The edge lift distortion mode is almost always due to poor drainage, excessively wet weather, or excessive watering practices. Foundation repair is rarely appropriate to correct an edge lift condition.
The downside of lifting the interior of the slab
All a repair company can do is lift low areas. A foundation in an edge lift distortion mode will be lower in the interior of the slab as opposed to the perimeter. Installing piles or piers under the interior of the slab cannot be installed without jack-hammering the slab or tunneling underneath the interior of the slab.
In my experience, what happens is this:
First: We experience an unusually wet winter and spring.
Second: The soil around the perimeter swells lifting the perimeter grade beams.
Third: The slab surface cannot normally be brought down, but it can almost always be lifted.
Fourth: After the interior of the foundation is lifted, the slab surface will initially be more level than before. As time goes by, the areas between the stiffening beams will begin to sag. This can make the slab surface less level than before. How much out of level the foundation becomes depends on the details for each project. What cannot be denied is that the foundation surface could become less level than before the foundation was repaired. This is the downside of lifting a slab-on-ground foundation in an edge lift distortion mode.
Fifth: So what has the poor owner gotten for his or her money? Not much. Underpinning a slab that is in an edge-lift distortion mode is not cost-effective, especially as compared to improving foundation drainage.