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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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