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RE: snow load surcharge

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Randy,

I have never included snow load as a surcharge on retaining walls for the 
reason that snow will only accumulate on the ground when it is frozen (as 
you've observed) and when the ground is frozen, the equivalent fluid 
pressure should be approaching zero, at least for the soil above frost line 
which is probably 3 feet which is equivalent to 300 to 360 psf of surcharge, 
depending on your soil density.   It seems the critical loading would be in 
the spring when the snow melts and the ground thaws and turns to mud and 
then absorbs all of the water making the soil more "fluid."  So I don't 
think the argument about duration of load is really applicable, or that we 
are overly conservative in the design of retaining walls.

Jeff Crosier, S.E.
 -----Original Message-----
From:     Randy Vogelgesang [SMTP:rvogel(--nospam--at)jps.net]
Sent:     Monday, September 29, 1997 10:43 PM
To:  seaoc(--nospam--at)seaoc.org
Subject:  snow load surcharge

Should the full ground snow load (Pg) be added as a surcharge on the soil
when desiging retaining walls?

A friend of mine called me the other day and asked me this question, when I
told him that I did add a surcharge for snow, he ask me why?  He said has
done hundreds of retaining walls in this area over MANY years without this
surcharge and there never been any problem with any of the walls.  He
offered a possible explaination in that full active soil presssure is
achieved over a longer period of time, and full Pg usually only occurs for
less than a month.  Of course it could also be that the traditional way that
we design walls is conservative enough to account for this short term
loading without any adverse effects.  The typical Pg in this area is 200psf
and up.  I would appreciate opinions.

Randy Vogelgesang S.E.
South Lake Tahoe