Deep foundation

1. Deep Foundation

2. DEFINITION
1.Deep Foundationsare those
in which the depth of the foundation is very large
in comparison to its width.
Which are not constructed by ordinary methods
of open pit excavations.

3. When Used?
Incaseswhere
Thestrataofgoodbearingcapacityisnotavailablenearthe
ground
Thespaceisrestrictedtoallowforspreadfootings
Inthesecasesthefoundationofthestructurehastobe
takendeepwiththepurposeofattainingabearingstratum
whichissuitableandwhichensuresstabilityanddurability
ofastructure.
Thebearingstratumisnottheonlycase.Theremaybe
manyothercases.Forexample,thefoundationforabridge
piermustbeplacedbelowthescourdepth,although
suitablebearingstratummayexistatahigherlevel.

4. Forms of Construction
Mostcommonformsofconstructionpertainingtodeep
foundationsare:
PileFoundation(morecommonlyusedinbuilding
construction)
Cofferdams
CaissonorWellFoundation

5. Pile Foundations
Theterm‘PileFoundation’denotesaconstructionforthe
foundationofawallorpierwhichissupportedonpiles.
WhereUsed:
stratumofrequiredbearingcapacityisatgreaterdepth
steepslopesareencountered
Compressiblesoilorwater-loggedsoilorsoilofmade-uptype
Examples:Pilesareusedforfoundationforbuildings,trestle-
bridgesandwaterfrontinstallations(piers,docksetc).
Advantages:
Providesacommonsolutiontoalldifficultfoundationsite
problems
Canbeusedforanytypeofstructureandinanytypeofsoil

6. Pile Foundations(contd.)
SituationsWhichDemandPileFoundation:
Sub-soilwatertableissohighthatitcaneasilyaffecttheotherfoundations.
Loadcomingformthestructureisheavyandnonuniform.
Wheregrillageorraftfoundationsareeitherverycostlyortheiradoption
impossibleduetolocaldifficulties.
Whenitisnotpossibletomaintainfoundationtrenchesindryconditionby
pumping,duetoveryheavyinflowofseepageorcapillarywater.
Whenitisnotpossibletotimbertheexcavationtrenchesinthecaseofdeep
stripfoundation.(stripfoundation-spreadfootingunderwall).
Whenoverlaysoiliscompressible,andwater-loggedandfirmhardbearing
strataislocatedatquitealargedepth.
Whenstructuresarelocatedonriver-bedorsea-shoreandfoundationsare
likelytobescouredduetoactionofwater.
Largefluctuationsinsub-soilwaterlevel.
Canalordeepdrainagelinesexistnearthefoundations.
Intheconstructionofdocks,piersandothermarinestructurestheyareusedas
fenderpiles.

7. Types of Piles Based on Function
a) Classification based on Function or Use
1.Bearing Piles or End Bearing Piles
2.Friction Piles or Skin Friction Piles
3.Sheet Piles
4.Tension Piles or Uplift Piles
5.Anchor Piles
6.Batter Piles
7.Fender Piles
8.Compaction Piles

8. Types of Piles Based on Function
(contd)
Bearing Piles
Drivenintothegrounduntilahardstratumisreached.
Actsaspillarssupportingthesuper-structureand
transmittingtheloadtotheground.
Piles,bythemselvesdonotsupporttheload,ratheracts
asamediumtotransmittheloadfromthefoundationto
theresistingsub-stratum.

