[TowerTalk] (Repost) Engineering advice on above ground foundation

[Mark Spencer]

My usual I am not an engineer and don't rely on this info discalimer applies, but I have seen some comericial towers intalled on what appear to be large free standing concrete structures that don't appear to be burried below grade.   I am assuming someone who knew what they were doing figured out the required mass and physical dimensions of the base to prevent the tower from over turning due to wind load.   Not sure how the issues of the base settling over time and or frost heave issues were addressed (if at all.)

I suspect some preparation and or analyis of the surface that the base rests on would be needed but I really don't know.


----- Original Message ----
From: Rick Karlquist <richard at karlquist.com>
To: Rudy Bakalov <r_bakalov at yahoo.com>
Cc: towertalk at contesting.com
Sent: Friday, June 5, 2009 1:55:02 PM
Subject: Re: [TowerTalk] (Repost) Engineering advice on above ground foundation

Rudy Bakalov wrote:
>> My property has a very high water table and as a result my builder and I
> decided to build the tower foundation mostly above ground. Specifically,
> we dug a hole, filled it with compacted gravel that is above the water
> table, covered the gravel with very thick sheets of plastic, and inserted
> 2' styrofoam boards around the base. Then we poured the concrete.  As a
> result, only about 1.5' of the foundation is below ground, 3.5' are above.
>  The overall dimensions are 10' x 10' x 5'.

All the books I have read say that in cold climates, foundations
must go below the frost line, or there will be "heaving".  You
are clearly in violation of this dictum.  Your only hope is to
prevent any freezing near the tower.  Seems difficult in Ontario.
You could also try installing a "sump pump" to drain away water.
This has to run semi-continuously because water will seep in
to equalize the water table.

BTW, I hear that in Florida, they install towers foundations below
the high water table all the time.

Rick N6RK

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