DEEP FOUNDATION WORKS

Deep Foundation Works: Techniques, Applications, and Challenges

Deep foundations are one of the most critical elements in civil engineering projects, particularly where structural loads are substantial or the surface soil is incapable of adequately supporting the weight of the construction. This type of foundation transfers the loads to deeper, more resistant layers of soil or rock, ensuring the stability and safety of the structure. This article explores the most commonly used techniques in deep foundation works, their applications, and the main challenges faced by engineers during the execution of these projects.

What are Deep Foundations?

Deep foundations are those that extend to significant depths below the surface, as opposed to shallow foundations, which are used on terrains with good surface bearing capacity. Deep foundations are necessary when the upper soil layer is unstable or incapable of supporting the weight of the construction, requiring the foundation to reach a more stable layer.

The main types of deep foundations include piles, caissons, and drilled shafts. Each of these techniques has unique characteristics that make them more suitable for different types of soils and structural loads.

Types of Deep Foundations

1. Piles

Piles are the most common type of deep foundation. They can be made of various materials such as concrete, steel, or wood and are driven or bored into the ground until they reach a more resistant layer.

• Precast piles: Manufactured off-site and driven into the ground by percussion or vibration. They are suitable for soils with good driving conditions and environments with limited space.
• Bored piles: These are cast "in situ" by drilling the soil and filling the hole with concrete. They are used in soils where driving precast piles would be difficult or inappropriate, such as in urban areas sensitive to vibrations.

2. Drilled Shafts

Drilled shafts are large cylindrical elements excavated manually or mechanically until they reach a firm soil layer. After excavation, the shaft is filled with concrete. This method is used when it is necessary to transfer very high loads to deep and resistant soil layers, common in large buildings and infrastructure works.

3. Caissons

Caissons are deep foundation systems made of large concrete structures that are cast and then sunk into place until they reach the desired soil layer. This technique is used in large-scale projects, such as bridges and ports, where the structure must withstand very high loads in submerged or unstable soil environments.

Applications of Deep Foundations

Deep foundations are applied in a wide range of construction projects, from tall buildings to bridges, dams, and heavy infrastructure. Some examples include:

• High-rise buildings: In skyscrapers and tall buildings, the structural loads are extremely high, making deep foundations necessary to transfer these loads to stable soil layers at significant depths.
• Transportation infrastructure: Bridges and overpasses, especially those built over rivers or unstable terrain, require deep foundations to ensure the stability of the structure over time.
• Marine works: Ports, piers, and offshore platforms use deep foundations, such as caissons and drilled shafts, to ensure that the structure remains stable even under adverse conditions, such as tidal action and underwater soil movement.
• Projects on unstable terrain: When construction is located in areas with low bearing capacity soils, such as floodplains or clayey soils, deep foundations are the only viable solution to ensure structural safety.

Challenges in Deep Foundation Works

Although crucial for ensuring the safety and stability of large constructions, deep foundation works present various challenges for engineers, who must deal with unpredictable soil conditions and technical limitations.

1. Detailed Geotechnical Investigations

The success of a deep foundation depends largely on accurate and detailed geotechnical investigation. Before the start of construction, deep soil drilling and field tests are required to assess soil conditions and identify the exact depth of more resistant layers. Insufficient analysis can result in design errors, leading to issues such as excessive settlements and foundation instability.

2. Vibration and Noise Control

Pile driving and drilled shaft excavation in urban areas present challenges related to vibration and noise control. In densely populated areas, the vibrations caused by pile driving can damage nearby structures and cause disturbances to the local population. The use of bored piles or techniques such as vibration driving can minimize these impacts.

3. Unknown Subsurface Conditions

During execution, it is common to encounter unforeseen subsurface conditions, such as rocks or high water tables. These unforeseen events may require design and execution adaptations, such as using specialized equipment for rock drilling or implementing dewatering systems to manage high groundwater levels.

4. Cost and Schedule

Due to the complexity and specialized equipment required, deep foundations typically represent a significant portion of the total construction cost. Additionally, the time required for the execution of these foundations is generally longer than for shallow foundations. Effective management of timelines and costs is essential to ensure the project remains viable.

Conclusion

Deep foundation works are essential for ensuring the stability and safety of large constructions, especially on terrains with adverse conditions. Although they present technical challenges, such as detailed geotechnical investigations and vibration control, the use of advanced techniques and proper planning can overcome these obstacles. The correct application of deep foundations ensures that structures withstand time and imposed loads, guaranteeing their durability and functionality in the long term.