pavement engineering materials_4

PAVEMENT MATERIALS PAVEMENT MATERIALS ENGINEERINGENGINEERING

(CE-862) (CE-862) Lec-04

Fall Semester 2016

Dr. Arshad [email protected] , Office Room#111, Tel:

05190854163, Cell: 03419756251

National Institute of Transportation (NIT)

School of Civil & Environmental Engineering (SCEE)

National University of Science and Technology (NUST)

NUST Campus, Sector H-12, Islamabad

ROADBED SOILS – CROADBED SOILS – C

GRAIN SIZE ANALYSIS & GRAIN SIZE ANALYSIS & ATTERBERG’S LIMITSATTERBERG’S LIMITS

3

OutlineOutline1.Soil Texture2.Grain Size and Grain Size

Distribution3.Particle Shape4.Atterberg Limits

4

1. Soil Texture1. Soil Texture

5

Soil TextureSoil TextureThe texture of a soil is its appearance or “feel” and it depends on the relative sizes and shapes of the particles as well as the range or distribution of those sizes.

6

Coarse-grained soils:

Gravel Sand

Fine-grained soils:

Silt Clay0.075 mm (USCS)

Sieve analysis Hydrometer analysis

CharacteristicsCharacteristics

7

(Holtz and Kovacs, 1981)

2. Grain Size and Grain Size 2. Grain Size and Grain Size DistributionDistribution

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Grain SizeGrain Size

9


Clay-size particlesA small quartz particle may have the similar size of clay minerals

Clay minerals. For example:Kaolinite, Illite, etc

.

Sieve sizeSieve size

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Rectangular opening4” (101.6 mm) to # 400 (.038mm)Below #200 is not practicalLeast dimension passingSieve numbering?

Grain Size DistributionGrain Size Distribution

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Particle ShapeParticle Shape

Important for granular soils Angular soil particle higher friction Round soil particle lower friction

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Rounded Subrounded

Subangular Angular


Coarse-grained soils

Particle Size DefinitionParticle Size DefinitionSystem based only on particles

smaller than 3-inchesCobbles are 3”to 12”Boulders are > 12”

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Gravel / Sand / FinesGravel / Sand / Fines

Gravels are between # 4 sieve and 3”Sands are between # 200 sieve and

# 4 sieveFines are smaller than # 200 sieve

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ExperimentExperiment

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Coarse-grained soils:

Gravel Sand

Fine-grained soils:

Silt Clay0.075 mm (USCS)

Sieve analysis Hydrometer analysis

(Head, 1992)

Commonly used larger size sieves◦3 inch◦2 inch◦1-1/2 inch

◦1 inch◦3/4 inch◦1/2 inch◦3/8 inch

10 openings per inch

# 10 sieve

1-inch

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

Commonly used smaller size sieves◦# 4◦# 10◦# 20◦# 40

◦# 60◦# 140◦# 200

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Log scale


Fine

r

Effective size D10: 0.02 mm

D30: D60:

Describe the shapeExample: well graded

Criteria

QuestionWhat is the Cu for a soil with only one grain size?

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2)9)(02.0(

)6.0()D)(D(

)D(C

curvatureoftCoefficien

45002.09

DDC

uniformityoftCoefficien

2

6010

230

c

10

60u

mm9Dmm6.0D

)sizeeffective(mm02.0D

60

30

10

)sandsfor(6Cand3C1

)gravelsfor(4Cand3C1

soilgradedWell

uc

uc

AnswerAnswerQuestionWhat is the Cu for a soil with only one grain size?

21

D

Fine

r

1DDC

uniformityoftCoefficien

10

60u

Grain size distribution

◦ Use of curve Inside gradation envelope Uniformly, poorly or skip grading Effective size D10 Coefficient of uniformity, Cu = large

value non uniform soil, >5well graded, <2 poorly graded

Coefficient of curvature, Cu = D302

/(D60 x D10) greatly differ from 1, indicate missing sizes

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Engineering applications It will help us “feel” the soil texture (what the

soil is) and it will also be used for the soil classification

It can be used to define the grading specification of a drainage filter.

It can be a criterion for selecting fill materials of embankments and earth dams, road sub-base materials, and concrete aggregates. It can be used to estimate the results of grouting and chemical injection, and dynamic compaction.

Effective Size, D10, can be correlated with the hydraulic conductivity (describing the permeability of soils).

Predicting soil movementsFrost susceptibility

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◦ Limitations/ salient features Sieve sizes Statically representative sample Sample size Sampling procedure Shape

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4. Atterberg Limits 4. Atterberg Limits and and

Consistency IndicesConsistency Indices

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Consistency limits an Consistency limits an IndicesIndices

◦ General Property of soil manifested by

resistance to flow. Cohesive and not inter granular. Affected by moisture contents of soil.

