In order to be sure there is vast offshore wind energy potential on the Japanese coastal areas, we observed offshore wind climate on the Pacific Ocean near Fukushima pref. And to use the energy, we developed offshore wind power generation systems. At first, this paper presents the observation result that shows wind climate characteristics are good for wind turbines as well in Europe. Also, we developed two types of offshore wind power generation systems, one is installed on seabed and another is floated on water. And both can be safe from Japanese severe natural conditions.
The energy of waves to Japan's coasts is estimated to be at about 35 million kW, which is the one-third of the total electric power generated in Japan. Many attempts to exploit wave energy have been made from old times. After the first oil crisis research and development projects of wave power converters have been made in the world and various converters were developed including a wave power extracting caisson breakwater. However no system has been employed as a practical power plant due to cost of the system and irregularity of the electric output. Recently the challenges started again to develop the converters as a consequence of recent high oil price. Innovations are needed for the technologies of wave power converters and the social systems to utilize the wave energy.
A feasibility study on the tidal current power generation by making use of a bridge pier in the narrow strait is introduced. Current velocity increases near the pier, therefore the tidal power generation becomes more efficient because the power is proportional to the cubic of the current velocity. Furthermore, the pier is convenient for the maintenance of the hydraulic turbine and the power unit. The project is now underway at the Ikitsuki Bridge in Tatsuno-Seto Strait of Nagasaki Prefecture. A Darrieus turbine is adopted for tidal current power generation because it is simple in structure with straight wings rotating around a vertical axis, so that it has no directionality against the motion of tidal flow which changes its direction twice a day. However, there is one defect in the Darrieus turbine; its small starting torque. Once it stops, a Darrieus turbine is hard to re-start until a fairly fast current is exerted on it. To improve the starting torque of the Darrieus turbine, a hybrid turbine, composed of a Darrieus turbine and a Savonius rotor is proposed. A combined Darrieus and Savonius turbine was tested in the circulating water channel. Finally, power generation experiments using a 48 pole electric generator were conducted in a towing tank and the power coefficients were compared with the results of experiments obtained in the circulating water channel.
Bio-productivity at the continental shelf is relatively high. Bio-productivity in this region should be maintained or improved for establishing sustainable fishery system. Authors reviewed methods for evaluating current structure and developing fishing grounds in this region. Three-dimensional current in the western of the Japan Sea was calculated by the hydrodynamic model. The performance of artificial reef for Upwelling nutrients from the bottom layer was estimated by the same numerical model. New measurement techniques were introduced, and importance of field survey, monitoring environment should be needed for maintaining and developing fishing grounds at the continental shelf.
Recently snow crab resources in the western Japan Sea have gradually gained a certain degree of recovery through measures such as limiting catches and establishing protective reefs. Fisheries Agency of Japan carried out maintenance of protective developmental reefs newly from 2007 in future in an offshore sea area by the direct control of the country to plan more resources recovery. Current snow crab protective developmental reefs have been aiming at the protection effect by the fishing operation prevention mainly. The effect of propagation that protective reefs possess will be confirmed in the future, and more efficient, more effective maintenance is requested. For that purpose, this report summarizes the actual effects of a snow crab protective developmental reef created at a depth of 290 meters in the Tajima-Oki Sea Area of Hyogo Prefecture over 1994 to 1996, in terms of (1) a habitat environment study, (2) a study of catch quantity, and (3) a visibility study using ROV. It also involves an examination of the functions and effects of protective developmental reefs.
Artificial upwelling producing structure is recognized to be effective for fertilization of the sea in recent years. In this paper, we describe the basic functions, benefits, and field observation results of artificial upwelling producing structure. The field observation results show that vertical mixing of seawater and propagation of phytoplankton appeared.
This paper summarizes the special session “Coastal Disaster Prevention-Asset Management for Coastal Disaster Prevention Facility-” This session has been planned on the basis of the discussion of the last year special session (Fukute et al., 2007). Presentations include (1) risk curve formulation and utilization on the life cycle cost, (2) an approach for asset management of decrepit social infrastructures and there perspective for the future, (3) development of evaluation system for asset management of port facilities, (4) research direction about changes in tropical cyclones associated with global warming, and (5) development of shore protection facilities database using GIS. After presentations, the subjects for applying the asset management to coastal disaster prevention facilities have been discussed. Throughout the presentations and discussions, many important matters have been pointed out.
