SM 07 Soil Classification

SoilMechanicsICE222CE 222

SoilClassificationSystems

1

UnifiedSoilClassificationSystem(USCS) 2

ASTMD2487isbasedonUSCS. USCSwasdevelopedbyCasagrande in1942forUSArmy. USCSisthemostcommonsoilclassificationsystem

amonggeotechnicalengineers.USCS id i i di t ib ti d l ti it f USCSconsidersgrainsizedistributionandplasticityoffines (passingNo.40sieve).

Inthissystem,soilfallswithinoneofthreemajory , jcategories: coarsegrainedsoils

f d l finegrainedsoils highlyorganicsoils

Coarse grained soil if P200 < 50% CoarsegrainedsoilifP200

Namingconvention 3

AtypicalUSCSclassificationwouldbe:SM SiltysandwithgravelGroup Symbol

FinegrainedSoilFirstLetter SecondLetter Example

y gGroup SymbolGroup Name

p

M Silt L Lowplastic ML,MH

C Clay H Highplastic CL,CH

O Organic OL OHO Organic OL,OH

CoarsegrainedSoilFirst Letter Second Letter ExampleFirstLetter SecondLetter Example

S Sand P Poorlygraded SP,SW,SM,SC

G Gravel W Wellgraded GP,GW,GM,GC

M SiltM Silty

C Clayey

Terminology 4

Clay:SoilpassingNo.200(0.075mm)sievethatexhibitsplasticity.IthasPI4andplotofPIandLLfallsonoraboveAline.

Silt:SoilpassingaNo.200(0.075mm)sievethatisnonplasticli h l l i d h hibi li l horveryslightlyplasticandthatexhibitslittleornostrength

whenairdry.IthasPI

Terminology(contd.) 5

Organicclay:Aclaywithsufficientorganiccontenttoinfluencethesoilproperties.Fororganicclay,itsliquidlimitvalueafterovendryingislessthan75%ofitsliquidlimitvaluebeforeovendrying.

i il il i h ffi i i i fl Organicsilt:Asiltwithsufficientorganiccontenttoinfluencethesoilproperties.Itsliquidlimitvalueafterovendryingislessthan75%ofitsliquidlimitvaluebeforeovendrying.q y g

Peat:Asoilcomposedofvegetabletissueinvariousstagesofdecompositionusuallywithanorganicodor,adarkbrowntoblackcolor,aspongyconsistency,andatexturerangingfromfibroustoamorphous.

Terminology(contd.) 6

W WellGraded:Goodrepresentationofallparticlesizesfromlargesttosmallest.

P PoorlyGraded:Uniform,mostparticlesaboutthesamesize;orskip(orgap)gradation,absenceofoneormoreintermediate sizesintermediatesizes.

Coefficientofuniformity (Cu)andCoefficientofcurvature(Cc)aredefinedasbelow:

( )1060230

10

60 , DD

DCDDC cu == ( )

whereD60,D30,D10 arediameterof60%,30%and10%passingongradationcurve,respectively.p g g p y

Particlesizedefinition 7

Systembasedonlyonparticlessmallerthan3inches.

Bouldersare>12inch

Cobblesare3inchto12inch

Gravels are between No 4 sieve and 3 inch GravelsarebetweenNo.4sieveand3inch

SandsarebetweenNo.200sieveandNo.4sieve

FinesaresmallerthanNo.200sieve

No. 200 No. 4 3-in.

cobblessandfines gravel

.075 mm 4.75 mm 75 mm

Organicdesignation 8

Aliquidlimittestisperformedon:

One sample that is only airdriedOnesamplethatisonlyair dried.

Onanotherthatisovendriedpriortotesting.

The liq id limit al es are compared b comp ting the ratio of the 2 Theliquidlimitvaluesarecomparedbycomputingtheratioofthe2values.

If the ratio of the ovendried soils LL to the airdry soils LLIftheratiooftheoven driedsoil sLLtotheair drysoil sLLvaluesis

Additionalevaluationoforganicsoils 9

Ignitiontest.ASTMD2974

S il l h t d i ffl f t t ith Soilsampleheatedinmufflefurnacesetateither440oC or750oC andweightlossmeasured.

PeatClassificationD4427

D10,D30,andD6010

DeterminingD10,D30,andD60

p

a

s

s

i

n

g

60

P

e

r

c

e

n

t

30

10D60D30D10

Grain Diameter

Cu andCc11

C ffi i f U if iD CoefficientofUniformityHighValuesIndicateWell

G d d S il10

60

DDCu =

GradedSoil

CoefficientofCurvature

ValuesBetween13( )230

DDDCc =

IndicateWellGradedSoil( )1060 DD

Alsocalledcoefficientofgradation,Cz

Cleansandsandgravels 12

CleanWellGradedSandsandGravelshavelessthan5%finesandawiderangeofparticlesizesthatareg pequallydistributed.

