We verified an accuracy of previous investigation technique of benthos in artificial tidal flat. In addition, we studied a characteristic of benthos by an investigation depend on a division of using height and clay ratio in artificial tidal flat. As a result, (i) A species richness is increasing in artificial tidal flat, (ii) An identified the ratio of species richness was 77% by sampling using the division, on the other hand, 72% by sampling at random. Therefore the previous investigation technique of benthos is effective, (iii) A benthos of no identified in natural tidal flat was fixed on artificial tidal flat.

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 The objective of this study is to clarify effects of changes in the physical characteristics of sediments after flood on macrobenthos using simple model easily forecasting benthic community structure in estuarine tidal flat at the Yoshino river mouth. We focused on physical characteristics of sediments such as silt clay contents and differences in elevation at the 50 stations. Prediction accuracy by sediment-benthic community model was low after flood, because the relationship between sediment group and benthic community did not correspond to that in a normal condition. However, prediction accuracy by sediment-benthic community model increased in the next year. These results indicated effects of flood on sediment and benthic community. Moreover, it was suggested silt clay affected benthic community rather than difference in elevation. It could evaluate the change of prediction accuracy and the characteristics of sediment group by the sediment-benthic community model.

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 Field experiments were conducted to investigate the restoration effects of biological environment in reduced sludge under the use of alkaline material. The sewage-derived sludge that accumulated on seafloor was collected and used in the experiments. To restore the biological environment, an alkaline material that mainly comprised of SiO₂, Al₂O₃, CaO was used. The restoration effects were investigated through analyses of soil properties in cases of with/without the alkaline material. It was found that the biological environment of reduced sludge was restored by the use of the alkaline material; namely, macrobenthos are able to inhabit in the sludge within the alkaline material. The results also ensured that dissolution of the alkaline material removed electrons and protons that accumulated during the biodegration of organic matter in sludge. Therefore, COD and hydrogen sulfide declined, leading to the enhancement of biological environment restoration.

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 In this study, the effect of elevation, vegetation and sediment stability of habitat for the endangered tiger beetle larvae were examined in a sandy shore created for the purpose of mitigation for the loss of their original habitats. We found that the following three requirements of larvae. 1) The elevation of habitat was within a range of T.P. 0.7m - 1.0m. 2) The vegetation was under 25%. 3) The coefficient of variation for sediment stability was under 6.7%. We extracted the locations that correspond with these three conditions of the habitat by GIS analysis and found a place suitable to the larval habitat. We propose the creation method for the larval habitat that is a vegetation removal, making relatively small impact on the environment and securing a large area.

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 The Yatsushiro Bay in central Kyusyu, southwest Japan is representative enclosed sea in Japan. Recently, various environmental degradations are reported occur in Yatsushiro Bay, as decrease of fishery resource and eelgrass bed.
 In this study, we tried growth environment evaluation of eelgrass by using HSI model in Yatsushiro Bay “Nosakanoura”. As a result of field data, eelgrass had been grown at the unique environment in Yatsushiro Bay “Nosakanoura”. We showed the restoration technique and the factor which obstructs growing of eelgrass bed.

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 We observed the seasonal changes in eelgrass (Zostera marina L.) beds formed in the natural state off Miya, in Mikawa bay, Aichi Prefecture, Japan from 2009 to 2011. And we calculated Shields numbers on the sea floor from the sediment composition and wave heights and underwater light quantum density at the position of the sea floor and 0.5 m above the same point. This eelgrass bed had been maintained by nutrition shoots from winter 2009 but disappeared completely in winter 2010; it then reappeared from seedlings in summer 2011. The maximum Shields number observed was 0.23, in summer 2010—this was more than the limit at which eelgrass beds form, namely value. The cause of the high value was found to be the large waves. The light quantum density at noon was below the saturation value for eelgrass, namely 300 μmol m^-2s^-1, on 50% or less of the observation days. The cause of these low values was found to be water turbidity. These results suggest that any eelgrass-bed construction engineering to be performed in this area will need to be able to stabilize the bottom sediments and increase the amount of light reaching the bottom layers.

