Layer | Fill | Outline |
---|
Map layers
Theme | Visible | Selectable | Appearance | Zoom Range (now: 0) |
---|
Fill | Stroke |
---|---|
Collaborating Authors
Analysis of Rubble Mound Foundation Failure of a Caisson Breakwater Subjected to Tsunami Attack
Esteban, Miguel (United Nations University, Institute of Advanced Studies Yokohama, Japan) | Thao, Nguyen Danh (Ho Chi Minh City University of Technology, Ho Chi Minh City, Vietnam) | Takagi, Hiroshi (Yokohama National University, Department of Civil Engineering Yokohama, Japan) | Shibayama, Tomoya (Yokohama National University, Department of Civil Engineering Yokohama, Japan)
ABSTRACT Presently, there is no methodology to evaluate the deformation that the rubble mound of a caisson breakwater would suffer if it was attacked by a tsunami. The present paper proposes a methodology to evaluate this deformation based on the method of Esteban and Shibayama (2006), which originally was developed for wind waves. The method was verified by carrying out laboratory experiments using solitary waves and comparing the results to those obtained using the new methodology. INTRODUCTION The reliability of the different available tsunami counter-measures is being re-assessed following various recent disasters, with the effectiveness of hard and soft measures being compared in order to obtain the most suitable solutions. The development of these countermeasures is of paramount importance in order to prevent the loss of life and property that might occur as a result of these waves. Various researchers such as Shibayama et al, (2006), Sasaki (2006) and Jayaratne et al. (2006) have noted the effects that various types of coastal terrain have on the attenuation or magnification of the damage due to tsunami attack. However the degree of protection that the various natural or artificial coastal structures offer against tsunami attack is not yet properly understood. The 2004 Banda Aceh tsunami has highlighted how coastal forests do not always offer effective protection against tsunami attack as previously thought (it appears that if the tsunami height exceeds the height of the trees these are ripped from the ground and carried by the force of the wave). Hence it is not clear which is the best method to protect against tsunami attack and what degree or risk is related to the different methods of defence. In Japan, sea dikes have been built along the coast to protect against tsunamis, high waves and storm surges, and numerous records can be found of the construction of such structures.
- Asia > Japan > Kantō > Kanagawa Prefecture (0.29)
- Asia > Indonesia > Aceh Province > Banda Aceh (0.24)
Pressure Exerted By a Solitary Wave On the Rubble Mound Foundation of an Armoured Caisson Breakwater
Esteban, Miguel (United Nations University, Institute of Advanced Studies Yokohama, Japan) | Thao, Nguyen Danh (Ho Chi Minh City University of Technology Ho Chi Minh City, Vietnam) | Takagi, Hiroshi (Penta-Ocean Construction Co., ltd, International Construction Divistion, Yokohama, Japan) | Shibayama, Tomoya (Yokohama National University, Department of Civil Engineering Yokohama, Japan)
Although a lot of attention has been paid to develop formulas and methodologies to assess the effect of wind waves on caisson breakwaters, there is still limited understanding of the loadings due to tsunami waves. More specifically, no methodology exists to determine the effect that a partially destroyed armour layer would have on the overall stability of an armoured caisson breakwater. Although Esteban et al. (2008) developed a method to estimate the deformation of a caisson breakwater subjected to solitary wave attack, this method is known the be greatly influenced by the presence of an armour layer in front on the caisson. Thus, laboratory experiments with solitary waves were carried out to clarify the failure mechanism of an armoured caisson breakwater against a comprehensive range a tsunami type events (bore-type, breaking and non-breaking). The results of the experiments show how the load which is exerted by the caisson onto the foundation depends on the depth of water in front of it, the shape of the armour layer and whether the wave strikes the caisson or the armour layer first. Of particular interest, it was found how the presence of armour (in particular a failed or partially constructed armour layer) can sometimes be detrimental to the stability of the caisson itself. INTRODUCTION The reliability of the different available tsunami counter-measures is being re-assessed following various recent disasters, with the effectiveness of hard and soft measures being compared in order to obtain the most suitable solutions. In order to evaluate the effectiveness of the hard solutions it is necessary to accurately estimate their reliability, i.e. what degree of protection they would offer against a range of tsunami wave types and heights. For the case of Japan, sea dikes have been built along the coast to protect against tsunamis, high waves and storm surges, and numerous studies (e.g. Naksuksakul 2006) can be found of the construction of such counter-measures.