Recovery of the marine resources in Exclusive Economic Zone (EEZ) is the urgent subject in Japanese fisheries. Therefore, the Fisheries Agency revised the Act on Development of Fishing Ports and Grounds, and established the fishing ground development program under the direct government control what is called “Frontier fishing ground development” in 2007. This paper presents a summary of the special session “Development of Fishing Grounds in Offshore Deep Sea”. The target of the special session is to identify new technologies which are necessary to promote the fishing ground development program in the offshore deep EEZ. The special session consists of the presentation of the papers regarding “Development of Fishing Grounds in Offshore Deep Sea”, and the other part is discussion among panelists presenting the papers.
It was reported in model experiments that the tsunami wave penetrated to very shallow water area is dispersed to solitary waves. A long period tsunami wave, however, cannot be generated in a usual experimental flume due to limitation of flume length or hydraulic scale effect. In this paper, the numerical experiments using a Boussinesq type wave transformation model are conducted to observe the deformation of the long period tsunami wave on a slope or a step reef. The numerical experiments have shown that solitary waves dispersed in front of long period tsunami wave start to appear at the small depth on the slope and grow up on the step reef. The solitary waves in front of the reflected long period tsunami wave also grow up on the slope with negative gradient.
It is concerned that indirect damages due to tsunami like collisions of drifted objects such as boats, automobiles. containers, etc. are severe as well as direct damages. To predict and reduce these kinds of damages, the characteristics of drifted container are experimentally investigated with installing different types of structures on the apron. As a result, it is found that in case a sea wall is installed, drifted container has less possibility to collide sea wall because water between the container and sea wall is working as a buffer. On the other hand, there is good possibility for the container to be drifted to offshore and fall down. The wave force acting on the fixed container can explain well the mechanism of this phenomenon. Moreover, it is found that in case rectangular finite structure is installed, drifted container would flow away beyond the structure due to long period wave.
A sediment transport formula coupled with dynamic effective stress inside a sand bed was proposed and incorporated into an existing topographic change model so that local scour could be reproduced under severe wave action such as run-up tsunamis, and topographic change simulation on tsunami-induced local scour around a square structure was performed to verify the applicability of the proposed model. Compared with hydraulic model experiments, the present model improved the computational accuracy of not only the initial stage of local scour at the seaward corner of the structure but also the maximum depth of a scour hole after tsunami wave action; hence, the present model was very useful in predicting deposition and erosion patterns under a strong influence of effective stress inside a sand bed.
Disasters caused by coastal hazards such as tsunami and storm surge tend to exceed protection targets for structural design. Such disasters, whose frequency of occurrence is very low, cause severe damage. In case of considering countermeasure for preventing disasters, mitigation of disasters by facilities of port and harbor is important. Therefore, this paper describes the results of two-dimensional simulation by ground height model. This results suggest a possibility of mitigation of disasters by facilities of port and harbor.
In the design of a horizontal plate, uplift forces generated not only by normal waves but also by tsunami must be considered. In this study, we conducted a hydraulic model test and a numerical simulation (CADMAS-SURF) in order to investigate the characteristics of uplift forces by tsunami exerted underneath a deck of horizontal plate. The maximum uplift pressure by tsunami is almost equal to the hydrostatic pressure induced by the rise of water surface, and the uplift force can be reduced by preparing openings to discharge the trapped air under the plate. The calculated results of water surface and uplift pressure by CADMAS-SURF were fairly well in agreement with the experimental results.
Four prefectures of Shikoku Island, Japan were appointed as the promotion areas for a countermeasure against preventing Tonankai-Nankai earthquake disaster. In the coasts of Shikoku Island, the hazard maps based on tsunami numerical simulations are usually made as the basic data for making plan of preventing tsunami disaster. Tsunami numerical simulations performed on the various conditions in different areas, and they become data basis for a countermeasure of preventing. Using integrated numerical research system, which facilitates the tsunami numerical simulation on coasts of Shikoku Island, this report evidences the problems about the tsunami prediction, examining the effect of input condition on the numerical results. It is recommended considers using the tsunami numerical simulations as the basic data for the hazard maps of disasters area.