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 Barren ground is widely distributed in the sea area. The coastal structures to make the algae place have been constructed for about ten years. However, it is feared that the decrease in the effect of seaweed creation by the aged deterioration of the substrate. The occurring condition of Barren ground is that feeding pressure of sea urchin is greater than growth rate of seaweed. It is necessary to calculate the growth of the seaweed and the revenue and expenditure of sea urchin's food consumption correctly.
 In this study, the quantification of the seaweed biomass was examined by factors of environment with a remarkable change. Variability characteristics of the seaweed amount and a physical environment were clarified. Finally, the improvement of the calculation method of the amount of the seaweed was achieved.

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 The aim of this study is to utilization substitute and reproduction by a seaweed flora damage, a decline of the fauna on the seaweed. This study on artificial fish reef use a gin block(30 cm×30 cm), four experience plate(Fig. 3, Blank(no plate), flyashi (4 cm×4 cm:B), flyashi and charcoal (4 cm×4 cm:C), flyashi and charcoal(10×20:D)) is disposed inside the inter frame and fixed at 4 cm of intervals(C, D).
 This fish reef, B and C have much biomass, approximately equal to a contrast point (F, G), an attached algal coating rate, increased with progress of the time, not the fall, too. It was revealed that the artificial fishing bank sufficiently functioning as a fishing bank in an early stage after being sunk in water.

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 Marimo is a spherical algae, which consists of freshwater filamentous green algae, in Lake Akan. The process for making a spherical algae, whose diameter is up to 30 cm, has not been clarified. Although Marimo is registered as a nationally protected speices, the number of Marimo has been revealed to decrease. Wind wave is considered as one of the most significant factors for a formation of Marimo. However, the mechanisms of the formation have not been clarified, which could provide policies how to protect Marimo in Lake Akan. This study thus aims to investigate how a spherical shape is formed under wind wave conditions by using video camera, wave measurements, and meteolorogical observations. As a result, wind wave is revealed to be one of the significant factors that form Marimo in Lake Akan.

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 This study used numerical analysis to evaluate Enhalus acoroides seed dispersal in the northwestern sea area of Iriomote Island, Japan. Input data for numerical simulations were provided based on results of an ecological investigation of Enhalus acoroides and field observations of physical phenomena. Reproductions of coastal currents in the northwestern sea area of Iriomote Island were conducted using an ocean current model CCM. Enhalus acoroides seed dispersal characteristics were examined using particle tracking analysis.
 Results showed that the average value of seed migration distance is 261 m per 2.4 hours, which is the average time of the seed flotation. Moreover, the exchange of seeds between the remote colonies was slight because of the short migration distance. The results show that Enhalus acoroides seed dispersal in the northwestern sea area of Iriomote Island is extremely weak.

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 An areawide research result of Enhalusacroides, subtropical seeglass and the endangered species, distributions and growing conditions and the simulated area wide distributions of wave and current, using hydeleulic model of SWAN and CCM for typical winter high wave and spring tide conditions . The suitable condition of the wave and current have been extracted that, D.L. -0.76 min depth, 25-32 cm in H_1/3, 11-19 cm/s in bottom flow, and 0.1-0.3 m/s in residual current. The numerical simulations with these conditions can reproduce the present state of the distribution of E.a. phytocenosis, and reveal that the physical conditions affect strongly the distribution.

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 We developed estimation technique of spatial coral distribution using data of coral distribution investigation, oceanic-atmospheric-river observations and numerical simulations using ocean and wave models. The conclusions are in the followings; (i). There is good correlation between estimated value of this technique and surveyed coverage of coral. (ii). Polygonal line function that has been optimized using artificial intelligence by genetic algorithm, were obtained better results than multiple regression analysis. (iii). This technique make clear the characteristics of the physical variables of impact on coverage of coral.