9. Types of Piles Based on Function
(contd)
Friction Piles (Floating Piles)
 Pilesaredrivenatasitewheresoilisweakorsofttoaconsiderable
depthanditisnoteconomicalorratherpossibletorestthebottom
endofthepileonthehardstratum,
 Loadiscarriedbythefrictiondevelopedbetweenthesidesofthepile
andthesurroundingground(skinfriction).
 Thepilesaredrivenuptosuchadepththatskinfrictiondevelopedat
thesidesofthepilesequalstheloadcomingonthepiles.
 Skinfrictionshouldbecarefullyevaluatedandsuitablefactorofsafety
applied,asitisthiswhichissupportingthewholeofstructureoverits
head.
 Theloadcarryingcapacityoffrictionpilecanbeincreasedby-
 increasingdiameterofthepile
 drivingthepileforlargerdepth
 groupingofpiles
 makingsurfaceofthepilerough

10. Types of Piles Based on Function
(contd)

11. Types of Piles Based on Function
(contd)

12. Types of Piles Based on Function
(contd)
Sheet Piles
Sheetpilesareneverusedtoprovideverticalsupportbut
mostlyusedtoactasretainingwalls.Theyareusedforthe
followingpurposes:
Toconstructretainingwallsindocks,andothermarine
works.
Toprotecterosionofriverbanks.
Toretainthesidesoffoundationtrenches.
Toconfinethesoiltoincreaseitsbearingcapacity.
Toprotectthefoundationofstructuresfromerosionbyriver
orsea.
Toisolatefoundationsfromadjacentsoils.

13. Types of Piles Based on Function
(contd)
Figure: Sheet Piles

14. Types of Piles Based on Function
(contd)
Anchor Piles
 Pilesareusedtoprovideanchorageagainsthorizontalpullfromsheet
pilingwallorotherpullingforces.
Batterpiles:
 Pilesaredrivenataninclinationtoresistlargehorizontalandinclined
forces.
Fenderpiles:
 Pilesareusedtoprotectconcretedeckorotherwaterfrontstructures
fromtheabrasionorimpactcausedfromtheshipsorbarges.
 Ordinarilymadeupoftimber.
Compactionpiles:
 Whenpilesaredriveningranularsoilwiththeaimofincreasingthe
bearingcapacityofthesoil,thepilesaretermedascompactionpiles.

15. Types of Piles Based on Function
(contd)

16. Types of Piles Based on Function
(contd)
Figure: Under-reamed Piles

17. Types of Piles Based on Materials
a) Classification based on Materials
1.TimberPiles
2.ConcretePiles
3.Composite Piles
4.SteelPiles
5.Sand Piles

18. Types of Piles Based on Materials
(contd)
1.TimberPiles:
Transmissionofloadtakesplacebythefrictionalresistance
ofgroundandthepilesurface.
Economicaltosupportlightstructure.
Pilesmade from timber of treelike
Sal,Teak,Deodar,Babul,Khairetc.
Khairpilescanstandactionofseawaterandthususedfor
marineworks.
Maybecircular,squareinx-section.
Pilesaredrivenwiththehelpofpiledrivingmachineinwhich
drophammersdeliversblowsonthepilehead.
Broomingofpileheadispreventedbyprovidinganironring
oflessthan25mmindiameterthanthepileheadatthepile
top.

19. Types of Piles Based on Materials
(contd)
1.TimberPiles:
 Tofacilitatedriving,thelowerendispointedandprovidedwithacastiron
conicalshoe.
 Pilesshouldnotbespacedlessthan60cmcentertocenter,thebest
spacingis90cmc/c.closerspacingdestroysfrictionalresistance.
 Maxloadshouldnotexceed20tonnes.
 Pilesaresubjectedtodecayforalternatedryandwetcondition(on
accountofvariationofgroundwaterlevel)
 Assuch,timberpilesarecutalittlebelowthelowestwater-markand
cappedwithconcrete,steelgrillage,stoneortimber.
 Iftimbercappingisused,thecapshouldbepermanentlyunderwater.
 Diametervariesfrom30to50cm.
 Lengthshouldnotbemorethan20timestheleastsectionaldimension.

20. Types of Piles Based on Materials
(contd)
AdvantagesofTimberPiles:
 Economicalwheretimberiseasilyavailable.
 Canbedrivenrapidly&assuchsavestime.
 Becauseofelasticity,timberpilesarerecommendedforsites
subjectedtounusuallateralforcese.g.ship,ferryterminals.
 Donotneedheavymachineryandelaboratetechnicalsupervision.
 Beinglight,theycanbeeasilyhandled.
 Theycanbeeasilywithdrawnifneeded.

