 As a result, it was clarified that the "equivalent improvement rate (a_se)" can be defined by the "equivalent improvement rate (a_se)" using the correction coefficient α, not by the equivalent sum of the "improvement rate by mortar injection (a_s)" and the "cyclic volume rate (CVR)". The "equivalent improvement rate" can be defined by the following formula.

 𝑎_se = 𝑎_s + 𝛼𝐶𝑉𝑅

 This correction coefficient α is obtained by a function of "cyclic volume rate (CVR) ". When the "cyclic volume rate (CVR)" of the U/D method is 20 % in this model experiment, the correction coefficient α is about 0.5, and the "cyclic volume rate "of 20 % can be expected to have an improvement effect (increase of density, K0 value and liquefaction resistance) equivalent to the "improvement rate (a_s)" of 10% by mortar injection.

 In general, unconfined compressive strength is used to evaluate the effect of solution-type chemical injection as a countermeasure for liquefaction. The authors introduced an in situ dynamic cone penetration test to supplement the conventional unconfined compression test, which is susceptible to disturbance during sampling. As a result, we proposed a method of appropriately estimating the unconfined compressive strength after improvement. However, the ground reclaimed with construction surplus soil has large variations in soil texture, and despite the fact that grout material have been injected, the ⊿N_d value which is the difference between the dynamic cone penetration test before and after the improvement, may not be judged improvement effect properly. In this paper, we consider an evaluation method that confirms the improvement effect against liquefaction using multiple indexes comprehensively.

 This paper examines evaluation measures that comprehensively using multiple indexes confirm the improvement effect against liquefaction.

 Efficient and economical ground surveys are required for the design of offshore wind offshore wind farm constructed in vast sea areas. The design of the grounding type structure requires various surveys because the ground conditions have a great influence, but the optimum survey planning guideline has not been established.

 This paper summarizes the contents of the ground survey according to the procedure for constructing the offshore wind farm, and considers the concept of the ground survey considering Reduction of ground risk.

 While the importance of national resilience has been recognized, various studies are being conducted about the redundancy and ductility in harbor structures. In this study, redundancy and ductility are considered the characteristics having limited strength reduction along with deformation, and the new geo-material utilizing converter steel-making slag was examined. First, it was manifested that a higher mixing ratio and larger grain size of steel-making slag were effective for redundancy and ductility as well as higher confining pressure. Furthermore, the contribution of fine/coarse fraction of steel-making slag on redundancy and ductility was clarified. Second, a desirable mixing ratio of steel-making slag was arranged for the effective use of dredged soil, and criterion proportion of fine/coarse fraction of steel-making slag was proposed.

 While the importance of national resilience has been recognized and various studies on the redundancy and ductility in harbor structures are being conducted, new persistent geo-material that is a mixture of steel-making slag and dredged soil has been suggested by the authors. In this study, seismic resistance characteristics of the new geo-material were examined by model vibration test of sheet-pile quay wall. Through comparative study with cement improved soil, it was manifested that crack growth and deformation of the new geo-material was more limited, and shear resistance properties were more prominent than cement improved soil.

 Dredged soil stabilized with steel slag has the characteristic that its flowability decreases in the unsolidified state. It is known that the flowability of dredged soil stabilized with steel slag can be evaluated by the slump value. However, there are many problems in applying it to construction studies. Therefore, analysis of flow characteristics showed that flowability of dredged soil stabilized with steel slag can be expressed by the Bingham model. In addition, the yield value of the Bingham model can be set from the slump value. By managing the flowability of dredged soil stabilized with steel slag, it can be used to fill the voids in the wave fissipating block.

 We have devised the on-site reforming method to improve a seabed clay ground by mixing with a steelmaking slag at the original position. In the research, we have considered to apply the method to plastic state clay ground. A series of 1/5 scale model experiments was carried out to verify the effectiveness of the improved mixing machine and the method of adding water to clay before supplying the slag. As the result, plastic state clay was found to be mixed with the slag more homogeneously in the machine. It was also found the mixability of the improved soil was enhanced by pouring water simultaneously with the fine granulation process of clay. While it should be noted that the lack of mixing time of clay and water increases the variation in the strength of the modified soil, the on-site reforming method could be applied sufficiently to improve a seabed clay ground in a plastic state.

