Foundation engineering refers to the engineering discipline that designs how a structure that transfers loads to the earth. Foundations are generally divided into two categories: shallow foundations and deep foundations. Foundation engineering requires careful consideration of many factors that can influence the behavior of the structure.
Shallow foundations are, usually, embedded from one to two meters beneath the final finish elevation. Spread footings are one of the most common types of shallow foundations. Spread footings consist of strips or pads of concrete (or other materials) which extend below the frost line and transfer the building loads to the underlying soil or rock. Another type of shallow footing is the slab-on-grade footing where the building loads are transferred to the soil through a concrete slab placed at the surface. Shallow foundations mainly work by distributing loads on a greater area where the contact pressure is limited within acceptable limits.
A deep footing is an engineered structure used to transfer load from a structure to stronger deeper soil layers or bedrock. Different types of deep foundations include driven piles, drilled piles, drilled shafts, caissons, piers, earth stabilized columns, and helical piles. Historically, timber piles were amongst the first used. Today most piles are constructed with steel , reinforced concrete, or pre-tensioned concrete.
Footings must be designed to have an adequate load capacity with limited settlement by a geotechnical engineer, while the structural design is performed in collaboration with a structural engineer.
The primary design concerns are total and differential settlements, and bearing capacity. Differential settlement refers to conditions is when significantly different settlements are experienced in different parts of the foundation. Excessive differential settlement can cause severe cracking problems to the supported structure. It is necessary that a foundation is not loaded beyond its bearing capacity otherwise the foundation will "fail".
Other design considerations include scour and frost heave. Scour is when flowing water removes supporting soil from around a footing (like a pier supporting a bridge over a river), while frost heave occurs when water in the ground freezes which causes the ground to expand (and collapse when the ground thaws).
Foundation design should be carried out by highly-qualified licensed engineers.
Engineers must be well-trained and experience with the local conditions and need to balance with the needs of safety and economy.
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