Soil Classification & Systems

This presentation covers the topic of particle size classification, dry sieve analysis, wet sieve analysis, sedimentation analysis, stokes law, methods of sedimentation analysis, Indian Standard Soil classification system.

1. SOIL Classification
& systems
Arbaz Mubarak Kazi,
B.E, M.E (Civil Engineering)
Email:[email protected]
https://gtearchives.wordpress.com
www.linkedin.com/in/arbaz-kazi-20747570
“Everyday is an
Adventure
When you are
Civil Engineer”

2. CONTENTS
➢PurposeofsoilClassification
➢SoilClassificationsystems
▪ParticleSizeClassification
▪Dry &WetSieveAnalysis
▪Sedimentation Analysis
▪Stokes Law
➢IndianSoilClassificationSystem

3. Purposeof Soil Classification
1.Soilsinnaturerarelyexistseparatelyasgravel,sand,silt,clay
ororganicmatter,butareusuallyfoundasmixtureswith
varyingproportionsofthesecomponents.
2.Classifyingsoilsintogroupswithsimilarbehavior,intermsof
simpleindices,canprovidegeotechnicalengineersageneral
guidanceaboutengineeringpropertiesofthesoilsthroughthe
accumulatedexperience.
3.TwocommonlyusedapproachforClassifyingsoilsisbased
onparticledistributionandAtterberglimits

4. SoilClassificationSystems
1.ParticleSize Classification
2.TexturalClassification
3.HighwayResearchBoard (HRB)Classification
4.UnifiedSoil ClassificationSystem(USCS)
5.IndianStandardClassificationSystem(ISCS)

5. ParticleSizeClassification

6. ▪Inthissystemsoilsarrangedaccordingtograinsizes.
▪Termssuchasgravel,sand,siltandclayareusedtoindicate
grainsizes.
▪Thesetermsareusedonlyasdesignationofparticlesizes.
▪Theydonotsignifynaturallyoccurringsoiltypes,asnaturally
occurringsoilaremixtureofparticlesofdifferentsizes.
▪Plasticitycharacteristicsofsoilisnotaccountedforsoil
classificationinthissystem.
▪InIndiaParticlesizeclassificationisdoneonthebasisofIS
1498:1970
Introduction

7. MITSoil Classification

8. US BureauSoilClassification

9. ISClassificationofGrainSize

10. ▪Thepercentageofvarioussizesofsoilparticlesinagivendrysoil
sampleisfoundbymechanicalanalysisorparticlesizeanalysis.
▪Bymechanicalsieveanalysisismeantforseparationofasoilintoits
differentsizefractions.
▪Themechanicalsieveanalysisisperformedintwostagesasshown
below:
ParticleSizeDistribution
Mechanical Analysis
SieveAnalysis
Sedimentation or wet
mechanical analysis

11. SieveAnalysis:
•Sieveanalysisconsistsofshaking
thesoilsamplethroughasetof
sievesthathaveprogressively
smalleropenings.
•IntheIndianStandard(IS:460-
1962),thesievesaredesignated
bysizeofopeningin(mm)as
given.
•Thecompletesieveanalysiscan
bedividedintotwoparts-the
coarseanalysisandfineanalysis.
Sieve
Number
SizeofOpening(mm)
4 4.750
6 3.350
8 2.360
12 1.680
16 1.180
20 0.850
30 0.600
40 0.425
50 0.300
60 0.250
80 0.180
100 0.150
140 0.106
200 0.075

12. •Anovendriedsampleofsoilisseparatedintotwofractionsby
sievingitthrougha4.75mmISsieve.
•Theportionretainedonitistermedasgravelfractionandiskeptfor
coarseanalysis,whileportionpassingthroughitissubjectedtofine
sieveanalysis.
•Soilpassing4.75mmI.S.Sieveandretainedon75micronI.S.Sieve
containsnofines.Thosesoilscanbedirectlydrysievedratherthan
wetsieving.
SieveAnalysis

13. MechanicalSieve Shaker
DrySieving:
•Take500gmofthesoilsampleaftertaking
representativesamplebyquartering.
•Conductsieveanalysisusingasetofstandard
sievesasgiveninthedatasheet.
•Thesievingmaybedoneeitherbyhandorby
mechanicalsieveshakerfor10minutes.Weigh
thematerialretainedoneachsieve.
•Thepercentageretainedoneachsieveis
calculatedonthebasisofthetotalweightof
thesoilsampletaken.
•Fromtheseresultsthepercentagepassing
througheachofthesievesiscalculated.
•Drawthegrainsizecurveforthesoilinthe
semi-logarithmicgraphprovided.

