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RE: Retaining wall of sawdust

• To: seaint-seaosc(--nospam--at)mail-list.com
• Subject: RE: Retaining wall of sawdust
• From: "Lloyd Pack, P.E." <lloyd(--nospam--at)advantage-engineers.com>
• Date: Wed, 13 May 2015 17:12:36 -0600
• List-subscribe: <mailto:SEAINT-SEAOSC-on@mail-list.com>
• Priority: normal

```Hello Joe,

You'd find the friction angle the same way that you'd do it for
soils.  Either direct shear test or a triaxial test.  You can get a
pretty good idea from the natural angle of repose of the material,
if it's being loaded in a pile that is feed by a conveyor belt and
dropped.  It's like a cone shaped pile of sand, the angle of the
sides of that cone with the horizontal is the natural angle of repose
and very close to the friction angle for that material.

In a confined situation the internal angle of friction is a little higher
than the natural angle of repose, so using the angle of repose is
conservative.

As for using an equivalent fluid pressure, EFP, you kind of need to
know what the wood species is if you want to be close.  If you use
some really, really light weight soils.  Soil that is about 110 pcf will
have an EFP of about 50-55 psf/ft, for Rankine's active pressure.
If you're going for a Rankine at-rest pressure you'd be in the 35 psf/ft.
area.  That's quite a bit higher than most woods.

Douglas Fir has a specific gravity of 0.5 so it weighs about 31 pcf when
kiln dried.  Lignumvitae, one of the heaviest woods, has a specific
gravity of about 1.2 so it weighs 75 pcf.  This is still less than soil at
110 pcf.  So it all comes down to the water.

Hope this helps,
Lloyd

On 13 May 2015 at 21:59, Joseph Goldbronn wrote:

> Thanks Lloyd for the info.  When I went to the site there was sawdust
> still
> in the room and it was very dry.  It had the feeling of being kilned
> dried which makes sense because they are taking this sawdust right
> into their
> hopper which then is pressed and turned into fire logs.  From my
> internet searching it seems like it is in the 5%-10% range.
>
> Any idea how you would determine friction angle?  I may end up just
> using an E.F.P. which is around what I see around here for the local
> soils and call it a conservative design.
>
> Thanks,
>
> Joe
>
> -----Original Message-----
> From: seaint-seaosc(--nospam--at)mail-list.com [mailto:seaint-seaosc(--nospam--at)mail-list.com]
> On Behalf Of Lloyd Pack, P.E. Sent: Wednesday, May 13, 2015 1:03 PM
> To: seaint-seaosc(--nospam--at)mail-list.com Subject: Re: [SEAINT-SEAOSC] Retaining

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neers.com>
>

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