Pile foundations are extremely deep foundations. They are composed out of long, slender columnar parts that are normally made of steel or reinforced concrete, but can also be made of wood. When the depth of a foundation exceeds three times its breadth, it is said to be "piled." Pile foundations are used when the ground is stable and solid, such as under buildings or along roads. The size of the piles depends on how much load they will have to support. For example, if the foundation is for a two-story building, each story needs its own pile group. Each group may be several hundred pounds or more in weight.
The length of each pile should be at least twice its width. The goal is to create a network of strong, slender columns that will resist bending forces from heavy objects on top of the foundation.
There are several different types of pile foundations: capillary, open, closed cell, and hybrid. In capillary pile groups, the spaces between the piles allow water to drain away from the base of the structure. This type of foundation is most appropriate for dry locations where water is not an issue. Open-cell foundations are similar to capillary groups except that the cells are exposed on the surface of the ground. Closed-cell foundations have holes (or cages) drilled into the ground around the perimeter of the foundation area. These provide space for water to drain while still maintaining the stability of the ground under the foundation.
Pile foundations are primarily utilized to transmit loads from superstructures to stronger, more compact, less compressible, and stiffer soil or rock at depth, increasing the effective size of a foundation and resisting horizontal stresses. Pile-supported structures tend to be more resistant to overturning because they distribute load over a large surface area in order to reduce the risk of collapse.
The basis for using this type of foundation is the fact that most soils will not support heavy loads directly; instead they will bear their weight through an intermediate structure called an "interlock". An interlock is any material between the soil and the foundation that prevents two surfaces of the same material from bearing down on each other with great force. For example, if a column of soil is under pressure but no pillar supports it, then an interlock has formed between the soil and the foundation wall. The only way to prevent this kind of failure is to put something in between that can withstand the load.
An example of where this method is appropriate is when building on sandy soil where footings would be expected to sink below their frost line during winter months. A pile-supported structure will not be affected by this movement because the soil will remain between the piles rather than inside the foundation walls.
This method is also useful when constructing buildings close to unstable objects such as cliffs, steep slopes, or large rocks.
When it is not possible to build the structure on shallow foundations, pile foundations are used. As described in the article, pile foundations are chosen based on the type of the building and for other reasons. Let us concentrate on the key points of this essay. Let us begin with comprehension. You should understand that pile foundations are required for:
- Concrete buildings - where wood is considered dangerous because it can burn and release carbon dioxide into the atmosphere (remember the greenhouse effect?) - concrete is a good material for building with because it does not emit any gases when it burns. Also, burning concrete produces very little smoke or ash.
- Wood buildings - where wood is preferred over concrete because it is sustainable and emits less CO2 when it burns - pile foundations are needed in this case too. The reason is that deep holes have to be dug in the ground to provide support for the heavy weight of the building. If no pile stones are used then even deeper holes have to be dug which would be difficult or impossible with just hand tools. Pile foundations are easy to make with the help of a tractor or excavator.
Now that you know why these foundations are necessary, let's see how they are built.
First, the area where the house is going to be built is cleared of all existing structures such as trees, cars, etc.
Pile foundations are classified into three varieties based on their construction methods: driven piles, cast-in-situ piles, and driven and cast-in-situ piles. Driven piles are excavated to a certain depth and then loaded with equipment to drive them into the ground. As they get deeper, they can be stacked on top of each other. Cast-in-situ piles are natural or manufactured objects that are placed directly into the ground without any excavation. They can be made of rock or concrete and usually require some type of adhesive to hold them in place while they cure.
Driven and cast-in-situ piles can be used together for increased stability. These types of foundations are most commonly used for buildings that will not be moved after they're built because they are more expensive than driven piles or cast-in-situ rocks alone.
There are also combination piles that are driven and cast-in-situ at the same time. These are used when space is an issue but driving and stacking individual piles would be difficult or impossible. Combination piles are usually made of metal and plastic and can be seen as an alternative to steel beams in traditional building techniques.