[TowerTalk] tower base concrete or not

[Jim Lux]

At 04:37 PM 9/8/2004 +0000, kb9cry at comcast.net wrote:
> > Then why do the manufacturers specify the hole at about twice as deep
> > as it is wide?
>
>
>You'll need the bottom of the base to extend down past the local frost 
>line.  If you don't then you'll get frost underneath it and it may heave 
>on you.  Phil  KB9CRY

And in areas where it does not freeze, you can make a wide shallow hole 
instead.  There was some discussion about this around a year ago on the 
list. I seem to recall some folks talking about casting "beams" in a 
cruciform pattern as well.

Anything can be done with sufficient engineering analysis to make sure it 
will work.  The narrow, deep hole approach tends to be popular (especially 
if you're digging with a machine) because of the frost line issue, and 
because it has the least disruption on the surface (so you can plant stuff 
around it, etc.).  In Southern California, you'll see a lot of beams being 
set on very deep, but small diameter piers, which they drill the hole for, 
rather than dig.  Particularly in hilly areas with loosely consolidated or 
highly fractured geology (like the Santa Monica Mountains above Malibu, for 
instance).