Geometrical coastal line in big maritime cities is usually complex, since there are many reclaimed lands, many rivers and canals flowing into the sea. For such complex sea area, fine mesh scale is required for the estimation of tsunami propagation and deformation, resulting in increase in the computational time and cost. In this study, a new calculation method, called the Cartesian cutcell method, is used for predicting tsunami propagations and the numerical results are compared with the experimental observations. In the Cartesian cutcell method, the finer mesh is not required even for the complex geometrical coastal shape.
Numerical simulations of tsunami run-up have been carried out to investigate the effect of open gap in a coastal forest zone parallel to the shoreline. First, a straight open gap perpendicular to the shoreline is considered and the gap width is changed. As the gap width increases, the current velocity at the end of the open gap increases first, reaches to the maximum and then decreases, while the run-up height increases monotonously. The maximum velocity is 1.8 times comparing with the velocity without the coastal forest at the opening ratio of 0.075. This is mainly due to the effect of in-flow from the both sides of the open gap. Next, for the condition of the opening ratio with 0.075 the effects of an open gap parallel to the shoreline in the forest and a zigzag arrangement of the open gap are investigated. It is concluded that the effect of those difference in the arrangement is not large on the run-up height.
An innovative ‘buoyancy-driven vertical piling breakwater’ is under development to protect harbor facilities against high waves and tsunamis. This breakwater consists of rows of steel pipe piles and each pile consists of upper and lower steel pipes. The movable performance and hydraulic characterisitics of the breakwater have been verified by the large scale hydraulic model tests. In addition, the performance of the breakwater in the sea has to be clarified for its realization. This paper reports the results of the field experiment by a real scale structure. The results clearly demonstrate that: 1) The fabrication accuracy and the placing accuracy of the steel pipes were excellent; 2) The rising time of the breakwater in the waves was within a few minitues; 3) The transmission mechanism of the wave force from the upper pipe to the lower pipe has been proven; 4) The marine growth around the upper pipe was little.
We evaluated the safety of four moored ships in the port of Shimizu against the Tokai earthquake tsunami based on the numerical simulations. We first carried out the tsunami simulation and obtained the tsunami wave profiles at four berths in the target port. And then we performed the ship motion simulations by using the tsunami waves as the external forces. The main results are: 1) The surging is the significant motion of the moored ship because the tsunami flows along the quay, 2) The larger moored ship moves widely and influences the mooring system because its natural period for surging is closer to the dominant period of the tsunami, and 3) The mooring systems for the large ships are relatively unsafe against the tsunami.
As an urgent and temporal evacuation facility from tsunami, floating-type evacuation shelter is proposed in this study. In order to understand incipient motion of the floating-type evacuation shelter after tsuami atacks, hydraulic experiment was carried out. In the experiments, On the basis of experimental results, the relationship incipient motion of floating-type shelter and wave property is presented.
The present paper gives the dynamics for the float-counterweight type wave energy conversion device which consists of pulley (s), wire (s), floats (s), counterweight (s), ratchet mechanism and tension pulley for the purpose of energy store. So far, authors have developed the mechanical dynamics model of the author's wave energy conversion device without tension pulley. The model has been found to be applicable by the preliminary test in the water tank experiment. However, it was recognized the wire between the driving pulley and the float can be slack in a period when water level is rising. This phenomenon is dangerous in operating the system, since wire suddenly changes form no tension state into stretched state when water level changes from ascending to descending. In this paper, the authors have developed the dynamics model which includes the effect of the tension pulley to prevent from the occurrence of wire slackening, and compared the results with those of the system without tension pulley.
The coastal areas of Japan are estimated to have vast offshore wind energy potential. In order to use large quantities of offshore wind energy, developing a floating body for offshore wind power generation applicable to deep sea areas. Several researches have been made to meet the requirements. In this study, we proposed truss spar and semi-submersible bodies, they have a long track expand about deep water drilling rig operation results. And solved the response and stress characteristics of the floating bodies. And the optimum floating body size and the mooring facilities were determined by the analysis systems.
