Type Seawall Research Articles

Effect of Wave Power Device Arrangement in Double-Water-Chamber Type Seawall towards Wave Power Extraction Rate and Wave Dissipation

Utilization of the ocean energy to meet the electricity need is important to realization. The increasing need for electricity and environmental issues are the reasons. In last several decades a number of studies on wave energy device have been carried to find the effective one. In this paper, the double-water-chamber type seawall is basically adopted that has a similar structure to the OWC was examine to extract wave power. In the experiment various arrangement of wave power device inside the double water-chamber was tested to obtain optimum of wave extraction rate. Another function of the double water-chamber as wave dissipation is also clarified in the experiment. Based on experimental result the maximum wave energy conversion efficiency is about 30% and the reflection coefficient of the double-water-chamber seawall is about 0.3 on average.

Computation of sliding displacements of seawalls under earthquake conditions

To understand the serviceability aspects of seawalls, it is essential to study the permanent displacements of seawalls that occur during the earthquakes. Studies in the existing literature have concentrated on displacements of retaining walls with dry backfills; to the authors’ observation there is no specific analytical investigation devoted to the earthquake-induced displacements of retaining walls with submerged backfills. This paper focuses on sliding displacements of gravity type seawall retaining a submerged backfill under active earth pressure condition during the earthquakes. The threshold seismic acceleration coefficients required for initiation of sliding and the amount of sliding displacement due to seismic loading are calculated by adopting Newmark’s sliding block method. One of the prime features of the study is the estimation of seismic inertia forces in the submerged soil and wall applying the modified pseudo-dynamic method. The comparison of the results obtained using the proposed analytical formulation with the existing literature found to be in good agreement. A comprehensive parametric study has been conducted to understand the effects of different parameters such as seismic horizontal and vertical acceleration coefficients, soil and wall friction angles, width of the wall, wall inclination and excess pore water pressure ratio.

Experimental and calculation study on overtopping of framed seawall

In recent years, more and more seawalls have been used in tidal areas along coastal areas. The frame type seawall has the advantages of no water occupation, land saving and light weight. It is a difficult problem to determine the overtopping and the elevation of the embankment. In this paper, a physical model test was carried out to measure the average overtopping of a framed seawall at the design frequency of wave height, and the average overtopping was calculated by using the theoretical formula. The results of physical model test and theoretical calculation were compared and analyzed. The results showed that the theoretical formula was 6 to 20% larger than that of the physical model test. Finally, the theoretical formula was proposed to predict the wave overtopping of frame seawall, which met the design requirements and provided a basis for determining the height of the top of the seawall. At the same time, the physical model test showed that the anti-arc cantilever wave absorber on the upstream side of the frame seawall can reduce the overtopping volume by 7%-32%.

Efficacy of Water Chamber Type Seawall to Dissipate Incident Wave and Its Performance to Extract Wave Power

This study examined performance a water chamber type of seawall to dissipate incident wave and also extract wave power. The model of water chamber is consists of two water chamber type. The low reflection wave resulted by flow separation in lower end of vertical wall and it occurs after wave resonant condition. This structure is appropriate for short and long wave condition. A horizontal plate was setup in the end of vertical wall in order to improve performance of water chamber type seawall. This trial test taken to dissipate much longer waves condition and it’s related to utilize the wave energy inside the water chamber. Additional trial of the cross section, such as an adoption of a bevel edge instead of a right angle edge was also examined. It was seen that the seawall of a water chamber type with a horizontal plate is very effective to reduce reflected waves for both short and long waves. Also it was confirmed that large amplifications of pumping mode wave motions in the two water chambers appear for comparatively wide range of wave frequency

胸壁に作用する非越流時の津波波力に関する実験的研究

A large number of breast type seawalls behind the fishing ports were damaged due to the Great East Japan Earthquake on March 11 in 2011. The collapse of seawalls without tsunami overflows was confirmed in many fishing ports, so we needed to reconsider the present calculation methods of tsunami induced forces on seawalls. In this research, physical model tests were conducted in a wave flume to investigate the tsunami induced forces on breast type seawalls under non-overflow condition. As a result of the tests, we propose the calculation formula of hydrodynamic pressure exerted on seawalls composed of both of as a function of the Froude number and maximum incident tsunami wave height and as a function of inundation depth in front of seawalls.

