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A new method for the numerical creation of random single-layer systems of concrete armour units is illustrated. The armour layer pack is created by a FEMDEM solver that ensures mechanical equilibrium between all concrete units and rocks of the underlayer. The local and average packing density together with geometric constraints indicative of randomness and interlocking are assessed using analysis tools and shown to be in accordance with unit designer requirements. This solids modelling research is an essential pre-requisite to future simulation of the armour layer response to wave loading and more realistic modelling of wave run-up and overtopping on rubble-mound structures.

The ability of concrete armour units for breakwaters to interlock and form an integral single layer is important for withstanding severe wave conditions. In reality, displacements take place under wave loading, whether they are small and insignificant or large and representing serious structural damage. In this work, a code that combines finiteand discrete-element methods which can simulate motion and interaction among units was used to conduct a numerical investigation. Various concrete armour layer structures were built using a carefully researched placement technique and then subjected to a boundary vibration. By analysing the displacements and assessing the number of units that were displaced by more than one-third their nominal size, the numerical test programme indicated clearly that the initial build packing density was the most important parameter influencing the stability of concrete armour layers under vibration. The size of the underlayer rock and the type of unit also affected the numerical performance of the single-layer concrete armour systems under vibration. The results presented are for full-scale systems and therefore add further insights into simple laboratory 'shake tests', although the oscillatory loading in this study is acknowledged to be profoundly different to wave action.