Stability Of Breakwaters Research Articles

An experimental study on the hydraulic stability of Icelandic-Type berm breakwaters

One of the key aspects of breakwater design and safety assessment is their stability evaluation. In the present paper, hydraulic stability of a multi-layer berm breakwater (MLBB) has been studied through varying the parameter of eroded area. To this end, a 2-D experimental model has been carried out in the wave flume of Tarbiat Modares University using irregular waves with a JONSWAP spectrum. A total of 150 tests have been performed to cover a wide range of sea state conditions and geometrical parameters such as wave height, wave period, water depth, berm width, berm elevation, stone class I height, front slope and nominal diameter of stone class I. In this study, a new dimensionless parameter is introduced to indicate that the wave breaking type plays a fundamental role in stability of MLBBs. Eventually; a new formula is derived to estimate the damage of MLBBs, based on different sea state conditions and various geometrical parameters. Comparisons are made between the estimated damage parameter of MLBBs by the proposed formula and those estimated by existing formulae. The results denote that the present formula not only performs well for MLBBs experimental data, but also indicates a reliable performance for some of Lykke Andersen's (2006) data in statically homogenous berm breakwaters (HBBs) outside the range of given formula. Furthermore, an innovative approach is presented to examine the eroded area based on the berm recession and the intersection point of reshaped and initial profile from SWL, which performs faultlessly rather than the existing one.

Stability Assessment of Rubble Mound Breakwaters Using Extreme Learning Machine Models

The stability number of a breakwater can determine the armor unit’s weight, which is an important parameter in the breakwater design process. In this paper, a novel and simple machine learning approach is proposed to evaluate the stability of rubble-mound breakwaters by using Extreme Learning Machine (ELM) models. The data-driven stability assessment models were built based on a small size of training samples with a simple establishment procedure. By comparing them with other approaches, the simulation results showed that the proposed models had good assessment performances. The least user intervention and the good generalization ability could be seen as the advantages of using the stability assessment models.

Study on the Influence of Harbour Channel Excavation on the Stability of Breakwater

A large number of soft clay layers are distributed in coastal areas, which brings risks to port construction. Especially in the course of channel excavation, the construction will affect the overall stability of the outer riprap breakwater. Through numerical simulation and Geocentrifuge model test, the influence of waterway excavation on the overall anti-sliding stability of a breakwater in Tianjin harbour is studied and analyzed. The experimental results show that when the excavation boundary line is 38.9 m away from the foot of the breakwater and the excavation depth is 10 m, the overall anti-sliding stability of the breakwater is less affected. The vertical displacement of the top of the breakwater is 6 mm, and the horizontal displacement of the foot of the breakwater is 23.4 mm, all within the safety control range.

Wave parameters influence on breakwater stability

This research paper experimentally explored the wave parameters effects on the breakwater armour layer stability. Breakwater stability mainly depends on the armour layer that guards the inner layers against the wave attack and the wave condition affects the breakwater stability. The wave height, length and steepness effect were investigated during the test program. Different formulas were available in the literature to predict the breakwater stability. The laboratory results were thus employed to assess the applicability of existing design equations. Experimental results showed that under normal wave condition (Hs) the breakwater was stable, whereas under storm condition (Hs of 1.2 designed wave height) the roundhead reached the failure state. The results approved the impact of wave parameters on the breakwater stability and damage progression. Results revealed that the existing design formulas underestimate the structure stability.