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 We investigated the relation between massive coral distribution and physical variables in Amitori Bay, Iriomote Island, Japan using coral distribution investigation, oceanic-atmospheric-riverine observations and numerical simulations using ocean and wave models. The conclusions were the following: (i) Massive coral coverage shows an inverse relation with water depth. (ii) Massive coral coverage shows an inverse relation with other coral coverage. (iii) Massive coral coverage shows a weak relation with wave height. (iv) Genus numbers and coverage of massive coral show an inverse and a direct relation with soil particle quantities, respectively. The relation in (iii) is attributable to the strong wave tolerance of massive corals because of their form and stiff skeleton, and to the slight difference of wave height between the east and west sides of the bay. The relation in (iv) results from the fact that Porites with strong ability of mucus removal can survive easily on the east side with large quantities of soil particles, although various coral genera can inhabit in the west side with small quantities of soil particles.

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 The relationship between beach topography and coastal vegetation was investigated by field investigations in the marginal area of Banzu tidal flat in Tokyo Bay. The longitudinal profiles, grain size distribution, and the distribution of coastal vegetation were measured across the barrier (sandy beach). When sandy beach is eroded, the shoreline shape becomes to be concave with the formation of a scarp, which results in the reduction of vegetation zone. To preserve the coastal vegetation area, the relation between the coastal vegetation area and the deformation of sandy beach (barrier) must be deeply understood.

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 Fluorescent and colored sands have been used to trace sediment movement in coastal field observation. A huge cost is required to detect these tracers from sediment samples by use of conventionally human inspection. Many computer-assisted digital image analysis techniques for the detection system have been developed in the context of price reduction of digital imaging devices in recent years. However, these methods give insufficient accuracy of detection. For instance, it would be difficult to find one tracer particle from the large-volume sediment sample by using fully automated image analysis. In this study, we developed a detection method of colored sand tracer based on a combination procedure with computer image analysis and human visual inspection. The digital-image-scanning procedure was determined experimentally by laboratory tests with regard to sediment sample weight, means of pasting sediment and its image resolution. Furthermore, final check of results from the image analysis made high accuracy of detection by the human inspection with trimmed-image outputs from the analysis program. This method was well balanced for cost-benefit among analysis time, the accuracy and human workload. In particular, it is efficient for colored sand detection tasks with a large number of sediment samples because of untired computer-assisted procedure.

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 For wave disaster mitigation, it is essential to collect and analyze a wide range and long-term continuous information of beach monitoring, for which the required cost and time can often be enormous. On the data collection stage, the authors have already established an inexpensive local remote sensing method to obtain continuous beach images from a network camera. In this study, accordingly, focus was placed on the improvement of the efficiency and availability of the shoreline extraction in the image processing. In the previous studies, binarization analysis based on the threshold of luminance value or manual processing with digitizing device have frequently been used as a method of the shoreline identification. The former lacks applicability and stability in the field, and the latter has drawbacks in efficiency. In order to improve the efficiency as well as to extend the range of applications, this study proposes a novel image analysis method that can automatically extract the position of the shoreline under a wide range of conditions. The applicability to the analysis of waves and currents has also been examined.

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 X-band radar measurements have been applied for rip current observation. Radar images were collected at research pier HORS on a straight sandy coast. Time averaged images of every 2 minutes have been processed, which frequently display characteristic cross-shore patterns that resemble to neck and head of a rip current. An image analysis program is developed to detect rip current occurrence and estimate migration speed of rip heads. Results were compared with manually inspected results of the radar images, and fairly well agreement was confirmed. Results of the detection are correlated with tide and weather conditions.

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 The coastal areas of eastern Japan suffered extensive damage from the tsunami that followed the 2011 earthquake off the Pacific coast of Tohoku. The damage to coastal woods on the Sendai plains of Miyagi prefecture was particularly significant. For future management of the surviving coastal woods, it is necessary to analyze time series changes and to maintain the area effectively. To date, the use of time series satellite observations in assessing the recovery process has not been adequate, and long term monitoring with high-resolution satellite remote sensing has only rarely been performed. In this study therefore, the disaster and recovery of coastal woods on the Sendai plains were evaluated using high-resolution, time-series satellite remote sensing, and changes in the woods were analyzed using a detailed image interpretation of the images acquired. Furthermore, the distribution of the vegetation index value was observed using these images, and the recovery process of the coastal woods was assessed in this respect.

