Failure Of Breakwater Research Articles

Numerical analysis of the breakwater failure at the Sergipe Terminal Port

The breakwater failure at the Sergipe Harbor is a well-known event among the Brazilian geotechnical community, which provided great knowledge about the behavior of embankments on soft soils, although some questions still remain, since the back analysis diverged from the field outcome. In this context, this work aims to carry out a numerical analysis of the construction of the breakwater using the finite element method to understand the mechanisms of failure. A fully coupled flow-deformation analysis was performed in Plaxis 2D software, using the Soft Soil Creep and Mohr-Coulomb constitutive soil models. The Volume Method was also applied to estimate the stability of the slopes, from the calculated numerical displacements. The interpretation of the results allowed to verify that the analysis simulated behaviors that had been raised as responsible for the failure. High excess pore pressure levels were generated in the phase at which failure occurred, in addition to a strain softening behavior, which, alongside the progressive failure, could justify why the back analysis considering unrealistic gains in undrained strength, calculated by the increase of the vertical effective stresses, had provided missed factors of safety. Although shear deformations and horizontal displacements were verified for both sides of the breakwater, the “shared failure” assumption could not be verified, since the shear stress was mobilized in the rockfill.

Experimental study on time-varying failure evolution of armour blocks on sloping breakwaters

The time-varying failure evolution is significant for revealing failure mechanism of breakwaters. Physical experiments were conducted to investigate the time-varying failure evolution of armour blocks on sloping breakwaters, and the effects of the block placement density, wave height, wave period, wave impact time, and block type on the stability of armour blocks are discussed. The results showed that the time-varying failure evolution of armour blocks was not uniform with an increase in wave impact time. However, a large-scale rapid damage maybe occur in a certain period of time, which was enhanced with a decrease in block placement density and an increase in the incident wave height and wave period. With the same block placement density, the instability rate with uniform reduction per row was generally lower than that with centralised and decentralised reduction. Furthermore, when the design wave height was increased by less than 30%, the protection effect of the accropode was superior to that of the dolosse. However, the protection effect of the two was opposite when the design wave height was increased by over 30%. The results reveal the time-varying failure law of breakwaters, which will contribute to further study the risk assessment and early warning of breakwater failure.

Seepage failure prediction of breakwater using an unresolved ISPH-DEM coupling method enriched with Terzaghi’s critical hydraulic gradient

This study develops a new numerical simulation model for rubble mound failure prediction caused by piping destruction under seepage flows. The piping has been pointed out as a significant cause of breakwater failure during tsunamis. Once boiling and heaving occur on the mound surface, the piping suddenly propagates in the opposite direction of seepage flow. For the seepage failure prediction, a coupled fluid-soil-structure simulator is developed by combining the ISPH for fluid and the DEM for rubble mounds and caisson blocks. The ISPH, a Lagrangian particle method for incompressible fluids, can simulate seepage and violent flows such as tsunamis. The DEM has been applied for discrete particle and rigid body simulations that include discontinuous deformation, as in the rubble mounds failure and large displacement of the caisson block. ISPH-DEM coupling simulations have already been proposed as a technique for multi-phase flows. Still, the technique cannot reproduce the sudden onset of piping from a stable mound. Two simple assumptions are applied to reduce the numerical cost for the fluid-soil-structure simulators of a breakwater structure composed of a rubble mound and the caisson block. Firstly, each rubble is modeled as an idealized spherical DEM particle with the mean diameter of the rubble. The ISPH particle size is assumed to be the same size as the DEM particle. Under these assumptions, the unresolved coupling model between rubble mound particles and fluid, which obtains the interaction through empirical drag force, should be applied. At the same time, the interaction between the fluid and the caisson block is fully resolved with the spatial resolution with the ISPH and DEM particle size. Our new contribution in this paper is how to model the interaction as an unresolved coupling between seepage flow simulated by ISPH and rubble mound particle modeled with DEM. Our original seepage failure experiment is simulated using the proposed ISPH-DEM coupling simulator. We identified the conventional drag force models as the unresolved coupling model are insufficient to initiate the boiling and piping observed in the experiment. It may be due in one part to excessive averaging of flow velocities caused by unresolved coupling. Therefore, Terzaghi’s critical hydraulic gradient is introduced to initiate the boiling and heaving. Unstable DEM particles, judged by Terzaghi’s critical hydraulic gradient, gradually lose their mass to represent unresolved suspended fine rubble mound particles. Our models qualitatively reproduce the sand boiling and backward erosion in the opposite direction of the seepage flow, as shown in the experiment.