Modeling Study on the Hydrodynamic Environmental Impact Caused by the Sea for Regional Construction near the Yanwo Island in Zhoushan, China

Waves are one of the most important factors affecting offshore marine engineering. Accurate calculation of wave distribution is an important prerequisite to ensure the safety of coastal engineering construction. Due to the influence of complex topography, hydrological conditions, and marine structures on the propagation of waves offshore, slowly varying topography, refraction, diffraction, reflection, shallowness, and other phenomena may occur. This article combines the MIKE21 Spetral Waves (SW) wave model and the MIKE21 Boussinesq Waves (BW) wave model which are developed by Danish Hydraulic Institute (DHI) for a joint application (SW–BW nested model). It simulates the hydrodynamic environment of the Yanwo Island scenic area, located in Zhoushan, in both large and small ranges. In addition, wave height distribution and berthing stability of different breakwater planning schemes are calculated to optimize the layout of the breakwater. Through the analysis of simulation results, it is concluded that the hydraulic performance of Scheme 2 (the broken line section on the west side is 100 m long, and that on the east is 1200 m long, and the breakwater is rotated 8 degrees counterclockwise along the axis on the basis of Scheme 1) is better than that of Scheme 1 (the broken line section on the west side is 100 m long, and that on the east is 1100 m long), which can provide a more reliable construction reference for the construction of the Yanwo Island scenic area.

Stability of Rubble Mound Breakwaters—A Study of the Notional Permeability Factor, Based on Physical Model Tests

The Van der Meer formulae for quarry rock armor stability are commonly used in breakwater design. The formulae describe the stability as a function of the wave characteristics, number of waves, front slope angle and rock material properties. The latter includes a so-called notional permeability factor characterizing the permeability of the structure. Based on armor stability model tests with three armor layer compositions, Van der Meer determined three values of the notional permeability. Based on numerical model results he added for a typical layer composition one more value. Based on physical model tests, the present paper provides notional permeability factors for seven layer compositions of which two correspond to the compositions tested by Van der Meer. The results of these two layer compositions are within the scatter of the results by Van der Meer. To help determination of the notional permeability for non-tested layer compositions, a simple empirical formula is presented.

Development and Applicability of Multiscale Multiphysics Integrated Simulator for Tsunami

In this research, we develop a numerical fluid simulator coupled with a structural analysis. The purpose of this system is to efficiently calculate all stages of a tsunami from source to runup, including structural deformation. We also investigate the stability of breakwaters at Kamaishi port. The numerical results are compared with physical experiments, revealing good agreement. The system is applied to the local conditions at Kamaishi port to verify its applicability. Most of the breakwaters are washed away, which is similar to the actual reported damage, indicating that the proposed system can effectively reproduce tsunami structural damage.

Calculation of breakwater stability by strength reduction method

The breakwater is the first barrier to prevent sea wave for entering the port basin and vital to provide a safe environment for ships or vessels. The stability of a breakwater in North China is studied by strength reduction method. This breakwater is constructed with silt-solidified fills in bags and armoured with accropode blocks and four-pin concrete hollow blocks. Calculation result shows that the factor of safety calculated by strength reduction method is 2.52, and the breakwater is in a good stable state since the ground and breakwater have no trend to slip.

NUMERICAL ANALYSIS OF INTERLOCKING CAISSON BREAKWATER USING MODULAR SYSTEM

Breakwaters have been severely damaged quite often since they are directly exposed to large waves. And damage level of breakwaters has been scaled up because of abnormal global climate changes. In particular, according to the report of caisson breakwater damages in Japan(Takayama, 2002), it was found that damages caused by caisson sliding, account for more than 70% of breakwater failure modes. So, the design criteria for new breakwaters is being intensified to cope with abnormal global climate changes and unusual waves. In the case of a long structure, the wave force is reduced due to the phase difference in oblique waves. Therefore, if a caisson is made as long as possible, the stability of breakwaters could be ensured even if unusual high waves occur. Recently, interlocking caisson systems, which are to form a long caisson by interlocking individual caissons with each other, have been much attention to enhance the structural stability of conventional caisson breakwaters. In the present study, a modular caisson was proposed that can improve structural stability and workability by using the shear-key interlocking system; and the wave force reduction effects of the modular caisson breakwater were evaluated by numerical analysis method.

