Safety of Breakwater Armour Layers with Special Focus on Monolayer Armour Units: (Discussion Based Upon Four Decades Experience of Breakwater Damage)

There seems to be a trend over many years that for new concrete armour units, daring designs are developed and constructed until breakwaters were damaged and new insight into the nature and behaviour of the particular armour units under complex wave loading was gained. For all these units (except perhaps Xbloc where no damage to the authors knowledge has occurred yet), the damage experienced led to more conservative and more safe use of the units in question. This paper presents some of this historical development and the lessons learned as experienced by the author. Based on this the situation today is assessed. The personal experience ranges from the severe damage to the Bilbao Breakwater armoured with rectangular blocks to Tetrapod armoured breakwaters, where especially the Arzew el Djedid breakwater in Algeria is an important case study. The paper also makes reference to the most important breakwater failure in Sines Portugal; where the breakwagter armoured with Dolosse failed in 1978. More recently in the last decade, we have also seen damage to monolayer armoured breakwaters although the general rules of the inventor/patentee had been followed. These monolayer armour units are all very good and valuable inventions, but according to the author’s opinion, in some cases, their use is associated with too high risk of future damage. It is the hope that the paper can assist in initiating the necessary discussion in the coastal engineering community about the safety of these breakwaters.