Hydraulic Characteristics of Flaring Shaped Scawall (FSS) in deepwater were investigated experimentally. A minimum crest height on which no wave overtopping is allowed, a reflection coefficient and a wave overtopping rate were measured for two types of FSS with aquadrant circular cross section and a semicircular one. Above three factors of FSS were compared with those of a conventional vertical seawall to clarify efficiency of the proposed seawall in deepwater. The minimum crest height of FSS is smaller than that of the vertical seawall and this effectiveness becomes large with increase of offshore wave steepness. The same results were obtained for the wave overtopping. The reflection coefficient of FSS with a semicircular cross section becomes smaller than that with a quadrant circular cross section and the vertical seawall.
Wave reflection and transmission characteristics about a curtain-walled breakwater of gravity-type were examined in both regular and irregular wave environments. At first, the representative wave analysis for a group of irregular waves with different statistical properties was adopted to examine reflection and transmission coefficients of the breakwater. These coefficients were also obtained for regular waves and compared with each other. Secondary, frequency characteristics of reflected and transmitted waves about the breakwater were examined through the use of spectral analysis. Reflection and transmission coefficients as a system function of a linear system were obtained and again compared with those of regular waves. It was confirmed that the reflection and transmission coefficients for regular waves can be used for the case of irregular waves if the significant wave is used as a representative wave. However, it must be noted that frequency characteristics of incident and transmitted waves are different about the breakwater.
In order to mitigate secondary effects caused by high reflection waves from a curtain-walled breakwater, a new type of curtain-walled breakwater was proposed. It consists of two vertical walls with different draft depths. The distance between the two walls is comparatively narrow, e. g., having a similar size to the width of its super structure. The mechanism of effective dissipation of wave energy is to enhance the generation of vortex flows from the curtain walls, especially from the front curtain wall placed on the offshore side, which consists of an array of inclined plates with the same gap. By using the wave resonance of Helmholtz mode between the two walls, enhancement of the vortex flow is realized. In the experimental and theoretical examinations, changing the water depth and the distance between the two walls, important hydraulic properties of a double curtain-walled breakwater, such as reflection and transmission coefficients, wave energy dissipation rates and so on, are clarified.
Offshore man-made islands and reclaimed lands are planned for making use of ocean space. Seawalls are important to reduce wave overtopping rate. Recently, seawalls with low crown height are needed to reduce construction cost. Hydraulic model tests were conducted to evaluate overtopping quantity of four kinds of composite-type seawalls with low crown height. Firstly, wave overtopping quantity is measured to determine the crown heights. Secondly, wave pressure on caissons and parapet is measured to design four types of seawalls considering the site condition. At last, volume of wave dissipating concrete block and concrete caisson is compared with each other in order to evaluate cost reduction of seawall construction. It was found out that the seawall with concrete block on the top of caisson has the highest performance on reduce wave overtopping.
The basic characteristics of a non-wave-overtopping type seawall in shallow water were investigated through a wave tank experiment and a numerical simulation. The minimum crest height which satisfies non-wave-overtopping condition, a wave pressure, a wave reflection and a water spray transported behind the seawall were measured in the experiment. The fluid motion near the seawall was obtained by numerical simulation based on SOLA-VOF method. These hydraulic factors of non-wave overtopping type seawall were compared with a conventional upright seawall and advantages of nonwave overtopping type seawall in control of wave overtopping were discussed.
Damages due to wave overtopping were investigated through a nationwide questionnaire distributed among regional construction bureaus and local governments. Wave overtopping in recent 7 years was found to be reported at more than 250 coasts facing open sea as well as inner bay. In addition to the tangible damages of flooding and destruction of coastal structures, wave overtopping also causes serious damages of salt invasion to land and traffic interruption, which were not included in conventional cost-benefit analysis. The relationship between the damage level and the strength of wave overtopping was investigated, revealing high correlation for coastal structure destruction and low for salt invasion.
The large number of coastal and port structures has been damaged by severe marine climates. Sea bed scoring at the foot of coastal structures such as sea walls is one of the main causes of damages and more than 50% of damaged sea walls is caused by it. The damaged sea walls are selected from the annual books of damaged facilities edited by Port Bureau of Ministry of Transport. Though the wave conditions at the damage are generally described, they are estimated by SMB method for the case without wave descriptions. The stone piled type vertical sea walls are likely to be entirely damaged by scoring, but blocked type ones are only damaged partly. Once the sea bed had been scored, incident waves are increased due to deepened with depth. Consequently, wave forces or wave overtopping become more severe. The required block weight calculated by Hudson's formula also increases. Therefore the countermeasures against scoring should be established immediately.
