Rubble Mound Breakwaters Research Articles (Page 1)

ABSTRACT Rubble-mound breakwaters play a fundamental role in protecting coastal areas against wave action. Understanding the damage evolution and failure of the breakwaters is essential for effective design and adaptation strategies, particularly in light of ongoing climate change scenarios, where extreme events are becoming more frequent and intense. The present study introduces a practical image-based approach for assessing the damage progression of a small-scale model of rubble-mound breakwater in laboratory environment. The physical model, armored with a single-layer of concrete armor units, was subjected to climate-driven extreme storm conditions representative of failure scenarios beyond standard design thresholds. At a number of intervals, an Unmanned Aerial Vehicle (UAV) was operated to capture aerial images of the breakwater. The analysis of these images enabled the assessment of erosion and accretion patterns along the model, the identification of the most vulnerable areas and a detailed understanding of damage evolution and progressive failure mechanisms. The experiment captured the onset and speed of the progressive failure of the single-layer concrete armor units under extreme wave action. The resulting insight into damage evolution may prove highly valuable for the future adaptation strategies for coastal structures originally designed without accounting for the effects of climate change.

Experimental study on the hydraulic performance and stability of a homogeneous overtopped rubble mound breakwater

The stability of rubble mound breakwaters is highly affected by extreme wave loading. While extensive research has been devoted to wave-induced scour and liquefaction around breakwaters, comprehensive stability evaluations of the rubble mound breakwater core remain limited. This study develops a numerical framework to investigate the stability of rubble mound breakwaters subjected to solitary wave loading. Wave motion is modeled using the Navier–Stokes equations, wave-induced pore pressure is computed based on Darcy’s law, and soil behavior is represented through the Mohr–Coulomb constitutive model. The numerical model is validated against experimental data. To assess structural stability, the strength reduction method is employed to calculate the Factor of Safety (FOS) during wave propagation, with the minimum FOS serving as the stability criterion. Furthermore, the influence of key parameters, including wave height, soil shear strength, wave–current interaction, berm dimensions, and slope gradient, on breakwater stability is systematically analyzed.

Perforated thin-plate structures, which can effectively dissipate wave energy and also serve as base structures for growing corals in nature-based solutions to shore protection problems, can be promising alternatives to traditional rubble-mound breakwaters for shore protection. The growth of corals may be affected by the geometrical shapes of the base structures. This study investigates wave interaction with one or multiple submerged perforated thin-plate structures, emphasizing effects of structure's shapes on wave transmission and wave loading. Using a multi-domain boundary element method (BEM) and a parameterization of the pressure drop across a perforated thin plate, six cross-sectional shapes that belong to the following four types are considered for different ratios of structure height to water depth: rectangular, trapezoidal, triangular, and semi-circular shapes. For the purpose of verifying the BEM codes, an analytical solution was also developed for a single structure with a rectangular shape. The results show that for a given number of structures, the rectangular and trapezoidal shapes are more effective in reducing wave energy transmission, providing protection across a range of wave periods. The reduction of wave energy in the transmitted waves is controlled mainly by the energy dissipation into turbulence. Resonant reflection, found when multiple structures are used, can only slightly affect wave transmission in the frequency range of practical relevance. The wave loading on the structures for promising designs is studied. The results reported here are useful for marine biologists and coastal engineers to choose a suitable shape for the base structures for reducing wave energy and growing corals and geotechnical engineers to design foundations and anchoring schemes.

This study investigates submerged rubble mound breakwaters as an eco-friendly alternative for coastal protection. The purpose of this research is to experimentally analyze the effectiveness of different core configurations of submerged rubble mound breakwaters in dissipating wave energy and reducing coastal erosion. The study utilized a 2D wave flume to simulate coastal wave conditions, testing various breakwater models reinforced with geotextiles, geotubes, and without additional reinforcement. The experimental results demonstrate that submerged rubble mound breakwaters can significantly attenuate wave energy, with reinforced models showing enhanced structural stability and reduced material displacement. The findings suggest that incorporating geotextile or geotube materials improves the performance of the breakwaters, particularly in high-energy wave conditions. This research aligns with the Sustainable Development Goals (SDGs), particularly SDG 13 (Climate Action) and SDG 9 (Industry, Innovation, and Infrastructure), providing valuable insights for sustainable coastal management. These findings support the development of more resilient coastal defenses that protect against wave-induced damage while maintaining ecological integrity.

