Foundation is the most important and the lowest part of a structure. Foundation transfers the load of a structure to the underlying soil. The type of building and the nature of the underlying soil are two key factors for selecting foundation types.
Various types of materials are used for constructing the foundation. for example materials such as stone, brick, concrete, steel, reinforced concrete, etc. Generally two types of foundations can be identified in the field of construction depending on the depth.
1. Shallow Foundations
Shallow foundation transmits the weight on to immediate subsoil. Shallow foundation may be of following types.
- Strip foundation
- Mat foundation or Raft foundation
- Pad foundation / Footings
- Spread footings
- Combined foundation
- Strap footings or Cantilever
2. Deep Foundations
A deep foundation will transmit the load on to inner hard soil or bedrock. It is usually at depths of 3 meters below finished ground-level. The deep foundation may be classified following types.
- Pile foundation
- Pier foundation
- Caissons or Well foundation
Factors are considered before choosing foundation types
- Bearing Capacity of the soil.
- The load applied from structure to the foundation.
- Type of Superstructure is going to construct.
- The depth of the soil at which safe bearing strata exists.
- The Condition of the soil.
Strip foundation is suitable for subsoils and light structural loadings like low and medium-size buildings where mass concrete can be used. For medium loads, strip foundation may be provided reinforcement, along with special design features where induced tension exceeds concrete’s own tensile resistance.
When the ground condition is good, strip foundation can be used because it is less expensive. The trench depth is variable but in most cases should be at least 1m with a width of 600mm.
The concrete should have a minimum depth of 300mm, but special factors in your site may require more depth and a greater use of steel reinforcing bars in the concrete.
Raft Foundation or Mat Foundation
A raft foundation is fundamentally a large combined slap foundation designed to cover large part of the building. When a soil is weak and columns are so closely spaced in both direction or carry high loads, Mat foundation may be used in this situation.
Cantilever or Strap Footings
Consist of two single footings connected with a beam or a strap and support two single columns. A strap footing may be used where the distance between the column is so great that trapezoidal footing becomes quite narrow.
A combined footing commonly upholds 2 posts (columns). In case there’s a wall or barrier at or near the boundary of an external post (column), a footing is placed differently beneath this support and it is be probable to gradient. External footing changing is ceased by assisting the 2 supports on a universal footing.
Pile foundation is a common type of deep foundation. A pile can be defined as a long vertical load transferring elements made by steel, timber, concrete or a combination of them. Heavy loads are transferred into the soil by two mechanisms that are:
- By the friction between the pile and surrounding
- By the bearing of pile on a hard rock bed at certain depth.