Oops! Repairing a Broken Guy Anchor Rod

In a previous article I teased a picture showing a small pit dug up in the 80 meter vertical antenna field. As I said, I had an accident with a tractor. It was careless of me to let the vegetation grow high and then not mark the guy anchor rods, which poke up only a few inches above grade, and then fail to watch for them when I'm working in the field. 

The new anchors were installed a year ago as the first step in rebuilding the 80 meter array. I have been proceeding in steps and I hope to replace the tower this year, as time and weather allow. A consequence of my slow schedule is that the guy anchors are so far unused and have no attachments to make them particularly visible. They were vulnerable.

Guy anchor rods are designed to be strong in tension. They are not typically designed to withstand an impact from the side. The soil can be a poor support for a long steel strut projecting from a deeply buried concrete guy anchor. Hardened steel driven by many horsepower via a reduction drive can do a lot of damage. 

The vulnerability to impacts leads some commercial tower sites to construct concrete or steel bollards on either side of guy anchors to prevent accidental collisions with vehicles and heavy equipment. These incidents can and have occurred.

Since I want to rebuild the central tower this fall the anchor needed to be repaired. It is not as difficult as it might seem but must be done properly if it is to have at least the strength of the original. The steps were as follows:

1. Dig down to inspect the damage
2. Assess the point below which the rod is undamaged
3. Cut the rod at the transition between damaged and undamaged
4. Fabricate an extension rod that overlaps and is joined to the remaining rod
5. Align the rod extension (azimuth and elevation angle) to the original spec
6. Coat the new and old rod to prevent corrosion
7. Backfill the hole and compact the soil
8. Confirm that the rod is still aligned

In the worst case, there is not enough undamaged rod to splice to or too deep to effect repairs. This is not a large anchor or very deep, but I was happy not to have to remove it and make a new one. After cutting off half the rod there was enough left to work with it.

After performing steps 1 and 2 last month I included a new extension rod on my shopping list when I visited the metal yard. Since I had to cut 2' (60 cm) down, the extension had to be at least 2.5' (75 cm) to account for overlap to make the splice. Splicing angle stock is far easier than for round anchor rods. The extension is wider (2.5" vs 2") and thicker (3/16" vs ⅛") to make the repair easier and a little stronger than the original.

I used a short straight edge in step 3. I slid it up and down the rod to precisely determine where the steel began to curve. The objective was to preserve as much of the original as possible to make the repair easier. If the cut is too far down it may be impossible to work on with hand and power tools other than by making the excavation wider and thus significantly more toil with a shovel. 

Do not attempt to straighten the bent rod! This will in most cases weaken the steel, especially if it is tempered to any degree. Even mild steel can be weakened when bent. Steel is inexpensive so don't try to "cheap" your way out of this problem.

I had to cut a radial while digging since it was in the way of the repair work. I was able to keep the radial intact and running over the excavation when the anchor was installed last year since I didn't need to fit tools down there. It can be spliced after the repair is complete.

I scooped out ~2 ft² of soil around the shortened rod to fit tools for the repair work: a hacksaw to cut off the damaged part and a drill to make the splice holes to join the new section to the old. The paint on the old one was damaged during digging and had to be repaired as well. That required washing and drying the surface before applying new paint coats. For convenience I used cold galvanizing compound since it dries faster than rust prevention paint. Since the painting must be done outdoors pay close attention to the temperature range specified for the product. I painted the extension indoors where it is warm.

The exact positions of the splice holes is not critical which is great because precision is difficult when working in the tight space. Holes should be set back from from the edges and far enough apart that the upper section can't wobble. Assuming the remnant is correctly aligned, the new extension should also be aligned. Notice that the larger extension is placed behind the remnant to make maximum use of the available surface area. The cut and drilled holes are filed and reamed to remove metal ridges that would prevent the pieces from sitting flat against each other. 

Support the upper end of the extension with a piece of lumber as shown at right. Sight the extension to confirm that it is lined up with the tower (azimuth angle) and use an inclinometer for the elevation angle. Don't rely only on the clamps and the trueness of the metal.

⅛" pilot holes are drilled first in the remnant. Next I firmly mated the extension to the remnant with small C-clamps (one on each face) and continued the pilot holes by drilling through the extension. I separated the sections and widened the holes to accommodate 5/16" grade 5 fasteners. 

Drilling in the hole is awkward and it can be difficult to apply pressure on the bit on axis and without wobble or bending. Don't rush it and wear eye protection! You could shatter the bit and fling fragments into your eyes. Widening the holes with a large bit is much easier than drilling the pilot holes. Holes in the extension can be widened on site or on a drill press. I found it easier to do all the drilling on site. I hope it is obvious that the drill bits should be of suitable type and quality, and sharp enough that they cut quickly without wandering. Use coolant on large bits cutting through steel or you can ruin them.

When I was done the alignment of the repaired anchor rod was within 1°. That's pretty well perfect, and stayed correctly aligned when the lumber support was removed. I spray painted the hardware and let the pieces dry overnight. Then I backfilled the hole while compacting it, paying particular attention to the underside of the repaired anchor rod. However, don't tamp too aggressively since you might alter the alignment or scrape the paint. Guy wire tension can correct a misalignment but it's better to keep the rod aligned throughout the job.

The backfilled hole and rod looked great when I was done. I just had to be careful to keep the broken ends of the cut radial from being buried. After several years they get "absorbed" by the vegetation and might be difficult to find later when you want to splice them together.

The rebuild of the 80 meter tower won't happen in October. I hope to do that in November while the weather is still warm enough for concrete work. There are other priorities at the moment.