A cracked slab means the ground under it stopped helping.

Floor Cracks: diagnosed and explained.

A concrete slab is strong when it is fully supported and surprisingly fragile when it is not. Concrete resists being squeezed but has little strength in bending, so when the soil under a section of slab compresses, shrinks away, or washes out, that span becomes a bridge over a void, and bridges made of unreinforced slab do not last. The crack you see in the tile, the ridge you feel under the vinyl, or the visible line across the garage floor is the slab breaking along the edge of its lost support. Some slab cracks are innocent: concrete shrinks slightly as it cures, and most slabs develop a few hairline shrinkage cracks that never move again. The meaningful cracks are the ones with displacement, where one side sits higher or lower than the other, the ones that widen over time, and the ones that arrive with sloping floors, cracked walls, or sticking doors in the same area. In Southern California, Arizona, and Nevada the soil movement behind slab cracking is usually expansive clay cycling between wet season swell and dry season shrink, though plumbing leaks and poor drainage can carve out support in any soil. Whether the crack is a cosmetic scar or a structural symptom is exactly what a floor elevation survey determines.

For the repair side of this, the foundation repair solutions page lists every method Dalinghaus installs, including the ones that fix problems other than floor cracks.