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In engineering, a foundation is the element of a
structure A structure is an arrangement and organization of interrelated elements in a material object or system, or the object or system so organized. Material structures include man-made objects such as buildings and machines and natural objects such as ...
which connects it to the ground, transferring loads from the structure to the ground. Foundations are generally considered either shallow or
deep Deep or The Deep may refer to: Places United States * Deep Creek (Appomattox River tributary), Virginia * Deep Creek (Great Salt Lake), Idaho and Utah * Deep Creek (Mahantango Creek tributary), Pennsylvania * Deep Creek (Mojave River tributary), C ...
. Foundation engineering is the application of
soil mechanics Soil mechanics is a branch of soil physics and applied mechanics that describes the behavior of soils. It differs from fluid mechanics and solid mechanics in the sense that soils consist of a heterogeneous mixture of fluids (usually air and wat ...
and
rock mechanics Rock mechanics is a theoretical and applied science of the mechanical behavior of rock and rock masses; compared to geology, it is that branch of mechanics concerned with the response of rock and rock masses to the force fields of their physical env ...
(
geotechnical engineering Geotechnical engineering is the branch of civil engineering concerned with the engineering behavior of earth materials. It uses the principles of soil mechanics and rock mechanics for the solution of its respective engineering problems. It als ...
) in the design of foundation elements of structures.


Purpose

Foundations provide the structure's stability from the ground: * To distribute the weight of the structure over a large area in order to avoid overloading the underlying soil (possibly causing unequal settlement). * To anchor the structure against natural forces including earthquakes, floods, droughts, frost heaves, tornadoes and wind. * To provide a level surface for construction. * To anchor the structure deeply into the ground, increasing its stability and preventing overloading. * To prevent lateral movements of the supported structure (in some cases).


Requirements of a good foundation

The design and the construction of a well-performing foundation must possess some basic requirements: * The design and the construction of the foundation is done such that it can sustain as well as transmit the dead and the imposed loads to the soil. This transfer has to be carried out without resulting in any form of settlement that can cause stability issues for the structure. *Differential settlements can be avoided by having a rigid base for the foundation. These issues are more pronounced in areas where the superimposed loads are not uniform in nature. *Based on the soil and area it is recommended to have a deeper foundation so that it can guard any form of damage or distress. These are mainly caused due to the problem of shrinkage and swelling because of temperature changes. *The location of the foundation chosen must be an area that is not affected or influenced by future works or factors.


Historic types


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 A post in ground construction, also called earthfast or hole-set posts, is a type of construction in which vertical, roof-bearing timbers, called posts, are in direct contact with the ground. They may be placed into excavated postholes, driven ...
construction may technically have no foundation.
Timber pilings Piling foundations support many historic structures such as canneries, wharves, and shore buildings. The old pilings present challenging problems during restoration as they age and are destroyed by organisms and decay. Replacing the foundation enti ...
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 Staddle stones (variations include steddle stones) were originally used as supporting bases for granaries, hayricks, game larders, etc. The staddle stones lifted the granaries above the ground thereby protecting the stored grain from vermin and wa ...
are a specific type of padstone.


Stone foundations

Dry stone Dry stone, sometimes called drystack or, in Scotland, drystane, is a building method by which structures are constructed from stones without any mortar to bind them together. Dry stone structures are stable because of their construction m ...
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 A gabion (from Italian ''gabbione'' meaning "big cage"; from Italian ''gabbia'' and Latin ''cavea'' meaning "cage") is a cage, cylinder or box filled with rocks, concrete, or sometimes sand and soil for use in civil engineering, road building, ...
. One disadvantage is that if using regular steel
rebar Rebar (short for reinforcing bar), known when massed as reinforcing steel or reinforcement steel, is a steel bar used as a Tension (physics), tension device in reinforced concrete and reinforced masonry structures to strengthen and aid the concr ...
s, the gabion would last much less long than when using mortar (due to rusting). Using
weathering steel Weathering steel, often referred to by the genericised trademark COR-TEN steel and sometimes written without the hyphen as corten steel, is a group of steel alloys which were developed to eliminate the need for painting, and form a stable rus ...
rebars could reduce this disadvantage somewhat.


