The foundation for my100 Ft. self-supporting Sabre tower was engendered by
Sabre. The "Mat & Pier" is 18 inched "BELOW" grade, all except for piers around
the legs bolts. You want the legs (or in my case bolts) to come out of the
concrete above ground so they stay dry (dryer than below grade) and dirt does
not come in contact to were they would wick moisture. If you don't have
inspections that make you match a PE drawing, then you could do it 4 or even 2
inches high and be fine, if you have good drainage were water and dirt will
stay away from the leg/bolt. Or, make the base any height you want including
below ground and have a pier (column) around the leg. My piers are 2.5 feet in
diameter and come above grade 6 inches. They go below grade 18 inches and then
the mat (slab) starts. The mat is 13-1/2 feet square but only 18 inched thick
with 2,000 pounds of 1 inch rebar, as required. It was engineered this way to
let the dirt be a large part of the weight that holds the tower,
very efficient and it reduced the soil loading (I think it was 1,500 lb per
square foot) to the point were the county didn't make me have a soil's analyses
done, and that saved me $3,000 not counting the concrete it saved with a
smaller "Buried Mat Foundation".
You can see this at http://kc0ll.home.comcast.net/~kc0ll/tower/tower003.html
Good luck.
David F. Branson
Senior Technician
Action Communications, Inc.
Tucson, AZ
520.792.0326
520.792.2709 fax
KC0LL@comcast.net
www.kc0ll.net
www.ActionCommunications.com
"America will never be destroyed from the outside.
If we falter and lose our freedoms, it will be because we destroyed ourselves."
--- Abraham Lincoln
Freedom isn't Free, Support our Troops
----- Original Message -----
From: W7CE
To: towertalk@contesting.com
Sent: Sunday, April 05, 2009 10:18 AM
Subject: [TowerTalk] Height of tower foundation with respect to grade
I'm preparing to dig a 5'x5'x8' hole for a US Tower HDX-572. Because of the
proximity to a sidewalk, I would prefer that the top of the foundation be at
the same height as the sidewalk, rather than 6" above grade. I assume that
tower foundations are normally above grade to minimize that chance for
standing water at the base of the tower. Is this assumption correct?
Assuming that standing water isn't a problem and that I keep the area around
the base of the tower free of debris, does anyone see a problem with keeping
the foundation level with the grade?
73,
Clay W7CE
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