II.Physical Properties

1

Outline

1. Soil Texture1. Soil Texture2. Grain Size and Grain Size Distribution3 Particle Shape3. Particle Shape4. Atterberg Limits5 Some Thoughts about the Sieve Analysis5. Some Thoughts about the Sieve Analysis6. Some Thoughts about the Hydrometer Analysis7 S t d H k7. Suggested Homework

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1 Soil Texture1. Soil Texture

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1.1 Soil Texture

The texture of a soil is its appearance or “feel” and itThe texture of a soil is its appearance or feel and itdepends on the relative sizes and shapes of theparticles as well as the range or distribution of thosesizes.

Coarse-grained soils: Fine-grained soils:

Gravel Sand Silt Clay0.075 mm (USCS)

0.06 mm (BS) (Hong Kong)

Sie e anal sis H d t l i

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Sieve analysis Hydrometer analysis

1.2 Characteristics(Holtz and Kovacs, 1981)

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2. Grain Size and Grain Size Distribution

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2.1 Grain Size

4.75USCS 0.075

BS 2.0 0.06 0.002

USCS: Unified Soil Classification

BS: British Standard

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Unit: mm (Holtz and Kovacs, 1981)

Note:

Cl i i lClay-size particlesFor example:

A small quartz particle may have the similar size of clay minerals.

Clay minerals

For example:

Kaolinite Illite etc

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Kaolinite, Illite, etc.

2.2 Grain Size Distribution•Sieve size

9(Das, 1998) (Head, 1992)

2.2 Grain Size Distribution (Cont.)( )

Coarse grained soils: Fine grained soils:•Experiment

Coarse-grained soils:

Gravel Sand

Fine-grained soils:

Silt Clay0 075 (USCS)0.075 mm (USCS)

0.06 mm (BS) (Hong Kong)

(Head, 1992)

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Sieve analysis Hydrometer analysis

2.2 Grain Size Distribution (Cont.)( )

Log scaleEffective size D10: 0.02 mm

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(Holtz and Kovacs, 1981)

ec ve s e 10: 0.0

D30: D60:

2.2 Grain Size Distribution (Cont.)( )

• Describe the shapeExample: well graded

•CriteriaExample: well graded

mm6.0D)sizeeffective(mm02.0D

30

10

4Cand3C1soilgradedWell

uc

uniformityoftCoefficien

mm9D60

6Cand3C1)gravelsfor(

uc

curvatureoftCoefficien

45002.09

DDC

10

60u

)sandsfor(

•QuestionWhat is the Cu for a soil with

l i i ?2

)9)(02.0()6.0(

)D)(D()D(C

curvatureoftCoefficien2

6010

230

c

12

only one grain size?))(())(( 6010

Answer

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

ner

DuniformityoftCoefficien

Fin

1DDC

10

60u

D

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Grain size distribution

2.2 Grain Size Distribution (Cont.)( )• Engineering applications

It will help us “feel” the soil texture (what the soil is) and it willalso be used for the soil classification (next topic).

It can be used to define the grading specification of a drainagefilter (clogging).

It can be a criterion for selecting fill materials of embankmentsand earth dams, road sub-base materials, and concrete aggregates., , gg g

It can be used to estimate the results of grouting and chemicalinjection, and dynamic compaction.Effective Size D can be correlated with the hydraulic Effective Size, D10, can be correlated with the hydraulicconductivity (describing the permeability of soils). (Hazen’sEquation).(Note: controlled by small particles)

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The grain size distribution is more important to coarse-grained soils.

3. Particle Shapep

Rounded SubroundedCoarse- Rounded Sgrained soils

Subangular Angular

Important for granular soils Angular soil particle higher friction

R d il i l l f i i

Subangular Angular

(Holtz and Kovacs, 1981)

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Round soil particle lower friction Note that clay particles are sheet-like.

