Chap: 3 Soil ClassificationOutline of chapter

Objective Field identification of soil Soil classification systemApplication of classification system

Field identification of soilCoarse grained soil (sand and gravel)Fine grained soil (clay and silt)Sand Vs silt

Gravel Vs SandGravel size 4.75mm to 80mmSand size 4.75mm to .075mmSpread the coarse grain soil in the flat surface and visualize, if 50% of the particle are visible to the naked eye soil is gravel else sand.

Fine grained soilVisual examinationDry strength test Shaking test / dilatancy testPlasticity testDispersion test

Soil ClassificationMIT SystemTextural ClassificationUnified Soil Classification System(USCS)Indian Standard Classification System(ISCS)British Soil Classification System(BSCS)AASHTO Classification System

MIT systemDeveloped by: prof. G.Giloby, Massachusettes Institute of Technology,USAGravel: > 2mmSand: 0.06 mm to 2.0 mm 0.6-2.0= C 0.2-0.6= M 0.06-0.2= F Silt: 0.002 mm to 0.06 mm 0.02-0.6= C 0.006-0.02=M 0.002- 0.006=FClay: < 0.002 mm(i.e. 2 )C= coarse

M= medium

F= fine

Textural Classification

BY US bureau of Public Road

USCS Fine GrainedCoarse GrainedSands (S)Gravels (G)High Plasticity (H)Low Plasticity (L)Clean GravelGravel with finesClean SandSand with FinesHighly Organic Soil Highly Organic SoilsGWGPGMGCSWSPSMSCMLCLOLMHCHOHPtMore than 50% smaller than #200More than 50% larger than #200

USCS Coarse GrainedSands (S)Gravels (G)Clean GravelGravel with finesClean SandSand with FinesGW GPGMGCSWSPSMSCMore than 50% larger than #200More than 50% coarse smaller than #4More than 50% coarse larger than #4Fines < 5%Fines > 12%Fines < 5%Fines > 12%

Coarse Grained(USCS) Coarse GrainedGravels (G)Clean GravelGravel with finesGW GPGMGCMore than 50% coarse larger than #4Fines < 5%Fines > 12%5% < fines < 12%Dual symbolGW-GC, GP-GM, etcGP Cu > 61< Cc

Coarse Grained(USCS) Coarse GrainedSand (S)Clean SandSand with finesSW GPSMSCMore than 50% coarse smaller than #4Fines < 5%Fines > 12%5% < fines < 12%Dual symbolSW-SM, SP-SC, etcSP Cu > 41< Cc

Fine Grained(USCS)CHMH or OHCLML or OLCL-MLA-line50%CLAY (C)SILT (M)Low Plasticity (L)High Plasticity (H)

Organic or Inorganic?Examine odor and colour

Organic:

ISSCSSimilar to USCS only differ for Fine Soil.

Indian Plasticity ChartCHMH or OHCLML or OLCL-MLA-lineCIMICLAYSILT35%50%

British Soil ClassificationFine SoilsCoarse SoilsMore than 35% smaller than 0.06 mmLess than 35% smaller than 0.06 mm

COARSED GRAINED(fines < 35%)SandsGravelsMore than 50% coarse smaller than 2 mmMore than 50% coarse larger than 2 mm

GRAVELSGroup SymbolSub-group symbol% finesSlightly silty or clayey GRAVELSilty GRAVELClayey GRAVELGWGPGWGPu, GPg0 to 5 GMGCGWM, GPMGWC, GPC 5 to 1515 to35Very silty GRAVELVery clayey GRAVEL GMGCGML, etcGCLGCIGCHGCVGCE

GRAVELSWell graded GRAVELPoorly graded/gap graded GRAVELWell graded/poorly graded silty GRAVELWell graded/poorly graded clayey GRAVELVery clayey GRAVEL of Low,Intermediate, High, Very High or Extremely High PlasticityVery silty GRAVEL of Low, etc, Plasticity

SANDSGroup SymbolSub-group symbol% finesSlightly silty or clayey SANDSilty SANDClayey SANDSWSPSWSPu, SPg0 to 5 SMSCSWM, SPMSWC, SPC 5 to 1515 to35Very silty SANDVery clayey SAND SMSCSML, etcSCLSCISCHSCVSCE

SANDSWell graded SANDPoorly graded/gap graded SANDWell graded/poorly graded silty SANDWell graded/poorly graded clayey SANDVery clayey SAND of Low,Intermediate, High, Very High or Extremely High PlasticityVery silty SAND of Low , etc, Plasticity

FINE GRAINED(65%

British Plasticity Chart

FINE GRAINED WITH COARSE(35%

AASHTO CLASSIFICATION

Used for highway subgrade soil to evaluate:

- Stability under vehicle load- performance in freezing and thawing

AASHTO CLASSIFICATIONGranular Material (>65% retained on # 200)A-1 : Well graded Gravel and SandA-3 : Clean, poorly graded Sand (35% pass on # 200)A-4: Silty soilsA-5: Silty soilsA-6: Clayey SoilsA-7: Clayey Soils EXCELLENTPOOR

Coarse Material 51% pass # 40< 50% pass # 40< 10% pass # 200Non-plastic< 15% pass # 200

Coarse MaterialA- 2

Fine MaterialFine Material: >35% pass # 200A-4A-5A-6A-7-5A-7-6L.L10PI(LL-30)

AASHTO PLASTICITY CHART

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