Foundations are the most important element while constructing any building. The foundation of the building determines its strength. Foundation distributes the weight of the structure over a large area of soil and avoids unequal settlement. Also, it prevents the lateral movement of the structure and increases structural stability. There are usually two types of foundation. They are shallow foundation and deep foundation. The shape, dimensions, and depth of a foundation also varies from building to building. In this article, we have further categorized types of foundations that are used according to the requirements of the construction projects.
Shallow foundation is the most popular type of foundation for lightweight structures. Here, the shallow foundation depth is low, and it is economical. It is suitable for a depth of up to only 3 feet (1 meter) and used on firm soil. With a combination of concrete and steel rebar, they are a set of structural footings. They are also known as open foundations. The types of open foundations are as follows:
- Strip Footing: Strip footings are those whose base is wider than a typical load-bearing wall foundations. It equally spreads the weight of the structure across the entire surface area. It runs along the direction of the wall. The width of the wall foundation is usually 2-3 times the width of the wall.
- Individual Footing: This foundation is for a single column. The entire weight of the structure is calculated with the help of a safe bearing capacity (SBC) method, which depends on the strength of the soil. The load is then divided equally on each column.
- Raft Foundation (Mat Foundation): This foundation is for the situations where the bearing capacity of the soil is inadequate. They are spread across the entire area of the building to support heavy structural loads from columns and walls. However, they should not be used where the groundwater table is above the bearing surface of the soil.
A deep foundation is used at a construction site where the soil is weak. It also helps to provide strength to extremely large structures. The depth of the foundation is greater than shallow foundation and are more expensive. Also, it can be provided at a greater depth and can carry a huge load. They can go as deep as 60 – 200 feet (20 – 65 meters). The followings are the types of deep foundation.
- Pile Foundation: Pile is a common type of deep foundation. They are used to reducing cost, and when as per soil condition considerations, it is desirable to transmit loads to soil strata which are beyond the reach of shallow foundations. Also, they prevent uplift of the structure due to lateral loads such as earthquake and wind forces.
- Drilled Shafts (Caisson Foundation): This foundation is generally for the structures that require foundation beneath a river or similar water bodies. It resists loads from structure through shaft resistance, toe resistance and/or combination of both of these. The construction of drilled shafts or caissons are done using an auger.
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