Experimental Study on Destroy of Dolos Armored Breakwater, Pacitan in Indonesia

The breakwater armored with 15 T Dolos block had destroyed several times during constructing even the section verified by experiment study in wave flume, and it was destroyed again after the repair design and test verification. The damage phenomena were compared between on site and in the lab. In the third model test study, it proposed the problems of rod broken caused by block shaking and rolling impact, as well as overall sliding caused by small block supporting the big block. The stability of the repair plan was verified again by increasing the block weight, and the section was verified under the wave impact after on-site implementation. The study also revealed the fact that shaking led to the broken of the rod and the breakwater failure .

Breakwater subjected to tsunami–impact: Physical modelling of geotechnical phenomena

As dramatically demonstrated by the failure of Tsunami-resistant breakwaters during the 2011 Tohoku earthquake, the behavior of structures subjected to Tsunami-impact is not fully understood. This paper studies experimentally the behavior of a simplified breakwater subjected to Tsunami-impact using a novel Miniaturized Tidal Generator (MTG). The response is monitored through a combination of image analysis and a unique instrumented-breakwater that allows direct measurement of the developing forces. Experiments reveal strong coupling between the scour-feature, the hydrodynamic forces acting on the breakwater, and its mechanical behavior. Upon overtopping, a plane-jet of water falling at an inclined trajectory results in progressive undermining of the foundation. Measurements reveal that the commonly assumed simple sliding-type failure on level-ground is difficult to promote. The failure mechanism consists of combined (VHM) bearing capacity failure due to combination of loss of support, hydrodynamic loading, and buoyancy effects.

Analysis of the Power Plant Breakwater Failure Subjected to Typhoon Mangkhut Based on Model Experiment

Growing social concern regarding the environmental and visual impacts associated with coastal structures due to climatic change is leading to a reduction in breakwater failures. After Typhoon Mangkhut passed through the southeastern coast of China on September 16 in 2018, the breakwater of a Power Plant was serious failure. As a case study based on model test, the failure process and causes of breakwater were explored in this paper. The wave height and water level were used as the wave parameters, which were accurately extracted by the GOHS system when the typhoon transits, and the breakwater failure process was reproduced based on the typhoon wave forces action at that time. By the experimental result investigating, it was found that the joint of the caisson breakwater and the mound breakwater was firstly failure, then the armor blocks and stones near the seawalls became to be unstable, the seawall was collapsed finally. Based on the analysis of the experiment, the distribution in time and space of the damage of the protective blocks are obtained and divided into different damage areas according to the degree of failure. The wave energy concentration as a important factor were proposed in this paper and the conclusion would be provide as a reference for the study of breakwater engineering.

Application of SPH-DEM coupled method to failure simulation of a caisson type composite breakwater during a tsunami

During the 2011 Mw9.0 Tohoku Earthquake, caisson breakwaters in several ports experienced severe tsunami damage. Such failures were probably caused by a combination of scouring and seepage destruction of foundations and by large horizontal forces caused by the tsunami. We use a coupled Smoothed Particle Hydrodynamics (SPH) – Distinct Element Method (DEM) analysis method based on locally averaged equations of motion to analyze scouring and seepage flow phenomena at caisson-type breakwaters during the tsunami. Permeability tests and numerical simulations verified the coupled analysis methods that calculate the forces between solid and liquid phases. Numerically simulated triaxial tests determined the numerical parameters. Experimental simulations of caisson-type breakwater failures under centrifugal conditions validated the numerical method. Numerical simulations of the collapse process in the breakwaters agreed fairly well with experimental results at centrifugal acceleration fields. Thus, the SPH-DEM analysis method is applicable for predictions of collapse or failure in composite type breakwaters during a tsunami.

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.

