Some effects of desiccation of clays in relation to their compression

(1)

!H B tR

OOM ~ RBSSIOL .._,+=:;•: . I=~

(2)

THE C SOLIOOMBTERS WI'rH THE SUCTION PLATE APPARATUS

(3)

ENGINEERIN'i

Lllli:ARY

lA

[(0

./(4b

)95'"6

CCfj

2

in Civll 'C~in~_crtng. It i s presont~d a~ a t>artial

(4)

Laboratary te-sta of Oallpl'easion, abriQ)cage under air drying condJ.tione and meal\\U"ententa

or

negative

(5)

~h~ Olay....>go.ter .t;ys~o

U.r Set

Dre.ifltlt'!C. by .ll¢siocation

State5 of Vnsa~atiM

'Ztfeotiw s~~s

r;;x··-~:Rtm!"'ri'-lf, !~~{r.,;n~

S~!~"J.f:W !;~~) ~s;;Jlitl wmr,tr;;USS

0-C·ll8~1iiJ.&tiQI'l

(;~(!otioo

tor

llaoh.ini.t Str.a:tns

E}ilf'intmg& Ur.d.s~ Oontt::nt Curves floU Uoi.atll''N T$rtBi.oo :.;tac.sur~mcnt·fl

S~o ~ion :"lata

T~J;"...t"atut"a 1;t»foct~ Oentl"if'ug_e UetttiA

:. ~f!:SSi.U'O :r:mnon.n~

lm~r•,ne t&ter·ial

2

l.,

4

6

g

S"brlnkago Curves 2:1

pP vorautJ ~tur~ Content C~a-s

J3

~Y\#Jl"VJ.l

!i:tteots

cf Pcn.5:.o-oot1.on

35

'V<dda Uatic V~!.!a f,og

ct"'

NEV'-.. ~e 4res:l!IU:'¥>

Curq~s

'7

(6)

I wish to thank 1\tr.. P .. J.. AJ.ley for his

assistano~ in matters oonoerQing soil mechanics, .Mr. W. E.

Pascoe and Mr.

a.

T. Watson for their oheerfully given aid in practical matters and

Mr.

F. A. Roper for guidance

with philosophical problems and matters of Great Import.

· l.fy thanks are also due to l.fr. F ~ Downing of the Chei'nistry Department, who knows no differentiation between creed, colo~r or University Department when anyone needs

(7)

flle behaviour- o · fine ~r1.llnl'ld !>oils 11n ·ler a di rP.ot oorn;>resaion

force has always been a s ubj:o:o t or gc·eat interest to :'oil~ inw~sti·~ators and. praotioin1 COI{incars. I n p:.rtiou] v.t' , thf• ~'n•l""oo(,~1.)1 U··tion

load na.S a.ttr.ooted a ttention. Cfn:l&et'an•..ie (i), in 19_36 , pr O:'IOSOd

an eqirica.l oonotruotion t o ..letermine th.:Ln loal from th~ Vf)ils r-atio

vers us log o" ar~rlied lo i ourven. lfo 'I':OrkcJ. from result~ obto.ined

from a aer ies of' t es t.L on c lays Tihic!l h u ... ar.en n!l tura] l y cnm t•r. s~J.

The effeotc or ro~ulding from

the

natural state ( uo wcul i be oaused by an.v dis turbance dur1Q3 mun.,>lintd have a lso b0en sub 'ect-cd to fairl y thr,ro•AJ~h investigation no thnt the o~rosnlon curves for sampl e s in the laborat ory can be related as nearly as l)uosi 'ble t o those 1:bioh ooulu be e xpected unl er na tl.lT.'al cond.i tion!l in the field e~g. unler a rounlation load.

ffo~ver, vary little inv~stigation seems to hav e been oarriod

out on th.e e r f'eots oi' ue:<Jiccetio'1 o ~' olo.yo in rnl a.ti on to thoir

preoonsoli d.ation 1ond ana to the gone.ro.l inf'lucnoe on, o.ntl. o.lterntions

·t;c the s hape

or

the Ol').n;>reasion cu r v& o f' .ier.:reanin , moisture c ontents .. . It i s wiJ.o1 v known tha t the internal force:J G<'!t u, i·1a o1ay

structure d.uring :.lryin can cause ~f'f"~ct!:l c·1ual to ti1osc .tu~ to the In many oaac3,

(8)

2.

gren.ter dep tbs. r.a '1\gl"anJ.e (2), ror on" ,

ob~f!rv~ ~.!.'d.t~

o'!"l

Uansena ola.ya c~., flf' • (1 } ).

I

:X:

1-Cl. w Q

due to ove rburden

PR€CONSOLIDATION LOAD

The so .. •r-cce· --solid tion loa·l.s ttre

j i.tF~cr~o.~tt. ~ith 1tl: t.:~ 1.n e. non-11n .. ":r

U3nn"'t' • an-1 tllt!o tnoronue n .!ain

1 incr,..o.!les ani

tnc.ro

b.av P: bl'!e rt n ....

1 _a.~loturo

cflarlf:e f'lffaetn ..

.

•rnua

1 t · a·~mo i l,hat an

FIG 1

!

inv. stinatton or

th~

Jr7in

~

e l"ec

to

Q.rt the cvm re::;~1h11i.tj1 ,;urve!l • pay ltv ott·-· ,n~; t'-'l to U1e pr."'<lcns· 111..1-'tti.on

(9)

,.

'l'his water may be olaased in three categories (Grim ref: (3) ) ( 1) The wat~tr in pore!~, on the sw:fooos and arounJ th.&

.e(l~('!S or the io:livi~'i.ual l>O ··tioles of the olay min~rals.

(2) l!lt~rlay('r l'te.ter, bet, ~n unit-cell layers o'"' oort ain

mineraJo e .g .. !:tont·norillonitf:l.

{3)

7Jater whiclL oocurs in tho tubulnr· opening hetv,een

elcn~rate struotural 1nits e . ft . 3"·· i 1•l lte - ott~ >lt1 :ite

-pal,y.J,oJ.'"Sk i t oe min.-.ral s .

•rype ( 1) ~l:lt~:t· re qttir~c li·l. tle E:l'nerzy t o <lrive off o.nd oa n be los·& a t r o an t"'t1t·J~rature s.

'l'ynes ( 2 ) nnl (3 ) re quirf1 1110!'(' e nar -:tY , i.e. t(!l'rr;'~rntur~s 'lt least ap,)roachinr 100°0 D to s uiJst .':1t il:11ly r~movr' 1 t. I n th.~ c aoe

of ilo.11oysito tile roaetion is no t. l.'eve·'s :tbl e, but moat othel., mlnTrals \Vill .l'eform the h.yJ r a te.l state e asily if' th" .ater bAs noi. been lo.;t at too high a tcmr~cratura. Gener.ally spealcinP.: , the pore ai..cr iG liquid, voith

a.

layer o·r non ... liquid a laorbed wn't"r on the au.rface of the pores ant be·tv.een the olay particles.

The e xact at rungcmcnt of the l'!ater ll1,,lncllle s aJso.cb C'd at the sur.race of 1lisoreto clay [H:tt'tiolel'l ac e:n.s t o be a oub,'Seot or debate

8.'!10n"'; 8xpot'ts, but it is genera.1ly a~ref!d that t~lC V are uon !ell in some fixed pattern, fJt.Ut th~ al~oroc·l "' uter i s \ t erea t prot:oure a and •nay h ave thf> s tr1.toturc of ioe nel" r the sur "uoe of tbe ?nrtioles •

Aitchi son

(4.)

~:rr..::wri!lo!"l the otate~ o!' tiv · "'.31;or. in a c1~y mass, in the li~1t o~ t~~ 3hC'ar rorcnn n~c~no~ry t o ~is 11 c~ the

(10)

q..

viseooit;y c'laractcriotlog

or

ice.

