[TowerTalk] Tower base depth vs. hardpan

[Randy]

Hi all:
I'm pretty sure that I have a hardpan, most likely limestone, about 5 feet 
down from the surface.
The problem is that the spec sheet calls for a 5X5X6 1/2' pour. This is for 
a U.S. Towers TX-472
tilt/telescopic tower. The reason I suspect that the hardpan is there is 
that I tried jetting a piece
of 1/2 hard copper in 3 spots in the area in question today, and hit 
immovable things; a friend
of mine tried digging a pond on his property less than 3 miles from here 
and hit limestone at
about 3 feet, although he did find either the end of that rock, or a 
depression in it, although
I don't know how much deeper he attempted to go with it. On the brighter 
side, I checked
where my US Tower TX 489 is going to go, and I think I can make the 
required 8' depth for that
tower. Not sure if that's a variation in the subsurface strata, or fill 
dirt added way back when.
I realize that I'm not going to know for-sure what the story is until I dig 
down there, and I'm
going to probe some more before deciding on the exact location, but, my 
question is:
Does anybody have any specific data for a suitable base for a depth limit 
of 5'? I haven't
emailed US Tower as of yet, just figured out the bad news this evening. 
I'll do that as soon as
I finish this email.

The spec sheet for the tower says:
Overturning Moment: 35.0 ft. kips
Base Shear:                1.22 kips
Structure Weight:        1.33 kips

I'm *really* hoping I don't have to hire a PE to tell me what I want to 
know; there are NO requirements
for getting a permit in this county....as was verified in a 'test case' I 
inadvertantly caused some years
ago....well, there was one other ham also, but his tower didn't show up in 
the papers and Channel 40
News...

Thanks for any help y'all can offer...

73 de KZ4RV

Randy..