In my area, we have booqoo clay. Ram Jack a popular foundation contractor will dig down until he finds bedrock or stable strata that will not shift and settle. In my area that is about 6 feet. Far apart, Ram Jack again goes 8 foot apart. Piers are built and they MAY be 5 to 6 feet thick. then jacks are installed, and the slow process of jacking up begins. A water level is used in some cases across the floor and intersects like an X Y Graph.
Ram Jack finds level then cements the jack in place and is done with it. Each jack and hole cost in material and labor about $500.
This is in my region only, please check yours first. This is to give you an idea how this company works as I have had it done to my slab foundation.