 Asignificant amount of foam shield tunneling surplus excavation soil, which contain a foaming agent and a blow off inhibitor, has been produced on shield tunneling construction. To utilize the surplus soil effectively for reclamation of harbor areas, engineering properties of the mixture of the surplus soil and steelmaking slag, which is an industrial byproduct in steel manufacturing, have been studied. In this study, the material separation characteristics of the mixed geomaterials were investigated when they were put into water. In particular, the effects of the water depth and the mixing of the materials on the material separation were investigated. The results showed that the material tended to separate more easily as the water depth became deeper. In addition, it was not confirmed that the mixing of materials reduced the material separation. In comparison with the model experiment conducted separately, it was shown that the material separation could be reduced by increasing the amount of soil mixture.

 Steelmaking slag is utilized for material of sand compaction pile method. The improved ground by steelmaking slag compaction pile has high strength, so steelmaking slag can reduce improved area in design of circular rupture. In this study, we have investigated steelmaking slag parameters for seismic response analysis based on the in-situ test of improved ground and the laboratory test of material. As a result, the internal friction angle and shear modulus of improved ground with steelmaking slag have been about 10% larger than those of natural sand. In addition, we carried out seismic response analysis of gravity type quay wall and found that the displacement amount of the quay was the same for steelmaking slag even if the improvement width was reduced compared to natural sand. This is because the unit density and internal friction angle of steelmaking slag are larger than those of natural sand.

 The strength developments of dredged soil mixed with converter steelmaking slag and steel slag mixed clayey soils are uneven, and many factors of strength development are unclear. Therefore, in this study, the shear strength development of clayey soil mixed with steelmaking slag was investigated by examining the physical and chemical factors of clayey soil or steelmaking slag that affected the shear strength development by solidification of the mixed soil. As a result, it was found that the type of clayey soil affected more on the development of shear strength by solidification than the effect of the particle size distribution of steelmaking slag and the amount of free lime, when the maximum particle size of steelmaking slag was 4.75 mm, the fine fraction content of steelmaking slag was 0 to 30 %, and the amount of free lime in steelmaking slag was more than 3.5 %. Specifically, it was suggested that the amorphous silica content and the compositional ratio of amorphous silica in the clay affected the shear strength and the tendency of shear strength development.

 The mixture of dredged soil or clayey soil and converter steelmaking slag has the solidification property. Previous studies showed that the shear strength of the clayey soil mixed with steelmaking slag increased when cured under a certain overburden pressure. However, the influence of an increase in dry density and a decrease in water content ratio caused by consolidation, and confining pressure during curing on the increase in shear strength was unclear. This study examined the effect of dry density, water content ratio, and confining pressure during curing on the shear properties of the mixture of clayey soil and steelmaking slag. As a result, it was found that the effect of an increase in dry density and a decrease in water content ratio caused by consolidation mainly influenced an increase in shear strength when cured with consolidation by applying overburden pressure.

 Generally, the behavior of the subgrade reaction of the flexible wall under the lateral load depends on the deformation mode of the wall. Furthermore, structures such as walls are predominant in two-dimensional behavior, but when this is handled in model experiments, the stress state in the model ground is affected by the friction between the ground and the rigid container’s surface. In this study, several loading experiments using two-dimensional model ground were conducted. The model ground was simulated with aluminum rod laminate. The deformation mode of the wall was changed by the balance of the loading level at the two loading points (x=0 mm and -150 mm). In addition, the deformation state of the ground was compared by photographing it during the experiment. As a result, it was found that the subgrade reaction differ behavior in the depth direction depending on the deformation mode. When evaluated this behavior using the coefficient of subgrade reaction, it was shown that its distribution differs in the depth direction. Also, the degree and spread of shear strain differ in the ground behavior.

 In order to use the premises of the off shore waste disposal site highly, it is necessary to construct piles into the bearing layer. In such a case, piles penetrate through impermeable layer. At that time, the pile is thought to bring the waste below the impermeable layer. In this research, we focused on waste that is larger than the pile wall thickness of the steel pile, simplified it into a flat plate, modeled it, and conducted an experiment in which the pile pushed it in. We observed the relationship and examined the behavior when waste larger than the pile wall thickness is pushed into the pile. As a result of the experiment, it was found that the waste larger than the wall thickness of the pile is brought in as much as the width of the waste, and the inclination coefficient value tends to be larger than that proposed by Meyerhof.

 Authors have developed a technique called the cement-mixing and mechanical dehydration method. This technique enables to manufacture high strength soil block bycement-mixing and mechanical dehydration.The purposeof this study is to evaluate the effect of a radial drainage to accelerate consolidation and investigate the consolidation and strength characteristics of soil block. Furthermore, the consolidation behavior and unconfined compressive strength were estimated by the radial drainage theory. The results obtained from this study are summarized below.