Analysis of Waikelo Port Breakwater Failure through 2D Wave Model

Waikelo Port is located in South West Sumba of East Nusa Tenggara. The port facilities are protected by breakwater with a vertical wall construction and it was built in a relatively deep ocean at -15m of Low Water Sea Level (LWS). On 21 of January 2012, an earthquake with magnitude of 6.3 Richter scale occurred around Sumba Island and it caused cracking in the concrete wall of breakwater. Then, 4 days after on 25 st January 2012, a heavy wind of 20–23 knots generated a high wave around 4.0–5.0m in Sumba strait. These high waves caused a critical damage on the west part of the breakwater. The damage of port facilities were getting worse when a storm called Lua hit on March 2012. This study was conducted to observe the effect of the extreme event in the failure of breakwater. The result of two-dimensional (2D) wave model shows that the wave heights in the area of breakwater are varied 3.80 to 4.0m. It is quite greater than the wave design of 50 years return period (= 2.00m) which was used in breakwater design and calculation. This observable fact confirms that the failure of breakwater was caused by the continuous extreme events that exceed the design criteria

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.

Numerical study on loosely deposited foundation behavior around a composite breakwater subject to ocean wave impact

In this study, an integrated model is developed to investigate the potential risk for failure of caisson-type breakwaters caused by liquefaction in its loosely deposited sand foundations. In the present model, the Volume-Averaged Reynolds Averaged Navier-Stokes (VARANS) equations are used for solving flow inside and outside the porous media, while Biot's consolidation equation is used for linking the soil skeleton-pore fluids interactions. A new developed poro-elastoplastic model is implemented to reproduce the behavior of loose sand foundation under cyclic shearing. Verification of the present numerical framework includes (i) comparison with the laboratory experiments in terms of water surface levels around the structure, and the fluctuating component of the pore water pressure inside the rubble mound and seabed foundation; and (ii) comparison with the geotechnical centrifugal wave tests for the wave-induced residual component of pore water pressures in a porous seabed. Based on the present model, the hydrodynamic process and the associated dynamic foundation behavior involved in the interactions between the ocean waves, a composite breakwater and its loose sand foundations was performed and analyzed. Particular focus is put on the residual pore pressure development and the resulting liquefaction around the structure under combined actions of both wave and structure rocking motions. Based on the numerical examples presented, under combined actions of both wave and caisson motions, liquefaction starts on both edges of the breakwater and spreads sideways until reaching an equilibrium state where the maximum liquefaction depth can be observed. The liquefied zone around the breakwater is asymmetric in nature, and the maximum depth of soil liquefaction appears at the seaward side of the structure. Furthermore, the parametric study indicates that the maximum liquefaction depth around the composite breakwater increases with increasing wave steepness (H/L0) and relative water depth (d/L0) and decreasing soil permeability (ks).

Reliability Analysis of Waste Tires Semi-Submersible Breakwater

With the continuous development of social economy, China's port construction scale has become saturated. As an important part of the harbor, the breakwater plays a crucial role in the safety of the working environment in the harbor, and the reliability of the breakwater is an assessment of its safety. Build on the previous studies, this paper puts forward a semi-submersible breakwater using waste tires. The reliability of this breakwater is analyzed by Monte Carlo method of artificial neural network based on Matlab, and the results are compared to those of Direct sampling Monte Carlo method and Important sampling Monte Carlo method. The results show that the Monte Carlo method is able to analyze the reliability of overturning failure of semi-submersible breakwater of waste tire. Compared with the other two consequences, the result is more accurate. The Monte Carlo method of artificial neural network based on Matlab has the obvious advantage in being devoted to the problem of complex structure and variable. Safety of the breakwater meets the relevant requirements and can be applied to the actual engineering. It can be seen that waste tires has a high degree of reliability, daptability, and a wide range of applications.

Analysis and classification of stepwise failure of monolithic breakwaters

Analysis, interpretation and classification of stepwise failure of monolithic breakwaters are presented. Through the stepwise failure mechanism, monolithic breakwaters develop incremental residual displacements with each wave load event. This mode of failure is associated with the highly complex processes involved in wave–structure–foundation interaction and may occur even under relatively moderate wave conditions. Based on the results of the analysis of a well validated CFD–CSD model system and large-scale physical model test data, a new concept, named load eccentricity concept, is proposed to classify the response of the foundation in four load eccentricity regimes. This concept is based on the relative eccentricity e/B, i.e. the ratio of eccentricity e of the vertical force resultant from the mid-point of the foundation–structure interface related to width B of this interface. In fact, the relative eccentricity carries all significant information related to the wave loads (horizontal and uplift forces) and to the properties of the structure (mass and geometry). Further, a new 3-DOF model, which can handle the system nonlinearity (e.g. soil plasticity), is developed for preliminary analysis. For the application of the model, only two parameters are needed: the relative load eccentricity and the relative soil density.

