I don’t know if they still do it, but, there used to be a copper plug that fits in a hole that was drilled in the pool. You have to chip out the marcite to get it out. That way if the water table comes up, it just fills the pool. I remember they guy using a metal detector to find ours.
I didn’t look at the article, but I know of a neighborhood in Coral Springs, where a bunch of pools popped when they were being refinished. On the one I inspected, they tried to make up the difference with thick pavers, unfortunately, the crack all the way around the pool about two feet from the floor, gave the game away.