SoilMechanicsICE225CE 225

Originofsoilandgrainsize

1

2WhySoilproblemsareUNIQUE?

Soildoesnotpossessalinearoruniquestressstrainrelationshipp

Soilbehaviordependsonpressure,time,andenvironmentThesoilatessentiallyeverylocationisdifferentI l ll h f il i l d i d dInnearlyallcasesthemassofsoilinvolvedisundergroundandcannotbeseeninitsentiretybutmustbeevaluatedonthebasisofsmallsamplesobtainedfromisolatedlocations

Mostsoilsareverysensitivetodisturbancefromsampling,and thus the behavior measured by a laboratory test may beandthusthebehaviormeasuredbyalaboratorytestmaybeunlikethatoftheinsitusoil

Soilparticlesize 3

Soilsaregenerallycalledgravel,sand,siltorclay.

Gravelsarepiecesofrocks.

Sandparticlesaremadeofmostlyquartzandfeldspar.

Siltsaremicroscopicsoilfractionsthatcontainveryfinep yquartzgrainsandsomeflakeshapedparticles.

Claysaremostlyflakeshapedmicroscopic/submicroscopicparticlesofmica,claymineralsetc.

No.200 No.4 3in.

cobblessandfines gravel

.075mm 4.75mm 75mm

Clays 4

Whatmakesclayssuchinterestinganddangeroussoilsforfoundations?

Thissimpleexperimentshows the range ofshowstherangeofstrengthforasingleclaysample

Clays 5

Thetermclayreferstoanumberofearthymaterialsthatarecomposedofmineralsrichinalumina,silicaandwater.Clayisnotasinglemineral,butanumberofminerals.

Whenmostclaysarewet,theybecomeplastic meaningthatcanbeformedandmoldedintoshapes.

Whenclayisfired,thewaterisdrivenoffandtheybecomey , yashardasstone.

Clay is easily found all over the world. As a result, nearly allClayiseasilyfoundallovertheworld.Asaresult,nearlyallcivilizationshaveusedsomeformofclayforeverythingfrombrickstopotterytotabletsforrecordingbusinesstransactionstransactions.

Soilcomposition 6

Thecompositionofsoilandrockisquitedifferentfromthatofothercivilengineeringmaterials.g g

Engineeringpropertiesofsoilsvarysignificantlyfromplace to place and even across a single building siteplacetoplace,andevenacrossasinglebuildingsite.

Soilisaparticulatematerialthatconsistsofindividualparticles.

Soil can contain all three phases of matter (solidSoilcancontainallthreephasesofmatter(solid,liquid,andgas)simultaneously,andthesethreephasescanbepresentinvaryingproportions.p p y g p p

Soilasaparticulatematerial 7

Mostcivilengineeringmaterialsconsistofacontinuousmassheldtogetherwithmolecularbonds.

Incontrast,soilisaparticulatematerialthatconsistsofindividualparticlesassembledtogether.g

Itsengineeringpropertiesdependlargelyontheinteractionbetween these particles, only secondarily on their internalbetweentheseparticles,onlysecondarilyontheirinternalproperties.

Thethreephases 8

Soilisdifferentfrommostcivilengineeringmaterialsinthatitcansimultaneouslycontainsolid,liquid,andy , q ,gasphases.

The liquid and gas phases are contained in the voidsTheliquidandgasphasesarecontainedinthevoidsorporesbetweenthesolidparticles.

The three phases often interact and these Thethreephasesofteninteract,andtheseinteractionshaveimportanteffectsonsoilsbehavior.

Soilcomposition 9

Thesoiliseithercoarseorfinegrained.

Coarse grained are visible to the naked eye: G (gravels) + SCoarsegrainedarevisibletothenakedeye:G (gravels) S(sands)

Finegrainedareinvisibletothenakedeye:M (silts)+C (Clays)

Coarsegrainedsoilsarealsocalledgranularandfinegrainedsoilsarecommonlyreferredtoascohesive.

ThenamegravelcomesfromFrenchwordgreve.ItssymbolisG.

ThesymbolSforsandcomesfromFrenchwordsable.

ThesymbolMforSiltcomesfromSwedishwordmjala.

Mechanicalanalysis 10

Mechanicalanalysisisthedeterminationofthesizerangeofparticlespresentinasoil,expressedasapercentage of the total drypercentageofthetotaldryweight.

Two methods used:Twomethodsused: Sieveanalysis:forparticlesizeslargerthan0.075mmingdiameter.