i

n

g

Wellgraded

r

c

e

n

t

p

a

s

s

i

P

e

r

Grain Diameter

Poorlygradedsandsandgravels 13

EitherMostlyOneSizeParticle Orgapgraded

a

s

s

i

n

g

e

r

c

e

n

t

p

a

PoorlygradedGapgraded

P

e

G i i i i

p g

Grain Diameter Grain Diameter

Clean,well/poorlygradeddefinitions 14

Sands lessthan5%fines Cu>6 Cc=1to3

IfthiscriteriaissatisfiedthenWELLGRADED

Gravelsl th 5 % fi

otherwisePOORLYGRADED

lessthan5%fines Cu>4 Cc = 1 to 3

IfthiscriteriaissatisfiedthenWELL GRADEDCc=1to3 thenWELLGRADEDotherwisePOORLYGRADED

Flowchart coarseandfinegrained 16

MeasurepassingNo.200sieve

50%ormore Lessthan50%passes

No.200sievepasses

No.200sieve

Fine grained Coarse grainedFinegrainedsoils

Coarsegrainedsoils

Flowchart organicsoils 17

Determinewhetherorganic

or notornot

Ratioofoven RatioofovendrytoairdryLLvalueis0.75

Organicsoils Inorganicsoils

AirdryLLis

Flowchart coarsegrained 18

Lessthan50%passNo.200sieve

Morethan12%passNo.200sieve

From5%to12%passNo.200sieve

Lessthan5%passNo.200sieve

Clean coarse Dual coarse Dirty coarseCleancoarsegrained

Dualcoarsegrained

Dirtycoarsegrained

Flowchartfinegrained 19

50%ormorepassNo.200sieve

LL50LL

20

S il i i d

Are50%ofparticles>0.075mm?

S il i fi i d

Yes No

Soiliscoarsegrained

Yes No

Soilisfinegrained

Isgravelfraction>sandfraction? Coarsegrainedsoilclassification

Soilissand,FirstletterisS

Yes No

Soilisgravel, FirstletterisG

Isclay+siltfraction

classification

Yes

y

>12%? siltfraction?

Yes NoIsclayfraction>siltfraction?

Plastic clay fines Nonplastic silty fines

Yes No IffirstletterisGCu 4and1Cc 3,

IffirstletterisGCu 4and1Cc 3,

Yes No

PlasticclayfinesSecondletterC

Non plasticsiltyfinesSecondletterM

IffirstletterisG,Cu 4and1Cc 3,then GW otherwise GP

u cthenGWGC,elseGPGC

u cthenGWGM,elseGPGM

IffirstletterisG IffirstletterisGthenGW otherwiseGP

IffirstletterisS,Cu 6and1Cc 3,thenSW otherwiseSP

Cu 4and1Cc 3,thenGWGC,elseGPGC

Cu 4and1Cc 3,thenGWGM,elseGPGM

21Are50%ofparticlessiltfraction?Soilisorganic,FirstletterisO

S il i l fi S il i il fi

Yes No

Is LL > 50%

Soilisclay,firstletterisC

Soilissilt,firstletterisM

IsLL>50%

Yes No

Plasticityishigh,secondletterisH

Plasticityislow,secondletterisL

Procedureforclassificationofsoils 22

Fromsieveanalysisandthegrainsizedistributioncurvedeterminethepercentpassingasthefollowing: >3inch:CobbleorBoulders 3toNo.4(76.2~4.75mm):Gravel No.4toNo.200(4.75~0.075mm):Sand

23

FineGrainedSoils

FIG.1FlowchartforClassifyingFineGrainedSoil(50%orMorePassesNo.200Sieve)

Finegrainedorganicsoils 24

GroupSymbol GroupName

FIG.2FlowchartforClassifyingOrganicFineGrainedSoil(50%orMorePassesNo.200Sieve)

25CoarseGrainedSoils

FIG.3FlowchartforClassifyingCoarseGrainedSoils(50%orMoreRetainedonNo.200Sieve)

Plasticitychart 26

27

Mediumplasticity/ibili

Highplasticity/compressibility

Lowplasticity/compressibility

compressibility

28

Cohesionlesssoil

Organicclays

Silt

Example 30

Gravel=9862

=36%

SandSand=628

=54%

Fines=8%

SoilA:D60 =4.2mm,D30 =0.6mm,D10 =0.09mmCu =46.67Cc =0.95

Example 31

LL = 42LL=42PL=31PI=4231=11

MLML

32Gravel=36%Sand=54%Fines=8%Cu =46.7Cc =0.95

LL=42PL=31PI=4231=11

ML

FIG.3FlowchartforClassifyingCoarseGrainedSoils(50%orMoreRetainedonNo.200Sieve)

SoilAisclassifiedas[SWSM:wellgradedsandwithsiltandgravel]

USCS Example,SoilA 33

SoilAGravel =100 80 =20%Sand =80 52 =28%Fines =52%>50%=>Finegrainedsoil

USCS Example,SoilA 34

LL=30PI=8

CLCL

35

CL Sandy lean clay with gravelCL Sandyleanclaywithgravel

SoilAGravel =20%Sand =28%Fines = 52%Fines =52%

AASHTOClassification Introduction 36

AASTOsystemofsoilclassificationwasdevelopedin1929.

