That's very interesting ME, it's what they used in Llanddulas when they built the A55. each Dolas has a consecutive number there. It's a pity they didn't use them on the West Shore instead of importing the sand
Dolosse are normally made from un-reinforced concrete, poured into a steel mould. The concrete will sometimes be mixed with small steel fibers, to strengthen it in the absence of reinforcing. Construction is done as close as possible to the site of installation because the dolosse are very heavy.[citation needed]They work by dissipating, rather than blocking, the energy of waves. Their design deflects most wave action energy to the side, making them more difficult to dislodge than objects of a similar weight presenting a flat surface. Though they are placed into position on top of each other by cranes, over time they tend to get further entangled as the waves shift them. Their design ensures that they form an interlocking but porous wall. However, they are not indestructible. Under extreme storm conditions they will hammer one another and be pounded into rubble