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RE: Have you heard of watering your foundation?

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David, a french drain system probably won't work because the clay typically has a very low permeability (unlike sand) not allowing the water to move out of the soil and into the drainage system.
The key as others have said is that the movement needs to be consistent.  If there was a tree sucking water out of the foundation on one side of the house and poor drainage on the other side of the house it could cause the foundation/house to slope as high as the PVR.  As Eric said this could be in the order of 9" to 12".  Suddenly, you have oranges etc rolling off your kitchen table because of the floor being unlevel, doors that swing open by themselves etc.
 
Greg Meyer
-----Original Message-----
From: M. David Finley, P.E. [mailto:pec(--nospam--at)isgroup.net]
Sent: Monday, November 18, 2002 12:02 PM
To: seaint(--nospam--at)seaint.org
Subject: Re: Have you heard of watering your foundation?

Instead of watering, couldn't a french drain system be provided in order to keep the clay at a low moisture content?
 
M. David Finley, P.E.
2086 SW Main Boulevard - Suite 111
Lake City, FL  32025
386-752-6400
----- Original Message -----
Sent: Monday, November 18, 2002 12:54 PM
Subject: Re: Have you heard of watering your foundation?

I was asked this question by my brother who is building a house in the Dallas area. I am a structural engineer in New York state and my response was- What? Why? I have not heard of this practice and neither has anyone I work with. The people he has spoken to (who are not engineers) saythat if you don't water the concrete it somehow loses strength and cracks. The only thing I can figure is that the clay soil there has not been preconsolidated by glaciers as it has here and the moisture is kept up to prevent consolidation and settlement of the house. Am I on the right track?Bruce C. Trobridge PE
Senior Building Structural Engineer
NYS - Office of General Services
(518) 486-1749 


North Texas has a large area of expansive clays with tremendous shrink-swell potential.  Geotechnical reports commonly give PVR (Potential Vertical rise) estimates for our soils. The Woodbine formation which runs from just on the east side of Fort Worth in an ESE direction can have a PVR of up to 8 inches. Due to our expansive soils, it is common practice to "water your foundation" on a weekly practice to prevent the soils from drying out. Soaker hoses should be laid along the foundation and used every two weeks during a dry spell.  The intent is to ensure a constant moisture condition around the perimeter of the foundation to reduce the shrink-swell potential.
 

--
Davis G. Parsons II, PE RA AEI
a practical architectural engineer
in Fort Worth, Texas