The point of a foundation is to provide stability to the structure. The weight of the house sits on the foundation, which sits on the ground.
There are a number of different kinds of foundations. Most of them extend below the ground, and the large the building, usually, the deeper the foundation reaches. Slab Foundations are rather common, and mostly consist of a hole the size of the house dug directly below the house and filled with concrete (this is of course, a very simple explanation, there is more to it, but that is the basic idea.)
There are a number of dangers to a foundation, but the two most common are shifting soil and uneven support. Underground rivers can move the soil under your building, which then will put stress on the foundation. Another common damaging factor is the amount of water in the soil. In areas where there is regular, heavy rainfall, followed by a dry season (like, for instance, much of the southwestern USA) the soil tends to be a little unpredictable. Moisture seeping into the soil will cause it to expand, and moisture leaving will cause contraction.
When soil freezes and thaws it also tends to expand and contract. The removal of deep soil will affect the freezing and of this soil, in come cases, so there are often freezing units put into the foundations of such large buildings in areas where it’s cold almost year round.
More about foundation repair:
Stone foundations can crack for several reasons
Stone foundations are not used very much in the construction of homes or buildings today. However, there are several old homes and buildings were these structures still existent.
About foundations and the frost line
In geological terms, the frost-line is the lowest point at which soil freezes during the winter. (often around between 5 and 8 feet or 1 and a half to 2 and a half meters.)
What to do when hiring a contractor
After you contact a contractor, the first thing he or she should do, is visit your home and examine the extent of damage to your foundations. The estimate they present you should be based on their inspection. Most contractors do not charge for estimates. You should acquire at least three estimates.