Hydraulic performance of CoastaLock armour units

Master thesis (2022)

Authors

A. Molenkamp Civil Engineering & Geosciences

Contributors

Bas Hofland Hydraulic Structures and Flood Risk - CEG (supervisor 1)
Jeroen van den Bos Royal Boskalis Westminster (supervisor 2)
M.R.A. van Gent Coastal Engineering - CEG (supervisor 2)
Jorge Gutiérrez Martínez ECOncrete Tech Ltd. (supervisor 2)
Faculty
Civil Engineering & Geosciences
Copyright: © 2022 Auke Molenkamp
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Published Date

30-06-2022

Language

English

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Faculty

Civil Engineering & Geosciences

Abstract

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.