I recently posted a message about guying towers to the reflector. I
got a number of replies, which seem to follow 2 basic trends:
1. Use disc anchors from the electric utility, or
2. Pour a concrete block in a large hole (4 ft or so deep, with the
concrete 18 inches thick) and then backfill. This apparently is the
Rohn specification.
I haven't yet decided which approach I'm going to use, pending some
input from the REA which services my house, but I'll be doing
something soon. Attached is my original message with the responses
I received. Hope this helps someone. 73 - Alan NS0B
=====================================================================
Original message:
I was working on my tower yesterday and noticed a potential problem.
The tower is 100 ft of Rohn 45 with a Mosley Pro-67 on top, guyed at
3 levels (33, 63 and 93 feet) with 6700 lb Phillystran. The guy
points consist of 4 ft long screw-in anchors (the big ones sold at
the farm & home store for tying down mobile homes). I dug holes and
poured concrete since I couldn't get them to screw. The holes are
roughly straight down, bigger at the bottom, but the anchors themselves
are at a slant, roughly parallel to the axis of the guy cables. The
concrete cylinders are each about a foot in diameter. This
installation has been in place for almost exactly 5 years.
I think that 2 of them may be starting to pull out a little. The
concrete pad for one of them now sits about 2 inches above the ground
level, and the other is about 1 inch above. There are spaces just big
enough to fit my fingers into that go at least 6 inches into the ground
on the side away from the tower. I noticed the 2 incher last spring
but it didn't occur to me at the time what was happening. I don't think
it has changed much since then.
The ground in my area is mostly clay and rock without a lot of topsoil.
My questions are these:
1. Is there anything I can do to salvage the installation, such as
putting something into the holes to fill the spaces?
2. Should I do something right away or could it wait until the spring?
I'm going to be hard pressed for time to plant new guy anchors before
it gets cold.
I realize that the best solution is to put down new anchors. I also
understand that it isn't possible to give reliable answers without
having seen my situation. However I'd appreciate whatever thoughts
anyone might have. Thanks and 73 - Alan NS0B
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Bummer. Sorry to hear of your potential problem. I don't have any
pithy comments for you but would suggest you post this on TowerTalk.
There are some good engineers on there and would be able to give you
some helpful info.
The other thing I would suggest is to contact a local contractor or
two to see what they would recommend. They're more familiar with
your regional conditions and would also be able to do the work for
you.
You could put another screw-in anchor behind the existing ones and
connect the two. That would give you more capacity.
73, Steve K7LXC
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Having lost a 120' tower due to a faulty cable clamp on the top guy
wire, I became very conservative where guying is concerned. It would
be my recommendation to get some professional anchors from the power
company or a REC. I know that REC can power screw anchors down about 6
feet. I use their obsolete anchors, the ones that require a breaking
tool which spreads the "petals" of the anchor into the ground at the
anchor base. The strength of these anchor installations is approx
12,000 lbs without any concrete. Does take a little effort. Perhaps
you could offer some teenagers to dig the holes for say $10/hole. You
should be able to rent a post hole digger locally if you don't have one.
If you were closer I would loan you mine. BTW, my REC loans me the
anchor breaking tool.
Lew K4VX
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Yep. Put in new anchors and don't wait for anything. For towers this
large, I put in anchors with 8 foot rods and go down about 6 feet. I
don't think your anchors are up to the job . . . Hurry!
Stan w7ni@teleport.com
PS I forgot to mention: DON'T CLIMB THE TOWER UNTIL YOU HAVE REPLACED
THE ANCHORS.
---------------------------------------------------------------------
In this part of the country, the REA goes 5' down, plants the anchor
and at the bottom 2 feet (above the plate) they put in over sized rocks
(2"). They then tap the rocks with a bar and fill the rest of the hole
with dirt. Their directives state that this is better than concrete.
John (Jay) KB0UY
Macks Creek, Mo
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I'll be interested in the answers you get from the pros, but from what
I understand you may be pretty lucky that everything has held this long.
