Unified Soil Classification System Training. Sections of Course v Part A - Terms and Definitions v Part B - USCS using Laboratory Data v Part C - USCS.

Unified Soil Classification Unified Soil Classification System TrainingSystem Training

Sections of CourseSections of Course

Part A - Terms and DefinitionsPart A - Terms and Definitions

Part B - USCS using Laboratory DataPart B - USCS using Laboratory Data

Part C - USCS using Field TechniquesPart C - USCS using Field Techniques

ObjectivesObjectives

Define terms important for Unified Soil Define terms important for Unified Soil Classification SystemClassification System– Percent FinesPercent Fines– Mechanical AnalysisMechanical Analysis– Liquid LimitLiquid Limit– Plastic Limit, Plasticity IndexPlastic Limit, Plasticity Index– Water ContentWater Content– OrganicOrganic

ObjectivesObjectives

Using supplied laboratory data, correctly Using supplied laboratory data, correctly classify soils by USCSclassify soils by USCS

Correctly classify soils in field situations by Correctly classify soils in field situations by USCSUSCS

BackgroundBackground

The Unified Soil Classification System The Unified Soil Classification System

was an outgrowth of the Airfield was an outgrowth of the Airfield

Classification SystemClassification System

Grouping is based on engineering Grouping is based on engineering

propertiesproperties

USDA Textural ClassificationUSDA Textural Classification•USDA Textural System only considers grain size.

• Clay mineralogy and how it affects water holding and plasticity characteristics are not evaluated with this classification system

Engineering PropertiesEngineering Properties

PermeabilityPermeability

Shear StrengthShear Strength

ConsolidationConsolidation

Shrink/SwellShrink/Swell

Parameters Used in Parameters Used in Classification SystemClassification System

Particle SizeParticle Size

Water Holding and PlasticityWater Holding and Plasticity

Organic ContentOrganic Content

ASTM StandardsASTM Standards

Lab Data Classification is byLab Data Classification is by

ASTM D2487 ASTM D2487

Classification of Peat Samples, see Classification of Peat Samples, see

ASTM D 4427ASTM D 4427

Field Classification is by D2488Field Classification is by D2488

DefinitionsDefinitions

Particle SizesParticle Sizes– Gradation or Mechanical Gradation or Mechanical

AnalysesAnalyses

– Sieves for larger particlesSieves for larger particles

– Hydrometer for fine particlesHydrometer for fine particles

Sieve AnalysesSieve Analyses

Sieve AnalysisSieve Analysis

Sieve Designation - LargeSieve Designation - Large

Sieves larger than the #4 sieve are designated by the size of the openings in the sieve

Review Activity 2Review Activity 2

Commonly used Commonly used larger size sieveslarger size sieves– 3 inch3 inch

– 2 inch2 inch

– 1-1/2 inch1-1/2 inch

– 1 inch1 inch

– 3/4 inch3/4 inch



Sieve Designation - SmallerSieve Designation - Smaller

10 openings per inch

# 10 sieve

1-inch

Smaller sieves are numbered according to the number of openings per inch

Review Activity 3Review Activity 3

Commonly used smaller size Commonly used smaller size sievessieves– # 4# 4– # 10# 10– # 20# 20– # 40# 40

– # 60# 60

– # 140# 140

– # 200# 200

Activity 4, 5 & 7 (skip 6) Activity 4, 5 & 7 (skip 6)

Class Exercise - Convert weights Class Exercise - Convert weights

retained to percent retainedretained to percent retained

Convert percent retained to percent finerConvert percent retained to percent finer

Plot Data on FormPlot Data on Form

Grain-size DistributionGrain-size Distribution%

F

iner

Grain Size, millimeters (log10)

Sieve Designation# 20

81

Particle Size DefinitionParticle Size Definition

System based only on particles smaller System based only on particles smaller

than 3-inchesthan 3-inches

Cobbles are 3”to 12”Cobbles are 3”to 12”

Boulders are > 12”Boulders are > 12”

