Bridge foundation

Given by Sir Mr. Muhammad Naeem

3. Afoundationisthepartconstructed
underthepier/abutmentandoverthe
underlyingsoilorrock.
Theloadstransmittedbythefoundation
totheunderlingsoilmustnotcausesoil
shearfailureordamagingsettlementof
thesuperstructure.

4. Foundationistheimportantstructural
partofbridges
Foundationisthecomponentpartof
bridge.
Itreceivestheloadfromthepiersand
abutmentsandtransfersittothesoil.

5. Purposeoffoundationistodistributethe
loadofbridgeoveralargebearingarea
andprovidestabilityofbridgeagainst
settlementandtilting.
Itisprovidedsufficientlydeepsothatit
notaffectedbythescouring.

6. Thetypeoffoundationisdesignedwhen
subsoildataofbridgesiteisobtained.
Thedifferenttypesoffoundationsfor
bridgesaregivenfollowing;
ShallowFoundation
SpreadFoundationandRaftfoundation
DeepFoundation
Pile,caissonandwellFoundation

7. Subsoil
data of
bridge site

8. SpreadFoundationisgenerallyconstructed
forculverts
Itmaybeprovidedforsmallbridgeswhen
bedisofrockorofsoilhavinggoodbearing
capacity.
Itissuitablewhenflowinstreamislessand
hencethescouringeffectisless.
Atypicalspreadfoundationisshownin
Figure.
Itisconstructedwithstoneorbrickmasonry.

11. Raftormatfoundationissuitablefor
smallbridgeswhenbedcontains
differenttypesofsoil.
Itmaybeprovidedwhenbearing
capacityofsoilisless.
RaftormatfoundationisshowninFigure.
InthistheRCCslabislaidatthroughout
thespanofbridge.

14. oin which the depth of the
foundation is very large in
comparison to its width.
oWhich are not constructed
by ordinary methods of
open pit excavations.
Deep
Foundations
are those

15. Incaseswhere
oThestrataofgoodbearingcapacityisnotavailable
neartheground
oThespaceisrestrictedtoallowforspreadfootings
Inthesecasesthefoundationofthestructurehasto
betakendeepwiththepurposeofattainingabearing
stratumwhichissuitableandwhichensuresstability
anddurabilityofastructure.
Thebearingstratumisnottheonlycase.Theremay
bemanyothercases.Forexample,thefoundationfor
abridgepiermustbeplacedbelowthescourdepth,
althoughsuitablebearingstratummayexistata
higherlevel.

16. Most common forms of construction
pertaining to deep foundations are:
oCaisson Foundation
oWell Foundation
oPile Foundation

18. Thecaissonmeans,“Box”.Acaissonisahuge
boxmadeupofreinforcedconcrete.Insideof
theboxiskepthollow.
Caissonsarewaterlightstructures,employed
wherethefoundationisunderwater
Itisconstructedforfoundationsofbridges,piers,
abutmentsinriver,dockstructureandshore
protectionetc.
Thecaissonremainsinitspositionandultimately
becomesasintegralpartsofthepermanent
structure.

19. Caissonfoundationissuitablewhendepthof
waterintheriverismoreandqualityofbed
soilisgood.
Thesearebestforadepthof20m.
Caissonmaybeofcircular,rectangularor
anyothershape.

20. Thecaissonispreparedatbankofriver
andthentransportedtotherequired
pierpositiononthebridgesite.
Duringsinkingsoilfromthecaissonis
removed byexcavatorsorgrab
buckets.Whenthisissunkuptothe
desiredepththeninsideofcaissonis
completelyfilledwithconcrete.

21. Caisson can be broadly classified into the
following three types:
oBox Caisson (Floating Caisson)
oOpen Caisson
oPneumatic Caisson

22. Box Caisson
Box caisson is as like a box that is
opened on topside and other sides
are closed.

23. Box Caisson

24. Open Caisson
Open caisson is as like well that is
opened on top and bottom ends.
Bottom edges are made sharp.
During digging and sinking the inside
material is taken out.
Open caissons are used in soft soil and
in high water level.

26. Pneumatic Caisson
Pneumaticcaissonisspecialtypeofcaisson
thatissuitableforheavybridges.
Thereisaworkingchambermadeatits
lowerendandsealedatthetop.
Apressurehigherthanwaterpressureis
maintainedintheworkingchamberwith
thehelpofcompressedair.
Thuswaternotenteredinthechamber
andexcavationworkiscontinuedindry
conditions.

27. Workersexcavatethesoilfromtheedgesof
theworkingchamber
Excavatedmaterialisremovedmanuallyor
acraneremovesthesoilwithagrab
bucket.
Inearlybridgeconstruction,whentheybuilt
withthehelpofcaissons,numerousworkers
werekilledorpermanentlyinjuredby
caissondiseaseduringitsconstruction.
Afterwardadoptingpropermeasuresthe
diseasewascontrolled.
Pneumatic Caisson (Cont.)

28. Excavated
material shaft

31. Large,open-endedcompartments –
shellorboxwithcuttingedgeatthe
bottom
Sunkintothegroundbydiggingthesoil
outofthecenterandloadingthewalls
Filledwithconcrete(andcompacted
gravel)

32. Well foundation is suitable when heavy
loads are applied on the bridge.
Well foundation can be construct in
granular soil and in cohesive soil.
Some year ago the well foundation was
the common type of deep foundation.
It is usually constructed of stone or brick
masonry.

33. The well may be of many shapes but
mostly it is constructed in circular shape.
The inside of well is filled with granular
soil.
Well foundation can be constructed for
a depth more than 7m.
Piers are constructed on single well or
over several connected wells.