Ocean wind is larger and more suitable for wind farm than inland wind. Recently, ocean wind farm has been constructed in Europe using 5MW wind power facility. Japan is surrounded by ocean and seems to be suitable for construction of ocean wind farm. However, the amount of the shallow and low wave energy area for ocean wind farm is limited except semi-enclosed bay like Tokyo bay. When we see Tokyo bay, shallow area (shallow more than 15m) is located north of Futtsu Point in Chiba prefecture. Such a shallow area is near to urban area, so the construction cost seems to be lower. In this paper, feasibility study on the ocean wind farm north of futtsu point in Tokyo bay is done compared with the other coasts of Japan.
It is strongly desired to develop a cost-effective wind turbine system of floating-type in order to gain the renewable energy resources. In this study, the SPAR-type floating foundations using reinforced concrete are examined. The regular and irregular wave experiments are performed for 1/100 scale models of the prototypes. Three models are examined, that is, a uniform cylinder moored at the gravity center, a uniform cylinder moored at the upper position and a stepped-type floating cylinder moored at the upper position. The experimental results are compared with numerical predictions using potential theory and Morison's equation. The stepped-type floating cylinder moored at the upper position has shown smaller motions than the uniform cylinders.
In order to utilize the offshore wind energy, the wind turbine of a floating type is expected for its realization. This paper presents motion analysis of a floating offshore wind turbine due to wind loadings considering the effect of rotor-rotation. The horizontal axis downwind turbine is mounted on a floating foundation of a spar-type. The wind forces acting on the blades are calculated by the blade element momentum method. In order to account for the effect of finite amplitude motion of the floating body and the rotor-rotation, the multibody dynamics theory is employed. The dynamic analysis is made in time domain. The numerical results have shown that the transverse and rotational motion around the axis of the tower is generated due to the effect of gyro-moment of the rotor-rotation.
In this investigation, numerical simulation for tsunami inundation was performed by using a detailed topographical model along the Ibaraki Coast. As a result, products such as tsunami inundation maps, computer graphic animations, GIS data, etc. were made to be used by local governments for making tsunami hazard maps or promoting tsunami disaster prevention measures. The tsunami source model of Empo Boso-oki earthquake was adjusted using tsunami run-up heights along the coast evaluated from damage rate of buildings at each village. Furthermore, characteristics of tsunami run-up along the river were examined by numerical simulation, which is carried out under both conditions that the river discharge exists or not.
The Niigataken Chuetsu-oki Earthquake occurred on July 16, 2007. The maximum magnitude of this earthquake was recorded 6.8 and the maximum JMA seismic intensity scale was recorded 6 upper, and Chuetsu area, especially around Kasiwazaki city, was damaged extensively. The Tsunami was occurred due to the earthquake, however arrived to Akita and Ishikawa shoreline. This wave was not big and there were not the extensive damage this time. However, the big tsunami following the extensive damage sometime occurs in the Sea of Japan. For example, the Tsunami due to Niigata Earthquake in 1964 became over 4 m wave height at Niigata City. Therefore, even if it was a small-scale wave and small damaged in this time, it is necessary to analysis how the people on the beach when the earthquake occurred thought, for example, how they imaged the arrival of tsunami and how to evacuate from the tsunami. Then, this study researched the hearing investigation for the people who was near from the shoreline when the earthquake occurred. The results mainly indicate that the more any evacuation route information should be shown, because the most people who come from another place do not know the information.
The primary objective of tsunami disaster mitigation is to reduce the casualties. The major cause of the deaths is drowning by tsunami current, especially during evacuation. In the paper, the causes of deaths are discussed through reference to past experiences. A fault tree is presented to summarize the physical danger posed by tsunami waves to the human body, and the personal danger is discussed based on the tree. The stability of the human body against wave front collision and tsunami currents is discussed and threshold conditions are proposed. The time for evacuation is usually very limited and the risk of encountering a tsunami during evacuation is often high. Walking in inundated areas during a tsunami attack is especially dangerous. Vertical evacuation is highly recommended.
Tsunamis cause various damages, resulting in a heavy toll in human live in many areas. From post tsunami surveys, it is also confirmed that some coastal and harbor structures, sand dunes and coastal vegetations can reduce the tsunamis behind them and mitigate disasters there. To prevent and mitigate tsunami disasters especially in the area that a tsunami comes soon after an earthquake occurs, structural measures to control tsunamis and non-structural measures to save human lives should be integrated depending on topographic, social, economical and cultural characteristics of the area. In this paper, a dynamic hazard mapping technique is developed to help the understanding of vulnerable areas against not only the worst tsunami in the area but possible tsunamis and the enhancing of people's tsunami awareness to increase preparedness against possible tsunamis.
