What you will notice
This one is easy to spot from the yard, usually in July or August:
A dark gap along the slab
The dirt has pulled back, leaving a crack between the soil and the concrete.
You can see more slab than before
A strip of bare concrete shows where the soil used to sit.
Deep cracks in the yard
The ground near the house splits into a pattern of open cracks.
The gap is worse on one side
Often the sunny side, or the side near a big tree.
Flower beds sink
Mulch and soil drop away from the wall.
The gap closes after rain
A good soaking swells the clay back up against the slab, and the gap disappears.