Ok, I am beyond frustrated! I am still trying to level this 20' diameter clay/gravel pit that we had "roughly" excavated about 1'. I have been spinning my wheels out there for weeks trying to get the bottom level for our 18'x52" Intex Ultra pool. I was leveling with the lowest point, when I hit my husband's drainage pipe that is connected to the drain tiles he put around our patio. I have had to completely reverse my strategy and use this relatively high point instead. Unfortunately, I discovered this after removing the clay soil from the center to level with low side. Now, I'm faced with having to build this and the low side back up with clay. I read where someone has deliberately made their Intex pool have a gradient depth. I am wondering if it would be ok to have a gentle slope to the center. This would mean that aprox 6' diameter area in center being 3-4" inches below outer edge with all pavers leveled and set on undisturbed clay. As far as the drainage pipe, I am fairly certain it will be ok under the weight of pool. This is a 3" dia heavy PVC pipe that slices through aprox 1/4 of site. It enters at roughly 2 o'clock and exits 5 o'clock. It is still buried, the small area that has a thin strip on top exposed is at 2 o'clock. It is below the level of the two paver's it is centered between. The buried portion will still be a couple feet from the lower center area. We are going to finish the bottom with a shallow layer of sand and 1/2" extruded foam covered with a tarp. I know this is complicated, but I would really appreciate someone with experience and/or an engineering mind to tell me if this might work. The amount of work this would save is huge, and I think it would be cool to have a deeper center, so I'm really really hoping it will.