Soil ClassificationN. SivakuganDuration: 7 min. 20 s

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ObjectivesTo develop a systematic way to describe and classify soils;

To assign symbols.

To group soils of similar geotechnical characteristics; and

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Major Soil Groups

Grain size (mm)BoulderClaySiltSandGravelCobbleFine grain soilsCoarse grain soilsGranular soils or Cohesionless soilsCohesive soils

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Grain Size DistributionTo know the relative proportions of different grain sizes.

An important factor influencing the geotechnical characteristics of a coarse grain soil.

Not important in fine grain soils.

Significance of GSD:

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Grain Size DistributionIn coarse grain soils ... By sieve analysis

Determination of GSD:In fine grain soils ... By hydrometer analysis

Hydrometer Analysis

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Grain Size Distribution Curvecan find % of gravels, sands, fines

define D10, D30, D60.. as above.

Chart2

0

19.2

37

63.5

70

75.5

81.5

87.3

100

D

30

sieve

hydrometer

D10 = 0.013 mmD30 = 0.47 mmD60 = 7.4 mm

sands

gravels

fines

% Passing

Grain size (mm)

Sheet1

0.0010

0.119.2

137

1063.5

1570

2075.5

2581.5

3087.3

37.5100

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D

30

sieve

hydrometer

D10 = 0.013 mmD30 = 0.47 mmD60 = 7.4 mm

sands

gravels

fines

% Passing

Grain size (mm)

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Well or Poorly Graded Soils

Well Graded SoilsPoorly Graded SoilsWide range of grain sizes presentGravels: Cc = 1-3 & Cu >4Sands: Cc = 1-3 & Cu >6Others, including two special cases:(a) Uniform soils grains of same size(b) Gap graded soils no grains in a specific size range

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Relative Density (Dr)

Measure of how densely the grains are packed in a coarse grain soil in %.

0100LoosestDensestAlso known as density index (ID).

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Granular Soil Consistencies

As per AS1726 - 1993Relative Density (%)Consistency Term0-1515-3535-6565-8585-100Very looseLooseMedium denseDenseVery dense

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Atterberg Limits

Border line water contents, separating the different states of a fine grained soil

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Atterberg Limits

Liquid Limit (wL or LL):Clay flows like liquid when w > LLPlastic Limit (wP or PL):Lowest water content where the clay is still plasticShrinkage Limit (wS or SL):At w 50I = 35 < LL < 50L = LL < 35XAe.g., GPYBe.g., CHXYe.g., SMXA-XYe.g., GP-GC

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Summary

Sieve analysis for coarse grain soils Hydrometer analysis - for fine grain soils

Classifycoarse by GSD and

fines from Atterberg limits (PI-LL chart).