Construction Methods - Chapter02.pdf - po ang - Januszek66

PARTONE

Earthmovingand

HeavyConstruction

EarthmovingMaterials

andOperations

2–1INTRODUCTIONTOEARTHMOVING

TheEarthmovingProcess

Earthmovingistheprocessofmovingsoilorrockfromonelocationtoanotherandpro-

cessingitsothatitmeetsconstructionrequirementsoflocation,elevation,density,mois-

turecontent,andsoon.Activitiesinvolvedinthisprocessincludeexcavating,loading,

hauling,placing(dumpingandspreading),compacting,grading,andfinishing.Thecon-

structionproceduresandequipmentinvolvedinearthmovingaredescribedinChapters3

to5.Efficientmanagementoftheearthmovingprocessrequiresaccurateestimatingof

workquantitiesandjobconditions,properselectionofequipment,andcompetentjob

management.

EquipmentSelection

Thechoiceofequipmenttobeusedonaconstructionprojecthasamajorinfluenceonthe

efficiencyandprofitabilityoftheconstructionoperation.Althoughthereareanumberof

factorsthatshouldbeconsideredinselectingequipmentforaproject,themostimportant

criterionistheabilityoftheequipmenttoperformtherequiredwork.Amongthoseitems

ofequipmentcapableofperformingthejob,theprincipalcriterionforselectionshouldbe

maximizingtheprofitorreturnontheinvestmentproducedbytheequipment.Usually,but

notalways,profitismaximizedwhenthelowestcostperunitofproductionisachieved.

(Chapter17providesadiscussionofconstructioneconomics.)Otherfactorsthatshouldbe

consideredwhenselectingequipmentforaprojectincludepossiblefutureuseoftheequip-

ment,itsavailability,theavailabilityofpartsandservice,andtheeffectofequipmentdown-

timeonotherconstructionequipmentandoperations.

Aftertheequipmenthasbeenselectedforaproject,aplanmustbedevelopedtoef-

ficientlyutilizetheequipment.Thefinalphaseoftheprocessis,ofcourse,competentjob

managementtoassurecompliancewiththeoperatingplanandtomakeadjustmentsforun-

expectedconditions.

CHAPTER2

ProductionofEarthmovingEquipment

Thebasicrelationshipforestimatingtheproductionofallearthmovingequipmentis:

Production % Volumepercycle $ Cyclesperhour (2–1)

Theterm“volumepercycle”shouldrepresenttheaveragevolumeofmaterialmoved

perequipmentcycle.Thusthenominalcapacityoftheexcavatororhaulunitmustbemod-

ifiedbyanappropriatefillfactorbasedonthetypeofmaterialandequipmentinvolved.The

term“cyclesperhour”mustincludeanyappropriateefficiencyfactors,sothatitrepresents

thenumberofcyclesactuallyachieved(orexpectedtobeachieved)perhour.Inaddition

tothisbasicproductionrelationship,specificproceduresforestimatingtheproductionof

majortypesofearthmovingequipmentarepresentedinthechapterswhichfollow.

Thecostperunitofproductionmaybecalculatedasfollows:

Costperunitofproduction % Equipmentcostperhour

Equipmentproductionperhour

(2–2)

Methodsfordeterminingthehourlycostofequipmentoperationsareexplainedin

Chapter17.

Therearetwoprincipalapproachestoestimatingjobefficiencyindeterminingthe

numberofcyclesperhourtobeusedinEquation2–1.Onemethodistousethenumberof

effectiveworkingminutesperhourtocalculatethenumberofcyclesachievedperhour.

Thisisequivalenttousinganefficiencyfactorequaltothenumberofworkingminutesper

hourdividedby60.Theotherapproachistomultiplythenumberoftheoreticalcyclesper

60-minhourbyanumericalefficiencyfactor.Atableofefficiencyfactorsbasedonacom-

binationofjobconditionsandmanagementconditionsispresentedinTable2–1.Both

methodsareillustratedintheexampleproblems.

Table2–1 Jobefficiencyfactorsforearthmovingoperations(FromTM5-331B,

U.S.DepartmentoftheArmy)

ManagementConditions *

JobConditions **

Excellent Good Fair Poor

Excellent

0.84 0.81 0.76 0.70

Good

0.78 0.75 0.71 0.65

Fair

0.72 0.69 0.65 0.60

Poor

0.63 0.61 0.57 0.52

*Managementconditionsinclude:

Skill,training,andmotivationofworkers.

Selection,operation,andmaintenanceofequipment.

Planning,joblayout,supervision,andcoordinationofwork.

**Jobconditionsarethephysicalconditionsofajobthataffecttheproductionrate(notincludingthe

typeofmaterialinvolved).Theyinclude:

Topographyandworkdimensions.

Surfaceandweatherconditions.

Specificationrequirementsforworkmethodsorsequence.

EARTHMOVINGMATERIALSANDOPERATIONS

2–2EARTHMOVINGMATERIALS

SoilandRock

Soilandrockarethematerialsthatmakeupthecrustoftheearthandare,therefore,thema-

terialsofinteresttotheconstructor.Intheremainderofthischapter,wewillconsiderthose

characteristicsofsoilandrockthataffecttheirconstructionuse,includingtheirvolume-

changecharacteristics,methodsofclassification,andfieldidentification.

GeneralSoilCharacteristics

Severaltermsrelatingtoasoil’sbehaviorintheconstructionenvironmentshouldbeun-

derstood. Trafficability istheabilityofasoiltosupporttheweightofvehiclesunderre-

peatedtraffic.Inconstruction,trafficabilitycontrolstheamountandtypeoftrafficthatcan

useunimprovedaccessroads,aswellastheoperationofearthmovingequipmentwithinthe

constructionarea.Trafficabilityisusuallyexpressedqualitatively,althoughdevicesare

availableforquantitativemeasurement.Trafficabilityisprimarilyafunctionofsoiltype

andmoistureconditions.Drainage,stabilizationofhaulroutes,ortheuseoflow-ground-

pressureconstructionequipmentmayberequiredwhenpoortrafficabilityconditionsexist.

Soildrainagecharacteristicsareimportanttotrafficabilityandaffecttheeasewithwhich

soilsmaybedriedout. Loadability isameasureofthedifficultyinexcavatingandloading

asoil.Loosegranularsoilsarehighlyloadable,whereascompactedcohesivesoilsandrock

havelowloadability.

Unitsoilweightisnormallyexpressedinpoundspercubicyardorkilogramspercu-

bicmeter.Unitweightdependsonsoiltype,moisturecontent,anddegreeofcompaction.

Foraspecificsoil,thereisarelationshipbetweenthesoil’sunitweightanditsbearingca-

pacity.Thussoilunitweightiscommonlyusedasameasureofcompaction,asdescribed

inChapter5.Soilunitweightisalsoafactorindeterminingthecapacityofahaulunit,as

explainedinChapter4.

Intheirnaturalstate,allsoilscontainsomemoisture.Themoisturecontentofasoil

isexpressedasapercentagethatrepresentstheweightofwaterinthesoildividedbythe

dryweightofthesoil:

% Moistweight # Dryweight

Dryweight

Moisturecontent 1

$ 100

(2–3)

If,forexample,asoilsampleweighed120lb(54.4kg)inthenaturalstateand100lb

(45.3kg)afterdrying,theweightofwaterinthesamplewouldbe20lb(9.1kg)andthe

soilmoisturecontentwouldbe20%.UsingEquation2–3,thisiscalculatedasfollows:

Moisturecontent % 120 # 100

100 $ 100 % 20%

% 54.4 # 45.3

45.3 $ 100 % 20%

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