The report shows the damage structure of a layer armor block of gentle slope-type coastal dike by the model tests on stability. According to the experimentation this time, it has been found that there is a difference of tendency between Hudson's experimental results and a layer armor block's experimental results.
The wave direction giving the minimum safety factor for a breakwater caisson is adopted as the design wave direction in the present design method. However, offshore wave direction is varied in itself, and the wave direction estimated by wind observation or wave hindcasting is distributed around the actual wave direction. In this paper, the sliding failure probability of breakwater caisson is computed by reliability design method considering the variation of offshore wave direction. The sliding failure probability depends on the width of the variation. It is important to estimate wave direction exactly especially for the design of deepwater breakwater. On the other hand, it is not so important for the breakwater constructed in surf zone, because the incident wave direction becomes almost normal to the shoreline by wave refraction, and the incident wave height depends mainly on the water depth. Additionally, the multi-directionality of incident waves may reduce the sliding failure probability.
The sliding of the caisson breakwater placed in the outer region of breaker zone with the sea bottom slope of 1:100 is studied. Through the hydraulic model tests, it is found out that when the law-frequency surface variation makes the water level law, the breaking wave impact pressure is appeared and makes the caisson slide. In order to increase the sliding resistance force and to reduce the sliding distance, the crushed stone back filling method is proposed. The validity of this method was verified through the hydraulic model tests and the numerical simulation based on the non-linear dynamic spring model.
The relaxation of the construction criterion for leveling of armor stones in mound is expected to reduce the construction cost of a composite breakwater in Ise Bay. The “stability” of armor stones in the “non-leveling” and “heaping up” construction methods is studied in a hydraulic experiment. The result for these cases is compared with that for the general leveling. Additionally, the diagram giving the critical depth for an allowable damage rate of approximately 1% in the non-leveling method is proposed.
Pontoon type floating structure with submerged flat plate has been studied in this paper. Wave response analyses of the pontoons have been performed for several different attached positions of flat plate and the stability of the pontoons were examined. Furthermore, the characteristics of the hydrodynamics such as the reflection and a transmission ratio were examined. It was verified that the flat plate have worked effectively for mitigation of the heaving motion, especially it is obvious to the plate area of 2 times of surfaces area at the water line and 0.02 or more wave steepness. It was confirmed that the dimension and attaching depth of flat plates important factor for motion control of a floating pontoon. The possibility of the stable improvement and the effective wave control by the size and position of the flat plate were shown.
This paper treats the low frequency motions of floating body with asymmetric moorings. The phenomena could be grasped with use of the ready made numerical simulation code for the motions of floating body with arbitrary moorings or in the tank test. However the fundamental characteristics have not been clarified yet. By using a.simple numerical model, the parametrical study of the appearance of sub-harmonic motion is done. As the results, it is found that the sub-harmonic motion appears depending on the degree of the mooring asymmetry, that is the ratio of the restoring force coefficient in one side to the other side. And then the chart for judging the possibility of low frequency motion is presented.
Field observation on wave, current and long-period motions of a moored vessel at Reihoku Port was conducted. Highly accurate data of six motions around the center of gravity of the vessel, the tension of the mooring ropes and the displacement of the fender were obtained. It was confirmed that the longperiod motions, such as surging, swaying and yawing, were strongly affected by mooring system. By considering multi-directionality and frequency bandwidth of incident waves as input conditions for a numerical simulation, the calculation results of the vessel motions agree with the field observation data well.
In the previous experiments on a submerged breakwater, a very long period of oscillation of fluid velocity at the bottom is observed behind the breakwater in a two-dimensional wave flume. The period of the oscillation is far larger than the period of seiche in the wave tank, and thus the oscillation may influence the estimation of the mean water level and steady flow velocity. To clarify the effect of this long period oscillation, we conducted two-dimensional wave tank experiments with a submerged breakwater and also with a constantly sloped beach for comparison. Water surface oscillation, horizontal fluid velocity at the bottom and the motion of the paddle of the wave generator were measured. The time variations of the mean water level, the steady flow velocity, the amplitudes of wave harmonics were calculated.
