A pier foundation is a type of foundation used to support a building or structure by transferring the load from the building to a solid base beneath the ground. It consists of a column, or pier, that is placed deep into the ground and connected to the building’s foundation.
Purpose of pier foundation
The purpose of a pier foundation is to transfer the structural load of a building or other large structure to a stable, load-bearing stratum beneath the ground.
This is achieved by constructing vertical piers that penetrate through weaker soils and rest on more competent, load-bearing soil or rock layers.
Types of pier foundation
Masonry or concrete piers
These are typically constructed by excavating a hole in the ground and filling it with concrete or masonry blocks to create a stable foundation.
They are usually used for smaller structures or light loads, such as decks, porches, or small buildings.
Drilled caissons
These are deep foundation elements that are typically used for larger and heavier structures, such as high-rise buildings, bridges, and industrial facilities.
They are created by drilling a hole into the ground and filling it with concrete or reinforced steel to create a strong and stable foundation that can support the weight of the structure above.
Parts of the pier foundation
- Pier cap
- Pier
- Pile cap
- Piles
1. Pier Cap
The pier cap is the horizontal structural element that sits on top of the pier and supports the load from the superstructure. It is typically made of reinforced concrete and is designed to transfer the load from the superstructure to the pier.
2. Pier
The pier is the vertical element that supports the pier cap and transfers the load to the foundation soil. It is usually made of reinforced concrete, and its size and shape depend on the load it has to support.
3. Pile Cap
A pile cap is a structural element that sits on top of a group of piles and transfers the load from the superstructure to the piles. It is usually made of reinforced concrete and is designed to distribute the load evenly to each pile.
4. Piles
Piles are long, slender structural elements that are driven or drilled into the ground to transfer the load from the superstructure to the foundation soil. They can be made of steel or concrete, and their size and length depend on the load they have to support and the soil conditions.
Shapes and sizes details of the pier foundation
Here are some details about the shapes and sizes of pier foundations:
Concrete piers
Concrete piers are the most common type of pier foundation. They can be cylindrical or square in shape. The depth of the pier is determined by the load it is supporting and the soil conditions.
Helical piers
Helical piers are screw-like anchors that are drilled into the ground. They are typically used in areas where the soil is weak or unstable. The size and shape of helical piers can vary depending on the weight of the load they are supporting and the soil conditions.
Steel piers
Steel piers are similar to concrete piers but are made of steel instead. They can be round or square in shape.
Bell Pier Foundations
These are a variation of circular pier foundations that have a wider base to provide more stability in soft or loose soil conditions. The wider base also helps distribute the weight of the structure more evenly.
Where pier foundations are used
These types of foundations are often used in areas with unstable soil conditions, where traditional foundations may not be practical or safe.
They can also be used when the building is constructed on a hillside or other sloped terrain.
Advantages of pier foundation
1. Stability
These are designed to provide stability and support to structures that are built on them. They can support heavy loads and are often used for tall or multi-story buildings.
2. Versatile design options
These foundations offer a wide range of design options, with a variety of materials that can be used to increase the aesthetic view and remain within budget constraints.
3. Cost-effective
These foundations are often more cost-effective than other types of deep foundations, such as drilled shafts or driven piles. They require less excavation and materials, which can result in lower costs.
4. Reduced ground vibration
The construction of these foundations does not produce the ground vibration normally associated with driven piles, making it a quieter and less disruptive option.
5. Shorter construction time
These can be installed more quickly than other types of deep foundations, which can reduce construction time and costs.
6. Minimal soil disruption
This foundation causes minimal disruption to the soil environment, which is ideal for areas with sensitive ecological conditions. Existing roots and soil organisms remain mostly undisturbed, making it easier to restore the site to a natural state after the building’s useful life is over.
7. Better resistance to settling
These are less likely to settle or shift over time, which can result in a more stable and durable foundation for the structure.
Disadvantages of pier foundation
1. These foundations may not be suitable for all soil types. They may be difficult to construct in soils that are too soft or unstable, or in areas with a high water table. This can increase the cost and time required for construction.
2. The installation of piers demands meticulous supervision and quality control over all materials used in construction. This is essential to ensure the safety and stability of the foundation.
Uses of pier foundation
1. These foundations are commonly used in the construction of bridges, especially in areas with soft soil or high water tables. The piers can be constructed on land or in water and provide a stable base for the bridge to rest on.
2. These are also used in the construction of dams. Dams require a solid foundation to support the weight of the water and prevent leakage, and pier foundations are a popular choice due to their stability and durability.
3. Tall buildings, such as skyscrapers, often require deep foundations to support their weight. Pier foundations can be used in these cases, either as individual piers or in combination with other foundation types.
4. These are also used in the construction of offshore platforms and oil rigs. These structures require a stable base to support the weight of the equipment and withstand the forces of waves and currents.
5. In some cases, these types of foundations can be used to retrofit existing structures that were not originally built on a suitable foundation. By adding piers under the foundation, the load can be distributed more evenly and the structure can be stabilized.
FAQ
What is a pier foundation?
A pier foundation is a type of deep foundation that is used to transfer the structural load of a building or other large structure to a stable, load-bearing stratum beneath the ground.
When is a pier foundation used?
A pier foundation is typically used in situations where a traditional shallow foundation is not suitable due to poor soil conditions or where the weight of the structure is too great for a traditional foundation to bear.
What are the advantages of using a pier foundation?
Advantages of using a pier foundation include the ability to save time and money, ease of construction, minimal disruption to the soil environment, and the ability to install utilities easily.
What are the disadvantages of using a pier foundation?
Disadvantages of using a pier foundation include the need for careful supervision and quality control during construction, the requirement for adequate storage space for materials, and difficulty in construction in heavy flows of groundwater.
What types of structures are suitable for pier foundations?
Pier foundations are suitable for a wide range of structures, including bridges, dams, tall buildings, and other large structures.
Also read: Helical piles foundation, types, and uses
