Types of Deep Foundation – Foundations are broadly classified into shallow foundations and deep foundations. This article is a total overview of Deep Foundations and types of Deep Foundations.
What is a deep foundation?
The foundations having the depth more than the width are called deep foundations. Deep foundations are proposed when the sub soil strata lacks the safe bearing capacity to handle the loads induced by the structure. In such a case the founding level of the foundations are moved to a deeper area with required bearing capacity. The loads on the structure are transferred vertically into the ground.
Deep foundations are preferred when the subsurface bearing capacity of the soil is not competent to withstand the proposed loads coming on the structure. In that case, the loads are transferred to a designated design depth or rock/hard strata. The strata is at a deeper location below the ground level capable of negotiating the loads without failure.
Types of Deep Foundation
Deep foundations are adopted for many applications. They are preferred as the safest option for transferring heavy loads on soil strata with less bearing capacities. Common types of Deep foundation in use are as follows.
- Basement foundations
- Caissons Foundation
- Hollow Box Foundation or Buoyancy foundations
- Drilled shaft foundations
- Pile foundations
Types of deep foundation – Basement foundations
Basement foundations are substructure foundations designed to account for parking areas, underground tanks, Electrical systems, and storage spaces beneath a building below ground level. They are mostly adopted in high rise residential buildings and commercial buildings. Basement foundations cater to the functional requirements of parking and storage.
Caisson foundation is a water-retaining structure that serves as a working space to work on the foundations of piers. They are box-type structures made of timber, steel, concrete, etc. Caisson Foundation is sunken by excavating the earth within the foundation. Caissons are prefabricated above the ground level or water level and are sunk to the founding level as one single unit. They are constructed to facilitate excavation and related works for foundations of the dock structure, bridges, jetty, piers, foreshore protection, etc. These structures later form an integral part of the main structural components.
Hollow box foundation or Buoyancy foundations
The concept of a hollow box foundation is to design a structure with minimal or no impact on the original stress of soil before commencing excavation. Required overburden as per the design is removed and superstructure loads are transferred to the ground. These types of foundations are known as Buoyancy foundations because they adopted the principle of a ship floating in the water, where the displaced water equals the weight of the ship.
Drilled shaft foundation
The drilled shaft is a versatile foundation system used extensively nowadays. These foundations are also known as a drilled pier, drilled caisson, bored pile, etc. The basic concept is excavating a cylindrical shaft and casting after putting necessary reinforcements. Diameters ranging from 1-3 mtr and depths up to 100 mtrs are preferred for drilled Shafts can be drilled from diameter ranging from 1 to 3 mtr and a depth of 100 mtrs normally. But higher depth and diameter are also possible nowadays. These types of foundations can replace driven piles to some extent where a single drilled shaft can replace a group of pile.
Pile foundations are long slender members, which can be concrete, steel or any other material used for transferring the loads of a structure when the subsoil lacks the bearing capacity . The pile foundations transfer the load vertically through the less denser top layer to a high denser soil/rock layer which can negotiate the loads without failure.
Video showing different types of shallow foundations