Earth Anchors

GaryM · Aug 23, 2002

I'm planning to install a 70' radio tower on my property in the spring. It's guyed with Kevlar guys anchored with Earth Anchors (or augers if you prefer) just like those used for anchoring mobile homes. The ones I'll be using are 8 inch diameter and 48" long. They should be installed with the eye pointing to the top of the tower. So they will be inclined at about 40 degrees off the vertical.

Any ideas on screwing these things into the ground? The ground seems to have no rocks of major size, so I don't think that's an issue.

I'm considering substituting a concrete filled hole of about 12" dia and maybe four feet deep with an eyebolt anchored in the pour. I'd extend the pier a foot or so above grade to make it easier to trim the grass.

Any ideas for installation of the anchors. If they were vertical I'd try and rig a way to turn then with a 3p PHD.

Egon · Aug 23, 2002

Why do the anchors have to be angled so they point to the top of the tower? Exspecially the concrete ones?

Egon

Mike_Dumond · Aug 23, 2002

Egon, it's so the strain is in line with the pin. If they were vertical, over time the swaying of the tower would pull them in towards the center, causing loose guys and more swaying.

73's de WA1ZPD

Anonymous Poster · Aug 23, 2002

Screw in anchors should NOT be installed pointing in the direction of the object they will anchor, they should be installed by screwing them in vertical. This is the standard for any type of anchor. After screwing the anchor in, a slot is cut with a digging bar so the anchor rod can be tilted in the direction of the object being anchored.
This enables the anchor to pull against virgin soil.
Screw anchors will need to be retensioned after a period of time as they continue to align themselves with the tower.
Screw anchors can be installed with an adaptor on an anchor, or by inserting a digging bar thru the eye and walking in circles.

Mike_Dumond · Aug 23, 2002

Gary, I'd go with the anchors, personally speaking. We've done some towers up here with both, and they work equally well. However the anchors came in at a lower cost. We had the power company run some in for a couple of the towers. Takes them just a few minutes to do it. Down side was working around their schedule, which wasn't too bad.

73's de WA1ZPD

Mike_Dumond · Aug 23, 2002

Franz, I'll go with the power company's recomendation on this one. After all, they do it for a living./w3tcompact/icons/laugh.gif

GaryM · Aug 23, 2002

Mike,

Thanks for the advice. I'm planning on a Glen Martin 70' with the Voyager tram system. I'd rather have a self supporting tower, but I really like the idea of not having to climb it either.

I didn't know about the trick of screwing it in vertical and then leaning it over. But it makes sense.

Gary, W0GOM

Mike_Dumond · Aug 23, 2002

Gary, the vertical installation is easier if you're doing it by hand, but if you can get the power company to do it using their anchors, I guarantee it won't move. Those things are 8 feet long. Maybe you can find a ham who works for them, make it easier to schedule.

Mike_Dumond · Aug 23, 2002

Of course, if you were closer, I'd go give you a hand, just so I could drool over your setup.

Mosey · Aug 23, 2002

One trick that might help if you have hard soil is to wet the ground before screwing the anchors in. Soak the area with a garden hose for about 5 minutes, then start screwing the anchor in. When it gets too hard to turn, put the hose on it again for 5 more minutes. The water will go right down to the end of the anchor by following the existing slot and loosen up the soil at the bottom. I have to admit I've never tried this on anything 48" long, but it sure has worked good on shorter ones! I was amazed what a difference it made the first time I tried it.

N4IMO

GaryM · Aug 23, 2002

I'll keep the water trick in mind. My only experience with earth anchors has been the ones that are about 1.5 inches in dia. Have used them for temporary guys during Field Day. And they are hard to get into the ground here in MO. I wasn't sure how it would be to drive a 8" one.

A related question:
I want to run both coax and AC to the base of the tower underground using the grey plastic conduit. I'm looking for a good type of box to mount on the outside wall that would let me come through the wall and turn 90 degrees and go underground. I probably should not run AC and coax through the same conduit. Might be nice to have the Polyphasers in the same box too. I don't really need the AC, but thought that it would be handy to have at the base of the tower.

