Footings used in building construction
1. Strip Footing (basically known as Wall Footing)
It is a component of shallow foundation which distributes the weight of a load bearing wall across the area of the ground.
2. Isolated Footing
A spread is given under the base of the foundation so that the load of the structure is distributed on wide area of the soil in such a way that the safe bearing capacity of the soil is not exceeded. It is square, circular or individually rectangular slab of uniform thickness, provided under each column.
3. Stepped Footing
The main purpose of using stepped footing is to keep the metal columns away from direct contact with soil to save them from corrosive effect. They are used to carry the load of metal columns and transmit this load to the below ground.
4. Combined Footing
When two or more columns are supported by a footing it is called combined footing. This footing may be of rectangular or trapezoidal in plan. Combined footing is provided under following situations.
- When columns are close to each other and their individual footings overlap.
- Soil having low bearing capacity and requires more area under individual footing.
- The column end is situated near the property line and the footing can not be extended.
5. Sloped Footing
Sloped footings are trapezoidal footings. When compared the trapezoidal footing with the flat footing the usage of concrete is less. Thus, it reduces the cost of footing in concrete as well as reinforcement.
6. Matt Foundation
This foundation covers the entire area under the structure. This foundation has only RCC slab covering the whole area or slab and beam together. Matt foundation is adopted when heavy structures are to be constructed on soft made-up ground or marshy sites with uncertain behavior. Matt foundation is also known as raft foundation.
Types of Foundation
Generally, there are two broad categories of types of foundation.
Shallow foundation (3m depth)
- Individual Footing or Isolated Footing
- Combined Footing
- Strip Footing
- Mat Footing or Raft Foundation
Deep Foundation (20 – 65m depth)
- Pile Foundation
- End Bearing Pile
- Friction Pile
Types of Shallow Foundation
A shallow foundation is typically 3 metre in depth.
This types of Foundation mostly built for lightweight buildings where the condition of the soil is extremely good with uniform layer and low water table.
Open Foundation or Spread Footings
Shallow foundations also referred as spread footings or open foundation since the earth soil will be completely removed to construct the footing and later filled by backfilling.
It is referred as Spread footing because the footing base width is wider than the typical load bearing wall.
- Individual Footings or Isolated Footings
( Square, Rectangular, Circular, Continuous Spread, Combined & Ring Spread )
It is the most common type of foundation widely used for buildings.
Image:- Individual Footing - Square, Rectangular and Circular.
In this foundation, each column has its own footing.
These foundations connected with plinth beam just below the ground level. It comes in various shapes such as rectangular, circular and continuous according to the load distribution.
Note – You can get a rough idea of the foundation shape using SBC of soil. If the soil bearing capacity is 10 T/m2 and the column has a vertical load of 10 T/m2 then the size of the footing will be 1 m2.
Footing Area = Column Load / Safe Bearing Capacity.
You can also design different geometrical shapes of foundation such as circular, square or rectangular. There are no limits. Also, You can find if the Safe Bearing Capacity of soil in this met or not
- Combined Footing
Sometimes two or more footing may be combined because the adjacent footing might be closer where shuttering is not possible at all for the given procedure like below one.
Images:- Combined Footing
- Strip Footings
Strip foundations are continuous footing which will be constructed at the load bearing masonry construction where walls will be acted as load bearing structure.
Image:-Strip Footing
The footing will be constructed continually under the walls to support the load developed on the walls. These types of footings constructed in old masonry construction still these are in existence in local construction.
Image:- Strip Footing Plan
- Mat or Raft Foundation
You mostly see these type of foundation for High Residential Building construction where it has a basement.
Image:- Mat Foundation
This type of foundation will be constructed under two situations,
- Inconsistent Earth Soil Layer – The condition of the soil extremely differs in various places under the building layout where designer can’t able to calculate the load and design the foundation as we done in spread footings. So they come up with Mat or Raft Foundation where the total load of the building will be spread throughout the foundation
- Cost Effective – Once the designer designs the foundation they analyze the cost of the foundation construction. If the foundation has a number of columns very adjacent to others, it will likely to increase the stuttering cost and concrete cost, Comparing these conditions the designer will design mat or Raft foundation where the construction will be easy and cost effective.
Types of Deep Foundation
Deep foundation means as the name suggests the foundation will be penetrated through the weak soil layer at a great depth and supported on top of strong soil layer or on the rock.
The foundation shall be greater than the shallow foundation (>3m). Normally all deep foundations are referred us pile foundation. But there are other types,
Normally all deep foundations are referred us pile foundation. But there are some other types,
Caisson or Pier Foundation
Caisson or pier foundations are often used in large construction under water bodies such as river, sea.
Image:- Caisson or Well Foundation
Drilled Shaft Foundation
These type of foundations are used in bridges and large structures (metro train projects) where a long cylindrical casing will be inserted and then poured with concrete along with reinforcement. Once the concrete hardens the shape will be removed from the hole.
Step 1 – Driving the Casing
Image:- Driving the casing
Step 2 – Drilling the shaft
Step 3 – Placing the cage
Step 4 – Pouring the concrete
Image:- Drilled Shaft Foundation
- Pile Foundations
Images:- Pile Foundation
Pile means the vertical member which will be penetrated through great depth. As the function of the pile is to carry the load to the deep there are different types according to construction methods and materials used.
I hope, it helps!
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