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THE INFLUENCE ~F LEA~ING AM9RPHOUS MATERIAL', ON THE

MEC~ICAL PROPERTIES OF A SENSITIVE CLAY

r . '

by

~onny Becker i

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,A'tqesis subm~tted to the Faculty of Graduate Stu~ies and'

Research in partial fulfillment of the .. . requirements for the degree of

Master of Engineering

Auqust, 1979

Department of Civil Enqineer1no and App11ed Meohanics o

McGil! University

Montreal, Ouebec

Canada

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ABSTRACT

. .~ i The purpose, of this ~e"arch was to study the

effect of leaéhing amorphous material from a sensitive , '

clay o~ Outardes 2 on the strenqth properti~s of the soil.

Amorphous materi~l is found to be one of the compounds of

1 the cementation bond.

An accelerated le~chino experiment was copducted • 1 , ,

" , on th1s soil to simulate in a' laboratory experiment the '. .' , field .,condit'ions in which the+ pH of the environment could

affect the chernical and physical properties of, the soil •.

The mechanical properties of the soil samples after leach­

ing were compared wi~h those before leachinQ by conducting

the following tests:- - /

.. rall-Cone Tests to rneasure the sensit1vity~ ~

, • d

Atterberq LirTli~ Tests to examin'e the effect

,of leaehing on the consistency of the soil~

Consolidation Tests to examine changes irl

the PC' and cc~ < •

CIU Tr1axial Tests to ob~erve the effect , li .

of leaching on C' and ~ ,- parameters of 'the

soi l,.

rt WBS shawn that leaçhinQ of salt from the marine

Clay had a small effect on the strenqth of the soil fram

Hawever the effects ot both pH and àmorphous outardes 2. ~!;> ~~_/I"

material on strength were found to be more pronounced • .. . Th~s study was 'one of the continuing investigations of bond

effectson sens\tive clay.

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,Le but de ces recherches ~tai t dl êtudier l'effet du , ,

d~lavage des mat~riaux amorphes de l'argile instable sur les

propriêtês de rêsistance du sol. , Le matêriau amorphe est ~n , "

des composants de la liaison de cêmentation.

" Le sol a êtê soumis a une expfirience de dêlavage accêl~rêe' ~

afin de simuler en laboratoire les conditions sur le terrain,'

dans lesquelles le pH ~e l'~nviron~ent pourrait agir sur les

propriêtês chimiques et physiques, du sol. Les propri~t~s , ./ . ,

m~caniques,deslêchanti110ns de sol ap'r~s dêlavage ont êtê , . ,

comparêes ~ celles des êchant~llons avant dêlavage par les

essais suivants: i , Il

- Les ItFa11cone" pour mêsurer la' stabilitê: >; - Les essais de limite ''''Atterberg'' pour examiner les

consêquences du dê1avage sur la consistance du sbl,

Les essais de IICo,Solidation"

changements de P jet C ; c c Les essais CIU Triaxiaux pour

pour examiner les ç'

observer comment le

dêlavage moaifie les param~tres du so~ CI et ~'. , '

ili-~ Il a êtê dêmontr~ que le sel a un% influence minerre ~

les propriét~s de rêsistance du sol de "Outardes 2". Par contr , ( ,

, le ,.,H ~ ~. . f ~ e~ les mat~riaux amo~es êta1ent plus ~OUCh~S~ Cette

étude êtait une investigation suivie des effets de liaison sur ,

l'argile instable.

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The author'wi.~es to express his gratitude t~ ,.

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, Profeslsor R. N. Yong for his qu1danee and adv1ce, to

}. -Dr~ A. suzuki for his encouragement, and to Dr. D.E.

, ' Sh.~ran and Dr. A. Seth! for their advlce and -coo~ra~ion

àur"ing the exper1ment,al work.

In addition, thanks are 'due to M1a.y for help1ng to

, orqani:ze the thes1. and to Mrs. Sheila White for typinq •.

The financial ass1stanëe received from the Ministry

" of Education of Quebee made th!s study p0atSible.

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TABLE OF CONT!N1S \1 ','

ABSTRACT

RESUME

ACKNOWLEDGEMENTS

TULE OF CONTENTS

'LIST OF FIGURES

LIST OF TABLES

INTRODUCTION

The General 'Prob1em

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" ii

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iii

iv

vi

xi

1.1

1.2

1.3 , . '

~he Role of Amorphous,Material in Sensitive Clay

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1.4

1.5

1~3.1 The Str~cture of' Amorphous Material

. 1.3.2~ Remova1 of Amorphous Material from

Sensitive Clay

Present Knowledge

Proposed Method of Evaluating the ROle of

Amorphous Material in Sensitive Clay

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12

14

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- V -

Page " .

CHAPTER II GENERAL CHÂ~TERISTICS OF OIL FROM OUTARDES 2 20

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2.1 Geological Fe~tures of

. 2.2 . Material

, CHAPTER III METHOD AND.A?PARATUS

i 3.1 -(

Leach±n~ Experiment

3.1.1 Trir:nming.

3.1.2 ~lectton of the Leaching Solutions

3.1:3 Selection of the Leaching pressu;e

3,,1.4( Chemical Analyses of the Effluent

3.1.5 Pore Fluid Control of the Leached Sample '

CHAPTER IV EXPERIMENTAL RESULTS ,AND DISCUSSION

~.l

4.2

Composi tian and Basic p~oper"(js

Leaching 0 ,

4.2.1 Sensitivity and ~tterbe~g Limit

4.2.2 Consolidation Tests )

4.2.3 Trlaxial Tests

4.2.4 Comparison of Related Wark

4.2.5 Theoretiçal Analysis and General DIscussion

CHAPTER V CONCLUSIONS

o' APPENDIX.I LITERATURE REVIEW

APPENDIX Il ~ER:I.rŒwrAL PROCEDURE'

APPENDIX III TEST RESUUrS

BIBLIOGRAPHY

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23

24

24

26

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28

30

30

34

34

41,

59

63

70

92

96

102

105

114

123

126

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" LIST OF FXGUR!S • ! ~, Tit1e t Page

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Figure 1.1 Stress'-Stra!,n Relationship for . ' Leda Clay in Cycled· Test » 7

'\; eP-l·

, \ Figure 1.2 Stress-St.rain Oiagram of Unbonded .

and Bonded Clay \" 7 ~

, ;) .. Figure 1.3 ~ed-Amorphous Model o 11

( ~

Figure 1.4 The Solubility of Silica and Alumina

as a Function of pH 13

( ) . Figure 1.5 Research Flo,", Chart lB

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#,Figure 1.6 Experimental Flow Diaqram ...... ,.""~ 19 (

Figure 2.1 General Looation of Outardes 2 Project . 21

Figure 2 .. 2 stte of P;ast and West Dike Onder C

êon s truc tion ... \ 22 .:,

-\ Fig~e 3.1 Leaching Cell 25

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Figure 3 .. 2 Block S~ple Before Tests 27 10

Figure 3.3 Consolidation Curve of Sarnple Before

l ' Leaçhing ,from S1;.andard Test / 29 (

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Figure 4.1

Figure 4.2

Figure 4.3

;Figure 4.4

Figure 4.5 ...,.,

"Figure 4.6

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.Figure. 4.7

Figure 4.8

'Figure 4.9

- vii--

Tit1e

,Ii' variation 'or Water Content in the'

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B10ck Samp1e

,Leaching Gurv/es of Amorphous Al2 ° 3

Using Buffer Solution of pH.4• 0

Leachlng Curves pf Àrnorphous Fe203 usi~g Buffer Solution of pH:4.Ô

Filtration Cu~ves of Leac~ed Samp1es

Using Buffer Solution of pH.4•0

Leaching Curves of Amorphous Si,02 ,.-0 H .

Using Buffer Solution of P .10.5

Filtration CUFves of Leached Samp1~s

Using Buffer Solution of pH.10 • 5

Leaching Curves ot' Di valent Cation . Using ~olution of Distilled Water

Leaching Curves of Monovalent C~tion.

41Eting Solution of DistÜ:1ed Water ,#

Filtration Curves of Leached Samples

Using Di!lti11ed Water

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Figure 4.11

Figure 4.12

Figure 4.13"

Figure 4.14

Figure 4.15

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Figure 4.17

\ Figure 4.18

- .viii -

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,Stabilization Curves of pH During'

Leaching

Consolidation, Curves .of Sample Before

Leaching and Samp~es Atter Leaching,

fram Con~ro1 Gradient Test

, . Normalization of E-1og P Curvéè, from

Control Gradient Test

Stress Path of Sample Beiore Leaching

Stress Path of Sample 3, After Removing

Salt~

stress Path of Sample l, After Removing

58·

68

69

80

81

.... j 82

stress Path of Sample 2, After Removi~g,t

Amorphous Si02 , 83

stress-Strain Curves of Samples Before '"

Leachipg, from (CIU) . Triaxial ~est , 84

Stress-St:'rain

Removing Salt, from (cru) Triaxial Test 85

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Figure 4.20

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Stress-S'tJ;:ain 'Curves of Sample 1 After

Removing A12

03

and/Fe2

03

" from ,(CIU)

'l'riaxfa1 ..Tes~ )

, Stress"'Strain çurves of Sample 2 After

R~moving Amorphous Si0 2 ' from (CIU)

'l'riaxial Test ~ '.

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Figure 4.21' Pore Pressure Deve10pment of Sample

Figure 4.22

Figure 4.23

Figure 4. i4

Figure 4.25

Figuré 4.26

Figure 4.27

Before . Leaching

Pore Pressure Developme,nt of Sample 3

Pore Pressure Development of Sample 1

v

Pore Pressure Developrnen t of· Sazrtple 2 '\

Relationship Between Amount of Amorphous

Material and Sensitivity

/

compressibili ty Curves

€onsolidation Tests on Chemically 'l'~\eated

Specimèns

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86

'87

·88

89

90

, 91

94

95 -

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Figure I.4 ,

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Structure

Relation B,tween sensitivity'an~ Salt

Concentrat~on of Some No~egian Clay

Dep~sits

l ,1

Cementation and Exchangeab1e Ions on \

Strength Properties

Control of EDTA Treatment J"

Lea~hing Test proceciur~\USin~ EDTA~ "

107

107

112 :

113

113

Figure III.! Grain-Size DistributionoCurves of, Samples,

After Control Gradient Tests , .

Figure III.2. Grain-Size Distribution;.Curves of Samples, ;.~~, "'i \

:> ~fter Triaxial,Tests 125 '

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Table 4.4

Table 4.5

Table 4., Table 4.7

Table 4.8

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LIST

'ritle

, Description of Soil Samples and Their ..,

Test Procedure

Index Propetties of the Soil

Mineralogical Composition and Amorphous

Contënt

33

37

" Pore rtuid Chemistry of, th~,. Black Sample 3~

Peom~ability Values of Samples from

Consolidation ~nd Leachin~ Tests

sensitiv~d Att~rberg Test R~sUlts Consolidation Test Results, From Control

Gradient Test

Tr~axial Test Results, from CIU Test

'C' and ~' Values as Obtained from Stress-

Path

49

62

67

78

79

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CHAPTER l

INTRODUCTION

1.1 The General problern

The Outardes 2 project is the site of the hydro-

electric development in Quebec, Canada. This project , '

4 . consists of replacement of an existing 5.2 x 10 kw

capacity generating station et outardes Fall with a new i

5 plant capable of developing 4.6 x 10 kw. The height

of the existing dam has to be raised to form the reser­

'voir to retain the new water level. Earth dikes will " '

ri~ the reserv9ir gaps. These dikes will be 4 to 5 km

.in length wi th heights ranging from 3 to 30 m. The,

foundat1on of the dikes 1s located on a sensitive', ce-

mented, blue-grey silty clay formation generally i?en­

t1fied as Champlain Sea clays. This clay is also used ~ III

as cônstruct!on~material (after mixing with, sand) to , f

forro, the impervious core of the dikès (Loiselle et al, ." 1971) .

The design engipeer :rn th~s projeèt faées stabi1ity 1

p'roblems of the construction.' Man'~ade modification _ . ,'" ~t 1

(leaching, increa~e of gradient, etc.) ca~ ae~e1erate

the altera~ion process. An accelerated' leach1ng prQcess,

induced by an increase of. the flow-gradient by ra1sing

the reservoir level, can modify the physical and mechan-\

1ca1 character1stics of the sensitive clay foundation.

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,. Amorphous rnaterial and salt can be leached from

the soil and changes in the mechanical, properties·

of the soi1 can occur- so that different factors of

safety have to be considered in the design.

1.2 Definition of the Prob1ern in the Present 'Study

The soil from Outardes 2 contai ne il1ite, chlorite,

hornblende, feldspar' and quartz as wae found previous1y

by Yong et al (1978). The presence of the prirnary

minerals hornblende and fe1dspar i~ this soi1 can alter

rapid1y by the weathering proc~ss to forrn iron oxide,

alumina oxide, si1ica and oth~r oxides. The iron and

alumina oxides are originated in the octahedral sheet

of the clay miner al and the' silica is orig1nated in

the tetrah~dral sheet of the clay minera1. It was found

by Laughman (1969) that the primary mineral hornblende

alters to form the clay minera1s chlorite, verrniculite ,

and a mixture of the two plus hydrous and anhydrous

oxides of iron, alumina, m~nganese a~d others.

The floccu1ated arrangement of the clay particles

deri ves from edge to edge and edge to surface b0:t:lds. 0 1 These b~ds can include both 1) cementin~ bo~ds an~) bonds resulting from interparti'cle forces. The cementing

bond could resulè from amorphous material camposed of

5i02, and Fe203' with trJ!,ce amount of A1 203 , as present

in the Outardes 2 soil: the amorphous material provides 1

<1/ a coating which surrounds the largest primary'minerals

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and which miQht contribute to the bond,mechan1sm

and resolut1oI( of the final fabric ar;d" result1ng struc-f ,

ture (Yong, 1973). The contribution of sorne of these

oxides and hyd'roxides tc---,the growth or precipitation ,

of ,mineraI continu! ty "at th. edqe of particles might

account for the ~ementing.

