Dolosse – a South African invention used over the world

Finnally something I have knowledge of. Dolosse were invent in South Africa many years ago, but they are only one type of concrete block for wave dissipation and protection. Many other exist and some of them are patent and require the payment of royalties to be used. Anyway, in Portugal we do not use dolosse ever. We used it once in Sines deepwater breakwater, which suffered a catastrophic collapse in 1979. The promise of dolosse is that the blocks work together because of their shape and thus the individual block can be lighter and cheaper. This does not work in practice, at least in high energy seas. The ocean is unforgiven. What happens is that if only a few blocks break the whole structure will quickly collapse during a storm. And things can break due to a series of problems and risks. Concrete is only good at resist compression stresses and reinforcement with rebar is almost always a bad idea in ocean conditions, so complex shapes are hard to make and to move without introducing unwanted stresses that reduce the design strength conditions. Other type of blocks rely mostly on its design weight and density and the shape is just used for increasing energy dissipation and overtopping. For example, tetrapods can be moved with only compression forces on the block.

Interestingly the author shows a photo of a spot in Cape Town where there are two distinct structures in use - close up, in the photo, are actually Tetrapods - as pointed out in other comments, these are an earlier invention from France and also used quite extensively throughout many parts of the world (including... right here where the Dolosse were invented).

Further down that jetty are structures with the actual Dolos geometry. It would be interesting to know if, specifically, those geometries were chosen specifically to be placed in those two parts of the wall as they are for specific properties, or if came down to having certain quantities made on hand and their distributions matched the shape of the wall required, or what.

You can see what I mean, this distinction in the exact location where that photo is taken on google maps, here:

https://maps.app.goo.gl/Vn3tGhM81oMqPVpm9

-33.899126, 18.412751 Mouille Point, Cape Town, 8005, South Africa

Interesting. Been to South Africa a bunch but never clocked that they were different from the more common antecedent, the tetrapod[1].

1: https://en.wikipedia.org/wiki/Tetrapod_(structure)

In Germany (on the island Sylt) they recently removed all of these structures again after decades of them being a staple on Sylt's beaches. They were found to have no positive effect on protecting their shores.

I'm having a hard time to find a good source to quote but look for: "sylt tetrapoden" if you want to dive deeper.

Save yourself the blogspam, go directly to https://en.wikipedia.org/wiki/Wave-dissipating_concrete_bloc... and enjoy the whole collection !

Not sure why Dolosse are so special?

There's lots of different forms and shapes of wave breakers, like the Tetrapods [1] that you can find over here across pretty much every coast in Europe.

Maybe I'm just not getting it why the Dolosse shape is superior?

[1] https://en.wikipedia.org/wiki/Tetrapod_(structure)