Concrete Armour Units Research Articles

Hydraulic Stability of Interlocking Concrete Unit-V (ICU-V)

Continuous research is conducted to improve the available coastal protection scheme, including to develop an innovative concrete armor unit with interlocking capability. Interlocking Concrete Unit-V (ICU-V) has light weight characteristic and developed specifically for mild wave condition. This paper discusses the performance of ICU-V represented by the Stability coefficient,KDand results of the damage progression investigation under different wave conditions. These were achieved by conducting a 2-D physical model investigation by using JONSWAP random wave spectrum. The damage ratio method was used to assess the damage progression. The optimumKDobtained was 12 with highest damage level of 0.4%, which is comparable with available armor units

Influence of armour porosity on the hydraulic stability of cube armour layers

Armour placement and packing density directly affect construction costs and hydraulic performance of mound breakwaters. In this paper, the literature concerning the influence of armour porosity on the hydraulic stability of single- and double-layer armours is discussed. Qualitative and quantitative estimations for the influence of armour porosity and packing density on the hydraulic stability are given for the most common concrete armour units. The analysis focuses on specific 2D hydraulic stability tests of double-layer randomly-placed cube armours with different armour porosities and permeable core. The stability number showed a 1.2-power relationship with the packing density for double-layer randomly-placed cube armours considering armour unit extraction and Heterogeneous Packing. The literature review and experimental results with small-scale breakwater models protected with a variety of armour units clearly indicate that a significant increase in armour porosity above the recommended values substantially decreases armour hydraulic stability. To avoid uncontrolled model effects, packing density should be routinely measured in small-scale tests, and armour placement techniques should be monitored at prototype scale. The actual packing density obtained in small-scale models and prototypes has to be explicitly reported, because packing density significantly affects hydraulic stability during service time.

Placement Test, Porosity, and Randomness of Cube and Cubipod Armor Layers

AbstractAlthough little attention is usually given to the armor porosity and armor randomness of randomly placed concrete armor units in mound breakwaters, significant model effects may occur if armor porosity and randomness are different for prototype and small-scale models. Armor randomness and porosity are easier to control in small-scale models because they are generally constructed by hand in dry and perfect viewing conditions; equipment and environmental constraints make control at prototype scale more difficult. Results from three-dimensional small-scale placement tests are analyzed when cube and Cubipod units are placed with a small-scale crawler crane and pressure clamps. Armor porosity was not workable below 37% for cubes and 35% for Cubipods; placement grids were obtained for feasible armor porosities, considering row settlements during construction as well. A methodology to measure armor randomness using high-precision laser scanning, similar to terrestrial LIDAR, was tested with small-scale c...

Heterogeneous Packing and Hydraulic Stability of Cube and Cubipod Armor Units

AbstractThis paper describes the heterogeneous packing (HEP) failure mode of breakwater armor. HEP reduces packing density in the armor layer near and above the mean water level and increases packing density below it. With HEP, armor units may move in the armor layer, although they are not actually extracted from it. Thus, when HEP occurs, armor-layer porosity is not constant, and measurements obtained with conventional methods may underestimate armor damage. In this paper, the Virtual Net method is proposed to calculate armor damage considering both armor-unit extraction and HEP. The Cubipod concrete armor unit is then described as a solution to the effects of HEP on conventional cubic block armor. The hydraulic stability of cube and Cubipod armor units was compared in two-dimensional laboratory experiments. Cube and Cubipod armor layers were tested in two wave flumes under nonbreaking and non-overtopping conditions. The hydraulic stability was higher for double-layer Cubipod armor than for single-layer ...

Wave Overtopping over Crown Walls and Run-up on Rubble Mound Breakwaters with Kolos Armour under Random Waves

The design of rubble mound structures like breakwaters and seawalls are influenced by the wave run-up and overtopping over them. The above phenomena largely depend on the type of the armour units as they directly interact with the incident waves. The hydrodynamic characteristics of various concrete armour units have been established by several researchers. A new armour block, ‘Kolos’, a modified version of Dolos, is considered in this study for a detailed investigation. An attempt is made to establish empirical relationships for the estimation of wave overtopping discharges over crown wall and run-up on Kolosarmoured slope exposed to random wave from the results of a comprehensive experimental program. Further, the results are compared with that of a tested section with natural rocks as armour layer and with that of other investigators.

