Stability of breakwater armour layers Deterministic and probabilistic design

New practical design formulae have been developed which describe the stability of rubble mound revetments and breakwaters under random wave attack. The formulae are based upon a series of model tests. More than two hundred and fifty tests have been performed in order to ensure that all the relevant variables could be varied systematically. As a result of the present series of investigations the main shortcomings in Hudson-type formulae have been solved. Stability formulae are given which include the influence of wave period, number of waves, armour grading, spectrum shape, groupiness of waves and the permeability of the structure. A clearly defined damage level parameter is introduced in the formulae. The development of these new formulae is given in the first part of this paper. The second part shows how the formulae can be used in both deterministic and probabilistic design.