[TowerTalk] Tower base over ROCK (shale) experience??

[J. Hunt]

Interesting discussion.

>20 years ago, I installed my 118' radio tower within a rock base.
The guy post holes were bored out with Bobcat with attachments.
About 2' topsoil, then 5' into rock.
The post holes.... >7' depth, >3' width.
Tower base, ~5' depth, with about 3' into the rock base.
A lot of work, but nothing has moved.
The steel posts were painted over with metal primer paint prior concrete pour.
No rust or corrosion after 20+ years.

Cheers,
James
ki5dq 
--------------------------------------------
On Fri, 10/13/17,  <john at kk9a.com> wrote:

 Subject: Re: [TowerTalk] Tower base over ROCK (shale) experience??
 To: towertalk at contesting.com
 Date: Friday, October 13, 2017, 7:43 PM
 
 It is probably less money just to jackhammer the hole(s) to the factory
 specifications.  My house in Aruba had very hard rock/coral ground and the
 holes were put in by hand by a local using this method. There are also
 attachments for a Bobcat that will break up shale.  What has the original
 poster tried so far?
 
 John KK9A
 
 
 
 To:    towertalk at contesting.com
 Subject:    Re: [TowerTalk] Tower base over ROCK (shale) experience??
 From:    "Joe Subich,
 W4TV" <lists at subich.com>
 Date:    Fri, 13 Oct 2017 19:35:58 -0400
 List-post:    <mailto:towertalk at contesting.com>
 On 10/13/2017 3:53 PM, bear wrote:
 
 > Hiring a soils engineer and PE is beyond the scope of the budget at present.
 
 You really need to bite that bullet.  Shales have a wide range of strength and you need to know exactly
 both the compressive and tensile strength of your particular shale.
 
 this stuff is a step down from bluestone, which is quarried not far
 from here... it will break down once broken up, and used as something
 like driveway fill, turning from large chunks back into granular
 soil in about 10 years, but as found in the ground it is stable.
 That is true only so long as no forces are applied.  Both the tower
 base (compression) and the guy anchors (tension) will apply forces
 that are likely to cause the shale to fracture.
 
 Bottom line, *don't guess*.  Get the soils engineer, pay for the
 necessary load testing and have the base anchors designed properly
 for the application.
 
 73,
     ... Joe, W4TV
 
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