Single Layer Armour Research Articles

Investigation Of Coastalock Performance On A Breakwater With Porous Core

Hard stabilization methods have traditionally been employed to mitigate coastal erosion. Concrete armour is widely used due to its high level of dependence, robustness, ease of production and cost effectiveness (Cooke et al., 2020; Pikey and Cooper, 2012). It is inevitable that coastline ‘armouring’ will continue to rise because of the growing human population and urbanization, desire for and value of coastal property, opposed to predicted climate change (Chapman and Underwood, 2011). The environmental impact of such 'armouring' on coastal systems can be detrimental, resulting in a degradation or destruction of habitats and the loss of ecologically trivial species (Gittman et al., 2015). The CoastalockTM, a single-layer armour unit, aims to blend coastal protection with marine habitat creation. This armour unit is designed to mimic inter- and sub-tidal habitats, with chemical composition of substrate and micro and macro features that provide niches for various species. The key feature of CoastalockTM is the cavity that is integrated into the design, that caters to diverse marine life needs depending on its orientation (ECOncrete Tech Ltd., 2019). CoastalockTM's hydraulic performance is under research. Preliminary tests conducted in the Hydraulic Engineering Laboratory (HEL) of the Technical University of Delft (TUD) on a 2V:3H impermeable slope in deep water conditions highlighted that with tight placement of the units significant pressure gradients across the top layer led to damage. The introduction of spacings between units for enhanced permeability improved stability significantly (Gutiérrez et al., 2023). A redesign of the unit was proposed incorporating protrusions to enforce the spacings between the blocks (Molenkamp, 2022). This research focuses on evaluating the influence of a porous core on the hydraulic performance of a CoastalockTM armour layer, specifically assessing its stability, overtopping, and reflection on a 2V:3H breakwater slope in deep water conditions—from the toe to just below the crest. A pivotal aspect of this research is the investigation of the impact of protrusions on the hydraulic performance. Furthermore, the study explores the influence of different toe configurations, aiming to comprehend the vulnerability of the armour layer to sliding. Toe scour falls outside the scope of this study.

Rocking Of Single Layer Armour Units Measured By Embedded Sensors

Single layer randomly placed armour units are used in many rubble mound breakwaters around the world. For these armour layers, breakage of armour units due to rocking could be a major damage mechanism, but no good methods exist to evaluate and quantify rocking. The aim of the study is to quantify the rocking impact velocities for irregularly placed single layer armour units. This study utilizes embedded Rocking Sensors to obtain the first measurements of rocking impact velocities of single layer armour units. More generally, the paper (Hofland et al. 2023) shows how novel measurement techniques can be used for the investigating the stability of single layer armour layers.

Rocking of single-layer armour units measured by embedded sensors

Single layer randomly placed armour units are used in many rubble mound breakwaters around the world. For these armour layers first extraction of units starts at high loads and can then progress quickly. Before the first extraction of a unit, typically no quantitative description of damage can be given. But additional to extraction, breakage of armour units due to rocking could be a major damage mechanism. This paper treat novel embedded Rocking Sensors. The technique is used to obtain the first measurements of rocking-impact velocities of single-layer units. They are also the first tests where the instrumented units can naturally move with the compacting layer during storm build-up. Physical model tests were performed on an armour layer with XBloc units. With 8 to 10 instrumented units per test run, in total 640 single measurements of the rocking motion of a unit during a 1200 wave test run were obtained, for three water levels and five wave heights. From the Rocking Sensors the number of impacts and rotational impact velocities were obtained. From an image analysis the along-slope settlement of the units during the tests was quantified. The rotational motion expressed by was found to be most convenient to express the motion. It can be seen that the units in the armour layer rock much more often than visually observed. Settlement seems to be a continuous progress, with most units rocking intermittently. Highest impact velocities are seen to occur around the water line, and in the uprush phase of the waves. A maximum impact velocity for all tests of 0.34 m/s (model scale) was measured. A preliminary design expression for rocking impact velocities of single layer units (Xblocs) is given. The paper shows that novel measurement techniques like the Rocking Sensors and vision techniques can and should be used to quantify damage mechanisms to rubble mound single-layer armour, additional to counting the extracted number of intact units.

FIRST APPLICATIONS OF XBLOCPLUS: EXPERIENCES FROM AFSLUITDIJK AND VISTULA SPlT PROJECTS

XblocPlus is a pattern placed single layer armour unit which was developed between 2015 and 2018 (Reedijk, 2018). The unit is applied on the Afsluitdijk Project in The Netherlands where 75,000 blocks are used. The second project followed at Vistula Spit in Poland. Valuable experiences were gained during the first practical application of the unit which are described in this paper.