The interparticle forces are a

pH environment and the salt concent

in part by

of the soil •

Changes in the pH environment can ly effect ~; ~

bonding. When the pH of the soil environment is low,

the positive ,charges on the clay particles increas,

and the net attraction forces 1ncrease; edge to edqe

and ~dqe to face bonds der1ve. In the alkaline environ­

ment when the pH is high"the net attraction forces

decrease as the negat1ve charges on the clay particles

increase: surface to surface ~onds derive from parallel

orientation (See Sect1g.n 4.2.5). The effect of iri-.

creased salt concentration would be a decrease in the

net attraction forces (Alexander and Johnson, 1949) so

that the soil particles will ~xhibit 8 more flocculated

arrangement.

Changes in the pH ~nvironment by impound of water , 1

or rainfall will accelerate the natural leaching process \

and the application of leaching ~ressure (Section 3.1.3)

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may approxima te the end results of leaching and may

bevuseful as an index in the attempt to modify the

physical and mechanical changês of the soil. In a

shorter tirne larger atnounts of amorphous material and •. ",/} \ ~$~"

salt can be carr1ed away from the s01l during the

accelerated leach1ng in ,the laboratory than in the

.'

natural leaching process so that disrupt10n of the'

bonding mechanism can occur. AS ~oted in Section 1.3,

.the' sensitive clay from the northeast of Canada does

not seem to be as 9reatly affected by salt as by the

amorphous rnater1al. As carbonate and organie matter l

are found in minQr quantities in this soil.more atten-

tion will be paid. to the amo:ç-phous material 'in this j

studYj.

1. 3/ The Bole of ,Amor-phous Material in Sensitive Clay

Most of the naturally cemented Canadian sensitive

clays are of glacio-lacustrine or glaeio-marine in

origin. It was indicated (Sangrey, 1972a) that the

sèil particles developed by glacial action are qUite

different from s1milar sized particles eroded and de­

posited by fluvial processes. The glacial process

produces fine particles by physical scratching and

grinding of unaltered Ol;' unwea-thered rock. The 're­

sUl61'19 fine material, often called "rock flour lt even

though 1t may be silt or clay sized, is mineralogical

similar to fresh rock.

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The Champlain Sea clay is derived from Canadian

shield rocks of'northern Quebec, Ontario and Laprador

which are high in iron content,. Post-glacial uplift

of these soi18 has' allowed drainage and salt leaching

from the profiles, l!r condi tion which bas led to cOJn­

parisons of these clay so~ls with sensitive Scandinavian

clay with similar histories. ,po.

, 1

,The dominant factor in Scandinav1an sensitive

clay causinq sensitivity 1s 'the salt content. Most '" \ research i8 not concepned with amorphous,mate~ial. ' Law

salt content as ,la cause Ofr' hiqh sensitivity has previ-

,.. ously been reported for Norweqi8;n marine clay (Rosenqvi"st,

195~). The relationship betwéen sensit1vity anq' 8a1-

ini~y found in ~orway did not apply for the Canadian l' •

clay as indicated by Penner (19fi5). ;--

,1 1

The Leda type clays of the St. IJawr:enceiRiver "1 , -'. 1;'

Val~ey almost invariably have a higber undisturbed shear

strenqth even if minera~ogy, void ratio, rneohanical "

and testing conditions are similar t~ Scandinavian marine " olay. The reason for this appears to be ;r cémenta.tion

phenomenon which i8 important in the Leda clays but is

of minor consequence in Scandinavian clays (Torrance,

1975) •

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Sensitive claY$ have unusual str!epth parameters. ,)

Previous investigation of the clays f om Outardes 2 "

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indicates that they are sensitive, stiff and'highly , consol1dated. T~e presence of cementation-~on~"be-

tween the clay partic1es of·this'soil was established

ear1~er by ~~inani ~~ al (1967).' ~.f'

There are basic differences between cemented and

non-cemented soils~ 'Th~ sensitive clays of Eastern

Canada are very compressible and fail abrupt1y at

small strains. From the stress-strain relationship

(Fig. 1.1) it appears·that the bonded structure domin­

ates the strenqth behaviour of the clay at low confining

pressures, but is progressively destroyed as h1gh con­

solidation pressures alter the soi~ fabric. The result

i~ 8 completel~ uncemented system of soil particles.

The clays exhib1t a brittle behav10ur when sheared

at 8 conY1,ning pressure be10w the appare~t preponso1i­

dation pressure (Townsend et al, 1969). At low con­

f1ning pressures these clays exhibit a~wel1-defined

peak point, followed by a large, drop in strength at

large deforrnat1ons (Fig. 1.2).

Part of tMe behaviour, br1ttleness and sensitivity

of sensitive clay 1s due to the floccu1ated arrangement

of part1cles and to strong cementation bonds at 1nter­

pârt1cle contacts (Soderman and Quig1ey, 1965; Colon,

1966~ Ouigley and Tompson, 1966: Kenney, 1967: Sangrey, \ • Q

1972b: Yong,' 1973). ·When the'cementing bonds strongly

develop, the mineraI framework which forros the fabric

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CAFTER TOWNSENDJ 1969), !f' ,

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FIG, 1.2

FOR

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LenA CLAY IN CYCLED TesT

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c STRESS-ST/N DIAGRAM OF UNBONDED XND BONDED CLAY.'

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of,c~ays becomes stronçly tied et the point of bonding .

The resultant fabr1c is ~iqid and stebility of the sys-

tém is enhanced.

Most works on Champlain Sea clays established

the fact that the cementation bond of the so11 is ma1n-

o

Kenney (1967) used a solution of EDTA to leach carbonates

and amorphOlls 1ron from soil of Labrador" Canada. Leach-,

inç of ~lrQn f~om this soil chançed the Pc value of the

soil (Append1x 1-3). Soderman and Qu1gley (1969) indi-

cated that removal of aluminum and 1ron cornp~exes from

Ontario clays rnay alter the soil properties. They foun9

that glycol retenti on increases wh1ch generally sighi-,

fies an increase in ~xchange capacity, as weathering

processes change chlorite into vermicu11te in which ~

mobile Al and Fe hydroxide~ cations fix the vermiculite

sheets together, and create a greater surface area.

The hiqh surface ares was found to increase with the

arnount of amOrphous rnaterial (Yong and Sethi, 19781

j Suzuld. and Yong, 1978). The EDTA was used by Loise11e'

et al (1971) to leacH the cementing agents composed of

iron, Ruminum, silica, maqnesium and carbonate from

OUtardes 2 soi1. Chernical analyses of the EDTA out-~

flow shawed that the soil'had h1qh iron content and

small arnounts of trye other ceroent1ng'agents that are

r

. . ...... ·-----....... ~.-4-o,e_!I.J>._ h , .... ~~~~,,~ - ... ~,...,_ ••.•

" '

1,

t

(

(

1 (

(

\

,"

- 9

mentioned earlier (see 'Appendix 1-3). 5anqrey (1972a)

estab11shed the fact that the rnineralogy eompôs,ition

of cemented soil from Champlain Sea clay and that of

non-cemented soil from Lake St. Clair were different.

The X-Ray diffraction of the cemented soil 1dent1f1èd

the presence of the primary minerals amphibole, feld-~ ~

'spar and hornblende which alter ~o ~orm hydrous~and ~

anhydrous ox1des of iron, aluminurn and rnanqanese which ,-

accumulate at particle contacts and cement the parti-

cles toqether. Rernoval of amorphous 5102' Fe203 and

A1 203 by wash1ng of~amp1ain Sea clay (McKyes et al,

1974) greatly enhanced the x-ray diffraction peak in-

/tensities of quartz, feldspar and hornblende mineraIs.

Most of the prev10us work rnent10ned here did not

study the nature of the cementation bon4 and the na-

ture of its components, i.e. amorphous material, car-

bonates and organic matter. This etudy will put em-,

phas~s on the amorphous materia1, as 1ts presence in

the 5011 from OUtardes 2 1s more significant than'the .

other components of the cementation bond.

1.3.1 The 5tru~ture of Amorphous Material

As described in the previous section, the 1

amorphous mater1als rnight be one of the compounds of

the eementation bond in sensitive clays. The hydrous

and anhydrous oxides of iron, aluminum, manqanese,

· ' •

•

,

. ,

o

- 10 -

calcium carbonate and silica are precisely th'e

compounds"needed for the cement' (Qu-ig1ey, 1968).

A, model was bui1t by Yong et al (1978) to explain y

the ped-arnorphous interaction, and 1s presented by

Fig. 1.3. This model is based on the Cloos et al (1969) .s

propos al of a structural organization for arnorphous

silico-alumina, for the sarne rànge o~ molar ratios of

Fe and Al to Si. YonQ's mode1 was based on washing a

remoulded sample with SN HCl five times, followed by

pthree w~shings with O.05N tacl to remo~e A1 203 and 1

Fe203• To remove 5i0 2 tne sample was washed with 80-, ,

dium hydrox1de followed by ~od1urn chloride.

The disso1ving of silica and t~e repreci~

pitation of soluble silica after reducing the pH from

10 to 7 increases the arnoun€ of the-sma1ler pores and f

creates bridges, peds and domains. Thus , an 1ncrease

in the rernoulded shear strength pevelops.

On the other hand, the removing of amorphous iron

or alumina increases the voids around the domains or

clusters and decreases the cohesfon between these fa- . ,

bric units. This implies that decrease in cohesion may

be due to'only the solution of the cementing agent and

not general dispersive effect, since àCià~y causes

, "flocculation.

..

(­;;,

"" 1

!' a",

~

~ ~--

t'" .-.

..

...

• Fab,le WnU

Structure \

\

0.. .,....-0

l ,-

, '"

1

[

1 l' 1 <:>J [~~'?ej - ;-Si-O-Si-O-M- ,M,

1 l, t OH 0 (1) '- ln)

M= Fe orAl

UtHREATEO SAMPLE

..

, ...... .

~

...., ,""

"

,- Only negative charges on coatings and . destruCtion of ceme'nting bonds. -

li

/

"""1

"

idging Eflect ~ t~ reprecipitation

" ~-~i~Olved silica.

4

a~ ~ / "'--, ~ ~<~)lJ~

. ~~ ~/J ~ ""Amorph .... O;A ,,'

~ Material ~

~ -Structure

\ o , ,

'"

'-

fil 1 te]

-Si-O-SI-O-M- ' , l ,

(1)

ACID W:'SIiEO SAMPLE

~

----

\ Structure

\ n " / \.

00 '\

l & D are same as in untrealed -sample. The size 01 silica core is smaller due ..... io addllional precipit'al ion.

BASE WASHED SAMPlE

'-

, .

FIG, 1.3 PED-AMORPHous-floDEL (AFTER YONG ET ALI. 1978). ~ '-~ ~.""""

..

, •

.... ..

~

,

... 't.;,..::.)

!

.... ....

"

•

(. -

1 l

1

~I 1

• !

•

o

o

o

o

. ,

, .

-- ..... _ .. _--"""-~_ .. "" ......... , , '

12 '- ..

oLeaching o~ .tmorrhOUS material, should be conductedo

on nat~r!Ell 'so1l in ~rder to ~t~dY the role/of amorphous ,

mate rial in cementation bondinq. Leachinq may affect 9 •

the undist~fbed shear strength of ~he natura1 s01~ and l '

other mephanical propert'ies of the soil. '\t" _

1. 3.2 Remoyal of Amorphous Material' from Sensitive Clay

• The removal of amorphous material by leachin"Q ..

may chanqe the mechanical properties of sensi ti ve clay. 1

Natural cementation increases the res1stance of a' soil f

to\ deformation-. .... ,.' When a breakdown of the cementation ,

does oçcur, th~ maqnitûde and rate of subsequent de~

formations are 1a:,e 1 especially when accompanied by

al} increase in -~ore water pressure. ,'. •

The cementation bonds are considered to develop

during deposition of clay, (Cr~wford, 1963) and, are a .... -~ i./

) l '

result of the existing chemical en:vironment 1 both past

H ' and present. A change in the p, of the e~viroriment by ~ ,

rainfal! miqht dissolve the arnorpho.us comp\..un~s such ~ ,'~,

as iron oxide, a1uminum oXide, si1ica or carbonate in

the natural cenrnted __ soil and t~~ cementation bond may 1

break; or, re-p.recipltation of amorphous compounds such

as silica can build a new cemen~ing }:)o,nd. A"s a resu1t,

an increase 1,n strenqthwill oc(:ur.

_. ~"-"" ~.II~.~~ "_~f1r~_""tlttfq,,*,.~~\or"'--'''''',~,,----1

----

,"

,1

-------'

",'

"

,,{ .

. C

, / -..

« /

C:;' / / ._~r.. 1

/

. '. ~

) .

~ .. ~

~. t

THE" SOLUBILITY OF SILIC~ AND ALUMINA AS À t FfJNCTION aF pH '(FROM KELLER" 1968>'

" • . )

1.

... 'r •

-

)

[)

o

o

o

o

- 14

Fiq. 1.4 shows the effect of pE on .the solu-

bilities of Si O2 }f1nd A1203 •· At a pE of 10 and higher,

the 5102 i8 relatively soluble, and therefore likely

to he carried away in the solution. Tpe"A1203

ls s~ol-

J uble at values higher than 10.0 anç lower than 4.0.

At· very low values of pH (less than 4.'OL Fe 203 ls sol-'

uble. Special at~ntion will be paid in a late~ section

(3.1. 2) to the selection of the.,·leachiag solution in

the present study.

