真空预压发处理软土地基施工方案英文

ProposedDesignPhilosophy,Construction,InstallationandMonitoringMethod

(asper22.1.7ofsection1.0)

Sourceofborrowspitindicatingthelocationandquantity

WehavelicensegivenbyVietnamauthoritytoexploitaquantityof8,400,000m3inNhaBeriverandthelocationisinNhonTrachdistrict,DongNaiprovince.

Physicalproprietiesofproposedfillmaterial

ThesamplingtestofsandproposedtouseiscarriedoutaccordingtoAASHTOM45-89,C144-88(seeTestResultofAnalysesofSandcomponent).Thespecificweightofthesandis2.634,unitweight1.5g/cm3,organiccontent2.87%andmodules2.52.

3.Proposedmethodofstatementandmonitoringdevices

3.1Methodstatement

Accordingtothegeotechnicalreportofthesite,thevoidratioofthesoftsiltyclay(e)is2.377,andthepermeabilitycoefficient(Kv)5.5*10-7cm/s.Ifweadopt“wickdrainsandpre-loading”methodtoreachasoilbearingcapacityof50Kpa,75Kpa,100Kpaunderthesite’sconditions,theconsolidationperiodwouldbefarbeyondtheproposedworkperiod.Forthepurposeofreducingtheconsolidationperiodoffoundationsoilanoverloadshouldbeadded,thoughtheloadingwouldbe7.30mhightofulfillthebearingcapacityof100Kpa.Obviously,thistechniquewouldbearatremendousnumberofloadingandunloading,whichwouldalsomeanahighconstructioncost.Thestabilityofsideslopewouldalsobedifficulttomonitor.

BasedonourpreviousexperienceofsoftsoilimprovementofChinacoastalandHiepPhuocPowerPlantinNhaBe,15kmSoutheastofHochiminhCity,thepre-loadingmethodisappropriateonlyforgeneralarea.Inprocessareawesuggesttoadoptedthefollowingmethod(detailsseedrawings“ProposedProcessAreaPlan”and“ProposedProcessAreaZone”inpage6,7):

f=50Kpa,vacuumprecompressionmethod;

f=75Kpa,vacuumprecompressionandfillingwater(2.0m)onmembranemethod;

f=100Kpa,vacuumprecompressioncompoundwithloadingmethod.

Thehydraulicfillingofseasandshouldbeadoptedundertheelevation+2.80,whichisspecifiedinthetenderdocuments.Butbasedonoursiteinvestigationreport,weproposetousesweetwatersandinsteadofseasandforthesefollowingreasons:

Finegradeandhighmudcontentoftheseasand;

Nolocalfacilitiesavailablesuchashydraulicfillingmudabsorption.

Thebackfillmaterial(sweetwatersand)willbedeliveredbybargestothenearestdockandthencarriedbytruckstothesite.

3.2Monitoringdevices

Accordingtotherequirementofthetenderdocuments,settlementgaugeshouldbeinstalledat50mx50mgridandbemeasuredbylevelinginstruments.

Inaccordancewiththerequirementoftheowner,thestaticpenetrationtestshouldbecarriedoutatthe10specifiedpointsandthepenetrationinstrumentsshouldbeburiedthroughthewholedepthofthecompressiblesoillayers.

Thecompactiontestoffillingmaterialsinsiteshouldbecarriedoutwithheavycompactor.

Designphilosophytoachievetherequirementofthespecificationforsoilimprovement

philosophyofvacuumprecompressionmethod

Thevacuumprecompressionmethodisusedtoconsolidatefoundationsoil.Thismethodconsistsinlayingonthesurfaceoffoundationsoila

sandbed,andininstallingadrainagesystemwithwickdrains.Thesandbeddrainlineisburiedandconnectedwithvacuumsystemtoformanairexhaustandadewateringsystem.Asetofairtightsealmembranesislaidonthesurfaceofthesandbedwithitsedgeburiedinsoil.Thus,anegativepressureareawithinsandbedandfoundationsoilcanbeformedfromairexhaustanddewaturingpumps.Thevacuummethodcanreachasoilbearingcapacityof80KPa.Underthevacuumcondition,soilisinthestateofconsolidatingandporewaterisdischargedfromsoilunderthepressuredifference.Theconsolidationiscompletedwhenpressureofsoiltobeconsolidatedisreachingthesamepressureofthedrainagesystem.

