Foundations are classified as shallow and deep foundations. Types of foundations under shallow and deep foundations for building construction and their uses are discussed.
It is advisable to know the suitability of each type of foundation before their selection in any construction project.
Types of Foundation and their Uses
Following are different types of foundations used in construction:
- Shallow foundation
- Individual footing or isolated footing
- Combined footing
- Strip foundation
- Raft or mat foundation
- Deep Foundation
- Pile foundation
- Drilled Shafts or caissons
Types of Shallow Foundations
1. Individual Footing or Isolated Footing
Individual footing or an isolated footing is the most common type of foundation used for building construction. This foundation is constructed for a single column and also called a pad foundation.
The shape of individual footing is square or rectangle and is used when loads from the structure is carried by the columns. Size is calculated based on the load on the column and the safe bearing capacity of soil.
Rectangular isolated footing is selected when the foundation experiences moments due to the eccentricity of loads or due to horizontal forces.
For example, Consider a column with a vertical load of 200 kN and a safe bearing capacity of 100 kN/m2 then the area of the footing required will be 200/100 = 2m2. So, for a square footing, the length and width of the footing will be 1.414 m x 1.414 m.
2. Combined Footing:
Combined footing is constructed when two or more columns are close enough and their isolated footings overlap each other. It is a combination of isolated footings, but their structural design differs.
The shape of this footing is a rectangle and is used when loads from the structure is carried by the columns.
3. Spread footings or Strip footings and Wall footings:
Spread footings are those whose base is wider than a typical load-bearing wall foundations. The wider base of this footing type spreads the weight from the building structure over more area and provides better stability.
Spread footings and wall footings are used for individual columns, walls and bridge piers where the bearing soil layer is within 3m (10 feet) from the ground surface. Soil bearing capacity must be sufficient to support the weight of the structure over the base area of the structure.
These should not be used on soils where there is any possibility of a ground flow of water above bearing layer of soil which may result in scour or liquefaction.
4. Raft or Mat Foundations:
Raft or mat foundations are the types of foundation which are spread across the entire area of the building to support heavy structural loads from columns and walls.
The use of mat foundation is for columns and walls foundations where the loads from the structure on columns and walls are very high. This is used to prevent differential settlement of individual footings, thus designed as a single mat (or combined footing) of all the load-bearing elements of the structure.
It is suitable for expansive soils whose bearing capacity is less for the suitability of spread footings and wall footings. Raft foundation is economical when one-half area of the structure is covered with individual footings and wall footings are provided.
These foundations should not be used where the groundwater table is above the bearing surface of the soil. The use of foundation in such conditions may lead to scour and liquefaction
0 Comments