Egon · Aug 23, 2002

I'm still confused on Earth Anchors.

The concrete ones I've seen installed for a 150 ft. flare stack were so designed that the weight of the concrete was the anchor.

Drive in or screw types used to guy service rigs were always placed vertical or away from the object they support.

To me it would seem an 8 inch diameter anchor in line with the direction of strain would only provide 8 inches of soil resistance. A vertical one would provide 8in. x depth of soil resistance.

All the guy lines I've seen have alway been equiped with turnbuckles to properly tension the lines.

Egon

Mike_Dumond · Aug 23, 2002

Egon,
While neither one will pull out under normal circumstances, the vertical one will need readjusting as it's pulled toward the center. The reason most people put in a vertical is because of ease of operation. The angled won't have that problem. As for strenght, an 8 inch anchor driven in to a depth of 7 or 8 feet will have more resistance than a 4 foot deep anchor, whether it's vertical or angeled. A properly inserted angled anchor, (talking power company installed), disturbs the soil very little sinced it's screwed in smoothly. Hard to do that by hand, especially in hardpan.

A well designed concrete anchor will probably out preforn a dirt anchor, but the cost is usually prohibitive, and if you decide to sell the property later on it can be a hinderance to the new owner.

Hmmm, I've probably been more confusing than helpful here. /w3tcompact/icons/laugh.gif Someplace in my junk, I have a book with drawings and formulas and stuff concerning towers and anchors. I'll see if I can dig it up.

phalynx · Aug 23, 2002

Gary, OK I have wondered about these trams. My question is, when you put the antenna on the tram, what keeps the antenna from hitting the guys on the way up or down? I have never understood this? I like the idea, but if it doesn't work, what's the point?

GaryM · Aug 23, 2002

Phalynx,

OK, here's the short story.

There are two types of tram sold by Glen Martin.

The first is made to wrap around the triangular tower and actually rides on the tower legs. With this type you can only have guys at the top of the tower because there is no way that the tram's frame, wrapped around the tower, could pass over the guy attachment points on the tower. This is marketed as the "Hazer".

The second type has a set of rails attached to only one face of the tower. These rails are "T" shaped and the tram rides on sets of rollers with the stem of the T captured between the rollers. This system allows several sets of guys at different levels.

Here's the tricky part.

When you lower an antenna with a boom, the boom will not pass the guys. But if you loosen the two guys on the side with the rails and allow them to droop down along the tower edge the mast can pass by. Then when the antenna is clear, reattach the guys and finish lowering the tram to ground level. If there is a second, or third set of guys, the process is repeated as required. If you have only a small antenna such as a 2M beam the boom could be short enough to pass by the guys..

Of course you can't do this in a high wind!

I have my setup planned so that the guy that doesn't need to be loosened is on the prevailing wind side. That's West around here.

phalynx · Aug 23, 2002

Wow, that sounds almost scary... I would imagine that it should be horrible with no wind like you said. It does sound like a lot of work too, but climbing the tower is not what I would like either..... 250 lbs on a tower is a scary thought.....

Please post pictures of it when you are done. I am one person who is interested in seeing this as I am sure there are others.

Phalynx (KD5ILS) -- Scott

Egon · Aug 23, 2002

Guess I'll have to start putting in my tent pegs in at a different angle.

Egon

Mike_Dumond · Aug 23, 2002

/w3tcompact/icons/laugh.gif Egon, tent pegs are ok vertical, or preferably at a 45 degree angle away. Unless you're using a screw type of peg. As you might have noticed, us hams do some weird things at times. Like climbing a 100 foot tower. A scary climb, but the view is awesome.

JoeR · Aug 23, 2002

Egon,

Auger style anchors: If I remember correctly, an auger when pulled upon will exert its force outward from the auger at a 45 degree angle. The diameter of the auger has to be large enough so that it actually drills into the soil. Imagine the auger creating a pulling area that looks like a cone where the screw part would be the apex of the cone. Therefore, an 8' auger would create a cone with a volume of 536 cubic feet. This means you would have to have something strong enough to lift 536 cu feet or 20 cubic yards of dirt. Maybe a structural engineer reading the post can validate this information...

Joe R.