Abstract
Stability formulae for armour layers of rubble mound breakwaters are usually being applied assuming perpendicular wave attack. Often it is assumed that for oblique wave attack the reduction in damage compared to perpendicular wave attack is small. This seems however a very conservative assumption. Wave basin tests at Deltares provide information to assess the effects of oblique waves on the stability of rock slopes and cube armoured rubble mound breakwaters. This includes cubes in a single layer and cubes in a double layer. The results show that the few available formulae that include wave obliquity underestimate the effects of oblique wave attack; the observed damage to breakwaters with armour layers of rock and cubes is lower and therefore new stability increase factors and mass reduction factors have been developed. The tests were performed for wave directions between perpendicular (0ï‚°) and 70ï‚°. The results show that large potential savings in diameter and mass can be obtained for large angles of wave obliquity.
Highlights
Stability formulae for armour layers of rubble mound breakwaters are typically based on laboratory experiments in wave flumes
The objective of this research study was to assess the effects of oblique wave attack on the armour stability of a typical rubble mound breakwater
The study focussed on armour layers of rock and cubes on an impermeable or permeable core
Summary
Stability formulae for armour layers of rubble mound breakwaters are typically based on laboratory experiments in wave flumes They are generally developed for perpendicular wave attack and do not include the effect of oblique waves. A similar approach as the one by Galland (1994) has been used by Van Gent (2003) in his tests on the effect of wave obliquity on the stability of rock and cube armoured slopes. Since the expected damage for the available cubes and typical model wave heights (Hs 0.2m) was low, it was decided to test cube stability only for a double cube layer with an impermeable core, which was expected to increase the damage to the armour layer compared to a double layer with a permeable core such that damage could be obtained even for large wave obliquity.
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