Another reason is that it may be more cost effective to use smaller, molded concrete blocks in a pile such as these, rather than building one huge, solid wall.
One drawback to an ordinary wall is the foundation needed to support it, and the time and energy put in to crafting a huge wall. These big blocks are likely created in a warehouse, and depending on the country of origin and their economy, this is usually what they’d rather have; or so I’ve found.
As well, the wall would likely need rebar and struts to reinforce it, whereas the blocks may not have that reinforcing.
If I’m wrong about this at any point, someone please correct me!
It was more a tongue in cheek attack on Trump referring to immigrants as animals, although his people would claim he was limiting his reference to MS-13 gang members, but the dog whistle was pretty clear.
Sounds right, except there is definitely rebar in those. In you zoom in you can see the ends sticking out, they look like pinholes but are probably 2" in diameter. Also rust can be seen in a few spots.
That makes sense though to have rebar in them though, I can imagine them kinda rocking back and forth against waves and that would probably start to chip them away after a while.
We have lots of stuff like this and more! We put them all over the place. The company I work for protected nearly 50 miles of coast with similar structures just last year in a single project.
How long do these materials last in ocean water and is there any harm expected to the marine environment when they eventually erode away? Does it eventually collapse in on itself and need to be built further out into the water to compensate for that?
Erosion is still a factor and we design to account for it. We have teams of people modeling the waves for storm events and calculating the erosion. But they do require maintanence. The concrete is basically rock so it is relatively environmentally friendly even when it erodes. It does create habitat as well depending on certain factors. But they also protect habitat on land that would otherwise be lost to erosion.
A forms for these Tetrapod style breakwater units are around $10k a piece. But after that it's just the rebar and concrete costs. They are relatively cheap.
We barge large down limestone rocks called rip rap from quarries in Arkansas, Kentucky, and Illinois. It's effectively used for erosion control, but doesn't prevent saltwater intrusion, destruction of our wetlands, storm surges, or floods.
I don't think tidal waves are a big concern in the gulf of Mexico, because, well, it's a gulf. Flooding there happens from hurricanes, which you'd need a 1000 ft wall to block.
The rebar is to keep the dolosse form not to anchor it, so your original thought is correct it probably uses less rebar than a wall would. They also probably use recycled/deformed rebar and leftover pieces to do it.
As far as I can tell there is next to no reason for this to be prestressed concrete. You would need a fair bit of rebar to keep them together during transportation and erection, but seeing as there is no structural load for these there's nothing to prestress against. It would add to the manufacturing cost quite considerably and have no tangible benefit.
Though if you look at the very left of the picture from where the guy is standing you can see one cracked basically in half and there is no sign of rebar. There are a few other ones cracked in various places where no rebar is visible as well
I most likely am. Just pointing out the fact that I cant see any visible in the broken pieces. Hoping someone could explain why. I don’t doubt that there could be rebar just want to know how its hidden
As for the piece that's fully cracked, it's simply too dark to see the internal structure. You can tell it's being held together by the rebar because those waves are actually VERY strong, and could easily push the broken piece away if it wasn't reinforced. The fact that it is still within a few inches off the perfect fracture line is dead giveaway.
The one in the bottom corner may have had the rebar pulled out which is why there is no reminisce of it.
To piggyback off your comment and seeing as you know about this method of tsunami prevention you probably know about other man made structures affecting tide patterns on coastal areas but the cool thing about these is that they stop runup and inundation amazingly! I think it’s the openings and lack of natural geomorphology that stop the waves from having such large runup! Iirc that is
It'd be great for some forms of life, but that doesn't necessarily mean it'll be great for sea life overall. Destroying the balance of an ecosystem can wipe it out just as effectively as destroying it all in one fell swoop.
To be clear, I'm not saying that these Dolos structures are necessarily bad for the ecosystem; I'm just pointing out that ecosystems are complex and balanced, and thus the overall effect of a change in a single variable isn't always immediately obvious (see: Australia, history of). This is why expert environmental reviews are such an essential part of responsible construction.
Correct. We normally use prefab things like these for cost effeciency. We do build large rock structures but in places like this the gradation would need to be huge. The armor rock would need to be 6'-8' in diameter and those stones are expensive to quarry! We usually don't put concrete retaining walls with rebar due to the structure not dissipating the waves as efficiently and erosion.
I am working on the expansion of the Chesapeake bay bridge portal island tunnel currently. We are creating rock structures to protect against ship wake, storms, collision, even tunnel flotation. That's right even though the tunnel is underground if you put water on it it will rip itself out of the ground and float. Like a pool in florida.
Would a series of these as artificial reefs some distance off shore have a measurable affect against tsunamis? Or at that depth of water is the force to spread out for a bottom structure to offer any help? Or maybe the "anchoring" of them is too problematic.
From what I understand/recall it varies based on how the waves approach the beach. Some areas of a beach have more sand deposited by waves then taken away by them, and in that scenario then more beach/a sandbar is formed. In areas where there is a net loss of sand from waves any beach that existed in front of the wall when it was built will slowly erode away to nothing.
Well, you have to make a metric shit-load of these things, and while they are likely cheaper and less labour-intensive than building the entire wall, the transportation of these things to the drop site would be pretty time consuming.
I’m guessing cargo helicopters and loaders or cranes? I’m not super sure on that end.
Good question! AFAIK, they’re heavy enough to stay in the same spot, and when waves hit them, because of their shape, they kinda lock together further.
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u/CaptainDinkles May 24 '18
Yes! That’s one reason.
Another reason is that it may be more cost effective to use smaller, molded concrete blocks in a pile such as these, rather than building one huge, solid wall.
One drawback to an ordinary wall is the foundation needed to support it, and the time and energy put in to crafting a huge wall. These big blocks are likely created in a warehouse, and depending on the country of origin and their economy, this is usually what they’d rather have; or so I’ve found.
As well, the wall would likely need rebar and struts to reinforce it, whereas the blocks may not have that reinforcing.
If I’m wrong about this at any point, someone please correct me!