The function of a foundation is to transfer the structural loads reliably from a building into the ground. Every building needs a foundation of some kind: A backyard toolshed will not be damaged by slight shifting of its foundation and may need only wooden skids to spread its load across an area of the ground surface suffi cient to support its weight. A wood-framed house needs greater stability than a toolshed, so its foundation reaches through the unstable surface to underlying soil that is free of organic matter and unreachable by winter frost. A larger building of masonry, steel, or concrete weighs many times more than a house, and its foundations pierce the earth until they reach soil or rock that is competent to carry its massive loads; on some sites, this means going 100 feet (30 m) or more below the surface.
Because of the variety of soil, rock, and water conditions that are encountered below the surface of the ground and the unique demands that buildings make upon their foundations, foundation design is a highly specialized fi eld combining aspects of geotechnical and civil engineering that can be sketched here only in its broad outlines.
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