1.4 Present Knowledge (.

Most of the previous work on natural sensitive

clay, as descri bed in Section 1.3, observed mainly the

pro~erties of ~~e cemented ~oil. The naturè of the ~e-

mentatipn bond is not completely clear as yet~

In a recent study by Yong, et al (1978), a model ,.

•

of ped-amorppou~ interaction was built (Fi9. 1.3) b~sed . on results that were .st~died on remoulded soil from

.Outardes 2. The amorpl)ous material was removed· rtom

t,he 1 remoulded soil by washing (Section 1. 3.~ 2) and sen-. /" \

si·tivity was then measured by the fal·l-cone test. The 1

samples that were washed in an acid environment (Fe203

' ..

and A1 203 'were rêmoved) show very'lew ~émoulded strength.·

The samples from whicha~o~PhoUS j si1ica was ref..~ved s1}owed

an increase in the 'remoulded strength after decreasing

pH df the treated sample to pH =7.0. The pH was decreased \. '

80 that the bridginq ~ffèct could be created. -~ 0

1 •

. ,

,

•

..

•

<. '

15

Suzuki and Yong (1978') based tbis work on the , "

rnqdel of "ped-amorphous using àn art~ficial sample witn

d~.~ferent molar ratios of !e2o/Fe203 + Si'02' ~orphoU8

rnater,ial. They concluded that the plastic l1mit an9 o -

liquid ~imit increase with a rnolar ratio of-amorpoous .

rnaterial higher than 0.25. The sensitivity~-'shear

) strength and suction distinctly decreased c;.gainst the

J -amount of amorphous mat'erial at constant water con"tent.

Sensitivity, shear strength and suction increased with

a decrease in the molar ratio •

In their recent note, Hendershot and Carson (1978)

s~ow the effect'of th~ amount of a~orphous material on

the plasticity of Gatineau clay. As a resu1t of excess

washing! they found the behaviour of collapsible vermi-

'" culite mineraI with the ~émoval of amorphous iron and

alumina. The plastic limit changed from 28.2% to 22.U.'" . . This change might be the result of the change in the (

crystallinityas weIl as the removal'of amorpbous material •

A recent study by Yong and Sethi (1978) shows that . .. ~

in m1xing quartz grains with artificial1y synthesized

mixed silicon-iron hydroxide, the arnorphous material 1s

\ held instantaneously and tenacious1y by the quartz grains 0'

through electrostatic attraction. . .

Moré study should be done to understand the role

that the amorphous materials play in\cementa~ion bonds /

of natural so~l •

. ;

"

, .. 1

\

etttW tllHM'W' t f

•

•

--

..

o ..

,

- 16 -

, 1.5 P~oposed Methg~ of Eval~sting the Role of Amorphous

Material in Sensitive Clay

Changes in the properties of natural.soil might be

caused by the leaching process (Fig. 1. 5). • The structure '. .

of a s011 is cornposed of a fabric and interparticle for.c~

system that reflects, to sorne· degree, all facts of the soil's

composition and history.

In order te stud~ the effect of arnorphous material. on ~ ,

the soi1 properties, an accelerated leaching experiment was 0

conducted in th: laboratory on the )atural soil fr~m Outardes

2 (Fig. 1.5 and Fig. 1.6).

. , H Depending on the P .of the water, the arnorphous ma-~

1

" terials Fe203 , ?i02 and A1 203 separate out in varying amounts . . . from the naturel 'soi1 ~ the soluble Salt from èhe pore fluid

l' cqntaining the catio~s Na, K, Ca and Mg separate out in the

same rnanner ale~g with organic compounds and carbonates which

contribute to the cementation bond. -

. '. AS a result of leachi~g with different chemica1 solu-

tions (Section 1.3.2), the amorphous rnateria1jSi0 2, Fe203

and A120j' were i'dent1fied, a10ng with the cations Na, K, Ca

and Mg. At th~ end of the'leach1ng processwhich var1ed ~

frorn 140 to 250 days, consolidation tests, Attergerg ).im1t

tests and triaxial tests were conducted to obsérve the changes

in the mechan1cal properties of the so11. Pc' sensitivity, " l

consistency (liquid limit and plasti~ l(imit), C' and ~' were ('

, "

_T .. -"'~.iW'Io\~~_ ... ,(('." wu. U174t&tt"", ... w"w,.....~ ... ", ... ~ ... '." __ J_-- , : , 1 \. '

• ,1 ~ 1

t

J

•

J

,

•

,

c

,

17

measured (Chapter 4), so that the effect of leaohing of o •

~orPhOUS mat~rlal on the mechanical propertles o~en-

sitive clay could be studied. Also, the results ~ained

woulq be studied to see if there 18 any-correlation w1th

the resù1ts that were obta1ned on an ar,t,1f1c1al sample

(Suzuki and Yong, 1978; Yong et al, i978) based- on the ped-1

" amorphous ~9del. From the re8~lts of Hend~rshot and Carson

(1978) on rert:l0u16ed ~lay; it, ia hard to c04e to any conc:l~­\ si~n as to the effect of- amorpho.us material on the mechani­

cal properties of 'sensitive clay.

1:1

t'

y ,

, ~~ ~i '.

~ ~'I •

#

'.

.1 i

t "

o o

.. ..", .~

...

"

'.

C'

,.

,

Amor.phous material:

.,

Fe20 3 , Si02 , A1203

- ,

o Or • •

~eacbing

Salt:

Na + 1 K+, Ca ++', Mg ++

Effect of Leaching on Properties of Sensitive Clay:

Sensitivity, L.L., P.L., P , C 1 C' and ~' cc,

'I~:.

FIG, 1.5 RESEARCH FLOW CHART

\

~ ... 1

'-~

, \-

....

• • •

~ . 0)

~

"- .'

.

. \

1 , 1

~ > ;

c'

" -,

f Î-

" "

»

,

1: '

,

• .. ,

,.

•

•

<-

t

- 19 -

/

/

... ~

~.

1

1

,

Accelerated

) - Leaching ~ , L

,

Leached Unleached Soil {

-

.... /

.. Triaxial Sensitivity

(faU-cone tes't) At terberg Limi t

Test:C l, , {6'

The Influence of Leaching of Alnorphous Material on the, Mechanical Properties of Sensi tiye Clay_

FIG. 1.6 EXPERIMENTAL FLOW DIAGRAM. /"

.,

,. ,

Ir 1 Iii 1Uij',w:"n 1 Il 1 1

{

...

y

"

Soil

Con sol ida tion Test: P ,C

c,/c

..

, "

.". '\ "

,

•

o

1 )

1 1

0

1)

/" /'

il'

- 20 -

CHM'TER II

GENERAL CHACTERISTICS OF THE SOIL FROM OUTARDES 2 -, '

.'

2.1 Geological Features of the Area

-----Thi's project is the site' of the hydro-electric

developm~nt of the" large Mani~ougan-Outardes power com­

plex currently under construction by Eydro Quebec in the ",

Province of·Quebec, Canada.

In the geologically recent past (Pleistocene), this 1 ,

area wes subjectea to periods of glaciation, land subsi-'fi

dence~ invasion by the Champlain Sea, and subsequent land ,l,

emergency. It is likelY.that these Outardes clay deposits

were laid down in a bracki~h water environment with fresh

water encursions fram adjoining rivers. Eowever, the sa1--o _

inity was probably sufficient to obtain flocculated sedi-

ment:Js. The large sandy inclusions and sand lenses may have ,

resulted from'the shallowness of the water of the site.

, The site area can be seen 1n Fig. 2.1 and 2.2

l,

l

/' , ,

'\;

• ~

_f

. ! " ',',',

t

1

~~ ,

• i '\--

~

•

t

(

- 21 -

ONTARIO /' r ,

FIG. 2,1 GENERAL LOCATION OF THE OUTARDES 2 PROJECTr

i l ~ 1

ï ,

'.

~l i

'" "-,

-.. ' .....

"~ "

\0.

" "

r

0

--.... , , \ ,

0

SAM PLI SITE

~

--

0 ~ 0 0-

OUTARDES - 2

SUAGE

rCHAMBER

..

""

- 1 J

J" J 1 , \ ,

"~

•

'0, "~.

FIG. 2.2 SITE OF EAST AND liEST 1)IKE UNDER CONSTRUCTION.

/ Jf

• •

~ ------ -

.4

"-

~

t..) t..)

f -J

1

l ~ 1 \-

'"

~ 1 l ,

,

(

(

•

t

(

(

, \ (

23

2. 2 Material'

The soil sample from Hydro-Quebec was received

courtesy of Mr. O. Pascal. The sampl~ was cut at a

depth of 2.8m to 3.lm in a trench excavated in the clay

formation. The bloc~ sample was 30 x 30 x 30qm. In

the ~ample area l the clay was overlain by 3.lm to 6. 2m

thick fine to medium alluvionary sand layer. ~he water

~able is generally situated O.6m to 1.Om above the clay 1

layer. Section 3.1.1 describes the bloCK cutting. , ,

The in~ex properties of this bloCK sample wete , exam1ned and the results that were obta1ned (~ection 4.1)

shc;>w that the sample was extremely nonhomogeneous. The.,

samp1e analyses were conducted on the block sample from

different zones of the bloCK and there were sorne varia-

tions in the properties such as water oontent, amount of

1 amorphous material l grain size and salt content.

1 1

-' ,.'

" .'

1 ".

-- ....... ""- u_~._. __ ..... ____ .... ________ .. __ ,... __ 1Ir,: .. *. . Cd$t,

.,.,

. )

. -1

•

D

1)

o

f)

o

o

- 24

CHAPTER II!

METHOD AND APPARATUS

3.1 Le8ching Experirnent

The 9 leaching eells made of plexiglass, (0.320 cm

i~ thickness) were ll.44crn in diameter. The cel1s of ~

Sarnples 1,2 and 3 (Table 3.1) were 7. 63cm in hei ght

and the cells ~ Sarnples lI' 1II , 2I , 2II , 3I and 3II

were 3.81crn in height. The 0.64cm circùlar space was

fi11ed with wax to forrn a seal. The wax used was a

eornbination,of paraffin 12~-l27 -and vasoline. The en­

eased sarnple was then firmly fitted between two porous

dises. From the bottorn porous dise an eut1et pipe was

connected to a co11ecting flask and the top porous dise

was connected te a reservoir containing the leaching

solution. Pressure of 17.5 Kpa (Seétion 3.1.3) was

app1ied to the reservoir to cause an acee1erated leaching. ,

Fig. 3.1 shows a schematic diagram of a leaehing celle \...,

Di fferent factors __ had to be considered through

the long duration of this test. These factors will be

described separately.

1

J

p -• '1,: ' H ... " ,-

) 25 ~

..

r \ ,

1

1 • I.eaching solution j

~ 1

(

\'

•

, Î

)

,1Mk

(

FIG. 3.1 LEACHING CELL~ , '~. .'-v ..... _ 1- ;1" t. u '11 , • q 1:1l1li.

•

•

)

o

.f)

'0

- 26 -/

3.1.1 Trimminq

The block sarnple was used by Yong "et al (1978)

for rese'ëirch purposes '(the block was identlfied in that

",'

,research as block No.6). 'The remainder of the block was

used for this work. Fig. 3.2 which follows illustrates . '

the shape of the block sample before trirnrning. The soil • lit' •

sample was kept in a hurnid roorn in order to \prev~nt dis­

turbance of the sail sarnple.' ....

The blook sample was eut into a rectallgle· 20 x 10 x

,~~~m as indicated in Fig. 3.2 (b). The bottom 20cm was ""

used for the leaching e:itperiment. The rernainder was used ~Y

for other tests 'such a's chemical analysis, consolidation . J

.... ' test, sensitivity test, Atterberg lirnit and triaxialtest

, ,0

before leaching. These tests will be described in more

detail in a later chapter.

The black was trirraned into 9 samples as shown in

Fig. 3.2(b). __ These 9 samples wer-e divideÇ! into 3 groups. c

Each group was leaclJ.ed with a different st>lution. Il} each

group there are 3. samples. Two samples are 3. 8lcm in ~

'height 'and 10.16crn in diameter. The c9nsolidation tests,

sensi ti vi ty tes ta and Atterberg lirni t , 1

"

on these two sarnples after leaching. " .

tests were conducted

\" , The third sample o,f

each group was,' ~réd for the tri axial tests after leaching ." / J V

"

._~ .. _-~- -

'-

(

l'

(

"

· ..

, .

• "

" '. ~ .. , ,

l' ...

t

...

• c .. "

r · 1.

,

1,

\'-

.;/ ,~.

" ."

., .

, . 27

,

'1 ~ ....

) -- ," . , 1

f 1-~

"

. -.

l,' .. - ·,1 : :t

. 1 " .!-_- -'-...-- - -r\~ -

'JI l" 211 ." l' 3D .

.~-: 'If -.-t- 2r'~ ~ï - 3~-J. -,:--1---,-1- --',

, 1 , 1 2 3" :

1

L

?

~ c,? ~ 3~ ...... ~m.A&. ___ --+-r .' . Section A-A

FIG. 3.2 BLOC K SAMPLE BEFoRE TESTS.

;

,/

"

(a

.-~

.'

'0

- 1

(b

.-

, 1

,

•

{)

o

o

o

o

28

3.1.,2, ,Selection of the Leachinq Solutions . "

~ ,

The leaching solutions used in this'experiment , ' ' H ~ " .

, were buffer solutions of pH-: 10 • S , P =4.0 and ëisti11ed

water. The b~ff'er solution of pB= 4.0 was made from ~ 1<,.

potassium hy~rogen phtha1atè and hydroch1oric acid. This <,

buffer solution was",applied on èe1l No. 1, ce1l N(O. II_

1

and ceU No. III 1n order to leach .. the amor];~hous material

Fe2 0 3 and A1 20 3 • The buffer solution of pH=lQ.5 was ~~de

fr'om a solution of sodium bic';~bo6~te and' sod;i.um hlJ;.roXi?e.

