unified training-part-a
TRANSCRIPT
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
– 1/2 inch1/2 inch
– 3/8 inch3/8 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
Parameters Used in Parameters Used in Classification SystemClassification System
Particle SizeParticle Size
Water Holding and PlasticityWater Holding and Plasticity
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
Water Holding and PlasticityWater Holding and Plasticity
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
LL Test ProcedureLL Test Procedure
Cut groove in Cut groove in
soil paste with soil paste with
standard standard
grooving toolgrooving tool
LL Test ProcedureLL Test Procedure
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”
LL Test ProcedureLL Test Procedure
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 ??
Parameters Used in Parameters Used in Classification SystemClassification System
Particle SizeParticle Size
Water Holding and PlasticityWater Holding and Plasticity
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