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Re: Retaining Wall Question

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A couple of issues. First, the problem I had described assumed that the
footing heel projected some distance beyond the back face of the wall and
that the vertical plane at the footing heel was in earth. Although this
material is sometimes removed to build the wall and replaced, it usually is
(or should be) properly compacted during backfill thereby restoring the
angle of internal friction and the resistive vertical component. Based on a
lot of the retaining wall sections I have investigated recently, ignoring
the vertical component of the active earth pressure has a significant
impact on the footing size.

If the back of the retaining wall is on the property line and the footing
stops at the back face of the wall, the problem is a little different.
However, there still exists frictional resistance between gravel backfill
and the back of the wall. While friction still exists between the back of
the wall and the soil, care should be taken since the back of the wall is
usually (or should be) waterproofed in some manner. This waterproofing
would (should?) reduce the amount of frictional resistance one would
normally assume between either masonry or concrete and the gravel backfill.

Bill Allen
> From: PRSE(--nospam--at)
> To: seaoc(--nospam--at)
> Subject: Re: Retaining Wall Question
> Date: Friday, August 22, 1997 6:26 AM
> After reading assorted responses to this issue, I will stand by my
> design philosophy of ignoring the vertical friction component.  As
before, I
> think the gravel backfill will not allow significant friction to develop
> between the wall and the gravel, or for that matter between the gravel
> the soil.  As to the additional soil behind the gravel, but on top of the
> heel (assuming the heel extends beyond the gravel, of course), seeing as
> soil is placed on top of the heel as opposed to the heel being poured
> the soil(!), it is safe to assume that the soil on top of the heel has
> removed and replaced, or at least placed.  I would imagine this creates a
> weaker frictional plane between the natural soil and the backfill,
> especially, as someone pointed out, if the backfill is placed in a wedge
> it often is.
> Lastly, it appears that this issue is complex, and not well documented or
> understood, and as such requires significant judgment and understanding
> the part of the design engineer.  As a company owner, with several
> working under me, I like the added confidence I get by instructing my
> engineers to ignore the vertical friction in all cases.  While it may be
> bit conservative at times, it does not appear to be excessively so, and
> way I just have one less thing to worry about.  There is no need to make
> job any more complicated than it already is.
> Bruce Resnick