Hydrometeranalysis:forparticlesizessmallerthan0.075mmindiameter.

Sieveanalysis 11

Sievedesignation larger 12

SieveslargerthantheNo.4sievearedesignatedbythesizeoftheopeningsinthesieve.

Commonlyusedlargersievesizes: 3in. 2in. 1.5 in.1.5in. 1in. 3/4in. 1/2in. 3/8in.

Sievedesignation smaller 13

Smallersievesarenumberedaccordingtoth b f i

10openingsthenumberofopeningsperinch.

Commonly used smaller

perinch

Commonlyusedsmallersizesieves: No.4

1 inch

No.10 No.20 No 40No.40 No.60 No.140

N 200No. 10 sieve

No.200

USstandardsievesizes 14

SieveNo. Opening(mm) SieveNo. Opening(mm)

3inch 76.200 20 0.8502inch 50.800 25 0.710c 50 800 5 0 01.5inch 38.100 30 0.6001inch 25.400 35 0.5003/4 inch 19.000 40 0.4253/4inch 19.000 40 0.4253/8inch 9.520 50 0.355

4 4.750 60 0.2505 4 000 70 0 2125 4.000 70 0.2126 3.350 80 0.1807 2.800 100 0.1508 2 360 120 0 1258 2.360 120 0.12510 2.000 140 0.10612 1.700 170 0.09014 1 400 200 0 07514 1.400 200 0.07516 1.180 270 0.05318 1.000

15

Book:GeotechnicalEngineering(CODUTO)Page115

16

Coarsegravel19 0 75 0

Finegravel4 75 19 0 mm 19.0 75.0mm4.75 19.0mm

Coarse SandM di S dFi S d CoarseSand2.00 4.75mm

MediumSand0.425 2.00mm

FineSand0.075 0.425mm

Sieveanalysis 17

Soilusedinsieveanalysisisovendriedandalllumpsarebroken.

Thesoilisthenshakenthroughastackofsieveswithopeningofdecreasingsizefromtoptobottom.p g g p

Apanisplacedbelowthestack. Breaking lumps in clayey soils may be difficult Breakinglumpsinclayeysoilsmaybedifficult.

Inthiscase,thesoilmaybemixedwithwatertomakeaslurry and then washed through sievesslurryandthenwashedthroughsieves.

Portionsretainedoneachsievearecollectedseparatelyandovendried.

Massretainedoneachsieveisdetermined.

Sieveanalysis calculations 18

Determinethemassofsoilretainedoneachsieve(i.e.M1,M2,...,Mn)andinthepan(i.e.Mp).

Determinethetotalmassofthesoil:M=M1 +M2 +...+Mn+Mp.

Determinethecumulativesoilmassretainedaboveeachsieve.Fortheith sieve,itis(Mi)retained =M1 +M2 +...+Mi.

Themassofsoilpassingtheith sieveis(Mi)passing=M (M1 +M2 +...+Mi).

Thepercentofsoilpassingith sieve(orpercentfiner)isF=(Mi)passing/M100.

D10,D30,andD6019

DeterminingD10,D30,andD60

p

a

s

s

i

n

g

60

P

e

r

c

e

n

t

30

10D60D30D10

Grain Diameter

Cu andCc20

C ffi i f if iD Coefficient of UniformityHigh Values Indicate Well-Graded Soil10

60

DDCu =

Coefficient of CurvatureValues Between 1-3 ( )

230

DDDCc = Indicate Well-Graded Soil( )1060 DD

Alsocalledcoefficientofgradation,Cz

Cu andCc21

D

10

60

DDCu =

2D( )1060

30

DDDCc =

Cu andCc22

Grainsizedistributioncurve 23

A fi i d ilA:finegrainedsoilsCu =5Cc =0.8

B i d ilB:coarsegrainedsoils

Cu =13Cc =0.83

Grainsizedistributioncurve 24

C l d d

Cu =1.63Cc =0.96

C:poorlygradedoruniformlygraded

Grainsizedistributioncurve 25

D ll d d il

Cu =190Cc =1.18

D:wellgradedsoils

E:gapgradedsoils

Cu =111C = 0 18Cc =0.18

Grainsizedistributioncurve 26

Wellgraded poorlygradedsoil (uniformlygraded)soil

27Grain-size distribution curve

3/4 in No 4 No 10 No 40 No 200 Hydrometer3 in

80

1003/4 in. No. 4 No. 10 No. 40 No. 200 Hydrometer 3 in.

