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What are Pile Foundations?
Pile foundations use piles — long members of wood, steel, or concrete that can be driven into the ground — as substructures to support structures built on top of them. These foundations are often used in marine construction for bridges, piers, docks, oil rigs, and wind farms. They are also commonly used where poor soils will not support other foundation designs, and for supporting loads that would be too heavy for other types of traditional construction.
Historically, the members used in pile foundations prior to 1800 were wood. Wood piles have been in use for all of recorded history. After 1800, steel piles were developed, and in the 1900s, concrete became available. Each of these materials has advantages and disadvantages, and all of them are still used in this kind of construction.
Often, pile foundations are driven into place by a pile driver, a piece of heavy equipment that raises a weight to a certain height and drops it forcefully onto the top of the pile. The weight forces the pile into the ground. This is repeated until the desired depth is reached. Steel is particularly easy to drive into the ground in this manner. Driven concrete piles have to be specially reinforced to withstand being hammered with the weight.
Piles can also be drilled and poured in place to create this kind of foundation. This is often done in areas where pile driving may not be practical, such as where there is low headroom. Drilling also allows for pile foundations to be used in areas where soil is very dense or hard. Often, drilled piles are formed by using permanent casings, which can then be filled with concrete.
Once all of the members are put into place for a pile foundation, a pile cap is then usually placed over them. This usually takes the form of a large thickness of concrete, into which the tops of the piles are embedded. The cap acts to transfer the weight of the construction above it to the members below, which generally support the structure by absorbing its load, and transfers this to the deep subsurface upon which they rest, as well as the soil surrounding the pile.
Sometimes, grade beams are connected directly to the tops of piles. In these pile foundations, the load of the structure is transferred through the grade beam to the piles. This type of foundation is often seen in pier construction.
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![Pile foundations are often used in wind farms.]()
By: Richard VillalonPile foundations are often used in wind farms. -
![Piling helps create a deep foundation for large structures.]()
By: mawardibaharPiling helps create a deep foundation for large structures.
Discussion Comments
Concrete piling is the best if only the handlers do the right thing, e.g., use quality materials and the right mixture of concrete.
@Mammmood - Personally I think that steel is better than concrete pile foundations. Concrete is strong but it can crack. I don’t know if steel can crack – maybe it can warp, but I think it’s stronger. I definitely can’t see why anyone would use timber nowadays as wood can rot, especially when you’re talking about something that’s underwater.
@Charred - That’s interesting. I thought the pile cap evenly distributed the weight to the wood, so there should not be a collapse of the timber. I’m not an engineer but that’s what I gather from the article.
I think there must have been other issues. At any rate I think the principles for secure structures such as bridges are the same principles you have for other structures like tall buildings.
Basically you want to dig deep as far as possible. With buildings I am told that for each story above ground you want to dig one story below ground. I think for bridges that same principle would be true, and thus you would want deep pile foundations to ensure that the structure does not shake or wobble under the strain of repeated, heavy load.
Your structure is only as strong as its foundation. There was a bridge collapse in DeKalb County Georgia in 2008. Some of you may remember it.
Anyway the bridge used timber piles. When they conducted the investigation they found out that the bearing capacity of the timber piles was not sufficient to withstand the weight that was placed on it, and so the bridge collapsed.
Why that happened in one bridge and not another one that used timber piles, I don’t know. In either case I believe that we have many bridges that have been worn out over the process of time.
Their pile foundation systems may be weak or there may be other structural issues with them, and we need to retire these bridges as soon as possible to ensure that our roads remain safe for years to come.
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