The homeowner wanted a pool. The property sits six feet from a canal.
Think of a pool as a giant concrete bathtub buried in the ground. When it is full, the water weight keeps it in place. When you drain it — for maintenance, resurfacing, whatever — the only thing holding it down is its own weight and the soil around it.
Six feet from a canal, the water table is permanently high. When that pool is empty, the groundwater pushes up against the shell. That is hydrostatic pressure. If the pool is not built to handle it, the shell lifts. It cracks. Sometimes it comes right out of the ground.
This happens in South Florida. It is not theoretical.
The pool contractor on this job knew they needed a foundation plan that could anchor the shell against that uplift. They could not produce one. We could.