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 Coastal environmental sound was measured at three locations, the Sagami-nada Coast, Odawara; Oiso; and Fujisawa. The loudness of the sound was correlated with distance from the shoreline at a wind speed of less than 4 m/s. The sharpness of the sound had a negative correlation with wind speed. Moreover, organoleptic examination was conducted to investigate the comfort level of the sound. From the results, we found that the coastal environmental sound consist of two factors, a power factor and a clarity factor. The power factor can be estimated from loudness, and the clarity factor can be estimated from sharpness and the wave breaker index.

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 It is approved that retaining walls, reinforced by geogrid, have considerable earthquake resistance. Thus, it can be also effective to use a reinforced earth work by geogrid in harbor structures (for example, sheetpile quaywall). It is important to obtain friction characteristics in order to consider reinforcement effects by interaction of mesh of geogrid and soil particles. In this study, pull-out tests are conducted with defferent soil particles sizes or surface loads, in order to obtain the friction characteristic due to the interaction of a geogrid and backfill. The results show that larger friction angles can be obtained by usuing a backfill of smaller soil particles.

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 Wharves comprised of wave absorbing concrete units had a destructive damage by the 2011 Tohoku Earthquake tsunamis. With such structures, a cover concrete plate is generally placed on the top to resist wave loadings and earth pressures. However, the thickness of the cover plate is usually minimized for the purpose of easy handling of cargos and economical constructions. Therefore, the cover plate may be easily damaged when a tsunami attacks a wharf and an overflow above it begins. In this study, the stability of a cover concrete plate and wave absorbing units under it against tsunamis was examined experimentally. Especially the stability of the cover plate against tsunami inundations was precisely observed not only for the steady state condition but also for the initial unsteady situation. For the practical design, the hydrodynamic coefficient such as a lift coefficient of the cover concrete plate has been examined extensively. Also the possible counter measure of a low reflective wharf comprised of wave absorbing concrete units against tsunamis was proposed.

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 Authors have developed a wave power generation system using a vertical slotted breakwater with water mills in the chamber. It has been already shown that the wave absorption function of the wave power generation system is superior than a vertical slotted breakwater without watermills. In this study, reaeration capacitance of the wave power generation system is investigated on the basis of experimental results and previous research knowledge. It is presented that the reaeration capacitance of the wave power generation system can be estimated by experimental formula for a vertical slotted breakwater with wave reflection coefficient. It is presented that the reaeration capacitance of the wave power generation system can be estimated by experimental formula for a vertical slotted breakwater with wave reflection coefficient.

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 Design method for single layer armor units is proposed considering wave dissipation characteristic and structural strength. A new wave dissipating block has been developed from the viewpoint of stability, hydraulic characteristics, construction condition and so on. In order to investigate impact strength of the block, drop test was carried out, and corresponding FEM analysis was conducted to elucidate fracture mechanism of the block. Design method to satisfy the requirement of void ratio and structural strength is discussed based on FEM analysis.

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 Lack of technical experts and inheritance of skills to the next generation has been serious problems in construction sites. In this study, the authors try to quantify experiences and skills of technical experts on how to handle a mooring cable and how to operate a winch. In the trial, the tension in the mooring cable and the oscillation of the caisson were measured in installing caissons. The authors show that the cable with larger tension at the time when a caisson is drawn is different from that at the time at the time when a caisson is placed on a rubble mound under the conditions targeted in this study. They also show that the tension of each cable is the largest when a caisson is drawn.

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 Tsunami generates water level difference in front of and behind a caisson-type breakwater, and it induces seepage force acting on the mound. Although it has been found that seepage force reduces the bearing capacity, a specific reduction ratio and the method to calculate the stability under seepage has not been clarified yet. The present study investigated the effect of seepage force by comparing two different tests: a loading test and a compound test of loading and seepage. Furthermore, the model tests were simulated using the finite element method. The two different tests showed the same failure mode and the reduction ratio of the bearing capacity of 10 ~ 16 % due to seepage. The analysis could reproduce the same failure mechanism as the model tests, and it could also simulate the limit load.