New modelling and analysis methods for concrete armour unit systems using FEMDEM

Rubble mound breakwaters armoured with concrete units rely on collective behaviour between adjacent concrete armour units but existing largely empirical approaches have been unable to provide a detailed understanding of how these gigantic granular systems work. The problem has been that current methods cannot investigate the interdependence of hydraulic and structural stability at the scale of individual units. Numerical methods have the potential to provide such answers but there are many challenges to overcome. We present a solution to the first major bottleneck concerning the solids modelling: the numerical creation of a breakwater trunk section of single layer concrete units with geometrical and mechanical properties that conform to realistic prototype structure placements. Positioning of units is achieved with a new versatile software tool, POSITIT, which incorporates user-defined deposition variables and the initial positioning grid necessary to achieve the required design packing densities. The code Y3D, based on the combined finite-discrete element method, FEMDEM, solves the multi-body mechanics of the problem. First, we show numerically constructed breakwater sections with armour layers of 8m3 CORE-LOC™ units placed on rock underlayers. The numerically-generated packs are deemed acceptable when examined according to a range of criteria indicative of acceptably placed armour layers, as set by concrete unit designers. Breakwater sections with packing densities ranging from 0.59 to 0.63 are then created. Using a set of analysis tools, local variation in packing density as an indicator of heterogeneity, centroid spacing, unit contacts and orientation of unit axes are presented, together with mechanical information showing the variation in contact forces. For these five packs examined, an increasingly tighter pack was associated with a steady increase in coordination number and a more steeply and accelerating increase in average maximum contact force per unit. The force distribution results and discussion presented illustrate the potential of discrete unit FEMDEM modelling methods to address initial placement quality, armour layer design and future innovation in rubble mound structures.

A FEMDEM NUMERICAL MODEL STUDY OF RUBBLE-MOUND STRUCTURES ARMOURED WITH CONCRETE ARMOUR UNITS

A new method for the numerical creation of random single-layer systems of concrete armour units is illustrated. The armour layer pack is created by a FEMDEM solver that ensures mechanical equilibrium between all concrete units and rocks of the underlayer. The local and average packing density together with geometric constraints indicative of randomness and interlocking are assessed using analysis tools and shown to be in accordance with unit designer requirements. This solids modelling research is an essential pre-requisite to future simulation of the armour layer response to wave loading and more realistic modelling of wave run-up and overtopping on rubble-mound structures.

Modified Heel Pressure Formula to Simulate Tilting of a Composite Caisson Breakwater

Susami West Breakwater, a composite caisson breakwater located in Japan, was damaged by high waves caused by typhoon Tokage on the 20th of October 2004. The failure mode was characterized by the sliding/tilting of the caissons and the removal of the concrete armoring units. The failure of these armor units is believed to increase the pressures exerted by the waves on the caisson, and thus exacerbate the expected deformations in the rubble mound foundation, a fact which has thus far been ignored in previous research. The present paper proposes a methodology to take into account the effect of these concrete armor units to estimate the deformations that took place in the rubble mound foundation. The methodology uses a modification of the method by Goda [1985] proposed by Esteban et al. [2009] that can approximate to the right order of magnitude the vertical deformations at the back of the caisson by using a Monte Carlo simulation.

STABILITY OF INTERLOCKING ARMOUR UNITS ON A BREAKWATER CREST

The hydraulic stability of single layer, interlocking armour units on low crested and submerged breakwaters was investigated in 2D hydraulic model tests. Displacements of armour units and rocking were monitored and have been applied as indicators for the armour layer stability on the crest, front and rear slope. The effect of freeboard, packing density and wave steepness on the armour layer stability have been investigated. The stability of interlocking concrete armour units on low crested and submerged structures is qualitatively different from rock armour. About 40% to 50% larger armour units are required on the seaward slope and crest of low crested structures (as compared to conventional high crested breakwaters). About 35% larger armour units are required on the rear slope. Larger armour units are not required on submerged breakwaters if the water depth on the crest exceeds 50% of design wave height.

USE OF SINGLE LAYER CONCRETE ARMOUR UNITS AS TOE REINFORCEMENT

Detailing and optimization of the toe reinforcement is presented as a case study from the construction of the 5.2km long main breakwater for the new Colombo South Harbour in 18m water depth. During the breakwater design the environmental constraints on supply of large rock armour were recognized, and CORE-LOC™ single layer concrete armour units were selected for the primary armour protection. During construction, supply of relatively small quantities of 8-12t rock for use in the toe reinforcement became an issue, and use of CORE-LOC™ units placed on the flat rock armour apron as an alternative to rock armour toe reinforcement was investigated and implemented. This use is unusual as there is no in-plane compression between units as found when they are placed on the slope. A site based prototype scale trial was conducted to evaluate placing method and criteria, and an "alternate opposing cannon† pattern placement, in rows going seaward from the primary armour, was successful. Packing density and unit spacing is the same as for the primary armour. Hydraulic stability of this alternative toe reinforcement was verified in 2D physical hydraulic model testing.

