Construction of building definitely involves foundation because it transfers the weight of the building to the ground. The term “foundation” is a general word with every building having a number of individual foundations called as footings. Since the weight of the building rests on the soil or rock, engineers have to study first the properties of the soil very carefully to ensure that it can carry the loads imposed by the building by determining the ‘safe bearing capacity’ or SBC. Different depths of soil have different capacity. Generally, the greater the depth, the greater SBC there is. The soil must be very firm and strong to properly support a building. Thus, building contracts will dig until they reach a very firm, strong, soil that cannot be dug up easily before constructing a foundation.
Foundations are divided into two categories: shallow and deep foundations, which refer to the depth of soil which the foundation is made. Shallow foundations can be made in depths as little as 3 feet or 1 meter, and is used for small, light buildings. While, deep foundations can be made at depths of 60 up to 200 feet or 20 to 65 meters, and are used for large, heavy buildings.
• Shallow Foundations
These are also spread footings or open footings. The term ‘open’ is used due to the fact that the foundations are made by first excavating all the earth materials until the bottom of the footing, and then constructing the footing. In the early stages of work, the entire footing is visible to the eye, therefore called an open foundation. In cold climates, it is important to protect the foundation from freezing because the water in the soil around it can freeze and expand, thereby damaging the foundation. Shallow foundation should be built below the frost line, the level in the ground above which freezing occurs. As an alternative, the foundation can be protected by insulation. It can be done by providing little heat from the building that will permeate into the soil and prevent freezing. Examples of this type of foundations are: individual footings, strip footings, and raft foundations.
• deep foundations
One example of this is pile foundation, where a pile or a long cylinder of a strong material like concrete is pushed into the ground so that the structures can be supported on top of it. This kind of deep foundation is used when: there is a layer of weak soil at the surface and the layer cannot support the weight of the building; or when a building has very heavy, concentrated loads like in a high rise structure.