Types of Foundation and Their Uses in Civil Engineering

Types of Foundation and Their Uses in Civil Engineering

There are different types of foundation in civil engineering which can be divided into two part-1. Shallow foundation, Deep foundation. This post will give you information about the classification of the foundation and their uses.

What Foundation is all about in Civil Engineering?

I know that you have an overall idea about Foundation from the civil engineering point of view. If not, let's have a basic discussion about Foundation.

In civil engineering Foundation is actually a medium by which the super-structure* is not only connected with the ground soil but also the total load coming from the super-structure is transmitted to the soil.

*['Super-structure'-It is the portion of structure entirely above the ground level]

OR,

Foundation is a type of structural components that gives stability to the structure by resisting the total forces caused by the weight of the structure.

After knowing the basic concept, you may now understand the importance of the foundation for construction purpose.

Any structure or building may have different purposes but the main purpose of the foundation is to transmit the load(caused by the weight of building) to the soil level.

Hence it gives enough stability to any structure to stand tall without any structural failure.

That's not all.

There are different types of foundations which can be used depending upon the types of building construction, soil profile, the durability of structure etc.

 Factors affecting the selection of Foundation

Did you ever think, Why there are so many types of Foundation not only one?

This is something we really need to know about.

The nature of soil can be different(clay, silty, sandy etc.) therefore one particular type of foundation is not suitable for all construction process.

There are various factors which affect the selection of Foundation.

Here we listed these major factors:

Factors affecting the type of Foundation

1. Location of structure 
2. Type of structure(whether it is residential building or education building or any other).
3. Durability requirement of the structure.
4. The magnitude of structural load(weight of super-structure)
5. Distribution of structural load(area permitted for distributing the total load).
6. Ground condition(depends upon types of soil-clay, silty etc.)
7. The ratio of the height of the structure to the weight of the structure.

Types of Foundation and their uses

Generally, There are two types of foundation.

1.Deep foundation

• Pile foundation
• shaft foundation
• cylinder
• buoyancy raft-hollow box foundation 

2.Shallow foundation

• strip footing
• raft foundation
• isolated footing
• combined footing

➤ Deep Foundation

When the depth of the foundation is larger than the width of the foundation is called Deep foundation.

Deep foundation is most suited when the upper layer of ground soil is weak and the strong bedrock lies at a certain depth.

The main theory is that Foundation must be supported on any soil that can absorb the total load coming from the structure.

When bedrock is not near the ground surface, we need to increase the depth of the foundation to reach the bedrock soil.

This types of the foundation are often used when :

• There is soft clay soil near the surface.
• The huge amount of load is to be transmitted to the soil within a small area.

1.1 Pile Foundation

SOURCE: http://www.basiccivilengineering.com

Pile foundation is the most common type of deep foundation.

Especially for skyscrapers or high rise buildings where the magnitude of load is significant(vertical & lateral load imposed on the structure is huge), this type of foundation is the right choice.

in this case, it is important to support the total loads on piles(It could be single or piles group) located beneath load-bearing walls.

Using piles group settlement of the structure can be minimized.

Also, this will enhance the load carrying capacity of the structure compared to the single pile.

Based on its function There are few types of pile foundation-

• Friction piles
• End bearing piles
• settlement reducing piles

1.2 Shaft Foundation

SOURCE: HAYWARD BAKER

This is also termed as caissons or bored piles.

Huge load(vertical and lateral)coming from the structure is generally supported by excavating cylindrically shaped shafts into the ground soil which is filled with concrete.

This type of foundation is most suitable when the foundation has to be placed beneath the water level.

As this is an expensive option, it is only restricted to some major construction project.

1.3 Pier Foundation

There is another type named as Pier foundation.

Here, Load transfer can be done by bearing only. When the ground soil is stiff clay(which produces high resistance for driving the bearing piles), pier foundation is adopted.

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1.4 Well Foundation

This is a type of deep foundation mainly used for bridge purposes where the foundation is to be constructed below the water level.

Meaning of the word caissons is 'Box'.

Hence well foundation is a box-like structure which can be rectangular, circular, hexagonal etc shaped.

Caissons are divided into three types-

1. Box caisson
2. open/well caisson
3. pneumatic caisson

➤ Shallow Foundation

In this case, the width of the foundation is more than the depth of the foundation.

For the construction of low rise building, the shallow foundation is very common types of foundation.

If the ground surface is not weak or the bedrock is near the ground soil level then the shallow foundation is adopted.

Here we don't need to drive any pile to the depth of bedrock as the ground surface will take care of the structural load.

However, For high rise building, such a shallow foundation may not be able to resist the force(coming from vertical and lateral load).

Hence it is most suitable when:

The Total load of the structure is not huge.
The ground surface is made of stiff soil.

• Bearing capacity of the soil is high.
• Area permitted for distributing the load is high.

2.1 Raft foundation

Sometimes it is termed as Mat foundation. To support the load coming from the building of moderate height is possible by raft foundation.

Soil stiffness is an important parameter while designing the Raft foundation. The Upper and lower bound set of soil stiffness should be taken in design considerations.

Mat foundation is relatively large in size. 

Hence a significant amount of load can be transmitted over the large area by considering this type of foundation.

Settlement of the structure can be also be minimized here.

2.2 Isolated footing

This is the simplest and the popular types of foundation. To support the load which coming from the column is taken care of by isolated footing.

Each isolated footing is designed to carry the concentrated load.

The isolated footing is adopted when:

• Load on footing is relatively small.
• bearing capacity of the soil is safe.
• Cost is limited.

Three types of Isolated footings are:

1. single footing
2. stepped footing
3. slopped footing

2.3 Strip footing

The strip footing is also known as wall footings. It is a type of foundation in which a small strip of reinforced concrete placed into a trench.

Here the length of the foundation is relatively large than the width of the foundation.

This types of the foundation are generally considered for supporting the Load bearing walls or support a slab.

Another reason for adopting strip footing is-when columns are closely spaced.

Conclusion

There could be various options for selecting the types of foundation but selecting the right one is the key thing.

From the soil profile to the types of structure-you cannot avoid any stuff.

Consideration of bearing capacity of the soil, types of soil, the magnitude of the structural load and budget of the project is very important while designing the foundation.

Foundation/footing should be designed in such a way that it should:

• Easily resist the pressure exerted from the structure.
• not show any significant amount of settlement with respect to time.
• be economical.

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