Thephilosophyofvacuumrecompressionmethodisthatunderthepressuredifference(Pa-Pv),soilcanbeconsolidated;PaindicatesatmosphericpressureandPvindicatesairpressureinthesandbedandtheverticaldrains.Inthecalculationofconsolidationofthefoundationsoil,theRENDULIC-TERZAGETheoryandBICOTTheoryofConsolidationcanbeadoptedwhicharethesameofthoseadoptedinloadingrecompressionmethod.Thedropofthegroundwatertablemayalsoacceleratetheconsolidationoffoundationsoilbesidethepressuredifference.

Theeffectivestressinthesoilincreasessuccessivelyduringtheperiodofconsolidationofthefoundationsoilwithvacuumrecompressionmethod.Thehorizontaldisplacementofthesoilistowardthecenteroftheconsolidationareafromthebeginningoftheperiodofvacuumrecompression,whichisdifferentfromtheloadingrecompressionmethod.Sothestabilityofthefoundationsoilwillnotbecomeaproblem,andtherequiredvacuumcapacitycanimmediatelybeobtainedandconsequently,theperiodofvacuumrecompressioncanbecurtailed.Detailsisshownindrawings“DesignPhilosophyforVacuumPrecompression“and“FlowDiagramofVacuumPrecompressionMethod”inpage8,9.

Regardingtheshortworkperiodofthisproject,thevacuumcompoundwithloadingrecompressionmethodisusedintheprocessareawheretherequiredbearingcapacityofthefoundationsoilis100Kpa.Ithasbeenprovedfromthetheoreticalcalculationandourpreviousexperiencethattheeffectsofvacuumandloadingrecompressionmethodsontheconsolidationcanbecoaxed.Forthispurpose,asoilcapacityof150KpahadbeenobtainedinoneofourpreviousprojectintheturbinehouseofHiepPhuocpowerplantlocatedatNhaBedistrictinHochiminhcity.Duringthevacuumprocessandunderthepressuredifference(Pa–Pv),theporewaterpermeatesintotheverticaldrainsandtheconsolidationoccurs.Ontheotherhand,whenusingpre-loadingmethod,theairpressureraisestoPpandtheconsolidationoccursunderthepressuredifference(Pp–Pa).Therefore,byusingthevacuumcompoundwithpre-loadingmethod,thepressurecanbeincreasedto(Pp–PV)andthe

consolidationeffectwouldbeimprovedasaresult.

Theprocessofvacuumcompoundwithpre-loadingmethodisshownindrawing“TheProcessdrawingofVacuumPrecompressioncombinedwithLoadingMethod”inpage10.

4.2Monitoringmethod

Theloadingheightandloadingperiodofeachstepofgeneralareaismainlycontrolledbythestabilityofthefoundationsoil.Thesettlementmonitoringshouldbemainlyconcernedinthisarea.

Becausethevacuumprecompressionmethodwillnotcauseasoilstabilityproblem,thesitemeasurementshavelesssignificancecomparabletopre-loadingmethod.Accordingtotherequirementofthetenderdocuments,settlementgaugesshouldbeinstalledat50mx50mgridandbemeasuredbylevelinginstruments.Thetotalsettlementandsettlementspeedofthefoundationintheloadingareaaswellasthesettlementortherisingheightinthesurroundedareamustbemonitored.

ThefinalsettlementScanbecalculatedfromthesitemonitoringdata.TheconsolidationsettlementScandtheaverageconsolidationratioareobtainedfromthisvalue.Moreover,thevaluecanalsobecalculatedaswellastheaverageconsolidationcoefficientCv.