A CASE STUDY ON PERFORMANCE OF RESHAPING BERM BREAKWATERS: ORDU GIRESUN INTERNATIONAL AIRPORT, TURKEY

In this study, the stability and serviceability (wave overtopping) of hardly-reshaping berm breakwater of Ordu-Giresun International Airport and four alternative cross-sections of fully- and partly-reshaping berm breakwaters are assessed by physical model experiments. Ordu-Giresun International Airport is a public airport constructed on an approximately 1.77 km-square reclaimed land at the eastern Black Sea coast of Turkey. The reclaimed land area is protected with a 7345 m long hardly reshaping rubble mound berm breakwater at a depth of 11 m (MSL). The design high water level (HWL) corresponding to 100-yr return period is calculated as +1.12 m. The bottom slope from deep water up to 20 m water depth is around 1:50 and becomes steeper (1:20) towards the shore. The design wave characteristics at the toe of the structure (100-yr return period) is determined as Hs = 6.68m, Tm= 10.80 sec.

Hydraulic Stability of the Armor Layer of Overtopped Breakwaters

Mound breakwaters with significant overtopping rates in depth-limited conditions are common in practice due to social concern about the visual impact of coastal structures and sea level rise due to climatic change. For overtopped mound breakwaters, the highest waves pass over the crest producing armor damage, not only to the front slope, but also to the crest and the rear slope. To guarantee the breakwater stability, it is necessary to limit the armor damage in the three parts of the structure: Front slope, crest, and rear slope. This paper describes the hydraulic stability of the armor layer of medium and low-crested structures in wave breaking conditions. Small-scale physical model tests were carried out with different relative crest freeboards and three armor units: Rocks, cubes, and Cubipods. The armor damage progression in the front slope, crest, and rear slope was analyzed using the Virtual Net method to consider the heterogeneous packing and porosity evolution along the armor slope. A comparison is provided between the hydraulic stability of the different armors and their relationship with the measured overtopping volumes.

Least Squares Support Vector Mechanics to Predict the Stability Number of Rubble-Mound Breakwaters

In coastal engineering, empirical formulas grounded on experimental works regarding the stability of breakwaters have been developed. In recent years, soft computing tools such as artificial neural networks and fuzzy models have started to be employed to diminish the time and cost spent in these mentioned experimental works. To predict the stability number of rubble-mound breakwaters, the least squares version of support vector machines (LSSVM) method is used because it can be assessed as an alternative one to diverse soft computing techniques. The LSSVM models have been operated through the selected seven parameters, which are determined by Mallows’ Cp approach, that are, namely, breakwater permeability, damage level, wave number, slope angle, water depth, significant wave heights in front of the structure, and peak wave period. The performances of the LSSVM models have shown superior accuracy (correlation coefficients (CC) of 0.997) than that of artificial neural networks (ANN), fuzzy logic (FL), and genetic programming (GP), that are all implemented in the related literature. As a result, it is thought that this study will provide a practical way for readers to estimate the stability number of rubble-mound breakwaters with more accuracy.

Stability analysis of a composite breakwater at Yantai port, China: An application of FSSI-CAS-2D

In offshore areas, quaternary loose seabed soils widely distribute around the world, and a great number of offshore structures actually have been constructed on quaternary seabed floors. In practical engineering, it is highly necessary to evaluate the stability of offshore structures built on quaternary seabed floors under the impact of extreme ocean waves. Based on the VARANS equation and the dynamic Biot's equation, an integrated numerical model FSSI-CAS 2D has been developed by Ye et al. (2013b) to investigate the interaction between ocean waves, marine structures and their seabed foundations. In this study, taking the composite breakwater project in the west harbour zone of Yantai port in China as an engineering case, the integrated numerical model FSSI-CAS-2D is used to evaluate the stability of the composite breakwater under the impact of fortified ocean waves with a 50 years recurrence period. Computational results indicate that the composite breakwater at west harbour zone of Yantai port would be generally stable during its service life. This application demonstrates that the integrated model FSSI-CAS-2D is applicable, and suitable for practical engineering. The case study illustrated in this study can provide ocean engineers with an excellent case demonstration of engineering application, to evaluate the stability of offshore structures under the impact of extreme ocean waves.

