I only read the first page so dont mind me if it's been covered... From an engineering standpoint this seems like a bad idea. that looks like some slick clay and I can just imagine the wet season it going to cause it to cave in alot. It will be shaped more like a bowl IMO. Then again i'm not an engineer.
amazing how someone can be born in the right place in the world where everything is possible in Serbia, I can only dream about tropical weather can only grow Carp in which such pool