Session A.11: Single Layer Armouring

Chris Brown, Seabee Developments

All three authors have presented cases for single layer armour units, some with rocking units. Have they considered and tested the effect of random failure of one or more units? How many units can be lost before the underlayer begins to be lost?

Authors replies -

S Zwanenburg

Extraction of one or more units has not been extensively tested during this research. The model test setup was focussed on rocking. Since rocking occurs for a less severe wave load than extraction, extraction of armour units did not occur during these tests. Previous research on Xbloc armour layers showed that displacements of the under layer start when more than 4 units in a cluster near the sea water level has been displaced. Displacement of a single unit from the armour layer has no effect on the stability of the underlayer. Extraction of a single unit does not necessarily result in extraction of the neighbouring units. Displacement of a cluster of 4 units (and consequently the start of displacements of the underlayer) can be expected when more than 3-4% of the armour units has been extracted.