◦ Consistency Limits. Atterberg’s six stages of soil consistency range

◦ liquid limit◦ Sticky limit ◦ Cohesive limit◦ Plastic limit◦ Shrinkage limit

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The presence of water in fine-grained soils can significantly affect associated engineering behavior, so we need a reference index to clarify the effects. (The reason will be discussed later in the topic of clay minerals)

27(Holtz and Kovacs, 1981)

In percentage

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Liquid Limit, LL

Liquid State

Plastic Limit, PL

Plastic State

Shrinkage Limit, SL

Semisolid State

Solid StateDry Soil

Fluid soil-water mixture

Incr

easi

ng w

ater

con

tent

Liquid Limit-LLLiquid Limit-LL

Casagrande Method(ASTM D4318-95a)

Professor Casagrande standardized the test and developed the liquid limit device.

Cone Penetrometer Method

(BS 1377: Part 2: 1990:4.3)

This method is developed by the Transport and Road Research Laboratory, UK.

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Liquid Limit DefinitionLiquid Limit DefinitionThe water content

at which a groove cut in a soil paste will close upon 25 repeated drops of a brass cup with a rubber base

LL Test ProcedureLL Test Procedure

Prepare paste of soil finer than # 40 sieve

Place Soil in Cup

LL Test ProcedureLL Test ProcedureCut groove

in soil paste with standard grooving tool

LL Test ProcedureLL Test ProcedureRotate cam

and count number of blows of cup required to close groove by 1/2”

LL Test ProcedureLL Test ProcedurePerform on 3 to 4 specimens that

bracket 25 blows to close grooveObtain water content for each testPlot water content versus number of

blows on semi-log paper

LL Test ResultsLL Test Results

Log N

water content, %LL= w%

Interpolate LL water content at 25 blows

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LL Values < 16 % not LL Values < 16 % not realisticrealistic

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 DefinitionThe water content at which a soil

changes from a plastic consistency to a semi-solid consistency

Defined by Laboratory Test concept developed by Atterberg in 1911.

Plastic Limit DefinitionPlastic Limit DefinitionThe water content

at which a 1/8”thread of soil can be rolled out but it begins to crack and cannot then be re-rolled

Plastic Limit w% Plastic Limit w% procedureprocedure

Using paste from LL test, begin drying

May add dry soil or spread on plate and air-dry

Occasionally evaluate 1/8” thread

Plastic Limit w% Plastic Limit w% procedureprocedure

When point is reached where thread is cracking and cannot be re-rolled to 1/8” diameter, collect at least 6 grams and measure water content. Defined plastic limit

Definition of Plasticity Definition of Plasticity IndexIndex

Plasticity Index is the numerical difference between the Liquid Limit w% and the Plastic Limit w%

w% LLPL

PI = LL - PL

Definition of Plasticity Definition of Plasticity IndexIndex

It represents the range in water contents over which a soil behaves in a plastic manner

w% LLPL

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

Liquidity index LILiquidity index LI

For scaling the natural water content of a soil sample to the Limits. contentwatertheisw

PLLLPLw

PIPLwLI

LI <0 (A), brittle fracture if sheared0<LI<1 (B), plastic solid if sheared LI >1 (C), viscous liquid if sheared

Definition of NonplasticDefinition of NonplasticIf the soil has a PI of zero, or

either of the Atterberg tests cannot be performed, the soil is said to be non-plastic

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 Non

plasti

c Soil

s

“A- Line”

U-Line SignificanceU-Line Significance

“U- Line”

Correct tests never plot above U-

line and LL values are never < 16

Unrealistic

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Criterion for Organic Criterion for Organic DesignationDesignation

A liquid limit test is performed on:◦One sample that is only air-dried◦On another that is oven-dried prior

to testing◦The liquid limit values are compared

by computing the ratio of the 2 values

Organic DefinitionOrganic DefinitionIf the ratio of the oven-dried

soil’s LL to the air-dry soil’s LL values is < 0.75, the soil is organic by definition.

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

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

Shrinkage Limit-SLShrinkage Limit-SL

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Definition of shrinkage limit:

The water content at which the soil volume ceases to change is defined as the shrinkage limit.

(Das, 1998)

SL

Shrinkage Limit-SLShrinkage Limit-SL

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(Das, 1998)

Soil volume: Vi

Soil mass: M1

Soil volume: Vf

Soil mass: M2

)100)((M

VV)100(M

MM

(%)w(%)wSL

w2

fi

2

21

i

Shrinkage Limit-SLShrinkage Limit-SL “Although the shrinkage limit was a popular classification

test during the 1920s, it is subject to considerable uncertainty and thus is no longer commonly conducted.”

“One of the biggest problems with the shrinkage limit test is that the amount of shrinkage depends not only on the grain size but also on the initial fabric of the soil. The standard procedure is to start with the water content near the liquid limit. However, especially with sandy and silty clays, this often results in a shrinkage limit greater than the plastic limit, which is meaningless. Casagrande suggests that the initial water content be slightly greater than the PL, if possible, but admittedly it is difficult to avoid entrapping air bubbles.” (from Holtz and Kovacs, 1981)

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Typical Values of Typical Values of Atterberg Limits Atterberg Limits

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(Mitchell, 1993)

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