Experimental studies on the effects of placement method and packing density of cubic armour units on the stability of low-crested breakwaters

Although concrete armour units have traditionally been used in two layers, the application of single-layer armour has attracted more attention in recent years because of its lower concrete volume and faster construction pace. Single-layer amour relies mainly on the contact between units to provide stability; however, installation of special armour types with surface projections for better interlocking, increases the possibility of breakage. During the last decade the idea of using bulky armour units such as cubes has been raised, and the application of these single-layer armour units has become common for high-crested breakwaters. However, the application of cube armours for low-crested breakwaters has not yet been fully investigated. This paper describes a set of experiments conducted to study the effects of the placement method and packing density of cubic armour units on the stability of low-crested breakwaters. The results show that the orderly placement of cubic armours on the slopes of low-crested breakwaters provides better hydraulic stability than an irregular placement. Regarding the packing density, the experiments reveal that it is possible to apply different placement densities on the breakwater slope below and above a certain level with respect to the toe of the breakwater.

STABILITY OF XBLOCPLUS ARMOUR LAYERS AFTER INITIAL DAMAGE

XblocPlus is an interlocking single layer armour unit that is placed with uniform orientation. The unit is applied with a large safety margin. Physical model test were performed without damage up to stability numbers of Hs/dDn=5.5 whereas a design stability number of Hs/dDn=2.5 has been adopted. The behaviour of an XblocPlus armour layer after initial damage is has been investigated by physical model tests with broken and manually removed model units. XblocPlus armour layers (with uniform orientation) respond differently to initial damage than interlocking armour units with random orientation. The latter are moving and re-arranging in order to bridge a gap in the armour layer (de Rover et al., 2008). XblocPlus units in contrast hardly move and nonetheless maintain the hydraulic stability of the damaged section. Details of the experiments and findings as well as implications for design and maintenance of breakwater armour layers will be discussed in the final paper.Recorded Presentation from the vICCE (YouTube Link): https://youtu.be/izwm60IBx-4

XBLOC-PLUS: THE INTERLOCKING, PATTERN PLACED AND EFFICIENT ARMOUR UNIT

Most breakwaters are built with randomly placed single layer armour units as these are most cost-efficient. Most single layer blocks require random unit orientations, which requires the crane operator to assess the orientation of each individual unit during placement. DMC noticed the desire for an interlocking block which can be placed in a regular pattern as many crane operators find it easier to place units uniformly, which requires less intuition. Fifteen years after the introduction of Xbloc, DMC introduces a new interlocking breakwater armour unit called XblocPlus which is placed with uniform block orientations.Recorded Presentation from the vICCE (YouTube Link): https://youtu.be/oEb1vsYfjL8

HYDRAULIC STABILITY AND OVERTOPPING PERFORMANCE OF A NEW TYPE OF REGULAR PLACED ARMOR UNIT

The XblocPlus is a new type of interlocking single layer armour units that is placed with uniform orientation. This is novel and different from all other single layer, interlocking armouring systems. The hydraulic stability of the XblocPlus breakwater armour unit was tested in 2D and 3D hydraulic model tests. Wave overtopping tests were performed to determine the roughness coefficients of the EurOtop overtopping formula for the XblocPlus. Model tests on a rubble mound breakwater with XblocPlus armour included 2D tests with a 1:30 seabed slope and with 1:2 and 3:4 breakwater slopes and 3D model tests with a flat seabed and with a 3:4 breakwater slope. Wave heights up to 150% of the design wave height were tested in the 2D tests and up to 200% with wave directions 0° to 60° in the 3D tests. No armour unit displacements were observed in 2D tests with 1:2 slope. In the 2D tests with 3:4 slope one armour unit was displaced when the wave height reached 159% of the design wave height. No damage to the XblocPlus armour layer was observed in the 3D tests. A roughness coefficient of 0.45 was deduced from overtopping tests with wave heights of 60% to 100% of the design wave height. The model test results indicate little or no influence of wave steepness on XblocPlus stability and no adverse influence of wave obliquity while the seabed slope in front of the breakwater may have some impact on the XblocPlus armour layer stability.

STATIC AND DYNAMIC LOADS ON THE BOTTOM ROW OF ARMOUR UNITS: A THEORETICAL AND PHYSICAL MODEL STUDY

A physical model study on the row averaged static and dynamic load on the bottom row of single layer armour units in order to investigate the influence of various parameters such as the number of rows on the slope of a breakwater and the initial relative packing density.