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 Caisson-type breakwaters attacked by tsunami have large wave force on the side and uplift force on the bottom. One of the reinforcement methods is to pile up rocks behind the caisson, and the resistance mechanism, however, has not been clarified yet. The present study investigated the deformation and failure characteristics of a breakwater subjected to a horizontal load by using the centrifuge technique, which can simulate the prototype scale stress. Fine sand was utilized to visualize a failure mode, and two modes could be seen in the tests. The resistance mechanism in the case of rocks would be thought to be the same as one of sand. In addition, the study conducted circular slip analyses. Although the location of the slip surface had some problems, it could accurately simulate the limit load.

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 Water-level difference induced by tsunami may cause boiling in a caisson-type breakwater's mound, because it generates seepage force in there. The present study investigated a field of seepage force by numerical analyses taking into account the non-linear relation between hydraulic gradient and flow velocity. In addition, centrifuge model tests were conducted to know whether boiling occurred or not. Seepage analyses showed that the seepage force around the corner of a caisson was particularly large and it might generate boiling. The analyses indicated that the seepage force around the corner became larger and could reproduce centrifuge model tests by using the non-linear relation. The model tests using large-particle diameter stones demonstrated that boiling hardly occurred by the seepage force around the corner.

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 When The Tohoku-Pacific Ocean Earthquake occurred on 11th March, 2011, harbor facilities, such as breakwaters and tide embankments, suffered serious damages from the TSUNAMI. The following three mechanisms are considered to be related to the collapse of the breakwater: 1) scouring of the mound due to overflow, 2) the horizontal force originated from the difference of water level between the sea side and the harbor side on the breakwater, and 3) reduction of bearing power of the mound resulting from seepage flow. However, the mechanism of the instability of the rubble-mound by overflow and seepage flow induced by TSINAMI is not fully clarified. In this study, the formula to calculate the stable weight of rubble-mound was proposed in consideration of the overflow and seepage flow, and hydraulic model experiments were conducted on Kamaishi Bay breakwaters as the subject in order to confirm the effectiveness of the proposed formula. Using the results, the stability of the breakwater was evaluated from the view point of the geotechnical engineering.
 As the result from this study, following conclusions were obtained.
 (1) More accurate stable weight of the rubble-mound can be calculated than the existing formulas by considering the seepage flow.
 (2) The validity of the proposed formula was revealed from the results of the hydraulic experiments.

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 After the field survey of structural damages in Tohoku earthquake disaster, coastal engineers recognized the importance of persistent coastal structure to reduce tsunami inundation on coastal area. In order to realize the persistent structure, it is important to understand the mechanism of structural damage under tsunami actions. This study focuses on the failure of breakwater caused by the local scouring on a rubble mound due to tsunami overflow. The problem of the local scouring due to tsunami overflow includes complex interactions between vortex flow and rubble mound. This study employs a numerical simulation method based on SPH model to reveal the characteristic of rubble mound deformation under several tsunami overflow conditions. Furthermore, this study proposes a countermeasure that consists of a horizontal plate to check the rubble mound scouring. Efficiencies of this countermeasure are also investigated in this research.

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 Disposal of waste becomes the problem with radioactive cesium caused by the first Fukushima nuclear plant accident of March 2011. In this study, we focused on the coastal disposal facility which can dispose of the mass waste and developed the cutoff materials for the disposal facility. As a cutoff materials for the disposal facility, we mixed bentonite and zeolite in marine clay and examined the cutoff performance and the adsorption performance for cesium by an indoor experiment.
 As a result of experiment, the cutoff performance improved by adding bentonite to marine clay and maintained regardless of addition in zeolite. In addition, the adsorption performance for cesium reduced by adding bentonite to marine clay, but improved drastically by addition in zeolite.

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 Steelmaking slag is recently applied as coastal construction material, especially for coastal environmental improvement works. Steelmaking slag has higher CaO concentration so that alkalinity of surrounding seawater is important for appropriate utilization. In this study, influence of alkaline elution from steelmaking slag in ocean construction area was investigated, and alkaline elution simulation from steelmaking slag piled in seawater was calculated. Early stage after the construction, pH value tended to rise near the sea bottom, and its value is around to 0.05. This pH rising decreased gradually with time, and this gap was not observed one month later. Alkaline elution abilities of steelmaking slag recovered from sea bottom were confirmed that they became lower than initial slag's one. By using these alkaline elution properties, the pH value observed in this investigation was reasonably simulated by an analytical elution model from the slag piled.

