Chapter 5 - Soil-Water Characteristic Curves for Unsaturated Soils.pptx

8/9/2019 Chapter 5 - Soil-Water Characteristic Curves for Unsaturated Soils.pptx

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oil-W ater Characterist ic

Curves for Unsaturated o

ils

Chapter 5

Section 5.1 and 5.2Pages : 184 - 200


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Section 5.1

Introduction

Background of Unsaturated Soil Mechanics

Early develo!ents on the SWCC in Soil "hysics

Early e#ui!ent for !easuring SWCC Early concetual !odels of flo$ in unsaturated s

oils

%he SWCC in early Soil Mechanics &eed for Unsaturated Soil roerty functions

%er!inology and 'efinitions


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Section 5.(

)olu!e Mass Constitutive relations

'esignation of a!ount of $ater in Soil

'efor!a*le and non defor!a*le soils 'esignation of stress state

Uer li!it for soil suction

)olu!e + !ass constitutive relationshis


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Introduction

SWCC + interaction *et$een the !ass ,andorvolu!e of $ater in a soil and the energy stateof the $ater hase.

%he SWCCs have an i!ortant role in the deter!ination of unsaturated soil roerty functions.

%he rocedures that have *een roosed for unsaturated soil roerties are aro/i!ate *utare generally satisfactory for analysing unsaturated soil!echanics ro*le!s.


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Background of Unsaturated Soil Mechanics

Early Soil Mechanics ,102-1032 focused !ainly on saturated soil $ith ositive ore $aterressure.

Consideration of residual soil4 e/ansive soilsand collasi*le soils ,ro*le!atic soils doesnt fall under saturated soil !echanics rinciles.

It $as clear that there $as need for a theoretical fra!e$ork that e!*raced all unsaturated soil *ehaviour.


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Early develo!ents on the SWCC in Soil "hysics

Use of Caillary Model - Briggs ,1607 and 8aines ,10(7.

a !athe!atical relationshi *et$een the radius of curvature of the air-$ater !eniscus and the ressure differenc

e *et$een the air and $ater hases. ,Ua- U$ $as sho$nto *e *alanced *y the surface tension %sacting at the $etting angle 9 along the solid surface.

%er:aghi ,103 and %aylor ,1036 used the caillary !o

del to e/lain the differences in hysical *ehaviour *et$een saturated and unsaturated soils.

Micro !echanical !odel + not useful in !acro !echanical geotechnical engineering


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Early e#ui!ent for !easuring SWCC

Buckingha! ,1027 !easured SWCCs for a variety of soils.

;ichards ,10(64 8aines ,102 and )alle-;odas ,1033 also!easured SWCC Long cylinders were

flled with soil ater was allowed to

co!e to e"#ili$ri#!

with a waterreser%oir at the $aseo& the col#!n.

'he gra%itationalpotential energy

within each col#!no& soil was calc#lated$ased on thedistance a$o%e the&ree-water s#r&ace in

the reser%oir and wasre&erred to as the

*arly !eas#re!ents o& water content%ers#s !atric s#ction on two soils

+a&ter,#cin ha! 1/0.


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)alle-;odas ,1033

)alle-;odas ,1033 erfor!ed oen-tu*e and caillari!eter tests on unifor! sands.

)arious sand article si:e ranges $ere s

earated using sieves. Each !aterial $itha li!ited range of grain si:es $as lacedin the oen tu*e and the caillari!eter.

%he *otto! end of the sand in the oen tu*e $as i!!ersed in $ater.

E/eri!ental results sho$ed a gradual change in the $ater content in the sand $ith distance a*ove the $ater reservoir

istri$#tion o& capillary water

in sands o& %arying gradation+a&ter 3alle-odas 1/44.


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Early concetual !odels of flo$ in unsaturated soils

Childs ,1032 - there $as a relationshi*et$een the SWCC

and the coefficient of er!ea*ility for anunsaturated soil.

Caillary !odel < S

WCC led to the definition of an effectiveore-si:e dia!eter.


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%he SWCC in early Soil Mechanics

%he =irst International Conference on Soil Mechanics and =oundation Engineering ,10>)an Mourik Broek!an and Buis!an ,10> - not

ed that negative ore-$ater ressures layed an i!ortant role in the sta*ility of sloes.

In the 1062s and 1002s4 the SWCC *eca!e

the *asis for the esti!ation of nonlinear unsaturated soil roerty functions for all tyesof geotechnical engineering ro*le!s.


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&eed for Unsaturated Soil roerty functions

Measure!ent of unsaturated soil roerty functions are unacceta*ly costly.

SWCCs have e!erged as a ractical and suffic

iently accurate tool for the esti!ation of unsaturated soil roerty functions for !ost geotechnical engineering ro*le!s.

%he SWCC has *eco!e vie$ed as the ?key@ tothe i!le!entation of unsaturated soil !echanics in engineering ractice ,'.A. =redlund4 (22(a.


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%er!inology and 'efinitions

SWCC4

Suction+Water content relationshi4

;etention curves4

Moisture retention curves4

Soil !oisture retention curves4 and Water retention curves ,W;Cs.