21. Types of Piles Based on Materials
(contd)
DisadvantagesofTimberPiles:
 Timberpilesmustbecutoffbelowthepermanentgroundwater
leveltopreventdecay.
 Liabletodecayordeterioratebysaltwater/insects.
 Restrictedlength.Itisratherdifficulttoprocurepilesinrequired
sizeandlength.
 Lowbearingcapacity.
 Theyarenotverydurableunlesssuitablytreated.
 Itisdifficultorratherimpossibletodrivethesepilesintohard
stratum

22. Types of Piles Based on Materials
(contd)

23. Types of Piles Based on Materials
(contd)
Figure: Timber Pile

24. Types of Concrete Piles
ConcretePilesareof3types:
Pre-castPiles
CastinsituPiles
PrestressedConcretePiles

25. Concrete Piles (contd)
Pre-castPiles:
Reinforced concrete piles, molded in
circular,square,rectangularoroctagonalform.
Castandcuredinthecastingyard,thentransportedtothe
siteofdriving.
Ifspaceavailableitcanbecastandcurednearthework
site.
Driveninsimilarmannerastimberpileswiththehelpof
pilesdrivers.
Diameternormallyvariesfrom35cmto65cm,lengthvaries
from4.5mto30m.

26. Concrete Piles (contd)
Pre-castPiles:
Functionofreinforcementinapre-castpileistoresistthe
stressesduringhandling,drivingandfinalloadingonthe
pileratherthanstrengthenthepiletoactasacolumn.
Longitudinalreinforcementsusually20mmto50mmin
diameter,stirrups6mmto10mmindia.
For90cmlengthatheadandtoe,stirrupsspacingis8cm
c/candforremainingintermediatelengthitisabout30cm
c/c.
Circularpilesareseldomtapered.Whentaperedpiles
lengthisrestrictedto12m.
Aconcretecoverof5cmismaintainedthroughout,overthe
mainsteelbars.

27. Concrete Piles (contd)
AdvantagesofPre-castPiles:
Veryeffective
Simplequalitycontrol
Improvestheentirearea
DisadvantagesofPre-castPiles:
Limitedinlength
Difficulttotransport
Notsuitablefordenselybuiltuparea
Requirescostlyequipment

28. Concrete Piles (contd)

29. Concrete Piles (contd)
Cast-in-SituPiles:
Castinpositioninsidetheground.
Firstofallaboreisdugbydrivingacasingpipeintothe
ground.
Thenthesoilfromthecasingisjettedoutandfilledwith
cementconcreteafterplacingnecessaryreinforcementin
it.
Cast-in-situpilesareoftwotypes:
I.CasedCast-in-SituPiles:metallicshellisleftinside
thegroundalongwiththecore
II.UncasedCast-in-SituPiles:metallicshelliswithdrawn

30. Concrete Piles (contd)
AdvantagesofCast-in-SituConcretePiles:
Notlimitedinlength
Canbecastatanyplace
Requireslessequipment
Costislessandisdependedonthesize
DisadvantagesofCast-in-SituConcretePiles:
Qualitycontrolisdifficult
Loadcarryingismostlydonethroughendbearingonly
Skinfrictionalresistanceisverylow.

31. Concrete Piles (contd)
Figure: Cast-in-Situ Pile

32. Concrete Piles (contd)
AdvantagesofConcretepiles:
Durabilityisindependentofgroundwaterlevel.
Forlargesizeandgreaterbearingpowernumberofpiles
requiredismuchless.
Canbecasttoanylength,sizeorshape.
Canbeusedtomarineworkwithoutanytreatment.
Materialrequiredformanufactureiseasilyobtainable.
Concretepilescanbemonolithicallybondedintopilecap
whichisnotpossibleinwoodenpiles.

33. Concrete Piles (contd)
DisadvantagesofConcretepiles:
Costlierthantimberpiles.
Cannotbedrivenrapidly.
Requiredelaboratetechsupervisionandheavydriving
machines.
Mustbereinforcedtowithstandhandlingstresses.