When I was researching the subject someone on one of the reflectors gave
me a short course in soil mechanics, but the gist of it is that any guy
anchor effectively pulls against a conical volume of soil centered
around the axis of the ground wire, whose conicalness depends on the
type of soil, etc. It's fundamentally the weight of that cone that
determines the pull-out strength of your anchor.
The Rohn catalogue calls for poured anchors 3 ft wide by 3 feet long
by 18" thick, buried 4 feet in the ground (to the bottom of the block)-
roughly 1800 pounds each, and with a lot of area to drag against the
ground. Doesn't sound like yours are near big enough.
73, Pete Smith N4ZR
n4zr@contesting.com
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>From your description I could not tell how deep the concrete anchors
were. Since you started with 4 foot long screw in anchors that exit
the ground at an angle, I would suspect that the screw blade of the
anchor is only about 2.5 feet below the ground surface. If this is
the case, it sounds like the concrete and screw blade may well not be
below the frost line. With the constant tension on the anchors and
the frost action you are likely experiencing some extraction of the
anchor.
My advice would be to fix this "soon". It could be next spring or
summer is soon enough, but that is hard to tell. Obviously, if the
tower comes down before you get it fixed, that was not soon enough.
I would recommend you use longer anchors, like the ones available
from Rohn. I have Rohn 55 and the anchors are down at least 4 feet
below the ground surface in at least a yard of concrete each. This
installation is into its 17th year. Hopefully, you have space enough
to install new anchors BEHIND the existing ones.
Wade W0EJ
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I'd fix the problem right away. Ask yourself how you'd feel if it
came down, now that you are aware of the problem, but haven't fixed it
yet?
As for fixing it, I guess my best advice would be to place new, proper
guy anchors right next to the old ones, so you don't disturb them
further. Use new Guy Anchor Rods from Rohn. When the new anchors are
ready, you can move the guys over one at a time.
-Tony, K1KP, fisher@hp-and2.an.hp.com
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>1. Is there anything I can do to salvage the installation
No. From the sounds of it, I would say your guy anchors are really
sub-par for that application. You didn't mention how much concrete
you used, but I bet it wasn't a lot.
>2. Should I do something right away or could it wait until the spring?
Do something right away. I suggest new anchors built for concrete (use
the Rohn ones) and follow the Rohn guylines for the amount of concrete
in each anchor. I don't have my book handy, but I would say that will
be between 1 and 2 yards of concrete per anchor.
Don't wait. Start fixing the problem now! I think you may have a
dangerous situation should you have excessive rain, wind, or ice occur
before you fix it. 73, Richard K5NA@BGA.COM
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I recommend using a can of spray paint to mark the actual location of
your anchors. I thought mine were pulling out, but they weren't. The
paint helped me keep my sanity.
Darin
WG5J
divinia@ti.com
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Sounds like you need to park your truck on top of, at least, the upwind
anchor until you can install a Rohn specified anchors next spring. I
just installed some for my 120' of 25G tower .. a 4'deep 3'by3' with
rebar filled with 18" of concrete. It wasn't that difficult to do.
Gud Luk.
de KD7LS
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I related your antenna guy problem to Jim WD0GLF. Remember? He is a
building contractor. He thinks it may just be frost heave. Look at
fence and sign posts. They also sometimes lift a couple inches...
73, Randy WA0I
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Have you thought about adding two "parallel" anchors (one on each side
of the existing anchors)? May not be as strong or as neat but may get
you by for a while until you can do it right.
I think your basic mistake was putting the original anchors in concrete
the way you did.
