All pools built in areas of a POSSIBLE high water table should have a dewatering system like the one John referred to. For most concrete pools it requires only about a 40" difference in the water level from inside to outside to cause them to pop or crack. The copper plug that was referred to by Eric is rarely if ever used any more, instead we use a “hydrostatic relief” valve. Basically a check valve typically installed in the main drain. Many pool contractors skip the hydro relief due to their tendency to leak, not the best plan. My pool construction company has to actually buy “pool pop” insurance in addition to our GL and there are damn few companies that sell it.