I recently ordered our first INTEX Ultra Frame 18x52 pool that should be arriving next week, and we are very excited to get it setup. Being a mechanical engineer, I decided to create a 3D model of the pool to design a fence for the top, as our city code requires the encloser to be at least 5 feet including the pool side wall. Since I had already created the model, I decided to investigate the effects the horrific consequences of setting up a pool on an unlevel surface from an engineering perspective.
Luckily, we have an area in our backyard that is completely flat, so I don't anticipate any issues. However, I recall reading in our local paper last summer that a pool collapsed from being unlevel, which I suspect is more common that people realize. No one was hurt, but their next door neighbors basement was partially flooded.
I was amazed at the huge effect that was caused by only a couple of degrees of unlevelness. It is not uncommon for a backyard to have a slope of anywhere between 3-6 inches per 10 feet, depending on where you live, to aid in draining water from the foundation.