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RE: Landscape Retaining Wall

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First the disclaimer (those pesky lawyers made me do it <grin>): I am no
geotechnical engineer, but I have slept in a Holiday Inn Express or two in
my life time.  <grin>  And I actually have had geotech courses like many
others on the list...

Having said that, I agree with degree.  I would modify his
statement to be "For some types of soil, 2' of soil can practically hold
itself up."

Since I assume that you want a nice vertical edge to your retained soil, I
doubt that you can realistically have the soil "hold itself" up,
especially if you have rather sandy soil.  Not to mention that "external"
forces (i.e. water runoff, stuff falling on the soil such as branches,
squirrels, dogs, etc) could cause problems.  Thus, I would certainly think
that you need something there.  Eli's point does, however, potentially
allow you to explore some other "materials" to use as the "retaining
wall"...depending on the type of soil that you have.

Have you looked to see what, if any, plastic or composite materials you
might be able to get your hands on to use?  As Eli points out, you likely
will not have a lot of lateral force to resist, so you need not have a
"super strong" material.  I could see something like fiberglass or maybe
some ABS plastic.  You may have to have something that has some "ribs" or
other reinforcing that goes back into the soil side depending on soil
type, thickness of material, and strength of material.

As to your idea of using steel, I don't see a problem with it.  You could
do either a "corrosion allowance" or protect it with some protection
barrier.  Even if you did not do a corrosion allowance (or not much of
one), it just becomes a "maintance issue" as when it becomes too corroded,
you just replace it.  You could see if you could get some Corten (i.e.
weathering steel that was/is used for bridges) steel.  To me, the
biggest issue with using steel (or some plastic or composite too) is
appearance.  It would be relatively easy to replace a rusted steel 2'
retaining wall (about the same easy as installing it except that you may
also "damage" some planting that you do in the mean time), but assming
that you have your rusted steel wall and it has not reached the point
where it needs to be replaces, how will a rusted steel wall fit within
your landscaping?  (OK, enough of playing architect/landscape architect
for me...talking about how things look is making me feel
light-headed...must go do some good ol' number crunching!).


Adrian, MI

On Tue, 21 Feb 2006, Eli Grassley wrote:

> Sounds like a good place to use a rock wall.  I guess that's not the look
> you want though.  You could use pressure treated or cedar lumber with some
> simpson concrete embeds to hold it back too.  2' of soil can practically
> hold itself up really.
> ~~ Eli G
> -----Original Message-----
> From: Daryl Richardson [mailto:h.d.richardson(--nospam--at)]
> Sent: Tuesday, February 21, 2006 11:31 AM
> To: seaint(--nospam--at)
> Subject: Landscape Retaining Wall
> Fellow engineers,
>         I have a piddly little retaining wall about 12' long retaining up to
> 2' of soil.  For landscaping reasons it is desirable to have this as thin as
> possible.  One possible design is an L shaped bent steel plate about 3' high
> with a 2'  "footing" under the high side utilizing the weight of soil for
> stability.
>         My only concern about this design is corrosion.  I have some
> thoughts on this. First is to use a low alloy steel which will perform well
> on the "air" side but I don't know about the "soil" side (I believe A242
> might be such a steel).  Second is to provide a corrosion allowance and not
> worry about it.  Third is to use a protective coating such as asphalt
> foundation spray.  Fourth is to give up on the whole idea; tell my wife she
> can't have it (tactfully, of course); and look for a completely different
> solution.
>         Does anyone have any thoughts on this?
> Thanks in advance,
> H. Daryl Richardson

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