The buffer :~olution "of pH: 10.5 'lIas 'applied on ceti No. 2, ,~

-" ce~'l No. ~ 2,1: ,and cel:1 N~)o 21I to leach the' amorphous rna-, -

t.eria1 Si.~2 on,.' The third cell g~ouP.:" 3, 31 and ,3 II1 , ,:was,"

treated with di,stilled water' to "leach aw:ay the ,soJ,uble ,'~ .#', .,- ,

salt' composed of the cations Na/K,ea and Mg.

, <'

'Table 3.1 pres~nts the diffe~ent cells and leaching , ~ . ...

sol utions that were used. 1 .. '

3.1.3 ,Selection of the Leaching Pressure t

The air pressure wh1ch was applied on the' leaching

cel1s was 17.5 Kpa. The Pc' vë;,lue of the natural block _. • 1 :",

sample wàs 400 Kpa '(Fig •. 3.3,). The so1l sample was over-',""

consol1datèd, -as '~t:he blo~k semple was eut at a dep.th of ,

2.8 to 3.lm •. The Pc of the block sample is a function of

the overburden .pressure· in the field conditions, . whièh" 1s -

about 55.0 Kptl, and the geologicàl ~tress conditions: The " , , ,

soil. samples~ 1,n the 1eaehing ce1ls were "s~bje'cted ~ to a. , " . ~

(

li! IlaliaJUI __ me_._ 1 • Il Il ••• Mal'''' T 'I!I"' ..... iOI_.'! ~--' , ....... < ,

,',

,\ ,

. ,_':

}'" --

o

"

T------/"

J. " ~ ~ ~'"'-{'-

""' tilt ta .. - • ~ '< .. .~

'.' , " ",

": ,-, 'j. ....

~ -\

! ~~ ;: ,

1

t 1 !

" ..j .;

'" ~ "'!

.\t .~

~

1! i

..> . • - Samp'ie before Gleaching

"

'" i 1

1 f " " ..., i ~

\0

/

'1 i

tl _J '\ . -/ 1 . 1

1.0

Pressure - Kpa ~ .

FIG, 3.3 CONSOLID.a.TION CURVE OF SAMPLE BEFORE LEACUING) FROM STANDARD TEST.

t7 1 mm Si '0' an 1 P, ... ~_ ~ or"'_" __ / ~. -

... ,..~ ...

•

" • '-",

, -.

il \

o

--;:" _ 30"_

;-

pressure which is faF less than the overburden pressure

of the natural,sample. The standard consolidation test ,f'., ,. ,

t-ha-t: was conducted on a sample' before le'aching '('Fig. 3.3)_

shows,that. the sample suffered very small deformations . ./

For 17.5 Kpa the deformation under pre s'sure of 17. 5 Kpà. .. ~..... , j,

was 0.31% as can be calculated f~ Big. 3.3. At the Pc

value, of the natural soil, th~ strain was 6.1 %. Tlilere-

fore,- unde~ pressure o~, 17.5 Kpa 'cl,e s01l in trer~eaChing " l' "\

cell had a very small volume change, and the changes in the " mechaniea! pr'operties under this pressure were considered

" to be ne~ligib+e. The,"'application ,of'thiS pre~sure accel-

~ erated . ,

this leach1ng process. ~, "

Ch~icàl ~alYSeS of the 3.1.4/ Effluent

The chend;cal analysis of the effluent from the

leaching solutio~ determined the amount{6f amorphous \..J . u

\ material Fe203, A1 203 an~ 8102 and the amount of the ca-

tions Na,K"a and Mg in the soluble salt that had been

leached from the soil. Tpe pre'sence of the elements of

, 1nterest in the extractants was determ1ned by using the

~ec~- D~ spectrophotometer aceording to the method of

Viono~itch et al (1966) (se~ Append~x II) •

.J

3.1.5 Pore Flu1d Coptro~ of the'Leached sample

At the end of th leaching~eriment the soil

samp~e~~that had bee~ t~, d by

solutions, respeet1vely, ~ wa

H - , - H- -," P =4.0 and P =10.5

~

1,

ed w1th water which' -,._, "~-'

,'-

fil

-'"

"

"-

,', ./

r

,.. '1

" . t

(

"

« l '

•

1

<:

t

had the sarne amou~t of cations as that determined by

tests performed on the natural soil sample (see Table

4.3). This was done so that the pore fluid chemistry

of the soil could he controlled. The smaller sarnples

were treated for two weeks and the,bigger samples for

one month so that more than three vOld volumes (2 lit.

of solution for tlfl- sample, with 7. 63Qn height) of so~

lu.tion would pass through the samples and the pore

f1uid would have the sarne composition as the pore fluid

in the sample before leaching. This behaviour of soil

was previous1y dèmonstrated by Bigger and

During this period the pH of ;re effluent

and it was found to be the sarne as before

water. r From Fig. 4.10 it seems that

Nie1son l1962).

was measured

the wash wi th

100 d,ays were

needed to change the pH of the pore fI id from 8.5 ~"~\-té" 7.0. This implies that more than 00 days were need-

1

ed to change the pH of the pore fLuid from pH= 10.5,

H H and p = 4.0 to P = 7.0. From this observation ~he H '

effect of P on the'strength properties of the Boil should

be considered a10ng with 1eaching of amorphous rnaterial 1

Section 4.2.5).

The method of identification of the solutions in-•

"cIuded the measuring of the pH and the volume of the

solution (Section 4.2). At the end of the experiments,

$

...... ,----

•

•

•

•

,-

,.

, 1. .,

0

0

"

0

0

/l

" ------------ 32 -

leach1ng c~rves were plotted to observe the amount

of amorphous material (Smectite was not found in the

.natura~ soil by x-ray diffraction) ,nd a180 the cations

tbat had been leached from the so11 w1th various leach-o

inq solutions.

-ç.t.

:1 . ,

..

t "-

"

'l.

) ~ ,'.

.If

~

'-

j" '.

!

.. 1

Ir

;

: ~ :\

1

t ' t

.\1 :,1 v

- ,33

"

J

TABLE,3.1 DesclUPIIQN OF SoIl SMLEs AND IHEIR TEST PRoCEWRE, , . - :.

, , Test Aftci

~arrple ~ch.iIlg Solution I.eachaht Oepth (m) , ~cr~g fi . ,.

1 , ,

Buffer ~ =4. P : o. 3'025-0 • 3100 1 Fe

203, Al2P3 Triaxial

, ,

{ i -<..; 11 Buffer ~.4. 0 Fe

203

, Al2

03 0.2988·0.3025 COns. ,Sens., ( • At. L • > .

~

.; .. , , .1

( "

1

III ' H

Fe2

03

, Al203

O. 2950-0~'29'88 . COnS. ,Sens. , , Buffer,'p =4.0

\ '- At. L. . 1

:

2, Buffer ~ -10.5 Si02 0 .• 3025-0.3100 'Triaxial

J , . .' Buffer ~ =10.5 21 Si02

O. 2988-0. 3025 Cons. ,Sens,' , At. L.

\ , ,1

2II

Buffer ~_10.5 Si02

0.2950-0.2988 Cons. ,Sens., , . At. L • ... ,

"

" ·c

3 Distillep. Water Na,K,ca,Mg 0.3025-0.3100 Triaxi.al •

0

1

( 31 D1stilled Water Na,K,ca,Mg o. 2988-0.3025 Cons. , Seris. ,

, At. L. "

'" ,

3I ! Distil1ed Water . Na,K,ca,Mg 0 .. 2950-0.2988 Cons.', Sens. , At. L • . Triaxial,

S.L. Untreated - - Cons. ,Sens., . At. L •

,

•

•

J.

o

:0

/' o

\

- 34

CHAPTER IV

lMENTAL RESULTS AND OISCUSSION

4.1 and Basic Properties '1

For the purpose of 'characterization, a sample was . 1

taken from the middle of the block. The basic properties

of the blocK sample are shawn in Tables 4.1,' 4.2 and 4.3.

The grain size distribution curve is shown in Appendix

111-1. The X-~ay diffraction patterne were determined

by using the Phillips X-Ray d1ffractométer. ,1

The soil minerals comprise quartz, feldspar, illite,

hornblende and dolomite. Table 4.2 summarizes the re-

sults of the X-Ray. The amorphous content was determ1ned

by washin~ (Segalen, 1968) using the Ségaleri method \ -

. (Appendix II) and the results are pres~nted in.Table 4.2. ,

The cat~ns of the pore flu~d were,deterrn1ned by two; j J ~

different methods. One method used the ratio of soil to

water (1:10) and' the other, the satur~tion extract method

(Appendix II)~ Both results are presented in Table 4.3.

The results presented in Table 4.1 through 4.3 show ~

the nonhomogeneity of tpe ~1ock sample. Yong et al (1976)

d~cussed the variability of the block sample of Orleans

clay. Parameters indicated in that work included thé

static modulus, dynamic modulus, Atterberg limit, tensile

strength and water content. The ~arameters used in the

presen~ .study appear in Tables 4.1 through 4.3.

).

1

t

".

t

{.

35

1 ~

For the purpose of cornparison, ,the results of Yong

et al (1978) on the top 7.5cm layer (Fig. 3.2) were put

in Tables 4.1 through 4.2. These results show a large

variation in the index properties, mineralogieal com-

position and pore fluid chemistry. The chernieal analy­

sis procedure was sirnilar to~the procedure in the present

study.

The water content of the bloCK semple. was measured

in stretch of the 30cm height: a variation in water con-" • 1 /.

tent with heignt was found in each 7.5cm layer. Thes~

resu1ts are shawn in Fig, 4.1. ~ o / .

The variation in the water-content was more than f"""-"" v

17.0%. This,~bservation can be explained by differences /'

./ F in the amount of amorphous content (Young and Sethi; 1978). 1

The arnount of amorphous material as shown in "Table 4.2

was\almost lO~rnore for the sample with the higher wate~ /-~

content. The ~orphous material which is colloidal ma-

teria1 has high surface area and when it accumulates

around the prirnary mineraIs, rnore'water can be retained.

Soderrnan and Ouigley (1965) found that g1yco~ absorption

tends to increase when weathering processes cause the

ion of a-\uminum and iron hydroxides (Section 1.3) ~

sarne observation holds true here. ~

Table 4.2 shows a big difference in theftotal amount

of minerals pres~nt. The samples with the higher arnorphous ~

/

/

/ /

~-------• .-.....,..------------~--------~--~ _. ~---- ---l~

a. / -/1 /

•

•

•

o

,0

o

o

o

/ ?

/ /

'"

/ / - --- -- -'-"- - --- ,-_. -_.

/

36 -

content (18.9t)ehad 10w minerals present (21%', whereas

the samp1eo with the lower amorphous content (8.02%) qad

high mineral content (82 .• ~4%). McRyes et al (1974) ex­

plained tle above. finding by comparing the X-Ray diffrac-

t:1Jon of washed samp1e and unwashed sample for C,hamplaj,.n

Sea 9ley. The lower mineral content pres7nt 1s attri­

buted to the coating of amorphous material (higher amor­

phous content) surroundi,ng the primary minerals., This

could be another ~eason for the claim of non-homogene1ty

of the blocK sample.

To study the grain size dist~ibution, Sample No. 2

(after leaching) wes cut into four sub-samples: the tri­

~ia1 test was perforrned on this group. The grain size 1 ~ ..

distribution êurves show a big variation in the sand, s11t '"

and clay content (Appendix III-l). The water content of ,

the two samples with the higher clay content was 40% and

139.54~~ and 31.00~ (Tàble 4.7). Note that the variation

in the water content within the same cell 1s more than :

lOt. (Sample No. 2).

It 1e difficult to draw firm conclusions from these

results based on the variations mentioned and th~,nonnomo­

gene1ty of the sample. One must account for the s1gnifi-?

cance, if any 1 of the mechanicjX properties.

• 1

, 1 , '~--------------'

1,'

.' .

"

""~. ~"'. ~

r '.;,

-~

1>

, ft 1 1

+" - .. ' '1

~l ; l

.. ".j. ... ,

'" -:-,:,~~c.-\:,,::r ~

"f' .,. -~- -

,.

~ , ~ ~'-,.,

TABLE Il.1 '-

, ....... :O.;,6~.~"'" ~; " - ~ - t~

... .::-~ ....

... ..

.s

·INDEX PRœER1"l~S ~ DE Soll,

- .. 1""\ lit

>,

\,

'"

"" PlU?EKî'1&i Dept:h (an) Water Content Atterberg IJmit Shear Strength Sensitivity Spec. Gra,vity/ , (Swedish Cene) .. ~ ~-

• in the Block li % '\. % Wp % Undisturbed Rarou1ded Gs

11.5-19.0 33 33 21.5

0.0-7.5* 47 45.4 o~7.3 ' ~

0

.. Results were taken.fran Yongft al (1~78).

,; ~

",

, "

Kpa - - --Kpa

13;1..4 15.39'

98.00 3.63

" .. ~

s- ~

8.5

27.0

, ~

2.85

~

"

-"

W -.J .-"

\w, _~t1if.

l , {

l' 1

l

:- 38

1 18

TABLE 4.2 MINERALQGlCAL CotfosITIQN AND fWRPliJUS CcwENI. 1

, .- 0'; \'

•

1

Ji'

o

,

0 0.0-7.5* Quartz " 8 Si02 7.8

Fe1dspar 3 Fe203

4.0 -

I1lite 5

L Al20

3 7.1

0 Tôtâl 18.9

Hornblende . 2

Chlorite + 3 I<aolinite

0 Total 21

* Resulta were talœn fran YOff1 et al (1978). ,

o , ,

o

... t II 1 r If l 'dllS'" " . " "_"'~Mt 1 7 PI'.",. 11* 1 • t ,1 ~ ... ~rlO .......... M' ... .,.- --- ~~- ...

• t~ .. " . ./""'\ .

