What Is Happening Below the Slab
Clay soil expands when wet and shrinks as it dries. Over repeated cycles, that movement can loosen support below driveways, sidewalks, garage slabs, patios, and exterior concrete.
Water is usually part of the pattern. Downspouts, poor grading, edge washout, and long wet periods can move fine soil away from the slab base. Once a void forms, traffic and slab weight can push the concrete down.
What to Check First
- Whether the slab is intact or fractured into several loose pieces.
- Whether water drains toward the low area or away from it.
- Whether the height difference creates a trip edge or door clearance problem.
- Whether nearby slabs or foundation-adjacent concrete are moving too.