Effect of overflow and seepage coupling on tsunami-induced instability of caisson breakwaters

In this study, a new tsunami overflow-seepage-coupled centrifuge experimental system was developed and applied to investigate the concurrent processes, and to elucidate the mechanism, of the instability involving the scour of the mound/sandy seabed, bearing capacity failure and flow of the foundation, and the failure of caisson breakwaters, with high-resolution image analysis. A series of experiments were conducted with and without the effects of the seepage by keeping the same overflow conditions (water volume, overflow velocity, fall height and water depth), and with different mound cross-sections. All of the experiments were conducted under 50 gravities and comprised of 3 series. The first series of experiments targeted the instability of the mounds themselves by constraining the caisson movement (sliding and overturning). The second series of experiments then allowed the caisson movement and clarified how the mound scour would affect the overall stability of the caissons. The third series of experiments examined the effect of a countermeasure on the basis of the results from the two series of experiments. The experimental results first demonstrated that the coupled overflow-seepage actions promoted the development of the mound scour significantly. Notably, the scour front developed in the form of progressive slip failure at the vicinity of caissons, regardless of the mound thickness. This stems from the fact that the development of the mound scour shortened the seepage path around the shoulder area of the mound, enhancing the coupling effect of the overflow and seepage. Indeed, the scour stopped far from the caisson toe in the absence of seepage without affecting the stability of the caissons. By contrast, the scour development due to the coupled overflow-seepage approached the caisson toe and brought about bearing capacity failure of the mound, resulting in the total failure of the caisson breakwater, which otherwise remained stable without the coupling effect. The velocity vectors obtained from the high-resolution image analysis illustrated the series of such concurrent scour/bearing-capacity-failure/flow processes leading to the instability of the breakwater. The influence of placing an embankment as a countermeasure was also examined by employing different bank thickness. It is shown that the stability of the breakwaters was significantly improved with decreasing hydraulic gradient that manifested underneath the caissons due to the embankment effect. These findings will facilitate better assessment and improvement of the stability of caisson breakwaters with rubble mound foundations.

On the role of uncertainty for the study of wave–structure interaction

We present a methodology to quantify the breakwater failure by means of the partial coupling of a nonlinear wave transformation model and a structural dynamic model. Nonlinear wave transformation is simulated by a two-dimensional VOF-type model (Cornell Breaking Wave and Structures), which solves the Reynolds-averaged Navier–Stokes (RANS) equations with a turbulence closure and a free-surface tracking scheme. The numerical model is used to calculate wave-induced forces and overtopping volume on low mound breakwaters. This information is further employed as the boundary conditions in a structure dynamic model to quantify the structural failure. Simulations over a wide range of wave conditions allow us to investigate the role of both epistemic-type and aleatoric uncertainty on wave-induced sliding and overtopping. Monte Carlo simulations are employed to conduct several realizations for an assessment of the aleatoric uncertainty in the failure prediction. The latter approach allows us to obtain ensemble values and the corresponding (natural) variability of overtopping, lateral forces, and sliding for a given forcing. Moreover, numerical results show that the structure displacement is sensitive to frequency spread values (epistemic uncertainty), whereas wave overtopping is less sensitive to such parameter. This approach can be employed to develop parameterizations that include the aleatoric uncertainty in their prediction.

