I had a Rohn screw anchor fail a few years ago. Fortunately
I was at home, noticed the loose guy wire, and was able to
take action to prevent the tower from falling over. The subject
was discussed quite a bit on this reflector in November, 1996.
The consensus was that the anchor failed due to electrolytic
action. The top 18 inches of soil is clay, the next 6 inches
is Caliche, and below that is sand. The rod failed at the depth
of the Caliche layer. They tell me that non-homogeneous soils
are problematic from an electrolysis standpoint. I was not able
to unscrew the other anchors for examination, so they were obviously
in much better shape than the one that failed. I replaced them all
anyway, and will probably replace them again in another few years.
The anchor that failed had been in the ground for 17 years.
Dave Hachadorian, K6LL
Yuma, AZ
K6LL@juno.com
On Mon, 01 Jan 2001 13:19:14 -0800 Jack Hicks <jackhicks@qwest.net>
writes:
> A 70 ft. ham tower 2 blocks down the street from me came down about a
> week before Christmas in a windstorm we had here in Western
> Washington.
> Was just a pile of scrap steel and aluminum when I saw it a couple
> of
> days later. Fell on his roof and that of his neighbor. He had just
> installed a new Force multiband yagi on it last summer. The tower
> has
> been in place for at least the last 7 years that I have lived in the
> area and probably a lot longer than that, maybe up to 20 years.
>
> I stopped to chat with him and he said one of his tower guy earth
> screw
> anchors had totally disintegrated in the ground and the guys broke
> free
> in the wind. The other two anchors were like new he said. It is a
> mystery why one anchor virtually dissolved or rusted out and the
> other
> two were ok. He wonders about potentially corrosive soil or
> electrolytic
> corrosion. The anchors are the standard earth screw kind used by the
> power companies. Fortunately, no one was injured and he said
> insurance
> will cover the replacement cost.
>
> Is screw anchor corrosion a typical problem? How does one keep tabs
> on
> this? Can it be detected or prevented?
>
> Jack
> KD7OE
> Des Moines, WA
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