Mean wave overtopping discharges at rubble mound breakwaters were measured in a wave flume for various rock-armoured slopes. In the physical model tests, the structure slope was varied: 1:1.5, 1:2, 1:4, 1:6 and 1:8 slopes were studied. The mean wave overtopping discharges appeared to be strongly dependent on the structure slope for both “breaking waves” and for “non-breaking waves”. Existing expressions that also account for friction, a berm (if present), a protruding crest wall (if present), and the angle of wave attack, were extended by incorporating both the slope angle and the wave steepness of the incident waves at the toe. The match between the empirical equations and the data (new and earlier tests) is good. The guidelines to estimate wave overtopping discharges as presented here perform much better than existing guidelines since most existing guidelines for rubble mound breakwaters ignore the explicit influence of the structure slope and the wave steepness. Both for “breaking waves” and for “non-breaking waves”, the structure slope and the wave steepness clearly affect wave overtopping discharges, and therefore expressions that ignore these effects should not be used if accurate estimates of mean wave overtopping discharges are required.

Wave Runup and Reflection at Rubble Mound Breakwaters with BPPT-Lock Armor Layer

Integrated approach incorporating experimental validation for predicting wave-induced pressures in rubble mound breakwater–seabed systems under long-period waves

Estimates of wave overtopping generally determine the required crest level of coastal structures. Wind affects wave overtopping, especially for coastal structures with crest walls because these can cause a vertical wave motion above the crest that is susceptible to wind. Within the relevant range of overtopping discharges, the expected wave overtopping discharge at coastal structures with a crest wall can be up to 5 times larger than for situations without wind. For smaller discharges the influence factor for wind can be significantly larger. In the present study based on physical model tests the maximum influence of wind on wave overtopping discharges has been studied for (impermeable) dikes and (permeable) rubble mound breakwaters with crest walls. The influence of wind on wave overtopping is mainly determined by the magnitude of the overtopping discharge itself and by the height of the crest wall. The result of the study is a guideline to estimate the maximum influence of wind on wave overtopping at dikes and rubble mound breakwaters with a crest wall.

Recent land reclamation projects where maximization of land use is crucial have resulted in the appearance of types of coastal defenses that have not been extensively studied. Rubble mound breakwaters with open filters or geotextiles are increasingly used in reclamation projects. Due to placement of landfill material (e.g. dredged sand with silt) close to the rubble mound, these structures are potentially vulnerable to internal erosion and material loss through the coarser breakwater layers, a process which is often characterized as suffusion. Several past studies have highlighted these issues (Cantelmo et al 2011; Polidoro et al 2015). Incipient of sediment motion in the landfill area is highly dependent of the pressure gradients developing and reliable prediction of pressures is of great importance. This work presents a methodology for modifying existing formulas for estimating internal pressures in rubble mound breakwaters in the presence of reflective surfaces. The methodology follows a relatively simple concept and is applied to correct predictions of the formula proposed by Burcharth et al (1999). The corrected formula is compared against numerical modelling predictions published in Dimakopoulos et al (2023). Comparison and further verification of the formula will be performed following additional numerical (CFD) model simulations and experimental data.