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 The burden of the thermal power generation for national power supply has been increasing in Japan since the Great East Japan Earthquake that occurred in 2011. The coal is used as the main fuel for thermal power generation, and ash is discharged after utilizing coal for fuel. Because a lot of coal ash has been forced to landfill to waste disposal sites, bulk compression of coal ash is urgently required to keep sufficient space of the sites for waste dumping. This paper is to propose two methods for bulk compression of coal ash. One is a vibrating compaction method by inserting a rod into the ground while excess pore-water pressure is dissipated through a drainage layer. The other is a pressure injection method of fly ash after the fly-ash ground is unsaturated by use of dewatering method. The effects of the proposed methods have been confirmed by laboratory experiments and numerical analysis.

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 Increase of sludge sedimentation caused muddy condition of tidal flat in the Ota River estuary. To improve the sediment condition and make a habitat for short-necked clam, granulated coal ash (GCA) layer was built as permeable layer in tidal flat in 2011. In this study, groundwater flow and groundwater quality in GCA layer were measured to understand the groundwater flow after 2 years from GCA layer construction. Groundwater fluidity was investigated from continuous measurement of groundwater level in GCA layer.
 Groundwater fluidity in GCA layer was kept high after 2 years from GCA layer construction. Moreover, it was understood that chlorophyll-a, oxygen, and suspended substance were transported due to the groundwater flow.

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 The vacuum consolidation method with prefabricated vertical drains (PVD) is one of the most effective methods to improve the soft ground. In this method, the PVD installed in soft ground was bended along with the consolidation settlement. As a result, the drainage performance of the PVD might be decreased. A series of laboratory tests were performed to evaluate the bending effect on the consolidation behavior in PVD. First, the large scale model tests were performed to measure the bending shape of PVD by the vacuum consolidation. In these tests, the clay slurry at a water content of 150 % was consolidated under the vacuum pressure of 60 kPa in the consolidation cells, which were 5 m in height and 30 cm or 76 cm in diameter. Second, the permeability tests for PVD were carried out under a given constant water head difference. In these tests, three types of PVD were used as samples, i.e., the straight PVD, the moderately-bended PVD whose shape was observed in the large scale consolidation test and the sharply-bended PVD. It was confirmed, based on all the test results, that the consolidation speed was not delayed even by the bended PVD on usual site.

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 This study investigates the generation of excess pore pressure during sequenced earthquake motions. Such sequenced earthquake motions possibly contributed to the devastating liquefaction in coastal areas in the 2011 Tohoku Earthquake. A series of shaking table tests were performed with a model ground of a uniform sand layer constructed in a laminar box. The significance of the intensity of earthquake motions and quiet intervals between shocks are studied. The test results are compared to a numerical calculation based on the Finite Element Method. Furthermore, the applicability of a conventional intensity measure for liquefaction, i.e. shear stress ratio, is examined for sequenced earthquake motions. The analysis shows that, for a certain range of quiet intervals, pore pressure generation during aftershocks can be reasonably explained by shear stress ratio.

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 The present study investigated and elucidated the liquefaction characteristics of sand-clay layered ground under sequenced earthquake motions by performing a series of shaking table tests. In particular, we evaluated the influence of aftershoks on the liquefaction. Futhermore, we examined the effects of two different compaction methods, namely, sand compaction pile and compaction grouting, on the liquefaction in sand-clay layered ground. The resuts demonstrate that the CPG-induced sand densification and increase in the horizontal effective stress contributed to surpressing liquefaction. By contrast, the application of the SCP is found to work effectively in light of the three distinct mechanisms involving densification, stress enhancement, and partial drainage through the sand pile penetrating the clay layer. These findings are important for the rational liquefaction assessment and its countermeasures of sand-clay layered ground.

