Casting concrete structures up from the sea floor

Syndicate replies to “Casting concrete structures up from the sea floor” topic Mon, 08/25/2008 - 05:37 — Herman Melville

(1) Select a place where the ocean is about 1000 feet deep.

(2) Construct a steel cylinder 1000 feet in diameter and 30 feet high.

(3) Construct another steel cylinder 1020 feet in diameter and 30 feet high.

(4) Drop them down to the sea floor to form a doughnut shape.

(5) Pipe down concrete to cast a concrete cylinder.

(6) Jack the forms 20 feet higher, and pour again.

(7) Repeat until you're several hundred feet above sea level.

(8) Pump out the water.

(9) Use cranes to stack large (e.g., 32'x32'x96') prefabricated housing units into the cylinder; connect utilities.

(10) Progressively pour in more concrete to fill the voids between their floors and walls.

Notes:

(A) How thick must the wall of the cylinder be? The concrete walls and floors inside will give it additional bracing, but it must resist the water pressure while the inside is being constructed.

(B) How do you reinforce the bottom, where it meets the sea floor? Dig down to rock and pour a thick slab? Drive piles?

(C) I suppose the cylinder wall should get thinner as it goes up.

(D) What is the optimal ratio of diameter to height -- or is a larger relative diameter always more efficient?

‹ INDIGO ISLAND What does David Friedman think of the project? ›

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Mon, 08/25/2008 - 14:41 — Carl Pålsson

Some possible issues: That

Some possible issues:

  • That is a lot of concrete (and rebar). Requires massive investment before construction. I realize this is the crazy forum but this is still worth mentioning.
  • Living deep below the surface of the ocean withouth windows (and without light even if there were windows), are people really going to go for this?
  • Keeping the forces on the cylinder within limits should be interesting (currents trying to topple it, water pressure should be manageable). Still there is the potental for major disaster if there is even one leak near the bottom if there are no pressure-proof bulkheads between floors. You have a long way to safety if the water somehow gets in when you are 1000 feet below.

Check out the Troll A platform. It was built elsewhere and towed to location, and consists of four connected cylinders, but I am sure there are some similarities.

 Regarding the foundation/anchoring of this structure, if you built three cylinders and connected them like a truss (in the shape of a triangle seen from above), perhaps with a distance equal to the sea depth, the whole thing would sit rather stable on the sea floor without the need to pour massive foundations.

One thing is keeping the density higher than one (higher than water). If not it will want to float away. Concrete is only like 2,5 times water, and with all the free space inside it might be very buoyant.

Wed, 08/27/2008 - 23:23 — Patri

 If the bottom of the

 If the bottom of the pillar touches the ocean floor, then the pillar does not need to be heavier than water, actually.  Water is only exerting hydrostatic pressure horizontally.  If the water can't "get underneath" the structure, then there is no force trying to make it float.  You can verify this yourself in the sink.

Wed, 08/27/2008 - 23:21 — Patri

 Interesting idea.

 Interesting idea.  Concrete pillars are a reasonably mature technology.  I don't see why you need to cast them in-place though, why not just cast your sections, float them horizontally, assemble your 1000 foot pillar horizontally, and then sink one end?  You can move enormous masses around in the water by ballasting/deballasting different areas of them, so there is no need to do the underwater construction.