Deep foundations are used when shallow foundations are not suitable, typically in areas with soft, unstable, or expansive soil conditions. They involve driving or drilling piles or constructing caissons into the ground to provide support for the building.
A deep foundation is a type of foundation which is placed at a greater depth below the ground surface and transfers structure loads to the earth at depth. The depth to width ratio of such a foundation is usually greater than 4 to 5.
Types of Deep Foundations:
- Pile Foundations:
- Driven Piles: Long, slender elements that are driven into the ground using a pile hammer. They can be made of wood, steel, or concrete.
- Bored Piles: Hollow cylinders that are drilled into the ground and then filled with concrete. They are often used in areas with obstructions or sensitive environments.
- Auger Piles: Piles that are formed by drilling a hole into the ground and then filling it with concrete. They are often used in soft or cohesive soils.
- Caisson Foundations:
- Open-Ended Caissons: Cylindrical structures that are drilled into the ground and then filled with concrete. They can be used in a variety of soil conditions.
- Pneumatic Caissons: Caissons that are pressurized with compressed air to prevent water from entering the excavation. They are often used in areas with high groundwater levels.
Advantages of Deep Foundations:
- Suitable for challenging soil conditions: Deep foundations can provide support for buildings in areas with soft, unstable, or expansive soil.
- High load capacity: Deep foundations can support heavy loads, making them suitable for tall buildings, bridges, and other large structures.
- Reduced settlement: Deep foundations can help to reduce settlement, which can cause damage to buildings.
Disadvantages of Deep Foundations:
- Higher cost: Deep foundations are generally more expensive to construct than shallow foundations.
- Longer construction time: The construction of deep foundations can take longer than shallow foundations.
- Noise and vibration: Driving piles can generate noise and vibration, which may be a concern in urban areas.
When to Choose Deep Foundations:
Deep foundations are a good choice for buildings that are located on unstable or expansive soil conditions, or for buildings that need to support heavy loads. However, it’s important to consult with a structural engineer to determine the most appropriate foundation type for your specific project.
