The most crucial purpose of providing Foundation is Structural Stability. Strength of the foundation determines the stability of the structure be constructed.
A properly designed and the constructed foundation provides an even surface for the development of superstructure at a proper level at over a firm bed.
A well-designed foundation prevents the lateral movement of the supporting material(which is the soil in this case) and thus ensuring the safety of the superstructure from the detrimental effects of the lateral movements of soil.
The foundation serves the purpose of completely distributing the loads from the structure to a large base area, and then the soil underneath. This uniform transfer of loads helps in avoiding unequal settlement of the building, which is one of the detrimental defects in building construction.
These are the simplest form of foundation which is used to uniformly transfer loads from the superstructure to the subsoil below it.
In the case of a shallow foundation, the water table exists at a considerable depth, so there are very little chances of foundation to encounter water table, thus saving the close of application of different waterproofing techniques to the foundation.
Compared to other types of foundation, the design for this type of foundation can be quickly done, thus saving time & cost.
In this type of Shallow foundation, a stepped footing is provided below each column of the structure.
The dimensions of the steps are generally determined by design, generally, each step projecting 50-75mm from the previous step. These are generally three stepped courses provided.
This is the most common types of footing which is being used in low-cost buildings, where the soil condition is very good.
A combined footing is that in which a single footing is common to two columns.
These are used in conditions where the clear span between two columns are very low, which results in overlapping of stepped courses if isolated column footings are provided.
There are two types If combined footing, Rectangular footing(used when the loads on the two columns are same) and Trapezoidal Footing(used when the columns carry unequal loads).
In simple words, Cantilever footing is the combined footing connected by a tie beam, which is of lower width and greater depth.
This type of footing is necessary for conditions where there is a strict restriction of space and it is not possible to project the footing further to it’s column face.
The tie beam helps in stabilizing the columns, thus making a uniform distribution of loads beneath the footing.
In places where the soil is of inferior quality and the safe bearing capacity of the soil is lower compared to ordinary soil, a common footing is provided beneath each column.
This type of footing is known as Raft Footing. Raft Footing is used in places where the distance between each column are very less, thus making it unsuitable for Isolated footing.
Where the columns of Raft footing are connected by a Tie beam, it is known as Mat Foundation.
Deep foundation can be used at places where is soil is only strong enough to withstand intense loads, thus this type of foundation is suitable for all places.
A deep foundation is the only type of foundation which can be used at places where the water table prevails at a lower depth from the ground surface.
For the construction of marine and advanced structures, a deep foundation is used, due to the high stability it provides to structures from the effects of settlements and overturning.
Depending upon nature of pile: Compaction Pile, Uplift pile, Batter pile, Sheet file, Anchor pile or fendor pile.
Depending upon material:Concrete Pile, Steel Pile, Timber pile, Composite Pile etc.
Depending upon load transfer: End Bearing pile(transfers the load by bearing) and Friction pile(transfers the load by friction between the pile and the surrounding soil-suitable when hard stratum is situated at a great depth)significant.
This type of foundation is suitable for the construction of bridges, and at marine structures, where the soil present at river beds are weak and consists of stones, rubble, forming an uneven surface.
Well foundation is also classified in Cassions. There are generally three cassions, Open, Box and Pneumatic Cassion, within which, the Pneumatic cassions ate being used the most.
Foundations provide the structure's stability from the ground: To distribute the weight of the structure over a large area in order to avoid overloading the underlying soil (possibly causing unequal settlement).
The foundation serves the purpose of completely distributing the load from the structure over a large base area and then to the soil underneath. This load transferred to the soil should be within the allowable bearing capacity of the soil.