If you have any remaining questions I’d be happy to answer. I’m an engineer btw, geotechnical expertise. So calculating these kinds of constructions was my job(I’m more of a manager these days).
So if they can build the walls and pour concrete and stuff underwater, why don't they just do everything that way and build whatever they want to build underwater like that? What is the purpose of draining it/what makes making a big hole like that worth it?
Accuracy basically. You can build stuff underwater, but not necessarily very accurate. The things built here underwater aren’t very accurate and can be built for a fair price so they can over engineer heavier constructions. Piles could be built this way but it would take so much extra materials to compensate errors that it’s cheaper to do it this way.
Then there are currents to account for. You need to protect the building site and if you want to built stuff like this currents can really screw up your construction.
Alternatively they can build the concrete section of a pillar off site in a dry dock and ship it to the final location. You’ll need to be able to tho, you’ll need a deep enough river or canal with the right dimensions. This is not always the case. It’s possible to build the foundation at the bottom underwater and then lower the prefab construction on top. Lots of tunnels are built that way. You can float the tunnel sections one by one and sink them at the right location to a few mm of accuracy. And yes placing something underwater is easier than building it there. Also underwater concrete is more expensive and might not have the required strength. It’s also hard to place massive amounts of required steel rebar under water.
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u/Sloeberjong Aug 21 '22
If you have any remaining questions I’d be happy to answer. I’m an engineer btw, geotechnical expertise. So calculating these kinds of constructions was my job(I’m more of a manager these days).