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Re: Retaining Wall Design Methodology

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Stan,

I think Nels has described our practice perfectly, the only thing I can add
is part of the "why".  The method 2 solution is consistent with the overall
design assumptions and methodology for all parts of the wall, not just the
heel.

Paul Feather

----- Original Message -----
From: Nels Roselund <n.roselund(--nospam--at)worldnet.att.net>
To: <seaint(--nospam--at)seaint.org>
Sent: Wednesday, July 12, 2000 10:00 PM
Subject: Re: Retaining Wall Design Methodology


> Regarding Stan's questions about 3 soil-pressure-determination methods.
>
> I use method 2), so that the heel is designed to support the pressure due
to
> the superimposed weight of soil as decreased by any upward foundation
> pressure.  Usually, however, I will quickly make the judgement that the
> effect of the upward foundation pressure is not significant and will
ignore
> its contribution in designing the heel.  For the height of walls I
generally
> need to design, I think that there is usually little practical difference
> between method 1) and method 2), unless the footing is oversized.
>
> I haven't encountered method 3).  It sounds like assumption of a
rectangular
> stress block somewhat like that used in strength design of concrete in
> flexure.  Is that the way soil acts?  Is it supported by research?
>
> The assumed triangular stress block of methods 1) and 2) matches the
rotated
> configuration of the footing, but the sudden drop of stress from maximum
in
> the soil under the edge of the footing to zero in the soil adjacent to the
> edge doesn't seem probable.  Maybe a parabolic stress block [one that
> extends beyond the edge of the footing] is more realistic.  Does anyone
know
> of problems because the wrong stress block was assumed, or has anyone
saved
> the client lots of money by assuming a different-shaped stress block?
>
> Nels Roselund
> Structural Engineer
>
>
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