Understanding Deep Foundations: What They Are and Why They Matter

As a fundamental principle of construction, foundations are foundational to the strength and stability of any structure. No matter the size of a building, a foundation is the basis that transfers load to the earth. A poorly constructed foundation can lead to serious structural problems in the future. 

To support heavy structures such as skyscrapers and bridges or when the soil near the surface is weak or unstable, deep foundations are used. The primary purpose of deep foundations is to improve the stability of the structure and increase load-bearing capacity, which is a structure’s ability to support its own weight and any additional loads placed upon it. Load bearing capacity is the maximum ability of a structure to take loading before failure occurs.

True to its name, deep foundations are constructed at greater depth below the ground surface, transferring structure loads to the earth at depth.  Depth to width ratio is usually greater than 4 to 5.

The depth of a deep foundation depends on how tall the building is. Unlike shallow foundations which can be constructed in as little as a one-foot depth, a deep foundation can be made at a depth of 10-300 feet. Shallow foundations are used for small or lighter-weight buildings, whereas deep foundations are needed for larger or hillside developments, or those on poor soil.

Benefits of using deep foundation

  • Enhanced and even load-bearing capacity, thus improving the structural integrity of a building 
  • Provides a stable base in weak or unstable soil conditions
  • Can withstand resistance to natural forces like wind and earthquakes
  • Can be customized to each project, taking into account loads, climates, geographic location, lateral forces, and soil conditions
  • A strong stable deep foundation can help avoid costly repairs or maintenance in the future

Real-world examples of structures heavily reliant on deep foundations

Take a look at some of the most famous structures to use deep foundations:

  • One World Trade Center (USA): As the tallest building in America at 546 meters tall, One World Trade Centre has foundations as deep as 150 feet. 
  • Taipei 101 (Taiwan): One of the world’s tallest structures between 2004 and 2009, this deep foundation consists of 380 concrete piles drilled at 262 feet deep, making it one of the deepest foundations on record.
  • Shanghai Tower (China): At a whopping 632 meters, Shanghai Tower is the third tallest building in the world. Architects and engineers needed the structure to be able to withstand the area’s infamous and unpredictable earthquakes, so the answer was a massive foundation at 282 feet deep.
  • Petronas Towers (Malaysia): Boasting the world’s deepest foundations at 400 feet deep and comprising 104 concrete piles, these foundations are designed to spread the load of the massive building on land that is notoriously unstable.

Common types of deep foundations 

Deep foundations are flexible in design and there are various types used, with two of the most common being:


A pile is a long cylinder of a strong material like concrete, wood, or steel that is pushed or drilled into the ground to act as a steady support for structures built on top of it.


A foundation used in deep water or soft soil, caissons are a series of large, watertight cylinders filled with concrete and then sunk into the ground, providing a stable base for structures built on top of it.

Connolly Engineering: Your Trusted Resource For Deep Foundations

The long term safety and integrity of your structure depends on your foundation. Deep foundations offer numerous advantages such as providing a more stable base in weak soil conditions and the ability to bear heavier loads and distribute weight evenly.

In construction, it’s imperative to count on engineering experts to provide guidance and expertise when it comes to determining the right foundation for your project. Offering civil and structural engineering services in New York City, the Hudson Valley, and the surrounding areas Connolly Engineering, offers a depth of experience with deep foundations.  

We encourage you to reach out to our team today to discuss how deep foundations might play a role in your next infrastructure projects. We look forward to connecting and collaborating with you soon!


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