,: ' - 39 -

:

TABlE 4.3 !:mE 1=1 UIIl, û-tEMI STRY CE ~ BI O!:K SAt.PL.E 1

Met:hxi(/ catioo ~ • LI. of Pore Fluid , Depth (an) in the Block Na K ca M:J

" ll. 5-19. 0 Ratio 1:10 r 23.6 6.1 6.1 7.56

( "

Saturation 19.8 3.B5 B.8 11.0 Extract

(

/' 0.0- 7.5* Ratio 1:10 14.5 8.3 0.9 1.3

• * Results° were taken fran Yong et al (1978) •

. '

t

/'

o

('

( -

~4

• r

/

• -

• ~

;r

•

D

o

o

o

ü

.'

. ,

.5 . '22.5

: C

f

'\ 40

.r /"

1

,,-

~, "' . jf

'0

~~ FIG. 4.1 VARIATION OF HATER CONTENT IN,'THE BLOCK .SAMPLE •

. .

.., 0

.' L-~....,

, Q

, ~ -

, .

, ~ ,1

. '

" " ,

"

,

, 1

,

'. <=

t

~ .

• ")

. ~ ..

~

•

c

t

- 41 -

4.2 Leaching

The leaching experiment was conducted earlier by

Rosenqvist (1946), Skempton and No~h~y (1952) and Bjerrum

and Rosenqvist (195~) on Norweqian ma~ine clay. The leaching < \

of this kind of so~l dealt with salt, since the Scandinavian

clay his hiqh salinity.

From the results of this work one can observe that the

salinity of the clay from Outardes 2 is low and the amorphous <

material can play a more important ro1e in t~e Canadian sen-

'sïtive clay (~ection 1.3). 1", " Three series of leaohing ~urves derived from the results

r

of the leaching experiment are described in Figs. 4.2 - 4.9.

llf each series there are two types' of curves. One curve,

emphasizes the cumulative amount of leached material over time.

The other curve ~hows th~ filtration of the leaching solution

tprough the s~mile, by _~resenting the cumulative volume of

solution against time. Fig. 4~10 shows the pH stabilization

. ~f the leaching solutions duting the test from wh1ch the be­

. haviour of the leachinq experiment could be explained • ~

the

Leachinq with bUfferzo tion of pH & 4.0 will dissolve \ .

amorphous A1.20 3 and a orpho~s Fe203

: a buffer solution

of pH = 10.5, amorphous 5102' Both sol~tions will dissolve

the crystalline minerals. The selective dissolution technique, 1t '

proposed by ,Segalen (1968)-., was used by Mc1<ye~, et al (1974), , t ,. ~

Yong~ et al (1978) and Yong and Sethi (1977). The ba~is of .. ~J

. ,

1

1 'i

/

•

•

,

1 1

1

-0

o

o

o

=q

- 44 -" , , /

this technique is that with alternate strong acid and .--

a~kaline washing of the soil (S.ON HCl 'and O.SN NaOS) \

both the crystalline and arnorphous cornponents will dissolve.

However, the rate of dissolution for the amorphq~s material ,

is rnuch h1gher than for the crystall1ne material's. The .... ""

"H l p,: va ues tqat were used in th1s study were on the high

,.1 (P~= 4.0) and low (pH=lO.S) extrernes of the solUb1lity -

cu~ves of A1 203 , Fe203 and 810 2 • Decrease in the low pH

(pH ~ 4.0) and inorease in the high pH (pH = lO.5)'will~in-crease the solub1li~y of the amorphous mate+1al but might

destroy the crystallini ty of the minerals ~ The b-lock sarn­

ple was not homogeneous (Section 4.l~ Grain-size analyses "-. "

" (Appendix III-l) can show changes' in t'he clay size parti-

cles thàt could be affected by the pH. Howev.er, the non­

h010geneitY of the sample prevents the ident1fica~ion of

~h~~hanges. The changes in the mechanical properties are

due more to the leaching of amorph~us material than te the -

changes in the cr;"stallini ty or clay si·ze particles if .

Segalen's observation would, be taken into acceunt. The or

r ,

plast~'c lirnit of this soil as shown in Seit10.~ 4.2.~1 ëUd

not change much and could be a reason for the assumption

that' theré was.no change in the crystalline mineraIs (see

Section 1.4, Hendershot and Carson, 1978).

Samples l, II and III were leached with a buffer so-" H

lution of P = 4.0 (Table 3.1). The leaching curves 4.2

and 4.3~~escribe the a~bunt ~ the amorphous material Al20~

\ "

p .. , • ,e'f=< _~ ________ ""---" )~. _! .. 0 ~._ ...... __ ~" ...... _~"...,.~ ~ ....

'l' /l'

,

(

. . '

1

(

43

, • and Fe

203, plotted against time. AlI three samples

emphasize chat)ges in the slopes ?f the l'eaching curves.

Fig. 4.2 shows a change in the slope of the leach­

ing curve 'of amorphou,s Al 203 after 20 days for Sample Il

and a change in the 'slope after 35 days for Samples III

and 1. The reason for these changes can be explained by

the curves in Fig. 4.10. In the ~atural condition the

sample wa~ in an alka~ine environment. The pH of the

50il was between 8.0 and 9.0. H '

At this Po , the sdlubility

o~ the amorP90us Al203 and amorphous Fe203 is very low.

Therefore, a small amount of·amorphous material will dis-E -

solve. After 35 days the P of Samples III and l was .,.

bro~ght to 4.4, and the solubility of the amorphous ma-

terial ~ncreased, resulting in an lncrease in ~he slope/

of the leaching curve. ~e'same behaviour was Ob~erv:Jd; H 1

for Sample Ir aft,r 23 da ys when th, P was 4.55. Sa : , 1

III shows a linear relationship w tfme until the end~'

of the· test, whereas Sample ~! change in. tn.,e slop

after 120 days; the slope th~n approached ze~o. The sa e 1

behaviour can be seen from the curve of sample 1 after i

150 days. Under the test condi·tions (constant leach~nJ \..

pressure, limited time and constant pH = 4.0), ~morPhofs

1 Al 203 was not leached totally from the soil (Fig. 4.2),

and a typica1 leach1ng curve'- (Fig. 4.7 and 4'. B) could not

be achieved. Overall, peheability will 'reflect the averag~~-"-'

• l , ,

o

o

-~.

1 )

•• ~ ..... " ..... -..k .. ,...~... ,~~ ,~ ...... ~ .. , ..... ~ ....... ..., .. " '" ,.,,,, ,

- 44 -\

value of per~eahility measured through PhYSiC~_Phenomen~ of fluid flow through macro and micropores.~he amorphous

A1 203 which provides coating around primary miner91s

(Section 1.2) has be~n proposed to be a continuing ,structure

~Section 1.3.1) running through the macropores (inter fa­

bric unit pores). an'd micropores Cintra fabric unit pores ).

Assumi~ that water will flow more easily through the large

channeis (macropores) th an through the smaller channels

(In1cropores),it could be that the amorphous Al 203 \was not

leached from the micropores.

Fig. 4.3 shows the leaching curves of amorphous Fe 203.

The changes in the slopes of the curves are due mainly to

the same reasons as discussed above, but the differences

were in the solubility of th~ amorphous Fe203 and Al 203•

Between 14 da ys and 28 days the pH of Samples II and 1

changed from 5.55 and 5.20, respectively, to 4~5 (Fig. 4.10).

The solubility of the two samples in this interval of time

After 28 days, when the pH was between (

was the highest.

~---4.5 and 4.0, tt(elslope decreased and remained constant.

In both sarnples the amorp~us Fe 203 was still soluble within

the macropores. This became evident from the fact that the

leaching curve did not show a flat curve wh~n the,leaching

: experiment was stopped. Sample III shows) the s~ behaviour

as the previous sample with one difference; the change in

the slope o~curred after 40'days when the p~ of the effluent

'was 4.3. T~e reason behind this behaviour might he in the

higher amoun~ of amorphous Fe203 in the ~acropores.

" san '." '~~$'HAW_"'" pr , q '\

J

---;-~·-:W";"""""""'''''l''''''''I1",,,,,, .. _r~,.,~, _-' __ ._ .... /;II_I."'_,.,: __ ~_.,.,. ____ ~.

('

,

(

•

1

c

<-

)

- 45 -

~The natural soil was in an àlka1ine environment, as

can be observed from Fig. 4.10. Keller (1968) (Fig. 1.4) 1

pointed out the fa ct that the si11ca lS still. soluble at H E r

P = 8.0. Therefore, increasing the P of the soi1 environ-

ment to 10.5 will still allow the amorphous silica to dis-

solve. However, the leaching curves of amorphous silica 1

(Fig. 4.5) did not show a large amount of amorphous silica

(lees than 2%). The changes in thê slopes of the leaching ,

curves of Samples 2, 21 and 2II are less sharp than those

of Samples l, Il and III (Figs. 4.2'and 4.3). The pH of

Samples 21 and 2I1 reached a pH of 10.5 from a pH of 9.0

and 9.2, respectively, after 28 da ys (Fig. 4.10). Ther~fore,

the changes in the slopes of the leaching curves of Samples

2I an~,2I1 are very srn~ll. After 42 days the pH of Sample

2 was 10. 3 ~ th~reafter,' there was a sharp change in the slope ""

of the,leaching curve.

In Roth of the cases discussed, the amorphous material

was still in the leached sample at the end of the leaching.

More time ,(perhaps yea~s) would be needed to leach aIl the 'G

amorphous material from the soil.

~he filtration curves (Figs. 4.4 and 4.6) obeyed Darcy's

law for sa~urated flow:

" Q, = KiAt

~ o = volume of water flow

A = crossl:"'section'al area of bed 1

"

1 = 9h = hydraulic qradient dx

J<f = hydraulic conductivity i

1

'--==-m;J;ID;JWP 11; E$li 1 !il iiii Li.,I-.JIiMI ii!l1L i idIITI L 1 1 J t

1· 1

•

•

,

, l ,

o

o

o

, , .

~ -_..-- .... -" ..... ~ .......... ~'t ,....,. .......... -" ..

- 46 -

When the grad;ent is cons~n ,'as in this case, the

volume of water flow depends on t e properties of the soil~

K = f (1< 1) when KI is the permeabi i ty of 'the soil. '

~he flow rate 'is constant an the curves pass through

th~ origine (Sample III had som losses of solution at, the

beginning of the test as a result of leakage through the J

cell). This might explain the fact that the flow was ma1n-

ly through the macropores and might explain the changes in

the slope of Sample II and III (Fig. 4.2) at the end of

leaching. Yong and Warkentin (1975) denote that it is ap~

, parent that the fluid flows dominantly betwee~ fabric units.

If the permeability o~ the soi1 was changed during the

leaching process as a result of opening the S~l cha~nelS (micropores), the flow rate could be changed.

"

From all thr~e series (Figs. 4.4, 4.6 and 4.9) of

filtration cu~ves, it seems that not all of the solution

passed thfough the samples. There was sorne leakage petween

the wall of the leaching cell and the wax, or between the

wax and the sample. Table 4.4 shows the calculated values

of KI from the filtration curves and from consolidation

test results by using Cv values, under the sarne pressure

(leachinq pressure). However tbere are differences between .,

the ~ established by direct measures and ~ computed from

consolidation test results, as the water flow conditions of .

"

~

the two tests ,are different (different t~st technique). Al-

though all the curves showJ~Jlinear relationship (Darcy"s

- ----... ~-~Vfl • • ,. il if 1 APi sr !'"w"II'IW!~,~U<looI''''''Ir-_._---

"

,

«

•

,

t

.J

~-lpw), it i8 hard to come ~o a final conclusion on the kind ~ ..

of flow exhibited through the"samples, from the aboveLresults. -

Skempton and Northey (1952) used, un~sturbed samples "

of a marine clay from,Horten in Norway which they leached

gradually from a salt content of 12.6 gr/liter to a salt

content of 2.2 gr/liter. They observed a slight change in

the sensitivity.

Torrance (1974) used distil1ed water as the 1eaching

fluide The sa1inity of a 20mm thick sample of marine clay

was reduced from 26 gr/liter to Ieee than 1 gr/liter, and

'it was found that the Pc value of the sail was redueed.

As Table 4.3 indicated, the total amount of the na-

tural sample from Outardes 2 has 1ess than 1 gr/liter of

salt content in the pore fluide The Outardes 2 .sOi1 s~ows

,Smal1 amounts of salt concentration in the pore fluid com-

pare'd to the salinity of other soils mentioned here (Skernpton

and No~they, 1952; Torrance 1974). Fig. 4.7 and Fig. 4.8

show that a small amount of salt was leacb~ from the Outardes

soil (Samples 3, 31 anp 3II ). This fact, together with the

observed mechanical response to the leaching of salt (Sections ,

4.2.2) can support the discussion madè on the role of amor-

phous material in Outar9rs 2 soi1 (Section 1.3) •

Figs. 4.7 and 4.8 show the arnount of the divalent ca­

tions, Ca and .Mg and the amo~~; the monovalent cations Na

and K, respectively, that~ha' been leached 'from Samples 3, .

F

o

•

•

•

•

o

o

o

o

o

4 ;:::

--_._ .... * .. _.-.--~--~.~-_.- -- ~

- 48 -

t 3I and 3II " The amount ot the monovalent cations removed

with distilled water was greater than the amount of diva­

lent ca~ions Ca and Mg that were removed. After 21 days

there were no divalent cations in the solution that draineà \

oùt from Sample~ 3, 3I and 3I ! (Fig. 4.7), and less than 0.2

meq./liter was found in aIl three samp1es. The'leaching of

the monovalent, cations Na and I<: lasted for more than 21 days

as shown. in Fig. 4. B. The divalent cations are c10ser to'

the clay surface and held stronger than the monovalent ca­

tions whic~ are held m~re likely in the free wate~

Aft'er leaching, these samp1es were subjected to the

consolidation test, sensitivity test, ~tterberg 1imit test • \ 17

and triaxial test to determine the effec~ of leaching, of

amorphous material on the mechanica~ properties of the soil \

from Outardes 2.

