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RE: pool wall design

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Pat:
 
The way this is most commonly done in Texas is to core drill one or two holes in the deep end, and then grout them up prior to refilling the pool.  You can probably forget the idea of adding extra weight ... just calculate the volume of displaced soil and multiply by 62.4 pcf to see why.  Also, if you have expansive clay soils like we do, draining a pool for any length of time is risky business even without considering uplift.
 
Down here, most pools are free-form gunite and, to be honest, they typically aren't designed by engineers.  I have designed two.  The first one cracked due to shifting soils, leaving a nice 40 ft. ugly dirt collector right up the centerline.  The owner chose not to sue the engineer, since they were one and the same.  My second design is performing better, probably due more to stable soils than to my design efforts.  After 12 years holding water, the owner (me again) is cautiously optimistic.  From this track record, I would never want to design a pool for any other owner!
 
Your approach of designing the shell as cantilevered walls is reasonable, but it would be more accurate to simply use a 2D computer model with about 20 nodes across a transverse section.  Using a 3D computer model is unwarranted, especially considering that the design lateral soil pressure will be a crude approximation at best.  That "hardened overcoat" you refer to is probably just plaster.  It is there to keep the water in and to present an attractive appearance.  Plaster is not a structural material.  Use at least 6 in. (preferably 8 in.) of zero-slump gunite, with plenty of rebar in a single layer.  Insist on chairs to provide 3 in. minimum cover to the face of the soil, and don't let the contractor substitute bricks or chunks of wood.
 
Good luck ... and best regards,
 
Stan R. Caldwell, P.E.
Dallas, Texas
 
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Don't go around saying the world owes you a living.
The world owes you nothing.  It was here first.
                                                .... Mark Twain
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
   
-----Original Message-----
From: Pat Clark [mailto:bcinc(--nospam--at)nanosecond.com]
Sent: Thursday, November 13, 2003 3:28 PM
To: seaint(--nospam--at)seaint.org
Subject: RE: pool wall design

Would it be fair to say list several alternatives to prevent the uplift... say drains, extra weight, or simply not draining the pool when the soil is saturated?  Obviously different contractors and different sites will demand different approaches?
 
 Pat,

You probably know this but just in case you don't here's a reminder.  One of the most important considerations in pool design is to accommodate or eliminate uplift due to buoyancy for pool empty - water table high.  Subsurface drains and/or projecting the pool bottom to enable backfill weight to be included are possible solutions.

Regards,

H. Daryl Richardson

Pat Clark wrote:

 I am looking for additional references on designing pool walls.  We have started by analyzing these walls as cantilevered retaining wall, but this does not consider the curvature at the bottom of the pool, and additional hardened overcoats on the pool walls, etc. Also, any input for my specifications about leaving pools in a drained conditioned, etc. would be greatly appreciated.