( b ) A thicker film ex tentling ou t •:•ards f:rcm thtol ao..lsorbod •

f ilra (a), f'or. t~. Jiotanco of. up to 200 A. , p os!H'lssin;7, viscosity enaraoter 1ut:lca &lsnging £'ro11 thooet of ice

nt i·~s inner boundary to those of Cree "'ate:t~ ot Hs

outer extrere.,

(o) All ater more .tban 200 A from a particle

•

sud'~co,

h.nvinr, tho cllaracteriotios of' f!ree ,. ater ( 110ro water) • Air Set t

Grin1 and Cutb'bert (:5) have shown that w'.aen certain olay-.:ater •:Jixtures are allowed to Gtanl un·lor o~rtain o cnditic na, thore 1r' an increase in c cm,'rc s sion s trent; t il without lol!a of wator. They

oa.ll this "air-sot11

.• 'l'he explanation appe.:u-s to be t.h.nt a oertsin

amount of time ifJ re q,uirod for the ~~a ter to pen!! tra te o C"llr. or the

allthors state tha t a. clay i s deyen.lont on th-:> d.evelop.n~nt of

non-Drainage by Oeolcoatio~ t

The ;~~ ne.~~al theory of' drainage 'by dP.dco~tion, as 1lCHC:t'i oed

by TerZaghi (6 ), can be e::r,.la:incd as follo"~s

s

On e'ltt1onure to air, the di~Cil&rge velocity of tho pore water

(11)

either ver.t slightl~T ncsi tive or f"lo~ nega tive. Yet on exposure or the surface th'"! .• a t er drains fr,,r.l the interior ..

~radient. lleaoe i t t.nust be c ouM!.t 'by ~urraoe t~n~ion a t the

exterior.

In order to vit.ltalize this :~tnte

or

streM i'l n 1'~ rtly

deaiccatod mae9

ot

ol~y, un ::t.l'lalo -ry lV\:l be~ a drawn. liat\'JMtn the pllrtiole

stTUC~e o~ a fine grainP.d soil and a bunlle of highly oo~re.sible

capillary tubes

or

ra·J.iun 11_r'' (~tee

_·rig.

_{( 2 ) .}

Saturated f~ter evaporation- tubes

[<iJGURE 2

compressed und tuP.t1isci ll.t

radius '' r'• of Cfl.piJ1aries

f I 11. roa.l tty ,

I t

:or

oo.a .. se, ti·~e~H"

!

ltub~a would eon•

sis

t

of a. very

. tm~·tuous ohantlel

I

of voids.; Ilow~ver, the ef'reot woul d be the s~. as the forces are acting a t the fr~e surf'ace whea all poro spaces are 1\all. Th.e · maximum angl e

or

contact o<. of tho pore water is as sumed equal to

90° ~iten t he Goil. .is oan~lt'! :.ely satu:rt.llie•i . .As ev~:)oration proceeds.

val11e of tl11s rodius is e qual to the , .. alius nrot

or

t!lt' tubes. The tensile stress in t.h~ vrater i n tho t.ube.s, 9", can be found by erpAtinr.: hydrt '•:l l;,u;tio ar\'1 surf'aee tension f orces :

2 ·.

2 1r r T

(12)

G.

p'* o - 21~ s eos o<

r

... ( 1)

y/aere T

=

surface tension. s

· (Of oourM, in time the water will eva>1orate enouft)l to bring aoout ttlr: atatf.'l t<Jh~re the p orea iJX'O n.ot all f'illcdo only

th-0 smnller o~s oontaini~ '\'-later a t a ~reatcr ne.-,ativo 1'J.V;!~nare, and eventually the free ~.ater remain in .., i.ll be of> a lflntioulnr natu-re oetween particles).

Now i n o soil, tlw aotunl air""\"ltltnr intert'nce 13 n•J~ a

h oms. above o. rroP- ~ater aur!'aoc

i.e.

( ¥

=r uenoi

t.:r

or •·atr>•" ),

r;

as h can be aeanured expw·i!l.t·Jn tally. The mo$t or.mVt.mi.ent meacurc of the r·or~ v:atel' ~.>rnustu·c

J et'icienoy seorus to bo that pro •oscJ. by ~:ohof'ield - hio 1>P eo .le.

wh~re h i s in ems.

Tltio has boon used ·by the! majority of 'l.<ork~··s in 1his f'iel:J. Ai tcrliaon

(4)

points ou. t tbo.t if thl: J) @ scale 1a to be used as a measure

o-r

the f':r·et~ oner.gy., then it should only be a "plie.l. to soils in which the osmotic e rrects o:" U.issolved. s 1 ts are neo;lir::aole, as this a.f f<'!ots t:1e ll:O:w;ll me tho.is or m~anuring this q·umt i ty (e.g.

suction plate or p.ressure membrane) States of' Un3atu.ration :

(13)

con tent , Ai tob.Rson ( ~ ) rroo.mL~P-0 the follo·nin'~ s t.u tes of s~tturation

or unsa~ation.

D. Part ial Sa t uration

E. ~odir ied or imary Un ~aturation

The follo-1'1111.'~ parrunet crs t,J.rP. needed t o defi ne t hese sta.t ns

p" :a pore 1at er pro llaure

{\llhm:e p"

<

0 i t i~ equal t o tho nc({ative ~wre

o soil moisture tension or

pr.·~su ~e defio l..,ncy in the pore water

Ai tchison·

(4)

r·~.:~ ~· w p'* a s being

;>O

if i t 1s nega. tive.. ll11r e i t i s r.t-~t~r.ioJ. as a.l p;ebra l oally e qua.J t o th.e \nr e water preitSu:re , the zet'o datum

~r :a ll(:-,rreo of' :>ore spuc~ s nt u.r ntion

/l r. :a soil mc·in tur e d~f.'loit - i.e. the Vol\~ of wa t er

.~

p et- un :l.t arou wh io!l !llU ::t t bf.l au :. ··liod t o the s oil t o

achieve a c ondit i on of Z'-'!C'O oo.il lilOisturc t-ension .

ry •

t llf' rc 1a tiVe C!'Mi)r~n.;,;lbiJil..y Of t he por e f'l ui<J..

(14)

a.

Of :1t OOe f'r i oiont of COl~Jrl"s::dhili't.y Of tne pore fluid

(it may. contain air)

C •

.

ooetricient of oom>~~asibili~·

.

_~

or

air-trer~ wat er . Us ing th.e above -pa.rametorB

s

A. qcmi)lcte Satumtion - All v are spaces filled Vlith wat er (no air uubbl-~s)

B. .PriLdA\'V Unaa tur.ation - This i s the firnt ntage i n <lrainage by denieoo.tion of an initially satu.t·ated s oil. '~1\<':r.e ~1-e

no air b11l'lblos 11n·l a ' 1 ·tho voi ds o.r.o m.1.tcr fillcJ, but t l4er(-l ie

~ w ) 0

Thi o r~:? va'luc i s c \".lus~d hy the

r•·d

is

the

critical ,)r<'lssurc

def.i.ciency nt V"'hioh t h.o largest

o.

S,Con.ioey Unsaturation - In the seoona ntage of desiccation aome of the vores have drv.ined

••• p"

'='

p" d

s

<

10($

r .

p ::r 0 ao the air in the •lrained pornB io not occluded

g

or aJsorbed an:l i:.i therefore a t o.t ,.ospb.erio nr~s sure₁

The thrc~ s t o.tes D, Bt a"ld lJ nt·e parallel t o those A, B, and C

for a soil wtliob h.as 80!1'&.?. adsorbed. or occluded air in the •'>or e .Pluid

(15)

thus :

~ ::1 0

s

<.

100

w

r

i.e. there is no ne·r.t:~tive pore pressure, but the soil cannot he

p"d ..(, Po

<..,

0

t'lf

>

1

sr

normally exof.~~J.s 9(])~ Case parallel to B

? ., Modified Sec ondar;y l1ru"l_s.turat1on ; ( lase rarallol. t o C 0 1 00 ... _{/ •r}

s ...

_~0

Pg m9i'f be a complex function with. varying

pressures i n <lH'ferent phase~ of the soi l

atr.

One

or

tb.e b-a$iO e quations

or

soil mec!tan5.C$ is the l"~1ationship

p"

=

pore water pressure.

·rhis l a1i? as ar~te.i by 'Pe:rz.a;&hi ( 6 ) is the bosis soil mechanics involving pc->sitive v alu"'a

or

po-.ce v.:at at• pz•essuras.

(16)

10.

grainel.l soi l when the pores are water filled.

Squation (2) ap">liea a t dctly , o1· e otlrso , only to

a saturat ed sotl in vmicb there is perf~ot .•oint oontaot beL,··~on the particles, there bein•• no reu.uction in ibf'l e ffact of" the hy..a.coa~:}tic rorcea on the particles duo

to

an ap~reoiO:blc a~o. of' oontaot.

Tbe i dea behin.~. the cxt:>t1t·im~nto.1 work then, wa~ to inveati,,a.te the oxtf.!l'lai o'1 of' e<pation (2 ) in the ca-e of clays, by measuri ng the mag litude· of th~:1e soil "10isture foronG , for Yarious moi:ltl.lre eont~nts and throtqil the moisture oontcnt ..

(17)

11.