 (1) It took about 45 hours to complete the consolidation for soil block without a radial drainage. The consolidation time was shortened to about 370 minutes byusing a radial drainage.The radial drainage mechanism was extremely effective in shortening the consolidation of soil block.

 (2) The water content of the soil block for the cement content of 40 % was reduced by about 40 % by using a radial drainage.The unconfined compressive strength ofthe soil block with cement content of40 % was 10.56 MPa at28 curing days. By using a radial drainage, the water content of the block decreased, and the strength increased.

 (3) The consolidation coefficient obtained fromthe constant strain rate consolidation test, it was the most effective for consolidation prediction using the radial drainage theory. The prediction result considering the well resistance was 130 minutes faster than the actual consolidation behavior. Furthermore, the strength estimation using the radial drainage theory indicated high accuracy with an error of 1.5 MPa (14%) or less.

 Authors have developed a technology to utilize dredged soil with high water content as a high-strength block by cement mixing and high-pressure dehydration. In this paper, we investigated cement hydration products quantified by X-ray diffraction method and strength properties by uniaxial compression test. The results obtained from this study are summarized as follows. (1) For the cement content of 40%, there was a strong correlation between unconfined compressive strength of cement-treated soil and the mass percentage of Ca(OH)₂, which is one of the cement hydration products, with R² = 0.82. The unconfined compressive strength increased up to 14.6 MPa when the mass proportion of Ca(OH)₂ increased up to 6.3%. (2) For the cement content of 80%, there was a strong correlation between unconfined compressive strength of cement-treated soil and the mass percentage of Ca(OH)₂ with R² = 0.82. The unconfined compressive strength increased up to 20.9 MPa when the mass proportion of Ca(OH)₂ increased up to 1%.

 Recycled soil that has been mechanically granulated by mixing generated soil, construction sludge and the cement-based binder is being reused for various construction works. In this study, the applicability of the recycled soil as a landfill material for port construction was examined through laboratory soil tests. It was found that the recycled soil used became finer due to the water immersion. The compressibility increased due to the water immersion and the liquefaction strength was low as a landfill material. When a small amount of cement is added to the recycling soil, the compressibility decreases and the liquefaction strength increases significantly. It is considered that it can be used as a landfill material if it is used as improved recycled soil by the premixing method.

 Liquefaction prediction of the mixed sandy soil containing fines content is conducted by predicting the liquefaction strength from the N-value corrected according to the fines content (Fc) and the plasticity index (Ip). However, the effects of the physical characteristics of the fines content Fc on the correlation between corrected N-value and the liquefaction strength has not been adequately investigated. In this study, in order to examine the effect of fines content on the liquefaction prediction of mixed sandy soil in more detail, a series of undrained cyclic torsional shear tests and prototype-scale standard penetration tests were conducted under conditions where Fc, mineral properties and particle size of the fines content were changed. As a result, it was clarified that the accuracy of liquefaction prediction and assessment becomes low in conditions where Fc ≥ 15% and Ip of the mixed sandy soil is less than 10 if the current criterion is used. Specifically, it was shown that the risk of liquefaction is assessed on an excessively safe side in cases where fines content is clay and meet the above conditions. In contrast, the risk of liquefaction is underestimated in cases where the fines content is essentially non-plastic silt under the above conditions.

 This paper discusses the experimental findings pertaining to the instability of the submerged rubble mound on sand bed 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 development of sinking of rubble mound 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 rubble mound on the sand bed started sinking significantly upon the progress of liquefaction to the soil region below the mound in association with vibration of liquefied sand. The experimental results also show the importance of control of progress of liquefaction as a countermeasure of sinking of the mound.

 A white layer containing magnesium hydroxide (Mg(OH)₂) as the main component deposit on the surface of cement treated soil under seawater. This Mg(OH)₂ layer has the function of suppressing the progress of deterioration. In this study, an immersion test of cement treated clay was carried out using the solutions with different magnesium concentrations, simulating tidal river areas. The results showed that the Mg(OH)₂ layer was deposited when the pH at surface of cement treated clay specimen was maintained above 10 for a certain period of time under relatively low concentration of Mg solution. Furthermore, when the Mg(OH)₂ layer was deposited on the cement treated clay, leaching of Ca ion and infiltration of Mg ion were greatly suppressed, and the deteriorated region was also reduced.

 To lift up coarse and heavy ores from deep seafloor, a method by using carrier material (mixture of viscous fluid and fine particles, CM) was proposed. However, appropriate mixing proportions of CMs have not been studied yet. Bentonite suspension is one of the candidate viscous fluids since it is widely used as drilling fluid for removing cuttings. Thus, this study focused on ore lifting efficiency of CMs of mixture of water, bentonite and sand particles.

