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RE: augered piles

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Cardboard void forms under structural slabs work much better in theory than they do in actual practice.  Often, the subgrade gets wet and the void forms slide around.  Sometimes, they get wet and collapse prematurely, before the concrete slab has set up.  Construction workers' boots and tools can destroy void forms before the concrete is even placed.  Vertical pipe penetrations are rarely sealed properly at the top of the void forms.  This allows wet concrete to flow into and around the void boxes.  Few of these problems are obvious to whatever inspectors or engineers might be present at the pour because there usually is a discontinuous layer of black plastic film over the top of the void forms.
On three different occasions, I have had the "opportunity" to excavate and crawl under structural slabs that were placed over cardboard void forms in order to forensically inspect the actual result.  Not a pretty sight, especially since my PE seal was on the construction documents for all three projects.  That is why we now require legitimate crawl spaces beneath all structural slabs, and employ cardboard void forms only beneath grade beams and walls.
Stan Caldwell, P.E.
Dallas, Texas
-----Original Message-----
From: Stuart, Matthew [mailto:mStuart(--nospam--at)]
Sent: Wednesday, June 04, 2003 3:44 PM
To: 'seaint(--nospam--at)'
Subject: RE: augered piles

It is common to pour the structured slab on top of a collapsible cardboard void form mold which provides an air space between the slab soffit and the top of soil thereby preventing any impact on the slab from the soil heave.

D. Matthew Stuart, P.E., S.E., P.Eng.