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RE: Residential Cantilevered Retaining Walls.

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Hi, Tony.
 
It's been my experience that it is sometimes difficult to get the contractor to pour a slab at the bottom of a retaining wall before backfill because they can't get the concrete trucks close enough. If I think that there is a possibility that this can happen (like at a garage cut into the slope of a hill), I will specify that the slab is to be installed before backfill believing that the concrete truck can approach at the open (low) side. If I get that telephone call telling me that the contractor can't/won't pour the slab prior to backfill, I will redesign the footing to be unrestrained, usually requiring a big a** key, wider footing, etc. At this point, the contractor will figure out a way to pour the slab. IMO, shoring opens up another can of worms (design, specifications, etc.) and (probably) gets another engineer and sub-contractor on the job.
 
With regards to designing the wall as restrained, if the wall is backfilled before the diaphragm is installed, it has rotated prior to restraint and will not see much load from earth pressure. I agree, however, that any live load surcharge will be applied to the wall in a restrained condition and it would be prudent to look at some nominal steel on the inside face around midheight just for safety's sake.
 
Regards,
 
T. William (Bill) Allen, S.E. (CA #2607)
-----Original Message-----
From: LEDSTRUCTURES(--nospam--at)aol.com [mailto:LEDSTRUCTURES(--nospam--at)aol.com]
Sent: Wednesday, March 05, 2003 8:33 AM
To: seaint(--nospam--at)seaint.org
Subject: Re: Residential Cantilevered Retaining Walls.

Hi, Bill

I usually design the wall as a cantilevered retaining wall first noting on the detail that the wall is not to be backfilled until the slab is poured. as an alternate I will provide a note that specifies " the contractor is to provide shoring for the wall if backfilling is to take place prior to pouring the slab. In addition I will redesign the wall as a restrained wall with a higher active pressure. I will provide reinforcing on both faces because your wall will most likely see both loading conditions unless the shoring option is used.

Tony Hoballah, S.E
Long Beach