Moored ship motions due to long period waves become the serious problem, those phenomenon are happened in harbors which faces the open sea. Container terminals have been built in harbors at inside bay by now, however, some container terminals are planned and built in a harbor which faces the open sea area because of container carriers of larger sizes. Container carriers have more serious limit values of cargo handling than bulk carriers, tankers, etc. In this study, firstly, we research about the operation situation of container terminals which are working now and operational plans of new container terminals that which faces the open sea. Secondly, we examine about the design of mooring equipment of container terminals by using numerical simulations of moored ship motions considering long period waves, swells and winds. At last, we consider about the facility design of container terminals which faces open sea in the future.
Field measurements were conducted using specially developed wave measuring devices at Hazaki coast in Ibaraki Prefecture. Based on the data, characteristics of infra-gravity waves have been studied. Infra-gravity oscillation becomes dominant in offshore side of secondary breaking point. The low frequency wave components around f=0.02-0.05Hz are found to be in good correlation with the envelop of incident group waves. The lower frequency wave component of f≤0.01Hz, however, does not show clear relation with the incident group waves. The existence of standing edge waves is suggested by the analyzed coherence and phase results on horizontal velocity components. Most of these results show typical characteristics as the dissipative beach which Wright-Short have classified.
The natural coast continues to undergo changes, but structures such as seawalls now serve only one purpose, i. e. protection. In recent years, as ecofriendly structures are desirable, artificial rocky beaches are now projected as places of recreation where people can learn about shorelife. Unfortunately, in many cases, due to the lack of storing water in rocky beaches at low tide, the biota therein shows little diversity. Observation of a natural beach was conducted at Kominato in Chiba. Tide pools provide very valuable, habitats for seaweed and sea creature. They have the important function of not only storing water, but also providing micro-topographes in the pool such as cracks, crevices and pits. Accordingly, new artificial tide pool units have been developed, which fill up with seawater during the ebb tide to ensure suitable micro-topography for shorelife. An example of the design method of such a system is provided.
To develop a waterfront area as an attractive space, it is essential to ensure that the area has a comfortable natural environment. In other words, it is important to study how physical factors and phenomena that greatly influence the natural environment, and human beings, are interrelated; and to compile, based on study findings, necessary concepts and techniques for realizing waterfront areas that are urban environments highly compatible with human activities. From the above viewpoint, as a study of the waterfront environment, basic investigation and a questionnaire survey were conducted in a waterfront area in Northern Kyushu to collect data on its acoustic environmental comfort, as reported in detail previously. Subsequent to the previous report, a field measurement was conducted and analyzed to investigate the fundamental characteristics of acoustic environment (sound of waves) in Northern Kyushu coastal zone.
The numerical simulation system for flow and water quality in estuaries (DELFT3D) was improved to assess the environmental impact of 3-dimensional large marine structures. Two models were developed. One is called “floating model” which simulates a floating structure by applying the additional atmospheric pressure on the water surface. The other is called “block model” which adds an infinite friction on a numerical grid to simulate flow around 3D structures. The environmental impact assessment with these models was conducted for an offshore airport in Tokyo Bay. The effects of floating and island types of airport on the water environment were compared. The environmental impact of a floating type was weaker than that of an island type. The basic impact of the airport is to change the residual current or the estuary circulation, and this affects the material circulation in a bay.
In this paper the forecast evaluation technique for the increase and decrease of the short-necked clam change in an environmental condition is considered by using the cell-automaton which is one of the artificial life techniques in this research for the benthic animal. The adaptability of this technique is examined. The cellautomaton is the method to pursue inhabiting animal's rise and fall according to an environmental change by the number of animals in the cell by dividing the area where the object animal is inhabited into a lot of cells. We clarified that it was possible to forecast to some degree by giving a constant rule of an increase and the decrease concerning the change of the short-necked clam by using the cell automaton.
Communities of algae have disappeared from the shallow waters along the Japan Sea coastline in southwest Hokkaido. A large number of studies have been made on coralline flats, it has been shown that the consumption of algae by sea urchins is an important factor affecting the formation of coralline flats, and is closely related to the physical environment of coastal areas. Recent investigations have shown that algae communities have formed at the region surrounded by sand and gravel in coralline flats. The effects of drift sand on the consumption of algae by sea urchin are experimentally studied. The smaller sand diameter is, and the larger fluid velocity is, the harder sea urchin moves to algae due to drift sand. Therefore consumption of algae by sea urchin decreases under these conditions. Strongylocentrotus intermedius dislikes drift sand more than Strongylocentrotus nudus, so consumption of algae by Strongylocentrotus intermedius decreases.
