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RE: Foundation Pinning

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Gail,

 

I would think that it would greatly depend on the soils’ engineer’s recommendations for the piles or drilled piers and the techniques each contractor uses to drill or drive piles, shore, and strengthen the foundation. On lightly loaded buildings, I like to use drilled piers with a corbel to pick up the edge of the existing foundation. Then I tie the piers together with a grade beam along or within the wall base.

 

Also, some times closely spaced drilled piers can act as a retaining wall (I forget the term soils engineers use to describe it-something like arch action…) but basically if they are on the order of 2-3 diameters in spacing, you get resistance effect (not sure if it’s true in all soils, I wouldn’t think so).

 

If you are going into mud, I would think you are talking about deep piles, at least 30 feet long (out here, the piles into bay mud are about 200 feet long). If the underpinning is being done to correct settlement in a building, perhaps the engineering is not required. If it is because of placing an adjacent building next to it and possibly compromising the existing building, I would most definitely think that would require a licensed engineer.

 

Just some thoughts…

-gm

 

-----Original Message-----
From: GSKWY(--nospam--at)aol.com [mailto:GSKWY(--nospam--at)aol.com]
Sent: Saturday, May 07, 2005 7:30 AM
To: seaint(--nospam--at)seaint.org
Subject: Foundation Pinning

 

I recently turned down a request to work on a foundation underpinning project in Alexandria, Virginia (several houses in a subdivision built on mud from the Potomac, fill, and who knows what else.)

 

There were  estimates from three different contractors on the number and location of piles required.  These estimates were completely different, by like orders of magnitude.  The project was already headed for litigation,  and some of the parties involved did not have pleasant personalities, so I backed out.

 

But I am curious,  in locations where this is commonly done (Houston comes to mind),  what is the accepted procedure for determining the pile placement and particularly the number of piles.   Does the design have to be done by a registered engineer?

 

Does it make a different whether the foundation is post-tensioned?

 

Gail Kelley