Method for Quick Assessment of Caisson Breakwater Failure due to Tsunamis: Retrospective Analysis of Data from the 2011 Great East Japan Earthquake and Tsunami

Given the importance of ports to immediate disaster relief operations after a major tsunami, breakwaters are necessary to sustain a minimum level of functionality required to carry out port operations. However, most breakwaters that protect fishery or industrial ports are not designed to withstand a tsunami. For this reason, many of these breakwaters were destroyed by the 2011 Great East Japan Earthquake and Tsunami. However, some breakwaters withstood the tsunami, which facilitated the rapid resumption of port operations. In this study, 67 ports were investigated by using satellite images to identify the percentage of breakwaters that suffered damage due to the 2011 tsunami and how the tsunami height and breakwater width influenced the degree of breakwater damage. Because tsunami heights were not measured at the breakwaters, they were estimated by interpolating the data observed at nearby locations with a Gaussian weighting function at a reasonable accuracy. Possible drawbacks of this simplified method are also discussed because a certain degree of estimation error is inevitable. Breakwaters less than 8 m wide were quantitatively demonstrated to inevitably experience extensive damage when the tsunami height exceeded 14 m. In contrast, breakwaters that were more than 14 m wide, exposed to tsunami heights of less than 6 m, or both were not greatly damaged. An examination of the effectiveness of armor blocks also revealed that their placement could substantially reduce breakwater damage due to a tsunami. The results suggest a simplified method, particularly for assisting local fishery administrators or other authorities concerned, to practically estimate the risk of a port suffering damage because of future tsunamis. The proposed method should contribute to prioritizing the protection of ports in order of their likelihood of failure.

Hybrid modeling of pore pressure damping in rubble mound breakwaters

Rubble mound breakwaters dissipate the incident energy of waves using friction through different layers of porous media. The porosity of these layers decreases from the external slope to the core. The flow through the breakwater induces high internal pore pressures, which might cause breakwater failures. Indeed, high pressure in the core can provoke failure of the armor layer and geotechnical instability. The experimental study of the pressure evolution inside a breakwater is tough and the existing semi-empirical approximations diverge. Consequently, the analysis of pore pressure damping through a porous media is still an open task. However, nowadays there are powerful numerical models that can be used with that aim. Therefore, pressure evolution inside the breakwaters is analyzed in this work by means of a combination of experimental, numerical and previously existing semi-empirical formulations. Hence, a hybrid modeling of pore pressure damping in rubble mound breakwaters is presented here, taking advantage of the strengths of each approach. After a validation of the numerical modeling using the experimental data, the numerical model is used to analyze the pressure field inside the breakwater. Numerical and physical model results are also compared with existing semi-empirical formulae.

SPH-DEM Modeling of the Hydraulic Stability of 2D Blocks on a Slope

AbstractThe numerical simulations of wave interactions with armor blocks on rubble-mound breakwaters will enable a stronger understanding of breakwater failure and therefore increased malfunction prevention. This paper presents a two-dimensional (2D) SPH-DEM model, which combines smoothed particle hydrodynamics (SPH) and the discrete-element method (DEM) to simulate the wave-structure interaction on a slope and predict the hydraulic stability of the 2D structure. A particle method combined with a Riemann solver evaluates the hydrodynamic loads on the discrete blocks, while a multisphere DEM describes the movement of the solids from the wave attacks. An interfacial force-balance condition enables coupling between the fluids and the solids. A series of experimental tests were conducted to validate the SPH model. The simulation of water entry of the wedge was compared with previous experiments. The wave interactions with massive cross-shaped blocks on a slope were also simulated in 2D. Numerical results are ...

Practical Methods of Estimating Tilting Failure of Caisson Breakwaters Using a Monte-Carlo Simulation

The authors propose a new method to estimate the tilting failure of caisson breakwaters, using a Monte-Carlo simulation that can quantitatively and stochastically estimate failure probability. An index, referred to as “Expected Frequency Exceeding of a Critical Load (EFEC)” that expresses the potential tilting failure probability of caisson breakwaters is proposed and adopted in this model. Application of the model to 40 breakwaters in Japan reveals that the threshold value of EFEC that specifies whether a caisson breakwater is safe or unsafe could lie in the range from 0.02 to 0.04. The authors also found that unstable caisson geometry, showing a large value in the aspect ratio of the caisson, can provide additional indication of when tilting failure is likely to occur. It is expected that the present method can provide a practical way for engineers to judge the possibility of tilting failure in caisson breakwaters.

混成防波堤の越流破壊解析と対策工検討のための粒子法型数値波動水槽の開発

混成防波堤の越流破壊解析と対策工検討のための粒子法型数値波動水槽の開発