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Re: wood post retaining wall

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By dead man anchors, I am assuming you are referring to what are called anchored retaining walls, where horizontal tension members are placed within the upper third of the wall. The far end of each tension member is carried in to a zone beyond the potential soil failure surface. IT IS NOT TO BE TERMINATED IN THE COMPACTED ZONE.

Many years ago, I did such a design. I don't recall the details. You may want to look at USACE Eng Manual 1110-2-2502 and Navy Design Manual 7.02 for design principles. There is also a book called Florida Soil & Foundation Handbook published by Florida DOT.

You may want to use a conservatively sized rod and galvanize it. Also coat the surface of the galvanized rod with coal tar epoxy. The plate at the anchor end needs to sized to transfer the rod tension to soil. The above noted manuals should give formulas.

I hope your client is aware of the fact that the bottom end of the post will be embedded in soil to a depth dictated by design formulas and, not according to his fancy.


"Andrew Kester, PE" <akester(--nospam--at)> wrote:
We are being asked by a client to design a 5' max tall retaining wall using PT wood members spanning horizontally between posts. Rather than relying on embedded posts in concrete (how I have done it before), they are wanting to use dead-man anchors, with the ends of the wood posts just embedded into the ground. The fill will be clean sand, it has already been excavated.
I have never designed a wall with dead-man anchors. They envision threaded rods with a steel plate, which besides the obvious corrosion issues, I don't imagine that giving you much resistance. I envisioned a block of concrete, but if you are going to do that, why not just embed them in a circular concrete footing?
Does a geotech normally supply the resistance for either type of system? Can you get any resistance out of a steel plate just sitting in compated soil? Would a better option be to do something with helical anchors? Or I think they cheapest and easiest would be to just auger holes and embed the posts in concrete...
My first thought is to run fast and far away from this project after we and the contractor could not talk the cheap school board owner into a CMU wall. We told them you will be luck to get by 5 years out of the wood without having problems. But the contractor has to do something, and we have done work with the GC and want to keep working with them.
Obviously all the steel will need to be hot dipped or stainless. Would you put a piece of PVC pipe around the all-thread?
Please CC me directly if you don't mind:
Thanks in advance.
Andrew Kester, PE
ADK Structural Engineering, PLLC
Lake Mary, FL
N:Andrew Kester;PE
FN:Andrew Kester, PE

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