4. Atterberg Limits andand

Consistency Indices

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4.1 Atterberg Limitsg• The presence of water in fine-grained soils can significantly affect

associated engineering behavior so we need a reference index to clarifyassociated engineering behavior, so we need a reference index to clarifythe effects. (The reason will be discussed later in the topic of clay minerals)

In percentage

17(Holtz and Kovacs, 1981)

4.1 Atterberg Limits (Cont.)g ( )

Li id Li it LL

Liquid StateFluid soil-water mixture

Liquid Limit, LL

l i i i

Plastic State

r con

tent

Plastic Limit, PL

h i k i i

Semisolid State

asin

g w

ater

Shrinkage Limit, SL

Solid StateD S il

Incr

ea

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Dry Soil

4.2 Liquid Limit-LLq

Cone Penetrometer MethodCasagrande Method Cone Penetrometer Method

(BS 1377: Part 2: 1990:4.3)•This method is developed by the

Casagrande Method

(ASTM D4318-95a)•Professor Casagrande standardized •This method is developed by the

Transport and Road Research Laboratory, UK.

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

•Multipoint test

•One-point test

•Multipoint test

•One-point test

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4.2 Liquid Limit-LL (Cont.)q ( )

Dynamic shear test Particle sizes and watery• Shear strength is about 1.7 ~2.0

kPa.•Passing No.40 Sieve (0.425 mm).

•Using deionized water.• Pore water suction is about 6.0

kPa. (review by Head, 1992; Mitchell, 1993).

The type and amount of cationscan significantly affect themeasured results.measured results.

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4.2.1 Casagrande Methodg•Device

N=25 blows

Closing distance = 12 7mm (0 5 in)12.7mm (0.5 in)

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(Holtz and Kovacs, 1981)The water content, in percentage, required to close a distance of 0.5 in (12.7mm) along the bottom of the groove after 25 blows is defined as the liquid limit

4.2.1 Casagrande Method (Cont.)g ( )•Multipoint Method

w

)(/l

, 21 valuepositiveachooseNN

wwIindexFlow F

NDas, 1998

22

.log

/log 12

contNIwNN

F

4.2.1 Casagrande Method (Cont.)g ( )•One-point Method

l htan

N• Assume a constant slope of the flow curve.

• The slope is a statistical result of 25

blowsofnumberN

NwLL n

p767 liquid limit tests.

121.0tan contentmoistureingcorrespondw

blowsofnumberN

n

Limitations:• The is an empirical coefficient,

i i l 0 121so it is not always 0.121.

• Good results can be obtained onlyfor the blow number around 20 to

23

30.

4.2.2 Cone Penetrometer Method•Device

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

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(Head, 1992)

4.2.2 Cone Penetrometer Method (Cont.)( )

•Multipoint Methodf c

one

20

ratio

n of

(mm

) 20 mm

Pene

tr

LL

25

Water content w%

4.2.2 Cone Penetrometer Method (Cont.)( )

•One-point Method (an empirical relation)

%4015d thP t ti(Review by Head, 1992)

2644094.140LL,094.1Factor

%,40w,mm15depthnPenetratioExample:

4.2.3 Comparisonp

A good correlationbetween the twomethods can beobserved as the

i l hLL is less than100.

27Littleton and Farmilo, 1977 (from Head, 1992)

Question:Which method will render more consistent results?

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4.3 Plastic Limit-PL

(Holtz and Kovacs, 1981)

The plastic limit PL is defined as the water content at whichThe plastic limit PL is defined as the water content at which a soil thread with 3.2 mm diameter just crumbles.

ASTM D4318-95a BS1377: Part 2:1990:5 3ASTM D4318 95a, BS1377: Part 2:1990:5.3

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4.4 Shrinkage Limit-SLg

Definition of shrinkagelimit:

Th t t t tThe water content atwhich the soil volumeceases to change isdefined as the shrinkagedefined as the shrinkagelimit.SL

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(Das, 1998)

4.4 Shrinkage Limit-SL (Cont.)g ( )

Soil volume: Vi

Soil mass: M1

Soil volume: Vf

Soil mass: M

(Das, 1998)

Soil mass: M2

)100)((VV)100(MM

(%)w(%)wSL

fi21

i

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)100)((M

)100(M w

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4.4 Shrinkage Limit-SL (Cont.)g ( )

• “Although the shrinkage limit was a popular classification test duringthe 1920s, it is subject to considerable uncertainty and thus is nolonger commonly conducted.”

