Shallow foundation 1

Shallow foundationA shallow foundation is a type of foundation which transfers building loads to the earth very near the surface, ratherthan to a subsurface layer or a range of depths as does a deep foundation. Shallow foundations include spreadfooting foundations, mat-slab foundations, slab-on-grade foundations, pad foundations, rubble trenchfoundations, and earthbag foundations.

Shallow foundation construction example

Spread footing foundation

In ground reinforced concrete foundation incyclonic area, Northern Australia.

A spread footing foundation, which is typical in residential building,has a wider bottom portion than the load-bearing foundation walls itsupports. This wider part "spreads" the weight of the structure overmore area for greater stability.The design and layout of spread footings is controlled by severalfactors, foremost of which is the weight (load) of the structure it willsupport as well as penetration of soft near-surface layers, andpenetration through near-surface layers likely to change volume due tofrost heave or shrink-swell.

These foundations are common in residential construction that includesa basement, and in many commercial structures. But for high risebuildings they are not sufficient.A spread footing which changes elevation in several places in a seriesof vertical "steps" in order to follow the contours of a sloping site oraccommodate changes in soil strata, is termed a stepped footing.

Mat-slab foundations

Mat-slab foundations, also called on-grade mat foundations for expansive soils, are used to distribute heavy columnand wall loads across the entire building area, to lower the contact pressure compared to conventional spreadfootings. Mat-slab foundations can be constructed near the ground surface, or at the bottom of basements. Inhigh-rise buildings, mat-slab foundations can be several meters thick, with extensive reinforcing to ensure relativelyuniform load transfer.

Shallow foundation 2

In ground reinforced concrete foundation incyclonic area, Northern Australia.

Slab-on-Grade foundation

Example of slab on grade foundation

Raft slab house foundation in cyclonic area,Northern Australia.

Slab-on-grade or floating slab foundations are a structural engineeringpractice whereby the concrete slab that is to serve as the foundation forthe structure is formed from a mold set into the ground. The concrete isthen placed into the mold, leaving no space between the ground and thestructure. This type of construction is most often seen in warmerclimates, where ground freezing and thawing is less of a concern andwhere there is no need for heat ducting underneath the floor.

The advantages of the slab technique are that it is cheap and sturdy,and is considered less vulnerable to termite infestation because thereare no hollow spaces or wood channels leading from the ground to thestructure (assuming wood siding, etc., is not carried all the way to theground on the outer walls).

The disadvantages are the lack of access from below for utility lines,the potential for large heat losses where ground temperatures fallsignificantly below the interior temperature, and a very low elevationthat exposes the building to flood damage in even moderate rains.Remodeling or extending such a structure may also be more difficult.Over the long term, ground settling (or subsidence) may be a problem,as a slab foundation cannot be readily jacked up to compensate; propersoil compaction prior to pour can minimize this. The slab can bedecoupled from ground temperatures by insulation, with the concretepoured directly over insulation (for example, extruded polystyrenefoam panels), or heating provisions (such as hydronic heating) can be built into the slab (an expensive installation,with associated running expenses).

Slab-on-grade foundations are commonly used in areas with expansive clay soil, particularly in California and Texas.While elevated structural slabs actually perform better on expansive clays, it is

Shallow foundation 3

Raft slab house foundation in cyclonic area,Northern Australia.

generally accepted by the engineering community that slab-on-gradefoundations offer the greatest cost-to-performance ratio for tracthomes. Elevated structural slabs are generally only found on customhomes or homes with basements.

Copper piping, commonly used to carry natural gas and water, reactswith concrete over a long period, slowly degrading until the pipe fails.This can lead to what is commonly referred to as slab leaks. Theseoccur when pipes begin to leak from within the slab. Signs of a slableak range from unexplained dampened carpet spots, to drops in waterpressure and wet discoloration on exterior foundation walls.[1] Copperpipes must be lagged (that is, insulated) or run through a conduit orplumbed into the building above the slab. Electrical conduits throughthe slab need to be water-tight, as they extend below ground level andcan potentially expose the wiring to groundwater.

Rubble trench foundation

A cross section view of a rubble trenchfoundation

The rubble trench foundation, a construction approach popularized byarchitect Frank Lloyd Wright, is a type of foundation that uses loosestone or rubble to minimize the use of concrete and improve drainage.It is considered more environmentally friendly than other types offoundation because cement manufacturing requires the use ofenormous amounts of energy. However, some soil environments (suchas particularly expansive or poor load-bearing (< 1 ton/sf) soils) are notsuitable for this kind of foundation.

A foundation must bear the structural loads imposed upon it and allowproper drainage of ground water to prevent expansion or weakening ofsoils and frost heaving. While the far more common concretefoundation requires separate measures to ensure good soil drainage, therubble trench foundation serves both foundation functions at once.

