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To David Finley, Re: Foundation on Expansive Clay

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My original tack was to treat these masts this way.  I ran some numbers on
shaft size, and opted for a spread footing -- until I got the soil report
about the expansive clay.

I'm about to go full circle and back to the drilled pier.


> From: David Finley <pec(--nospam--at)>
> To: seaint(--nospam--at)
> Subject: Re: Foundation on Expansive Clay
> Date: Thursday, April 05, 2001 7:01 AM
> Fountain,
> What diameter are the masts?  You were originally planning to embed them
> sleeves in your spread footing - can you instead place each mast in a
> in the top of a single drilled shaft (aka drilled pier) and eliminate the
> need for any other concrete on top of the shaft?  The concept is very
> similar to high mast lighting, mast arms, etc. except that they do use a
> base plate.  The shaft diameters and lengths typically are such that a
> utility type truck can do the drilling (4'-0" x 20')
> Some thoughts about using drilled shafts:  Any idea where the water table
> is?  How deep is the clay layer?  Is there a possibility of caving soils
> within the anticipated shaft length?
> David Finley, P.E.
> -----Original Message-----
> From: Fountain Conner <fconner(--nospam--at)>
> To: seaint(--nospam--at) <seaint(--nospam--at)>
> Date: Wednesday, April 04, 2001 6:50 AM
> Subject: Foundation on Expansive Clay
> >
> >I need to put some lightly-loaded foundations on clay "with the
> >for expansion".
> >
> >These foundations will carry a bark blowline in a paper mill.
> >
> >If all were normal these foundations would be 7 feet long x 8 feet wide
x 3
> >feet thick.  They each would have a vertical pipe 20 feet tall, carrying
> >horizontal blowline.  Maximum soil pressure (max load and wind) would be
> >about 2000 psf.  Static maximum load is about 650 psf.  The geotechnical
> >report allows at least 2500 psf, plus 25 percent for short-term live
> >(like wind).
> >
> >Plain vanilla...  Until I factor in the potentially expansive soil.
> >
> >My thinking is to turn down the outside edge of the footing an
additional 6
> >inches.  If this clay is expansive, it shouldn't be given to capillary
> >action, and will provide a seal, preventing the soil beneath the
> >from seeing the varying moisture content.
> >
> >What do you think?
> >
> >Item 2:
> >
> >I had intended to place each "mast" in a sleeve, plumb it and grout it
> >into position -- cheap, but effective.  I *can* put a mast on a large,
> >thick
> >baseplate, and perch it on nuts below the base plate, with double nuts
> >above.  If I do this, I can allow enough room below the lower nuts to
> >adjust each mast plumb if there is some movement.  I'm hoping you guys
> >convince me that this step is overkill.
> >
> >Ideas?
> >
> >Thanx,
> >
> >Fountain E. Conner, P.E.
> >Gulf Breeze, Fl. 32561
> >   Phone 850-932-5547
> >   Fax      850-934-1916