Communities of algae have disappeared from the shallow waters along the Japan Sea coastline in southwest Hokkaido. A large number of studies have been made on coralline flats, it has been shown that the consumption of algae by sea urchins is an important factor affecting the formation of coralline flats, and is closely related to the physical environment of coastal areas. Field investigations have shown that sea urchin moves to offshore avoiding strong fluid velocity when waves are big, on the contrary it moves to onshore in order to eat algae when waves are small. On-offshore movement of sea urchin due to waves are not quantitatively studied. Movement of sea urchin to offshore due to increasing of wave height, and these to onshore due to decreasing of wave height are experimentally understood. Decrease of sea urchin velocity under large fluid velocity are quantitatively investigated.
This study examined the conditions in order to make most suitable habitats for hatchery-reared Japanese flounder. Flounder's critical velocity of bottom-clinging was estimated almost the same the swimming velocity under steady flow, which was about the four or six times of its total body length (TL). The value of the coefficient of flow tolerance took from 0.2 to 03, and the coefficient of mass force did about 1.0. On the basis of that result, the relationship between the thrust (Ft: dyn) and TL was closely resembled as Ft=15.2×TL2.73, and the wave conditions (Hmax: a maximum allowance wave Height) allowed to be suited for making habitats of flounder, a wave period (T: second), and the depth of liberation area (h: m) was described as Hmax=23.02T-1.36TL0.97h based on the theory of micro amplitude. Further more, the maximum burrowing depth observed the tendency of gradual decrease with its body length's increase. In this experiment, no population was observed washed away in spite of the hard drift sand conditions.
Seaweed forests of Eisenia bicyclis Setchell and Ecklonia cava Kjellman are broadly distributed along the rocky coastal area of central Honshu Island, Japan, facing the Pacific Ocean. We aimed to clarify a zonation of these plants and their causes. We measured irradiance at each depth of their habitat in a field and their photosynthetic rates in a laboratory. Seasonal changes of photosynthetic rates were higher in summer to fall and lower in winter. Initial slopes in Photosynthesis-Irradiance (P-I) curve of Ec. cava were higher than those of Ei. bicyclis at shallower depth. Daily compensation light quantity of Ei. bicyclis was higher than that of Ec. cava. This study showed quantitative facts that they were adapted to each photo-environment.
In Hamada fishing port of Shimane Prefecture, the new technical strategy like application of grooved armor block (for propagation of abalone and top shell) and so on have been taken into consideration in planning of the improvement works with the purpose of amplifying the function as seaweed bed on the submerged mound portion and also base mound portion of revetment · breakwater. This paper presentsthe results of monitoring survey conducted over two years from the completion ofthe partial section of the works.
Parts of plant body of Eisenia bicyclis or Ecklonia cava are often torn off due to waves and/or marine animals' gnawing, thus become to drift along sea bottom asdrift algae. The useful Abalone and Sea Urchin eat these drift Algae. But a considerable mass of drift algae will move and is diffused due to wave and tide without being eaten by useful marine animals. Accordingly, in Japan, the development of drift alga trap works has been tried since about ten years ago. The aim of the study is to show a new type of concrete blocks which are suitable for drift alga trap, and also to show the method of disposition and anti-wave design of the blocks.
Recently, eggs of sandfish were found on seaweed adhering to a coastal structure built on the coast at Tomakomai. This shows that a coastal structure can functionas a spawning ground for sandfish. However, we have little knowledge on the environmental conditions of a coastal structure for it to function as a spawning ground because of few reported cases of sandfish spawning on seaweed adhering to structures. We investigated the environmental conditions of the spawning ground of sandfish. As a result, we found that the spawning ground of sandfish needs a sandplace around a reef, and the coastal structure fulfilled this condition. We foundthat no difference exists between current velocities of the water at the naturalspawning ground and near a structure and that water currents of both naturaland structure spawning grounds were comparatively calm.