Countermeasures against Tsunami disaster are an urgent matter in Kushiro region, which is located at south east of Hokkaido, since the region has experienced large-scale earthquakes several times in the past. The key role of Kushiro Port as a principle center for shipping activities mainly between eastern Hokkaido and Tokyo Metropolitan Area must be secured from Tsunami disaster. However, conventional countermeasures such as development of breakwater often requires considerable time and investment. Focusing on reduction rather than prevention of damage, this paper introduces a new concept of Tsunami countermeasure and shows a case study to design and construct “Tsunami Screen”in time and cost effective manner in Kushiro Port.
A system of performance-based design was introduced to the new technical standard for port and harbor facilities, revised in April 2007. The new standard allows greater flexibility of design while requires more advanced technical knowledge to designers. As an example, a high seismic resistant quay wall at Yokohama Port is designed in conformity with the new technical standard, examining a concrete method to specify performance requirement for quay walls..
New methods of evaluating the seismic coefficients for earthquake resistant design of quay walls against the level-one earthquake ground motion were introduced in the technical standards for port and harbour facilities revised in 2007. The methods are for caisson type and sheet pile type quay walls, and those for other structural types have not been examined yet. In this paper, we examined and proposed the methods of evaluating the seismic coefficients for cantilever sheet pile quay walls. The proposed methods are in consistent with those by the previous study and take into consideration of the effect of frequency characteristic and duration time of earthquake ground motion on the deformation quay walls.
New methods of evaluating the seismic coefficients for earthquake resistant design of quay walls against the level-one earthquake ground motion were introduced in the technical standards for port and harbour facilities revised in 2007. The methods are for caisson type and sheet pile type quay walls, and those for other structural types have not been examined yet. In this paper, we examined and proposed the methods of evaluating the seismic coefficients for double sheet pile type quay walls. The proposed methods are in consistent with those by the previous study and take into consideration of the effect of frequency characteristic and duration time of earthquake ground motion on the deformation quay walls.
The inertia force acting on open-type wharves on vertical piles changes according to the natural period of the wharves. The natural period also changes according to the section modulus of the piles. This means that an iterative calculation is needed in the design of the wharves and an effective method is desirable to reduce the number of iteration. In this study, we conducted the optimal design of the wharves using the conjugate gradient method. It was shown that the number of iteration can be reduced focusing on the shape of the response acceleration spectrum.
The reliability-based design method was recently introduced to the technical standard for port and harbor facilities. The standard method is partial factors method, however, other methods that evaluate the reliability index directly can also be applied. Taking the design of pile supported wharves as an example, performance function is implicit and the application of the methods that evaluate the reliability index directly is difficult to the practical design. This study aims at clarifying the applicability of response surface method for pile supported wharves. As the performance function can be evaluated explicitly by the method, the calculation of reliability indices is comparatively easy. The applicability of first-order second-moment method is also discussed.
A high seismic resistant quay wall at Yokohama Port is designed in conformity with the new technical standard for port and harbor structures revised in April 2007. The cell type quay wall is largest in the world (24.5m in diameter and 32m in height of the cell). Two-dimensional finite element analysis in effective stress is conducted for dynamic response of the quay wall. Stresses of steel cells, arcs and their joints are examined with three-dimensional static finite element analysis, in case of not only uniform but also inequable quay wall foundation.
Technical standards for port and harbor facilities were revised in 2007 and the deformation of quay-wall during earthquake became the controlled object in seismic safety verification. As an introduction to the establishment of the method for the determination of the allowable deformation for gravity type and sheet pile type quay-wall, this paper shows the statistical analysis on correlation between deformation of quay-wall during earthquake and its damage. Firstly, we gathered the damage data from the report of past several earthquakes and closely examined the collected data set. Secondly, we surveyed the correlation among the parameters focusing on the failure loss cost and recovery days. Finally, we conducted the multiple regression analyses and proposed the regression equations for the failure loss cost and recovery days according to the deformation of the quay-walls and other design conditions.