 Firstly, rheological characteristics of CMs were measured. The results of measurements demonstrated that CMs can be assumed as Bingham fluid. Then, a series of model tests of ore lifting were conducted using CMs of various mixing proportions of water, bentonite and sand particles. The test results showed that heavier and larger ores were lifted using CMs than by the conventional lifting method in which crushed ores were pumped up with sea water. Moreover, the yield stress of CMs was found to enhance ore lifting efficiency if CMs can be assumed as Bingham fluid.

 The flap gate type movable breakwater, which was developed in Japan for the purpose of disaster prevention and mitigation measures in response to national resilience, pumps concrete over long distances with complicated pipes and fills it in water. However, there is little knowledge of the fluidity and filling property of concrete. A full-scale test to grasp the properties of concrete in advance is effective, but it requires a large cost and a long period of time. In this study, a full-scale test was conducted. As a result, the pumpability and the fluidity and filling property of concrete in water were confirmed. Furthermore, the flow analysis of concrete was performed. As a result, the fluidity of concrete in water could be reproduced.

 Japanese Reinforcing Concrete (RC) wave-dissipating blocks are a technology with excellent stability, economy, and wave-dissipating performance in severe marine environments. Taking advantage of this characteristic, it is expected to expand overseas, such as in the northern region of Africa, where the waves are large. However, in the case of overseas where RC wave-dissipating blocks have not been used, there is a strong concern about salt damage, and a quantitative evaluation of 100-years durability is required. Also, due to the difference between Japanese concrete and local concrete, it is difficult to refer to the use results of blocks in Japan. Therefore, mainly targeting Morocco, various tests were conducted on the strength characteristics and durability of concrete using local materials, and evaluations were made based on the results to clarify the applicability of RC blocks. The results of this examination provide information on indicators that should be considered regarding the durability of concrete in severe marine environments when disseminating Japanese technology to Africa, where it has become increasingly important in recent years.

 Eight years have already passed since the MLIT announced the concept of CIM (called BIM / CIM from 2018). The port construction started as a trial construction in 2017, and in 2023, all construction projects are subjected to CIM except for some exceptions. CIM aims to accumulate and utilize information centered on 3D information in all phases of survey, design, construction, and maintenance. In construction, we make a three-dimensional construction plan, discover problems such as interference prior to construction, a safer and more efficient construction methodology, and use it to manage how accurately the results can be implemented on-site. The guidelines of utilizing these data in the future were studied based on the conventional construction method, the current utilization method, and the future.

 Selecting the south and north coasts of Futtsu cuspate foreland with high and low incident waves, respectively, as the study sites, the relationship between the change in coastal vegetation zones and wave height was investigated. Although vegetations of several species were found on south and north coasts, the vegetation of high probability of occurrence distributed in the vegetation zone with the same elevation. On the south coast, annual grass growing along the front line of the zonation was not confirmed and the perennial grew from the front line of the vegetation zone. On the north coast, clear zonation was found with the growth of digitaria ciliaris and growth of the perennial and low trees. The wave height on the north coast was approximately 30 cm lower than that on the south coast, so the coastal environment in which one-year grass can grow was maintained.

 In coastal areas where the production of short-necked clams is significantly decreasing, a new tidal flat construction method using dredged mud is required to construct a tidal flat that improves the production. The development of new utilization technology is desired. In this study, the effectiveness of dredged mud utilization was evaluated from sediment analysis and benthic organism survey, targeting tidal flats created by sand covering with a time lag after dredged mud was added. At the point where the sand cover was completed, a layer of dredged mud and sand was confirmed on the sand layer, and it became clear that many organisms lived in that environment. In the target tidal flat, a good sand-mud mixed layer is formed as a place for clams to settle, but the nutrient state is phosphorus-restricted, so the growth of clams is not sufficient. The amount of algae is considered to be the cause of the suppression of the growth of clams and the like. For the production of short-necked clams, a source of phosphorus for tidal flats is required, and dredged mud is expected as a source of phosphorus.

 In recent years, decline in clams production has become a problem in many coastal areas. Creation of an artificial tidal flat using dredged sediment has been proposed to solve this problem, but settling of clams in the artificial tidal flat remains uncertainties. The purpose of this study is to create a habitat for clams using dredged sediment covered with granulated coal ash (GCA) in an oligotrophic sea area. A pilot study for clams habitat was conducted in an in situ artificial tidal flat made of dredged sediment and GCA. Survival and growth rates of clams, nutrients supply from tidal flat materials, and productivity of diatoms were investigated for about 14 months. Results showed that season and ground height (flooding time) significantly influenced the survival of the clams. In addition, GCA promoted nutrients supply to the sediments to create the habitat for clams.