It wan .tt1SircJ t 0 r~ ··r a iuce in tho J a l.h.Jl"a.tory

th'3 conUitions whioit woull exiat as an aHuv.ia.l d.cro~it of oJay uas desicJo ated lltll or air dz~rtl"b ~ oonJition.s. B:onoe a . ~rta in amount

slurried well pru1t the liqu~ llmit to a consiRtency whioh, wbile ueing definitely liquid, would not allow appr aoiable se>:rega.tion of the T.lartioles t o take place bof'ore the mixture re-r:elled. '!'his slur.cy ~·,ao then allowed to nir dry amt wan used us a remoulded sample.

Standurd : Na.tu:ral ·toi stu.re O<lntent

Liquid Liwi t

r>l 11&tio t.imi t

Speo1~1c Gravit,y

24.

Hour HiY·lrrJJleter Oonsoli.d.ation z

On

notural

sample

On re~noulJeJ. ~a near to vir~in ourvG as r os sible anJ a t ueoro~sing moist~ contents.

PF· Uoisture Oont~nt ~

On natural and rem.oul<Jo.i ss.m,;:;l ea . Shrinkag~

(18)

12.

Oonao lid.a tion :

Ltd. E'lreatually tile:re we:r.e three ll!UOhincs; the se-cond at't"iving

in .April and tb.e third towards tb.~ end of the year in October.

hourly intervals. The sample• on the unloading eyole, was not

allov~d to swe1 1 under zero loail., but th.~ final reading of> the dial

~e.uge was made with the 0.5 tons/sq.ft. load in pl ace. The '>7atE'tr

and a moisture content taken.

It nas considered t hat in this

wn,y

a more positive valu~ o f" -~he final height

or

the specimN~

..

oould be obtained. No ohal'lge in the roadin~ of' the

specimen thickness was noted as tJ1.e CUX'roundin~ \·1atcr was

constant.

l't. rigi d conore·te slnh was eonetruoted w.itr~ its o-;m

foundation CO'Jlpletely independ.:mt of' the t'loot• of. the

the wall friction on the specimen, a.l though v an ilelst

(7)

sh ul>l'ed tht1

t

tnis wa.s only th.o oause or S'llall ettors oom.,?ared fttctol"S

(19)

On

the se machines there 1a sli~utly too much clearance

!lrOUM the u '"per :>orou.a -ol a te, and the centring of tnis plttte on

~be to~~ porol.ls r~late is ·pi\rote,l a~inst the ri<~id

r.t:ame of'- the machine and the lo~1a. i~1 a.,,~li<:ld Ur,Jwnrda througli

a hang~r fral'.lle on whic h th t't sal'll:1l e cell oonta in1np: tt'l" oamr.>l~ and

bottoa porous plate r~sts (sec fig. (3) ).

t

Load Applicti Upwarcls

ol low On!:le Of' 'l'!lP.

Conso'l j d.ornc tc:!r

Con f inemen t Of' Hn ngCl~ Allows

'

---

- s n.mp l e

Ce ll

1.::.. ter~1.J Movemc n t Anu Caunes

Poor Ccnt1·eing Of' 1' he Uppe r Pl a t e

F'JGtTR~;

3

(20)

be automatic.

men not quite central, an.:l h.enoo atuok e. g . t"i g.

(4).

rhi s

of repeating the test at that rno·iuture cont&nt ..

i'tith red.uoed cleara:toe on 't'~e up:~r pl ate , th.o sa:n~>le 'Would not have the same tendency t o eqt.teeze out tl1r0ugh the annular

spacA l eft. 'l'hio introducea on error in a1l t eete ond although in tests on natural s~les thin :lo small, it is impoociblc

to

run a test on a remoulded aatnple much above the liqui<l l1ml.

t.

Sh

•

_4x

~ IT

•

.. ·U.,1x

In most tents _{' om p l¢}

ri ng

So :s 1 + e

-

S..>t b

FIG 5

~· 2 6:

,.. ·~

This oan

·:alter

the VI>:Lis rl.l.tio roadin:'l; by

Se

2.5

x .. 141x 0.35x

No\f average ral iuo oi' sam}le ring (See fig . 5.)

1.498

It

Average radius of toJ r>orous plate

(21)

=-"'I

0

21

I•]'

"!I

~-t!

(22)

Now i f the sample is squee~d into this a nnular s pace t o a b.eight

h

•

0.2n

2

z

:r ~1\r (r

1 • r22) eu. ins.

2 2

:r ₀₂_{l i {} _{1 .4.98 - 1 .483 )}_{eu. ins.}

•

0 .. 028 ou. ins •

;,hioh is :, 1.0:'; of the- .i.ni tial voids ratio .

In

ext-reme casco it woul d be much rnm·e •

The 100thoiJ. of oolctlla ting the V• itls ratio .J.urin~ tho

test was tnat given in Ca~ror and Oaaaie (8 ) •

the initla.l l1eight aanurne..l to be oxaotly that of the sample ring. The dial gau~ readine was then takefi. ·~he loading and

11nloadint.~ cycl e was carried out. and after the finul readin~ was

taken the BOII'lple was removed anJ. a moisture content taken. tlO\v at this atage the sample wao f\tUy atura.teJ •

• •. e₂=

ms

e₂ • rinal voids ratio m :r mostur~ content

g • sJeolfic gravi~ h

1

=

initial heiront

(nasu.med · that of th•"' Sl!'•tn l !'l r ing )

t1;z

:s · final hoi.f!ht

h1~

=

e!1a~e i n dial gau~e rca ling.

(23)

16.

dial gauge i s

e oorreapon.d.in!~ to os.ch load ·througi1out the (• vole c ttn be

oaloulatali. The value o.f Se , lloi'Tever ,<.tor eru.l.::; l1pOn e₂ (X'.n:i.oh

Sh

we know ocour~tte ly) o.nJ. u9 <m 1:1

2, wfllt'Zh in turn de ·ends on h,

bein(~ exactly the height

ot

th~ sample ring . N<rvr aasume sonx:

dishing:: or the sample wh.en we are cuttin tt i t off level with the too

or

tbe ring, or that th<:l samo l e cont:l.nucn to bulg~ after

it

bas been levelled off (as sometimeo hay>!)enn men tho ring baa pressed into a wat clay ). It is ensily noseible to have an error

ot

1/50"

in the initial height. Ualng avera~o figures

tor

the measurements

:-Se =» 1+e o 1 .G :a

1.6 - -

-

-S't

0.

775 ...

Ab 0.

775-0.1

:a

2.37

asmumin~ hc1ttht is thAt

ot

tho

Ml:lpl c ring .

::1

1.6

-h

1:1 2.44 for coiTeot initi.al •et .,ht.

Thi:J gives an error of nenr:ty ,3.Q • tio-.1 this ~t'ror

is onerative throutdlout the ••hol~ of" th~ ~a)h., ~lthouaj1 i t is due only to one incorrect readin.~ . It i a tnnrefore uot~r to

(24)

tbe sample will

oe

conf'inell

to

the Ocnlpre ssion rending f'or tb." initial load:) anl will not a~'f'ect t1:1e rriOO t important pe.X't of the p,raph. i . e.

the slope of the straight line portion of the e/log p ourve.

Oo:rreotion for Machine Straina :

It was t'ou:n.d that ther e w~e if'llerent 3tr~ins in the oonsolidometers which a;Jded to the dial galtgC readings givi ng a

m.a~biue r;i th no soil in them .... tl:l.e l.oa-.1 being app lietl .Urcct ly to

are to be subtracted frU'li. those o'bta.inBcl ·luring the test.

:01fi'!;Rt:>lT W:.CHl:N~ ~;TRAINS

Load

1!/ sq ..

ft.

Dial

Gauge 'Error in

Inones.

No .• 1 No. 2 Noo 3

..

o.o

o.oo21

0 .. 0025 ' 0.,0021

o.s

0 .. 0007 0 .. 0009 0.0007

1.0

0.0008

0 . 0007 0.0008

2.0

o.oo11

0.0012 0.,0011

4, ..

0

'

0.0015 0.,001.6 0.,0015

8 .. 0

0.00214- 0.0025 0.0024

16.0

0 .. 0019 0 .. 0020 0.0019

8.0

Oe001 2 0., 0013 0.001 2

t..O

0.0008 0.,0017

o.oooo

2. 0

Oo 000,5

o.ooca

O., (h'JOS

1 .. 0

o.oc,oq.

0 .. 0006

_o.ooat'"

0.5

(25)

18.

