A foundation is the thing that can be used to support a structure or building, by transmitting loads directly towards the underlying rock or soil. To be a useful foundation, it needs to satisfy two base requirements. First of all, it needs to provide adequate security against the failure of the supporting structure. Secondly, the settlement should not interfere in any way with the function of the structrure that is being built. Foundations, in general, can be separated into two primary types, shallow and deep.
Deep foundation is necessary for carrying the loads from a structure through fills and weak compressible soils into stronger, less moveable rocks or soils at depth. These foundations are low enough beneath the finishes surface of the ground that their base bearing capacity is not affected by the conditions of the surface. Usually, this refers to a depth of more than three meters below the finished ground level. Deep foundations can be useful for transferring the loading to a more competent and deeper strata if the soil at the surface of the ground is unsuitable
Basement foundations and Buoyancy rafts
Basement foundations are hollow structures that have been created to provide storage space or working space at a level below the ground. The design of these structures has been government by their requirements as a functional space, rather than as a consideration of the most efficient way to resist hydrostatic or external pressure.
Buoyancy rafts, or hollow box foundations are substructures that are hollow, and designed to provide a semi-buoyant or buoyant structure, under which the loading on the soil can be reduced to a lower intensity. Buoyancy rafts can be created like sunk caissons, or can be constructed in place of an open excavation.
Caissons, cylinders and shaft foundations
Another option for deep foundations comes in the form of caissons. Caissons are structures that are hollow, similar to buoyancy rafts, that have been created for the purpose of being constructed somewhere near the surface of a structure, before they can be sunk down as a single unit to the level they are needed at. Similarly, the term “cylinder” in this context refers to small caissons that contain only a single cell.
Shaft foundations, on the other hand, have been constructed deep within excavations that are supported by lining. These foundations are constructed in place as they are filled with pre-fabricated load-bearing units or concrete to form the finished product.
Finally, pile foundations are foundations that rely upon driven piles. These are often groups of piles that are connected by a large concrete block known as a pile cap. These driven piles distribute loads evenly across the piles that would otherwise be too large for a single pile to bare. Often, isolated piles and pile caps can be connected through grade beams in order to tie the elements of the foundation together. The lighter elements of the structure will bear down on the grade beams, whereas heavier factors bear upon the pile cap.