(

"

(j

, " ,-

49 -Il

TABLE 4.4 P.etfAsIUry VAuJES OF SAMeLES fRQ':1 CmSQ1,.IDATION & lEAcHING TESTS.

• ! SamPle K' an/sec. fran I.eaching Tests K' an/sec •. fran Cons. Tests P • 17.5 !<pa P = 17.5 Kpa

L . ,.

B.L. - 4 x 10.8

)- 1-c

1/ " , -7 '1 6'x 10.8

~ 3.2 x 10 '<

,;-'

" r .

.1 4.2 x 10.7 -8 -~ - 6.8 x 10 • >i

if"(r.. ,t'.r -. .,;:.

'2.27 x 10.7 ~

8.27 x 1()-8 21 -

- , , ,

• ,

2I1 2.7 x 10-:7 .. -7

2.1 x 10

" " ... " -~

31 2.24 x 10.7 -8 3.0 x 10

3II -7 2.07 x 10 3.35 x 10-7

1 1

t '\

"

;.

-.! . • "

"

,

c fI

(

" 1

'0> >,h"":'t':' '._'î, ." ".. -;;~I:.k;="j· -':' jI\ ;; • ië & P o '--- 0 - i 0 0 Cl 0 ~ 0 • w • •

r

,"

,~ .. ~

~:~:. 1

.. t~ '-

'il;] ... ~~ ,

~t

~ ~i:)~· :~~~

-/'

~ •

,";

...

--'

3601""' ~,

c !32

:::J '0 en

.. x· ~200~ c: <-

M 016 .S' c(

L. -0

4.60% of A1203 was leached fran Sant>le 1y out of total of 0.97% in 411gr dry soU.

6.69% of A1203 was leached fran Sanple ~I

out of total of 0.97% .in 411gr dry soil.

1.43% of A120~ was leached fran Sanple 1

out 'of total -of 0.97% in 9G5.85gr dry soil.

1·

~

c .,$> ~

-------

, ,.P

po

...

....

---

e-Sample 1.~

.A: -Sample 1r .

.-Sample 1U

"

..

O' , ~a::::p= 1 1 1 1 1 1 1 1 1 1 1 o 20 40 . 00 80 100 120 140 160 180 200 220 240 260

FIG, l'.2 US[N~ BUFFER SOLUTION OF pH_4.Q• ~ ~:::.; ... ~ .. ~ ..... =-- --"'--

_ Time-Days

lEACHING.CURVES OF AMORPH~S A~203

U'I o

j • ~ il .. ~

~

1

~".~ ,- ""-1 _"c', ..... :;~<"''''''!· ...... ~~-.t~ . ,,~

.~ ~"'~~,~_""'"o. ... j.~~ ...... ,r",: ~J'o\J:'S·~~~t";<.:'_~f'f·\.!~l~.),t~~~~~1"'f1,1!.:..~:.,.-: .. ~:~~'{. -~~~;-.:. "' ... -- ... ,~ .. --. ~.j.-~- ,

-~~~~ ~-- -:.~ ~:~~5~ ''.:j,!~- ~

i

-o

ë 1 tG

t ~ -:;. E ::"1

U

fi'

o

'" • .. "

14.35% of Fe203 \~S leached fran Sanple ~

out of total of 3.45\;Fe203

in 41:tQr dry soil. - .. . 1 -16.24% of Fe203 was!eac~ fran San\:>le ln

out of total of 3.45% Fe2~ in 411gr dry soil.

10.11% of Fe203

was leached from 5ample l

out pf -total of 3.,45% Fe20

3 in 965. 85gr dry sail.

~ . -

"

.... "

"

'.

-~ ...

~

~

e-Sample 1

Â:-Sample 1z • -Sample1n

1 _~l _L __ ~I. __ 1. l_---.-L.. __ 1 ____ 1 ___ 1~ 1 ___ 1 __ ._ , .

20 40-- 60 - -'-10 ~---- ~100 - - -1~- 140 160 180 200 220 240 , ~ 260 "-

Time-Oays- ..J , ~ H

FIG. '1.3 LEACHI Nf, CURVES OF A,.,ORPHOUS FF."O'Z Us 1 NG BUFFER SOLUT' ON OF P =4. n.

en .....

~

i

~

d'

~?l "

J. <

,l~ ,~

:~ !~i . ,

. -:~j . -"

... -, ~ ~.t'1.' .J..I'r,"

~~ :~-\ -' ,

~

• '1 !

0

.. .. GJ := C .-c: 0 -:::s 0 III -0

• E .a 0 ~

GJ .~

~ E :::s u

/

, ~_ .. ~ ... -

3Sr

28

o o

~ JJ • • -0 • • '" • , ~ !

'~x~

[}

e-Sample 1 .~ . A-Sampfe 1;r "W-

c.

.-Sarnple 1n

1

1

1 > V1

N

, 1 .,1- 1

~ .-

JI! ! 1 1 1 • J _--',_---:1---..1 60 80 100 120 140 160 180 200 220 240 260

Time-Days

FIG': 4.4 FILTRATION CURVES OF LEACHffD SAr·1PLES IIsJt.lG -BUFFER SOLUTION OF pH=4.fJ, ~

~

~. f. ~ ~,

q .-

1 , >

:] ~ . 1 .

1-

...

o

!J 0 -'" QI Q

'" CI ra C

_: 1&01- b

cr ën -0 .. c: :;, 0 a ..,

~ :::: .!! ~

E :2 u

0 0

.. ~

,., .. -

1.72% of Si02

was 1eached fron Sanple 21 out of total of 3.6% of Si02 in 396.5gr dry soi1.

1.9~% of Si02

was leached fram Sample 211 out of total of 3.6% of Si02 in 373.Ogr dry soi1.

-1.24% çf Si02

was leached f~ Sample 2

out of total of 3.6% of 8i02 in 846.6gr dry soil.

.If

----

(

fit i""I '"

lt

l / )

e-Sample-2

-J. - Sample 21

.-Sample 2u

~ ,. ,0, l , , • _ 1 1 • _I:-,I :--.l.-~I _...I--:1=--20, 40 60 80' 100 120 140 160 180 200 220 240' .. 280

. Time-Days H FIG. 4.5 LEACHIN<1 CURVES OF AMORPI~OUS SI02 USING BlJFFER SOLUTION OF P =10.5.

., ---'''- ...

U'I W

~

~

~'

~ Ji i ':1 i

J '~

~

1

, i. :

• .. Ct • - ,. -1 • " ~, ~ -

\ ,

, ~ 31St" ;; \

-::::::::::: 7 00

'-

e-Sample2

~

411 .-Sampte 2I ..

~2t w-Sample2n 1

li<

i ..

l c: 0

i~~ ''".\10 ..

'-, - . -; '\

0 V1 ..

:, ~ . e·"J ~

~ .. ~ ". .. '1 . . . r ,

:},...1 :, .....

~~t " " -

c r-->, " ! :"'1 \ ,~-

:~,,! ~ --',;1

«3 1+ , !

~~ '.

.;. ~ -------' . }

, 1

1

J ~;

al- .~ ~ ---- . ~ -

' .

. '/ 1~g/"/ J 110 ,k, l~O 2bo 2~O --24O&"" _-L._'" 260

'l

-. \ Time- Days

FI~ 4.6' .FILTRATÎO{ CURV'I;S OF LEACHED SAMPLES USING BUFt:ER SOLUTioN 'OF pH=10.5. i

'1

i

. '. J _ __ ._ ... _ ~ .... _--_ •• - - V!- "f

""'

" ~, ~

r - '*" • "' .. ( ;

J:.~~""'''''''''~->.."'t., <00-, ...,..,.~~. ~(_,"';"..,,:.. ~'?f)-..r "'_ t;<~",«."'::''1.~.:::~:r.,i'';,\,,j,,,,~~~.!'~ _"'::' ~:.>)~ ~-.,j. .... ~;J\~:"'- \ '-,\S~:~~' '~":'::~ , .... ""-40,_{ ... _~"- ~V·,: ;--

f,'\

; ,~

-c .~ -::J "0 fil. -o

i

go. f: èS -.. !. cr ~

_.5 .. 0.4'

. , ~ • -.. .....

"""--

•

..

J

1

.... ~ "-. .~ "

))

1; •

... ~l~"r~-. ~-~;,!- "'~

ft

e-Sample3

À - Sample 3.t 8:- Sample 3U

~ "

,

/. > ~

.,. ; F

"' t"

.. ~li "

c.a + .,-

C'I U

" ( 4-

~ ",'

io. . Mg. i Mf~ e ~+ ~ a <

l ' "'g"'-i :ct ... "3

-"1>

Î .

§ r U . 1 l. _____ --'

0.000 J 14 • 21 t'-

Time-Days

- ... -~ ''i 'j' ~~-:?î ",';'~ ">';~~~~-' 0~ ~:~w

• <Y '--

~

"--'

Ut" 0'1

1 •

.a

'.

. . \ , -~ FIG. 4.7

, "", LEAIHING CURVES OF DIVALENT CATION USING SOlUTION OF DISTILLED WATER,

ri . -_._---_ .... _----------

~ ... ~~" 1",*' ~"f ")dt

~""r

,~

\~:' ~

-;: ~"'Ji! "\

o

•. Or

8. e: .g -::i r

-'0 _111

ë 7.

g'

... Cl Co

c

o

o o

1

t

-t <l

• • • • '.."

i'

'~

<!

•

.-Sample3

.-Sample3;a:

.-Samp1e3U

Na'"

K+

• •

" 1

..

•

!

., ~ ~ 1.' "'S ~E 1 a ~ 1 r , li-:=-::=:' # * 14K-:t-.... ~K+

1 1 • 1 • , !"*'= 1 20 40~~~~60::-- - 80 -i06--~1w-- ~o 160 180 20U 220 240 260

~ Time'-Oays ' 4

FIG. 4.8

1 •• -

1.

-r .~

LEACHING €URVES OF MONOVALENT CATlaR IISING SOLUTION OF OISTILLED WATER,

~ ~

•• ,,"..,.:r~ • .......a., ____ .-. - ...

ÎI

<1 •

~

Q

,\ ~ "'

.J

r !

1 -1

1 : .

1 ~ 1 , l

1 1 1

If~

' ... h' (\ !;., - ,. ~~.';; ,; f~, '; !li ~ ... --: ~ ~t -

,'1;'?", r ". ~ ..

~ fit • -Co

/

-' -"

,-.., .. "~ __ ,/ .~p,~~ 'i~;,~!~

~ .~

If ~

3er·--------~------------------------------------------------------------~~----~----~ ·f

:,/

'il !.:l'

',~~ 7' \,

~j ,.

;-1 •

'"

.5 g j2 '0 'i 2

.ë i'

.11 :i

:::1

~> U 1

"

, , ,

'~

Time-Days

~ .j

i

180

..,

200

1'"

e-Sample '1

;,. - San1»1e 3;r .

--Samplean

•

220 240

FIG. 4.9 FILTRATION CURVES OF LEACHED SAt1PLE USING DISTILLED WATER • ..

260

U1 ...J

-----~---~~------------~------'

,.

r,{'r o , 0 0 ., Ct w .. • . • );' '~ 'l'

11 -1

l

c

. ~I; .l,

;-,:.;

