Drainage in Excavation.ppt

construction of civil engineering

1. Unit II: Drainage in
excavation

2. •Dewatering of excavations is required at
construction sites generally for foundation
works. Various methods for dewatering of
excavations are described in this article. Firm
and sound working conditions are
indispensable when construction of buildings,
powerhouse, dams, and other structures has
to be executed.

3. Thesestructuresnotonlyrequireadrybasefor
theirfoundationsbutalsogoodwater-tablestability
inthegirth.Dewateringofanyexcavatedareais
doneinordertokeeptheexcavationbottomdry,to
preventtheleakageofwaterorsandandtoavoid
upheavalfailure.Dewateringcouldturnouttobea
herculeantaskifonedoesn’tadopttheright
method.Thedifferentmethodsavailablefor
dewateringofexcavationsatconstructionssitesare
notnecessarilyinterchangeableaseachonehasa
narrowrangeofapplications,therefore,adopting
therightmethodofdewateringforaparticular
groundconditionisalwaysacriticalandadifficult
decisiontomake.

4. Methods of Dewatering Excavations at
Construction Site:
•There are four important dewatering methods
one should be aware of:Wellpointmethod of
dewatering,
•Eductorwells,
•Open sump pumping and
•Deep wellpointmethod

5. Wellpoint Method of Dewatering Excavations

6. Aseriesofwellsofrequireddeptharecreatedinthe
vicinityoftheexcavatedareafromwherethewaterhasto
bepumpedout.Thewellsarearrangedeitherinalineora
rectangularformwherethewellpointsarecreatedata
distanceofatleast2mfromeachother.2)Riserpipesor
dewateringpipesaretheninstalledintothoseclosely
spacedwellswhichonthesurfaceareconnectedtoa
flexibleswingpipewhichisultimatelyappendedtoa
commonheaderpipethatisresponsiblefordischarging
thewaterawayfromthesite.Thepurposeofusinga
flexibleswingpipeisjusttoprovideaclearviewofwhatis
beingpumpedandthepurposeofheaderpipeistocreate
suctionaswellasdischargethewaterofftheworkingarea.

7. 3)Oneendoftheheaderpipeisconnectedtoa
vacuumpumpwhichdrawswaterthroughnotches
inthewell-point.Thewaterthentravelsfromthe
well-pointsthroughtheflexibleswingpipeintothe
headerpipetothepump.Itisthendischargedaway
fromthesiteortootherprocessestoremove
unwantedpropertiessuchascontaminants.4)The
drawdownusingthismethodisrestrictedtoaround
fivetosixmetersbelowthewell-pointpumplevel.
Ifadeeperdrawdownisrequired,multiplestagesof
well-pointsmustbeused.

8. EductorWells Method of
Dewatering Excavations
Themethodisverysimilartothe
wellpointmethodofdewatering;the
onlydifferenceliesintheusageof
high-pressurewaterintheriserunits
insteadofvacuumtodrawoutwater
fromthewellpoints.Themethoduses
theventuriprinciplewhichisthe
reductioninfluidpressurethatresults
whenahigh-pressurefluidflows
throughaconstrictedsectionofapipe.

9. Open Sump Pumping
Method of Dewatering
Excavations
Thisisthemostcommon
andeconomicalmethodof
dewateringasgravityisthe
mainplayingforce.Sumpis
createdintheexcavated
areaintowhichthe
surrounding water
convergesandaccumulates
facilitatingeasydischargeof
waterthroughrobustsolid
handlingpumps.

10. Thank you