In coastal areas of the Japan Sea in southern Hokkaido, the isoyake phenomenon (seaweeds such as Laminaria withering on the beach) has been observed over a longperiod of time. The cause of isoyake is attributed to grazing by sea urchins andlack of nutrients and trace elements such as iron in the sea water. A method to prevent grazing by sea urchins while supplying trace elements to promote the growth of seaweed was looked into. Sea urchins can not move on a sandy bed, so blocks were placed thereon. Ferrous ions to promote photosynthesis were supplied. An experiment on seaweed bed formation was carried out continuously over a period of 5 years. Seaweed bed formation was successfully achieved, aided by the prevention of sea urchins entering. The standing crop of seaweed benefited from the supply of ferrous ions.
Topographic features of a sandspit and ebb tidal flat on the Natsume coast located at Konoshima Channel in Kasaoka City in Okayama Prefecture were investigated through field observation. The sandy beaches of this coast have been utilized as a spawning site of horseshoe crab Tachypleus tridentatus but recently large beach changes have been observed, narrowing the horseshoe habitat located at the downcoast of the spawning site. The beach changes were triggered by waves produced by ship navigation in narrow, funnel-shaped channel. A measure to stabilize the sand spit is proposed in order to prevent diffusion of sand over the ebb tidal flat.
The purpose of this study is to disclose the relationship between marine organisms and sediments in gravel beach. From this viewpoint, the field observations on marine organisms are carried out in a man-made gravel beach and natural one. It is found that the diversity index of marine organisms in gravel beach depends on the time of exposure from sea water and the volume of gravel. For this reason, the the diversity index on marine organism in natural gravel beach is larger than those in man-made one and natural rocky coast.
Nojima waterway is a typical closed water in Tokyo Bay. To improve its water quality and remove the sediment odor, the waterway was opened to outer sea and the sediment was dredged away. As a result, salinity in the waterway increased due to outer sea water flowing in, and successions of the biotic community occurred. Goby fishing is getting vigorously around this area.
Field observation of spawning sites of horseshoe crab Tachypleus tridentatus was carried out in Itoshima Peninsula in northern Kyushu. Horseshoe crab spawns around 15cm below the surface of the sandy beaches during high tide level in summer. Spawning sites were located at sandy beaches surrounded by ebb tidal flat without exposure to rough waves. In order to create stable spawning sites for horseshoe crab, coastal facilities such as groins must be properly installed to block littoral drift, which causes loss of nourished sand, even if wave height is sufficiently small.
A new construction method for a submerged tunnel has been developed. The new method is an application of the launching erection method for a bridge construction technique. Caissons that is an element of a tunnel are constructed at the tunnel entrance, and then they are pushed into the sea. Thus the method does not need huge construction space and navigation restriction. The technical subject of the new method is reduction of launching force. We developed the machine ‘HYDRO SLIDER’ to cut off the friction force. We carried out small and large scale experiments to investigate the problems in practical use of HYDRO SLIDER. The experiments show that HYDRO SLIDER makes possible to reduce the friction force. We also carried out experiments to investigate the wave forces and the fluid forces caused by a cruising a ship. The results show that the wave forces are larger than the fluid forces caused by ship. Finally, the motion of the caissons caused by waves are simulated numerically, and it was found that the motions are negligibly small.
This paper describes the removement works and corrosion investigation of the 200m long coastal observation pier at Ajigaura beach, which was composed of steel truss framework supported by steel piles. The pier was constructed in 1973 and extended in 1976. The pier was used for observation of waves, currents and beach deformation in surf zone and exposed to severe sea state for more than 20 years. Removement works were operated from the provisional pier constructed in parallel to the observation pier. The steel piles were extracted after being cut beneath the ground level since they were judged to be undurable for the entire extraction due to the corrosion at the splash zone. Corrosion investigation also confirmed the effectiveness of various rustproof techniques.
Two-dimensional finite element analysis on ground-structure interaction system is conducted. The FEM program consisits of a generalized elastoplastic constitutive moden (tij-model). Now using this program, movement of sheet-pile quaywall and reclaimed land of a fishing port on soft ground treated by the sand drain piles is estimated. Effect of the treatment by the sand drain method and width of preloading on the behavior of sheet piles and deformation of reclaimed land is shown.
