Foundations are the backbone of any structure, located below ground level. Without foundations, structures cannot gain stability and longevity. Different types of foundations are used for different soil types and structures, each offering unique benefits.
What is Foundation in Construction?
In construction, the foundation is a crucial part of a building or structure that connects it to the ground. The foundation transfers the load from the building evenly to the ground, ensuring that the building remains safe and stable even in extreme weather conditions.
Types of Foundations
There are different types of foundations that can be used for buildings. The selection of the foundation type depends on various factors, including the type of soil and the building type. Below, we have discussed the foundation types in detail.
- Shallow Foundation
- Spread Footing
- Mat/ Raft Footing
- Deep Foundation
- Pile Foundation
- Caissons Foundation
- Special Foundation
- Floating Foundation
- Underpinning
1. Shallow Foundation
A shallow foundation is a type in which the foundation is placed within a depth of 3 meter from the ground surface. Shallow foundations are suitable where hard soil is available at shallow depths, easily supporting the adequate load of the structure above.
Shallow foundations can be further classified as:
Spread Footing:
Spread footing is a type of shallow foundation, meaning it is placed at a shallow depth underground. Spread footings distribute the load of the structure over a large area through the individual columns.
Matt/ Raft Footing:
A mat or raft foundation is a type of shallow foundation in which the foundation columns are placed on a single thick concrete slab that evenly transfers the load of the structure to the ground surface. Mat or raft foundations are generally used in weak soil where spread footings would not be beneficial due to the high chance of settlement.
2. Deep Foundation
A deep foundation is a type in which the foundation is placed deeper in the soil surface as hard soil is not easily available to support the load of the building.
Deep foundations are further classified as:
Pile Foundation:
A pile foundation is a type of deep foundation usually adopted when the soil beneath is weak and high-bearing soil is not easily available at a shallow depth. Deep piles are driven until the strong or high-bearing soil is reached, which can easily take the load of the structure.
Caisson Foundation:
A caisson foundation is a type of deep foundation, which can also be used as a shallow foundation in some cases. Caisson foundations are typically used for bridges and underwater foundation construction. In some cases, the foundation may be constructed outside the water, while in others, it may be constructed inside the water.
3. Special Foundation
As its name suggests, a special foundation is used in unique cases and conditions. Special foundations are employed when neither shallow nor deep foundations can be used for the structure.
Special foundations can be classified as:
Floating Foundation:
A floating foundation is a special type of foundation designed to balance the pressure exerted on the soil, thereby minimizing settlement. This special foundation type is used where the soil is soft and weak, in areas with a high water table, and to avoid differential settlement.
Underpinning:
Underpinning is a foundation type applied to the existing foundation of a structure. Underpinning is the process of building a new foundation or adding supports to the existing foundation to strengthen and stabilize it, so that it can efficiently handle unexpected increased loads and soil issues.
The foundation types mentioned above are standard types commonly used by engineers. However, foundation engineering is highly diverse. A foundation type that is common in one region may be completely unheard of in another. This diversity in the construction industry is one of its fascinating aspects. Engineers adapt to current soil conditions and choose the ideal foundation type for structures worldwide.
Which Factors Are Responsible for Selection of Foundation?
To provide a structure with more stability and longevity, various factors are considered while selecting the foundation during the construction of the structure. The important factors responsible for the selection of the foundation include:
Soil Characteristics
One of the most important factors considered when selecting the foundation type is the type of soil where the construction is going to take place. Different soil types have different bearing capacities, and we cannot use the same type of foundation for each soil type.
Clayey soil might require a deep foundation as its bearing capacity is less, necessitating a foundation that can take the load of the structure. Sandy soil, on the other hand, has a greater bearing capacity, and a shallow foundation can easily take the load of the structure and provide the required stability.
Structure Load
The total weight of the structure, along with all the dead load and live load, is also considered while selecting the foundation. Whether the load is going to be distributed to the foundation uniformly or concentrated in certain areas is also taken into account. For industrial buildings, loads from vibrations of heavy machinery may lead to the selection of a special foundation.
Environmental Factors
Various environmental factors are very important when selecting the foundation type. The groundwater table can have a huge impact, especially for deep foundations. It can cause buoyancy (the tendency of an object to float in submerged water), which will adversely affect the stability of the building.
If the project site is located in flood-prone areas, normal foundations would make a bad choice, and the need for elevated foundations might be required.
Other factors include the height of the structure, available space on the construction site, budget of the overall project, building code standards, and zoning laws. Engineers consider all these factors while selecting the type of foundation that is ideal for the specified structure or building.
Selection of Foundation for Different Building Types
The type of building plays an important role in the selection of the foundation type. Different foundations are suitable and used for different building types.
- Residential Building: Residential buildings are mainly limited to 2-3 storeys; hence deep foundations are unnecessarily needed. For residential buildings, shallow foundations such as mat foundations or spread footing are best suited due to moderate loads and smaller structures.
- Commercial Buildings: Commercial buildings are generally taller than residential buildings, and the load produced by them is also greater; hence shallow foundations are not ideal. Deep foundations are used, especially for high-rise buildings. Deep foundations provide greater stability to high-rise structures compared to shallow foundations.