Types Of Footings Used In Building Construction
What Is Foundation?
The foundation is the lowest part of a structure that transfers the load into the supporting soil. Its main purpose is to distribute the total weight of the superstructure over a large area of soil. There are various types of foundations used in construction, which are described below.
Types Of Footings
- Shallow Foundation.
- Deep Foundation.
1. Shallow Foundation
When the depth of the foundation is equal to or less than its width, it is called a shallow foundation.
a). Isolated footing
b). Combined footing
c). Strip foundation
d). Raft or mat foundation
a). Isolated footing
Isolated footing is used to support individual columns. It can be either stepped or have projections in the concrete base. It is provided in cases where the soil has good bearing capacity at shallower depths. Isolated footings are relatively easy to construct.
b). Combined footing
Combined footing is a type of foundation that consists of a common footing provided to two columns. The shape of the footing can be either rectangular or trapezoidal, depending on the design requirements. Combined footings are used when the columns are close to each other and their individual footings would overlap or be too close. This type of footing helps distribute the load from both columns to a larger area of soil.
c). Strip foundation
This type of footing distributes the weight of a load-bearing wall across the area of the ground. The footing usually has twice the width of the load-bearing wall, sometimes even wider.
d). Raft or mat foundation
A raft foundation is a type of foundation that consists of a dense reinforced concrete slab covering the entire bottom area of a structure. It is used in areas where the soil has low bearing capacity and the structural loads are heavy. The raft foundation distributes the load of the structure over a larger area, reducing the pressure on the soil. It is particularly effective in mitigating differential settlement and providing stability in challenging soil conditions. Raft foundations are commonly used in buildings and structures such as high-rise buildings, warehouses, and industrial facilities.
Deep Foundation
A deep foundation is a type of foundation that is placed at a significant depth below the ground surface. It is designed to transfer the structural loads to the underlying soil or rock at greater depths. The depth to width ratio of a deep foundation is typically greater than 4 to 5, meaning that the depth is significantly greater than the width. Deep foundations are used when the soil near the surface is not able to support the loads of the structure, either due to weak or unstable soil conditions. Common types of deep foundations include pile foundations and drilled shaft foundations. These foundations provide stability and support for structures such as tall buildings, bridges, and structures on soft or unstable soils.
Deep foundation can be further classified into three categories:
Pile Foundation.
Cofferdams.
Caisson Foundation.
1. Pile Foundation
A pile foundation is a type of foundation where long, slender members made of materials such as wood, concrete, or steel are driven or inserted into the ground to transfer the load of a structure to the soil or rock below. Pile foundations are used when the soil at shallow depths is unable to support the loads imposed by the structure. The piles are driven or installed deep into the ground until they reach a stable layer of soil or rock that can bear the load. The load is then transferred from the structure to the piles, which distribute it to the surrounding soil or rock. Pile foundations are commonly used in the construction of tall buildings, bridges, and structures on soft or weak soils. They provide stability and support, preventing excessive settlement or failure of the structure.
2. Cofferdams
3. Caisson Foundatio
A cofferdam is a temporary structure that is built to create a dry working area in order to facilitate construction activities in waterlogged or wet areas. It is typically constructed using sheet piles, concrete, or other suitable materials to form a watertight enclosure. The purpose of a cofferdam is to exclude water from a specific area, allowing construction work to be carried out on a dry surface. Cofferdams are commonly used in various construction projects, such as bridge construction, dam construction, or for creating foundations in water bodies. Once the construction work is completed, the cofferdam is typically removed, and the water is allowed to fill the area again.