DROP TEST OF PROTOTYPE CUBE AND CUBIPOD ARMOR UNITS

The structural strength of concrete armor units (CAUs) is a key factor in the design and construction of armor layers for large mound breakwaters. This paper describes the prototype drop tests carried out to assess the structural strength of conventional cube and Cubipod CAUs. Low intensity overturning tests, high intensity free fall tests and extreme intense free fall tests were conducted to measure the structural integrity under impact loads of the Cubipod CAU
 compared to the conventional cubic block. The casting systems and pressure clamps were specifically designed to manufacture and handle the 15-tonne conventional cube and 16-tonne Cubipod prototypes used for the drop tests.
 Two reinforced-concrete platforms were used for overturning and free fall tests. The 16-tonne Cubipod prototypes withstand drops more than 50% higher than 15-tonne conventional cube prototypes of similar concrete strength. Two extreme free fall tests verified the robustness of Cubipod prototypes in accidental falls during construction. Both Cubipod and conventional cube CAUs have similar stacking and handling procedures as well as manufacturing cycle
 time.

INFLUENCE OF ARMOR UNIT PLACEMENT ON ARMOR POROSITY AND HYDRAULIC STABILITY

The handling procedure and placement grid of concrete armor units (CAUs) are the key construction factors of armor layers. This paper analyzes conventional cube and Cubipod CAUs which are handled by pressure clamps and placed randomly. Two methodologies for small-scale blind construction of armor layers in laboratories are compared using a Cartesian system and crawler cranes. Model construction by hand in laboratories is usually done in excellent conditions contrary to actual construction at prototype scale which is blind underwater and is influenced by wind, waves and equipment constraints. For randomly placed CAUs, the layer coefficient is an unnecessary and subjective concept which should be disregarded to prevent misunderstandings when considering armor porosity. For a given CAU, the placement grid affects armor porosity which is directly related to armor hydraulic stability. Crawler cranes can only place CAUs in a narrow armor porosity band; therefore, porosity of small scale armor models constructed by hand must be selected within that viable porosity band to avoid uncontrolled model effects. Armor layers of conventional cubes placed randomly by hand are not realistic if porosity is p%

PHYSICAL MODEL STUDIES ON STABILITY OF CONCRETE ARMOURED BREAKWATERS

ABSTRACT As the breakwater construction started moving in to deeper waters, the wave load on its armour increased resulting in usage of heavier armour units inviting environmental and logistical problems. With the advancement in the technology, concrete armour units have been extensively replacing the natural stones with benefits such as saving in the material and cost while reducing loads on the seabed and helping in construction of environment etc. Tandem breakwater and berm breakwater could be the alternative solutions for the above said case. This paper presents the two cases of physical model studies on the stability of concrete armoured structures, one with tandem breakwater and another on berm breakwater. Both the models are subjected to monochromatic waves with varying characteristics. From the study it was observed that in case of tandem breakwater the crest width of submerged reef and the distance between breakwater and reef are the defining parameter while in case of berm breakwater the height of the berm and its width are the characteristic factors in reducing the breakwater damage.

Prototype Drop Tests of Cube and Cubipod Armor Units

In this paper, an experimental methodology is described to assess the structural strength of unreinforced concrete armor units (CAUs). The methodology is applied to measure the structural integrity under impact loads of the new Cubipod CAU compared with the conventional cube CAU. The casting systems and clamps are described for manufacturing and handling the 15-t conventional cubic block and 16-t Cubipod prototypes used for the drop tests. Two separate reinforced concrete platforms were used for overturning and for free-fall tests, respectively. Compared with conventional cubes of similar size and concrete strength, Cubipods withstand drops that are more than 50% higher. Two extreme free-fall tests confirmed the structural robustness of Cubipod armor units. Manufacturing cycle time, as well as storage and handling procedures, are similar for both Cubipods and conventional cubic blocks.

