transporte clastico y flujo

8/3/2019 Transporte Clastico y Flujo

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CLASTIC TRANSPORT ANDCLASTIC TRANSPORT AND

FLUID FLOWFLUID FLOW

CHAPTER 3CHAPTER 3


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ChapterChapter--3 Clastic transport3 Clastic transport

and fluid flowand fluid flowWeatheredrockand minerals fragmentsWeatheredrockand minerals fragments

aretransported from sourceareastoaretransported from sourceareastodepositionalsites (wheretheyaresubjectdepositionalsites (wheretheyaresubject

toadditionaltransportandredeposition)bytoadditionaltransportandredeposition)bythreekindsofprocesses:threekindsofprocesses:

11-- dry (nondry (non--fluidassisted),gravityfluidassisted),gravity--drivendrivenmass wastingprocessessuchasrockmass wastingprocessessuchasrockfallandrockslides;fallandrockslides;


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22-- wet (fluidassisted),gravitywet (fluidassisted),gravity--driven massdriven mass

wastingprocesses (sedimentgravitywastingprocesses (sedimentgravity

flows)suchasgrain flows, mudflows,flows)suchasgrain flows, mudflows,debris flows,andsomeslumps;anddebris flows,andsomeslumps;and

33-- processesthat involvedirect fluid flowsprocessesthat involvedirect fluid flows

ofair, water,and ice.ofair, water,and ice.


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Mass wastingMass wasting

Fluid flowFluid flow

Reynolds NumberReynolds Number

Froud NumberFroud NumberEntrainment,transportandEntrainment,transportand

depositionofclastsdepositionofclasts

TransportTransport


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Mass WastingMass Wasting

Mass wastingprocessesare importantMass wastingprocessesare important

mechanismsofsediemnttransport.mechanismsofsediemnttransport.

Althoughthey movethesoilandrockAlthoughthey movethesoilandrockdebrisonlyshortdistancesdownslope,debrisonlyshortdistancesdownslope,

theseprocessesplayacrucialrole intheseprocessesplayacrucialrole in

sedimenttransportbygettingtheproductssedimenttransportbygettingtheproducts

of weathering intothelongerof weathering intothelonger--distancedistance

sedimenttransportsystem.sedimenttransportsystem.


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Mass WastingMass Wasting

Indry massIndry mass--wastingprocesses, fluidplayswastingprocesses, fluidplayseithera minorroleornoroleatall.eithera minorroleornoroleatall.

Inrockortalus falls,clastsofanysizeInrockortalus falls,clastsofanysize

simply fall freely.simply fall freely.

Downslope movementofbodiesofrocksDownslope movementofbodiesofrocks

orsediment inslumpsorslidesglideorsediment inslumpsorslidesglide

downslopeen masse withoutsignificantdownslopeen masse withoutsignificant

internal foldingor faulting.Fluidsneartheinternal foldingor faulting.Fluidsnearthebaseprovideslubricationandpromotesbaseprovideslubricationandpromotes

failurealongslippagesurface.failurealongslippagesurface.


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Reynolds Number

Re= 2rVp/Q

Sir Osborne Reynolds addressed the problemof how laminar flow changes to turbulent flow.

The transition from laminar to turbulent flowoccurs as velocity increases, viscositydecrease, the roughness of the flow boundary

increases, and/or the flow becomes lessnarrowly confined.


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Froud NumberFroud Number

TheFroud Number istheratiobetween fluidTheFroud Number istheratiobetween fluidinertial forcesand fluidgravitational forces.inertial forcesand fluidgravitational forces.

Itcomparesthetendencyofa moving fluid (andItcomparesthetendencyofa moving fluid (and

aparticlebornebythat fluid)tocontinue movingaparticlebornebythat fluid)tocontinue movingwiththegravitational forcesthatacttostopthatwiththegravitational forcesthatacttostopthatmotion.motion.

The forceof inertiaexpressthedistancetraveledThe forceof inertiaexpressthedistancetraveled

bya discreteportionofthe fluidbefore itcomesbya discreteportionofthe fluidbefore itcomestorest.torest.

Likereynolds Numbers,FroudnumbersareLikereynolds Numbers,Froudnumbersaredimensionless.dimensionless.


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Froud NumberFroud Number

Fr=Fr= fluid inertial forces .fluid inertial forces .

gravitational forces in flowgravitational forces in flow


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Deposition: What forces controlDeposition: What forces control

the settling of particles?the settling of particles?Assoonasaparticle isliftedabovetheAssoonasaparticle isliftedabovethe

surfaceofabed, itbeginstosinkbacksurfaceofabed, itbeginstosinkbackagain.again.

Thedistancethat ittravelsdependontheThedistancethat ittravelsdependonthedrag forceofthecurrent,andthedrag forceofthecurrent,andthesettlingsettlingvelocity of the Particlevelocity of the Particle..

Thevelocityat whichaclastsettlesThevelocityat whichaclastsettlesthrougha fluid iscalculatedusingthrougha fluid iscalculatedusingSTOKES LAWofsettlingSTOKES LAWofsettling


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Stokes Law of settlingStokes Law of settling

Thegravitational forcepullingtheparticleThegravitational forcepullingtheparticle

downversusthedrag forceofthe fluiddownversusthedrag forceofthe fluid

resistingthissinking.resistingthissinking.

