As we all know that foundation transfers the load of the building to the soil so it plays an important role in civil engineering structures.
The foundation is basically the combination of footing and soil. The footing is basically a structural member made of brick plus concrete or masonry.
The foundation is basically two types, the first is Shallow Foundation and the second one is Deep Foundation.
In this article we are going to talk about only the Shallow Foundation, then let’s dive into the shallow foundations:
The shallow foundation is one of the types of foundation which is located just below the wall or column that they support. Shallow foundation examples are combined footing, strip footing, spread footing, and stepped foundation.
A shallow foundation is usually defined as a foundation that has a width always greater than its depth.
The main advantage of a shallow foundation is it is economical because it requires less excavation (reduces the labor cost), less costly equipment, constructed in a short time.
Let’s talk about the different types of shallow foundations in civil engineering construction:
Types Of Shallow Foundation
Here are the different types of shallow foundations in construction:
- Spread Footing
- Combined Footing
- Strip Footing
- Raft Or Mat Foundation
- Strap Or Cantilever Footing
Spread footing is the combination of one column and one footing. The supporting footing can be Square, Rectangular, or Circular.
The selection of the type of supporting footing basically depends on the loading condition and the requirement of the soil.
The spread footing is also known as the isolated footing or individual footing.
The combined footing is the combination of two-column and one footing.
The plan of combined footing may be rectangular or trapezoidal.
It is provided when the two columns are so close to each other.
A strip footing basically a wall-type footing that is used in the case of a load-bearing wall.
The strip footing is basically more economical than the number of spread footing in the case when the row of columns are so close to each other.
The strip footing is also known as continuous footing.
Raft Or Mat Foundation
The raft or mat foundation is the combination of the number of columns and walls coming over a large single slab.
The mat foundation is required when the bearing capacity of soil is low and where the columns and walls are so close to each other that their individual footing would overlap.
The mat foundation is basically used in high-rise buildings.
Strap Or Cantilever Footing
In the strap or cantilever footing, two isolated footings are connected with concrete or metallic straps.
If there is more settlement in the soil (like clay soil) then there is more differential settlement happens between the isolated footing, so to decrease these differential settlements between footing we use the Strap or Cantilever Footing.
After connecting the two isolated footings they start to behave like one single unit.
Objective Of Shallow Foundation
The main objective of providing the shallow foundation is to distribute the building load uniformly just below the earth’s surface in a wide area for example the raft foundation basically distributes the load of the building over the entire covered area of the building.
Frequently Asked Questions(FAQ)
Which foundation is called a shallow foundation?
The foundation, which is provided just below the surface of the earth then this type of foundation is called a shallow foundation.
What is the definition of the shallow foundation as per Terzaghi?
As per Terzaghi’s definition, a shallow foundation is one that has a width greater than its depth ( Df/B <= 1, here Df is the depth of footing and B is the width).
How do I know if my foundation is shallow?
The shallow foundation usually has a width always greater than its depth, if your foundation width is greater than its depth then your foundation is the shallow foundation.
What is the lowest part of a shallow foundation?
The lowest part of the shallow foundation is the footing that supports the columns of the buildings.
What is the shallow foundation depth?
According to the IS code, 1904-1978 the minimum depth of a shallow foundation is at least 50 cm below the natural ground surface.
Is grillage foundation a shallow foundation?
Yes, the grillage foundation is a shallow foundation because a grillage foundation is recommended where the deep foundation is not applicable.
What are the limitations of various types of shallow foundations?
The main limitation of a shallow foundation is it cannot be used where the bearing capacity of top surface soil is less.