Lowest and supporting layer of a structure
Shallow foundations
of a house versus the
deep foundations
of a
skyscraper
.
In engineering, a
foundation
is the element of a
structure
which connects it to the ground or more rarely, water (as with
floating structures
), transferring
loads
from the structure to the ground. Foundations are generally considered either
shallow
or
deep
.
[1]
Foundation engineering is the application of
soil mechanics
and
rock mechanics
(
geotechnical engineering
) in the design of foundation elements of structures.
Purpose
[
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]
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
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The design and the construction of a well-performing foundation must possess some basic requirements:
[2]
- 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
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The simplest foundation, a padstone.
The Ethnographic Open-Air Museum of Latvia
Earthfast or post in ground construction
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Buildings and structures have a long history of being built with wood in contact with the ground.
[3]
[4]
Post in ground
construction may technically have no foundation.
Timber pilings
were used on soft or wet ground even below stone or masonry walls.
[5]
In marine construction and bridge building a crisscross of timbers or steel beams in concrete is called grillage.
[6]
Padstones
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]
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.
[7]
Staddle stones
are a specific type of padstone.
Stone foundations
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]
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.
[8]
Besides using mortar, stones can also be put in a
gabion
.
[9]
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
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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/m
2
(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
pallisade
construction) in the Beauvais House in Ste Genevieve, Missouri
-
PSM V24 D321 A primitive
stilt house
in Switzerland on
wood pilings
.
-
A granary on
staddle stones
, a type of padstone
-
Black Eagle Dam ? cross-section of construction plans for 1892 structure
-
Davis House dry-laid stone foundation ruin, Gardiner, NY
-
A basic type of rubble trench foundation
-
Typical residential poured concrete foundation, except for the lack of
anchor bolts
. The concrete walls are supported on continuous footings. There is also a
concrete slab
floor. Note the standing water in the perimeter
French drain
trenches.
Modern types
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]
Shallow foundations
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]
Shallow foundation construction example
Often called
footings
, are usually embedded about a meter 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 structure 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.
Another way to install ready-to-build foundations that is more environmentally friendly is to use
screw piles
. 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
[
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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
,
screw piles
, geo-piers
[
clarification needed
]
and earth-stabilized columns
[
clarification needed
]
. 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
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]
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.
Many monopile foundations
[10]
have been used in recent years for economically constructing
fixed-bottom
offshore wind farms
in shallow-water
subsea
locations.
[11]
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 meters of water.
[12]
Floating\barge
[
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]
A floating foundation is one that sits on a body of water, rather than dry land. This type of foundation is used for some
bridges
and floating buildings.
Design
[
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]
Inadequate foundations in muddy soils below sea level caused these houses in the Netherlands to
subside
.
Foundations are designed to have an adequate load capacity depending on the type of subsoil/rock supporting the foundation by a
geotechnical engineer
, and the footing itself may be designed structurally by a
structural engineer
. The primary design concerns are
settlement
and
bearing capacity
. 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
soils can also cause problems.
See also
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]
References
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]
- ^
Terzaghi, Karl
;
Peck, Ralph Brazelton
; Mesri, Gholamreza (1996),
Soil mechanics in engineering practice
(3rd ed.), New York: John Wiley & Sons, p. 386,
ISBN
0-471-08658-4
- ^
Ventura, Pierfranco (2019).
Fondazioni
(in Italian). Milano: Hoepli.
ISBN
9788820386443
.
- ^
Crabtree, Pam J.. Medieval archaeology: an encyclopedia. New York: Garland Pub., 2001. 113.
- ^
Edwards, Jay Dearborn, and Nicolas Verton. A Creole lexicon architecture, landscape, people. Baton Rouge: Louisiana State University Press, 2004. 92.
- ^
Nicholson, Peter. Practical Masonry, Bricklaying and Plastering, Both Plain and Ornamental. Thomas Kelly: London. 1838. 30?31.
- ^
Beohar, Rakesh Ranjan. Basic Civil Engineering. 2005. 90.
ISBN
8170087937
- ^
Darvill, Timothy. The concise Oxford dictionary of archaeology. 6th ed. [i.e. 2nd ed. Oxford, U.K.: Oxford University Press, 2008. Padstone.
ISBN
0199534047
- ^
Garvin, James L..
A building history of northern New England
. Hanover: University Press of New England, 2001. 10. Print.
- ^
Stones in gabion for foundation, done in Diez Casas Para Diez Familias (10x10)'s Casa Rosenda; see Design Like You Give a Damn 2 book by Kate Stohr
- ^
Offshore Wind Turbine Foundations
Archived
2010-02-28 at the
Wayback Machine
, 2009-09-09, accessed 2010-04-12.
- ^
Constructing a turbine foundation
Archived
2011-05-21 at the
Wayback Machine
Horns Rev project, Elsam monopile foundation construction process, accessed 2010-04-12
- ^
"Lynn & Inner Dowsing Offshore Wind Farms"
. MT Højgaard. Archived from
the original
on 20 December 2016
. Retrieved
15 September
2016
.
External links
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]