Dynamic response and liquefaction analysis of seabed-rubble mound breakwater system under waves

Dynamic response and liquefaction potential of granular seabed around a rubble mound breakwater is investigated under waves. Dynamic response of the system is assumed to be governed by coupled Biot equations of poroelasticity. Mathematical formulations in terms of governing equations of partially-dynamic and quasi-static cases are considered. Dynamic response of seabed soil is analyzed using classical finite elements and a number of parametric studies are performed to draw a complete picture of the response of the system. Vertical displacement, shear stress and pore water pressure distributions are considered as the most representative variables defining the variations of response of the whole system and which are thus evaluated along some key cross sections around the breakwater. The results indicate that inertial terms associated with solid skeleton have almost no effect on the dynamic response and liquefaction potential. It was found that large amount of wave-induced shear stresses are taken by a relatively rigid core layer contributing to the breakwater stability where also the pore pressures dissipate significantly towards the seabed interface. Standing wave-induced instability of the system is also investigated in terms of instantaneous liquefaction based on the effective mean stress criterion. There is liquefaction observed at the seaward surface of the rubble whose depth increases significantly with decreasing saturation. While the core overall provides more stability, the adverse effect of this is more liquefaction in the outer layer.

Stability Assessment Formulas for an Interlocking Caisson Breakwater under Oblique Wave Conditions

ABSTRACT Park, W.S.; Won, D.H.; Seo, J.H., and Lee, B.W., 2018. Stability assessment formulas for an interlocking caisson breakwater under oblique wave conditions.. In: Shim, J.-S.; Chun, I., and Lim, H.S. (eds.), Proceedings from the International Coastal Symposium (ICS) 2018 (Busan, Republic of Korea). Journal of Coastal Research, Special Issue No. 85, pp.1236–1240. Coconut Creek (Florida), ISSN 0749-0208. As a countermeasure for improving the stability of conventional caisson breakwaters, a method has been proposed in which adjacent caissons are interlocked with each other to consecutively resist the abnormal wave forces. It is not possible to reasonably evaluate the stability of breakwaters that have been elongated by interlocking, especially for oblique waves, by using the current design criterion defined for breakwater sections. Therefore, it was studied the stability assessment formula of an interlocking caisson breakwater under oblique wave conditions, in this study. To maintain consistency in che...

Deformation and Stability Analysis of Breakwater Structure in Morosari Coast, Demak, Central Java

Indonesia is an archipelagic country with the second longest coastline in the world. The problem faced by coastal areas in Indonesia is the erosion, mainly due to the development of ponds, as happened in Morosari Demak. Several segments of breakwaters from concrete blocks have been constructed. But it has not been able to withstand erosion-, even the breakwaters were damaged. This study is aimed to evaluate the stability and deformation of breakwaters that have been built. Evaluations include armoring stability, soil bearing capacity, land subsidence, and consolidation. Two segments of breakwaters constructed in different years, 2011 (A) and 2013 (B), are evaluated by measuring cross-sectional, and elevation. Measurements were made twice at different times. Changes that occurred during that period were compared with the difference between the initial condition (as built drawing) and the condition when the measurement was done. The results indicated that the breakwater have been deformed both horizontally and vertically. The breakwater tends to move northwest by 6.662 and 8.330 cm/year for breakwater A and B consecutively, and go down by 5.976 and 4.982 cm/year. There are two factors caused breakwater deformation, soil consolidation, and armoring. The consolidation rate measured in 2016 was 4.234 and 5.040 cm/year for breakwater A and B consecutively. The 300 kg of existing armoring was unstable, the stable armoring should be 365 kg.