Design input earthquake motions considering influence of characteristics of earthquake source fault and soil deposit are being used in seismic design of structures in recent years. It is becoming necessary to examine the behavior of the structure under ground motions with period and duration property which had hardly been taken into consideration. A series of gravitational and centrifugal model tests was conducted in this study, to investigate influence of long-period and long-duration earthquake motion on gravity type quay walls. Applicability of the finite element analysis, FLIP, to long-period and long-duration earthquake motions is examined by comparing the results of analysis and tests.
In order to investigate the effect of cement-mixing for reducing the seismic damage of caisson type quay-wall, a series of shaking table tests in 1g gravitational field were performed in terms of the shear strength and the improvement range of cement-mixing. The main conclusions obtained form this study are as follows; 1) Cement-mixing behind caisson type quay-wall is effective for reducing the seismic damage of caisson type quay-wall. 2) For cement-mixed ground with a large shear strength, the seismic behavior of quay-wall sympathizes with cement-mixed ground as if cement-mixed ground and quay-wall are a combined structure. Consequently, the seismic earth pressure from liquefied ground is absorbed by cement-treated ground reducing the seismic earth pressure to quay-wall. 3) A formula to evaluate the sliding safety of caisson type quay-wall with cement-mixing was proposed considering the cohesive component of shear strength in cement-mixed ground. Based on the proposed formula, improvement range of cement-mixing can be reduced from a conventional range in current design code for cement-mixing.
This field is located in the estuary. The tidal flat is formed at low tide, and many water birds come flying here. In addition, short-neck clams and corbiculas lives in the riverbed. Therefore, it was necessary to attempt the decrease of the environmental impact by shortening of construction period or construction range reduction in this river. When we constructed earthquake resistant reinforcement of new Yahata river bridge, we used dry repair industrial method by temporary steel caissons these problems. As a result, we contributed to shorten the construction period.
The role of Airport during and after large earthquake is important as assist emergency medical service, stating special operation for transporting living necessities for suffers' daily life immediately and restarting commercial logistic operation to support the activities of the enterprises located around the airport. Full-scale experiment using controlled blasting was conducted in the Ishikari Bay New Port (Ishikariwan-shinko) in Hokkaido Island, Japan, to assess the performance of airport facilities subjected to the liquefaction. Airport facilities in this study included runway pavement with full specifications for B747 aircraft and apron pavement with/without countermeasures for liquefaction, air traffic control facilities such as the Glide Slope Antenna, the Localizer Antenna, drainage conduit and etc. This paper presents that the earthquake resistance improvement strategy and some of the test results while the measurement and investigation are progressing now.
Former types of the reclamation system and the pier system for ground held a problem that it is difficult on improvement of the load reduction to the circumference environment in case of bigger water depth. From a viewpoint of the load reduction, a floating structure of the buoyancy use type effectively is proposed. Because a floating structure as the artificial ground is used on a large scale, there is the thing that a seismic response depends on stiffness and the leg spring. This research investigates the relation between float stiffness and a vertical seismic response by a tank test and numerical analysis. As a result, when float stiffness is enlarged and the leg spring constant is set up small, the action load to a supporting leg turns out that it is advantageous.
A questionnaire survey was conducted at three sea bathing places having different attributes on recreational users to investigate the user's consciousness for Tsunami disaster mitigation. It was cleared that the attributes of both recreational user's age and distance from user's dwelling place to the beach strongly affect the structure of consciousness for Tsunami disaster mitigation. The consciousness for Tsunami disaster mitigation tends to become lower in younger age groups. Also, recreational users visiting from distant places show lower consciousness for Tsunami disaster mitigation than the users near the beach. Through this investigation, it is implied that the education about Tsunami disaster mitigation is important especially for younger age groups. Furthermore, this study suggests the importance of giving effective information about Tsunami disaster mitigation to the recreational users from distant places in order to notice the dangerousness of Tsunami disaster at the beach.
An investigation team comprised of coastal researchers and engineers carried out field measurements of rip currents and experienced drift by the current on Sagara Sun Beach during August 23-24, 2007 with help of lifesavers and surfers. The waves and rip currents were observed near the breakwaters and the data were analyzed from the viewpoint of the safety of the beach users such as sea bathers and surfers. Various water safety problems related to the rip currents were discussed based on the field data, real experience of the drift and information of the lifesavers. A steady rip current around 0.25m/s generated along a breakwater under calm sea condition yields dangerous situation to sea bathers and the degree of the dangerousness depends on the water depth as well as current velocity.
