Foundation is the lowest parts of buildings and structures, usually below the. ground level, that is serve to transfer. the loads from the buildings or structures to a natural or artificial bedding.
The type of foundation chosen will depend on the following:
a. Geological engineering and hydrogelogical conditions at the construction site
b. The purpose and design of the building or structure.
c. The magnitude of the load imposed on the foundation
d. And the production capacities of the construction organization.
The depth of the foundation is chosen according to the
a. Properties and nature of the soil strata
b. The ground water level(with allowance for variations during the construction and use of the structure)
c. The magnitude and the nature of the loads acting on the foundation
d. The depth of underground communication lines and of the foundations under machines and equipment
e. The climatic characteristics of the construction region
The chosen depth of the foundation must be sufficient to ensure the stability of the bedding and to eliminate the possibility of the earth heaving during freezing and settling during thawing.
The Modern Foundation types are:
They are often called footings, and are usually embedded about a meter or more into the soil.
The dimensions of a footing are determine according to bedding conditions so that the average pressure on the bedding does not exceed a design value that depends on the nature and properties of the earth, the depth of the foundation and the design features of the structure.
In the assigning of dimensions for the footing of a foundation, allowance is made for the maximum vertical deformations(settling and raising) under which the necessary rigidity of the structures above the foundation will be retained and under which the building will still conform to engineering or architectural requirements.
One common type of a shallow foundation is the spread footing which consists of strips or pads of concrete or other materials which extend below the frost line and in turn transfer the weight from walls and columns to the soil or the bedrock.
Another common type of shallow foundation is the slab on grade foundation where the weight of the building is transferred to the soil through a concrete slab placed at the surface.
Slab on grade foundations can be reinforced mat slabs, they range from 25cm to several meters thick.
Shallow foundations are generally constructed in excavations or trenches. A common method is to pack down the area under isolated foundations or trenches under continuous foundations with tampers.
About 80% of residential and industrial buildings have shallow foundations.
2. DEEP FOUNDATIONS
A deep foundation is used to transfer the load of a structure down through the upper weak layer of topsoil to the stronger layer of subsoil below.
Deep foundations are laid with drill-filling and driven piles(pile foundation) deep piers(driven or made of casings) and caissons.
There are different types of deep foundations including impact driven piles, drilled shafts, caissons, helical piles, geo-piers and earth stabilized columns.
Their use is recommended for weak, subsiding, swelling and other soils having special properties and a high ground-water level, particularly in the building of bridges and deep underground structures.
DESIGN OF FOUNDATIONS
Foundations are designed to have an adequate load bearing capacity with limited settlement by a geotechnical engineer and the footing itself may be designed structurally by a structural engineer.
Design calculations for foundations are computed for strength and the size of cracks that may develop.
The primary design concerns are settlement and bearing capacity.
We have two types of settlement namely, total settlement and differential settlement.
Differential settlement is when one part of a foundation settles more than another part and it can cause problems to the structure the foundation is supporting.