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Re: Foundation on Expansive Clay

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What diameter are the masts?  You were originally planning to embed them in
sleeves in your spread footing - can you instead place each mast in a sleeve
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 potential
>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 a
>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 load
>(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 foundation
>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,
>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 can
>convince me that this step is overkill.
>Fountain E. Conner, P.E.
>Gulf Breeze, Fl. 32561
>   Phone 850-932-5547
>   Fax      850-934-1916