Floating raft is a land-based building

foundation Foundation may refer to: * Foundation (nonprofit), a type of charitable organization ** Foundation (United States law), a type of charitable organization in the U.S. ** Private foundation, a charitable organization that, while serving a good cause ...

that protects it against settlement and

liquefaction In materials science, liquefaction is a process that generates a liquid from a solid or a gas or that generates a non-liquid phase which behaves in accordance with fluid dynamics. It occurs both naturally and artificially. As an example of th ...

of soft soil from seismic activity. It was a necessary innovation in the development of

tall buildings A skyscraper is a tall continuously habitable building having multiple floors. Modern sources currently define skyscrapers as being at least or in height, though there is no universally accepted definition. Skyscrapers are very tall high-ri ...

in the wet soil of

Chicago (''City in a Garden''); I Will , image_map = , map_caption = Interactive Map of Chicago , coordinates = , coordinates_footnotes = , subdivision_type = List of sovereign states, Count ...

in the 19th century, when it was developed by

John Wellborn Root John Wellborn Root (January 10, 1850 – January 15, 1891) was an American architect who was based in Chicago with Daniel Burnham. He was one of the founders of the Chicago School style. Two of his buildings have been designated a National ...

who came up with the idea of interlacing the concrete slab with steel beams. The earliest precursor to the modern version may be the concrete rafts developed for the building of

Millbank Prison Millbank Prison or Millbank Penitentiary was a prison in Millbank, Westminster, London, originally constructed as the National Penitentiary, and which for part of its history served as a holding facility for convicted prisoners before they were t ...

in 1815 by Robert Smirke. For a floating raft foundation – or simply "floating foundation" – the foundation has a volume such that, if 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 not even

friction pile A deep foundation is a type of foundation that transfers building loads to the earth farther down from the surface than a shallow foundation does to a subsurface layer or a range of depths. A pile or piling is a vertical structural element ...

s will support the

building load A building, or edifice, is an enclosed structure with a roof and walls standing more or less permanently in one place, such as a house or factory (although there's also portable buildings). Buildings come in a variety of sizes, shapes, and funct ...

, these types of foundation are the final option and makes the building behave like a boat: obeying

Archimedes' principle Archimedes' principle (also spelled Archimedes's principle) states that the upward buoyant force that is exerted on a body immersed in a fluid, whether fully or partially, is equal to the weight of the fluid that the body displaces. Archimedes' ...

, buoyed up by the weight of the earth displaced in creating the foundation.

See also