Guide to Pile Foundations
Often used for bridges, tall buildings, and roads, pile foundations can be made of timber, concrete, steel or composite materials. This type of footing can be designed to distribute loads or support the soil in different ways, depending on the structure they support and how they are built.
What Are Pile Foundations?
Pile foundations are a type of deep foundation, they are made from long piles that are driven or bored into the ground and then joined together with a beam which creates a stable platform for building a structure. Usually made from concrete, steel, and sometimes timber, pile foundations are a useful way to distribute the load of a structure into more solid soil conditions below the surface. Generally, the depth of a pile foundation should be more than three times its breadth.
When To Use Pile Foundations
Pile foundations have many uses, a structural engineer can determine the most suitable type of foundations for your project, but here are a few possible situations where pile foundations might be used:
- When soil at shallow depths is loose and would be easily compressed by the weight of a building.
- In areas where the water table is high, including near water sources and drainage systems.
- For very heavy buildings with non-uniform loads.
- When soil conditions are poor and the area cannot be excavated fully for other types of foundations.
Types Of Pile Foundations
As well as classifying pile foundations by the materials they are made of, they are also classified according to the function or use of the foundations.
Sheet piles are used to provide lateral support to a structure. Rather than transferring the load vertically, sheet piles are used to resist pressure from loose soil or water. This type of pile foundation can be used for retaining walls, trench sheeting, and shore protection.
This type of pile foundation can be used to transfer the load of a structure vertically, usually through layers of soft ground and down to a deeper layer of more solid earth.
End-bearing piles transfer loads through the tip of each pile, which rests on a layer of rock or stable soil. The diameter of the pile and the area of its tip will have an impact on the amount of load it can safely support.
Friction piles transfer the load of a structure into the soil by using the frictional force between the surrounding soil and the surface of the pile itself. This type of foundation uses the entire surface of the pile to transfer load. Friction can be increased by making the surface of the pile rough or by increasing the diameter of the pile and the depth it is driven.
Soil Compactor Piles
Soil compactor piles are used to help improve the load-bearing capacity of the surrounding soil. The piles themselves are not used to carry any load directly.
Designing Pile Foundations
It is important to consider the required function of a foundation and consult a structural engineer to advise on the most suitable material, structure and construction method when designing pile foundations. The construction method of pile foundations can vary greatly and has some bearing on how and where each type can be used.
Mainly used for coastal structures, sea defences and jetties, driven piles are formed by driving a timber, concrete or steel pile into the ground. This method of construction forces the soil sideways rather than removing it, and compacts an area of the earth around the pile. The piles are created off-site or pre-cast, so they are fairly quick to build.
Bored piles are constructed on-site by removing the earth to form a hole, which is then filled with a poured concrete pile. As the piles are poured in situ, this type of pile foundation is useful where the length of each pile varies, or where the required length would be difficult to create off-site and then transport for installation. Bored piles usually require relatively cohesive soil.
Advantages Of Pile Foundations
Each type of pile foundation has a different set of advantages and disadvantages, meaning they all have different potential uses. Driven piles for example have the advantage of being relatively quick to construct, as the piles are pre-formed. Whereas bored piles have the advantage of causing fewer vibrations during construction, they can be used on urban and compact sites where vibration from driven piles might cause disturbance to existing structures.
Are You Considering Pile Foundations?
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