Accordingtotherequirementoftheowner,thestaticpenetrationtestshouldbecarriedoutatthe10specifiedpointsandthepenetrationinstrumentsshouldbeburiedthroughthewholedepthofthecompressiblesoillayers.

4.3Preliminarygeotechnicaldesignforverticaldrainsandsoildischarge

ThetypeSPBplasticdrainageplateisadoptedastheverticaldrainsinthisproject.Theverticaldrainswouldbedistributedaccordinglytoanequilateraltrianglepattern.

BasedonourpreviousexperiencesofsoftsoilimprovementintheMekongdeltaareaandaccordingtotheworkrequirementsfromtheproject,webelievethatthebearingcapacityofprocessedfoundationsoilcanbereached.However,itisarduoustoreachthesamerequirementforthe

deformation.Itneedsacomparativelylongperiodtoattainastablestateoffoundationsoilsettlement.

Inaccordancewiththetenderdocumentforthegeneralarea,thefillingmaterialshavetobewellcompactedtomeetthebuildingstandard.Still,therearenorelevantrequirementsofbearingcapacity,sotheinsertingdepthoftheverticaldrainsshouldbelessthanthethicknessofthesoftsoillayerstoavoidtheoccurrenceofextremesettlement.Intheoppositecase,thatwouldimplyalargeadditionalquantityofloadingmaterialsandasoaringconstructioncost.

Combiningvacuumtechniquewithloadingmethod,thedifferentrequirementsofbearingcapacityofprocessareacanbefirmlymet.Obviously,theairtightconditionduringvacuumprecompressionisacriticalfactortoensureasufficientvacuumlevel.Thedepthofverticaldrainsintheprocessareaisestimatedtobe10mtoensurethattheendofverticaldrainsiswithinthesoftsoillayerwhichisabout14mdepth.Thiswillavoidanyleakagefromlowersandlayer.

Theintervaloftheverticaldrainsingeneralarea:L=1.20m

Forprocessarea:f=5t/m2,L=1.2m.

f=7.5t/m2,L=1.1m.

f=10t/m2,L=0.7m.

Theinitialgeotechnicaldesignisshownintwotables:“GeotechnicalDesignofVacuumPrecompressionMethodofProcessArea”and“GeotechnicalDesignofPre-loadingMethodofGeneralArea”inpage11,12.

Proposedverticaldrainsmaterials

TheSPB0-IItypeverticaldrainisadoptedfromCHINA.TheproprietiesoftheproductionmeettherequirementsofChinesestandardDB3201Q18-87(detailsisshownbelowintable“QualityStandardofSPBVerticalDrains“).