• “One of the biggest problems with the shrinkage limit test is that theamount of shrinkage depends not only on the grain size but also onthe initial fabric of the soil. The standard procedure is to start withthe water content near the liquid limit. However, especially withsandy and silty clays, this often results in a shrinkage limit greaterthan the plastic limit, which is meaningless. Casagrande suggests thath i i i l b li h l h h PL if iblthe initial water content be slightly greater than the PL, if possible,

but admittedly it is difficult to avoid entrapping air bubbles.” (fromHoltz and Kovacs, 1981)

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4.5 Typical Values of Atterberg Limits yp g

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(Mitchell, 1993)

4.6 Indices•Plasticity index PIF d ibi h f

•Liquidity index LIF li th t l tFor describing the range of

water content over which a soil was plastic

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

PI = LL – PLPLLLPLw

PIPLwLI

Liquid State C contentwatertheisw

LI <0 (A) b ittl f t if h d

Liquid Limit, LL

Liquid State

Pl ti Li it PL

Plastic StatePI B

C

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

Plastic Limit, PL

Shrinkage Limit, SL

Semisolid State

l d

A

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Solid State

4.6 Indices (Cont.)( )

•Sensitivity St (for clays)Clay

particle> LLy t ( y )

)di t b d(St th)dundisturbe(StrengthSt

Water

w > LL

strengthshearUnconfined)disturbed(Strength

35(Holtz and Kavocs, 1981)

4.6 Indices (Cont.)( )•Activity A(Sk 1953)

Normal clays: 0.75<A<1.25Inactive clays: A<0.75(Skempton, 1953)

)weight(fractionclay%PIA

Inactive clays: A 0.75Active clays: A> 1.25High activity:l l h h tt d

mm002.0:fractionclay)weight(fractionclay%

•large volume change when wetted•Large shrinkage when dried•Very reactive (chemically) Mitchell, 1993

•PurposeBoth the type and amount of clayBoth the type and amount of clayin soils will affect the Atterberglimits. This index is aimed toseparate them.

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separate them.

4.7 Engineering Applications• Soil classification

(the next topic)

g g pp

(the next topic)The Atterberg limit enable

clay soils to be classified.

• The Atterberg limits are usually correlated with some engineeringproperties such as the permeability, compressibility, shear strength,and others. In general, clays with high plasticity have lower permeability, and they are

difficult to be compacted

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difficult to be compacted. The values of SL can be used as a criterion to assess and prevent the

excessive cracking of clay liners in the reservoir embankment or canal.

5. Some Thoughts about the Sieve Analysisg y

• The representative particle size of residual soilsp pThe particles of residual soils are susceptible to severe breakdown

during sieve analysis, so the measured grain size distribution is sensitive to the test procedures (Irfan, 1996).p ( , )

• Wet analysisFor “clean” sands and gravels dry sieve analysis can be used. If soils contain silts and clays, the wet sieving is usually used to

preserve the fine content.p

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6. Some Thoughts about the Hydrometer Analysis

Stokes’ law Assumption RealityStokes law

D)(v2

ws

Sphere particle Platy particle (clay particle) as D 0.005mm

18v

Single particle(No interference between particles)

Many particles in the suspension

Known specific gravity of

Average results of all theminerals in the particles,including the adsorbed waterg y

particles films.Note: the adsorbed water filmsalso can increase the resistanceduring particle settling.

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Terminal velocity Brownian motion as D 0.0002 mm(Compiled from Lambe, 1991)

7. Suggested Homeworkgg

1. Please derive the equation for calculating the1. Please derive the equation for calculating thepercentage finer than D (hint: please see thenote).

)%mR(

1GDG100DthanfinerPercentage d

s

2s

2. Please understand the calibration of hydrometer. hr R90.34.200H Please understand how to get this

ti

3. Please go over examples 1-1 to 1-3 in your noteshr equation.

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8. ReferencesMain References:Das, B.M. (1998). Principles of Geotechnical Engineering, 4th edition, PWS Publishing , ( ) p f g g, , g

Company. (Chapter 2)Holtz, R.D. and Kovacs, W.D. (1981). An Introduction to Geotechnical Engineering,

Prentice Hall. (Chapter 1 and 2)Others:Others:Head, K. H. (1992). Manual of Soil Laboratory Testing, Volume 1: Soil Classification and

Compaction Test, 2nd edition, John Wiley and Sons.Ifran, T. Y. (1996). Mineralogy, Fabric Properties and Classification of Weathered Granites

in Hong Kong, Quarterly Journal of Engineering Geology, vol. 29, pp. 5-35. Lambe, T.W. (1991). Soil Testing for Engineers, BiTech Publishers Ltd.Mitchell, J.K. (1993). Fundamentals of Soil Behavior, 2nd edition, John Wiley & Sons.

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