Shrinkage MOisture Content Curves

The volume eh.ange as tha soil shranlr. un.1e:r. air

m~oury displacement method. liT m this, a olot o f V"oids ratio

versun moisture content was ma-.~a, vrovidll1.6 n link betw~en thf! compression and soil moistui•e tension curvnse

A "!"18.!'1s dian with the rim grou.nd flat was f'ill~ with mC".re~

(see f'ig. -6 ) , anJ a

p~rspex ~i..t,

with a

f

6" h ole bored in it, plne-ed

on

top . A stanJarJ. ·~veight (4-lb::s) -..;:..s a!1plied in. the oentre

or

the perspqx cover and tho axo~os mercury esoa-peJ. through tht~~

hole in tho cover or aroun-.J. the oid.es. l,laoing a f•ixed weight on top waa f ounJ. mre definite tllo.n just pr*-'soing on tbe

lid with the hand, and. a~mured a. constant voluroo ot• mercury.

1. soil pet or abc:nt 20o.o. volwne wan ~ed makinl! sure ther(") were no aharP. pro .ieetions or . outf'aoe pockets, so that the merouey would follow the oontouro of' the satf1 _:-1l(l.

It

t7ae then submol'6ed in tile mercury by the tbreo u ,..m~-s on the lid

or

tl:te apparatus, anJ. th~ weight

or

liqui t 1i!1tllact!d taken to

.t

0.001 lbG, reprcoentin·t. an error :( + 0.5% •

-

-A series of volume rnem1urcments wan take11 for eoob

soil pnt, weigjlinr; it Jftcr ea~~ll ir.1:uersi on ant lottinrr it air dry bet?teen.

to dry to the point ~.here it c onta.infl!J. ;::ibout

5:;

of' water, fif1;cr which it was oven drieu anl the , ei ~ht or ~:-~olitla foun:lo Knowing

this ·and the specific gravity

ot

the noi l t;1e moi sture content an .. l

corresponding voi<la ratios l'iere then oaloulo.ted.

(26)

T

T _' I I I

I I I

I :

I

I Ho) r~ 1'o AlJ.ow

F.:<ta~ sa M<": t,'Ctu'y Esc(l.pc

\

II I I I

t:

I I I

I I _I

I I I

I I I I

I \ I

t" ,:.:_,.lH<l~ t:

---

...

--/f DIA

T

:

I

I I _I

I I I

I

.?er~p(~:< Ha nJ.l f:

/

y'~

14"

r'

_{a ..}

f

_j

~

I

I _I"

I Pron~~~ To Suhm<.:rge The Sa.rnple _I

J~ Dill

=-_j

" . "1

L -- - - ~•

(27)

Soil Moisture Tension Measurements

•a

·rilree mcthoJs

or

t'inJing the p ·"

or

tho sa!D.>les 11ere

trtea over t1e

follo•~ng ranges.

pP' Cms fig lba/sq.in. '1'/sq.ft.

Method

1 d8Q ~

5.0

0.06

2.13 10.0 0.12

l

_Suction

2.4.3 20.0 0.25 Pl..o.to

2.74

40 .. 0

o.so

2.~0

so.o

0.62

3.15

20.0

1.29

f'...en irif\t::o

3.45

40.0

2.571

(tJns11ccess-

ll'reom.-e

3.62

60.0

3.86

f"u.l) Pemlrane

3.85

100.0 6.4.3

( 1) r uction Plate :

The diagram (fig.

7)

shov;s the a • ·{ll"atus male f'or the Laboratory.. 'i:'he set tlp .i !l ~ .• centially the aam~ o.s that us~d by Oroney, C:ol em.an and 'BriJge (9) •

Tb.e po'ou.s pl ates used ooul:t not 'be obtaineu locally

anJ had to be aent fran

~gland. The ! ore size must be very uniform

aoo

of maximum diametor not greater than 1.5 microns

a pressure difference of 50 ems. or }.{ botT:nen i"aoes g

without the moisture i"llma breaking down an.:l al.lotdn~ the passage of

air.

'.l'h""se pl ates were available only in n•11all sizes (3.2 oms. in

dirun,~ter) ns they ore very diffio ·lt to ,.aanufll.~ture. Tlloae use 1 wet'e

in cut &mn nuchner funnels.

(28)

20.

6rU that tbc a~le ·,aa 1n lnti:.®tc contact ':Vith 1t.

I I,:•.

u;,;pc.t- surta.ce of tt"-..e :u::n:! l O af't'c .... L1t'l1 <t:1e l'inal m.o1,.,turd ··~i~·lte!'lt,

• 2T

-I"

at 11'17 f'lxel ~ . • Al'.?.~,.it'~

(rot.

10 )

{:) • ~naity ur the liquid

<S • denld.ty ol' the nutur~~ va_·or

pr c•surC'.

J.'ti !l fac t t o llCied 1n tile ID!!;Hl$l.U" nt Of bi~tl V~lur-s of'

P F beween

4.5

anl

7.

(-':f!f' CrortQY et al (5))).

(29)

SUCTION

Glo5s Disc

Suction Plot~

PLATE APPARATUS

Mercury Manomet er,

Suction Pump

Cu t Down

~ Buchnes Funnt-1

(30)

21.

apt)lll''a.tus was subjeot tt> th(: daily variaticnw of the labora tory

The change in pressure

or

the air between the mercury manomoter and the watoJ:- in tha tlaak could oau.se considerable

variations in the applie-<.1 auction. Oonsider the ea.so whert there was ~ variaM.on between minimu.111: night and nmximwn day temporature of

0 . . 0

20

c.

If' the maximum temperature wa..<:J

35 c ..

and the corres[.)onding minimum 15°011 then I'.Hl the ttolume

or

air in the a'[\l"Jal'atua X'erzi:aii'1S praotisall;y constant, we. OEtn nay that

l' • p • 5 !,)

T'

f

+.

5¥'

(The only change in volunm would b0 ti1{;'1t clue to the

air in the ~laak).

! + ST

;.

'1' +

? + SJ? p

=

273 + 35

=

308

=

273 +15

a

288

To avoid this ef'feot aa muoh as was possible • the

sau:~pl" was pl aced in the appa.r~tus 111 t!1e l ate afternoon and tb.e

saotion applied. In tho morning tb.e manometer readililft, would have changed slightly but was thereafter kept at that Vlllu~ by

adjusting tb.e sue tion throughout t he day .

(31)

22.

in tb.io period. Tlle soil ~as then rernove:.l , wt-i ileJ. to 0 . 001 or a

negative pore t;ater prP.nsw:-e oaleul a t od.

Ttle snmplo had to be -weighed ro.~idly as other-lise there

WfW an am~rooiabl.G losa of' moi sture during

tn"

prooe:.1o.

(2 ) Centrif'!!ge Method :

The a pparatus for the oent rl.fugc method was as ahown in fig.

(8).

The principl e in

virtually thr same ot~ tbat o!' the auction plate. Ins tead

or

having a c ...,lumn of.' wat er under o. suc t ion

ot

h OillS. of ft20 1n con tao t 1'11 til

tho !?ore wat er of the sample, we

ruwo t\ suotlon exerte.:l on the

a~">il moi s t u ro.

=

hx <J

mere

bill

hois')h t btan the centre of the

uter table

anJ

t«

2 t he centrirugal fiel~

ro tation

I

rl t

r,_ ]

1---

\',.·,·.~··::. £/~sample

1 saturated

1 porou s

J cy linder

. ~ l..;r; ~-~::: -~ ,:_ ...___

water tabl e j centri f uge cup

F IG 8

A pa i r of oent-.'ifuge c ups wer-e m&W.o, n.!\ving ecrEm tops and a smal l hol e (o. <~₁,t'D) at ro.diun .. ~ to o.ll oov nxca.1a water to esoilpe while ko~~ ing t he water tabl e at a coa Gta nt level.

(32)

These <:7ere turned on the soil l a the, bl'\lanoeJ. oni aaollacked on

t!le sideo to preven t l:'lakin .l undet" constant welt1. ng.

conaisti~g of C'llElo patterned to indicate the spof!ds rtJr,{llired when used

witn

a fif~ flashe s per ~eoond mercury vn~our 1~.

Now if

"r''

_{1 ,} nnd ''r2 were an ahcmn in fig . (8) then the eentrif~al ~ielJ

I~ow suction in oms. of f~O exerted on the EHltnple

2

=a (X'2- r1) (r2 + r1)

c.>_

2 s

and pi' • log

10

(ri - r

1 2

c.v 2 )

2

•

-Using t!le centd.fugc available in the laboratory and

t o

3.0.

