Welcome to the bedrock club, Mike. Same problem I have here in
southwest Colorado. Just inches under the soil is nothing but Dakota
sandstone. My solution was to do much as Hank, KR7X, suggested: drill
holes in the sandstone, cement rebar in place to form a cage, then build
an above ground tower base. You can see the project at my web page:
http://www.wd0m.com/
Click on Ham Radio, then Tower Project.
The US Tower TX-455 has been in place since 2003, and has withstood
winds of 90 mph. I hope this gives you some ideas on how to proceed,
and the confidence that it works.
73
Joe
WDØM
> Guys, I'm needing some help here.
>
> I am installing a HG52SS about 16 miles north of San Antonio
> in an
> area that is nearly all solid rock and I have two sets of
> factory
> specs on installation instructions from HyGain. One says (and
> I'm
> going from memory here, but I'm pretty sure I am correct)
> 30X30X42"
> for the hole and the other says 42"X42"X5.5 feet for the hole.
> The
> issue is that under an inch or so of soil here it is virtually
> all
> solid rock. We are now down about 3 1/2 feet into solid rock
> on all
> four sides, and it has required a large jackhammer and many
> hours to
> get there. Assuming the base hole is to be designed for both
> compressive and lateral movement, there is no way it is going
> anywhere, either way.
>
> This location is where I plan to live the remainder of my
> life, so I
> want it right. The tower will have a 2 el quad on it, and
> likely
> nothing every bigger than a 3 or maybe 4 el monobander as I
> have never
> owned a commercial antenna and have always built my own. With
> it being
> a crank-up, one antenna at a time (especially the 2 el quad)
> is
> sufficient for me.
>
> My question is: Is this sufficient, considering the ground
> materials?
> I am highly considering the hole as is, wth a pad one to two
> feet tall
> around it above ground and tied into the factory rebar base
> (which I
> will have to cut down and slightly re-do in order to make it
> fit the
> current hole). With a sufficiently tied-in top pad, the tower
> cannot
> move in any direction as the above ground part would try to
> push down
> onto the rock around it, which it cannot do (as the rock 1"
> and less
> underground is solid).
>
> An engineer is out of the questions as I am an average guy,
> teaching
> college for what often feels like minimum wage. I am also at
> least 16
> miles form the nearest possible engineer which would add to
> the cost
> factor.
>
> Again, this is an amateur tower installation. The load will
> never be a
> lot as the tower is not rated for a lot of load. It cranks up
> and
> down, and I monitor the weather here, so it would be lowered
> when
> conditions suggested that it would be prudent.
>
> I could sure use some opinions.
>
> Michael Goins, k5wmg
> Pipe Creek, Texas
> Fast cars, slow boats, big dogs, and summers off to write
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