Rubble mound breakwaters are by far the most common type of breakwater, the importance of which is clearly reflected in the vast amount of published research. Especially, the hydraulic stability of the main armour layer has been studied in order to obtain reliable design equations. It should be straight forward to assume, that a relation between the exerted wave loads and the stability of the armour layer would be of major interest, but the normal approach to the problem has simply been to relate easy accessible wave parameters, e.g. wave height and period, directly to the single unit weight, thus leaving the wave loading in a black box. This approach is observed in all formulae including the well-known Hudson-type formulae and the Van der Meer formulae. All shown formulae are modified from their original form to include the equivalent cube length Dn50 = (W50/ρm)1/3 instead of unit mass W50. Taking a closer look on the stability formulae large differences in the influence of the different parameters are observed although several points of resemblance are observed. Despite the major efforts in obtaining a reliable stability equation a large scatter between damage predicted by the stability equations and model test results still exists. When turning toward prototype the situation is even worse. With the objective to reduce some of the variability an alternative approach based on force considerations is presented. The paper will describe a new stability equation for rock armoured slopes derived on the basis of the recorded wave induced forces and the resistance forces. The work is based on a study carried out at Aalborg University in the period 1995 to 1998, Hald.
Coastal Engineering 2000: Proceedings of the 27th International Conference on Coastal Engineering, Icce 2000 : July 16-21, 2000, Sydney, Australia, 2000, p. 1921-1934