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 The authors propose a new configuration of columns, which is called irregular configuration. The presented configuration is considered to reduce the amount of subsoil that passes through the in-between gap of columns, compared with the square configuration. To design the cement-treated soil columns passing through laterally flowing liquefied layers it is necessary to quantify the loads that might be applied to those columns by the flowing soil. Pile bending moment were measured by using centrifugal model tests and lateral loads were calculated from the distribution of bending moment. It was found that lateral loads applied to piles by the lateral flow is similar to that of the Japanese Highway Bridges Code.

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 Characteristics of soil have to be changed in order to prevent lateral flow of liquefied soil completely. However, their construction cost is high and impracticable when the target area spreads widely. The improvement method should be more feasible. The authors are investigating the most effective arrangement of piles to optimize cost-effectiveness. It is proposed to shift the positions of the piles to prevent lateral flow in various directions. In the present study, centrifuge model tests and analyses were conducted to clarify the improvement effect of piles against the lateral flow and the pile arrangement in detail. The results of the model tests and numerical analyses showed that the improvement by piles dramatically reduced the lateral displacement and that the average total flow velocity was small in the irregular arrangement case.

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 In the vertical drain method using plastic board drain for a working disposal pond, it is important to maintain horizontal drainage because the subsequent dredged clay is piled up on the ground surface installed vertical drains. In this paper, the settlement of ground level installed vertical drains, thickness of subsequent dredged clay layer on the ground installed vertical drains, pore water pressures in the ground and water pressures in the vertical and horizontal drains were measured until 14 months after the installation of vertical drains, and these results were evaluated.

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 In this paper, the effect of artificial cavity beneath concrete slab on the mechanical behaviors of concrete pavement was discussed based on the results of FWD tests. Traffic loading was repeatedly applied to the pavement, and then the change of deflection and flexural strain at the bottom of the slab were evaluated by FWD. The following results were obtained from the tests. 1) Increasing rate of the deflection and the flexural strain due to cavity was larger at the edge of slab than at the center of slab. 2) Crack generated by traffic load was only observed at the bottom of the slab edge. On the basis of the test results, the authors indicated the possibility that cavity beneath slab edge had greater effect on soundness of pavement than cavity beneath the center of slab.

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 Box-shaped steel sheet pile with clayey geo-material has been constructed in order to apply as impervious seawall of the waste disposal site in coastal area. Box-shaped steel sheet pile has double joints where are sealed by water-swelling sealant, and it is secured a basic impervious performance. By filling the clayey geo-material into the chamber that sandwiched the joints as a fail-safe, the impervious performance of box-shaped steel sheet pile is improved. Field installation and permeability test for box-shaped steel sheet pile were conducted to demonstrate the workability and the impervious performance in the field. As results, breakage of box-shaped steel sheet pile did not occur during installation, and it was possible to install accurately. In addition, by simple method of observation on the change in water level, the impervious performance of box-shaped steel sheet pile was able to be evaluated easily.

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 The horizontal permeability of artificial cutoff geomaterial for off-shore waste disposal facility was studied. Considering the safety of waste disposal site against the strong earthquake, the permeability of geomaterial after shear deformation must be taken into account in the design. The horizontal permeability of cutoff geomaterial which was made of marine clay and bentonite was measured after K₀ consolidation and the torsional shear to 20% with the hollow cylinder torsional shear testing apparatus. It was found that the horizontal permeability of cutoff geomaterial was not affected by the shear deformation. Measuring coefficient of permeability of horizontal direction. The method presented in this study seems to be available to measure the horizontal permeability of clay after shear deformation.

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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. Precise estimation of bearing capacity has been required. Estimation of bearing capacity of large diameter and deep embedded piles complex problems such as bearing capacity increment because of deep embedment and bearing capacity decrement because of decrement of plugging effect by using large diameter piles. In this report, focusing on pile plugging phenomena, pile plugging mechanism was investigated. Open ended model pile penetration experiments were conducted and coefficient of earth pressure inside of the pile was estimated. Then inner friction force distribution was estimated. As a result, inner friction around the toe of the pile is large and it rapidly decreases along with upward of the pile.

