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RE: Self Driving Caissons

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I have only designed one of these structures, but it was circular.  With
the circular variety the caisson is designed as a circular concrete
tank.  PCI has a 32 page document called "Circular Concrete Tanks
Without Prestressing" that is very helpful.  The circular shape allows
you to design for ring tension - I'm not sure what approach you would
take for a rectangular one.  You may wish to rethink this direction.  A
few things to keep in mind:
*	Make sure you consider the possible loading conditions.  100
year flood and a dry interior, excavated on one side while the tank is
full, etc. ( take into account the possibility of the caisson distorting
due to uneven loading).
*	Brush up on working stress in concrete and ACI 350.
*	Be very aware of the fixity conditions of your wall.
*	Make sure you have enough weight to sink your caisson and hold
it in the ground during the 100 year flood, but not so much that the
caisson will keep going.
*	Don't skimp on the design of your tremie slab.
*	Geometry is very important during sinking.  A symmetrical
geometry will help ensure the caisson will sink evenly.
I was blessed to have a gentlemen with vast experience in this type of
structure around to help me through the design.  There is a lot of art
along with the science.  I would not recommend designing this type of
structure without a lot of guidance.  Good luck!
Bob Germaine, PE

> ----------
> From: 	Mark A. Scott[SMTP:MAScott(--nospam--at)]
> Sent: 	Tuesday, May 05, 1998 4:08 PM
> To: 	seaoc(--nospam--at)
> Subject: 	Fw: Self Driving Caissons
> Self driving caissons usually have a British chauffeur and.....
> As described to me by another and from self inflicted knowledge via
> Bowles,
> the self driving caisson uses a sharp lower bearing edge on an opened
> bottom retaining structure that will lower itself by gravity when the
> bottom soil is excavated from within and below the bottom edge. 
> Discussions with a contractor enlightened me to the use of pressurized
> slurry pumped under pressure to the ouside skin to redeuce the skin
> friction.  The non-cohesive granular soil is  minus in that it may not
> stay
> in place but would slough and build up the skin friction enough to
> preclude
> the gravitational settling of the caisson structure.  My mind
> wanderings
> are somewhat self answering but I would still appreciate any other
> input. 
> Ther are some interesting descriptions and pix in Bowles, *Foundaton
> Analysis and Design."
> Thanx Again,
> Mark
> ----------
> > From: Mark A. Scott <MAScott(--nospam--at)>
> > To: seaoc(--nospam--at)
> > Subject: Self Driving Caissons
> > Date: Tuesday, May 05, 1998 10:22 AM
> > 
> >
> ----------------------------------------------------------------------
> ----
> > Your following message has been delivered to the list
> >   seaoc(--nospam--at) at 10:28:51 on 5 May 1998.
> >
> ----------------------------------------------------------------------
> ----
> > 
> > 
> > To all in sunny CA and beyond,
> > Has anyone had any experience or know of someone with experience,
> good or
> > bad, with self driving concrete caissons.  I've talked to a few
> contractors
> > that have placed some circular ones.  I am contemplating a large
> > rectangular section that can be remotely excavated from the interior
> to a
> > depth of 60 to 70 feet in granular soils.  This may be a
> misapplication,
> > but I'm willing to learn.
> > Thanx,
> > Mark A. Scott, SE Washington
> > 
> >