There are generally two main types of foundation ( shallow & deep foundation) for constructing the structure like houses, buildings, etc.
The foundation selection criteria for a structure 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); 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.
Types of Foundation for houses:
In shallow foundation the depth of the foundation is less than or equal to its width.
These foundations are constructed where the soil layer at shallow depths (up to 1.5 m) is 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:
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 and are economical in dense sand and gravel.
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 gravel.
Isolated or Pad or Spread Footing:
Column footing is suitable and economical for depths greater than 1.5 m.
In this types of foundation, the base of the column is large.
Column footing is in the form of flat slabs and might be constructed by plain or reinforced concrete.
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.
Combined footing are foundations 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. Also, read types of Deep Foundation.
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.
Cantilever or Strap Footing:
When an edge footing cannot extend beyond the property line, edge footing is combined with other internal footings using a strap beam, it is called strap footing.
Strap footing is also well-known as cantilever footing.
Mat or Raft Foundation:
A mat foundation is a joint notch that covers the entire area under a structure and supports all walls and columns, it is also known as the fleet foundation.
The mat foundation economical when:
- The allowable bearing pressure is low.
- The structure is heavyweight.
- The site is with a highly compressed layer.
In 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:
This foundation can be classified into the following types:
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.
Different types of pile 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.
The Pier Foundation is an underground cylindrical structural member that supports heavy loads of structure that cannot resist shallow foundations.
Unlike pile foundations, pier foundations can only transfer loads by bearing.
The Pier Foundation is narrower than the Pile Foundation. Also, read types of Foundation FAQ.
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.
The term caisson refers to a box or a case; they are hollow inside, usually constructed on-site and drown in hard bearing parts.
As they are expensive to construct, they are usually restricted to major foundation works.
Well, this types of foundation is suitable when the soil has large boulders obstructing entry during the installation of the pier or pile foundation.
Caissons are used in bridge piers, rivers and lakes for mistreatment and other shore protection operations.
They are used to resist heavy vertical and horizontal loads and are used in the construction of large waterfront structures as pump houses.
Caisson foundation is economical when:
- When least pile is required.
- Need to reduce noise and vibration.
- The foundation is to be constructed in underwater bodies.
- Great axial and lateral loading capability are required.
Difference between footings and foundation:
The footing is the part of the foundation that is built with concrete or brickwork masonry and serves as the floor columns and floor partitions.
Foundation distributes the load of the structure over a large bearing area so that the intensity of loads is reduced within the safe bearing capacity of the soil.
Also, transfers the load of bearing surface at a uniform rate to prevent uneven disposal.