Types of Building FoundationsOn September 21, 2017 by fruof30098
Generally speaking, all foundations are divided into two kinds: shallow foundations and deep foundations. The terms shallow and deep refer to the depth of soil in which the foundation is made. Shallow foundations can be made in depths of as little as 3ft (1m), while deep foundations can be made at depths of 60 – 200ft (20 – 65m). Shallow foundations are used for small and light buildings, while deep ones are for massive and heavy buildings.
Shallow foundations are also known as open or spread footings. The open denotes to the fact that the foundations are created by first digging all the earth till the bottom of the footing, and then constructing the footing. During the first stages of work, the entire footing is visible to the eye, and as a result called an open foundation. The idea is that every footing takes the concentrated load of the column and spreads it out over a large area, so that the real weight on the soil does not surpass the safe bearing volume of the soil.
There are numerous types of shallow footings: individual footings, strip footings and raft foundations.
In cold weathers, shallow foundations must be protected from freezing. This is because water in the soil around the foundation can freeze and expand, thereby resulting to damage in the foundation. These foundations should be built below the frost line, which is the level in the ground above which freezing occurs. If they cannot be built below the frost line, they should be protected by insulation: normally a little heat from the building will permeate into the soil and avoid freezing.
Raft or Mat Foundations
Raft or mat foundations, are most frequently used in the construction of basements. In a raft, the entire basement floor slab acts as the foundation; the weight of the building is evenly spread across the whole footprint of the building. It is named a raft because the structure is like a vessel that ‘floats’ in a sea of soil.
Mat foundations are used where the soil is weak, and therefore structure or building loads have to be spread over a large area, or where columns are closely spaced, which means that if individual footings were used, they would touch each other.
Deep foundations use piles which are long cylinder of a sturdy material such as concrete that is pushed into the ground so that buildings can be supported on top of it. Pile foundations are used when there is a layer of weak soil at the surface that cannot support the weight of the structure or building, so the loads of the building have to detour this layer and be moved to the layer of stronger soil or rock that is underneath the weak layer; also when a building comes with an extremely heavy and concentrated loads like those high structures.
Pile foundations can either be end bearing pile or friction pile. These types of foundations are capable of taking higher loads better than spread footings.