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Re: Key Location in cant. retain. walls.

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The question is the optimum placement of the key to resist sliding.  I
agree that placement near the toe is easiest for constructability.  But
wouldn't placement near the heel cause more soil toward the toe to be in
compression beneath the footing, hence more sliding resistance?  Also, the
key near the heel clearly mobilizes the entire backfill height in resisting
rotation.

Another thought from the reinforcing standpoint -- if you align the uphill
faces of the wall and the key, there is no bending stress reversal, and
reinforcing details should be simpler.  The contractor should like that,
even if he had to dig a little more.

'No answers, just observatons.

Fountain E. Conner, P.E.
Gulf Breeze, Fl. 32561

----------
> From: dahil01(--nospam--at)ix.netcom.com
> To: seaint(--nospam--at)seaint.org
> Subject: Re: Key Location in cant. retain. walls.
> Date: Thursday, July 23, 1998 11:58 PM
> 
> I prefer to have the key either in the middle or close to the toe.  Not
> near the heel, especially in the example listed with a 2:1 back slope. 
> The key at the heel requires more excavation, thus more expense.
> 
> Roger Turk wrote:
> > 
> > I prefer to have it at the middle, as close to under the wall as
possible as
> > reinforcing can be extended from the wall into the key and development
> > lengths can be more easily accomodated.  Also, there would be less
concern
> > (and need) for additional reinforcing to resist the tension and
concentrated
> > moment in the footing caused by the forces on the key.
> > 
> > A. Roger Turk, P.E.(Structural)
> > Tucson, Arizona
> > 
> > rwhitsel wrote:
> > 
> > . > In the design of cantilevered retaining walls, say with a 2:1
backfill,
> > . > where is the "optimial" location of the key used to resist sliding
of the
> > . > wall,  I have seen it placed in three places
> > . > (1) at or near the Heel.
> > . > (2) at or near the Toe.
> > . > (3) somewhere inbetween perhaps near the stem to pick up some of
the
> > . > reinf.
> > . >
> 
>