In this article, we will discuss their basic Building Foundation Types. Generally, all foundations fall into two categories: shallow foundations and deep foundations. The words shallow and deep refer to the depth of the soil from which the foundation is made. Shallow foundations can be made at depths as small as 3 m (1 m), while deep foundations can be made at depths of 20 – 65 m (60 – 200 m). Shallow foundations are used for small, light buildings, while deep foundations are for large, heavy buildings.
Shallow foundations are also called spread foundations or open foundations. ‘Open’ means that foundations are made by first digging the entire surface to the bottom of the foundation and then building the foundation. In the early stages of work, the whole foot is visible to the eye and is therefore called an open base. The idea is that each foundation takes the concentrated load of the column and spreads it over a large area so that the actual weight on the soil does not exceed the safe bearing capacity of the soil.
In cold climates, shallow foundations must be protected from freezing. This is because the water in the soil around the foundation freezes and expands, thus damaging the foundation. These foundations should be built below the frost line, which is the level in the ground where freezing occurs. If they cannot be built below the frost line, they must be protected by insulation: normally some heat from the building penetrates the ground and prevents freezing.
Building Foundation Types
Here are the types of building foundation and their features:
Single foundations are one of the simplest and most common types of foundations. These are used when the load of the building is carried by columns. Usually, each column will have its own foundation. The foundation is just a square or rectangular concrete slab on which the column sits. To get a very rough idea of the size of the foundation, the engineer will take the total load in the column and divide it by the safe bearing capacity (SBC) of the soil. For example, if the vertical load of a column is 10T and the SBC of the soil is 10T / m2, its foundation area will be 1m2. In practice, the engineer will look at many other factors before preparing a construction design for the foundation.
Individual foundations are usually connected by a plinth beam, a horizontal beam built in the ground or below ground level. These beams are also called Bağ Beams.
Strip Foundations (Continuous Foundation)
Strip foundations are widely used in load-bearing wall construction. and acts as a long strip supporting the weight of the entire wall. These are used where building loads are carried by entire walls rather than insulated columns, such as in older buildings that give the wall the bearing role. These buildings are also called masonry buildings. Although continuous strip foundations are generally the most preferred foundation type in masonry buildings, today they are widely used in frame buildings.
The raft foundation, also called mat foundation, is a single concrete block slab standing on the soil that stretches across the entire footprint of the building, thus supporting the building and transferring its weight to the ground.
The raft foundation usually distributes the weight of the building over the entire area of the building when the soil is weak and does not distribute it over smaller areas (such as single foundations) or single points (such as pile foundations). This reduces the pressure on the soil.
The concept of pressure is fundamental to civil engineering. Pressure is simply weight divided by area. For example, if a 5 x 5 building weighs 50 tons and has a raft foundation, the pressure in the soil is weight / area = 50/25 = 2 tons per square meter.
If the same building is supported by 4 individual foundations of 1 x 1m each, the total area of the foundation will be 4 m2 and the pressure on the soil will be 50/16, which will be about 12.5 tons per square meter. . Thus increasing the total area of the foundation can significantly reduce the pressure on the soil, nothing more than weight per square meter.
The raft foundation is also very good for basement floors. Foundations are created by digging the soil to find strong, compact, undisturbed natural soil that is at least a few meters below ground level. This soil is much stronger than loose soil at the surface. If we build a raft foundation 10 feet below ground and we build concrete walls around the perimeter, it makes a perfect foundation. Therefore, an engineer designing a building with a basement will tend to choose a raft foundation over other types of foundation.
A pile foundation is made by hammering a strong material such as concrete into the ground so that the structures can be supported on top of it.
Pile foundations are used in the following situations:
- When there is a weak soil layer on the surface. This layer cannot support the weight of the building, so the loads of the building must bypass this layer and be transferred to the stronger soil or rock layer below the weak layer.
- When a building has very heavy, concentrated loads, such as a very tall structure.
Pile foundations can take more load than raft foundations.
There are two types of pile foundations, each working in their own way.
In end piles, the Pile lower end rests on a particularly strong layer of soil or rock. The load of the building is transferred from the pile to the strong layer. In a way, this stack behaves like a column. The basic principle is that the lower end rests on the surface, which is the intersection of a weak and strong layer. Therefore the load bypasses the weak layer and is safely transferred to the strong layer.
Friction piles operate on a different principle. The pile transfers the load of the building to the soil over the entire height of the pile by friction. In other words, the entire surface of the cylindrical cluster tries to transfer forces to the soil.
To visualize how this works, imagine you push a solid 4mm diameter metal rod into the frozen ice cream tub. Once it’s pushed in, it’s strong enough to support some load. The greater the embedment depth of the ice cream, the more load it can carry. This is very similar to how a friction pile works. In the friction pile, the amount of load a stack can support is directly proportional to its length.
In practice, however, each pile adheres to the load by a combination of end strength and friction.