BSK: Understanding Deep Foundations
What are Deep Foundations?
Deep foundations are a type of foundation that is used to transfer building loads further down the earth to utilize stable soil. This process is utilized when the existing soil is not stable enough to handle a foundation.
Deep foundations are essential for safety and maintaining the integrity of a building. Especially in California where we have liquification issues within our soil. Proper use of deep foundations will keep a building erect during an earthquake and prevent a structure from collapsing under duress.
Why use a Deep Foundation?
There are several reasons why you would want to use a deep foundation for the integrity of a structure. However, the main reasons would include weak soils, compromised soils, undocumented fills, and liquification.
Weak Soils: Essentially, weak soils is a term used when the existing soils could possibly fail if a shallow foundation were to be used.
Compressible Soils: These are the soils that have the capability to decrease in volume; soil densification. Basically, when a structure is placed on compressible soil, without deep foundations, over time the soil will compress and pull down.
Undocumented Soil: This term is used when we do not know the stability of the soil.
Liquification: Soil liquification occurs when saturated soil becomes loses strength, usually in an earthquake. Basically, what was solid becomes liquid.
Types of Deep Foundations
There are two main types of Deep foundations; Driven Piles and Drilled Piers. A driven pile is driven into the ground, as you would imagine a nail being driven into a wall with a hammer. In essence, the pile is driven into the earth with a strong hammer. Moreover, with drilled piers, a hole is drilled, a cage is installed, and the hole is filled with concrete.
There are several types of driven piles and drilled piers, there are also specialty piles, such as micro piles.
Driven Piles usually consist of; Timber Piles, Concrete Piles, Steel Piles.
Timber Piles would usually be used in a marine type environment. They usually last around 30 years and typically support between 15 to 20 tons.
Concrete Piles can be pre-cast or cast-in-place. They are usually reinforced with rebar to prevent breakage. Concrete piles are often used to support buildings that are very heavy; such as a high-rise structure.
There are two types of steel piles; steel H piles and steel pipe piles. H piles are solid piles and often used in commercial construction for bridges and large buildings. Steel piles are often used as an interlocking unit with other sources.
Drilled Piers include Augercast Piers, Helical Piers. While Augercast piers are drilled holes filled with concrete and rebar a helical pier is twisted in and used to lift things up. Often you will see the use of helical piers in situations where foundations need repairs.
In addition to the typical piles and piers referenced above there are several specialty piles that can be used. One of the most popular being Micro piles. Micro piles are usually used for underpinning and are extremely useful in areas that have limited access. They can also be a very cost-effective way to stabilize the foundation. To learn more about deep foundations check out the Deep Foundations Institute.
BSK’s team of geotechnical engineers and engineering geologists have the technical ability to provide creative, practical, and technologically sound recommendations suited to your budget. We are well versed in the soil and geological conditions throughout California. Furthermore, we have a solid history of providing cost-effective investigations and recommendations for your soil needs.
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