14. WetSieving:
Ifthesoilcontainssubstantialquantity(saymorethan
5%)offineparticles,awetasieveanalysisisrequired.
Alllumpsarebrokenintoindividualparticles.
•Take200gmofovendriedsoilsampleandsoaked
withwater.
•Ifdeflocculationisrequired,2%sodium
hexametaphosphatesolutionisusedinsteadofwater.
•Thesampleisstirredandleftforsoakingperiodofat
least1hour.
•Theslurryisthensievedthrough4.75mmsieveand
washedwithajetof water.
•Thematerialretainedonthesieveisthegravel
fraction,whichshouldbedriedinovenandweighed.

15. •Thematerialpassingthrough4.75mmsieveissievedthrough75μsieve.
•Thematerialiswasheduntilthewaterfilteredbecomesclear.
•Thesoilretainedon75-micronsieveiscollectedanddriedinoven.
•Itisthensievedthroughthesieveshakerfortenminutesandretained
materialoneachsieveiscollectedandweighed.
•Thematerialthatwouldhavebeenretainedonpanisequaltothetotal
massofsoilminusthesumofthemassesofmaterialretainedonall
sieves.
•Drawthecurveforthesoilinthesemi-logarithmicgraphtoobtaingrain
sizedistributioncurve.
WetSieving:

16. Grain-SizeDistributionCurves

18. •WellgradedSoilwillhaveparticlesfromalmostallthesize
rangesandwillgiveastablemix.
•GapgradedSoilwillhavedeficiencyofcertainparticlesofa
particularsizerange.
•UniformlyorpoorlygradedSoilwillhavealmostsamesize
orfromnarrowrangeofparticlesizesofsoilinthesample.
Thissamplewillcontainsinglesizesoil.

19. Coefficient of
curvature (Cc) should
lie between 1 and 3for
well grade gravel and
sand.
Cu should be more
than 4 for gravel and
more than 6 forsand.

20. ❑Sieveanalysiswasperformedon1000gmofdrysoilsampleandthefollowing
observationsweremadeasgiven:Useparticlesizeclassificationsystemand
classifythesoil,alsofindCuandCc
Sieve Size(mm) Mass Retained(gm)
20 33
10 49
4.75 85
2 140
1 160
0.6 142
0.425 118
0.3 82
0.212 56
0.15 35
0.075 23

21. Sieve
Size
(mm)
Mass
Retained(gm)
%Mass
Retained
%Cumulative
Retained
%Finer
20 33 3.3 3.3 96.7
10 49 4.9 8.2 91.8
4.75 85 8.5 16.7 83.3
2 140 14 30.7 69.3
1 160 16 46.7 53.3
0.6 142 14.2 60.9 39.1
0.425 118 11.8 72.7 27.3
0.3 82 8.2 80.9 19.1
0.212 56 5.6 86.5 13.5
0.15 35 3.5 90 10
0.075 23 2.3 92.3 7.7

23. D60 1.419
D30 0.465
D10 0.150
Cu = D60/D10 = 1.419/0.150 = 9.46 > 6, Hence it isSand
Cc = D30
2
/(D60*D10) = 0.465
2
/(1.419*0.150) = 1.01 > 1, Hence it is well graded
The soil may be classified as Well Graded Sand(SW)

24. Importance of Particle SizeDistribution
1.Usedforthesoilclassification.
2.Usedtodesigndrainagefilter.
3.Usedtoselectfillmaterialsofembankments,earthdams,roadsub-basematerials.
4.Usedtoestimateperformanceofgrouting,chemicalinjectionanddynamic
compaction.
5.EffectiveSize,D
10,canbecorrelatedwiththehydraulicconductivity.
6.Estimateapproximatevalueofco-efficientofpermeability.
7.Usedtodeterminesusceptibilityofsoiltofrostaction.
8.UsedofSoilstabilizationandpavementdesign.

25. ▪Forparticles≤0.075mm(siltandclayfractions)sedimentation
methodsbasedonStokeslawareusedtodeduceparticlesize
distribution.
▪Soilparticlessettleinaqueoussolutionattainingterminal
velocitiesproportionaltotheirmassandsize.
▪Theamountofsuspendedsoilafteragivensettlingtimeisused
todetermineparticlesizefractions.
▪Theamountofsoilinsuspensionisdeterminedbyeither
extractingasamplebythepipettemethodorfromadirect
hydrometerreading.
Particle Size Distribution -Sedimentation

26. •Buoyancyanddragforcesactagainst
thegravitationalforce.
•AsphericalsoilparticleD=5um
reaches99%ofitsterminalvelocityin
aqueoussolutionwithin0.017ms,and
forD=1mmthetimeis0.68s.
•BuoyancyForce(weightofdisplaced
liquid)DragForce(exertedbythe
surroundingliquid)Gravitational
Force
Stokes Law Three forces acting on a
spherical particle.

