Among the various building components, foundation is the most important component of a building. The reason behind foundation being the most important component is that it supports the building and allows it to withstand against all kind of forces that can cause dismantle or destruction of the building. In the words of civil engineering a building consists of two main components – the super structure and the sub structure. The super structure is that part of a building which lies above the ground level and the sub structure is the part that lies below the ground level. Therefore foundation is that part of the building which remains in direct contact with the ground to which the load is be transmitted.
The function of building foundation is to transmit the various loads of a building to the soil on which the building is resting. Firstly this transmission of the loads should happen in such a way that the settlement of the soil beneath the foundation is under permissible limits and secondly the soil should not fail in course of the period while the building should not develop cracks, fractures or distortion. These loads can be the dead loads of the building, live or the superimposed loads, wind load, frost load, and various other permanent and temporary loads.
Apart from the above mentioned functions there are other essential functions of building foundation which are equally important for a building in various perspectives. These functions are as follows:
- Distribution of the load of the building into the ground in a uniform manner so that the load does not exceed the safe bearing of the super structure.
- An even distribution of the load of the building to the sub-soil.
- The most important function of the building foundation which relate with the other function is the lateral stability of the building against the forces which causes sliding, distortion, overturning during seismic events and other reasons.
- Building foundation provides safety against soil movement and scouring.
Deep Foundation: As we already know that a foundation said to be deep foundation if the depth of the foundation is more than width of the building foundation. The deep building foundation is those types of foundations which transfers load to a greater and deeper extent beneath the surface of the ground due to unavailability of required soil strata for the desired building type.
The foundation can be classified into the following sub-divisions in building foundation
- Deep strip, rectangular or square footing
- Pile foundation
- Pier foundation or drill caisson foundation
- Well foundation or caissons
1. Deep Strip, Rectangular or Square Foundation: These type constructional layouts are similar to that of what we have discussed in the shallow foundation apart from the fact that they come under deep foundation if and only if the depth of the foundation is greater than the width of the foundations.
2. Pile Foundation: Pile foundation is a type of building foundation that has a depth more than its width. These types of foundations finds its utilisation in those area where the foundation beneath the ground level has to transfer a heavy and huge amount of loads into the sub- soil but there is an absence of proper strata of soil which can bear the loads of the building without being dismantle. Sometime the pile foundation is used in the place of raft foundation when the loading is uneven and load bearing strata does not exist at a shallow depth. CLICK HERE to read more about types of piles and their characteristics in building foundation
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3. Pier Foundation: It is a type of foundation which is very much similar to that of pile foundation, apart from the fact that they differs in their methods of construction. Pier foundation is preferable when the top stratum consists of decomposed rock overlying a stratum of sound rock. These conditions are not suitable for driving the bearing pile into the ground. Some of the common differences between pile foundation and pier foundation are:
- Pier foundation transfers the load of building only through bearing while the pile foundation transfers load through bearing or friction.
- It is cylindrical in shape with larger diameter and shallower in depth as compared to pile foundation.
The suitability of pier foundation is governed only in the case of stiff clays, which offers large resistance to the driving of a bearing pile, pier foundation can be conveniently constructed.
4. Well Foundation: well foundation is a type of deep foundation which is sunk from the surface of either land or water to the desired depth. Well foundation or caissons are mostly preferred for the foundation of bridge piers, abutments in river, dock, quay walls, and other shore protecting structures. Caissons are hollow box like structure which is filled with sand and plugged at the bottom with concrete. It provides resistance to both heavy vertical and horizontal loading faced by a structure.