Rubble trench foundations

Rubble trench foundations are a shallow trench filled with rubble or stones. These foundations extend below the
frost line The frost line—also known as frost depth or freezing depth—is most commonly the depth to which the groundwater in soil is expected to freeze. The frost depth depends on the climatic conditions of an area, the heat transfer properties of the s ...
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

File:Drawing of Poteaux-en-Terre in the Beauvais House in Ste Genevieve MO.png, Drawing of Poteaux-en-Terre
post in ground A post in ground construction, also called earthfast or hole-set posts, is a type of construction in which vertical, roof-bearing timbers, called posts, are in direct contact with the ground. They may be placed into excavated postholes, driven ...
type of wall construction (this example technically called pallisade construction) in the Beauvais House in Ste Genevieve, Missouri File:PSM V24 D321 A primitive lake dwelling in switzerland.jpg, PSM V24 D321 A primitive
stilt house Stilt houses (also called pile dwellings or lake dwellings) are houses raised on stilts (or piles) over the surface of the soil or a body of water. Stilt houses are built primarily as a protection against flooding; they also keep out vermin. The ...
in Switzerland on
wood piling 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. File:Hórreo tipo asturiano, O Piornedo, Cervantes.jpg, A granary on
staddle stones Staddle stones (variations include steddle stones) were originally used as supporting bases for granaries, hayricks, game larders, etc. The staddle stones lifted the granaries above the ground thereby protecting the stored grain from vermin and wa ...
, a type of padstone File:Black Eagle Dam - cross-section of construction plans for 1892 structure.jpg, Black Eagle Dam – cross-section of construction plans for 1892 structure File:Davis House stone foundation ruin, Gardiner, NY.jpg, Davis House dry-laid stone foundation ruin, Gardiner, NY File:Random rubble masonry1.jpg, A basic type of rubble trench foundation File:Concrete cellar 10007.JPG, Typical residential poured concrete foundation, except for the lack of
anchor bolt Anchor bolts are used to connect structural and non-structural elements to concrete.. The connection can be made by a variety of different components: anchor bolts (also named fasteners), steel plates, or stiffeners. Anchor bolts transfer diffe ...
s. The concrete walls are supported on continuous footings. There is also a
concrete slab A concrete slab is a common structural element of modern buildings, consisting of a flat, horizontal surface made of cast concrete. Steel- reinforced slabs, typically between 100 and 500 mm thick, are most often used to construct floors and ...
floor. Note the standing water in the perimeter French drain trenches.


Modern types


Shallow foundations

Often called ''footings'', are usually embedded about a meter or so into
soil Soil, also commonly referred to as earth or dirt, is a mixture of organic matter, minerals, gases, liquids, and organisms that together support life. Some scientific definitions distinguish ''dirt'' from ''soil'' by restricting the former te ...
. One common type is the spread footing which consists of strips or pads of concrete (or other materials) which extend below the
frost line The frost line—also known as frost depth or freezing depth—is most commonly the depth to which the groundwater in soil is expected to freeze. The frost depth depends on the climatic conditions of an area, the heat transfer properties of the s ...
and transfer the weight from walls and columns to the soil or
bedrock In geology, bedrock is solid Rock (geology), rock that lies under loose material (regolith) within the crust (geology), crust of Earth or another terrestrial planet. Definition Bedrock is the solid rock that underlies looser surface mater ...
. Another common type of shallow foundation is the slab-on-grade foundation where the weight of the structure is transferred to the soil through a
concrete Concrete is a composite material composed of fine and coarse aggregate bonded together with a fluid cement (cement paste) that hardens (cures) over time. Concrete is the second-most-used substance in the world after water, and is the most wi ...
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. Another way to install ready-to-build foundations that is more environmentally friendly is to use
screw piles Screw piles, sometimes referred to as screw-piles, screw piers, screw anchors, screw foundations, ground screws, helical piles, helical piers, or helical anchors are a steel screw-in piling and ground anchoring system used for building deep found ...
. Screw pile installations have also extended to residential applications, with many homeowners choosing a screw pile foundation over other options. Some common applications for helical pile foundations include wooden decks, fences, garden houses, pergolas, and carports.


