As you know, that shape, size, and depth of the foundation depends largely on the design of the building. The kind soil or earth in which the foundation is to be set is also very important. For example, soft or very loose soil may have to be compacted. Compacting is packing down the earth to make it firm. Compacted soil may require a different kind of foundation from one built on solid rock. Most foundation are constructed of poured concrete, concrete blocks, concrete slabs, or some combination of these and other materials.
A foundation is also called a substructure. This is because a foundation is below the surface of the ground. A foundation has three part:, bearing surface footing and upright support.
All foundation are designed to support the weight of the superstructure
The superstructure is the part of the structure that is above ground.