What is foundation
A foundation is a substructure component. the building structure that transfers its gravity load into the earth. and the total superstructure load is transferred into the foundation of the earth. the foundation is a reinforced cement concrete element.
The selection of a foundation system for a structure depends on the size, type and importance of the structure, the properties of the subsoil, the design of the structure and the overall cost, tempered by the engineering judgment of the designer.
There are different types of foundations used in the structure, the foundation types are,
Foundations types
the foundation is divided into two categories.
- Shallow foundation
- Deep foundation
Shallow foundation
A shallow foundation is the most commonly used foundation in building construction, a shallow foundation is constructed where the soil layer at a shallow depth of up to 1.5m can support the structural loads. The shallow foundation depth is low compared to the deep foundation. shallow foundation types following are,
The foundation is provided for structures of moderate height, built on sufficiently firm dry ground. it is used up to a depth of 3 m to 4m. it is convenient above the water table.
- Wall footing/strip footing
- Spread footing
- Isolated footing ( stepped footing, sloped footing, pad footing )
- Combined footing
- Strapped footing
- Eccentric footing
- Mat or Raft footing
Footing
they are typically made of concrete with rebar reinforcement that has been poured into an excavated trench. the purpose of footing is to support the foundation and prevent settlement. footing is an important part of foundation construction. Different types of footing are to be used in the foundation ( strip, spread, isolated, steeped, combined, slopped, strapped, eccentric ).
Wall footing/strip footing
A wall footing or strip footing is a continuous strip of concrete that spread the weight of a load-bearing across an area of soil. use in a situation where load-bearing capacity is low, a site that may be subjected to unequal settlement or where the subsoil is not uniform. this footing comes under a shallow foundation. this is the most common type.
it is mainly used where you have a strong soil base and a non-water-logged area. most small buildings of just a floor are constructed with this type of foundation
Spread footing
Spread footing is a greater base width in rectangular or square shape it evenly spread the structure load into the earth. The widened part of a foundation spread a column load over a broader area of soil.
its design is based on soil-bearing capacity and column load
Spread footing and wall footing is used for individual columns, wall and bridge piers. where the soil-bearing layer is within 3 meters (10 feet) from the ground surface. soil bearing capacity must be sufficient to support the structure’s weight over the base area of the structure.
spread footing is divided into four types;
- Rigid spread footing
- Eccentric rigid spread footing
- Flexible spread footing
- Eccentric spread footing
Rigid spread footing and Eccentric spread footing
Rigid spread footing is used when uniform settlement in soil (Every point will be settled uniformly in soil) the column comes in the centre of the footing base and a certain height slope will be given in above the footing and below the column area.
In eccentric spread footing, the only difference between rigid and eccentric rigid footing is the column position is slightly changed in the centre line of the footing.
Flexible spread footing and Eccentric spread footing
Flexible spread footing is used when no uniform settlement in soil (Every point will be settled differently in soil) The column comes in the centre of the footing base and the slope will be not given.
Eccentric spread footing, the only difference in column position. the position of the column is slightly changed in the centre line of the footing.
Isolated footing
Isolated footing is a single/independent footing also known as a pad or spread footing. it’s under comes in a shallow foundation. to carry and spread concentrated load into the uniform load. The isolated footing function is the same as the spread footing. There are some types of isolated footing used in the structure. followings are,
- Pad or Flat footing
- Slopped footing
- Stepped footing
Pad or Flat footing
Pad footing is also known as spread footing. all functions are the same in both types of footing.
Slopped footing
Slopped footing function is the same as the rigid spread footing. the slope projection is used in this footing because of rigid and load distribution
Stepped footing
Two or more step projection is used for this footing. the column load is converted into through steps and footing base.
Combined footing
A combined footing is constructed with two or more columns in a single footing. Both column loads are transferred into the single footing and the soil. A combined footing is mostly used when the two columns are nearly designed and the less area for excavation. the combined footing is constructed in two types ( Rectangular and Trapezoidal).
Eccentric footing
The eccentric footing comes in wall footing and spread footing. that must resist a moment in addition to the axial column load and it has the shape of the shoe. Sometimes, the slope is provided in the eccentric footing to resist overturning and the strap beam is constructed between two eccentric footings.Â
this is used in cases where restrictions exist on the usable ground area outside of the build-up foundation area such as perimeter boundaries. the building is exactly the boundary connecting the building.
Strap footing
Strap footing is a type of combined footing, but it’s connected to two or more footings with a Reinforced cement concrete beam. this type of beam is called a strap beam.
it is used to help distribute the weight of either heavily or eccentrically loaded column footing to adjacent footing, a strap footing is often used in conjunction with a column that is located along a building’s property to lot line
A strap footing connects two or more footing under a column together using of strap beam, strap footing is a footing like a concrete slab that spread the load of the load-bearing wall above it.
Mat or Raft footing
A raft foundation is also called a mat foundation. Is essentially a continuous slab resting on the soil that extends over the entire footprint of the building, thereby supporting the building and transferring its weight to the ground, this reduces the stress on the soil.
A raft foundation is a reinforced concrete slab under the whole of a building or extension floating on the ground and raft folate on water.
This type of foundation spread the load of the building over a large area than that other foundation, lowering the pressure on the ground.
Deep foundation
When the soil available at a reasonable depth of less than, say, 3 to 6 meters is not having the desired bearing capacity. A deep foundation is used
A deep foundation is a second type of foundation, that transfer the building load to the earth from down the surface. The surface that a shallow foundation depth to a subsurface layer or a range of depth. The foundation depth is high compared to shallow foundation depth. some deep foundation types are;
- Basement Foundation
- Buoyant foundation
- Caissons foundation
- Drilled shaft foundation
- Pile foundation
Basement Foundation
A basement foundation is an architectural structure, that secures a house or other building above a floor below ground level in addition to added storage space, the basement also offers protection against flooding and added insulators and climate control.
Buoyant foundation
A buoyant foundation is a type of amphibious foundation in which an existing structure is retrofitted to allow it to float as high as necessary during floods while remaining on the ground in normal conditions.
where used- buoyancy rafts or hollow foundations are also known as the floating foundation a type of deep foundation used in building construction on soft and weak soil.
why buoyant foundation used– Buoyant foundation is a cost-effective adaptive flood risk reduction strategy. that worked in sync with a reason for natural flood cases. when flooding occurs the buoyancy blocks lift the house with structure subsurface transferring the force between the house, block and posts.
Caisson foundation
It is a form of a deep foundation constructed above ground level that sunk to the required level by excavating or dredging materials from within the caisson ( caisson also sometimes called piers ) are created by auguring a deep hole into the ground and then filling it with concrete. A caisson is a watertight retaining structure that functions as a bridge pier, caisson foundation also known as a pier foundation is mainly used in the construction of dams or wells or ship repairs
this supplementary is a hollow box or cylinder that is sunk into the ground to the desired.
Drilled shaft foundation
Drilled shafts also referred to as drilled piers, caissons or boxed piles, are deep foundation solutions. used to support structures with large axial areas lately load by excavating cylinders as shafts inside the ground and filling them with concrete.
Pile foundation
A pile foundation is defined as a series of columns constructed or inserted into the ground to transmit load to a lower level of subsoil. A pile is a long cylinder made up of strong materials such as concrete. piles transfer the loads from the structure to hard strata rocks or soil with high bearing capacity.
A Pile foundation is needed in the area where the strength constructed is large and heavy and the soil underlying is weak. In areas where settlement issues are common due to soil liquefaction or water table issue, Then pile foundation is the best one
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