The 11 March 2011 East Japan Earthquake and Tsunami: Tsunami Effects on Coastal Infrastructure and Buildings

The 11 March 2011 East Japan Earthquake and Tsunami caused unprecedented damage to well-engineered buildings and coastal structures. This report presents some notable field observations of structural damage based on our surveys conducted along the Sanriku coast in April and June 2011. Engineered reinforced concrete buildings failed by rotation due to the high-velocity and deep tsunami inundation: entrapped air in the buildings and soil liquefaction by ground shaking could have contributed to the failure. The spatial distribution pattern of destroyed and survived buildings indicates that the strength of tsunami was affected significantly by the locations of well-engineered sturdy buildings: weaker buildings in the shadow zone tended to survive while jet and wake formations behind the sturdy buildings enhanced the tsunami forces. We also found that buildings with breakaway walls or breakaway windows/doors remained standing even if the surrounding buildings were washed away or destroyed. Several failure patterns of coastal structures (seawalls) were observed. Flow-induced suction pressure near the seawall crown could have caused the failure of concrete panels that covered the infill. Remarkable destruction of upright solid-concrete type seawalls was closely related with the tsunami induced scour and soil instability. The rapid decrease in inundation depth during the return-flow phase caused soil fluidization down to a substantial depth. This mechanism explains severely undermined roads and foundations observed in the area of low flow velocities.

Numerical study of wave overtopping of a seawall supported by porous structures

This paper presents a VOF-based two-phase flow model for the simulation of wave interactions with seawall supported by a porous terrace. Firstly, the model was verified against laboratory data in a simple case for wave overtopping of a vertical wall. Comparison of computed and measured wave properties showed reasonably good agreement. The model was then applied to study the interactions of waves and a seawall protected by porous structures with a permeable terrace. The application results showed that the overtopping rate was strongly related to the energy dissipation through the drag force; the porous reef and terrace were very effective to produce a low crest type seawall. It is concluded that there exist two optimum values of porosity of the submerged reef, about of 0.25 and 0.7, that give minimum overtopping rates. Whereas, there is an effective range of porosity of the permeable terrace varying from 0.4 to 0.65 for significantly reducing the overtopping rate. The verification results confirm that the VOF-based two-phase flow model is sufficient robust to simulate the wave overtopping of coastal structures with reasonable accuracy.

Performance of a Water Chamber Type Seawall for Vertical Mixing in a Density Stratified Field

Performance of a Water Chamber Type Seawall for Vertical Mixing in a Density Stratified Field

Study on Maintenance of Non-Wave Overtopping Performance of Flaring Shaped Seawall against Sea Level Rise

Hydraulic performances of a non-wave overtopping type seawall were investigated on a supposition of the sea level rise that might occur near future. Two-dimensional hydraulic experiments were carried out under some different water level conditions, which reproducing the sea level rise, to clear the effect of the sea level rise on the hydraulic performances of the non-wave overtopping type seawall. Furthermore, this study proposes an appropriate countermeasure against the sea level rise to maintain an excellent checking effect of the wave overtopping of the seawall. Both the efficiencies of the proposed countermeasure and characteristics of the maximum wave pressure acting on it were evaluated through hydraulic experiments.

Mitigation of Wave Overtopping Rate in Offshore Airport by Permeable Bed Type Seawall

Large wave overtopping due to storms sometimes causes heavy inundation damage in an offshore airport surrounded with the sea. The wave overtopping rate at seawall lines is significantly changed by the local sea bed topography and the type of seawall. In this paper the variation of wave overtopping rate along the seawall line including a corner part is studied in an experimental basin with a directional wave maker. In the later part of the paper, the countermeasures to reduce wave overtopping at the seawall are discussed. A seawall attached with a wave absorbing permeable bed behind it is proposed for the airport seawall and is investigated experimentally. Experimental results demonstrate the wave overtopping rate becomes remarkably small for the new type seawall.

大水深域非越波型護岸の波圧特性に関する基礎的研究

Basic knowledge on wave force acting on a Non-Wave-Overtopping Type Seawall in deep water has been experimentally investigated to advance practical design of this type of seawall. The experiments were conducted with a two-dimensional wave tank using 1/45 reduced scale models. Two different cross sectional shapes of the curved face of the seawall, by which wave overtopping is effectively prevented, were used for the model seawalls. Wave pressures were measured with a number of pressure gauges distributed along the curved face. The relations between the crown height of the seawall and the wave pressure distribution were investigated. It was found that the largest wave pressure along the curved face appears mostly in the vicinity of the crown, but also the largest wave pressure occasionally appears in the vicinity of the middle of the curved face depending on the way waves hit the wall. It was also found that the intervals of the occurrences of large wave pressures could be adequately accounted for statistically by exponential distributions.

Characteristics of Wave Overtopping on Vertical Type Seawall Covered with Wave-dissipating Blocks

In recent years, seawalls coated with wave-dissipating blocks heve been set in front of upright seawalls. However, wave overtopping on this type of seawall is not fully investigated. Therefore, in this paper, characteristics of wave overtopping on upright seawall covered with wave-dissipating blocks was examined experimentally. From the results, it is found that this type of seawall is effective to reduce the wave overtopping rate. The crest height of the seawall is less than the height in upright seawall case to get the same wave overtopping rate. In addition, an easy method to estimate the runup height on the seawall has been suggested.

