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re: thor's pool

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Thor,
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:
...
Thor
HTH,
Andrew Kester, P.E.
Orlando, Florida
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