, -'

~~~ ..... :­~~

:~

• 1

)

~ - -_ .. ~ ....,................ ~ ~_ ......

~ .

Il

X a.

IS

1 0

\\ ~

1 2'.)

..

_/

) ./

1 .cO ~

'q,

F'I G. 4.10 '\STABI LI ZA;i ON CURVES OF pH OI!JR ING LEACH 1 NG.

,

v-Samples ;1.\"u

A -Samp'es ;2.2z2n

.-Samples ;3.3ti3n

.-\'

,..-

'<,

-:'

U'I 0),

l

1

1 1 \

1 1

~ ~ ~

~

~

.)

r

, '{

1

1

t

_, _~~ _______ -< 4 '"'~ ~_ ... __ ~

\

59

'4.2.1 Sensitivity and Atterberg Lirnït

Table 4.5 shows the results of' the fall-cone tests

and Atterberg Limit t.ests after leaching in comparison wi th

the sample properties before leach1ng. .. ~ ,

rLeaching of arnorphous Al?03 and Fe203 from lamplel 11 B'

and ln ,by u~ing buffer solution of P = 4. ° did net show

a significant change in ,the liquid lim1t, whereas the plas­

tic lirnit decreased from 21.5% to 19.82% and to 19.10%. -" . ..;: .

Although the arnount of amorphQus material was reduced "~ ~

and consequently there was a decrease in,$urface a~a (Yong ~ .

and Sethi, 1978), the liquid lirnit did not decrease aS,was

expected. The reason for"this might be the effect of the

pH environment of th~ soil at the end of 1~acbing ~h was

4.0. At ihis pH the soil is more flocculated. As the'acid

environrnent decreases the negative charge on t~e ,clay par-, 1

t

ticles, flocculation increases. When the clay 1s remoulded

more water can be held in" the liquid lirnit~ This effect

of pH balances the decrease in the surface area. The plas­, H

tic lirnit depends on the P and depends more on interaction

between . the soil particles and on ,~the shape, size and type 1

of clay particle. A decr~ase in surface area by leaching

amcrphous material decreases the plastic limit but nbt in , l' i, ,

direct proportion. .This might be the reason for. the small

chang~ in' the plastic limite Warkentin (1961) observed that

the effect of pH on the liquid limit was higher than the ,

li~u"id limit of Kaolinite ~ith pH = 10.0.

1

\

1

1 1 1

, ~

1 1 1

1

$

•

•

•

,

•

'0

o

o

r')

.... ' - 60 -

In a pH = 10.5 environrnent, the negative c~arge of

the clay surface tends to increase so the soil exhibits

a more dispersive state. Remoulding the soil would bring

)the particles closer to each other and, therefore 1 the

i liquid limi t would decrease. Samples 21 and 211 show a ,

decrease in the liquid limit. The amount of the silica

that W8S leached from the ~?1.1 was ,very sma~l (less than

2") and this supports' the fact thé!-t the change in the "

liquid limit Wa.s due to the pH environment rather than to ~

the leaching of silica. The plastic lim1t is less depen­

dent on the pH: hence, the small changes in plastic limite ~

In Sarnples 11 and 111 the undistur~ed and ,the re­

moulded shear strength decreased. The amorphous A1 203 and

Fe203 played an important role in the strength properties

of these samples even though the plasticity index shows a

slight increase. This reduction în the strength might be il '

due to the cernentati~n bond that was broken by the removing

of the amorphous A1 203 and Fe203 • The remoulded strength

was reduced much more than the undisturbed strength and the

sensitivity increased. Suzuk; and'Yong (1978) concluded

from their resul( on a synthetic' sample that plastic limit

and plastic index increase with 'molar ratio (R203/R203+Si02) , 1

of amorphous material in molar ratio range of more than 0.25

and at the seme amount of amorphous material. This finding •

correlates with the above result on the shear strength of '

the Samples 11 and 111 • Yong and Sethi (1978) reported that

---~_. _. , .. -.. __ ........ IIJI\IIII.I ...... I •••• '.;( F ........ r""\".~I_'_f .... ""'_.I_ ... ""'J)9Ii .... ,.,._'li:IU;_._r ...... ~_~.......-,~',;--~II Of ~ - • ~~-;~-~-~---

r

,...f --------_________ ~ __ _

, ..

t

(

"

1

'.

..

1

t

1

C'

- 61 -

sensitivity increased w~h a decrease in the amount of

arnorphous material as found in this study on Samples Il

and 1 11 •

Results of Yong et al (1978) on the strength of r1-moulded soi1 from Outardes 2 from the fall-cone test shows

that after removing silica and decreasing the pH of the

environment to 7.0, the shear strength of the soil increased. o

This increase in the shear strength probably was due to

the bridging effect of freshinçr precipitated silica hetween

peds and domains. This observation was not found in this

study. The reduction in the /plastici~.y index as was des-

cribed above caused liquifaction ~ the remoulded shear strèn-

gth of Sarnples 21 and 211 could not he measured and the sen-, .. '

sitivity was very high.

Dascal and Eurtubise (1977) reported that the sail

from Outardes 2 bas a cr1tica1 sodium concentration of

10 meq./liter~ the soil 1s flocculated above this value.

The sodium concentration of the,soil in this study had 23.6

meq./liter ,(Table 4.3) which leads one to consider this

soil as flocculated.

Leaching of salt from the soil increased the'distance l

of the,double layer and consequently increased the r~pulsion .

forces between the particles, allowing higher water content \, -

in the plâ~tic lirn1 t and liqu1d lim1 t o~ the natural soil.

Th~ total arnount Of\Sodium that had bèen leached (Fig. 4.8) '1

o o o • • ..

TABI.E q;5 SENslJIVITY PIlI! AIIERBÈRG UMIT Js..uS. Properties of Soil - Sanple Before . ~ -4.0 Used to Rerove 5an:p1es Leaching - B.L. Al203 and Fe

203 1 ,

~ , 1

Il III

water Content - W% 33.1 30.77 33.36 , .

. Lit{Uid Limite - W % 33 .. 0 32.95 36.10 L

'1.

-.

Plastic Limit - w % p 21-.5 19.82 19.10 . v

Plastic Irdex - ~ . 12.0 13.13 17.00 ,

Fran Fa11-G:>ne Test: ,

."

undisturbed -<>, 131.40 39.22 50.00 Strength (Kpa)

Rsrou1ded Strength 15.39 " 2.74 2.16 (Kpa)

00<' '

- . 1 ,

Sensitivity ~ 8.5 l4.3 '--- 23.NJ ) !

l . ~ J

,<r

• •

~_10.5 Used to Renove 5i02

21 2II .

37.75 37.70 ,

23.32 27.70 - .

18.31 18.53

5.01 9.23 ,fi

c

0

47.-06 ~67 .65

very.lCM very low

very high very higl

1

.,

• •

w"

oistilled water Used te ~- Soluble Salt

31 3n

35.30 33~ 0'

49.70 . 54.00 .

26.72 25.87

22,.98 28.13

,

-.

97.46 69.61

11.67 7.06

8.4 9.9 .

----,.

"

1 1

0-~

.'

1 ,

l

r

{

•

,

•

(

( ,

, l, ~\~ "! tvt~4~,J~,,·,.,""f1"!~I""I;*l''''0->'i.,.~ .. :,'1T'!J!''f!I'' ""'l'W~JI'_~l"1~~~_ ........ _.,,.- ... ~_~

_.~-_ ...... _-- --=--. •.

- 63 -

was 'vep small. The sodium is held closer to ~he

~ neqative char,ge of the clay particles (penner 1965) ,

and distilled water was not effective in removing more

soc1ium, ,sc that after leaching the sail was still floc­

culated. This is the reason for the small decrease in

the undisturbed and remoulded shear strength cf Samples

Therefore, the sensitivity did not change )

significantly compared to the unleached sample. Penner

,(1965) shcwed tha\ Leda clay with high por" water salini­

, ties nad ~ow sensitivity, but if the pore water salinity

was low there was no relationship between sensitivity and

salinity. This observation'is valid for the soil from

Outardes 2 as was discussed before •

Otner strenqth properties should be exam1~ed after / ' r

leaching to stréngthen the above conclusion.s and to study

further the role of amorphous material and its contribution

to the bO~ding actio~ between the clay particles of sensi­

tive clay. The next section will examine the effect of

leaching pn the 80il parameters that were achieved from the

conso~idation test.

4.2.2 Consolidation Tests

The ability of the sensitive clay to withstand (with-

out greatly increasing settlementL' a pressure exceedinq the

existing overburden pressure may be the consequence of the ).

cementation bonds between indi vidual clay particles or groups '

""''-, ........ " p,.' _B.W'''. l 'JI .(". ':i"l'!"! :i;;ry,~:._, ~'">' ~?;t'f''r-'''' .,;;.~~.~ , .:,,'

•

•

•

J

D

o

o

()

( .

,1

- 64 -

of particl~s~ hence, the stress d1fference p = p - P b c 0

1s sometimes referred to as "bond stre~,gth" (Terzagh1, 1941).

It should be no~ed also that this ability in sorne instances

may be a consequence of a s11ght degree of overburden pres-

sure.

,f

'As shown in a later section, the amorphous A1 203 and

H r> Fe 203, along with the P environment of 10.5, had affected

fi>

to sorne extent the liqu1d limit, the plastic i~ex, the

sensitiyity and to a small extent the plastic limite A1so

leaching of salt changed the consistency of the soil. This

section will examine how the above resu1ts coincide with

the results from~conso11dation tests on the sarne s~ples of

the latter section (4.2.1).

The consolidation test.data on the soil samplesùare

summarized in Tâble 4.6. Figs. 4.11 and 4.12 present the

e-log,P and e/eo - log p curves ~f the se samples, respect-

iyely. From these curves one can ,observe that the P values le' C

of the,samples that were leached with a buffer solution of

pH ,: 10.5 and the samp1es that were leached with a buffer

solution "o,f pH = 4.0 to remove amorphous material were

reduced ln comparison wi th the sample before leaching. '

The Pc value of the soi1:as shown earlier (Kenney, l

1967~ Loise11e et al, 1971, and Torrance, 1974) is depen- .

dent also upon its environmental history as well as on thè ,

stress strain history.

fi, .

- ---·~_ ...... m .1' ____ ......... ___ .""' ............ _. _,... ... S'i) .... \ld~ .... _. __ .-I--'-~ .. ,",:," ~ ~ -- t' -,JS.",- •• 4~~'D):t .. a<l'~~/j{.4l..:....s ... ii..-u-, , ..

')';" ./l

,

,

'C

1

1

(

(

- 65 -

The sarnples that were leached with a pH solution of

10.5 had a reduction in the 'Pc by one-half. The increase "

in the pH dispersed the flocculated ~tural soil to sorne

o extent by increasing the negativity of the clay particles. '

~ The soil was disturbed under this environment and exhibited .. , a lower, p • These re~ults show a positive correlation with , -c

the observation on the decrease of the shear strength of

these Samples (21

and 211

>.

The increâse în the compressibility of samples,21 and

2I1 results from the decrease in the plastic index of these

sarnples. The soil lost its plastic behaviour under the load

applied.

The Pc valueS of Samples clI and 111 'Were between one­

half and 'two-thirds the value found in the sarnple'be~ore

leaching. In both samples the sharp break that 1s more clear

in Samples 31 and 311 oroSarnples 2r and 211 disappeared and ,

the two samples exhibited non-cemented clay behaviour for the

e-log P. Quigley and Tompson (1966) using X-Ray, attribu-

ted the lack in the sudden break in the e-log P curve of

undisturbed Leda clay to the rupturing of the bonds between

the clay particles. These disruptions might lead to the ~ "

fact uhat leaching of arnorphous Al203 and Fe203 from Samples

II and lII'destroyed the cementation bond. Renney (1967) , • rI

found that-t.~e Pc value of Labrador clay decreased after

leachin~ amorphous iron by uSing EDTA solution. The sarne

observation was found b~Loiselle ~t al on clay frJm Outardes 2

after removinq the amorphous compound Fe~o3 uSinqkDTA solution • ..

. ,

\

•

•

J

1

"

1)

o

- 66 -

The compressibility values of samples, Il and III

did not charge rouchi but the lower ~ompressibility of

Sample 11 may be a result of the lower initial void ratio

of the sample. Although the plastic index of Sample III

increased, the compressibility of this sam~le did not show

a significant change. This may be attributed to the low

pH = 4.0 environment of the soil which increased the attrac-,

tion forces and produced a more flocculated arrangement be-

tween the clay particles. This may have decreased the COID-

pressibility but the leaching of amorph~us rnaterial Al 203

and Fe203 broke the cementation bond, consequently reducing

the resistance of t

and :L,oisel.le

pressibility

to compression. Kenney (1967)

71) did not show a change in the com-

ing arnorphous iron.

Torrance (1974) concluded that the P of Norwegian c '

soil was reduced by leach ng of salt from marine clay. As

'denoted in Section 1.3, the Scandinavian clay has a high

salt content. Leaching of salt from this kind of clay

affects the strength properties of,\ this soil, as the amor-

phous material affects the strength properties of Canadian'

clay with the low sal.-inïty-.- The Pc results of Samples 31

and 3~I did not show significant changes because of the low

salinity and the soil reta~ned its cemented nature as seen

by the sharp break in the curve above P. The compressi-, c

bility increased slightly as the leaching of salt increased

the repulsion forces between the clay particles.

~" 1 1

i

" t

'.

." < . :: ,

f

~. ~

,;.,

f """

-(~ .. ft· 'l

~~. .. .. • , , ,:. .,.

y'" " .'

" " ~ " ~

li

TABLE 4.6 (;ooSOI...I&TIOO lEST REsuus, 'fml1 CooooL w.o T lENT ESIS... "

i .~

S

Properties of Soil Sanple Before lP!f =4.0 Used to Rarove ~ =10.5 USErl to RemJve Distilled water Used to Samples r.eaching - B.L. iAl203 and Fe203 dl Si02 Re:tove Soluble Salt

- 1

- Il III 21 2II

31 311 ~ 1

~ i i 1

1 '; ~ . /

D ~ .. - -

initial Void Ratio - e -, 0.95 (1.00)* 0.87, 1.03 1.08 1.10 1.05' 1.08 - 0 -

(f:ran' Conso1idation Test)

l

\ l , .. ~

; i ! j

.. : 1 From Precpnsolidatio P 450 (400)* 300 - 260' 226

I~ 450 420

Pressure -Pc - (Kpa) ,

1 !

, , ,

CclIpressibility - C 0.438 (0.410)~ 0.296 0.46.4 0.878 0.983 0.517 0.610 C' ~~-- ---

f . / ',' ,

~

*Results obtained !fan s~ COnsolidation Test! (Fig. 3.3). '. "

~~\ . ~

\

~

) ,.....

- -_. -- - ~--- _""-->. _ .. _~ ... _ ... -- h • 'If.

ri 0

,'-:

, ' .\

<

"'" . f:~::J .

., 1

.5

0' • " • •

o