Coastal areas in Japan have often been reclaimed for procuring new lands of industrial, agricultural as well as urban areas. In order to construct the new lands economically, it is always necessary to observe the settlement of the reclaimed land during and after construction. It is commonly used for settlement observation such systems as some electronic devices consist of pickups and cables or optical measuring method by use of a supporting tower. These conventional system also bring many troubles and accidents through backfill or reclamation works due to cable cutting and tower collision. Now we have developed a quite new system with magnet electronics. The magnet electronic flux can transmit signals through the soil and the water. The data on land settlement being transmitted by magnetic flux signal are easily received without cables by a receiver loaded on a boat.
In long-time extennsion works of a breakwater and a wharf facing the open sea, there have been many cases where some ends and corners of the base of structure are damage befor to next work starts. This was also the case with the extension work of the East Breakwater of Hitachi-Naka Port that faces the Pacific Ocean in a severe construction. Under such circumstances, a study meeting was estalished in 1994 by the Kashima Harbor Construction Office, No.2 Harbor Construction Bureau of the Construction Ministry. The meeting is composed of learned men of experience and businessmen concerned with the port and harbor works to study and discuss some stuructures that may replace the concrete aporon block. As a result, “protective equipment of steel frame with chain net (hereinafter called a net for foundation)”, which is lighter and larger in convering area than the concrete apron block, etc, was devised and used for the actual construction. This paper descrdes the construction status, results of followup investion and those of hydraulic model experiments of the net for a foundation at East Breakwater of Hitachi-Naka Port.
Hopper and split barges are frequently used in marine construction schemes for reclamation of offshore land for airports and caisson foundations. In order to realize a designed geometry accurately and effectively, the deposition configuration of earth and sand dumped by barges and the optimum interval of discharge sites of barges for a specified degree of uniformity in the mound surface must be predicted in advance. In the present study, a sailing arrangement system based on a prediction model was used in a construction project. It was confirmed by field engineers that the deposition configuration of earth and sand dumped by a hopper barge is different from that of earth and sand dumped by a split-type barge. The characteristics of the spatial deposition configurations resulting from dumping by each type of barge were investigated under the condition of a single discharge of earth and sand in field experiments
A system consisted of a personal computer and a digital video camera was developed for measuring a distribution of sand grain size. A sample of beach sand which had a median diameter of 0.28mm was prepared hi order to check this system. The distribution of sand grain size measured by this system was agree well with the data from the sieve analysis. Major advantages are that this system requires smaller amount of sand sample (2000-2500 grains) and less time for analysis than these for sieve analysis.
Antiwashout underwater concrete needs large amount of unit water-content than that of conventional concrete, because of developing an appropriate fluidity according to the condition of a site. As the excessive water content in a concrete mixture is not desierable to control thermal cracks and to make economic concrete, superplastisizer are used in the antiwashout underwater concrete to reduce unit water content. In some case, mineral admixtures such as blastfurnace slag and fly ash are used too. However, lime stone powder is not used so far. This paper reports the fluidity, setting, strength development, permeability, chloride penetration effected by lime stone powder used in the antiwashout underwater concrete.
Silt curtains are generally stretched around construction site in the coastal region to protect turbidity generated by the construction works from flowing out of the region. The hydraulic functions of silt curtain have been investigated in the two-dimensional wave tank. However, the silt curtains are stretched in a three-dimensional sea and three-dimensional effect becomes very important. In this study, the effects of a stand-up type and a hang-down type silt curtain on the unidirectional flow are investigated through experiments in a basin. The authors also proposed numerical model for predicting flow pattern around silt curtain and examined the validity of the procedures by using experimental results.
Recently a floating structure tends to be in-placed offshore as long as twenty years. As anchor chains for mooring system, not only conventional ones having a stud but also new type ones without a stud are used. In such a case, durability of chains, especially fatigue strength is required. Fatigue strength depends on stress concentration factor (Kt). Besides this, erosion or abrasion concentrated in a contact area of chain links is taken into considerations for the evaluation of fatigue strength. Therefor, we conducted two dimensional stress analyses for the intact chain and the chains subjected to erosion or abrasion by linear Boundary Element Method (BEM). As a result, the following conclusions are obtained: Firstly the Kt of new type chains is greater than that of the conventional ones but the Kt induced in outer edge of link is almost equal to that in inner edge. Meanwhile the Kt induced in outer edge of conventional chains is larger than that in inner edge. The Kt of both new type chains and conventional ones having erosion or abrasion are greater than the ones of the undamaged chain by 14%.
