Do we absolutely need a concrete base for poles/towers?
Do we absolutely need a concrete base for poles/towers?
(OP)
Hi, first of all, great site you guys have here.
Currently my boss has given an idea which I don't know is feasible or not. He wants to create a 50 ft pole foundation which does not use concrete. Instead, he wants to use a design that mimics tree roots, where the pole will be embedded into the ground and branches will spread out underneath to give leverage so that the pole will not move/overturn.
I have tried to find similar foundation types without much success. I am not very experienced in foundation analysis, and so have little knowledge as to why such foundations have never been used. Seeing as how concrete actually bonds to the foundation, as opposed to dirt, my boss is willing to accept that the branches will have to spread out and cover alot more area that a concrete slab. But I'm stuck thinking whether that will be enough.
Any comments/tips are very welcome. Thanks.
Currently my boss has given an idea which I don't know is feasible or not. He wants to create a 50 ft pole foundation which does not use concrete. Instead, he wants to use a design that mimics tree roots, where the pole will be embedded into the ground and branches will spread out underneath to give leverage so that the pole will not move/overturn.
I have tried to find similar foundation types without much success. I am not very experienced in foundation analysis, and so have little knowledge as to why such foundations have never been used. Seeing as how concrete actually bonds to the foundation, as opposed to dirt, my boss is willing to accept that the branches will have to spread out and cover alot more area that a concrete slab. But I'm stuck thinking whether that will be enough.
Any comments/tips are very welcome. Thanks.






RE: Do we absolutely need a concrete base for poles/towers?
Also, I have no idea what kind of analysis you would do to check the soil pressure under a 'tree root' foundation.
What material would you be using if not concrete? How would you embed the 'roots' without excavating a ridiculous amount of soil?
RE: Do we absolutely need a concrete base for poles/towers?
I picture your "concreteless" foundation as a series of horizontal members buried in the soil in a radial pattern, but I would also anchor each of them with a helical pile or two. You will need to consider both uplift and compression for each radial member. Then there is the question of dealing with the considerable moment transfer from the vertical pole to the horizontal foundation. Sounds like you need a geotech and structural engineer on staff.
RE: Do we absolutely need a concrete base for poles/towers?
RE: Do we absolutely need a concrete base for poles/towers?
RE: Do we absolutely need a concrete base for poles/towers?
This link is to the manufacturer:
http://www.metalfoundations.com/
I have photos if anyone is interested.
Steve wagner
RE: Do we absolutely need a concrete base for poles/towers?
DMcGrath, you have pretty much nailed the basis of the design. I am currently analyzing the forces similarly to how you have it outlined, to see how deep and wide the branches need to go. I will take into consideration the soil resistances and underground utilities as well.
The reason my boss wants this type of design is to cut costs on the concrete foundation building required (we work closely with a steel factory), but I'm wondering if the amount of soil that needs to be excavated is going to be worth the trouble, as I have read from your posts.
RE: Do we absolutely need a concrete base for poles/towers?
They were using conventional concrete piles and were therefore limited as to the uplift they could take in the pile. They ended up putting concrete weights on the platform to minimise uplift.
In your case the screw piles would have almost as much uplift capacity as compresion capacity and this should not be an issue.
I doubt that you will save anything on materials costs, but you will save on installation time (and therefore some site related costs).
You should get a structural engineer involved in this as there are many construction issues to consider.
RE: Do we absolutely need a concrete base for poles/towers?
Perhaps a helical auger might be able to provide this type of pullout resistance. You need some sort of drill rig to drill these into the ground. I believe there is a system where one helical auger can be used for short light poles (10 foot)instead of a concrete pole base.
RE: Do we absolutely need a concrete base for poles/towers?
Are you talking about a helical auger or a screw pile? I believe they are two different things.
RE: Do we absolutely need a concrete base for poles/towers?
Go to www.NFBA.org to get started
RE: Do we absolutely need a concrete base for poles/towers?
RE: Do we absolutely need a concrete base for poles/towers?
http://www.instant.com.au/a_light.asp
RE: Do we absolutely need a concrete base for poles/towers?
I was refering to helical anchors similar to Chance Anchors.
http://www.abchance.com/about/about.html
RE: Do we absolutely need a concrete base for poles/towers?
RE: Do we absolutely need a concrete base for poles/towers?
You could possibly bury one or more thin, reinforced mats fairly deep, using the slab as your root system. If you like, the steel would provide the strength, with minimal concrete cover for protection and to create a cohesive mat, like the tiny feeder roots seen in plants. You cannot achieve your root effect without considering that root networks are almost solid.
You could also use a soil nail/auger cast/micro pile foundation placed diagonally into the soil in radials from your center.
In any case, I think you would want two levels at the pole to provide sufficient "back span" for the 50 ft.
You might also consider two intersecting, vertical vanes which extend from near the surface to a depth sufficient to resist overturning. There would obviously need to be sufficient resistance for gravity, as well.
RE: Do we absolutely need a concrete base for poles/towers?
The contractor will be able to get it designed for you.
RE: Do we absolutely need a concrete base for poles/towers?
I'll be bringing this idea up with my boss. Thanks for all the replies.
RE: Do we absolutely need a concrete base for poles/towers?
RE: Do we absolutely need a concrete base for poles/towers?
We use spun cast concrete poles direct embedded to mount antennas and they cost less than 1/2 of a comparable steel pole and we use no concrete in the foundation unless the soil is extremely poor. In very poor soil, a steel casing can be driven and the inside excavated and the direct embedded pole can be put in and back filled with limestone.