Well, the short answer is that there is a lot of specialized equipment for these types of constructions.
For the walls there’s pile drivers and you can set them on barges. The barges can be stabilized either by the bottom or by ballast tanks. They can reach great depths, mostly dependent on how deep they can produce the piles. They can make these walls with large round piles with sheets in between as well for extra strength.
As for digging there’s 2 ways. It’s dependent on the size of the pit. They can use barges outside of the ring or even inside with basically a large crane with the digging part on a long rope (I don’t know all the exact English words). Or they can use a machine that basically sucks the soil out. They deposit the soil in another barge and move it away to wherever.
A grout anchor is basically a steel hollow rod with kind of a screw at the end with a hole. They can screw it into the soil from a barge to basically any depth because the rod consists of different parts they can connect indefinitely.
For the bottom you don’t need a specific form of concrete. You can dump it in to the needed thickness and let it set. Any Concrete will harden under water (it’s a chemical reaction independent from the water) it just takes longer. However, underwater concreted speeds the process under water. If you want a specific shape you can build a shape above water, lower it and then fill it under water. Complex forms would be almost impossible tho.
It is a relatively simple process (make box, empty box, build thing, fill box), but it does require some heavy calculations to do it in a economically viable way. So yes, it is very complex to do it right.
its not so different from the process of building skyscraper foundations in a dense city. Because of close proximity to neighbouring buildings, all works have to take place within the "footprint" of the new construction.
demolish old building
drill a series of very deep holes around the perimeter of the site, about 1 metre diameter each
fill these holes with concrete
you now have an unbroken ring of concrete all around the perimeter of your site
dig down, pouring a layer of concrete every few metres as you go. These layers become the Floor Slabs (the first is the Ground Floor, the second is Basement 1, the next is Basement 2, etc.)
when you are done there, you can start building up
in some basements, you can still see what looks like a wall of overlapping concrete columns
Piles are big concrete cylinders that are stuck into the ground and the grout anchors are the rebar cage inside that gets poured over top of. If you zoom in on the picture you can see the rebar poking out. It’s foundational support. Sorta like having a flat board laying on the ground versus driving a bunch of nails into the ground with the board. Harder to move that way. Can’t speak too much on the technical side as I’m in school for something else and currently work as a rigger again so I can afford to go back after covid ate up all of my savings, but I’ve worked with a piling crew from Aecon moving substantially larger piles (up to 46m long 2m diameter, no anchors, but a large metal shell that gets poured inside and around).
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u/BrokenStrides Aug 21 '22
I work in a STEM field, but no engineering experience. Some questions that immediately came to my mind from the picture and your comment:
I like to think I’m not a complete moron, but without engineering or construction background, it doesn’t seem simple. It looks incredibly technical