The holding power of the mooring anchors were verified by comparing the estimation with the results by the field test. The field tests on the silty sand seabed were carried out for the holding power of two different types of anchor, the concrete block anchor and the suction anchor. The pressure distributions were measured at the bottom of the concrete block anchors and inside the suction anchor by varying the drawing angles of the anchor line, the drawing speed. The holding power of both anchors for the drawing angle of θ=90°increases with the drawing speed, and approaches to the constant value. The holding power for the drawing angle of θ<45° approaches to the constant value independently of the drawing speed. The concrete block anchor shows a peak of the largest holding power when the drawing speed is large. The suction anchor always shows a peak of the largest holding power independently of the drawing speed. It was also confirmed that the internal pressure inside the suction anchor changes in proportion to the holding power.
On October 4, 1994, an earthquake of magnitude 8.1 occurred at east off Hokkaido. Many Port structures and fishery harbor structures in east Hokkaido were damaged. Therefore, two dimensional effective stress analyses are conducted for quay wall based on the data in there. This is analysis for -4.0m quay wall in Shibetu fishery harbor that was damaged by the earthquake.The results of the effective stress analysis of quay wall indicate that a fundamental pattern of the deformation of the quay wall is reasonably simulated by the present approach.
Okinawa Prefecture consists of many islands on the wide area of ocean. Therefore shipping and ports are very important in transportation of foods and goods for islanders' livelihood. Under the facts of those things, an earthquake proof berth is essential and should be constructed in this prefecture because earthquakes have occurred in series around Yaeyama Islands in recent years. Though there are many marine faults around Ishigaki Island, it was hard to decide an earthquake scale in the designing an earthquake proof berth of Ishigaki Port. On the other hand, in this occasion it was not clear to evaluate the characteristics of vibration and liquefaction of the coral gravel ground also with its static ones. A few things of this designing including characteristics of coral gravel ground are shown in the present paper.
In Toppusi-Wakasato fishery port lying at Lake Saroma in Hokkaido, the fishery infrastructures have been often built on a soft ground. This situation induced a severe problem of deforming in quay structure including steel sheetpile. The present study allowed to fully understand the cause of deformation. For this investigation, we created an analysis model based on Finite Element Method (FEM) in the purpose to examine the effects of soft clay consolidation and lateral flow on steel sheet-pile deformation.
The objective of this development is to increase the earthquake resistance performance of gravity caisson quay wall by employing sheet pile at the foot of the caisson. Gravity caisson quay wall with sheet pile realizes the 0.05 point increase of seismic coefficient by comparing usual gravity caisson quay wall. This method can apply existing gravity caisson quay wall which is short of sliding resistance during earthquake. Quay wall structure becomes hybrid type by connecting the head of sheet pile and the caisson and shows both advantages of gravity type structure and sheet pile structure. Underwater shaking table test and 2D dynamic effective stress analysis were done for the proposed hybrid type quay wall structure. Gravity caisson quay wall was designed at the condition of 0.15 design seismic coefficient and 10m water depth at the foot of the structure. The result shows the necessity of 900mmdia. steel sheet pile for the condition of 0.2 design seismic coefficient. 50 percent reduction of caisson crest displacement during earthquake is also obtained. Design criteria for this hybrid quay wall structure is also proposed.
Dynamic behavior of a caisson type quay wall resting on pile foundation against the 1995 Hyogoken Nanbu Earthquake was numerically evaluated by a liquefaction analysis based on effective stress model. The effect of pile length on seismic response of caisson type quay wall against earthquake motion was investigated through some numerical examples. The displacement response of the caisson quay wall with pile foundation was smaller than that of the caisson without pile foundation. When the pile length becomes longer, the displacement response of caisson type quay wall becomes smaller. As the deformation was mainly induced by the increase of pore water pressure in the soil behind the caisson type quay wall, it is indispensable to reduce the pore water pressure in case of applying longer pile to the caisson type quay wall.
A study has been conducted to investigate the nonlinear interactions among waves, composite breakwater and a multi-layered base. The problem has been simulated numerically by two models, BEMFEM model and poro-elastic FEM model. These models, developed by the authors, can simulate the nonlinear wave field and its interactions with the porous media. Modifications have been made in the models to account for the multi-layered base and applications have been made to various configurations and properties of the breakwater. It has been found that the nonlinear effects become more significant in case of a high base and the fine material of the base may suffer from tensile stresses. The base may also fail at smaller wave heights than that needed for causing a failure in the caisson.