The foundation is undisputedly the most important – and a building’s structural integrity is directly proportional to the quality of foundation. In a recent article about structural design for a building, we mentioned how three points, i.e. safety, serviceability and restorability are indicators of a building’s performance. However a building cannot imbibe the above mentioned factors unless it has a well laid foundation.
Classic Case of Foundation Failure – The Leaning Tower of Pisa
The leaning tower of Pisa is a monumental structure, and ironically so because of the foundation failure which happened due to the instability of ground underneath. The 185 feet tall tower that was made to house the bells of a cathedral leans at an angle of five and a half degree southwards. Reason – before the foundation was laid, soil was not tested. The soil underneath was soft and had sand like texture, and compressible, and hence there was differential settlement, where the tower started leaning.
Due to such failures, soil engineering and site preparation has become one of the most integral parts of foundation engineering.
What factors are taken into account before laying foundation?
Type of Foundation:
It is first important to decide what type of foundation design is suitable for the proposed building. For example – a building development project at a beach site or a hilly region requires raised foundation built on concrete or steel pilings. Besides, depending on the building design and structure, other raised foundation types where walls built of concrete, bricks, stone or concrete blocks with added piers underneath are also used as foundation for the building.
Basement walls can also be erected to double up as a strong support and foundation for your structure. Concrete slab foundation is one of the common foundations used for buildings; however it is important to take a slump test for the concrete before and during the process of laying a foundation.
The structure of the soil, at the place where a project is proposed to be built is an important element of scrutiny. Wet soil structure may require a lot of engineering to make it suitable for a foundation that will uphold the building.
If the soil has a shifting nature, then it is not advisable to build high rise structures here. Soil compaction tests can help decide what kind of foundation needs to be designed for the particular project.
Footings or footers are commonly laid beneath the foundation. Top soil that is not suitable for a footing is removed and footings are added, usually 12 inches below the frost line. It is a common practice to pour concrete footing with depth equal to and width twice as the wall thickness.
Some footing where loads are large, reinforcing is also a common practice. The footing is an enlarged base for the foundation that is designed so that the building load gets distributed over a larger area this restricts movement and settling after the building is built.
Building foundation – offers a base so that buildings can stand on the ground, secured to the base. The foundation must hence be built to carry the weight and load of the building across all conditions.