Introduction:A foundation is the most important element or structure of a building.This is simply because it’s the part of the building which essentially supports the weight of the building.It’s selection is based on the type of the building being constructed, as well as the type of soil present on the land in which the proposed construction of the building is being planned.It’s extremely important that the right foundation is done for a proposed building, otherwise the building could easily collapse if the foundation is not able to support the weight of the building, thereby putting lives of occupants of the building at risk.There is also the impact of the huge financial losses which could happen due to the collapse of a building.So, how exactly do we define foundation?Definition:A foundation can simply be defined as the element of a structure/building which connects it to the ground, and transfers load from the structure to the ground.
Types of Foundationa) Shallow foundationb) Deep foundation
Shallow Foundation types:a) Individual/Isolated footingb) Combined footingc) Spread/Strip foundationd) Raft/Mat foundation
I will briefly explain each of these foundation types…
a) Individual/Isolated footing:This is the most common type of foundation used for building construction.It is also known as pad foundation.This type of foundation is constructed for single columns & it’s used when loads from the structure is carried by the columns.The shape of individual footings is square or rectangular.The soil type comes to play in the construction of individual footings as the size of the foundation is calculated based on the load on the column and the safe bearing capacity of the soil.
b) Combined footing:This type of foundation is also used when loads from the structure is carried by the columns.It is usually recommended when there are 2 or more columns in the building which are close to each other.It’s simply a combination of individual footings, but their structural design differs. The shape of this type of foundation is rectangular.
c) Spread/Strip footings:The base of this type of foundation is wider than a typical individual footing or combined footing. This helps to provide better stability for the building by spreading the weight of the building over a wider area.It’s usually used on lands where the soil bearing layer is within 3 meters (or 10feet) from the ground’s surface, thus helping to provide a better stability & support for the building.It’s obvious thus that the type of soil on a land plays a crucial role in the selection of a foundation which will be suitable for the building being proposed.
d) Raft/Mat foundation:This type of foundation is increasingly being used nowadays in construction.This foundation is spread across the entire area of the building in order to better support heavy structural loads from columns & walls, especially where the loads from the structure is expected to be very high.It is suitable for soil types whose bearing capacity is less suitable for individual footings or combined footings, as it effectively carries the weight of the building much better since the foundation is spread over the entire area of the building.
DEEP FOUNDATIONDeep foundations are used to transfer heavy loads from buildings to a deeper soil layer if unsuitable soils are present near the surface of the land.Deep foundations are required to transfer loads from a building structure through weak compressible soils on the surface of the land to stronger & less compressible soils that are located at a deeper level, usually from depths greater than 3m below ground surface.Deep foundations are usually not affected by surface conditions as their foundation is deep below the ground surface.
Deep foundation types:a) Pile foundationb) Basement foundationc) Caisson/Drilled shaft  foundationd) Buoyancy rafts/hollow box foundation
I will briefly explain each of these examples of deep foundations…
a) Pile foundation:This is used in places where shallow foundations such as raft foundations & spread footings can’t be used due to unsuitable soil layer that’s present on the ground surface.It transfers heavy loads from the building structure to a hard rock strata much deeper below the ground surface.The depth of pile foundations may be 5metres – 50 meters (15 feet – 150feet) from the ground surface.It’s indicated in areas prone to earthquakes or strong winds like typhoons by preventing uplift of building structures and minimising possible damage to the buildings due to the effect of the strong winds or earthquake.
b) Basement foundation This is a type of deep foundation designed & constructed to provide working or storage space below ground level.It’s much more common in America & European countries.The structural design & construction is governed more by their functional requirements as it can be used for storage, working environment or even for accommodation purposes.
c) Caisson/Drilled shaft foundation:This is similar to pile foundations, however they can transfer and support load from buildings heavier than pile foundations and the depth of the foundation is much deeper.It’s used where the depth of hard rock strata which can support the weight of the building structure is located within 10 metres – 100 metres (25 feet – 300 feet) below the ground surface.
d) Buoyancy rafts/hollow box foundation:These are deep foundations constructed in places such as open excavations.They can be designed to go very deep into the ground like caissons foundation.These types of foundations are constructed to provide a solid foundation in areas where the soil on the ground surface is very weak, in order to ensure that the heavy loads from the building structure is fully supported, despite the poor soil conditions present on the ground surface.