The foundation is one of the most significant aspects of a structure, serving to transfer load from the structure to the ground by acting as a link between both.
Depending on the use, soil condition, and structure load Foundation can be classified and used appropriately. The first step in any construction project is to determine the suitability of the foundation for that specific structure.
Types of Foundation
Shallow Foundation
This classification is based on the foundation's depth-to-width ratio (which differs in the definitions of Tirzah and Skipton with values being lesser than 1 and 2.5, respectively).
This is further classified as:
Individual footing or Isolated footing
It is the most commonly used foundation in building construction. This footing can be square, rectangular, or circular, and it is utilized when the structural load is borne by columns in standard buildings up to five stories tall.
The rectangular shape is chosen when the foundation encounters moments of eccentric loads or horizontal stresses.
An isolated footing is used when one of the following conditions exists:
- The structural load is moderate.
- Columns are arranged freely.
- At a shallow depth, the soil has a high bearing capacity.
Combined footing
It is employed when two or more columns are close enough that their isolated footings overlap. It might be rectangular, square, or trapezoidal. A combined footing is shared by more than one column. These are also classified as slab and beam type, rectangle, raft, and strap beam type. The basic goal is to ensure uniform weight distribution across the whole area of the footing.
Strip footing or Wall footing
These footings, in particular, have a wider base than a standard load-bearing wall foundation, which spreads the weight of the building over a larger area and provides better stability. Strip footings serve as long strip that supports the weight of an entire wall and are appropriate for buildings where the load is carried by walls rather than isolated columns.
Raft or Mat Foundation
- For weaker soils and a vast region over which the load is to be distributed.
These are utilized when other forms of shallow foundations would not be appropriate. These are employed when the structural load is quite high. It is utilized to prevent differential settlement of individual footings and is thus built as a single mat of all the structure's load-bearing parts.
The following raft foundation is used:
- Other foundation types are not practical.
- The differential settlement must be avoided.
Deep Foundation
It is also classified based on the Depth base ratio of the foundation.
It is of basically two types:
Pile Foundation
Pile foundations transfer enormous loads from the structure to a hard rock stratum lying underground, whereas shallow foundations are ineffective. It primarily reduces structural rise caused by lateral loads such as earthquakes and wind forces.
- Areas where soil characteristics near the ground surface make large loads unsuitable.
- The depth of hard rock layers from the ground surface ranges from 5m to 50m.
- It is further subdivided into the following categories:
Functions or use of Pile Foundation:
- Sheet pilings
- Piles that support loads
- Piles at the ends
- Piles of friction
- Piles of soil compactors
Materials or construction method:
- Timber piles
- Concrete piles
- Steel piles
- Composite piles
Drilled shafts or Caisson Foundation
Its operation is comparable to pile foundations. However, it is a high-capacity cast-in-place foundation. It resists structural loads through the mechanisms of shaft resistance, toe resistance, or a combination of the two.
It is employed where the depth of hard strata below ground level ranges between 10m and 100m.
It is not appropriate for places with deep deposits of soft clays and loose water-bearing granular soils. It also does not operate well in regions with an artesian aquifer.