We had a fiberglass pool installed in July 2010. It has cracked in half this past winter. The installer is walking away stating it was the pool company who winterized the pools fault. I had an expert come out and survey what happened, they concluded that pool was set too low in the ground, about 18-20 inches below grade. Causing water to become trapped underneath the pool and causing it to pop from hydrostatic pressue. Any thoughts would be appreciated