60

s

s

i

n

g

D10 =0.10D30 =0.18

40

P

e

r

c

e

n

t

p

a

s

D60 =0.25

Cu = 2.50

0

20Cu 2.50Cc =1.30

0.0010.010.1110

Grain diameter (mm)

GRAVEL SANDSILT or CLAY

Coarse Fine Coarse Medium Fine

28

Hydrometeranalysis 29

Basedontheprincipalofsedimentationofsoilgrainsinwater.

Particlesinwatersettleatdifferentvelocities,dependingontheirshape,size,weight,andviscosity of waterviscosityofwater.

Particlesareassumedtobespheresandtheirvelocities can be expressed by Stokes law.velocitiescanbeexpressedbyStokeslaw.

2

18Dv ws

=where v = velocity(cm/s)

s = densityofsoilparticles(g/cm3) = density of water (g/cm3)w = densityofwater(g/cm3) = viscosityofwater(gsec/cm2)D = diameterofsoilparticles(cm)

Hydrometeranalysis 30

StokesLaw 31

2

18Dv ws

= where v = velocity s = densityofsoilparticlesw = densityofwater = viscosityofwaterD = diameterofsoilparticles

L1818 LDi

p

tLvD

wsws

==1818

tLv ==

TimeDistance where

wss G = ( ) tL

GD

ws 1

18=

StokesLaw 32

IfLisincm,tisinmin,w ing/cm3, ingsec/cm2,andDinmm,thenequationcanbewrittenas

( )( )

18mm = LD ( ) 60110 tG ws LL30

( ) tLK

tL

GD

ws

== 1

30

( )130 where, = sG

K Assumingw =1g/cm3

Stokeslaw 33

ValuesofKforseveralspecificgravityofsolidsandtemperaturecombinations

Hydrometeranalysis 34

Whenahydrometerisplacedinthesoilsuspensionatatimet,measuredfromthestartofsedimentation it measures the sp gravity in thesedimentation,itmeasuresthesp.gravityinthevicinityofitsbulbatadepthL.

Hydrometersaredesignedtogivetheamountofsoil,ingrams,thatisstillinsuspension.Theyarecalibratedforsoilsthathaveasp.gravityGsof2.65(forotherGsvalues,correctionisrequired).

Byknowingtheamountofsoilinsuspension,L,andt,wecancalculatethe%ageofsoilbyweightfinerthan a given diameterthanagivendiameter.

ForASTM152Hhydrometer(cm)16402916(cm) RL = (cm)164.029.16 (cm) RL =

whereR=hydrometerreadingcorrectedformeniscus

Particleshape 35

Theshapeofsilt,andgravelsvariesfromveryangulartowellrounded.

Angularparticlesarefoundneartherockfromwhichtheyaref d hil d d ti lformed,whileroundedparticlesarefoundfartherawayfromtheirorigin.

Angularparticleshaveagreaterstrengththansmoothones,because it is more difficult tobecauseitismoredifficulttoslidepastoneanother.

Thisiswhycrushedaggregateiss s y c us ed agg egate susedasthebasematerialinpavements.

Soil TexturesSoilTextures

To determine the texture of To determine the texture ofa soil sample, find itspercent for sand, silt, andclay.

The texture of the soil willbe where all three linesintersect.

Claysoils 37

Soilsthatconsistofsilt,sand,orgravelareprimarilytheresultofphysicalandmildchemicalprocessesandretainmuchofthechemicalstructureoftheirparentrocks.

Claysoilsexperienceextensivechemicalweatheringandareh d i i l i diff f hchangedintoanewmaterialquitedifferentfromtheparentrocks.

A lt th i i ti d b h i f l Asaresult,theengineeringpropertiesandbehaviorofclaysquitedifferentfromothersoils.

Clays 38

Physicalcharacteristicsofclaysare:

They can absorb water or lose water from simple humidity Theycanabsorbwaterorlosewaterfromsimplehumiditychanges.

When water is absorbed clays will often expand as the Whenwaterisabsorbed,clayswilloftenexpandasthewaterfillsthespacesbetweenthestackedsilicatelayers.

Due to the absorption of water the specific gravity of clays Duetotheabsorptionofwater,thespecificgravityofclaysishighlyvariableandisloweredwithincreasedwatercontent.

Claystendtoformfromweatheringandsedimentaryprocesseswithonlyafewexamplesofclaysformingin

hprimaryigneousormetamorphicenvironments.

Claysoils 39

Clayparticles