Gravel / Sand / FinesGravel / Sand / Fines

Gravels are between # 4 sieve and 3”Gravels are between # 4 sieve and 3”

Sands are between # 200 sieve and Sands are between # 200 sieve and

# 4 sieve# 4 sieve

Fines are smaller than # 200 sieveFines are smaller than # 200 sieve




Organic ContentOrganic Content

Tests to Define BoundariesTests to Define Boundaries

Water Content - DefinitionWater Content - Definition– Ratio of the weight of water in a sample to Ratio of the weight of water in a sample to

the weight of the dry soilthe weight of the dry soil

– Expressed as a percentageExpressed as a percentage

– Values greater than 100 % possibleValues greater than 100 % possible

Activity 8 Water ContentActivity 8 Water Content


Consistency States of Finer ParticlesConsistency States of Finer Particles– LiquidLiquid

– PlasticPlastic

– Semi-solidSemi-solid

– solidsolid

Increasing Water Contents

Activity 9Activity 9

Consistency StatesConsistency States

Tests to Define BoundariesTests to Define Boundaries

Tests are only Tests are only performed on the performed on the fraction of a sample fraction of a sample that is finer than the that is finer than the # 40 sieve.# 40 sieve.

Liquid Limit DefinitionLiquid Limit Definition

The water content at which a soil The water content at which a soil changes from a plastic consistency to a changes from a plastic consistency to a liquid consistencyliquid consistency

Defined by Laboratory Test concept Defined by Laboratory Test concept developed by Atterberg in 1911.developed by Atterberg in 1911.

Liquid Limit DefinitionLiquid Limit Definition

The water content at The water content at

which a groove cut which a groove cut

in a soil paste will in a soil paste will

close upon 25 close upon 25

repeated drops of a repeated drops of a

brass cup with a brass cup with a

rubber baserubber base

LL Test ProcedureLL Test Procedure

Prepare paste of Prepare paste of

soil finer than # soil finer than #

40 sieve40 sieve

Place Soil in Place Soil in

CupCup


Cut groove in Cut groove in

soil paste with soil paste with

standard standard

grooving toolgrooving tool


Rotate cam and Rotate cam and

count number of count number of

blows of cup blows of cup

required to close required to close

groove by 1/2”groove by 1/2”


Perform on 3 to 4 specimens that bracket Perform on 3 to 4 specimens that bracket

25 blows to close groove25 blows to close groove

Obtain water content for each testObtain water content for each test

Plot water content versus number of Plot water content versus number of

blows on semi-log paperblows on semi-log paper

LL Test ResultsLL Test Results

Log N

water content, %LL= w%

Interpolate LL water content at 25 blows

25

Activity 10Activity 10

Liquid Limit ProblemLiquid Limit Problem

LL Values < 16 % not realisticLL Values < 16 % not realistic

16Liquid Limit,

%

PI,

%

LL Values LL Values >> 50 - HIGH 50 - HIGH

Liquid Limit, %

PI,

%

50

H

LL Values < 50 - LOWLL Values < 50 - LOW

Liquid Limit, %

PI,

%

50

L

Plastic Limit DefinitionPlastic Limit Definition

The water content at which a soil The water content at which a soil

changes from a plastic consistency to a changes from a plastic consistency to a

semi-solid consistencysemi-solid consistency

Defined by Laboratory Test concept Defined by Laboratory Test concept

developed by Atterberg in 1911.developed by Atterberg in 1911.