Deep foundations

Used to transfer the load of a structure down through the upper weak layer of
topsoil Topsoil is the upper layer of soil. It has the highest concentration of organic matter and microorganisms and is where most of the Earth's biological soil activity occurs. Description Topsoil is composed of mineral particles and organic matt ...
to the stronger layer of
subsoil Subsoil is the layer of soil under the topsoil on the surface of the ground. Like topsoil, it is composed of a variable mixture of small particles such as sand, silt and clay, but with a much lower percentage of organic matter and humus, and it ...
below. There are different types of deep footings including impact driven piles, drilled shafts, caissons,
screw piles Screw piles, sometimes referred to as screw-piles, screw piers, screw anchors, screw foundations, ground screws, helical piles, helical piers, or helical anchors are a steel screw-in piling and ground anchoring system used for building deep found ...
, geo-piers and earth-stabilized columns. The naming conventions for different types of footings vary between different engineers. Historically, piles were
wood Wood is a porous and fibrous structural tissue found in the stems and roots of trees and other woody plants. It is an organic materiala natural composite of cellulose fibers that are strong in tension and embedded in a matrix of lignin th ...
, later
steel Steel is an alloy made up of iron with added carbon to improve its strength and fracture resistance compared to other forms of iron. Many other elements may be present or added. Stainless steels that are corrosion- and oxidation-resistant ty ...
,
reinforced concrete Reinforced concrete (RC), also called reinforced cement concrete (RCC) and ferroconcrete, is a composite material in which concrete's relatively low tensile strength and ductility are compensated for by the inclusion of reinforcement having hig ...
, and pre-tensioned concrete.


Monopile foundation

A type of
deep foundation 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 ...
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. Many monopile foundationsOffshore Wind Turbine Foundations
, 2009-09-09, accessed 2010-04-12.
have been used in recent years for economically constructing fixed-bottom
offshore wind farm Offshore wind power or offshore wind energy is the generation of electricity through wind farms in bodies of water, usually at sea. There are higher wind speeds offshore than on land, so offshore farms generate more electricity per amount of c ...
s in shallow-water
subsea Subsea technology involves fully submerged ocean equipment, operations, or applications, especially when some distance offshore, in deep ocean waters, or on the seabed. The term ''subsea'' is frequently used in connection with oceanography, marin ...
locations.Constructing a turbine foundation
Horns Rev project, Elsam monopile foundation construction process, accessed 2010-04-12
For example, a single
wind farm A wind farm or wind park, also called a wind power station or wind power plant, is a group of wind turbines in the same location used Wind power, to produce electricity. Wind farms vary in size from a small number of turbines to several hundre ...
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 meters of water.


Design

Foundations are designed to have an adequate load capacity depending on the type of subsoil/rock supporting the foundation by a
geotechnical engineer Geotechnical engineering is the branch of civil engineering concerned with the engineering behavior of earth materials. It uses the principles of soil mechanics and rock mechanics for the solution of its respective engineering problems. It als ...
, and the footing itself may be designed structurally by a
structural engineer Structural engineers analyze, design, plan, and research structural components and structural systems to achieve design goals and ensure the safety and comfort of users or occupants. Their work takes account mainly of safety, technical, economic ...
. The primary design concerns are
settlement Settlement may refer to: *Human settlement, a community where people live *Settlement (structural), the distortion or disruption of parts of a building *Closing (real estate), the final step in executing a real estate transaction *Settlement (fina ...
and
bearing capacity In geotechnical engineering, bearing capacity is the capacity of soil to support the loads applied to the ground. The bearing capacity of soil is the maximum average contact pressure between the foundation and the soil which should not produce she ...
. When considering settlement, total settlement and differential settlement is normally considered. Differential settlement is when one part of a foundation settles more than another part. This can cause problems to the structure which the foundation is supporting.
Expansive clay Expansive clay is a clay soil that is prone to large volume changes (swelling and shrinking) that are directly related to changes in water content. Soils with a high content of expansive minerals can form deep cracks in drier seasons or years; su ...
soils can also cause problems.


See also

*
Underpinning In construction or renovation, underpinning is the process of strengthening the foundation of an existing building or other structure. Underpinning may be necessary for a variety of reasons: * The original foundation isn't strong or stable enough. ...
* Structural settlement


References


External links


Common examples of possible deformations of foundations arising from improper construction.
{{DEFAULTSORT:Foundation (Engineering) Architectural elements Articles containing video clips Bridge components