- Research Report > Experimental Study (0.48)
- Research Report > New Finding (0.46)
Laboratory Experiments On the Sliding Failure of a Caisson Breakwater Subjected to Solitary Wave Attack
Esteban, Miguel (United Nations University, Institute of Advanced Studies) | Thao, Nguyen Danh (Ho Chi Minh City University of Technology) | Takagi, Hiroshi (Yokohama National University) | Shibayama, Tomoya (Yokohama National University)
ABSTRACT: At present no methodology exists to evaluate the failure mode of a caisson breakwater subjected to a tsunami attack. The present paper investigates the sliding and tilting failure of a caisson breakwater subjected to a solitary wave attack, and establishes a relationship between the sliding and vertical movement. The vertical movement of the caisson is evaluated using the method of Esteban and Shibayama (2006), originally was developed for wind waves. The method was verified by carrying out laboratory experiments using solitary waves and comparing the results to those obtained using the new methodology. The sliding failure will be discussed and a general expression for an upper bound limit to the sliding will be proposed. INTRODUCTION In order to correctly design structures to withstand tsunami attack it is necessary to evaluate how reliable they would be against a range of tsunami wave types and heights. The development of these countermeasures is of paramount importance in order to prevent the loss of life and property that might occur as a result of these waves. Researchers such as Shibayama et al, (2006), Sasaki (2006) and Jayaratne et al. (2006) have noted how various types of coastal terrain can attenuate or magnify the damage due to tsunami attack. However the degree of protection that the various natural or artificial coastal structures offer against tsunami attack is not yet properly understood. For the case of Japan, sea dikes have been built along the coast to protect against tsunamis, high waves and storm surges, and numerous studies (e.g. Naksuksakul 2006) can be found of the construction of such counter-measures. However, expected tsunami heights are often higher than the existing defences, and hence the potential damage due to a tsunami of a given height should be evaluated in order to formulate a correct disaster prevention policy.
Evaluation of Enhanced Performance for Caisson-type Breakwaters Using Interlocking System
Yi, Jin-Hak (Korea Institute of Ocean Science and Technology) | Park, Woo-Sun (Ocean Science and Technology School) | Seo, Jihye (Korea Institute of Ocean Science and Technology) | Won, Deokhee (Ocean Science and Technology School)
In this study, it was investigated the possibility for increasing the Damage level of coastal structures has been scaled up according to the stability through combining adjacent caissons simply. Using a caisson increase of wave height and duration of a storm due to the global breakwater composed of 10 caissons, numerical analyses were carried climate change. Therefore the design criteria for a new breakwater are out for major design parameters, i.e., stiffness of connecting cables and being intensified, and structural strengthening works are being also wave incident angles. In this study, the caisson was assumed as a rigid conducted for securing the existing breakwaters. Recently, an body, the foundation was replaced by springs attached to the caisson in interlocking caisson-type breakwater has gained much attention to the horizontal and vertical directions, and the connecting cables were enhance the stability of the conventional breakwaters. This study modelled as springs for simplification. The wave force acting on the investigated the dispersion characteristic of wave forces using an target caisson was calculated by using Goda's pressure formula and the interlocking system which connects the upper part of caisson with standing wave solution to consider phase differences.
Wave Reflection From Absorbing-type Breakwaters
Yueh, Ching-Yun (Department of Harbor and River Engineering, National Taiwan Ocean University Keelung, TAIWAN, China) | Chuang, Shih-Hsuan (Department of Harbor and River Engineering, National Taiwan Ocean University Keelung, TAIWAN, China) | Wu, Ming-Tsung (Department of Harbor and River Engineering, National Taiwan Ocean University Keelung, TAIWAN, China)
ABSTRACT The reflection of normal incident waves by absorbing-type breakwaters is investigated in this paper. The breakwaters consist of a perforated wall, a porous caisson and an impermeable back wall. The flow field is divided into four regions: a porous caisson region and three pure water regions. Under the assumptions of linear wave theory, the Darcy's law in the perforated wall, and the pore velocity potential theory of Sollitt and Cross (1972) in the porous caisson region, a 2-D BEM model is created to calculate the reflection coefficients of water waves by several properties of the breakwaters. The numerical model is calibrated by previous numerical studies of the limiting cases of a partially perforated-wall caisson breakwater and a vertical porous breakwater with an impermeable back wall. Generally speaking, the evaluation of the wave dissipation in absorbing-type breakwaters is bigger than a partially perforated-wall caisson breakwater. The reflection coefficient value implies the performance of wave absorbers in this study. Therefore, we examine the major factors that affect the reflection coefficient. INTRODUCTION Breakwaters that are widely used along shorelines, channel entrances, beaches, harbors, or marinas may vary in type according to their use. A traditional and the simplest form of breakwater, a rubble mound breakwaters, is quite suitable but very expensive for increasing water depths. Recently, many new types of breakwaters have been proposed and extensively studied for controlling ocean waves efficiently. In recent decades, perforated breakwaters have become popular as they can allow water waves to transmit through it, reduce the wave reflection and wave run-up in front of the structures. Thick permeable structures were considered by several researchers. Sollitt and Cross (1972) used Lorentz's principle of equivalent work to analyze the problem about ocean wave reflection and transmission at a permeable breakwater.