The lowest part of buildings or civil structures is known as “Foundation”. It directly contact with the soil and transfers loads safely from the structure to the soil.
A foundation is the element of a structural engineering which connects it to the ground, and transfers loads from the structure to the ground. Generally, the foundation can be classified into two, namely shallow foundation and deep foundation.
1. Shallow foundation: in this foundation the load is transferred to a stratum present in a shallow depth. While
2. Deep foundation: it transfers the load to a deeper depth below the ground surface. A tall building like a skyscraper or a building constructed on very weak soil requires deep foundation. If the constructed building has the plan to extend vertically in future, then a deep foundation must be suggested.
The construction of a foundation can be done with concrete, steel, stones, bricks and etc. The material and the type of foundation selected for the desired structure depends on the design loads and the type of underlying soil.
In construction of foundation, trenches are dig deeper into the soil till a hard stratum is reached. For stronger base foundation concrete is poured into this trench and the trenches are incorporated with reinforcement cage to increase the strength of the foundation. The construction of foundation has to be design to resist the external attack of harmful substances.
The design of the foundation must incorporate different effects of construction on the environment. For example, the digging and piling works done for deep foundation may result in adverse disturbance to the nearby soil and structural foundation. These can sometimes cause the settlement issues of the nearby structure.
A projected steel rods are projected outwards, it act as bones and must be connected with the substructure above. Once the foundation has been packed correctly the construction of the building can be started.
The foundation for a building structure should be designed in such a way that:
- The underlying soil below the foundation structure does not undergo shear failure
- The settlement caused during the first service load or have to be within the limit
- Allowable bearing pressure can be defined as the pressure the soil can withstand without failure.
Functions of Foundation in Construction
Based on the purposes of foundation in construction, the main functions of the foundation can be enlisted as below:
- Provide overall lateral stability for the structure.
- Scouring and the undermining issues are solved by the construction of foundation.
- Load Distribution is carried out evenly.
- The load intensity is reduced to be within the safe bearing capacity of the soil.
- The soil movement effect is resisted and prevented.
- Foundation serve the function of providing a level surface for the construction of substructure
Purpose of foundation in building construction
Foundation plays important role in building structures as they are provided for all load carrying structure for following purposes:
- For stability.
- It prevent overloading.
- It avoid lateral movements of the supporting material.
- It serves the purpose of completely distributing the load from the structure over a large base area and then to the soil underneath.
- Provide proper surfaces for development of the substructure.
- Loads are distributes to the surface of the bed uniformly.
- It provide a level surface for building operations.
Requirements of a Good Foundation
Foundation needs to be design in such a way that some basic requirements must not to be ignored. They are:
- The foundation should be able to sustain as well as transmit the dead and the imposed loads to the soil. The transfer of the load should be carried out without resulting in any form of settlement that can result in any form of stability issues for the structure.
- The foundation should be construct in location that is not affected or influenced by future works or factors. The area of the foundation must be sound and healthy.
- Deeper foundation is recommended based on the soil and area can be guard from any form of damage or distress. These are caused due to the problem of shrinkage and swelling because of temperature changes.
- Differential settlements can be avoided by having a rigid base for the foundation. These issues are more pronounced in areas where the superimposed loads are not uniform in nature.
Types of Foundation used in building construction
There are two different types of foundations used in construction, they are:
- Shallow foundation
- Deep foundation
1. Shallow foundation:
This type of foundations are also called spread footings or open footings. The ‘open’ refers to the fact that the foundations are made by first excavating all the earth till the bottom of the footing, and then constructing the footing. During the early stages of work, the entire footing is visible to the eye, and is therefore called an open foundation. The idea is that each footing takes the concentrated load of the column and spreads it out over a large area, so that the actual weight on the soil does not exceed the safe bearing capacity of the soil.
The shallow type foundation are classified into four. They are:
- Individual footing or isolated footing
- Combined footing
- Strip foundation
- Raft or mat foundation
2. Deep Foundation:
Deep foundation is required to carry loads from a structure through weak compressible soils or fills on to stronger and less compressible soils or rocks at depth, or for functional reasons. Deep foundations are founded too deeply below the finished ground surface for their base bearing capacity to be affected by surface conditions, this is usually at depths >3 m below finished ground level. The deep foundation are classified into two. Namely:
- Pile foundation
- Drilled Shafts or caissons