Strip foundations

Strip foundations consist of a continuous strip, usually of concrete, formed centrally under load bearing walls. This continuous strip serves as a level base upon which the wall is built and is of such a width as is necessary to spread the load on the foundations to an area of subsoil capable of supporting the load without undue compaction. Concrete is the material principally used today for foundations as it can readily be placed, spread and levelled in foundation trenches, to provide a base for walls, and it develops adequate compressive strength as it hardens to support the load on foundations The width of a concrete strip foundation depends on the bearing capacity of the subsoil and the load on the foundations. The greater the bearing capacity of the subsoil the less the width of the foundation is required for the same load. This is almost the simplest foundation used. Further options are required for less suitable ground conditions which range from raft foundations, basically a reinforced slab covering the whole of the building footprint to a floating raft foundation. A floating raft foundation is where the foundation has a volume such that were that volume filled with soil, it would be equal in weight to the total weight of the structure. When the soil is so soft that even friction piles will not support the building load, the final option is the use of a floating foundation, making the building like a boat that obeys Archimedes’ principle—it is buoyed up by the weight of the earth displaced in creating the foundation. Used in areas where the risk of ‘liquefication’ exists. In the case of piled foundations a strip foundation may be used to lock in the pile caps to create a level foundation to spread the load applied.