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
15
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
29
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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