Unfortunately the ~nchino ~aa too small for the j ob awl

could not rdaintain the spe.edo re quired f'or

24.

h ours w1.tltout itcu:ting up to suoit a degree t.hat the WA • in the out's eva:-•)ratrd. through

the small hole. In ,,~laotl of t lrl.s, the pressur~ mamb.,.r.m~ app o.ra.tus was made and used~

(3).

Pressure lmbrane

(33)

Pf?F.SSUR1~ Ml~MR!'Vd'\'!i: CELL

·t .. !I •P' "~-" ".;,r ..

i{'/~' -1--- - -tH

--0---

_____:_:_____~----~--,..

-/ ... ... - - - - -.... -~,;::---~---l-+--.

/ " "' .. - - -... ---' ... ~-,.,---\---4---4-+---.

0

1 / / " ' ' ' ' ,

'0

I I , \

I I I \ '

I , , .-.' ' ' I

1----l.----...ll:-::-:::-::::::::-::=-1.;:-: ::-.;-~ -. J ' ,' , • , ' \ I I

---:-- - -·-t;=.:=-! --·-·J-:.- j• I I

- - -- -. - - - • - - - - ==-.:--.:.~_;:-T: - ~ - -- - \-':::·· / ,' I I 11"-;;..;;.;;o..;:..'\--. - · \ ' , ,..:: ...' /

\ \

..

t (' c ,\' I l ; I 1 I~}.

.

/

(34)

---...-'"

__ ,.

_______

,..._

____

.

__

,

~(, ·.1rJ on ( c

:au!{c

... ~ ') i . ·: ~1 .... )

Go~n~~~c t i. OYl - ~~0:L2:z:z:::;wzz:;~zzz:zz;!ZZ:z:z:zzzzzzzzZ2£d

to ·::: o.llpr(!Sse:i

Ai:t• -:.;y11nd.ot•

'.V:3. 'tt':i'

Re:inf'<~rc(:.-j Hud.,~r

- - ====::::.

~BH ~{ et.

1/1+" Bolts 'Holdi.rH1. r;~:; 1 T \>IJ,?. th<;~r

--R<~servr•:l.:~.~ ;?.'/¥.'·---~

---

.

..--

...

---~---;t' ·~ ...

t"

!

(35)

It is le rt in

tOY.'

2Jt,

boll!"S to attain G<!Ailibr1W1'1.

'lbe Frinoi~,lo

o:r

the t?rcullt'e !ineti:lbrane apparot\13 is

proba.b)3 be lltnr."O G!OOOthly f.ad~d, h~nce ooin.g le~\S liable

to.

·: '\ .. ; .... , -:.·.;::';·!·

Membrane &te.rial ; . (11)

Riella.."'ds ' u.n eJ. «!! taero})rane Of So c:tell(lt)Ua!'\€! COQ'llf!I"'ially

(36)

25.

anJ. some pl &"\tloa inclW.ing nolyvinnl chlorido ·n~ro trica, but v;~re :rounl to be of no uae. The pl oatios generally were no t porous e nough whereas tho cellophane was t oo ro1"'ous M l ·,'tf.'lt.o also t"'las:i.ly

damllged . Finally, scwe Vis1· in~ t;"uoagt3 casi tl" was obtained frena the Soil Bureau Y.:.x)crim~ntal ~tativn by coad.e~y of Lk. R.

As a mambrane permoablo t o wate~ but not t<> air

Wlder nigh pres owes, t bis has been u sed nuecC' .sfull_r at pressu~s

of up to 250 lbs/sq.in. 'rbia membrane only roquires soal•ing in water far about fiv$ minute::; befo1·e the tost t o beootre oau. ·le tcly aaturo.t ed. It i ; fairly strong anl not liable t o bo d.ama . .:>;ed

(37)

in t:_u3 year.

l)e7;th of' Sem;;>l e

Nat.

WO

~11rfnce

L. L.

tJ.r~Of

P. I .

s.G.

Y;{ir~ter

Anal;tsia

D ;4. ~

D'

8 .9~.

0 22.2,; /rot

16.7 • :?..c::

~

%

Ct.,st~ ~and

2.t

;.m-\.1.25:a:u. :

j

~ Pin~ ;anl 0.25"m-0.05.~ - )

%

Si l t O. Q, r.n: - :i.W-3 ·--: •

%

Olf.\Y'

o. ·.v:

!l • •

'I>

Cvllvtdo O.lot~•

1).1 .

49. 0 ~

31 .. 9:~

12.0 ...

u.s.

Uu.rct.ll or ~.lo:i.lG Cln30ii'i.o.nth .. r'l

=

:Jt1 tural G ~

to..

o.,

"l. }

.uV ~rae., o,n,731,)U.I..\.O.C t. CCI :::1

~~;11

t.v

c 1c:w .

0. 056

0. 077

S..~ Ple No..

z

t

Wolp ora. ... clay trm limes toni') aoUA'tr,sr •·

1)-.Jp~l.

or

$ am ·le

llature or <Mrburden

Nat.

Lf/ C

L.t.

.?.L •

. >. I .

S.G.

!iydra:wtcr Ana.lyoin

'!; Coarse Sttnd

f'

Ploo Sao1

%

Silt

%

Cla.y

%

Oollo:Wa

• 1 • 6" ... ' . 0'' Hea•y :J1n-ck aoi l

•

24~~

#

51.&;

• 2*~.1' ~

• 29.7

• 2.59

2 .. 00.:::-~ ... !5m.n cr 9.q-~

·1.,;>5·

-o. o

QlZI "' 11 .5;";

o.o;mr::1-o.i

•05..;.~·= 27. 7f,

o. wsm

a51.~:.':

(38)

27.

U.S . Bureau or Soils Class.i.a' io a tic;.n

=

Clay

N&tural 0

0 ~

o.oca

Remoulded AvcragP. 0 : 0. 106

.0

Sample No. 8 :

Chrinte~1urch City - 'i'aitapu aorio1~ ~ilty olay (T

4 )

::a

G•o•' -

0'0"

Dflpth of nam1)l&

Nature

of

OVe~burden

Nat.

l.Vc

o•-1•

•f.op ·~;oit1'6' Ileav:y Sit~y Cla;y

::a 28.3,' ',

L.L,

P.L.

l.'•

Io

~.G.

Hydrometer /'l.nalysis :

%

Coarse ~anJ. 2.00m!-0.25um

: ; ~ine !land

~~ Silt % Clay

%

c, ..

lloids

u.s.

Bureau of Boils Ola.a:afiootion

Natural 0

0

Rem uldeJ Average 0

0

Samf?le rro. 9 :

-~

35.6-·

=

27.4'•

=

8.2

:J

2.56

::a q..o;~

• 1 .0,

=51.o;:.

a4J...O, ~

=22.8/{.

·~ilty Clay

=

0.04.7

Iiellthcote - To.itnpu s'•:d.cs ci:tlty Clay Dep tb o£' Sruurle

Nat.

tf/0

L.L.

P.L.

P.l.

s.G.

nrar~~ter Analysis :

~ :urf£loe

=27.~

::~.}3.

7,·:

·26.1(: • 7.€;.')

=

2 .£

e

%Coarae Sand 2.00an -0.25mm a O.~~

%

Pine Sand 0.2.5nm -0.05nm

=

3.1, :,

%

Silt 0.05Itra •0.005mm :.63.2.~

%

Clay 0.005.n:n =33.5' ~

1t

Colloids o.001 1ll!ll :::r17 .2;.

U. ~. B11reau of So-Us Clasaif'ioat1on :::r <;ill.,-, Clay Natural C

0 # 0.030

Re noulJ.ed Average 0

0 :::r

o.

060

ThaGo t$).blcs give the stanJard. yroportiea of the soils

(39)

28.

(40)

A. ~hrinkage Curves :

'.rb.e voids ratio versus moisture oontant r oJ ntionshlp for a "ly mixture oC s olid particle$ 1 wat t<".r and oir is

=

v

_a + mg

-were

_vv

::11 Total Volume of voids

va

::1 Volume

or

air

v

_w

_•

Vulu.me of water

vs

::1 Volume o f' acl ills

u

. : t moisture c ontent

G

·=

S;>eoific gravity

or

oolids.

Hence for a oom;;letely saturated mixture, tho nJot of voids r.a·t.io agtlins t moisture eon tent is a ntra.ip,ht lin~ ,

or

r.rrodion.t tan

e •

lh pasoing througb. the origin.

Tb.uo tho obrinka.ge curveo for soils in tho ronr~c of

"complete oaturation" an.d

"r_.riJ:mry

unsatw.·o.tionr• follow tbb

straight line, cliver~ing only when the otato of "ac<:ortaary unaatura tion"' io

roached.

