Corner cracks & wedge cracks
The large majority of slab-on-ground foundations will develop what are called corner cracks or wedge cracks. The name comes from the fact that these cracks develop at or very close to the outside corners of the foundation and frequently form a wedge at the corner.
What causes corner/wedge cracks:
These cracks develop as a result of the expansion of the brick veneer as it is warmed by the sun. When the temperature of the brick veneer rises, the brick veneer wall expands in length and pushes or slides against the slab surface. At the end of a brick veneer wall at an outside corner of the slab, there is nothing to push back and the concrete cracks at each side of the corner forming a wedge.
Builders will usually place a piece of plastic between the bottom of the first course of brick and the slab; this reduces the friction force when the brick expands and slides against the slab. This has the practical effect of reducing the cracking on the slab at the corners but it by no means eliminates the corner cracking.
How serious are corner/wedge cracks?
These cracks do not indicate anything unusual about the foundation. If the cracking at a corner becomes very bad, the concrete wedge may become loose and even fall off. In extreme cases, the wedge will no longer adequately support the brick veneer; when this happens, the corner will need to be repaired.
This is not a foundation repair; it is a concrete repair. Installing piles and piers will have no effect on this condition.