Deep Foundations Explained: What they Are and When to Use Them
There are two types of foundations when building: shallow foundations and deep foundations. Deep foundations are incredibly strong and are what have allowed us to build skyscrapers and other tall buildings.
What is a Deep Foundation?
A deep foundation transfers the weight of a building down to the earth. They go much further down than a shallow foundation. Piles or pilings are drilled down into the earth. Some skyscraper foundations go deeper than 250 feet. The depth of a deep foundation depends on how tall the building is.
The 5 Types of Deep Foundations
There are five types of deep foundations:
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Basements
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Buoyancy rafts
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Caissons
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Shaft foundations
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Pile foundations
Basements
A basement is a hollow substructure that provides working or storage space below ground level. Although some basements can be really unique and creative in design, they must be built to function as a foundation over their use as a storage or living space. These substructures are designed to resist bugs, dirt, soil pressure, water, and other elements so the structure of the building can remain upright.
Buoyancy Raft
A buoyancy raft is known as a floating foundation or hollow box foundation. They are used when construction takes place on soft, weak soil. In buoyancy rafts the soil underneath the foundation is removed and the foundation - in essence - floats. This foundation is equal in weight to the structure, maintaining stability through both forces counteracting one another in weight.
Caissons
Caisson foundations are hollow substructures that are first built on the surface but then sunk underground to the required depth. They are used when compact and stable soil is hidden beneath a layer of “weaker” soil.
Cylinders are a type of caisson with concrete. They are used in water environments and are common for bridges, docks, piers, etc.
Drilled Shaft Foundations
Drilled shaft foundations are constructed using concrete and other pre-fabricated load-bearing materials. Their purpose is to transfer the weight between the foundation and the heavy structure evenly. To construct these types of foundations, crews drill holes in the ground, add reinforced steel to provide additional support and then pour concrete into the foundation once inserted into the ground. All together this creates a highly reinforced concrete foundation.
Pile Foundations
Pile foundations are hollow tubes that are filled with concrete but then connected to one another to distribute heavy loads equally. These piles are connected together through grade beams which provide structural support to the building because all the piles are simultaneously connected to one another.
Equipment Used for Deep Foundations
The most common type of equipment used for constructing a foundation is a rig, like drilling or piling rigs. These rigs have many different uses in construction but are used is to break the ground when building foundations.
Drilling or piling rigs are used to drill out mud and any fluids that may be found within the soil. The rig collects this debris and removes it from the ground in order for a deep foundation to be placed. This step is important because anything that could interfere with the quality or strength of the foundation could cause a collapse later on.
Excavators and auger attachments can also be used during deep foundation construction.
When Are Deep Foundations Used?
Deep foundations are commonly used when building superstructures such as a skyscraper, apartment buildings, or shopping centers. They are commonly used in situations where the soil is soft or weak and not able to support the weight. These foundations help to provide a deeper and more stable base for any building.
Pros and Cons of Deep Foundations
Deep foundations have unique pros and cons.
Pros
There are quite a few pros for installing deep foundations. These foundations can be prefabricated off-site, resulting in efficient installation. The piles within the foundation are made with strong materials like concrete, which keep the structure safe and secure for many years.
Cons
Deep foundations also have cons. Piles within the foundation can be damaged from corrosion caused by water, larger rocks underground, or any type of natural force. Because deep foundations are usually used in larger buildings, the necessity to build a really strong foundation is extremely high. There is a lot of preparation, research, and planning that goes into these projects.
The construction of deep foundations can also cause some challenges. The vibrations produced by a rig during installation could impact both the new foundation and neighboring structures' stability. Shifts in weather can impact how concrete hardens or cause delays in project timelines. There is a lot that goes into building a deep foundation.
Deep Foundations 101
A foundation is the lowest part of a structure that is created to provide stability. Foundations provide direct contact with the ground and transfer the weight of the structure itself to the soil below to provide a firm, stable structure. Deep foundations are needed when a superstructure is being constructed as they provide stability to withstand the larger buildings.
