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RE: wood post retaining wall

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You need to get a copy of the California Trenching Manual

 

Matthew Stuart

Structural Department

Manalapan

Extension 1283

 

-----Original Message-----
From: Andrew Kester, PE [mailto:akester(--nospam--at)cfl.rr.com]
Sent: Thursday, November 30, 2006 3:31 PM
To: seaint(--nospam--at)seaint.org
Subject: wood post retaining wall

 

Listees,

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