A soil wb:icll ia initially in a state

or

17_{partial saturation"}

will hG.ve 1 ts allrinkage ourve lying

to

tile l e ft of tbia strai ght line the vartical distance above the line a~ rc~res~ntin~ the pro~ortion of voi<ls occ upi ed. by adsorbed and. oeclllJ.P..l a ir.

(41)

30.

(1) Voids ratio at \lb.iDh tbc curve J.epart:J fioan fue

sr

1:t 10(),~ line,

..Uiob we will define a~ t.l<te ,.breukawaytt point "

( 2 ) The shape or the eurvc after i t leaves tho "breaka\?&y'' ')oint, i.e. whether i t is curv('-J. a.lon tt::J l<""n.: th OJ> nearly ntrai1~ht.

(3) The :Jlq,e of' the Ot.\l'Ve after rtbrcaka-... aytt. Tb.ese ohal"lWterist lon ~•UJst dtllpenJ. on

(a ) The oom )ressibUi ty

(b ) The size of the v . .)ids i.e. maxlr.d11'0 . .~ore size. (o) The unifo:t~mty of ('lOre size.

Poo i.tion of "Breoka·uny0 :

Por a oomoro~oible soil, the shrinkage ourve ~ill follow the a traigbt line throughout tb.~) ata;,;e of "pri.mary unaaturation•t . Dt.&ring this period, the mole of the soil mo:ss will be ohrinking

under tbe eff'eots

or

tbe negative pore water -prcsDure. The

oa1>1llary o.;enings wlll be bl"cor.Jin ~ smaller and the t"adius of curvature o.f' the a i r water interfacAs mll ba abl.e to attain lo'\'ler ve.lur.s with o~ucequantly greate-r nP.·~ativr• :Jore VFCLter presn~a withoUt tbe VOlllO Of Sr dropJ?ing bol017 10()';' . '1'his wi.l l IJOViou.sly give a. low value tor the 11_brr-akaway" _{vc:ld.s ratio.}

'rhe "breokel'rny,. point wlll bo hig'a if thor.<! are some very

larg~ pores in the co1J. In thin oase the curve will d1verr.n sJi·htly

from the line e-mg aa soon as th~~" .1ores lo· c t heir water by evtl.porat:lonll {the state Of .. SE)Ot:.l'llc:.ry unsatu.ra.tiontt (.t;,•Vin~ b~<"ll

reocbed) and i f' the soil i.s or:-m~)ressiblo, the oloJ?P wil l be

~teep tmtU tb.e Ot4!lf)reoaion due to the n9ga tive pressure in the

smaller d iameter void& h as b eo n ur¥lergorw.

(42)

.31.

The shape after "breakaway" :

A au.dden breakaway into a·~other stra.i!;!Ut lint:~ occurs when tl~ pore size is very unifor.m, oo all. t.t~ v Gt."es draia at the GEUOO tila9

pore B;lr&o cl.istribu.tion t.,r-oduees a ou.rv~ • the le:llStb.

ot

\1hich:

is d01~nUe.ttt em the oon:r,;n."'essibility

ot

the S("..11.,

'i!M s-1 ope of the curve ttfter leavi ng tr~ line

or

aaturatten

te

ciepellicnt 6lmo5t mttlrl!'tly en the r:~s.ai.bili'ty of tho ~oil ..

?01nt

occur$ at a higher V\-,id~ t"'t"ltio althw.gh ta') ccr.ar.a-<!H\tt~icm

i!1de"X 0

0

=

0.017

far tb.t<· Nmtr~la..ed ~].~ as Oetilp&~d. 'fd in 0.056 tor the nAtural a~J..e.

'rhis was Jfr"obm.bly dut: to ~ ~moulded e~le h aving a fo.rp; largo voida whiob . drninod hefol"'e th~ r est.. tfue l"~lllOUld~ eurv~ show

'

(43)

o.9

o.e

o.7

0.6 o.s

0.4 .

0 .3

0 ·2

Q

.,_0. 1

<(

a:

V) 0

R

N

I

I/

I I '

I

I I

I

I I I_

I

I t:\ ~

_,

~I>"

/ I

I

[I

I / /

>"'::

I

SAMPL E N0. 6

I

SHRINKAGE CURV ES

v

/

,

v

~

v

---

VJ

_/

_,

-;

----I K- LI NE

E

=M.G FOR COMPLET E

/

e

I

E ~ Vv

=

V.+Vw

=

v.

+ M.G

I

V. v.

Vs

---

'

-~

0

5

10

15

20

25

MOI STURE CONTENT

PI G. 10

!I'

I

--I

SATURATION

(44)

~AM Pl .E N0 .. 7

-'

1·0

SHR

NKAGE

CURVE

s

.

0·9

I

I{

0·8

j

v

--v

~

kl

0·6

0·5

j

v

0·4

lj

N

b1

v

-. I

..a..----

I

~

.

0·3

I

-

~~I

((.

'

I

7

10 IS

20

25

30

35

40 CON TENT

(45)

SAMPLE NO. A

0·9---~---.---~~~~~r---r---r---~

SHRINKAGE CUR ''ES

0·71---

i - - - 1 - - -

1 -

-t---

v

!

~

0·

6_~-_ ---+_-

, -~-~---

;-- ---

--r--~"""""''~'--"'+--

- 1 - - - -. -

ij

I

,

0·5

1---t---~---

_J_I_

---..'---+---+·---1

I

l

0·4

_..

~

... R

,...

- .

....

v

;

-

""" """

,,

I

/ l

I

' ~-~-~

i

I

03

i

-,

I ; I

I

. !/

I

I _'

I

0·2

7 /

I

i

~cr

I

! i

0 {/

_I

-

I

b- I

~·I

_/

V)

I

Q

0 I

>

.

I/

I

0

5

10

rs

20.

25

30

35

MOISTURE CONTENT

. . .

(46)

SAMPLE

NO.O

j

0

9

S~RIN~AGE CU~VE

FOR

REMOULDE~

1 STATE

?NLY -

NA~UR~~

SAMPL_If WAS TO

-~-RITTLE-/--·--!

I

i

0·

8

··-~- _I

1 t ,

i

f

I

,

I ,

! I

I

i

0··7~---+i---~---~---~---~~----~----~

: I

I

i

v

!

I

I I

0·6 -

·---.

-l---

···· --·---+···--···---;---

-·+- ---

-·~

' I

I

I . • I

(.) 1 i ' V I

I

~~

\:) I

I

I I

I

-i

! · · -1 ! I ' ' I ! ! / ;

0·5 1---~~----~~----~---/~---~---~---~

I

I I

I

Q-.4

I

j

I

.

'

I

'

; I

' I

/

i

I ) I I ' ! i

i

'

i

!

I

!

I

_I

'

.

~ ! / I

0·31---~~---~~---~·---+---r---~

~/

l

~

I

!

I

$

I

<4 :

I !

I

' i I

!

l

I

l

j

0·21---it----~--:t---l.,---7,---+---t---t

I

1 I

I

l

j/

I

i

!

I

~0·1---/~+---~----~---+---~---~----~ I

'

~

I

S

I

~ o

1

5

10

MOISTURE CONTENT

15

FIG.

n

(47)

32.

Sample No.

7 (t"iz .

11} ;

Bene the nu tural s l.l.1T?le 1o obviouol y in th~ atato tha t Aitchi s on (4.) des c r i bed as '•partial

o~tur3tion".

It i s reasona ble ~o expect that moot soils will

have

some n~3orbed or ocol uJea air in thG po?o fluid in the aatural stato. In faot aome authors such. a s Den3on ( 'f.2) olair..n that they bavo nov('r founi a n undiaturbed sample

wi~1 a l l the vo1d9 completely filled with water. This may be so. but

in a lot ot' oases tile percent a ge oe" air is probably ao Smtlll that it w uld not b e obvious u~ing this method of measuring shrinkage

whether the e oil i s in a G tat~ o!' ~aturntion or of porLiol s aturation.

only ha s it a hiqb. porocnt~ve of.." (J]~V niz~ t;>nrtic les, but i t han 38;1.

of oolloicls), lle nce it reaches the l ow volueo of' e : 0.25 for the.

moistll.t'e content is zero , an.l the rcmoul:.l.eJ. cw:-vf:! does not br~aka\1ay from the line

sr

=

10();~ until Et='2.6.

