Deep foundations are used when the surface soils are not capable of supporting the loads of a structure. Two common types of deep foundations are replacement and displacement foundations.
1. Replacement foundations:
Replacement foundations are created by removing the soil beneath a structure and replacing it with concrete or other materials. This creates a solid, stable foundation that can support the weight of the structure.
Illustration: The process of creating a replacement foundation begins by excavating the soil beneath the structure, leaving a large hole. The hole is then filled with concrete, which is allowed to cure and harden. The concrete provides a solid base for the structure to rest on, ensuring that it is stable and secure.
2. Displacement foundations:
Displacement foundations work by pushing soil aside as they are installed, creating a cavity in the ground that is then filled with concrete. These foundations are often used when soil conditions are too difficult to excavate or when a more efficient installation method is desired.
Illustration: The process of creating a displacement foundation involves driving a steel pile or tube into the ground. The pile is typically filled with concrete as it is being driven, creating a cavity in the soil. Once the pile has reached the desired depth, it is left in place, and the cavity is filled with concrete. This creates a solid, stable foundation that can support the weight of the structure.
In summary, both replacement and displacement deep foundations are effective methods for creating stable foundations for structures when the soil conditions are not suitable for shallow foundations. The choice of foundation type depends on the specific site conditions, load requirements, and project budget.