Settlement and movement
Most of the time we take footings for granted, and sometimes we can: for typical soils, a common design applied project to project will perform as expected and is unlikely to have any long-term issues.
On the other hand, if you build on soft clay soil or if there’s a soft zone under part of your foundation, there can be trouble. A footing that performs well in good soil may not do so well in weak bearing conditions. We don’t often see outright failure, but it’s not uncommon to see excessive settlement when soil bearing capacity is low.
Further to this, correct selection, placement, installation and support for steel reinforcement may seem like a given but can be crucial to the footing/substructure’s long-term performance in resisting movement and any settlement issues.
If the whole house settles slowly and evenly, some additional settlement will generally not cause any significant issues, but if settlement is uneven (differential settlement), there could be damage.
It’s the unusual situations and sites that cause the most trouble. If you think there’s a problem ahead, you should stop and call the designer.
In these tough cases, having a thorough understanding of footing and slab design and construction requirements and what to look out for becomes important. In very strong and stable soils, minor construction issues within acceptable tolerances are unlikely to cause major concern. In weak or marginal soils, however, it’s best to be cautious and pay extra attention since getting something wrong, even simple things such as incorrect concrete cover to reinforcement, or not properly tying laps in trench mesh or slab mesh prior to the pour, can be very costly and difficult to rectify afterwards.