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RE: thor's pool

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Hi Andrew.
Thanks for your comments.  And thanks to all the other feeds back to me.  Yes, I have taken into account most of the issues that have been highlighted.  They have alerted me to some of the secondary details that I wished to not overlook.
The "soil" is a fractured "soft" rock - the sort of rock that is stable and competent, with good bearing values, when undisturbed but will reduce to rubble if broken up/down.  The pool is to be located adjacent to the ex. house foundation so, except for the nominal gap between (to make sure they are separate), the walls shouldn't have significant lateral loads (the wall of the house is/was a basement wall (full hght).  Similarly, looking at the rock exposed, I don't think there is a settlement problem (but I take note of your caution) and I know that ground water will not be an issue.  The site is at the top of a rise.
The "apron" idea is nothing more that a stiffening element to the pool wall and would only be a couple of feet wide at the most, however, I like your comment to lower that to allow for an extended walkway.  At the moment I have designed the walls for both cantilever and top restrained conditions, as well as allowed for the full/empty condition.
I have been advised that if a pool contractor is employed, then that contractor will probably have a preferred method/detail so I expect to be working together with whomever is chosen by the Client.
Thanks to everyone (I love this list) and, yes, I guess if anyone wants to see the final result, I'd be happy to share it.  My international peer review committee ...   :^)

Thor A. Tandy P.Eng, C.Eng, Struct.Eng, MIStructE
Victoria, BC

-----Original Message-----
From: Andrew Kester, PE [mailto:akester(--nospam--at)]
Sent: Saturday, January 31, 2009 9:43 AM
To: seaint(--nospam--at)
Subject: re: thor's pool

I think you have several things to consider with this project, which you may already be doing. The existing foundations of the house if within a certain distance (and depending on your soil) will put a lateral suracharge load on the wall of the pool. Also, you may have to give the contractor some shoring direction to avoid settlement issues with the existing house. I would include a preliminary site visit to review the existing wall and take lots of photographs and document any exterior and interior cracks, just in case down the road they start making lots of claims. I don't know the existing home construciton.
Also, in Florida, it would be very unusual I think to use the concrete deck as an apron. These are typically placed after the entire project is done, and are simply a slab-on-grade with a textured "cool-deck" topping. More popular now is the use of concrete pavers. If the owner wants a concrete deck and you can get them to OK your idea, then I would certainly explain to them this is structural element and cannot be removed ever (and note that on your dwgs). You may want to recess the structural concrete apron a few inches from the finished top edge of the pool so they can place a non-structural cool-deck topping or even a layer of sand and thin pavers.
My conclusion as well as any others (as previously stated) on this list is pool design is not an exact science, but somewhat of a mix of science and art. If the pool is non-rectangular it will behave more like a circular water tank and the pool water will balance out the soil pressure and put the reinforcement in tension. But I don't see how in a rectangular pool the walls, at least while being constructed and empty, do not act like cantilevered walls.
And I have seen several pools pop out of the ground when partially emptied during a storm event because of a high water table. One was up two feet and took the deck with it, the whole thing was a total loss. As mentioned by others, they do have valves that are supposed to pop and allow groundwater to enter the pool to balance the hyrdostatic pressure. But if you design it not to float in the empty condition with a high water table, and simply add mass in the form of lots of concrete, I would expect you will have a very angry homeowner and contractor... 
Conclusion- I don't touch swimming pools, seems like a no-win. Good luck, and let us know what you come up with.
"I guess i should.  i'm in soft rock and th 9' end is against the ex. house:
Andrew Kester, P.E.
Orlando, Florida