大水深域非越波型護岸の基本的越波特性について

A Non Wave-Overtopping Type Seawall in deepwater which effectively prevents wave-overtopping by its curved part has been studied. By using this seawall, the crown height can be reduced compared to a conventional seawall, and extremely large wave run-ups which suddenly occur due to the irregularity of the waves can be effectively prevented. However, it may sometimes be requested to use this seawall accepting some amount of wave-overtopping in exchange for lower crown height. Thus, in this study, wave-overtopping characteristics of the Non Wave-Overtopping Type Seawall were examined with numerical calculations and experiments, and the followings have been understood: 1) the relation between the height of the crown and the rate of wave-overtopping, 2) the influence of the shape parameters in section on the rate of wave-overtopping.

マウンドを有するフレア型護岸の護岸天端高と作用波圧

Hydraulic characters of a non-wave overtopping type seawall installed on a moundare investigated through experiments with a two-dimensional wave tank. A critical wave height, which is defined as a maximum wave height on which no wave overtopping occurs at all, was measured on different incident wave conditions as well as mound configurations. The wave reflection coefficient and wave pressure distributions on the seawall were also measured when the waves with the critical waveheight act on the seawall. In this study, the characteristics of the critical wave height and wave reflection coefficient are discussed under various incident wave conditions as well as mound configurations. And then, characteristics of wave pressure distributions are also discussed with comparing the design wave pressure act on the vertical seawall.

A study on the sealing structure of a waste disposal site at sea

Leaked pollutant from a waste disposal site at sea might cause a wider environmental problem of sea pollution. Recently, the requirements on such waste disposal are increased. However, the technical manual for the construction of them still has problems.Last year, authors showed that the new structure of caisson type seawall, which has a solid reticulation formation resin and seepage control materials filing the gaps in the rubble, has a high sealing performance.In this study, we pointed to the boundaries between rubble mound and caisson and between rubble mound and ground, and joints between caissons. Furthermore we noticed the sealing performance of them under seismic behavior.Based on test results and advection dispersion analysis, it was predicted that its sealing performance would keep a high performance under seismic condition and be sufficient even if it was added 100 years later.

関西国際空港２期空港島における藻場造成について

In the 2nd phase KANSAI international airport island, a gently rubble mound type seawall was adopted over more than 90% of the about 13km-long seawall, and also for the seawall, positive efforts toward seaweed bed formation are being made in order to create rich sea-area environment at early stage.As a result of supply of seaweed seedling that used seaweed blocks utilized in the 1st phase seaweed bed formation and net bag (spore bag) containing sporophylls, the area of the seaweed bed in the 2nd phase airport island where seaweeds are growing was about 18ha in October, 2002. We can say from this result that the artificial seaweed bed formation is contributing to the ecosystem in Osaka bay.

An analytic study on the seepage control performance of a waste disposal site at sea

In recent years in Japan, the number ofwaste disposal sites at sea where large volumes ofvvaste can be disposed has been increasing due to the lack of waste disposal sites on land. However currently the techical manual for the construction of such waste disposal sites still has some problems that require resolving. One important problem is the actual seepage control performance of the waste disposal site. This research analyzed a comparative review of a double steel pipe seawall and a caisson type seawall.In this study, it was anstuned that the water depth of the landfill was -20 meters.And it was asstuned that the ground conditions consisted of 2 types; soft ground and a comparatively stifffoundation. Three kinds of analyses were performed in this study, consolidation transformation analysis, seismic transformation analysis and advection dispersion analysis of a contaminating substance, from which a general evaluation of the seepage control performance was made.As a result of this study, on the assumption that there was no differential in the seepage from each joint, the performance of the caisson type seawall was better than the double steel pipe seawall in seepage control performance.

STUDY ON CHARACTERISTICS OF TRANSPORT OF SPRAY AND SOUND ENVIRONMENT BY NON-WAVE-OVERTOPPING TYPE SEA WALL

Authors have proposed a non-wave overtopping type seawall (Flaring Shaped Seawall) with deep circular cross section in order to facilitate a safe and excellent use of coastal space for various purposes. The seawall satisfies a non-wave overtopping condition with extremely lower crown height in comparison with conventional upright seawall. In this study, wind field near the seawall, water spray transported behind the seawall and sounds when waves running up were measured in the experiments, and compared with an upright seawall.

STUDY ON BASIC CHARACTERISTICS OF NON-WAVE-OVERTOPPING TYPE SEAWALL IN SHALLOW WATER

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.

Reduction of Impulsive Breaking Wave Pressures by Wave Dissipating Works with Low Crest Elevation

Low crested wave dissipating works with low void content were considered in this study to reduce the impulsive breaking wave pressures acting on a non-wave overtopping type seawall. The wave transmission coefficient and wave pressure distribution were measured through two dimensional wave tank experiments. The numerical computation based on Green's Identity Formula was also applied to estimate the transmission coefficient. The wave transmission coefficient decreases linearly with decreasing of the void content. The maximum wave pressures also decrease linearly with decreasing of the void content, and the variations of the maximum wave pressures depending on the relative water depth become small.