Coastal areas face increasing threat from erosion. The use of coastal protection structures is imperative to counter this. Concrete “armouring” is widely used due to durability and cost-effectiveness. Conventional methods of “armouring” result in habitat degradation and loss of biodiversity. ECOncrete developed Coastalock, an armour unit designed to provide coastal protection but also to create marine habitats.

Initial tests conducted on impermeable slopes in deep water conditions revealed, that tightly placed units experienced pressure gradients across the top layer, leading to failure. The aim of this study is to investigate the hydraulic performance of Coastalock, both with and without modification, within permeable breakwater structures. The study examines the influence of toe berms on different surfaces, assessing the armour layer’s susceptibility to sliding.

The research aims to bridge existing knowledge gaps regarding Coastalock behavior under varying wave conditions through literature review and physical model tests conducted in the 2D wave flume at TU Delft.

Structure from motion photogrammetry enabled the creation of 3D models of the armour layer after wave attack, facilitating the tracking of armour layer deformation of selected test series. The research includes measurements of overtopping discharge and reflection coefficient.

The findings shed light on failure mechanisms observed in Coastalock armour layers on permeable core slopes, attributed to built-up pressures exceeding self-weight and interlocking capabilities during wave run-down. 'Breathing' involves upward movement perpendicular to the slope during wave run-down and downward movement during wave run-up. Friction and partial interlocking contribute to the formation of a bulge in the armour layer, growing in size and magnitude, leading to extraction.

Observing increased 'breathing' and extraction thresholds with larger inter-unit void sizes, was confirmed for permeable cores. No stability increase compared to impermeable core was found, attributed to reduced maximum run-down levels. A lowering of overtopping and reflection was found for the permeable core.

The protrusions implementation necessitated a new configuration, termed the 'Protrusion Optimized' configuration, with an orientation change from cavity upwards to downwards at SWL. 10% protrusions reduced the stability number threshold for 'breathing', while 22.5% protrusions prevented filter layer migration and reached up 𝑁𝑠=4.2 without 'breathing' or extraction. A stability increase was found in 𝑠0𝑝=0.02 conditions, attributed to the ‘reservoir effect’. Incorporating protrusions and transitioning to the 'Protrusion Optimized' configuration increased reflection due to increased surface area and reduced permeability.

Changing the orientation location towards the midpoint between SWL and the bottom row or facing all units upwards resulted in increased stability in terms of ‘breathing’ and extraction, as well as a downslope shift of the damage location. Upwards-oriented units led to smoother slopes and higher reflection coefficients, both attributed to the water retaining properties of the cavity.

The presence of toe berms, showed no significant impact on damage progression or the location. Downslope movement well below the threshold indicative of near extraction was observed.

Recommendations for advancing 22.5% protrusions are proposed, advocating a Ns=2.6 for surging waves in deep water conditions. This design offers notable overtopping reduction, orientation flexibility, and reduced concrete usage and project duration.
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With the advance of urbanisation in coastal regions comes an increase in armoured shorelines and the destruction of coastal marine habitats. To combat this, ECOncrete Tech Ltd has developed a new eco-friendly armour unit, the CoastaLock. With its ecological advantages proven, its hydraulic performance is still largely unknown. This thesis aims to do the first exploratory research into the stability, reflection and overtopping performance of this CoastaLock armour unit, through a literature study and physical model tests. Data is gathered during physical model tests on a deep-water impermeable slope with different wave steepnesses, armour unit spacings, underlayer thicknesses and block orientations.

The mechanism of breathing is witnessed in tests with CoastaLock armour units. This mechanism shows the armour layer repeatedly getting lifted up from the slope and placed back on it as a result of pressure differences over the top layer during maximum wave run down. This mechanism causes movement of granular material in the underlayer, with large under deformations as a result. This thesis, therefore, advocates for listing the breathing mechanism as a failure mechanism.
The CoastaLock armour units show stability numbers of approximately 2 when tested at armour spacings below 10%, and stability numbers larger than 4 when tested at armour spacings larger than 10% for a wave steepness of 3.5%. Wave steepness is shown to be of a minor influence too, with the influence of underlayer thickness and unit orientation being negligible.
The reflection coefficient is shown to be mainly dependent on wave steepness, and minorly on armour spacing. Reflection coefficients of approximately 0.8 to 0.5 are measured for wave steepnesses between 1.5% and 4.5%.
Overtopping is shown not to play a role in situations with armour spacings lower than 10%, as the layer fails before overtopping can become an issue. For the more stable spacings, those larger than 10%, the overtopping discharge is quantified and the roughness factor is shown to vary from 0.732 for 10% spacing to 0.61 for 25% spacing. Factors other than the spacing are of a minor to negligible influence.

The CoastaLock armour units show promising results for situations with a short leakage length and large armour spacings, i.e. situations where the pressure differences over the top layer are small. However, this research is the first exploratory research into these armour units and should therefore be interpreted as no more than an indication of the behaviour of CoastaLock. It is recommended to expand the research into these units, both on the units in different situations as on the failure mechanisms of the units and the solutions thereto. ... Read more