Choosing the right foundation : A guide to different Types
Types Of Foundations
Types of foundations is the lowest part of the building or the civil structure that is the direct contact with the soil which transfer loads from the structure to the soil safety. While choosing the right foundation is a highly technical decision that is to be made by your architect, engineer & building professionals, it is always helpful to understand the process it takes to build your dream home. The foundation is the base of a building that sits on solid ground, called the foundation bed. It is important because it helps distribute the weight of the building, prevents uneven sinking, stops the building from shifting sideways, and makes the structure more stable. So let’s take a look at the different types of foundations that exist. All foundations can be primarily classified into two part :-
1.Shallow foundation (used for smaller structures like individual homes)
2. Deep foundations (used for larger structures like buildings).
Foundation System
The terms Shallow foundation and Deep Foundation refer to the depth of the soil at which it is placed. Generally, if the width of the foundation is greater than the depth, it is labeled as the “Shallow Foundation”. If the width is smaller than the depth of the foundation it is called a “Deep Foundation”. However, deep foundation and shallow foundation can be classified as shown in the following chart :-
1. Isolated Spread Footings
- Isolated spread footings are a common type of Shallow foundation used in construction projects to support individual columns or walls. They are called isolated because each footing is separate and does not interact with any other footings in the structure.
- This type of footing is suitable for relatively small and light structures, such as residential homes, small commercial buildings, and light industrial buildings.
- Isolated spread footings are typically square, rectangular, or circular in shape and are designed to distribute the load of the structure over a larger area of soil to prevent it from settling or shifting.
- The size and depth of the footing are determined by the weight and dimensions of the structure it supports, as well as the soil conditions at the site.
2. Wall Footing or Strip footing
- Wall footing is also known as continuous footing its is type of Shallow foundation. This type is used to distribute loads of structural or non-structural load-bearing walls to the ground in such a way that the load-bearing limit of the soil isn’t outperformed. It runs along the direction of the wall. The width of the wall foundation is usually 2-3 times the width of the wall.
- The wall footing is a continuous slab strip along the length of the wall. Stone, brick, reinforced concrete, etc. are used for the construction of wall foundations. Wall footings must be wider than the wall itself to provide stability and support.
- For block walls, the footing typically consists of several courses of bricks, with the lowest course being double the width of the wall above. For stone masonry walls, the footings are usually 15 cm deep, with the height of the course being 30 cm.
- In cases where the load on the wall is heavy or the soil has a low bearing capacity, reinforced concrete footings may be necessary for added strength and stability. Wall footings are most cost-effective when the loads being transmitted are relatively small and when they are placed on dense sand and gravel.
3. Combined footing
- A combined footing is used to support two or more columns in a row. It’s is type of Shallow foundation
- It is a single footing that supports multiple columns instead of each column having its own individual footing.
- Combined footings are often used when columns are close together or when soil conditions require a larger footing to distribute the load evenly.
- This type of footing is designed to support the weight of all columns and distribute it evenly to prevent uneven settlement.
- It helps to save space and cost compared to individual footings for each column.
4.Strap Footings
- Strap footings are similar to combined footings. The reasons for considering or choosing strap footing are identical to the combined one.
- In strap footing, the foundation under the columns is built individually and connected by a strap beam.
- Generally, when the edge of the footing cannot be extended beyond the property line, the exterior footing is connected by a strap beam with the interior footing.
5.Raft Or Mat Foundations
- Raft or mat foundations are utilized when shallow or pile foundations are not suitable, or when the soil’s bearing capacity is insufficient. They are recommended for situations where the structure’s load needs to be spread out over a large area, or when the structure is subjected to continuous shocks or jerks.
- A raft foundation comprises a reinforced concrete slab or T-beam slab that covers the entire structure’s area. In this type of foundation, the entire basement floor slab serves as the foundation, distributing the structure’s total load evenly across its entire surface. This method is referred to as a raft foundation because the building appears to float on a sea of soil.
Types Of Deep Foundation
The followings are the types of deep foundations.
Pile foundations
Piles are a common type of deep foundation used to reduce costs and transmit loads to deeper soil or rock strata beyond the reach of shallow foundations, taking into consideration soil conditions.
There are various types of pile foundations
- sheet piles,
- load bearing piles,
- end bearing piles,
- friction piles,
- soil compactor piles.
Piles can be classified based on function or use, such as
- Timber piles,
- Concrete piles,
- Steel piles, and
- Composite piles.
Piles can be classified based on function or use, such as Piles are slender members with a small cross-sectional area compared to their length and are essential for transmitting foundation loads to deeper soil or rock layers when the surface soil has low bearing capacity. They can spread load through skin friction or bearing, resist uplift forces, and provide stability against lateral and overturning forces for structures. Pile foundations are cost-effective in situations where soil with a high bearing capacity is at a greater depth, construction of irrigation canals is likely nearby, providing a raft or grillage is expensive, the foundation is under heavy concentrated loads, in marshy areas, when the topsoil is compressible, or in cases like bridges where scouring is prevalent in the river bed.
Caisson foundation
- A caisson foundation is a type of deep foundation that is used to support structures in areas where the soil is not strong enough to support the weight of the building. It consists of a hollow, cylindrical structure made of concrete or steel that is sunk into the ground and then filled with concrete. Caisson foundations are typically used for high-rise buildings, bridges, and other structures that require strong support. They are especially useful in areas with soft soil or high water tables.
- In conclusion, foundations are an essential component of civil engineering, providing support and stability for various structures. The type of foundation chosen for a project depends on factors such as the soil conditions, load-bearing capacity, and design of the structure. By understanding the different types of foundations and their applications, civil engineers can ensure the safety and longevity of their project.
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