[TowerTalk] Height of tower foundation with respect to grade

[David Branson KC0LL]

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 at comcast.net
www.kc0ll.net
www.ActionCommunications.com

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  ----- Original Message ----- 
  From: W7CE 
  To: towertalk at 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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