Joe had the right idea, and seems to have done a great job from the pictures
on his website.
The method used by Joe is what is known as an "above ground attached gravity
block". We have used it a few times when these conditions have occurred. Now
keep in mind, we build larger commercial towers, but for the most part, the
same design rules apply.
You should consult a local PE, but here is an unofficial breakdown of what
should need to be done.
#1 - Attach the structural cage rebar onto the bedrock by clearing the area,
drilling holes and grouting (or epoxy) it into place. I would recommend
getting a large hammer-drill with a bit that can bore at least 36" deep (48"
#2 Build the remainder of the foundation cage above ground, tying back to
the rebar in the bedrock. Depending on the type of tower and allowable wind
loading, you may need to upsize the in-ground foundation design by 1.5 to 2
times its original volume.
Grounding is a whole different issue. I have some dirty tricks that have
worked very well for us in the past, but are not cheap.
[mailto:firstname.lastname@example.org] On Behalf Of WD0M
Sent: Monday, December 24, 2007 9:41 PM
To: Charles Gallo
Subject: Re: [TowerTalk] Towers, and bedrock
Been there, done that. We have bedrock about 6 inches under the soil.
Nonetheless, I put up a US Tower TX-455 about 4 years ago, and it's
withstood 90 mph gusts. Works very well. Check my web page for details:
Click on Ham Radio, then Tower Project. Grounding is another issue -
check "Lightning Protection System". I've had a direct lightning
strike, and all worked as planned.
Joe Hannigan - WDØM
Pagosa Springs, CO
Charles Gallo wrote:
> First - Merry Christmas and Happy New Year
> There is a chance (small, but it's there) - that I will be getting a 2nd
QTH in the near future
> The think is, in that general area of the country, unless you live in the
bottom of a valley, you usually hit bedrock within a foot or 2 of the
surface - and if you choose right/wrong, you often have NO soil over the
bedrock (or a couple of inches)
> How do you put up a tower in that situation?
> BTW I know of exactly ONE in ground pool in the area - it was put in by
the owner of the local heavy equipment and blasting company - the pool took
significant amounts of ANFO to get dug
> 73 de KG2V
> For the Children - RKBA!
> "I can call K9 "him" if I want. He's my dog. "
> -- The Doctor
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