This classification is standardized by ASTM designation D 3282ThisclassificationisstandardizedbyASTMdesignationD3282andAASHTOmethodM145.

Itprovidesgeneralratingofthesoilassubgrade forroadconstruction.

Itconsidersgrainsizedistributionandplasticityoffines.

AASHTOsystemusesbothgrainsizedistributionandAtterberg limitstoassignagroupclassificationandgroupindexindex.

ThegroupclassificationrangesfromA1(best)toA8(worst).

i hl i il ( k d ) l d d Highlyorganicsoils(muckandpeat)areplacedundergroupA8.

Introduction(contd.) 37

Groupindexvaluesnear0indicategoodsoils,whilevaluesof20ormoreindicateverypoorsoils.

SoilsclassifiedundergroupA1,A2andA3aregranularmaterialsofwhich35%passthroughtheNo.200sieve.

Soilsofwhich>35%ofpassthroughtheNo.200sieveareclassifiedundergroupsA4,A5,A6andA7.theseare

tl ilt d l t t i lmostlysiltandclaytypematerials.

AASHTO&USCS 38

AASHTOClassification 39

Grainsize Gravel:fractionpassing3in.(75mm)sieveandretainedonthe

N 10 (2 ) iNo.10(2mm)sieve. Sand:fractionpassingtheNo.10(2mm)sieveandretainedon

theNo.200(0.075mm)sieve. SiltandClay:fractionpassingtheNo.200sieve.

Plasticity:Thetermisappliedwhenthefinefractionsofth il h l ti it i d f 10 l Th tthesoilhaveaplasticityindexof10orless.Thetermclayeyisappliedwhenthefinefractionshaveaplasticityindexof11ormore.

Ifcobblesorboulders(>75mm)areencountered,theyareexcludedfromtheportionofsoilsamplefromwhichl f d hclassificationismade.However,thepercentageisrecorded.

Granularmaterials 40

Granularmaterials(35%oftotalsamplepassingNo.200)

Note: To classify a soil apply test data from left to right in the aboveNote: Toclassifyasoil,applytestdatafromlefttorightintheabovetable.Byprocessofelimination,thefirstgroupfromleftintowhichthetestdatafitisthecorrectclassification.

Siltclaymaterials 41

Siltclaymaterials(>35%oftotalsamplepassingNo.200)

Note: To classify a soil apply test data from left to right in the aboveNote: Toclassifyasoil,applytestdatafromlefttorightintheabovetable.Byprocessofelimination,thefirstgroupfromleftintowhichthetestdatafitisthecorrectclassification.

PlasticityChart 42

RangeofliquidlimitandplasticityindexforsoilsingroupsA2,A4,A5,A6,andA7

GroupIndex 43

Groupindex(GI)iscalculatedusingthefollowingempiricalformula:

( ) ( )[ ] ( )( )101501.0 40005.02.035 200200 ++= PIFLLFGIPartialGIdeterminedfromLL PartialGIdeterminedfromPI

whereF200 = percentage passing through the No. 200 sieveF200 percentagepassingthroughtheNo.200sieveLL =Liquidlimit,andPI =Plasticityindex

GI is taken as zero if the equation yields negative value GI istakenaszero,iftheequationyieldsnegativevalue.

CalculatedvalueofGI isroundedofftonearestwholenumber(for example GI = 3 4 is rounded off to 3; GI = 3 5 is rounded(forexample,GI=3.4isroundedoffto3;GI=3.5isroundedoffto4).

GroupIndex 44

Thereisnoupperlimitforthegroupindex.

The group index of soils belonging to groups A1a A1b A2 ThegroupindexofsoilsbelongingtogroupsA1a,A1b,A24,A25,andA3isalwayszero.

When calculating the GI for soils that belong to groups A26WhencalculatingtheGIforsoilsthatbelongtogroupsA26andA27,usethepartialGIforPI,orthefollowingformula:

( )( )1015010 = PIFGI Ingeneral,thequalityofperformanceofsoilasasubgrade

material is inversely proportional to the GI.

( )( )101501.0 200= PIFGImaterialisinverselyproportionaltotheGI.

Groupindexisshowninparenthesesafterthegroupsymbolas A26(3), A6(12), A75(17), etc.asA 2 6(3),A 6(12),A 7 5(17),etc.

AASHTO Examples 45

P10 =80% P40 =52% P200 =20% LL=35 PL=20PI=15

Givendataobtainedfromgradationcurve

Since,P200 50,notA1a Since,P40 >50,notA1b

Si P 10 t A 3 Since,P200 >10,notA3 SomustbeA2soil,useplasticitychart A26 soil A26soil

( )( )101501.0 200 = PIFGI UsethisformulaforA26andA27( )( ) 025.01015152001.0 ===GI Therefore,soilisA26(0)

( )( )

46

A26soil

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SM 07 Soil Classification