There are generally two main types of foundation ( i.e. shallow & deep foundation) for constructing the structures like houses, buildings, etc.
The selection criteria for foundation depends on the soil and load on the structure.
A foundation is a lower part of a building structure that transfers its load to the soil (earth) and the structure must distribute the load equally within tolerable limits.
Functions of foundation:
- Distribution of load.
- Sliding and turning direction.
- Avoid settlement.
- Provide level floor.
- Reduce disaster to the motion of soil.
- Different Types of Foundation in Construction:
- 1.Shallow Foundation:
- Types of Shallow Foundation:
- A) Wall or Strip Footing:
- B) Isolated or Pad or Spread Footing:
- C) Combined Footing:
- D) Cantilever or Strap Footing:
- E) Mat or Raft Foundation:
- 2.Deep Foundation:
- Types of Deep Foundation:
- A) Pile foundation:
- B) Pier Foundation:
- C) Caissons Foundation:
Different Types of Foundation in Construction:
|Shallow Foundation||Up to 1.5 m|
|Wall foundation||More than 0.5 m|
|Isolated footing||Up to 1.5 m|
|Combined footing||Less than 0.75m|
|Strap footing||Up to 0.6 m|
|Mat foundation||Up to 0.5 m|
|Deep foundation||More than 3 m|
|Pile foundation||3.5m to 20m|
|Pier foundation||Up to 5 m|
|Caisson foundation||Up to 35 m|
In shallow foundation the depth of the foundation is less than or equal to its width.
These foundations are constructed where the soil layer is at shallow depths (up to 1.5 m) and capable of supporting structural loads.
The depth is usually less than its width.
Types of Shallow Foundation:
Based on the design, shallow foundations are further classified as follows:
A) Wall or Strip Footing:
Wall foundations spread continuously along the direction of the wall and help in transmitting the load of the wall into the ground.
This footing is suitable where the loads to be carried are small & economical in dense sand and gravels.
In this types of foundation, the width is 2-3 times the width of the wall on the floor stage.
Wall footing may be constructed by stone, brick, plain cement concrete (PCC), or reinforced cement concrete (RCC).
Wall footing is economical when:
- When small magnitude loads to be transferred.
- This footing is situated on dense sand and gravels.
B) Isolated or Pad or Spread Footing:
Isolated footing is most suitable for depths greater than 1.5 m.
This footing is in the form of flat slabs and it can be constructed by plain or reinforced concrete.
In this types of foundation, the base of the column is large.
The isolated footing is economical when:
- The weight of the construction is comparatively less.
- Columns are not usually closely positioned.
- The load-carrying capacity of the soil is higher at shallow depth.
C) Combined Footing:
Combined footing is types of foundation that are made wider by providing two or more columns in a row.
It is used when the footing property for a column can extend beyond the line.
It is also suitable when the two columns are closely spaced and the soil on which the structure resists low bearing capacity.
It may be trapezoidal or rectangular.
Combined foundations are economical when:
- The columns are constructed closer to each other.
- The property line crosses or becomes eccentric when the column is near the property line.
- The dimensions of 1 aspect foot are restricted to some decrease worth.
Also read: Types of Columns, Types of Footing & Types of Slabs
D) Cantilever or Strap Footing:
When an edge footing cannot extend beyond the property line, it is combined with other internal footings using a strap beam, it is called strap footing.
Strap footing is also well-known as cantilever footing.
E) Mat or Raft Foundation:
A mat foundation is a joint notch that covers the entire area under a structure, it supports all the walls and columns, it is also known as the fleet foundation.
The mat foundation economical when:
- The allowable bearing pressure is low.
- These types of foundation are heavyweight structures.
- The site is with a highly compressed layer.
In a deep foundation, the depth of the foundation is greater than its width, these foundations are constructed very deep below the ground surface.
Typically at depths 3 m below ground level.
Types of Deep Foundation:
Deep foundation can be classified into the following types:
A) Pile foundation:
In pile foundation, the stack is a tapered member that has a small area of cross-section relative to its length, they can move the load either by friction or bearing.
This foundation is a type of floating foundation in which footing is supported by skin friction.
This types of foundations are used when:
- The load is to be shifted to a stronger or less compressed stratum, preferably rock.
- The granular soil needs to be compacted.
- The horizontal and inclined forces are required to be carried from the bridge abutment and retaining walls.
B) Pier Foundation:
The pier foundation is an underground cylindrical structural member that supports heavy loads of structure that cannot resist shallow foundations.
Unlike pile foundation, this foundation can only transfer loads by bearing.
It is narrower than the Pile Foundation.
Pier foundation is economical when:
- The top-level is a decomposed rock intertwined within the type of a sound rock strut.
- Soil is a hard soil that has great resistance to drive bearing piles.
Also read: Pier and Beam Foundation & Grillage Foundation
C) Caissons Foundation:
The term caisson refers to a box or a case, they are hollow blocks usually constructed on-site and drown in hard-bearing parts.
As they are expensive to construct, usually restricted to major foundation works.
Well foundation is suitable when the soil has large boulders obstructing entry during the installation of the pier or pile foundation.
They are used in bridge piers, rivers and lakes for mistreatment and other shore protection operations.
Also, used to resist heavy vertical as well as horizontal loads and to construction of large waterfront structures as pump houses.
Caisson foundation is economical when:
- When least pile is required.
- Need to reduce noise and vibration.
- When the foundation is to be constructed in underwater bodies.
- Great axial and lateral loading capabilities are required.
Also read: Difference between Footing and Foundation
Frequently Asked Questions:
Basement, crawl space and concrete slabs are the three types of foundation.
Slab foundation is the most common foundation.
Concrete slab is the cheapest foundation.
Residential foundation walls are generally constructed with the unit 7-5 / 8 inches high by 15-5 / 8 inches long.
All types of foundations distribute the load of the structure over the large bearing area so that the intensity of loads is reduced within the safe bearing capacity of the soil.
They also transfers the load of bearing surface at a uniform rate to prevent uneven disposal.