To construct a rubble trench foundation a narrow trench is dug down below the frost line. The bottom of the trenchwould ideally be gently sloped to an outlet. Drainage tile, graded 1:8 to daylight, is then placed at the bottom of thetrench in a bed of washed stone protected by filter fabric. The trench is then filled with either screened stone(typically 1-1/2") or recycled rubble. A steel-reinforced concrete daro beam is poured at the surface to provideground clearance for the structure.If an insulated slab is to be poured inside the grade beam, then the outer surface of the grade beam and the rubbletrench should be insulated with rigid XPS foam board, which must be protected above grade from mechanical andUV degradation.The rubble-trench foundation is a relatively simple, low-cost, and environmentally-friendly alternative to aconventional foundation, but may require an engineer's approval if building officials are not familiar with it. FrankLloyd Wright used them successfully for more than 50 years in the first half of the 20th century, and there is arevival of this style of foundation with the increased interest in green building.

Shallow foundation 4

Earthbag foundationThe basic construction method begins by digging a trench down to undisturbed mineral subsoil. Rows of woven bags(or tubes) are filled with available material, placed into this trench, compacted with a pounder to around 1/3thickness of pre-pounded thickness, and form a foundation. Each successive layer will have one or more strands ofbarbed wire placed on top. This digs into the bag's weave and prevents slippage of subsequent layers, and also resistsany tendency for the outward expansion of walls. The next row of bags is offset by half a bag's width to form astaggered pattern. These are either pre-filled with material and delivered, or filled in place (often the case withSuperadobe). The weight of this earth-filled bag pushes down on the barbed wire strands, locking the bag in place onthe row below. The same process continues layer upon layer, forming walls. A roof can be formed by graduallysloping the walls inward to construct a dome. Traditional types of roof can also be made.

ScrewpilesScrewpiles, also called helical piers and screw foundations, have been used as foundations since the mid 19thcentury in screw-pile lighthouses. Screw piles are galvanized iron pipe with helical fins that are turned into theground by machines to the required depth. The screw distributes the load to the soil and is sized accordingly.

External links• Procedure of shallow foundation construction [2]

• Raft or Mat Foundations [3]

• Slab Leak Recognition [4]

[1] http:/ / hacklerplumbingmckinney. com/ slab-leak-repair/[2] http:/ / www. foundationengineering. info/ photo_galleries/ 08/ footing_construction/[3] http:/ / www. theconstructioncivil. org/ raft-or-mat-foundations/[4] http:/ / hacklerplumbingmckinney. com/ slab-leak-repair/

Article Sources and Contributors 5

Article Sources and ContributorsShallow foundation  Source: http://en.wikipedia.org/w/index.php?oldid=602245930  Contributors: A. B., Aaron of Mpls, Acroterion, Argyriou, BD2412, Basar, Billbeee, Billinghurst,ChrisHodgesUK, Floquenbeam, Foxandpotatoes, Gacelita, Hooperbloob, Hu12, Into The Fray, Jim Derby, Kliegmanmark, Luciodem, Matthew Brandon Yeager, Mattisse, Mfwitten, Newell Post,Paldipakce, SCFC2011, Sadelphoi, Samw, Scapler, Shawnmackey11, Svenboatbuilder, Tecarr, Telfordbuck, Tslocum, Wookdong2, 62 anonymous edits

Image Sources, Licenses and ContributorsFile:Construcción de una cimentación por zapata aislada.ogv  Source: http://en.wikipedia.org/w/index.php?title=File:Construcción_de_una_cimentación_por_zapata_aislada.ogv  License:Creative Commons Attribution-Sharealike 3.0  Contributors: C.calvo / Carlos Calvo Luna Texturas creadas por/ Textures created by 2013 pasmateRs 2011 Olivier Boyaval 2010 Luke.RUSTLTD2009 Georges "TRaK" Grondin(Submitted by bart) 2012 DowndateImage:Wall-foundation.jpg  Source: http://en.wikipedia.org/w/index.php?title=File:Wall-foundation.jpg  License: GNU Free Documentation License  Contributors: User:BillbeeeImage:In-ground-foundation.gif  Source: http://en.wikipedia.org/w/index.php?title=File:In-ground-foundation.gif  License: Creative Commons Attribution 2.5  Contributors: -Image:Slab on grade.JPG  Source: http://en.wikipedia.org/w/index.php?title=File:Slab_on_grade.JPG  License: Creative Commons Attribution 2.5  Contributors: Peter KapitolaImage:Raft-slab.jpg  Source: http://en.wikipedia.org/w/index.php?title=File:Raft-slab.jpg  License: GNU Free Documentation License  Contributors: User:BillbeeeImage:Raft-slab.gif  Source: http://en.wikipedia.org/w/index.php?title=File:Raft-slab.gif  License: Creative Commons Attribution 2.5  Contributors: sketch by Bill Bradley. billbeee 21:07, 21May 2007 (UTC) Original uploader was Billbeee at en.wikipediaImage:Rubbletrench.png  Source: http://en.wikipedia.org/w/index.php?title=File:Rubbletrench.png  License: Public Domain  Contributors: Kelly, Kickstart70

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