Definition of Deep Foundations

A deep foundation is one that transfers building loads past the weak soil farther down to the competent soil and/or rock. This type of foundation is best suited to taller buildings and structures that are heavy and require adequate support. Here’s what you need to know about deep foundations, how they’re built, and how they are used.

About Deep Foundations

Deep foundations can be used to support new or existing structures. They are connected to the structure and can be installed prior to building construction or as underpinning elements for existing structures. Deep foundations are typically used for taller and heavier buildings that require greater support.

They are designed with safety in mind. Deep foundations can be especially beneficial in areas where earthquakes are likely to occur. This can create peace of mind for the people in the structure. The two types of deep foundations are pile foundations and drilled shafts or caissons.

Pile Foundations

Pile foundation is a type of foundation that transfers heavy loads to a stratum made of hard rock that is found deep below the ground’s surface. Pile foundations are formed as long, slender, columns, which are typically made of steel, reinforced concrete, or timber.

Timber piles are placed under water level and will last approximately 30 years. Concrete piles have high-resistance to chemical and biological cracks and are of high strength. Steel piles are hollow, but filled with concrete and can reach greater depths than any other pile foundation.

A foundation is considered piled when its depth is at least three times its width. Pile foundations are used when soil at a shallow depth is compressible, there is a deep drainage system or canal near the structure, or the structure is heavy and consists of un-uniform loads.

Drilled Shaft Foundations

Drilled shafts, also called caissons are also known as caissons, drilled piers, and bored piles. This type of foundation is used extensively throughout the world. Drilled shaft foundations are used for tall buildings, bridges and other vertical load structures. These foundations are cast on site. The advantages of drilled shaft foundations include the ability to be extended through soft, compressible, or swelling soils into proper bearing material and the ability to extend below frost level.

Drilled shaft foundations also cause less disruption to adjacent soils, large excavations are minimized, and they are potentially more cost effective. To install a drilled shaft, a vertical hold is drilled into the soil using a bored piling machine. A drilled shaft can be drilled to a depth of up to 60 meters and have a diameter of up to 2.4 meters. After the hole is drilled, a reinforced steel rebar is lowered into the hole. Then the hole is filled with concrete.

Deep foundations are beneficial when supporting a tall, heavy structure. They are able to bear the weight of the structure and keep it steady as they transfer the load from the structure to the soil and deeper into the earth. Deep foundations can be dependable during seismic activity, protecting the structure and those inside.


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