Plastic Limit Definition - Activity 11Plastic Limit Definition - Activity 11

The water content at The water content at

which a 1/8”thread which a 1/8”thread

of soil can be rolled of soil can be rolled

out but it begins to out but it begins to

crack and cannot crack and cannot

then be re-rolledthen be re-rolled

Plastic Limit w% procedurePlastic Limit w% procedure

Using paste from LL test, begin dryingUsing paste from LL test, begin drying

May add dry soil or spread May add dry soil or spread

on plate and air-dryon plate and air-dry

Occasionally evaluate 1/8” threadOccasionally evaluate 1/8” thread

Plastic Limit w% procedurePlastic Limit w% procedure

When point is reached where thread is When point is reached where thread is

cracking and cannot be re-rolled to 1/8” cracking and cannot be re-rolled to 1/8”

diameter, collect at least 6 grams and diameter, collect at least 6 grams and

measure water content. Defined plastic limitmeasure water content. Defined plastic limit

Definition of Plasticity IndexDefinition of Plasticity Index

Plasticity Index is the numerical difference Plasticity Index is the numerical difference

between the Liquid Limit w% and the Plastic between the Liquid Limit w% and the Plastic

Limit w%Limit w%

w% LLPL

PI = LL - PL

Definition of Plasticity IndexDefinition of Plasticity Index

It represents the range in water contents over It represents the range in water contents over

which a soil behaves in a plastic mannerwhich a soil behaves in a plastic manner

w% LLPL

PI = LL - PL liquidsemi-solid plastic (remoldable)

Definition of NonplasticDefinition of Nonplastic

If the soil has a PI of zero, or either of If the soil has a PI of zero, or either of

the Atterberg tests cannot be performed, the Atterberg tests cannot be performed,

the soil is said to be non-plasticthe soil is said to be non-plastic

Complete Activity 11Complete Activity 11

Complete Activity 13Complete Activity 13

Comprehensive Review Terms Comprehensive Review Terms

and Definitionsand Definitions

Definition of PlasticityDefinition of Plasticity

Plastic soils plot

above the A-

Line on a Chart

Plasti

c Soil

s

“A- Line”

Definition of PlasticityDefinition of Plasticity

Non-plastic or slightly

plastic soils plot below the A-Line on a Chart No

nplastic Soils

“A- Line”

U-Line SignificanceU-Line Significance“U- Line”

Correct tests never plot above U-

line and LL values are never < 16

Unrealistic

16

Plasticity ChartPlasticity ChartUnified Soil Classification System Plasticity Chart

0

10

20

30

40

50

60

0 10 20 30 40 50 60 70 80 90 100

LIQUID LIMIT

PL

AS

TIC

ITY

IND

EX CH

CL

ML

MH

CL-ML

Example Plot of LL, PIExample Plot of LL, PI

LL PI

42 18

18 5

102 54

Plastic or Not ??




Organic Content

Criterion for Organic DesignationCriterion for Organic Designation

A liquid limit test is performed on:A liquid limit test is performed on:– One sample that is only air-driedOne sample that is only air-dried

– On another that is oven-dried prior to On another that is oven-dried prior to testingtesting

– The liquid limit values are compared by The liquid limit values are compared by computing the ratio of the 2 valuescomputing the ratio of the 2 values

Organic DefinitionOrganic Definition

If the ratio of the oven-dried soil’s LL to the If the ratio of the oven-dried soil’s LL to the air-dry soil’s LL values is < 0.75, the soil is air-dry soil’s LL values is < 0.75, the soil is organic by definition.organic by definition.

If the air-dry LL is 50 or more, it is a HIGH If the air-dry LL is 50 or more, it is a HIGH liquid limitliquid limit

If the air-dry LL is less than 50, the soil has a If the air-dry LL is less than 50, the soil has a LOW LL valueLOW LL value

Additional Evaluations of Additional Evaluations of Organic SoilsOrganic Soils

Ignition test. ASTM D2974Ignition test. ASTM D2974

Soil sample heated in muffle furnace set Soil sample heated in muffle furnace set

at either 440at either 440 or 750 or 750 Centigrade and Centigrade and

weight loss measured.weight loss measured.

Peat Classification D4427Peat Classification D4427

Unified Soil Classification System Training. Sections of Course v Part A - Terms and Definitions v Part B - USCS using Laboratory Data v Part C - USCS.

Documents

sieve slide

uscs v

objectives v

inch slide

background v

sieve v fines

classification system

uscs slide