Deep foundations are an essential element in construction projects that involve transferring loads from a structure through soft and compressible soils or fills to more robust and less compressible soils or rocks at a greater depth. They are typically required when the base bearing capacity of the soil near the surface is not adequate to support the weight of the structure.
The primary function of deep foundations is to provide structural stability by anchoring the foundation deep beneath the ground surface. This is achieved by placing the foundation at depths greater than three meters below the finished ground level, where the soil conditions are less likely to be affected by surface conditions. By doing so, the foundation’s base bearing capacity can remain unaffected by the unstable or unsuitable soils that may exist near the surface.
Deep foundations can also be used to transfer loads to a deeper and more competent strata at depth. This is particularly useful when the soil near the surface is unsuitable for supporting the structure’s weight. By transferring the loading to a deeper strata, the foundation can provide a stable base for the structure while also reducing the risk of settlement or subsidence over time.
Overall, deep foundations are an integral part of construction projects that require a stable and durable foundation. They provide the necessary support to transfer loads through soft and compressible soils to more robust and less compressible soils or rocks at a greater depth. This ensures that the structure remains stable and secure over time, even in challenging soil conditions.
Types of Deep Foundation
The types of deep foundations in general use are as follows:
- Basements
- Buoyancy rafts (hollow box foundations)
- Caissons
- Cylinders
- Shaft foundations
- Pile foundations
1. Basement foundation
The text is describing underground structures that are designed to serve as work or storage spaces. These structures are characterized by their hollow nature, which allows for usable space below ground level. The design of these structures is primarily driven by their intended function, rather than by the most efficient method of resisting external pressures from the earth and water. As such, their construction involves excavation of the ground and building the structure within the resulting open space.
2. Buoyancy Rafts (Hollow Box Foundations)
Buoyancy rafts are structural systems that are intended to decrease the net loading on the soil by creating a buoyant or semi-buoyant substructure. These rafts can be constructed as hollow substructures that are designed to be sunk like caissons, or they can be built in situ in open excavations. The primary purpose of these rafts is to reduce the intensity of the loading on the soil, thereby preventing any damage or instability that could occur due to excessive loading. By reducing the load on the soil, buoyancy rafts can improve the overall stability and safety of a structure. Additionally, these rafts can be designed to suit the specific needs of a particular project, making them a versatile and effective solution for a variety of construction projects.
3. Caissons Foundations
Caissons are a type of hollow substructure that are intended to be constructed either on the surface or close to it. These structures are then sunk as a single unit to the level where they are needed. This sinking process is accomplished by removing the water or soil from inside the caisson, causing it to gradually descend to its final location.
Caissons are commonly used in construction projects that require a foundation to be built in areas with deep water or soil conditions that are not suitable for traditional foundation methods. They are also used to create structural support for buildings or other structures that are built on soft or unstable ground.
By using caissons, construction projects can avoid the need for expensive and time-consuming excavation work. They can also provide a stable foundation that is resistant to soil liquefaction and other types of foundation failures. Overall, caissons are an important engineering solution for constructing buildings and other structures in challenging environments.
4. Cylinders
Cylinders are small single-cell caissons.
5. Drilled Shaft foundations
Shaft foundations are a type of foundation that involves constructing deep excavations and using lining for support. These excavations are then filled with concrete or pre-fabricated load-bearing units. This type of foundation is known as a Drilled Shaft foundation and is commonly used in construction. The process involves creating a deep hole and filling it with concrete or other load-bearing materials. The lining provides support during the construction process and ensures that the foundation is strong and stable. This type of foundation is typically used in large-scale construction projects where stability and strength are paramount.
6. Pile foundations
Pile foundations are structural elements that are used to support heavy loads by transferring them to deeper, more stable layers of soil or rock. They are typically elongated, slender members that are installed either by driving pre-formed units into the ground, or by drilling tubes or boreholes and then filling them with concrete.
One common method of pile foundation construction involves driving pre-formed units, such as steel or concrete piles, into the ground until they reach the desired depth. These pre-formed units are typically designed to resist both compressive and tensile forces, and are often reinforced with steel or other materials to improve their strength and durability.
Another method of pile foundation construction involves drilling tubes or boreholes into the ground, and then filling them with concrete to create a solid, load-bearing foundation. These tubes or boreholes may be lined or unlined, depending on the soil and rock conditions at the site, and may be drilled using a variety of different techniques and equipment.
Regardless of the method used, pile foundations are a critical component of many construction projects, providing a stable, secure base for structures ranging from buildings and bridges to offshore oil platforms and other large-scale infrastructure projects. By transferring loads to deeper layers of soil or rock, pile foundations help to ensure the long-term stability and safety of these structures, even in the face of changing soil conditions or other external factors.