Coupled FEMDEM/Fluids for coastal engineers with special reference to armour stability and breakage

Sea-level rise and increased storminess present huge challenges to coastal engineers worldwide. The seaward slope of many breakwaters and shoreline defence structures consists of thousands of interlocking units of concrete or rock making up a massive granular defence against wave attack. The units are placed freely to form an armour layer which is intended to both dissipate wave energy and remain structurally stable. Design guidance on the mass and shape of these units is based on empirical equations derived from Froude scale physical model tests. The two main failure modes for concrete armour layers are displacement (hydraulic instability) and breakage (structural instability) which are strongly coupled. Breakage mechanisms cannot all be faithfully reproduced under scaled physical models. Fundamental understanding of the forces governing such wave-structure interaction remains poor and unit breakages continue to baffle the designers of concrete armour units. This paper illustrates a range of DEM and FEMDEM methods being developed to model the granular solid skeleton of freely packed brittle units. Such discrete element methods are increasingly being used by engineers for solids modelling. They are especially powerful when coupled with a CFD model which can resolve ocean wave dynamics. The aim is to describe a framework for coupled modelling technologies applicable to coastal engineering problems. Preliminary simulation test cases, still at proof of concept stage, but based on a wealth of validation studies are presented. Thus, we report a snap-shot of progress towards a future where designers combine multi-physics numerical technology with knowledge from scaled physical models for a better understanding of wave energy turbulence, block movement, and internal stresses within armour units.

Development of New Artificial Reef Preventing Local Scouring by Controlling Shoreward Currents over Reef

Since the artificial reef has a submerged shape near the sea surface, strong shoreward currents are generated over the crown in general. These shoreward currents return offshore as rip currents from the openings of the reef, causing significant local scouring. A new type of artificial reef was developed in this study, preventing the development of shoreward strong currents, rip currents and resulted local scouring on the basis of the hydraulic model tests. The new type of artificial reef has the crown close to the mean sea level, and the offshore slope is protected by concrete armor units to enhance the stability.

Beach Erosion of Hamaju Coast and Controlling Effect of Littoral Drift by Detached Breakwaters

The Hamaju coast, located on the west part of a sandy beach with 11 km length extending west from the mouth of the Kuzuryu River in Fukui Prefecture, has been eroded by various anthropogenic factors in recent years. As a measure against beach erosion, 15 detached breakwaters had been constructed between 1973 and 1994. The shoreline advanced behind the detached breakwaters, showing the conservation effect, but in the offshore zone, water depth has been increasing. This caused damages of subsiding concrete armor units. In this study, beach changes of this coast were investigated, and numerical simulation was carried out, using the contour-line-change model. Measured beach changes were well reproduced by the model.

Experimental Study Of Salty Wind Damage

The height and distance of splashing generated by sea waves were simulated in a wave tank with a wind tunnel, and the prevention of salty wind damage is considered in the present study. The model test was carried out using a twodimensional wave tank (length: 30 m, width: 0.7 m, and depth: 1.2 m) with a wind tunnel. A 1/20 model of the seawall was set up on a fixed bed with a 1/15 slope at the end of the wave tank. Models of the concrete armor units were placed in front of the seawall in four rows and two steps. The windbreak net models were made of a 2 mm x 2 mm mesh. The heights of the windbreak nets were 15 cm and 20 cm. The windbreak net was set up at positions of 10 cm, 20 cm, 30 cm, 40 cm, and 50 cm behind the seawall. The main conclusions of the present study are that the splashing behind the seawall is prevented by the windbreak net, and the splash height is affected by concrete armor units placed in front of the seawall.

卓越沿岸漂砂の阻止に起因した海岸侵食‐紋別港〜サロマ湖口の例‐

The shoreline changes along the 64-km-long coast facing Ohotsuku Sea were investigated through the comparison of aerial photographs taken in 1947 and 2001. In this area, predominant direction of longshore sand transport is east. Port breakwaters and jetties were constructed, resulting in the disruption of continuous longshore sand transport. Severe downcoast erosion was triggered by the construction of these structures. Seawalls and concrete armor units had been installed to prevent erosion locally, but it failed to accelerate further downcoast erosion. Comprehensive measures are required to change this situation.

The modelling of particle systems with real shapes.

The numerical modelling of particulate processes in environmental science increasingly requires an ability to represent the properties of individual natural particles. Considerable advances have been made in discontinuum modelling using spheres to represent particles. In this paper, we discuss recent developments that illustrate a way forward for tackling the complexity of realistically shaped bodies such as those exhibited by rock fragments. To address the validation of such approaches, we present a comparison of cube-packing experiments and their equivalent numerical simulation. Sensitivity to initial conditions, highlighted for non-spherical bodies, enters the discussion of problems with validation of numerical simulation. The algorithmic details behind these advances in modelling large systems of realistically shaped particles are summarized in our companion paper in this volume.