27. Thethreeforcesactinguponthesettlingparticlequicklyequilibrateandthe
particlereachesaconstantsettlingvelocity.
Wecansolvetheforcebalanceequationtoobtainthesettlingvelocity
Sinceweknowthatvelocityequalslengthpertimewecancalculatethetime
particlesofacertainsizeneedtosettlethroughadistanceh:
tisthetimerequiredforparticlesofacertainsizetosettlebelowacertain
depthh.
Stokes Law

28. •Particlesarelargeenoughtobeunaffectedbythethermal(Brownian)motion
ofthefluidmolecules.
•Allparticlesarerigid,spherical,andsmooth.
•Allparticleshavethesamedensity.
•Thesuspensionisdiluteenoughthatparticlesdonotinterferewitheachother
•Fluidflowaroundtheparticlesislaminar.Thatmeansnoparticleexceedsthe
criticalvelocityfortheonsetofturbulence.
•Inpracticeweknowthatsoilparticlesareneithersphericalnorsmooth.Hence
thediametercalculatedfromStokeslawdoesnotnecessarilycorrespondtothe
actualdimensionsoftheparticles.Weratherreceiveaneffectiveorequivalent
settlingdiameter.
Stokes Law -Limitations

29. Methods of Sedimentation Analysis
PipetteMethod HydrometerMethod

30. IS SOIL CLASSIFICATION SYSTEM
IS:1498-1970describestheIndianStandardonClassificationandIdentificationofSoils
forgeneralengineeringpurposes.ItissimilartoU.S.Soilclassificationsystemexceptthat
theU.S.Soilclassificationsystemhas15groupswhilethissystemhas18groups
Significantprovisionsofthissystemaregivenbelow:
Soilsshallbebroadlydividedintothreedivisions:
1.Coarse-grainedSoils:Morethan50%ofthetotalmaterialbyweightislargerthan75μ
ISSievesize.
2.Fine-grainedSoils:Morethan50%ofthetotalmaterialbyweightissmallerthan75μ
ISSievesize.
3.HighlyOrganicSoilsandOtherMiscellaneousSoilMaterials:Thesesoilscontain
largepercentagesoffibrousorganicmatter,suchaspeat,andparticlesofdecomposed
vegetation.Inaddition,certainsoilscontainingshells,concretions,cindersandother
non-soilmaterialsinsufficientquantitiesarealsogroupedinthisdivision.

31. Coarse-grainedsoilsshallbedividedintotwosub-divisions:
•Gravels:Morethan50%ofcoarsefraction(+75μ)islargerthan4.75mmIS
Sievesize.
•Sands:Morethan50%ofCoarsefraction(+75μ)issmallerthan4.75mmIS
Sievesize.
Fine-grainedsoilsshallbedividedintothreesub-divisions:
❖Siltsandclaysoflowcompressibility:Liquidlimitlessthan35%(L).
❖Siltsandclaysofmediumcompressibility:Liquidlimitgreaterthan35%and
lessthan50%(I).
❖Siltsandclaysofhighcompressibility:Liquidlimitgreaterthan50(H).
Thecoarse-grainedsoilsshallbefurthersub-dividedintoeightbasicsoilgroups,
andthefine-grainedsoilsintoninebasicsoilgroups;highlyorganicsoilsand
othermiscellaneoussoilmaterialsshallbeplacedinonegroup

32. Thesymbolsusedtodesignatesoilinthissystemare
GW–wellgradedgravel
GP–poorlygradedgravel
GM–siltygravel
GC–clayeygravel
SW–wellgradedsand
SP–poorlygradedsand
SM –silty sand
SC –clayey sand
CL –clay of low plasticity
CI –clay of medium plasticity
CH –clay of high plasticity
ML –silt of medium plasticity
MI –silt of medium plasticity
MH–siltofhighplasticity
OL–organicsiltandclaysoflowplasticity
OI–organicsiltandclaysofmediumplasticity
OH–organicsiltandclaysofhighplasticity
Pt–peat

33. IS SOIL CLASSIFICATION SYSTEM
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