 In present study, the effect of the seasonal difference in photosynthetic activity of eelgrass on the absorption/release characteristics of dissolved inorganic carbon was clarified from the results of model analysis of changes in dissolved inorganic carbon by aquatic tank experiments using eelgrass and chlorophyll-a content analysis. It was revealed that the optimum value of the maximum photosynthetic rate for dissolved inorganic carbon by eelgrass varies depending on the season of the experiment. From the estimated values by the model and the results of the chlorophyll-a content of eelgrass, it was suggested that the difference in the growth stage of eelgrass affected the photosynthetic activity and the maximum photosynthetic rate. The results obtained based on the measured values of the detailed specifications of eelgrass were applied to the model to clarify the relationship between the characteristics of the vertical profile of dissolved inorganic carbon and the branching structure of eelgrass.

 Coral reefs is able to provide water purification, tourism, disaster prevention, cultural and environmental education, and fishery propagation functions such as feeding and spawning grounds for marine organisms. As coral reefs have declined in recent years, the catch of coastal fisheries in coral reef areas have also decreased. On the other hand, as one of the measures to promote thinning for proper forest management, the development and diffusion of wood breeding reefs are being promoted throughout Japanese fisheries projects to contribute for the propagation of marine organisms.

 In this study, we developed a wood breeding reef and verified it in a demonstration test with the aim of supplementing part of the fishery propagation function of coral reefs while effectively using the wood generated in the Okinawa area.

 The aim of this study is to predict and verify tidal benthic ecology-geoenvironmental dynamics associated with multiple typhoon events using the integrated platform developed based on a new cross-disciplinary research field called Ecological Geotechnics. The developed platform consistently predicted the distribution changes of a sand bubbler crab, Scopimera globosa, associated with typhoon-induced morphological changes in Naha sandflat and demonstrated its effectiveness in a comprehensive manner.

 In this study, in order to propose a method for strengthening protection and nursing function in the cold region fishing port, we examined the effect of wave height on fish behavior and the method of evaluating the evacuation shelter function on fish during high waves in the fishing port. For that purpose, we took interval photographs of fish, observed the physical environment, and analyzed the wave field around the fishing port. As a result of the analysis, the number of individuals and the frequency rate of appearance decreased as the wave height increased, and no fish were observed above a certain wave height. Therefore, it was considered that the high wave height affected the behavior of fish. In addition, it was possible to evaluate the difference in the strength of the function among the division areas, by the proposed method of evaluating the evacuation shelter function of each division area in the fishing port by the wave height threshold. Although detailed examination is required in the future, this evaluation method can quantitatively evaluate the evacuation shelter function, and is considered to be useful information for the functional enhancement.

 The purpose of this study is to determine the cause of Ecklonia kurome decline in the seagrass beds that have been formed and the seagrass bed's recovery. For that purpose, we observed by using a fixed-point camera and analyzed the DNA concentration of specific fish in seawater. In May 2019, there was a lot of Ecklonia kurome with only stems left in the seagrass bed, and there were traces of feeding damage, suggesting that the effects of feeding damage were large. There was no correlation between the proportion of Ecklonia kurome remaining only in the stem and the frequency of appearance of Siganus fuscescens, Acanthopagrus schlegelii and Stephanolepis cirrhifer, observed by the stationary cameras. When Ecklonia kurome declined, almost no Siganus fuscescens DNA was detected in the constructed area until May 2019. There is no direct evidence of feeding damage other than feeding damage marks that could be confirmed. In the artificial seaweed bed substratum, where seaweeds declined due to feeding damage, small seaweeds reappeared just after the creation. Ecklonia kurome also appeared in about 19 months, and the seaweed species just before the decline.

 Using a conceptual model with salt as a constraint, being considered to be important for the spawning of brackishwater clams, as well as suspended substances and iron, various conditions in Mokoto Lake and Shibunotsunai Lake that differ in the state of reproduction of brackishwater clams, the magnitude of the contribution of the physicochemical process was examined. In the model, the retention of inflowing river water in the lagoon, sedimentation/resuspension, elution of iron, and biological uptake were considered. Since the inflow of sediment in Mokoto Lake due to a large basin and broad farmland, the contribution of sedimentation and resuspension is considered to be relatively large. As a result of sensitivity analysis, Shibunotsunai Lake has a large impact on water quality due to changes in flow rate and residence time, and is vulnerable to river improvement and changes in lake topography.