[Ferro List] Swimming pool/Expansive soil

[Christopher Glasspool]

Kosta,
Not a expert but from my general construction knowledge I can give you these guidelines, opinions; the top of the pool and the deck should form one piece to create as dry an area as possible under the pool. Starting at the top, the deck or lip, and top of pool should be slightly higher than the immediate area with a drainage tile or gutter taking away any splash and storm water away from site. 
The vertical sides of the pool will have drainage mat, aka Enkadrainage or Enkamat under the sides which drain water down to the bottom. The bottom will have gravel with enough drainage tile (poly tubes with slits) that can leave the total area equally damp/dry. Draining this total bottom gravel area away from the pool site, and if that isn't feasible than a over kill of dry wells (french drains) are set around the perimeter.
The uplift from expansive soil can be as much as 5500 psi. If you have a hill or bank cut that you think might be giving the area a water flow or hydrostatic pressure then you will need to hire a local soils engineer, as the pressure will increase much over this, in any case it would be prudent to do this. 
One problem you shouldn't have but should be aware of is that regular rc pools are not actually waterproof as the blown gunite weeps and has flaws. Blown gunite pools reportedly sometimes have catastrophic failure due to the uneven amount of water released under the pool. The failure as I understand it is as much to do with the uneven uplift pressure as the pressure itself, and the system described above is also used for gunite pools as it not only takes the water away but evens out the dampness underneath. The physics of expansive soil uplift tend to push up more on the edges, and corners. 
Along with the drainage mat and drainage tile, may need a silt barrier between these things and the soil to stop them from eventually filling up with clay particles. I'm not sure of this, but you can find out from the vendors, and local contractors, engineers and inspectors, etc.
I think I would want safe overkill of the fc to be at least six to seven layers of mesh laid in the laminated fashion, about an inch thick. Make the technique easier and slope the sides of the pool significantly - work with gravity. - chris


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