Tb.e s trl'.l..i..gh.t line ~:orM.~. n of t h <" natural sllr.ln1<:~!~0 OUl"Ve r

e;>-resents tbe <!Orlditio n

or

>lmolH'i c l pri!llllrY unllatura.tion11_, _{t he v a lue}

A C! b .C _ , b .&.!.-. OQ • y ~ • ~ ;.. • (4) •

O.c. ~.. e~ near· Or a OVe vue 7 1.J IQ:lr.t: &3 ~ol."C1~J.SOn 8ll7.{tCS liS e

Sample No. 8

(fiS•

12)

' 4

The nuturo.l ae."'lple s-oem."'. to l>e c ompl etely snturnted,. Pore sizo must be very uniform as both the natural anJ. rem.oulded sam~.tle!s go from breakaway to zero moisture content in straight tlo~ lines. This soil is the leas t compre ssible

or

tne rour in the consolido~tcr, but ic more 'jrone to canpres sion by desi c cation than oaJllt' le

6 tor

ex~le, by vir tue of the fe.o t that its 1.tn.iformity of pore size ensurca

(48)

evaliorates troifl nearly all the poref..'l at once. This means that the negative po~e preGsure haa an over all compressiv~ ertect for a far greater range.

Sample No.

9.

{~ig.

13. ) :

aama silty c la.y group, but has a gr~nter silt ft'a.ction

(63. 2))

and h.enee a grnater maximum pore size.

higher breakaway voius ration. It i a not nearly an C(" l•·resldble as samples

6

and

7

as can t?e seen from. the cl a t carve otter brookaway.

submerged in the moroury oarts~J. tl'l(l so:ll p1:. t to S[>li t. ·~nis saopl e was taken from th,:· surf'aco and WHB obviousl y 1n the •partially acturntedd

state.

pF Verus ltoi~ture content curves (See fig. 14.l At'l far as the validity or th.c oq_uation

(p •

=

eff~ctive pressure on a plt~-tla in ~e soil structure

p D

t otal normal loud on e 1lane

pu

=

pore \roter presaure )

~oes, tha only rorti on of the pf!/ moisJ ture content curves ove~ t:hich

thin oo.n be expeoted 't:o hold 1 3 ·!;hat .;hieh. ~pr~sentc:: e:l:bher. the slate of "yrimaey unaa turation" or witb. some s li :l.lt va.riatiorJ.S tb.e a.te.te!t

true fer any t>oaitivn value of p•• le t a.1on"3 neEntivf' onea u.n)ert.is on the po;r:e pressure op~rllting over the v1h~lc

or

the- pltme o

(49)

1

::1

;2

...

~

-:x1

1-~

;.- - : r~. ~

4·01

~

I \

·\

\

PF,- MO I STURE CONTENl CURV ES

I

1

3.011-, - - - -

--4-I

:!~:~;;~

.l

'---.Q-~

I

2-01· _____ i __ _

-1

'

. . t · · - -· -- ·

u..

r~

--1 .

I

!

- - -- - - + - - - --- -

·--.~

,.

-~---- -1---l

7R

- - - - -- ----l

';,:(

\:_, ..~: .

~-J

_ I I

.t ;

I 1

'·~ i

1

17 2Q I

(50)

above relattonnhip lWllll ..i not hol d if it wa!': im.,oasibl e to ;>ass n sur.fllOte through tho sol at right angloo to tb.c d irection of' p without i t cutt.ing some of' th.one drainnd i?ores. In thia oaae the

it'lorea.~e irt effective p~ssure w-ould 'be prop ortional to th&

ne~ative pressure and to the area of u.ndrainc..! pores cut by this

surfaoe.

The g"noral shape of tile t>F/moisture content curves can be divided ·into three pnrts :

in pF \rlth 1:1. ttle 1ons in moiatllre. This then curvmJ over into part

B,. which bas a more qra Lual incrrar•e in ·pi! vttlut• f'ol" an equ:i.valent deoroase in moioturo content.

0. Tho curve once a;:r:ol.n ritHHl sh.arply.

when ev~oraticn is uousing Ute air water interfaces to beocmo

rise in th~ pP value. It should be reroombcrc l thoogtl, that the rwgatiwl pore pressure is plotted to a lo~srl.thmio soe.le and that this iricrr aao in ~~ at those low values is not a n great a3

it

It is obvious f'rom tho shrinlcn .,.c curves that G""Cti.Gn ~ lies within the primary unsa.l,uration or modif'ied range.

(51)

the pP curve. it do~s net do Go in. tlt~ ea!'le

or

sam 'l cs

7R

and

-,r.r.

It would be raaconable to exr>eot thr:1t this r a ,11 lncf.'e~sr. in p? with litt l e loss of' water M>l.l1,l be oau~,.u by the chan~e to tile state of seoondal"Y unsaturo.tion when the la.rget~ r'orf'G draln ani the water 1s held only in the nrn.aller pores and in'. l enticulor. t"orm.

13

'l.'he lengtl o f Of"etion "'( seom~ to Je~en:1 on the ec:a.lre~aibili ty

'l'be Genero.l T.:ft'cots of .:Jils:}.no:ltion ~

ftle consoli,lation tents ore sb.O~"in P,ra .hically in fi~~s. 15-1 8. '!'hey s ' lO?J tlle nutural ana retnouldcJ. lao; of' proosw·P. ourv,.a nn.:l the

pP versus voidu ratio curves. l.h:i.le r.pite a numbet:• of teats have been carrir.U. ollt lT.f workera in t.ltc soil mechanics :ftel•.l on remoulded.

sam~l~s to the oruoo Ol." lo .. et· moi~ture conte nts t hnn the na tural• these

have been m··.,stly in connection with smnplo disturbance a11!l other souroea of testing ercor anJ the ol~n hovr· not been allowad to re11,el

ratio V(trsus lo ~ of pre asUJ.•e curve is

e D e - 0 log P + ~

0 c 0 •

p

v.her(l p

.o

=

p1'econaoli·1aUon

0

~:N'SSUrc .

pre!lsurc .

0

=

Cc) ' t) rcsilion inJ.ex

c

TheretO.&.'' as f.Jce·~>ton (13) 11oints out. e

(52)

.36.

defining oonstanta au J. for !)l otn of C~ v orous e h.c otJt{\ltlS strai ght

11nos for a oingle ol.1y at V:!l'yln·: init1u1 moistur .... contents. Tlle

only sa:nple for dLioh. tbis holds is No. 9. In g~norul , tho chru~ge

in slo,'~"o is ao small tho.t 0

0, over the range · measured, does not change

by mora than 1Q: . Hence the errors th!lt it han b~Em seen oan

cree ~) into the consolidometer work, es~oially with swn.;_>le~

o.t

hign

moisture oontents, oould maek aqy exiuting pattern.

RutlP.dge ( 14) cli.l rnrk on

re.uould~d

aamplee in connection with un±istut<be.i testing. This. -.vork is diff'ert'Hl't as he diBturM tho

structure of the olay ,,11ere I am all o'Virtf·· it to builJ up. Naturally cnou!l!)l P on bia rtmlOU ldel s~cn 1 lNl 110

r

oun i the. t they a ll show~J. 1 ower valuP,s o t' voids ratio for the Milk., loa.i thlln they lti'l in tho natural

state. lith the c l ay P,iVo•l a o~umce to r~p;el thio

-.,w.

not the cas~.

tmding to revert to the oha.cuol.eri stics or the' nl\Wl'al ,.·:~:up l"l. Thia oe.n be seen in fig s. 10, 11. e.n:l 13 for sa:n.: lC!a

G, 7

anl

9.

Here tile

soil

at initially lL:lg;her moi:Jturo OO!l

tent

1~1tan the nn·tura.l

a a.'ll[.>le h an a ;-renter value o(' voiJ.!3 ratio for the t~ar~ lo<hl. 'i.'he

mois ture cont~n-t decreases.

8a:n:?le 8 iG one ea.s o -wh(!re the ol'\V has

uo.J.

a structure ~bioh

i t

does not

reg~tn o~letely

on regellinq.

The natural moisture

content was 26.8. and tbe remoulded. sample with 29.9..~ initinl moiDture content i fl d.isplaced do\'tnwards considerably. 'l!bi:'l clay

ma.1

be

similar to halloy~ito Tbieh, after deh.y.lration, do~a not ref•>rm the

snme eonf17,W"ation of interloyer· a.J~ol"l)eJ water betwe" n the unit

(53)

~~

·----

~--I

I

--1-~---~ :~ () ' I 1---- ----+---+ ---1---~ r- - ---~

:~~

;

-i

'

_ __ .i. _ __ ,__ _

I

I I l

I

I I

---

·r---1 I

!

I

- ··-- ---~ -I.,

I : .. ,

(54)

(55)

0

'!>

0

'()

,...