34. Concrete Piles (contd)
PrestressedConcretePiles
Thegreatestdisadvantageoflargeweighttanddifficultyin
handlingofpre-castpileiseliminatedbyprestressed
concretepiles.
Theweightisreducedbycasting200mmto300mm
diameterfibertubesinsidethepilesatthetimeof
concreting.
Thepretensioningcablesaresubjectedtorequiredpull
(tension)inthecastingbed.
Thefibertubeisheldinpositioninsidetheformworkand
thepilesreinforcedwithprestressedcablesareconcreted
inarow.

35. Concrete Piles (contd)
PrestressedConcretePiles
Prestressedconcretepilesareprovidedwithliftinghooks
at1/5th(0.2L,L=lengthofpile)ofpilelengthfromeach
end.
Pileslength50timesthethickness→singlepointpickup
Morethan50timesthethickness→twopointpickupat
0.2Lfromeitherend.
Piles500sq.mmandsmaller→castsolid.
Pilesover500sq.mmmaybecastwith200mmto300mm
coredhole(void).
Prestressedpilesarealwayspre-cast.

36. Concrete Piles (contd)
AdvantagesofPrestressedConcretePiles
Ithasgreaterabilitytowithstandextremelyharddriving.
Itismoredurableinseawaterbecauseofabsenceof
crack.
Ithasgreatercolumncapacity.
Ithaslesserhandlingcostsbecauseoflightweight.
Itrequireslesserpick-uppoints.
Ithaslargermomentofinertiathantheconventionalpiles
ofsamedimensionsincetheconcreteisallin
compression.

37. Composite Piles (contd)
Pilesoftwodifferentmaterialsaredrivenoneoverthe
other,soastoenablethemtoacttogethertoperformthe
functionofasinglepile.
Thistypeofcompositepileisusedwiththeobjectof
achievingeconomyinthecostofpilingwork.

38. Composite Piles

39. Selection of Type of Pile
Thenatureoftheground,wherepilingoperationistobe
carriedout,determinestoalargeextentthechoiceoftype
ofpiletobeused.
Inaddition,theotherimportantfactorswhichmustbe
consideredinthisregardare:
Thenatureofthestructure.
Loadingconditions.
Elevationofthegroundwaterlevelwithrespecttothepile
cap.
Probablelengthofpilerequired.
Availabilityofmaterialsandequipment.
Factorswhichmaycausedeteriorationofpile.
Probablecostofpile.

40. Causes of Failure of Piles
Loadonthepileismorethanthedesignedload.
Defectiveworkmanshipduringcastingofthepile.
Displacementofreinforcementduringcasting.
Bearingpilerestingonasoftstrata.
Improperclassificationofsoil.
Improperchoiceofthetypeofpile.
Insufficientreinforcementinthepile.
Decayoftimberpilesduetoattackbyinsects.
Bucklingofpilesduetoinadequatelateralsupport.
Defectivemethodadoptedfordrivingthepile.
Incorrectassessmentofthebearingcapacityofthepile.
Lateralforcesnotconsideredinthedesignofpiles.

41. Pile Driving
I.By Drop Hammer.
II.By Steam Hammer.
III.By Water Jets (Wash Boring ).
IV.By Boring (Auger Boring).

42. Cofferdams
Cofferdams may be defined as a temporary structure
constructed in a river or a lake or any other water bearing
surface for excluding water form a given site to enable the
building operation to be performed on dry surface.
Cofferdams may be divided into the following category based
on the materials used during construction:
Earthier cofferdam.
Rock fill cofferdam.
Single-walled cofferdam.
Double-walled cofferdam.
Crib V
Cellular cofferdam.(Circular or diaphragm type)

43. Earthen Cofferdams
It essentially consists of an earthen embankment built
around the area to be enclosed.
It is constructed where the depth of the water is not much
and the velocity of the current is very low.
The top width of the embankment is not less than 1 m and
the slopes vary from 1:1.5 to 1:2. The earth used to built
these cofferdams is a mixture od clay and sand or clay and
gravel

45. RockfillCofferdam
If the depth of water to be retained by the embankment of
cofferdam is of order of 1.8 to 3 m, stone or rubble is used
for the embankment.
The stones are assembled in a required shape and the
voids ae partially fillled with earth and stone chips.

