Re: Submerged Tower?

[DaveIrons@aol.com]

Subj:	 Re: Submerged Tower?
Date:	2/25/99 0:06:56 AM EST
From:	shawl@torchlake.com (Jonathan Shawl)
Sender:	owner-personal_submersibles@psubs.org
Reply-to:	personal_submersibles@psubs.org
To:	personal_submersibles@psubs.org



Paul Julius wrote:

> I was just thinking of a tower that stretches from the surface to the bottom
of some
body of water, say a lake, maybe 100 feet.  Inside the tower, it is dry and 1
atm.  Outside
the pressure varies from the top to the bottom.  This would make a great
tourist attraction,
as they could go down and see the underwater life!  Anything like this in
existence? 
What type of extra engineering concerns must we consider?
>
> Paul

The biggest problem is to make it heavy enough to stay down or to anchor it to
bed rock.
Lets say it's 20' dia, room enough for a spiral stair and a elevator down the
center, and
100' deep.
That's about   31,416 cubic feet of water displaced at 64 lbs (fresh) per
cubic foot.
64 x 31,416 =  2,010,619.lbs, even if you could build it for a low .50 cents a
pound, for
steel and concrete alone.
that would be about a $ 1,005,309.00 hole in the water. I think that $ figure
might be way
too low? Anybody into that type of work? Ever been to Weechie Wachie Springs?
Somebody from Florida correct my spelling on that one and tell him what that
place is
like.
Jon Shawl


Jon

I think your calculations are high.  A yard of high strength concrete costs
about $80  That
is 4,000 pounds a yard.  If the entire structure were concrete it would cost 2
cents per
pound.  Most of the weight would be ballast.  Crushed granite is about $10 per
yard. 
Massive concrete wall are far less expensive if large aggregate is added to
the mix. 
Including large chunks of granite would reduce the cost by half.  High
strength concrete
is about 4,000 to 9,000 psi.  Granite can be as hard as 80,000 psi.  Adding
more large
granite to the mix will make the concrete stronger.  Adding concrete or rock
rubble to the
bottom of the tower would add ballast and stability at very low cost.  I don't
see the
necessity of installing steel.  If the walls are massive enough they would
stop a freighter. 
I estimate a 20 foot diameter tower would need two feet thick concrete walls
to be
neutrally buoyant.  A tower cannot sink, because it is already on the bottom.
The worst
scenario would be a flooded tower and the people would have to scramble to the
top.  I
doubt that tourists would be allowed inside during heavy seas or other
dangerous
conditions.  I estimate the tower would cost $50,000 for the concrete.
Another $50,000
should cover the formwork and labor.  The tower could be built in an excavated
area near
deep water.  After completion the dam would be removed and the tower floated
out of the
excavation.  After the tower was towed to position it would be balasted and
anchored the
seabed.  
The viewports are another matter.  Viewports could easily exceed the cost of
the
structure.  However, a shallow structure would be relatively inexpensive.  The
most
spectacular marine life live in the first 20 feet, below the surface.
Pressure formed acrylic
hemispheres would serve nicely at this depth.  The cost would be only a
fraction of heavy
cast acrylic viewports.  

The esthetics of the tunnel is a different matter.  Some would think it ruins
the natural
beauty of the ocean. 

A different approach is to turn the tunnel on it's side and use it as an
underwater habitat. 
The only visible sign of human life would be a buoy.  But that is a matter for
other
discussions.

David Irons
Lansing MI