Foundations and retaining structures
The foundation is the portion of the building or structure that transfers the building’s loads to the soil or rock beneath the building. Foundations are designed to resist anticipated loads (which are based on the most current building code at the time the building is designed) that may occur during the life of the building, same as the other structural components of the building. To assess physical properties, which in‰uence the foundation selection and design param-
eters for a proposed building, the designer must understand the subsurface soil conditions. This requires speci‡c testing and sampling of the soil and rock, if present, to determine allowable bearing capacities. There are essentially three types of foundation systems commonly used in most building
construction, depending upon existing site and soil conditions. They are spread footings, mat-slab foundations, and deep foundations. Spread footings are typically designed for residential or moderate-height buildings with
‡rm soil conditions present at a minimum. They are the most typical type of foundation used in building construction. Mat foundations are more complicated because they are a combined footing, which support both column and wall loads and redistribute the loads to the soil in a uniform bearing stress. Deep foundations are the most robust and versatile foundation system of the three, because of its adaptability to almost any site for almost any type of building structure. Deep foundations are designed to utilize the stiffer soil strata found deeper below the surface as well as bedrock if accessible. Deep foundations can also be designed to take advantage of friction developed on the surface of the foundation component in weak soils.