.

11'1

I

r~~

, _____

o~

0.

·~

1/

)

--

---

t

-

---~

OIJ.VH

SGIOA

(56)

en ~ ~ lh • ) • n () Y. .. I~ 1• 1 (/ ) t:;l Cf) H

~l:

,.t".

,,, (/) (_:) 0

I

-T

---~.~ ('( I

•

<.0

,

.•

,

.

-..

-&

---·---·

I

f.J 0 I

g>

l

·d r· 'd •II <"J

.. ,

I

L

. --·

-...

0

2 I

I

·I

l

·I

-...

--..

I

,,

.

' JJ

•

· fl ; o-0 \ (o '\ ~ ... ,..._ '') ~' 0'\ ~ 0

I

<p

I

\0 _,...,

(57)

In f~en.::ral it is notieeabl" that ttl thc,ugh the remw.ld~d

O'lays show a nligh t l.nereane in t'~sia ta.nce t o oons-ol Ua tion prc~surar-~

over the straight lin .. ~ortion

or

tne curve, 1 t is not v&<r.v mnrk~d tor quite wide varia tiona in tho :i.ni 1;lo1 moitt tu!'e oontent i.

e.

Althou~h, ao th~ clay .'iriea • tho cur v, is at a lo .. ('r voidA ratio

f"lo.ttening

or

the ourvo, 0

0 ~oes not U.ao-rea.~e ~r£;atly for

oon"esponditli.tl¥ larga ehan;to~ in initial moi9ture content.

The 27.

7:u

initial m..;isture content rem; uldeJ. O'n'"Ve

tor

s~le

7

1a an int:eresting o.'lP..

the curve, thi~ aa:tvl c was Joa le--J. ,.-,ith. 0.2 '1'/nq. f't. to give an extr:1 P.Oint on. tho ollt"Vn... IJnler. th.is loa1 awol Ung took

r

l aoe.

ThiD is regarued a..'3 being due to the 81Jsoro t1on of IOOrl'l interlayer

water (Grim (

3)).

The rinal por·t of the curvo then

1~ b~twecm

the 4,0 .

7%

and the

4.3. 7fo

oneo. The adsorbed wo.ter a,•loat"s to be one

or

the major oontrolJin~ faotors in th~ otre"*h of a c lay structure.

'fhe Voi ds Ratio versus lo~

or

Nev;,ative ;tore l"rossure CUrves :

pore pressures ~or a soil n'l.ruoture io trut'l for ne_qntive valil,<O of' p", tnen tho voids !"1l-tir.l versus lo?.

or

n~;tgative pore .1reMttre curve

p lotted to the same o~aln aa the voids r3tio vet•sus 1o.~ of a .nlind pr4"SS".ll"e

moiatura ·eension wtd 1)- ~lie\l prtOssuro9 cun only be c q:Jute.i if

the aS~rrple in the o•·nsoliJometer' has OK!'otly tll"J a3ln~ i nitial

(58)

38.

moisture content at th.a end of.' portion (A)

or

the p?/ moisture

cont~nt curve bafore testi~o Then the oonavlidometer co~>reoeion

curve:IB starte1. on th0 soil a t thl;l r o1nt at •. hioh it enters the range of'"primary uno$turation rt , wilich ia. whon. the sllrf'a.o~ tension

forces begin to oompr~ss thr- non i.e. Sr :Ill 1

oo,::

p9

<

0.

This mois ture oon:tent oun be asse:1c1ed• but groat di~'f.J.o1.1lty was founded in attaining it exootly.

of aoil was cut from

the

eJge oC the s~lo t o be tcste-1, the

moisture content taken nnd. the rernai ndet' weighed. and loft in

a mt~le pan untU i t rcaoh.ed tho oorrect o a ,culn:(,r:J weight, it was

invariably foun.:i thbt the moJ.sturc content a.t the centre of the piece of soil (wh.ero the corwolidolr.eter sa.•nple was taken ) \?as

different to tba:e calculated.

Hence the ~sults can be vio\ol!d only !'rom a qualitative angle. The valuae of moisture oontent, pF anl ueeative pore fiater pres::mre calculated ~an fig. (1~) a,e ahown in t able

(2).

TABLE 2

Ref'er t o .P!ge

39

s

~!\!5>le llo.

6 :

l?rom f'igw·o

(15)

it can be t:een that

tne

vo-id.s ratio ver::~us lo-1 of negative pore \'later pre&su.-re follows a ourve pl"aotically parallol to fue remouldE"d c-cmpreaaion one.· dmm to £1 value of

p" • -2 .. 0 Tons/Sq .•

tt.

The curve starts from the point where a reooulded oonsolido-met er orunple of initial moi sture content 30.~~ would oom:~Umoe. Mtcr

the value of' p11 ~~»

(59)

pF

p"T/sq.tt.

m/c

2.039 - 0.1

~.60

2 • .3tf.O ... 0.2 30.00

2.7}8

-o.

.5

28.25

3.039

- 1.0

26.38

}.,34.0 _{- 2.0} 24-jJOO

3.

6l,.1

-4.0

21.90

3.817 - 6.0

21.05

3 .. ·94.2

- s.o

20.55 4..0.39

-10. 0

20.30

~ - - - -- --~---

---T A B L H 2.

6R e

0.800

0.785 0. 740

0.690 0. 628

0. 580 0.5€2

0.555 0•550

- - --- --- -·- - ~

7N

7R

m/c

c

m/o

e

22.55

0.600

39.00

1.005

22.15

0.598

38.90

1 .. 000

20. ~0 0. 55.5

37.25 0.96!.

19.88

0.530 :n.so

·;. 662 19.20

0.515

.20.25 _..

0.725

18 .. 70 0.50.3 24.. 3C· O.Oi-0 18 .. 45 0. 500 24..13 0.620 16.30 O.lo~-95 2}. 70

0. 607

18.20

0.492 2).,50 0.605

-~-·--- - -- - · ·-- ~

S

<

1 00 ~ 3e low

==t:::::===-r

8R

m/c

e

22.63

0.578

22.60

0.576

., 22.20

0. 565

21.80

0. 556

20.70 0.527

19.60

0.500 18.80 o.~.a.so 18.15 0.465 17. 63 0..452

, __ --'- -

-9R

rn/c

e

27.85

0.730

26~88

0. 705

25.4-0

0.667

... 40 C.f4.2

23.60

0.(;18 22 .7G

0.598

22

.4.5

0.592 22.15 I 0.588

21 . 90

o.sas

-·

:

VI

(60)

4,0.

of' tile consolidation ourves, f l uttenil'l.U.

011t.

Prom t able (2) wo c an e ee tltat nt'ter tbia polnt the soil is in th'! state of " aeoon.J.nry unsaturationl'f •

It would. O.PlHlM" that U,'l t o this point e quation ( 2) hol<.l~

true. It should also be noted from ~ig. (14) tha·t lJr..h ond. t h.1e

moistur~ content the pli' Cltrva 6R revernco 1 ts ourvQ tur.e • i.e.

embarks on section (0 ) of' the pE' ourve. Sample No.

z.

(fig . ) 6 ) :

The natural ne:!,ativo 1;orc pre :.Jsurc anl ·lit·~ct com, r nosion

curveo do not swear t o ·~1arnllal one another

to

any m·~rkeJ. extent .. The natural sampl~ is initio.Uy in a Gtuto of 1_\>ro:•tiol

Gaturation,.

( p"

::11 0 but Sr

<

100;.;). J!""nce the Ot'fectu of

soil moisture tennion and direct ootn::>reosion do not neem a wlogous. In tho case of th~ re~.ll:)uldcd e:a.:l >le , the au.rvc due to

c~ression by surface tension forces onoe again foll ows tho far.m

of tile remoulded oaq>J•cssion ou.rVes until just after the paint

wh.er~ pn 111 - 2.0 torw/ sq. f't. Vihich is, as in tbn' case of

s~le

No.

6,

~ere

the

~F/moistwre

oontont

~urve b ecomes

concave

upwards.

Sample No. 8.

(fiS·

~7

) :

Hero the pl? curve hR.!'; not l"(!)aoMd section

(c),

am neither bas the s oil entereJ into th• ranttc of" "seoonjary unaaturution" • i.e. Sr ~ 1()()."'..;, a.nywhere alo~ the ron~~ t'"rrnt

p"•·

o to

p" =r .. 10.0 tons/sq.

tt,

Tha ourve fol l()?j'S th~1 CIC:>ccted. form tor t he whol e of its length~

s~zle

No. 9.

(tig.

18) :