Sand or Styrofoam
This is a great site. I am impressed. I have just purchased an 18' x 40' AGP with the Gorilla pad and cove. In my last pool, I used sand as the base and noticed that the sand mixed with the soil base, wore/soaked away around under ground connect brace straps and the liner sucked into the ground at those points in the straps.
Can sheets 1" or 1 1/2" (4 x 8) Styrofoam be used in place of the sand or is it used with sand. What are the pro's and con's of Styrofoam? Is any brand of Styrofoam more suitable? If I use sand then how much should purchase and how thick should I make it?
Oval pools require a very firm base and a lot of packing to prevent sinking around the straps and pressure plates. This is very common.
The foam sheets make an excellent base if you take your time and do a good job of it. The biggest problem with using foam on an oval pool is working around the pressure plates. If you can figure that part out it's a good choice.
Because of the complication with the pressure plates I would normally recommend sand for an oval pool base.
Sand can be used without problems if proper packing is done. If your soil will not pack consider replacing some of it with crusher run. Packing something like this around the brace assemblies should eliminate sinking.
Using the Gorilla pad underneath the sand will also help to prevent sinking. The pool cove is an excellent choice for around the outside of the pool wall. You will never have a cove wash out.