This presentation aims to analyse ancient port structures, hoping that the ancient can tell us something useful for the modern, with special focus on breakwaters and quay walls. Archaic ships and the oldest known port structures are briefly presented. Vertical breakwaters and quays, large concrete blocks called pilae, arched breakwaters and rubble mound breakwaters are described in the ancient world. Some geomorphological aspects of a few coastal harbours are also reviewed. It is concluded that the Romans mainly used natural coastal shelters, but some major ports were built in places without any natural shelter, for strategic or economic reasons. Most of today’s concepts for maritime structures were already existing in Roman times and it seems that little progress was made until the 18th c. when large maritime structures started to be built again. The combination of concrete and steel enables modern engineers to build higher, deeper, and larger than Roman engineers could dream of, but some modern structures may not last as long as some Roman structures, especially in salt water ...

Simulating the flow depths and velocities occurring during wave overtopping events at coastal structures with a numerical model is challenging. Reproducing these variables is relevant since they can be used as design parameters if they can be predicted accurately. OpenFOAM® was used to analyse flow depths and velocities that occur during wave overtopping events at a rubble mound breakwater with a crest element. The model was validated with physical model tests. Even though the quantitative prediction of the numerical model was not extremely accurate, the model provided valuable information to study the physical processes occurring during wave overtopping events. In particular, the effects of varying wave conditions and the protrusion height of the crest element have been studied. For events occurring with high exceedance probability, the flow depths and velocities follow the trends found by other authors who performed physical model tests. Flow depths and velocities that happen under complex flow phenomena still require further research.

The design of maritime structures in Italy (and in Europe) is not supported by current technical standards that deal specifically with criteria and methods for evaluating the meteoceanographic loads governing the design. We refer specifically to port breakwaters or coastal defense structures involving gravity type structures, such as caisson breakwaters, concrete sea walls and rubble mound breakwaters. For the design of these structures, like for building structures in general, the 2018 “Technical Standards for Constructions” (NTC 2018) edited by the Italian Ministry of Infrastructures and Transport do apply. These standards, however, do not specifically address the key aspects affecting the design of maritime structures. Therefore, for marine engineering topics designers typically still refer to a specific standard dated back to 1996, the “Technical Instructions for the Design of Breakwaters” edited by the Italian Superior Council of Public Works (CSLLPP). While the 1996 Technical Instructions are still reliable guidelines for many aspects, they are not up-to-date and aligned with the limit state design method.

Rubble mound breakwaters are characterized by their considerable mass, as they generally consist of a quarry- run core, rock filter layer(s) and external armour layer made of rocks or concrete blocks. The weight (load) of the breakwaters is fully borne by the foundation ground. Since these structures are made at sea, foundation ground aligns with the seabed, which can be either natural or requires preliminary dredging. Consequently, the seabed and all subsoil layers experience a significant increase in tension. Depending on the nature and mechanical properties of subsoil, this could potentially lead to relevant geotechnical issues, ranging from lack of slope stability to large settlements. If thick layers of soft soil (e.g., normally consolidated clay) are present, critical settlement behaviour might be expected. Therefore, specific design solutions must be implemented. Due to the challenge of reducing the total amount of settlements, significant efforts are directed toward accelerating and concentrating settlements as much as possible during the construction phase.

Coastal regions have always been alluring places for settlements due to their proximity to the ocean, abundant natural resources, and the high quality of life they provide. Nevertheless, these areas face various vulnerabilities, including the effects of climate change like rising sea levels, storm surges, and more frequent extreme weather events. Rubble-mound breakwaters are commonly used as protective structures along the coast, but recent years have brought significant challenges due to climate change and growing environmental concerns. Coastal communities and managers are now seeking solutions that are more sustainable and have fewer impacts on the landscape and ecology. These demands are reshaping the conventional approach to designing these structures. To address these challenges, it is necessary to adapt breakwaters to meet present, future, social, and environmental expectations.

Hybrid artificial reef structures can be designed to promote the development of a self-sustaining habitat for reef organisms while simultaneously enhancing their effectiveness at coastal protection. Such hybrid structures also offer many additional ecosystem benefits over conventional engineering structures that are used to provide coastal protection (e.g., rubble-mound breakwaters). In this study we investigate the wave attenuation capacity of engineered oyster reef modules that have been designed through the Defense Advanced Research Projects Agency (DARPA) initiative Reefense: A Mosaic Oyster Habitat for Coastal Defense. The modules are designed with significant porosity (through misaligned holes), shelves to facilitate oyster recruitment, and an interlocking mechanism to maximize reef stability.

