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Re: Retaining Wall Question

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While debating this issue with one software author, the author referenced a
classical textbook titled "Foundation Analysis and Design" by Joseph
Bowles. Since I am an old geezer, I had an early edition of the book which
did not have inclusion of the vertical component. In my search for "truth",
I tried contacting Mr. Bowles who taught at Bradley University. I found out
(from the University) that he had retired. I found his home number (not
revealing my research techniques) and discussed this issue with him. He was
most happy to discuss this issue with me. He told me that, in his
subsequent editions, he had included the vertical component and it was a
valid force for either level or sloping backfills. This value is a function
of the angle of internal friction, tan phi, which exists even when the
backfill slope is level. I told him that, in several instances, we are
given an equivalent fluid pressure and not the angle of internal friction.
At that point, he said that it should be obligatory for the geotech. to
provide this information. This is where he displayed his academic
background-not reality. I told him that I conventionally use Pv=1/3Ph. He
concurred that this was a conservative number. I believe the EFP method is
"similar" to using the Rankine equation, but is simplified and allows the
geotech. to consider other factors.

You might want to check Retain Pro to see if it will give you a vertical
component when you have a level backfill and are using the EFP method (not
Rankine). I realize Amrhein's book gives a value of kv=0 for beta = 0, but
I think this is extremely conservative and produces footings that make
contractors laugh at us.

Regards,
Bill Allen

----------
> From: Kevin McCune <kmccune(--nospam--at)willdan.com>
> To: seaoc(--nospam--at)seaoc.org
> Subject: Retaining Wall Question
> Date: Wednesday, August 20, 1997 10:50 AM
> 
> >Another problem is that you may be using retaining wall software that
does
> >not include the vertical component of the active earth pressure.
> >Conservatively, this vertical component would be equal to 1/3 of the
> >horizontal component located at the heel of the footing. Without this,
> >retaining wall footings become rediculously large. Check your
input/output
> >and software algorithms.
> >
> >Regards,
> >Bill Allen
> 
> You have brought up something that I have wondered about.  When designing

> for a sloped backfill, do you include the vertical component for friction

> and for overturning (less conservative)?  From the references I have
read, 
> there seems to be some disagreement on this point.  (ie: Amrhein
recommends 
> excluding the force from the friction calc.  Other texts recommend 
> excluding it from overturning).  You are right in saying that this force 
> greatly affects the size of the footing.  The vert. component tends to
(in 
> many cases) move the pressure resultant TOWARD the kern.  By the way, I 
> have used Retain Pro 4.0 and it seems to include the vert component in
both 
> cases.  Comment would be appreciated.
> 
> Kevin McCune  
> 
>