Print

[KD0VE]

I recently inspected an extensive (40kw) solar array where the panels were oriented landscape and stacked 2 high.  The posts 2-7/8" diameter thick wall steel well drilling pipe sunk (no concrete) approx 10' with the bottom of the lower panel at about 6'.  The horizontal elements of the structure were also 2-7/8" pipe which was overkill.  (Around here the pipe is typically available in 30' lengths for about $100) The panels have a gigantic sail area and have been up for 3+ years.  I couldn't help but think maybe those same pipes sunk 10' (actually pounded in) would provide an adequate tower base in lieu of a concrete pour.  Even if supplemental guying was necessary this would be much easier and far cheaper than a concrete base.

wondering what advice anyone might offer.

[KL7JT]

1. The solar array is presumably much wider than the tower footprint and closer to the ground than antenna; the distributed torque is?

2. Tower height and wind cross section and antenna wind cross-section are major factors and not stated in your post.

3. The soil is a major factor. Sandy loam is quite a bit different than clay.

4. The mass and surface area of a 9 cubic yard block of concrete are quite different than three 10' lengths of drill pipe.

These are just a few things to consider.

If you are putting up a small tribander at 30', "you might get away with it".

On a windy day with wet soil, I would want to be upwind 100'.

I have seen a few things fail in wind; what happens can be counter-intuitive.

Additionally, if you have neighbors and believe in liability insurance, it is probably not the best idea.

As a Novice, I built a 20' "tower" out of 2x4s.

Its construction, use, and demise taught me some things.

If you do go with the pipe, it might be a good idea to have it galvanized if your soil holds water.

Perhaps of interest:

https://en.wikipedia.org/wiki/161_Maiden_Lane

73

[NA4M]

If the soil will allow pounding large drill pipe down 8-10 ft then it seems to me digging 3 holes 3-4 deep would be pretty easy.  Pay some teenagers to dig or hire/rent a cheap backhoe.   

I learned from hams with tall towers to find and use scrap-yard 8-12 inch steel "I" beams for guy anchors.  Torch off the "I" beam top-ends @45 deg and drill holes for guy-wire turnbuckle jaw attachment.  Instant guy-wire attachment equalizer plate.    Stand "I" beams on end in the hole leaving 1-2 feet sticking out and pour some concrete and back fill.  Done.

[VE3LZQ]

I know of solar panel supports that have an 8 inch diameter spiral at the end that are twisted into the ground with a powerfull machine to below grade to anchore them firmly and stop frost heave .This saves the expense of digging a hole and using concrete

[W7CXC]

Just some thoughts. At my place in Montana the well is 100' of six inch well casing with the static water level at 58'. It is a wonderful ground,HiHi, along with being rock solid. Have often thought of using well casing driven into the ground as tower anchor points as well. My non ME thought would be to use 4 or 5 inch casing so as to get more surface area to pull against along with going perhaps 15 foot deep. My place is on an alluvial fan of gravel with a soil cap between 1 and 3 feet. In fact there is a gravel pit about 5 miles down the road., Seems like a great idea. 73's David

[N0GV]

OK - drill pipe is pretty tough stuff but it really isn't up to the task for a tower support. The issue is simple: 3" is 1/4 of a foot and a tower that is 20 feet tall has an 80:1 lever acting on the pipe at the base. The force on a 20 sq foot area at the top at 60 mph is about 288 lbs. Multiply that by 80 and you get close to 2400 lbs of bending force at the ground. Add vibration and this won't stay anchored very well.

If you put in a cubic yard of concrete the bending force and distribution of load reduce the torque due to wind at the top is spread across the 3' wide base. The 2000 lbs of concrete also tends to reduce the amplitude of vibrations so it doesn't tend to loosen.

The 1st paragraph also shows why lattice towers with wider base sections (tapered) tend to be much stronger. A 12" on a side triangular tower has about a 10" effective diameter and, as a result, has over a 3:1 bending strength advantage over a 3" pipe, even if the three legs are only 1" in diameter.

Enjoy,

Grover

[WA3SKN]

Since towers are now covered in "building codes" in most all areas of the country, I would recommend checking those codes before investing any money to the project.  And, what are the codes for YOUR county?

-Mike.

[KB8VUL]

It really depends on the tower height and wind load. 
There was a company that sold a tower mount called a "wonder pole "
https://www.qrz.com/db/VE3PK
Scroll down to see the tower and mount.

These required no concrete but did require certain soil conditions and certain install methods.
The pole had wings on it that helped stabilize the thing in the ground and when the tower was up it had to be guyed. 
Installation required slowly filling and tamping the back fill and then filling the hole with water and allowing the water to naturally drain. 
This was done in 1 or 2 foot intervals to allow the back fill to settle around the pole.

I believe the tower cranked up to 40ish feet.  But I would need to measure mine to know for sure.  I have one but haven't put it up yet.  Another project for sometime before I end up in the ground myself. 

The issue becomes accessing the TOP of the tower once it's up.  A tower mounted on a pole like this is NOT something you should climb.  As seen in the pictures above, the mount allowed the tower to fold over and be serviced.  You need to consider that a REQUIREMENT for a setup like you are talking about. 

Another option, and again it's gonna depend on the application, would be the old school flag pole mast.  This is where you put TWO pieces of pipe going into the ground and a single piece of pipe going UP between them on a hinge pin at the top.  I have seen this done effectively to about 50 feet.  Obviously the pipe need to get smaller at the top.  But if you are putting up a small to medium vertical or a wire antenna (one guy opposite the wire direction should be used and use TWO guys if it's a corner of a long wire or beverage loop) this is also a 'cheap' method of getting something up in the air and allow you to get an effective signal going. 

BOTH of these are going to require welding skills.  Specifically with pipe welding.  and DO NOT thing you can thread the pipes together.  NEVER rely on threaded connectors as structural connections.  Threading pipe cuts the wall thickness by over 70% on a schedule 40 pipe. IT WILL FAIL.  Pipe should be purchased that slides into the section below it.  Slide them together and weld the joint and drill holes in the outer pipe and plug weld them 1 foot below the slip joint.  Failure to do this right will cause it to all fall down.