73 Paul N4XM
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ALAN, FIRST I AM NOT GOOD WITH THIS COMPUTER, I AM NOT SURE I AM
REPLYING CORRECTLY. FROM WHAT I UNDERSTAND YOU SAYING, I CAN SEE ONE
MAJOR MISTAKE YOU MADE. THE ANCHORS YOU USED ARE MADE TO SCREW INTO
THE DIRT, YOU ACTUALLY WEAKENED THAT INSTALLATION WITH THAT AMOUNT OF
CONCRETE. IF YOU HAD PROBLEMS GETTING THEM TO START INTO THE GROUND,
YOU MAY TRY SOAKING THE GROUND WITH WATER FOR SEVERAL HOURS,SLOWLY,
DON'T WASTE TOO MUCH WATER,THE GROUND CAN ONLY SOAK UP SO MUCH. AFTER
THIS YOU MAY HAVE TO TRY THE ANCHOR AT DIFFERENT ANGLES UNTIL IT GRABS,
THEN SLOWLY START TILTING THE ANCHOR BACK TOWARD THE TOWER AT THE
AVERAGE ANGLE OF THE GUY CABLES.ANOTHER THING,I HEAVILY RECOMMEND USING
AN ANCHOR AT LEAST 6 FOOT LONG FOR A 100 FOOT ROHN 45. A 4 FOOT ANCHOR
IS TOO MARGINAL FOR THAT SIZE TOWER AND ANTENNA, EVEN TOWER ALONE!!IF
YOU GET A 6 ft. ANCHOR ALL THE WAY DOWN, IT WILL NEVER PULL UP, IF IT
DOES,YOUR HOUSE IS ALREADY GONE, AND YOU ARE NOT WORRIED ABOUT ANY
TOWER. I PUT UP TOWERS FOR A LIVING,AND SERIOUSLY, I HAVE NEVER SEEN A
6 ft. ANCHOR BUDGE EVEN A LITTLE!! YOU CAN GET 6 FT. ANCHORS AT A T.V.
CABLE SUPPLY COMPANY,AND UTILITIES SUPPLY. YOUR CABLE COMPANY CAN FILL
YOU IN ON THEIR SUPPLIER. BE SURE YOU GET ONES WITH AT LEAST A 6" SCREW
DISC AT THE BOTTOM OF THE ANCHOR. ANCHORS SHORTER THAN 6 FT.(BUT NOT
LESS THAN 2-3 FT.), ARE FAIRLY PRACTICAL FOR TOWERS LESS THAN 80-90FT.,
AS LONG AS YOU DON'T HAVE A LARGE ANTENNA UP. AND THE TOWER SIZE I MEAN
IS LIKE ROHN 25, OR SO.I RARELY USE THE EARTH ANCHORS, FOR IN ORDER TO
WARRANTY MY INSTALLATIONS, THEY MUST BE BY THE BOOK. YOU CAN PUT IN NEW
ANCHORS WITH NO PROBLEM. PUT THEM IN ABOUT 1-2 FEET SHORT OF THE OLD
ONES, THIS ALLOWS YOU NOT TO PEICE YOUR GUYS, BUT YOU WILL SHORTEN EACH
GUY A FOOT OR SO. ANY WAY I CAN HELP YOU, MAIL ME BACK. BY THE WAY, IF
YOU SUSPECT AN ANCHOR HAS MOVED,IT WOULD BE A MAJOR GAMBLE TO TRY TO
"BUY TIME"!!!
73 DAN dann4gnr@hartcom.net
----------------------------------------------------------------------
I have the feeling from your description that you should be paranoid....
I use 8" ground augers with 7 foot long galvanized shafts from the local
power company, which I augered into clay - r e a l work... I pay about
$24 a pop, but they are built like a tank, and are holding up the 150
footer.. The power company says they expect them to last 30 years,
minimum...
I even got nervous about them (no problems in two years) , so for the
new tower, I now DIG A HOLE about 2.5' wide and 3.5' long and 4' deep...
I set the assembled auger and rod in and gouge the side of the hole
until the rod is at the angle i want... I cut a piece of #10 rebar mesh
(6" mesh) the size of the hole, and slide it down over the guy rod...
Then, I drop 2 bags (80#) premix on top of the auger/rebar, and back
fill.... These will not fail... I am in the process of going back to
the existing augers one at a time, and digging a hole, starting about a
foot outboard of the end of the auger (estimated with use of a yard
stick) and doing the rebar/premix... letting em sit for a month and I
will transfer the guys to the new anchors...
I strongly suggest a similar fix, soon, for your installation... if I
can help in any way, hollar...
Denny
k8do@aol.com
* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *
* Alan Braun MD, NS0B/V31EV *Internet: albraun@socketis.net *
* Jefferson City, MO *Packet: NS0B@N0LBA.#cemo.mo.usa.noam *
* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *
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