There are three types of foundation which are used in construction:-
i) Shallow Foundation
ii) Deep Foundation
iii) Special Types of Foundation
A shallow foundation is a type of foundation which transfers building masses to the earth close to the surface; instead of to a subsurface layer or a variety of depths as will a deep foundation.
A shallow foundation is convenient for foundations having depth is equal or less than the foundation breadth. It’s used if bearing capacity of the soil is high at shallow depth. For compressive soils, it helps to scale back settlement.
Different types of Shallow Foundation:
i) Isolated Footing
ii) Combined Footing
iii) Strip Footing
iv) Strap Footing
v) Mat or raft foundation
Isolated footings are most ordinarily used footings for reinforced cement concrete column as a result of it’s easy and most economical. An isolated footing is employed to support one column.
Isolated footings are independent footings that are provided for every column.
This type of footing is employed when:-
i) Columns aren’t closely spaced.
ii) masses on footings are less.
iii) The Safe bearing capacity of the soil is usually high.
Combined footings are made for two or more columns after they are near one another and their foundations overlap.
Combined footings are provided only where soil bearing capacity is low, when 2 columns are close enough, inflicting overlap of adjacent isolated footings.
A strip footing is a continuous strip of the concrete that serves to distribute the load of a supporting wall across a region of the soil.
Strip footings are provided for a row of columns that are thus closely spaced that their spread footings overlap or nearly touch one another.
In such cases, it’s very economical to provide a strip footing than to provide a number of spread footings in one line. A strip footing is additionally called continuous footing.
It’s a sort of combined footing, consisting of 2 or more column footings connected by a concrete beam. This kind of beam is termed a strap beam.
It’s used to facilitate distribute the load of either heavily or eccentrically loaded column footings to adjacent footings. A strap footing is commonly employed in conjunction with columns that are situated on a building’s property or lot line.
Since columns are loaded on the column footings, however in conditions wherever columns are situated directly adjacent to the property line, the column footings could also be offset so they do not encroach onto the adjacent property.
This leads to an eccentric load on a portion of the footing, inflicting it to tilt to 1 side. The strap beam restraints the tendency of the footing to overturn by connecting it to close footings.
Mat or Raft Foundation:
Mat foundations are the types of foundation that are spread across the complete space of the building to support significant structural masses from columns and walls.
The use of mat foundation is for columns and walls foundations wherever the masses from the structure on columns and walls are terribly high.
This sort of foundation is employed to stop differential settlement of individual footings, therefore designed as one mat (or combined footing) of all the load bearing components of the structure.
This type of foundation is appropriate for expansive soils whose bearing capacity is less for suitableness of spread footings and wall footings. This kind of footing is economical usually when half space of the structure is covered with individual footings and wall footings are provided.
These foundations mustn’t be used wherever the groundwater table is higher than the bearing surface of the soil. Use of foundation in such conditions might result in scour and physical change.
These are the types of foundation which transfers building masses to the earth farther down from the surface than a shallow foundation will, to a subsurface layer or a variety of depths.
Some of the common reasons are very massive style loads, a poor soil at shallow depth, or site constraints (like property lines).
Deep Foundation is required where the shallow foundation cannot support the structure. Deep foundations are used to transmit masses to stronger soil or rock at larger depths. Once the foundation is less than 6 meters deep it’s known as semi-deep.
Different types of Deep Foundation:
i) Pile Foundation
ii) Pier Foundation
iii) Cassions or Well Foundation
Pile foundations are the types of foundation that is employed to transfer significant masses from the structure to a tough rock stratum a lot of deep below the ground level.
Pile foundation is required to transfer significant loads of the structure through columns to hard soil strata way much below the ground level and wherever shallow foundations like spread footings and mat footings can’t be used.
These types of foundation are additionally used to stop uplift of the structure as a result of lateral masses like earthquake and wind forces.
Pile foundations are typically used for soils wherever soil conditions close to the ground surface isn’t appropriate for significant masses. The depth of hard rock strata could also be 5m to 50m (15 feet to 150 feet) deep from the ground surface.
The pile foundation resists the masses from the structure by skin friction and by end bearing. Use of pile foundations additionally prevents differential settlement of foundations.
A Pier foundation consists of a cylindrical column of large diameter to support and transfer large super-imposed masses to the firm strata below.
The distinction between pile foundation and pier foundation lies within the methodology of construction. Although pile foundations transfer the load through friction and/or bearing, pier foundations transfer the load solely through bearing.
Generally, pier foundation is shallower in depth than the pile foundation.
Pier foundation is most popular in a location wherever the highest strata consists of rotten rock overlying a stratum of sound rock. In such a condition, it becomes tough to drive the bearing piles through rotten rock.
Within the case of stiff clays, which provide massive resistance to the driving of a bearing pile, pier foundation is easily constructed.
When a decent bearing stratum exists up to five meters below ground level, brick, masonry or concrete foundation piers in excavated. The dimensions and spacing of the piers depend upon the depth of hard bed, nature of the overlying soil and super-imposed masses.
Cassions or Well Foundation:
Well foundations are the types of foundation that is usually provided below the water level for bridges. Cassions or well are in use for foundations of bridges and different structures from a very long time.
Cassion means a box-like structure, spherical or rectangular, that is sunk from the surface of either land or water to some desired depth.
Special types of Foundation
These are the types of foundation which is used for special purposes.
Different types of Special Foundation are:
i) Machine Foundation
Machine foundations are special types of foundation needed for machines, machine tools and significant equipment that have a wide selection of speeds, masses, and operative conditions.
These foundations are designed considering the shocks and vibrations ensuing from the operation of machines.