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)isgroup.net>
> To: seaint(--nospam--at)seaint.org
> Subject: Re: Foundation on Expansive Clay
> Date: Thursday, April 05, 2001 7:01 AM
> 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)pcola.gulf.net>
> To: seaint(--nospam--at)seaint.org <seaint(--nospam--at)seaint.org>
> 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
> >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
> >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,
> >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.
> >Fountain E. Conner, P.E.
> >Gulf Breeze, Fl. 32561
> > Phone 850-932-5547
> > Fax 850-934-1916