Effects of submerged berms on the stability of conventional rubble mound breakwaters

Berms deployed at the toe of conventional breakwaters may be needed to reduce bottom settlements and to limit scour in front of the structure due to coastal currents. In the mean time, they may be effective in increasing the stability of the armor layer and also in minimizing the wave overtopping discharge compared to straight sloped conventional breakwaters without a berm. This research aims to provide a new design criterion for the armor layer of conventional breakwaters with submerged berms marked by small thickness compared to water depth. Indeed, past researches focused on the influence of relatively high berms on the stability of the armor layer. The design of the berm itself is not tackled herein. The effects of submerged berms on the incident waves transformation have been evaluated by means of a numerical model, validated by using experimental data. Then, a parametric correction factor of the incident significant wave height at the toe of the structure is provided and included in well established design criteria. The experimental comparison confirms the reliability of the proposed method by highlighting the importance to use design criteria within their validity ranges, in order to avoid an unsafe dimensioning of the armor elements.

Stability of rubble-mound breakwaters under tsunami first impact and overflow based on laboratory experiments

Recent tragic tsunami events, like those that occurred in the Indian Ocean in 2004, and in Japan in 2011, have revealed the need of further work to reduce tsunami risk in coastal areas. An important aspect towards risk reduction is the study of the interaction between tsunami waves and coastal structures as these are the first to receive the tsunami's energy. Dikes and breakwaters must have an adequate structural behavior and maintain some functionality and operability under tsunami attacks to be able to contribute to the reduction of its consequences. Within this scope, laboratory experiments on scaled models of two typical Mediterranean rubble-mound breakwater typologies under tsunami waves were conducted for the first time. The tsunami's action was split into 2 parts: (1) the first impact of solitons was tested by means of large solitary waves and, (2) the subsequent overflow was approached by applying a pump-driven wave maker. The damage on the breakwaters due to these actions was measured and assessed. The result is an in-deep analysis of the relationships among Stability Number, Damage Level and Number of tsunami waves. The outcome of this analysis includes the development of a set of formulae that provide, in the range of the conducted tests, the value of the Damage Parameter, so that tsunami actions can be taken into account in the design of rubble mound structures. Finally, based on the results of these experiments, the threshold values of the Damage Parameter used to characterize damage in armors (Initiation of damage, initiation of destruction, destruction) was particularized for tsunami actions.

Effect of Wave-Induced Seepage on the Stability of the Rubble Mound Breakwater

Effect of Wave-Induced Seepage on the Stability of the Rubble Mound Breakwater

Countermeasures for enhancing the stability of composite breakwater under earthquake and subsequent tsunami

Many breakwaters have collapsed in the past due to earthquakes and subsequent tsunamis, resulting in considerable devastation as the breakwaters failed to prevent the tsunami from entering the coastal plain areas. Breakwater failures are mainly caused by damage to its foundation ground. However, the damage mechanism of breakwater foundation during earthquakes and tsunamis remains unclear. This study focuses on the breakwater failure mechanism due to collapse of its foundation under the action of an earthquake and subsequent tsunami. In addition, reinforcing countermeasures for breakwater foundation to mitigate damage due to compound geodisasters triggered by earthquakes and tsunamis are proposed. Sheet piles and gabions were used in the breakwater foundation as reinforcing countermeasures. To evaluate the effectiveness of the reinforced foundation, a series of shaking table tests and hydraulic model tests were performed. The tsunami overflow tests were conducted on the same model after the earthquake loadings, and comparisons were made between the conventional and reinforced foundations. It was observed during the tests that the reinforced foundation could effectively reduce the damage to the breakwater caused by earthquake and tsunami-induced forces. Numerical analyses were performed to clarify the mechanism of the soil–breakwater–reinforcement–fluid system. Overall, this study is useful in practical engineering, and the reinforcing foundation model could be adopted for offshore structures to reduce damage from earthquakes and tsunamis in the future.