Foundation (engineering)

Shallow foundations of a house versus the deep foundations of askyscraper.

A foundation (or, more commonly, foundations) is the element of an architectural structure which connects it to the ground, and transfers loads from the structure to the ground. Foundations are generally considered either shallow or deep. Foundation engineering is the application of soil mechanics and rock mechanics (Geotechnical engineering) in the design of foundation elements of structures.

Historic foundation types

The simplest foundation, a padstone. Latvian Ethnographic Open Air Museum

Earthfast or post in ground construction

Buildings and structures have a long history of being built with wood in contact with the ground. Post in ground construction may technically have no foundation. Timber pilings were used on soft or wet ground even below stone or masonry walls In marine construction and bridge building a crisscross of timbers or steel beams in concrete is called grillage.

Padstones

Perhaps the simplest foundation is the padstone, a single stone which both spreads the weight on the ground and raises the timber off the ground. Staddle stones are a specific type of padstone.

Stone foundations

Dry stone and stones laid in mortar to build foundations are common in many parts of the world. Dry laid stone foundations may have been painted with mortar after construction. Sometimes the top, visible course of stone is hewn, quarried stones. Besides using mortar, stones can also be put in a gabion.One disadvantage is that if using regular steel rebars, the gabion would last much less long than when using mortar (due to rusting). Using weathering steel rebars could reduce this disadvantage somewhat.

Rubble trench foundations

Main article: Rubble trench foundation

Rubble trench foundations are a shallow trench filled with rubble or stones. These foundations extend below the frost line and may have a drain pipe which helps groundwater drain away. They are suitable for soils with a capacity of more than 10 tonnes/m² (2,000 pounds per square foot)...

Gallery of shallow foundation types

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  Drawing of Poteaux-en-Terre post in ground type of wall construction (this example technically called pallisadeconstruction) in the Beauvais House in Ste Genevieve, Missouri, U.S.A.
 
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  PSM V24 D321 A primitive stilt house in Switzerland on wood pilings.
 
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  A granary on staddle stones, a type of padstone
 
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  Black Eagle Dam - cross-section of construction plans for 1892 structure
 
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  Davis House dry-laid stone foundation ruin, Gardiner, NY
 
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  A basic type of rubble trench foundation
 
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  Typical residential poured concrete foundation, except for the lack of anchor bolts. The concrete walls are supported on continuous footings. There is also aconcrete slab floor. Note the standing water in the perimeter French draintrenches.

Modern foundation types

Shallow foundations

Main article: Shallow foundation

Shallow foundation construction example

Shallow foundations, often called footings, are usually embedded about a metre or so into soil. One common type is the spread footing which consists of strips or pads of concrete (or other materials) which extend below the frost line and transfer the weight from walls and columns to the soil or bedrock.

Another common type of shallow foundation is the slab-on-grade foundation where the weight of the building is transferred to the soil through a concrete slab placed at the surface. Slab-on-grade foundations can be reinforced mat slabs, which range from 25 cm to several meters thick, depending on the size of the building, or post-tensioned slabs, which are typically at least 20 cm for houses, and thicker for heavier structures.

Deep foundations

Main article: Deep foundation

A deep foundation is used to transfer the load of a structure down through the upper weak layer of topsoil to the stronger layer of subsoil below. There are different types of deep footings including impact driven piles, drilled shafts, caissons, helical piles, geo-piers and earth stabilized columns. The naming conventions for different types of footings vary between different engineers. Historically, piles were wood, later steel, reinforced concrete, and pre-tensioned concrete.

Monopile foundation

Main article: Monopile foundation

A monopile foundation is a type of deep foundation which uses a single, generally large-diameter, structural element embedded into the earth to support all the loads (weight, wind, etc.) of a large above-surface structure.

A large number of monopile foundations have been utilized in recent years for economically constructing fixed-bottom offshore wind farms in shallow-water subsea locations. For example, a single wind farm off the coast of England went online in 2008 with over 100 turbines, each mounted on a 4.74-meter-diameter monopile footing in ocean depths up to 16 metres of water.