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 A new construction method of artificial tidal flat is developed, in which clay slurry is injected under the fixed layer covered by sand layer. The fixed layer of 70-100 cm thickness made of clay -steel slug mixture of clay is placed under the covering sand layer in order to increase the volume of clay slurry from a single injection point. To study the effect of the fixed layer, a numerical analysis and laboratory model tests were carried out. The volume of injected clay was 60% the calculated where the fixed layer was assumed as an elastic layer. This is because the fixed layer failed by the tension cracks. However, when the fixed layer was reinforced by the rope net method, the volume of clay slurry that could be injected was equal or more than that calculated in the analysis. By the reinforcement of rope net, the expansion of tension crack in the fixed layer was prevented and the injected clay expanded uniformly under the fixed layer.

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 Clay slurry has been used for various purpose in construction works of port and harbour, such as back-filling of revetments or cut-off layer covering sand seabed for off-shore waste disposal sites. For these uses, the large unit weight of clay slurry is desirable. The mixing the slurry with gravel or steel slug is a probable way for increase the unit weight of clay slurry. In this study, the time-settlement property of single solid in clay slurry was investigated by the laboratory test. The stability condition of single solid is given as a safety factor of bearing capacity of clay layer. The proposed safet factor was related to the results of experiment on serigration of clay-slug mixtures.

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 Steel making slag has a property of curing reaction with water as hydraulic solidification. Refined steel making slag of particle size of 75 μm or less may have more hydraulic solidification characteristics. Steel making slag is effectively used for raising ground level of port facilities or constructing levee, if geo-material mixed with refined steel making slag has enough solidified strength. In this research, characteristics of steel making slag and sand mixed with refined steel making slag were investigated considering to use these material used as an artificial geo-material used for near shore construction. This paper reports the effect of aging treatment of steel making slag to geo-material mixed with refined steel making slag and the effect of pore water to solidification acceleration to the mixed geo-material.

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 The artificial stone is produced by dredged soil mixing with steel by-products such as converter slag and ground granulated blast-furnace slag. We examined the ideal compounding ratio and performed some production tests for common artificial stone and light weighted artificial stone. In the combination test, we determine a relational expression which enable estimation of the target strength and slump, and we confirm some characteristics for two different types of artificial stone in the production test.

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 In this study, mix proportion, quality and construction performance of anti-washout underwater concrete using copper slag and electric furnace oxidation slag were examined. As a result, flowability and pumpability of concrete had good performance, but suspended solid content in water was increased. In the strength design must be considered the variation of compressive strength due to slag. However compressive strength can be estimated by using cylinder concrete specimens that was casted in water. Unit mass design can be estimated by mix proportion design. In this study, maximum unit mass was 3.0 t/m³. When flow distance in the water was 5m, quality of concrete had been keeping.

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 As a fundamental study for establishing numerical analysis technology that can compute dynamic interactions between tsunamis containing suspended sediment, behavior of coastal protection facilities, seabed profile change such as local scouring, and seabed response, parameters of an evaluation equation for the viscosity of a fluid containing suspended sediment were identified from laboratory experiments using a viscometer. It was confirmed that while clear water was a Newtonian fluid because its viscosity was independent on the shear stress, muddy water containing suspended sediment was a non-Newtonian fluid because its viscosity decreased with an increase in the shear stress. Furthermore, it was found that once suspended sediment concentration and shear stress are given, the viscosity of the muddy water can be determined from the evaluation equation using the identified parameters.

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 The rip current occurs at the wave breaking area near the beach, and the accident that is related to the rip current occurs every year in the world. Some generation mechanisms of rip current are known. For example, the rip current occurs at the sand beach that has the cusp topography, and occurs near structures such as the groins. In Niigata, there is not many large beach, and ordinary the beach is enclosed or semienclosed by the groins those were built to protect from the coastal erosion. This study tried to comprehend the generation mechanism of the rip current at the enclosed or semi-enclosed beach by the groins. Firstly, this study did field survey and comprehended the large scale and velocity of the rip current. In this method, the rip current was pigmented by the sea water colorant, and the pigmented current was observed by the velocity meter and recorded as the aerial photography by the UAV. Secondary, this study reproduced the rip current by the numerical simulation. The result was compared with the field data.

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