46. Single walled Cofferdams
This type of cofferdam is used in places where the area to
be enclosed is very small and he depth of water is more,
say 4.5 to 6m.
Timber piles known as guidepiles are first driven in to the
river bed. Longitudinal runners called walesare then bolted
to these at suitable distance apart. Steel or wooden sheet
piles are then driven into the river bed along the wales and
secured to them by bolts.
To increase the stability the sheets on two faces are braced
by trussed arrangement of struts.

48. Double walled Cofferdam
For cofferdams required to enclose large areas in deep
waters, single-walled type becomes uneconomical as large
sections of struts would be necessary to resist water, so
double walled cofferdams are used.
Their construction is similar except instead of one wall two
walls with a gap in between is used.
This can be used for waters with a depth of upto 12 m.
The thickness of the water is equal to the depth of water
when it is 3m, and 3m plus half the depth of water if it is
more.

49. Crib Cofferdam
In deep waters where it is difficult to insert the sheet piles or
guide piles into the hard bed below, Crib cofferdam is used.
A crib is a framework of horizontal timbers installed in
alternate courses to form pockets which can be filled with
earth and stones.
The size of the crib depends on the depth of water and the
velocity of water flow.
The crib is constructed on ground and then floated to the
water surface. Sand and other loose material overlying the
impervious hard bed is dredged out and the crib sunk to the
bed. The space inside the crib is filled with stone or other
materials to make it stable against sliding and overturning.
Timber and steel sheet piles are then driven around the crib.

51. Cellular Cofferdam
When he height of the water is from 18 to 21 m, this type is
used to dewater the large areas.
They are commonly used during the construction of marine
structures like dams, whares etc.
They are constructed by driving straight web sheet piles
arranged in form of a series of inter connected cells. Finally
the cells are filled with clay to make them stable. The two
common shapes of cellular cofferdams are:
a) Circular type
b) Diaphragm type

53. Caissons
Caissonsarewaterlightstructuresmadeupofwood,steelor
reinforcedconcrete,constructedinconnectionwithexcavation
forfoundationsofbridges,piers,abutmentsinriverandlake
dockstructureforeshoreprotectionetc.
The caisson remains in its pose and ultimately becomes as
integral parts of the permanent structure.
Caisson can be broadly classified into the following three types:
Open Caisson
Box Caisson (Floating Caisson)
Pneumatic Caisson

54. Open Caissons
Depending on shape they are classified in to:
-Single wall open caisson: This is a box type structure with
no top or bottom mainly consisting of vertical walls.
-Cylindrical open caisson: This may be defined as a
cylindrical shell made up of timber, masonry, steel or
reinforced concrete shod with a cutting edge and which is
sunk by excavating the soil within the shell. It is also known
as well caisson.
-Open caisson with dredging walls: This type of caisson has
the distinction of being emoyed for the deepest foundation
for bridge piers, abutments etc. The caisson is square or
rectangular in pplan which is sub divided into smaller
sections from inside forming open walls

56. Box Caisson
It is similar to open caisson except it is closed at the bottom.
Caisson is cast and cured on land and then launched in
water and towed to the site for sinking. They are used where
the strata of sufficient bearing capacity is available near the
ground.

57. Pneumatic Caisson
This type of caisson is closed at top and open at bottom.
The water is excluded from the caisson chamber by means
of compressed air. The working chamber and shafts are
made air tight. In order that the workmen can work
underneath the caisson and water may not find its way
inside from below, the pressure of the compressd air in the
shaft is just kept a little higher than the water at that depth.

58. Bibliography
Text: Building Construction by Sushil Kumar
Images: Internet