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'ypical desorption SCC showing distinct ones o&desat#ration.

'he ey transition points on the SCC are the air-entry%al#e and the resid#al %al#e &or s#ction and water content.

'hese transition points are defned on the degree o&sat#ration %ers#s soil s#ction plot and s#$di%ide the SCC

into the ($o#ndary e6ect) one the (transition) one andthe (resid#al) one.


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'esignation of a!ount of $ater in Soil

)aria*les used to define thea!ount of $ater in the soil aregravi!etric $ater content $4

volu!etric $ater content 4degree of saturation S4

volu!e of $ater4 )$4 referenced to the original volu!e o

f the seci!en4 )2,i.e.4 )$-)2.

'i!ensionless gravi!etric $ater content dg

where:w 7 gra%i!etric water

content w7 !ass o& waterand s7 !ass o& soil solids.

where:9 7 %ol#!etric water content

3w7 %ol#!e o& water 3%7%ol#!e o& %oids and 3s7

%ol#!e o& solids.

where:S 7 degree o& sat#ration.

where:w 7 any gra%i!etric watercontent andW

s7 gra%i!etric water

content at sat#ration


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'i!ensionless gravi!etric $ater content

'i!ensionless gravi!etric $ater content can *e $ritten in ter!s of the individual !easured !ass values as follo$s

D

M$2 !ass of $ater in the saturated soil at the start ofthe test4

Ms !ass of the soil solids4 and

M$ !ass of $ater at any oint under consideration. )$2 volu!e of $ater in the saturated soil at the start

of the test.


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&or!ali:ed gravi!etric $ater content ng and &or!ali:ed volu!etric $ater content n

v

ng

Wr residual gravi!etric $ater conte

nt nv

residual volu!etric $ater content

ata &ro! a sandy soil plotted in ter!s o&di!ensionless water content and nor!alied

water content.


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'efor!a*le and non defor!a*le soils

Classifcation o& SCCs $ased on a!o#nt o& %ol#!e change thatocc#rs as soils#ction is increased.

'he ter!s (de&or!a$le) and (nonde&or!a$le) are $eing #sed!ainly with respect to the !aterial response to changes in soils#ction. Sands are essentially nonde&or!a$le !aterials $eca#seo& their low co!pressi$ility. Sands are essentially nonde&or!a$lee%en when prepared as sl#rry. Clays can $e either de&or!a$le or

essentially nonde&or!a$le depending #pon the initial watercontent stress history and nat#re o& the


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Shrinage c#r%es

corresponding to %ario#s initialconditions

o& soil speci!en.

*6ect o& stress history and!ethod o& speci!en

preparation on !eas#redSCC.


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'esignation of stress state

Soil s#ction %ers#s gra%i!etric water content &or initiallysl#rry egina clay +&ro! ;redl#nd 1/


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Co!ponents o& soil s#ction and total s#ction &or eginaclay +&ro! ;redl#nd

2002a.


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egree o& sat#ration %ers#s soil s#ction &or a highlyplastic clay prepared as a

sl#rry +&ro! ;redl#nd 1/


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Uer li!it for soil suction

Ai**s free-energy state e#uation

ln,uv-uv2

$here F total suction4 k"a4 ; universal gas constant G6.13( H,!ol J4

%I a*solute te!erature4 ,%I (7.1> < % 4

$here % te!erature4 KC4

)$2 secific volu!e of $ater4 !-kg4 Lv !olecular !ass of $ater vaor ,16.

21> kgk!ol4 uv artial ressure of $ater4 k"a4

Uv2 saturation ressure of $ater vaor over a flat surface of ure $ater.

Soil s#ction as anction o& relati%eh#!idity in thea!$ient or internalpore-air.


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'heoretical soil s#ctions corresponding torelati%e

h#!idities in e=tre!ely high total-s#ctionrange.

'heoretical soil s#ctions corresponding t

relati%eh#!idities in e=tre!ely high total-s#ctio


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)olu!e + Mass constitutive relationshis

e eo Cclog , u$-o u$

$here

eo initial or reference void ratio at o u$4

u$ ore-$ater ressure4 o initial or reference total stress ,i.e.4 vertical stre

ss for

I2loading4

total stress state under consideration4 and

Cc co!ressive inde/ ,i.e.4 sloe of the virgin co!ression *ranch.


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e&erence co!pression c#r%es &or sat#rated soil +&ro!;redl#nd 200 +$ $ase-10

logarith! scale.


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; i i


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;evisions'otal S#ction atric S#ction and ?s!oticS#ction

e&er Section @.< ole o& os!otic s#ction pp:105-10


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Effective ore si:e dia!eter%he effective dia!eter of a ore is defined as th

e !a/i!u! dia!eter of a sherical article $hi

ch can ass through the ore in the !e!*rane%otal Suction N4 Os!otic suction and !atricsuction

Arahn and ;redl#nd+1/2


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Chapter 5 - Soil-Water Characteristic Curves for Unsaturated Soils.pptx

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