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RE: wood post retaining wall

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I did a short retaining wall using a dead man anchor made of a blob of
concrete.  I made the concrete with a face large enough to produce a passive
soil resistance large enough to resist the force of the anchor rod.  I
embedded to anchor rod in the concrete long enough to resist pullout.  The
blob of concrete (cube or cylinder) was for each anchor rod and placed
diagonally downward to get beyond the Rankine failure wedge.  According to
Peck, Hanson, and Thornburg you can place the rod horizontally whereas the
deadman is beyond the failure wedge drawn by reflecting the line of the
failure wedge behind the wall off the horizontal surface.  (a picture is
needed here!).

You mention a circular concrete footing as a possibility.  Is this retaining
wall forming a complete circle?  Can it be designed like a cofferdam?

A Structural Engineer
Glenn C. Otto, P.E.
2108 Flowerdew Ct.
Virginia Beach, VA
Go Lyman Greyhounds!
Go Gators!

-----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:
akester(--nospam--at)cfl.rr.com <mailto:akester(--nospam--at)cfl.rr.com>

Thanks in advance.

Andrew Kester, PE
ADK Structural Engineering, PLLC
Lake Mary, FL

I did a short retaining wall using a dead man anchor made of a blob of concrete.  I made the concrete with a face large enough to produce a passive soil resistance large enough to resist the force of the anchor rod.  I embedded to anchor rod in the concrete long enough to resist pullout.  The blob of concrete (cube or cylinder) was for each anchor rod and placed diagonally downward to get beyond the Rankine failure wedge.  According to Peck, Hanson, and Thornburg you can place the rod horizontally whereas the deadman is beyond the failure wedge drawn by reflecting the line of the failure wedge behind the wall off the horizontal surface.  (a picture is needed here!). 

 

You mention a circular concrete footing as a possibility.  Is this retaining wall forming a complete circle?  Can it be designed like a cofferdam?

 

A Structural Engineer

Glenn C. Otto, P.E.

2108 Flowerdew Ct.

Virginia Beach, VA

Go Lyman Greyhounds!

Go Gators!

 

-----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:

akester(--nospam--at)cfl.rr.com

 

Thanks in advance.

 

Andrew Kester, PE
ADK Structural Engineering, PLLC
Lake Mary, FL

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