Theparticle willbe initiallyacceleratedueTheparticle willbe initiallyacceleratedue

togravity,butsoonthegravitationalandtogravity,butsoonthegravitationaland

drag forcesreachequilibrium,resulting indrag forcesreachequilibrium,resulting in

aconstant aconstant Terminal Fall VelocityTerminal Fall Velocity..


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Thedrag forceexertedbya fluidonaThedrag forceexertedbya fluidona

fallinggrain isproportionaltothe fluidfallinggrain isproportionaltothe fluid

density (density (VVFF),thediameter(d)ofthegrain),thediameter(d)ofthegrain

(incentimeters),thedragcoefficient (C(incentimeters),thedragcoefficient (CDD))

andthe fallvelocity (V).andthe fallvelocity (V).

Drag force= CDrag force= CDD (d (d22/4) (/4) (VVFF VV

22/2)/2)


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Drag forceDrag force

Upward forceduetobuoyancyofthe fluidUpward forceduetobuoyancyofthe fluid

is:Fis:Fupwardupward = 4/3 (d/2)= 4/3 (d/2)33 VVFFgg

Downward forcesduetogravity:Downward forcesduetogravity: Fg = 4/3 (d/2)Fg = 4/3 (d/2)33 VV ssg, wherepg, wherepss isthedensityisthedensity

oftheparticle.oftheparticle.

Drag force= FgDrag force= Fg-- FFupwardupward


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Drag force= FgDrag force= Fg-- FFupwardupward

CCDD (d (d22/4) (p/4) (pFF VV

22/2)= 4/3 (d/2)/2)= 4/3 (d/2)33VVssgg-- 4/3 (d/2)4/3 (d/2)33 VVFFgg

V2=V2= 4gd (4gd (VVss-- VVFF))

3 C3 CDD VVFFForlow laminarflow atlow concentrationsofparticleandlowForlow laminarflow atlow concentrationsofparticleandlow

Reynoldsnumbers, CReynoldsnumbers, CDD isequalto24/Risequalto24/Ree..

V = 1/18 ([V = 1/18 ([VV ss-- VV FF]gd]gd22 /u)/u)-- Stokes Law ofsettlingStokes Law ofsettling

VV--velocity,gvelocity,g--gravity,ugravity,u--viscocity,eventhediffernce indensity (viscocity,eventhediffernce indensity (VVss-- VV

FF) isconstant foragivensituation.Itcanbesubstitute forC) isconstant foragivensituation.Itcanbesubstitute forCC =C = ((VV ss-- VV FF)g)g

18u18u

Stokeslaw reducesto V=CDStokeslaw reducesto V=CD22


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Stokes law reduces to V=CDStokes law reduces to V=CD22

Whendensityandviscosityareconstant,Whendensityandviscosityareconstant,settlingvelocity increases withthesettlingvelocity increases withthediameteroftheparticle.diameteroftheparticle.

Larger grains fall faster.Larger grains fall faster.

Settlingvelocitydecreases withhigherSettlingvelocitydecreases withhigherviscositiesand increases withdenserviscositiesand increases withdenserparticles.particles.C =C = ((VVss-- VVFF)g)g

18u18u


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Implications of the StokesImplications of the Stokes

LawLawHighdensity mineralssettle morerapidlyHighdensity mineralssettle morerapidly

thanlow density minerals.thanlow density minerals.

SlowSlow--moving,highlyviscous fluidssuchasmoving,highlyviscous fluidssuchasmudflowsanddensitycurrentscanmudflowsanddensitycurrentscan

transportcoarsertransportcoarser--grained materialsthangrained materialsthan

lessviscuos fluidssuchasriversandthelessviscuos fluidssuchasriversandthe

wind,despitethenormallyhighervelocitywind,despitethenormallyhighervelocityoftheselessviscous fluids.oftheselessviscous fluids.


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Lowertemperatures will increasviscosityLowertemperatures will increasviscosity

decreasingthe fallvelocity.decreasingthe fallvelocity.Becauseofturbulence,coarserparticlesBecauseofturbulence,coarserparticles

fall moreslowlythanpredicted.fall moreslowlythanpredicted.

NonNon--spherical flakessuchas mica willspherical flakessuchas mica willsettle moreslowlythanspheres withthesettle moreslowlythanspheres withthe

samedensity.samedensity.

Angulargrains willgeneratesmallAngulargrains willgeneratesmall

turbulenteddiesthatretardsettlingturbulenteddiesthatretardsettling

velocity.velocity.


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Hydraulic equivalencyHydraulic equivalency

Theterm referstoclaststhatsettleatTheterm referstoclaststhatsettleat

identicalvelocitiesdespitesubstantialidenticalvelocitiesdespitesubstantial

differences insize,shape,angularity,anddifferences insize,shape,angularity,and

density.density.

ie. Sediment mixesof finegrained,siltie. Sediment mixesof finegrained,silt--sizesize

magnetite, finesandmagnetite, finesand--sizebiotite flakes,andsizebiotite flakes,and

medium sandmedium sand--sizequartz.sizequartz.

transporte clastico y flujo

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