Rubble-mound breakwaters are structures specifically designed to protect coastal areas from wave action requiring robust design and ongoing monitoring to maintain their structural integrity. The study presents an experimental and numerical investigation of damage progression in a small-scale model of a rubble-mound breakwater, conducted at the EUMER laboratory. The physical model, featuring Accropode© II and Accroberm© I armour units, has been subjected to storm-like conditions, and the progression of damage has been assessed using an innovative UAV photogrammetry approach. The proposed method enabled the evaluation of areas where erosion and accretion occur due to the action of extreme waves, identifying critical zones most susceptible to damage. To complement the experimental findings, a numerical simulation using OpenFOAM libraries combined with OlaFlow, a Computational Fluid Dynamics (CFD) model, has been integrated using the observed data. The CFD model provided additional insights into the flow fields and forces distributions acting on the structure, contributing a more detailed understanding of the damage mechanisms. The combination of UAV photogrammetry and CFD analysis allowed for a deeper assessment of the damage evolution, offering a comprehensive approach to breakwater design and maintenance strategies.

At construction sites of rubble mounds, concern often arises regarding the vulnerability of these structures to high waves. To investigate potential damage to rubble mounds, both hydraulic model experiments and numerical analyses have been used. Numerical analyses typically employ methods such as the finite element method or particle-based approaches, which can involve high computational loads. In this study, the authors focused on the similarity between the damage process of rubble mounds and advection-diffusion phenomena, initiating repeatability calculations using analytical solutions of advection-diffusion equations. Results from hydraulic model experiments revealed clear relationships between diffusion coefficients and advection velocities, based on wave conditions and mound conditions. This insight enabled the determination of advection velocities and diffusion coefficients from the given wave and mound conditions. Therefore, an attempt was made to simulate the damage process of rubble mounds using advection-diffusion equations. The height reduction of the rubble mound’s crest was effectively reproduced; however, challenges remained, as the calculated results tended to underestimate the slope profile on the offshore side.

In the recent years, the effects of climate change are becoming increasingly evident (e.g., Naughten et al., 2023; Pörtner et al., 2022). Sea level rise, change in the intensity of storm surge, and wave heights are typical consequences of climate change in the coastal environment (e.g., Toimil et al., 2020). Therefore, coastal structures deployed to protect coastlines and harbors from wave action, may become ineffective due to the potential increase of wave loads, run-up, and overtopping phenomena (e.g., Galiatsatou et al., 2018). Indeed, several adaptation measures for existing coastal structures have been proposed (e.g., Burcharth et al., 2014). Past research studies illustrated how the deployment of a berm in the seaward side of conventional rubble mound breakwaters can significantly improve the performance of the structure. (e.g. Van Gent, 2013; Celli et al., 2018; Celli et al., 2021). Basically, the presence of a berm enhances the wave energy dissipation at the toe of the armor layer. Besides the stability of the structure, this could be effective in the reduction of wave run-up, and overtopping phenomena, potentially. To investigate the role of the submerged berm on the wave run-up phenomenon, a series of 2D experimental tests is being carried out at the Environmental and Maritime Hydraulic Laboratory (LIam) of the University of L'Aquila.

The role of adaptive solutions for reducing coastal risks is a crucial issue that is increasingly captivating the coastal community. The present work analyzes attached/detached rubble mound breakwaters designed to protect vertical walls with very shallow foreshores. In particular, we aim to understand the behavior of these protective structures in reducing wave overtopping at seawalls and, thus, softening flooding risks. Laboratory data and CFD numerical experiments have shown that these adaptive solutions have a beneficial effect as long as the seawall is not located in the inner surf zone. Finally, we have provided mean overtopping discharge predictive tools for walls protected by either attached or detached breakwaters.