With the popularization of diving, its safety is an important issue. One of the factors of serious diving accidents is an abrupt downflow called “down current” by divers. However, its reality and mechanism are poorly understood. In order to make them clear, a continuous observation of current, wave, temperature, and salinity at the fatal accident site near the coast of Kumano Nada was conducted. In the 15 days of observation, we succeeded in observing downflows with vertical velocity up to 22cm/s. Some of the major downflows were accompanied by oscillations of velocity, temperature, and salinity, which were associated with long-period waves. By analyzing an aerial photograph and satellite images, the frequent existence of a density interface between river water and seawater on the accident location was discovered. It is concluded that this interface, along with the steep slope topography, would convert horizontal velocities into vertical ones, and thereby be a cause of “down current.”
A lot of water accidents have occurred at sea bathing areas in Japan, and an honorable life of 200 people or more has been lost every year. The purpose of this study is to create a lifesaving system at sea bathing areas to reduce water accidents. Our investigations are three kinds of parts. In the first place, we examine a situation of a lifesaving system in Japan. In the Second place, we analyze facilities of a lifesaving system at 73 sea bathing areas. Furthermore, we investigate the management system of lifesaving at KATASENISIHAMA in KANAGAWA prefecture. As a result, we show a concept of creating a lifesaving system. Moreover we propose that how many facilities are necessary to create a lifesaving system and how a management system of a lifesaving is created.
A field investigation has been carried out to investigate the damage of coastal, port and harbour facilities caused by the Niigataken Chuetsu-oki Earthquake in 2007. The instrumental JMA seismic intensity of a strong 6 was registered in Kariwa village, Kashiwazaki and Nagaoka cities, in Niigata, Japan. The damages to coastal, port and harbour facilities were investigated. The old seawalls at Osaki coast in Kashiwazaki were broken due to strong seismic motions. Several coastal facilities ware partly broken due to liquefaction occurred by the severe ground shaking. The corners of concrete caissons used for a breakwater were broken off due to strong collisions. There are many old woods appeared on a sea bottom surface after the earthquake in the region offshore from Izumozaki town to Kashiwazaki city. The woods might appear to floating up to the sea bottom surface due to the liquefaction of sea bottom sediments.
Full-scale experiment using controlled blasting was conducted in the Ishikari Bay New Port (Ishikariwan-shinko) in Hokkaido Island, Japan, to assess the performance of airport facilities subjected to the liquefaction. This paper mainly describes effect of liquefaction remediation and behavior of runway pavement during and after liquefaction by optical fiber monitoring. As a result of Full-scale experiment, a lot of valuable knowledge was obtained. Especially three types of tried liquefaction remediation with cost reduction deign specification are effective. Additionally optical fiber sensor shows high possibility for utilization as a runway pavement performance monitor because its deformation induced by liquefaction could be measured.
It is known that “Blast Densification Method” is a technique which can improve the ground strength for the liquefaction by the artificial trembling with the shock wave of explosives detonation set in ground. It is carried out a full scale test which has the airport facility at Ishikari Bay New Port in Hokkaido Island, Japan. The shaking by blasting continues for about two minutes, with 1769kg explosives, 583 delay numbers, at about 1.6 hectares experiments. It is executed safely, surely without damage to structures by blasting. As a result of the experiment, it is confirmed the increasing excess pore water pressure, sand pumping phenomenon, and settlements after basting. This report is described a summary of experiment on this test
A micro-bubble is an independent bubble of 10-100μm in diameter. A soil improvement method injecting the micro-bubbles into ground was newly developed, which may provide a cost-effective and a simple countermeasure method against soil liquefaction. Although it is well known that soil resistance to liquefaction increases as the saturation degree of the soil decreases, it has been difficult to lower the saturation degree of ground homogeneously. A technique using micro-bubbles, however, can be expected to solve the problem because the micro-bubbles can easily permeate into voids between sand particles. In-situ applicability test in Ishikari, injecting water mixed with micro-bubbles was conducted. The test consisted of the injecting micro-bubbles into the ground and the liquefaction experiment by controlled blasting for improved ground. Based on these test results, the feasibility of the micro-bubble injection method were examined in the paper.