Effects of Rock Shape on Packing and Stability of Rock Armour: New Guidance

This paper discusses the need for further guidance on the packing and stability of armour layers made up of individually placed rocks. It uses the results from full-scale revetments and their laboratory replica models to demonstrate the need for the blockiness parameter in armour shape classification if physical models are to be representative. With both blockiness and aspect ratio of an armourstone source characterised, it is possible to predict porosity and layer thickness with accuracies not previously reported and these are presented in simple formulae. Both single and double layer models were tested to examine the ability of such layers to resist damage from wave attack. Performance of the structures is compared with the predictions of Van der Meer's stability formulae. Results are discussed in the light of limited full-scale armour layer porosity data from UK structures and research panels. It is suggested that the individual placement of blocky shaped rock armour tends to produce low armour layer porosities, which in turn, confers considerable reserve stability for such structures designed with Van der Meer's formulae.