QualityStandardofSPBVerticalDrains

Parametter

Unit

Type

Remarkss

SPB-1

SPB-2

SPB-3

Materiaals

Plasticcstrripccorecoattedwwithameembraaneffilteer

Sectionn

dimensiions

Width

mm

1002

1002

1002

Thickneess

mm

3.5

4.0

4.5

Longituudinaaldrraincapaacityy

m3/s

15*10-66

25*10-66

Sideprressuure3350KNN/m2

Tensionnstrrengtth

KN/10cmm

>1.0

>1.3

Elongattionis1100%

Elongattion

<10

<10

Permeabbilittycooeffiiciennt

cm/s

5*10-4

5*10-4

Capacittyoffinssulattingsoill

m

<75

<75

Tensionnstrrengtthoff

membranne

Dry

N/cm

>15

>30

Elongattionis110%

Wet

N/cm

>10

>20

Elongattionis115%

Linearweigght

g/m

90-100

90-100

Unitleengthh

m

200

200

Siteclearing

Geotextilelaying

Preparationofwickdrains

insertingequipment

Siteofficeand

controlcenter

Vacuumpipesinstall

Wickdrainsinsertion

Secondsandbedding

Firstsandbedding

Membranelaying

Airextractingequipment

Vacuumgaugeandrelayinstall

Airextractiontest

Precompressionbyairextraction

Vacuumpressureandsettlementreadings

intheprocessarea

Equipmentremovaloftheprecompressionmethod

Refillandleveling

Weirconstruc-tion

Controlandoperationcenter

Electricalandlightcircuit

Recheckthevacuumpumps

Temporarywaterpumpsinstallation

Vacuumpipepreparation

Membranepreparation

Settlementgauges

Initialreadingofsettlementandrelay

Resiliencereadingofgroundsettlement

Leakagerepairofmembrane

Resultsverification

FlowDiiagraamoffVaccuumPreccomprressiionMMethood

Geotechhnicaaldeesignnofvacuuumpprecoompreessioonmeethoddsoffproocesssareea

ProcesssAreea

(m2)

Averageedeppthoofsooftssoil

(m)

BearinggCappacittyofffouundattionsoill(t//m2)

Intervaaloffverrticaaldrrainss

(m)

Depthoofveerticcalddrainns

(m)

Calculaated

Finalcconsoolidaa-tioonseettleementt

(m)

Depthoofveerticcalddrainns

(m)

Calculaated

Finalcconsoolidaa-tioonseettleementt(m))

EstimattedSSettllemennt

(m)

Depthoofveerticcalddrainns

(m)

Calculaated

Finalcconsoolidaa-tioonseettleementt(m)

1

28254**

___________

25286

14.41

5

1.2

13.4

2.82

10.0

2.10

1.60

8.0

1.69

7.5

1.1

13.4

2.95

10.0

2.30

1.80

8.0

1.90

10

0.8

13.4

3.60

10.0

2.69

2.40

8.0

2.35

2

41428.000*

______________

37450.000

13.32

5

1.2

12.3

2.59

10.0

2.10

1.60

8.0

1.69

7.5

1.1

12.3

2.72

10.0

2.30

1.80

8.0

1.90

10

0.8

12.3

3.30

10.0

2.69

2.40

8.0

2.15

3

54313.000*

______________

49603.000

13.05

5

1.02

12.0

2.53

10.0

2.10

1.60

8.0

1.69

7.5

1.1

12.0

2.65

10.0

2.30

1.80

8.0

1.90

10

0.8

12.0

3.23

10.0

2.69

2.40

8.0

2.15

Note:TThe“*”shoowstthatthenumeeratoormeeansthepropposeddproocesssareea,wwhichhisexteendeddfroomthhearreasspeciifieddinthetendderddocummentss(deenomiinatoor)bbyexxtenddingedgeeto4.0m.

Whenf=7..5t/mm2,tthessettllemennt(11.8)isccalcuulateedbyyusiingttheaaveraagessettllemenntafftervacuuumpprecoompreessioonofftheemaiinbuuildiingoofHiiepPPhouccpowwerpplantt(1..55)addeedseettleementtocccurreedinnconnsoliidatiionpperiood(990dayys)whicchiss(900*3))mm.

Geotechhnicaaldeesignnofvacuuumpprecoompreessioonmeethoddinproccessareaa

Scheme

ProcesssAreea

(m2)

Averageedeppthoofsooftssoil

(m)

BearinggCappacittyofffouundattionsoill(t//m2)

Intervaaloffverrticaaldrrainss

(m)

TreatmeentDDepthh

(m)

EstimattedSSettllemennt

(m)

1

282544*

__________________

25286

14.41

5

1.2

10.0

1.60

7.5

1.1

10.0

1.80

10

0.7

10.0

2.40

2

41428**

__________________

37450

13.32

5

1.2

10.0

1.60

7.5

1.1

10.0

1.80

10

0.7

10.0

2.40

3

543133*

___________________

49603

13.05

5

1.2

10.0

1.60

7.5

1.1

10.0

1.80

10

0.7

10.0

2.40

Notee:1))“*”:thhenuumeraatorindiicateesthheprropossedpproceessaarea,,whiichi