t.10 r 1 ., , i 1 ~-===r 1 1 1 1

l.Q5.-- . •

1 t

• •

1

? ...,.

t \

~ t~ If

i i i 1 1

.'f

1 1 !

1

1 \ ~ "·1 1

{ 1 /. 'j " .1 - ,\,

'"

" ~

, o-Sample before leaching

- ----.-~te~

10- Sainp~ 2t ,2D 1 b,- Samples 1x .10

"'

--ed " l , , "I O'"lD _.-....... Inft .Iii!,.,ft

B.L. \

Ju

.1:t

\

1 1

1 !

(7\, 0)'

Il ' -.4

r ~

)\

"-

~

Pressure- Kpa ~

FIG. 4~11 CONs6LIDATION CURVES OF SAMPLE REFORE LEACHING AND SAMP~ES AFTER LEACHiNG J

FROM CONTROL GRADIENT TEST. ~ .... 01...:' .~~ \",~L

\~ _.Lr~

-,.ft<i. r ~': < ~""~

...

, ,1.00

o

~Ja? o ~ o ~ r: ~

:E o >

i' - .-: ."g .- 0

1 ~

.,

f "1

li ,;

~ ._"

"'.

"

10

'.

1

~

. " .. ~;, . ,. .. - ," ......

o-Sample belore 1.~Ch~ ( ""

.-Samples 3.I. 3D ./

.- Samples 2r , 20:

L- S,a mples 'Ir 1 lU

#

J

... . "-

p

~

Pressure - Kpa

r

j ~ •

{-

ft ,",

"1- , \ --,I <.: ...

20 •

j

~ • ,"

""

Y"

\ ~

.\l..\ :'J:

, B.l . •

FIG. ~t12 NORMALIZATION OF E-LOG P CURVES~ FROM CONTROL GRADIENT TEST.

.. ' <

1

~

, -~ i ~ ~ '" ~ j

-"' t " ;"~

,·1 -1

~ . :~

,,~

~ 1 1 ~ i

~ ~ï 'J !

;Jo

" ~I

•

•

,

,.

o

o

o.

1

l "~. ~ ...

- "'70 - l ,

,\,.. . ' -\

These resu1ts ref1ect the fa ct that the amprpho.us

A12

03 and Fe203 play ano important ro1e in the cementation ,

bond of the clay from Outardes 2~ Td study the effect of

these amorphous materia1s on cohesion and consequently .

their effect on ~I, Triaxial tests were conducted on the

saplp1es after feaching.-

"-

4.2.3 Triaxial Tests " l

• The brlttle behaviour of natura1ly cemented soi1

was discussed earlier (Crawford, 1963: Colon, 1966;

Tawnsend, 196~, and Sangrey, 1972b). The fissure nature

of the soi1 structure can 1ead to a significant scatter-

/

ing of strength data. The mechanica1 significance of ce-. ,

/

mentation was studied by means of a T~iaxia1 test, (Townsend,

1969). ~ initia1ly elastic stress-strain,behaviour was ...

observed ~nder triaxial compressive lo~ding at lo~ test

pressures.' 'The cementation bond strength is essential~y

lndependent of ef~ecti v~~tresses. At higher test pressures,

an "uneJ tructured" effective strength parameter 9 1 15 defined •

.. The Triaxia1 test was conducted in this study on ~am-

ples before and after 1eaching to study the role of amor-.P' \

pho~s rnaterial in the cementation bond.

Four sets of Triaxia1 tests are presented by the stress " . path (Figs. 4.13 - 4.16). All four sets have four .sarnples \

which were tested under consolidqted undrained conditions,

'" with por~ pressure measurements taken (Figs. 4.21 - 4~24). ,

"

"

------... l •• u.l •• n ............ ~~_ •••• _b _________ ~ __ --.~T.~--~·--~~

t

(

t

, • 0 •

•

1

,}

c

- 71 -

The effective consolidation press~res applied dur1ng 1

~he tests were 48, 103, 207, 379 Kpa for each set. The

sample before 1eachinq had a 'fiftn sub-sample under a con-, .

fining pressure oÏ 180 Kpa. These effective consolidation

pressures were chosen after examining the consolidation

tes~ resu1ts of Section 4.2.2. The first two samples of

each set (48 Kpa and 103 Kpa) had confining pressures be­~

low thej;r corresponding Pc values.

The lowes,t' P from the consolidation test (Table 4.6) c ,~

was 220 Kpa for Sarnple 2II~ ~hich is m~re than half the

value of the confining pressure of test No. 2. The two

samples below P gave . - c info~ation about the C' values in

which the cementation bond 1s important. The CO~fininy pre~sure of the·other two samples of each set were ab1i"e

the P values of the samples~ thereafter, the soil ex,-1

c . hibited frict'ional strength behaviour and the 9' values

were examined. The fifth sub-sample (Test No. 3) of the

sample before leaching was under the P value of the sample c

before leaèhing •

A rate of stra1n of O.OOOScm/m1n. was kept durinq

the shearing phqse and was èonstant through all the tests

(see Appendix II-S).

The test results of four series are presented in

Tables 4.7 and 4.8 w The sainples are referred to in Table

3.1.

"

, \

(

1 l' 1

~---------------.~~,~--~~----------------------~~----------~~

•

•

•

•

o

o

- 72 ...

,

Figures 4.13 - 4.16 give ~. stress path of eoct

sample, while Table 4.8 shows the C' and ~' of the s~mple

befora leaching ~ after leaching. Fforn the stress\path

one Cllan observe t-hat the Sample before leaching (Fig.\ 4.13)

and Sample 3 after leaching salt, (Fig. 4.14) both ha~e , ,

, , high cohesion values. The cementation bond i6 strong\ in

1

these two samples. Leaching of salt from Sample 3 di~ not

affect the cohesion ~alue of the soil as the salinity\of

the natural soil 1s 10w (Section 1.3). The P value ~f c 1

this sample did not change afte~ leaching of salt (Se~tion

4.2.2). But, under high confining pressures, sarnple ~ exhibi 'bed a higher (6" value than the sarnple before le1ching.

Samp~e,3 was m~re dispersive than the sample b~fore l~ach-i , .

ing. The dispe~sivity was respons1ble for the increa~e in . ," j

the liquid limit as despribed in Section 4.2.1~ und~1 high

confining pressure~~he particles can corne, close to eath' 1 •

other and the contact between the clay part1cles incrrases.

"-The two values of C' ,and 'l' were taken into accoun't ~tr

the sample before leaching as the samples had differe?t ini-"

tial water con~ent that predict two d1fferent envelopes.

The stress-strain curves of the above ~mPles are shown in , .

Figs. 4.17 and 4.18.. Tes'ts No. 1 and No. 2 of the sàmple , {, ._~.

before 1eaching reached to failure in lower strain than

Test No,' 1 and No. 2 of Sample 3. (::tee also Table 4.7).

This may be accounted for by·the high~r cementation bond of

" ~ . ------.-.JI~.-·".'IiIW'=.r 11."0_ ' .. ~~ .. r're:uw~ 1 -- ,

"l'lIl_ , . , ,

.-...... -" ~ : . .'

,

• f

, ,

,

"

1

t .

\ \ '

i, :,,; _tll) 4MhfilC4JtIAQ., i

"-

- 73 ...:

\

the samplé before leaching (upper envelope). The lower

wate~ ~ontent of Samples 3-1 and 3~2 compared to Samples \

B.L.-l and B.L.-2 (Table 4.7) may be accounted, for by

the presence of a lower arnount of amorphous rn#-er1a,1 in

Sarnple 3 in the natura1 conditions. Yong and Sethi (1978)

an~ Suzuki and Yong (1978) show the relations~ip between

amorphous material and water content. This fact led to

th~assurnption that the amorphous material plays a role in ("' -~ - ,

the cementation bond behaviour. The pore pressure develop­

ment o~ the ~bove tests of the sarnple before leach1ng,

(Fig. 4.21) shows higher pore pressure in sma1ler strain

than the corresponding tests of Sarnple 3 (Fig. 4.22). This

is ·another reason why the cementation bond in tbe sample "

before leaching i8 stronger than'in Samp1e 3.

The Af value of the two samples" the one before leach­

ing and 3, are low below Pc (Test No. land No.J

2) ~ the

cohesion is still h1gh pS the cementation bond was not des-

troyed under these confining pressures. The Af values of'

Test No. ~ and Test 5 of the semple before leachfng and the

A~ values of Test 3 apd Test 4 of ~ample 3 increased. Under

high confining. pressure the cementation bond was destroyed

and the pore pressure increased.

From the above resul ts i t 1s' shown' that both sarnples 1 p

the on~ before leaching and the sarnple atter leaehing'salt,

haVe high cohesion values, as the cementation bond 1$ strong. , " J

J

1 J

•

1

)

1

•

o

p

- 74 -

j

1

Leaching of amorphous material from Sample 1 land Sample , 1'" , H 2 and the P envirbnrnent affectea the strength behaviour of

the soil (Section 4.2.1 and 4.2.2). The test results of

Sarnple 1 and Sample 2 were compared with t~e samp1e before

1eaching and with Sample 3 whïch showed, almost the same be­

havio~r under low confining pressure and at smal1 strain. l '

1

Leaching of amorphous A1 203 and Fe203 as discussed in

Section 4.2'.1 decreased the undisturbed shear 'strength of

the soi1. The slope of the stress p~th (Fig. 4.15) of Sam­

pIe 1 increased compared to the slope of the stress path of

the sample before 1eaching (~~g. 4.13). Table 4.8 indiéates

that the CI value of Sample l decreased by more ,than thre.e

tirnes the CI of the sampI before Ieaching. Consequent1y,

the ~. of Sample 1 increa Leaching of amorphous A1 203

and Fe203 which rnight con ribute to the cementation decreased

the C' of Samp1e 1. end (1969) had shown that failure

of sensitive clay, plication of a sma11 strain, was -

due to the bri~tle behavi ur of the clay resulting from the

presence of cementation

cementation bond

Thus, the possibility of the

m1ght have directly been res-

ponsible for the failure f Sample 1 ati higher strain'. Al-. '

though the rernoval of

duction in the pH and

hous material 'brought about Q re­

sequent decrease in the nega-

tivity of the clay partiel sand hence an increase in the

flocculation, of the leaching'of S~mple 1 was

a deçrease in cohesion. is net decreas~ in cohesion can

, :l "

"

1

•

. ' 1

t

75 -

o be accounted for by the breaking of the cementation bond

which resu1ts from the,removal of amorpho~s materia1.

The samp1e after 1eaching (Samp1e 1) exhibited higher • 1

, frictional behaviour th an the samp1e before leaching under

conditions of high confining pressure (Test No. 3 and Test

No. 4). This phenomenon can be attributed to the breaking

of the cementation bond and hence.a decrease in the P val-, c • 1

,ue in the sarnp1e after 1eaching (Section 4.2.,2). L On the

other hand, under the sarne confining pressure, tne sample

before leaching had stronger cementation bond and a high . ,

P value and so, consequently, the sample exhibited low c --- _, .

frictiona1 behaviour. From the pore pressure 'curves of

tamp1e 1 and the.samp1e before leaC~ing (Figs. 4.2~ and·

,.21, respectively) one can observe that the development

ofi the pore pressure of the sample before leaching in-"

creased rapidly, whereas the pore pressure of Sample 1 in-

creased in higher

the loss in the s

ing

This supports the fi~ding that

low strain was due to the'l~ch­

rather than the pH environrnent.

The plastic index of the samp1e which was leached with pH

= 4.0 did not decrease (Section 4.2.1). From that 1t can

be concluded 'that the 10ss of strength was due more to the

108s in the bfittle behav10ur rathe~than to the plasticity

behaviour of the sail.

, . The stress path of Sample 2 wn1ch was leached w1th

buffer solution of pH = 10.5 shows two different.envelopes. 1

, 1 1

• 1

•

•

• 1

•

•

o

o

- 76 -

One envelope passes through the samples which have higher

water content (Test No. l and Test No. 4) and the other en-

velope passes through the sample w~th the lower water content ,

(Test No.~2 and Test No. 3). gAs reflected in the resu1ts in

Section 4.2.1, it seems that\the chan~es in the strength pro­

perties of this sample are due more to the pH = 10.5 environ-"'" ' ment rather than to- tl1e leach,ing of a small amount of arnor-

phous 5ilica (less than 2%). Reducing the arnou~t of sil~ca

increases the mOlkr ratio R203/R20'3 + 5i0 2 , and that shows

higher strength for art1ficia1 mater~al (Suzuki & Yong, 1978)

and for the rernoulded sample (Yong et al, 1978) from Outardes

2. The ~H of this sarnple after 1eaching was 10.5: more time

was needed to change the pH to 7.0 a?d ta examine the effect .i of amorphous 5i1ica solely. The str~gth properties, on 10w

confin1ng pressure, of samPle 2 did not increase after leach-

ing silica, in addition to the tact that a very sma11 arnount , "

of silica was 1eached. These findings 1ead one to suspect

that the changes in the strength properties from thé test on

Samp1e 2 are dependent on the high pH of the samp1e. The

resul ts of Samp1e 2 land ,2rr in' 'Section 4.2.1 show a decrease

in the plastie index of the soil w1th pH of 10.5. The sam-

pIes of Test No. 1 and ~est No. 4 have a,very high water content.

Replacing this water with water of a higher pH increased the

negative charge of the clay particles a~ the dispersivity

of' the natural floccula:ted sample. The sample ~i~h high water 1

content'show very low cohesion. As shawn in Fig. 4.13 the

, .

r

• 0

,

•

'.1

:, t " , f, t'

}

- 77 -

lower envelope of th~ sample before leach~ng (samples with 1 ~ ,

high water content) still has a high cohesion value. rt

H seems that th~ P was less effective-on the samples with the

lower water content (Test No. 2 and Test No. 3) ~s the cohe-

sion.did not chang~ compared to"the sample before leaching.

, !l'he ~', value 'of Sarnple 2 is higher th an the ~' value 1 ~

of the sample before leaching. The compressibility of

Samples 2 land 2II from the consolidatioti test (Section 4.2.2)

increased with the pH. Under high confining pressure the

sample had more contact between the part1cles and the f6'

value increased for the envelope of Test No. 1 and Test No. 4.

From stress-strain relationships, as shawn in Fig. 4.20,

one can see that the sample of Test No. 1 has higher strain o • 'f

at failure than Test No. 1 of the sample before leaching.

Disturbance (bigh pH, of the sample 2-1 destroyed some of the

cementation bond and the rnaterial" shows rernoulded clay be- ~

haviour.

The result of this section shows cross correlation with

the test results of Sections 4.2.1 and 4.2.2. From these

results, conelusions can be mad~ on the behaviour of the soil 1

from Outardes 2 in a different chem1cal env1ronment and the

role of amorphous iron in t~ementation bond.

~ , ,

,.",

:~-.i-;:-;;-S ~";~:~~-''':''--''

"

,

, ,~;

tA ,'. :.

.. ~~. -~ " ::' -

','; 1 ,.;; ~.

-

q o

Satp1e - Test No.

Before Leaching

B.L.' - 1

B.L. - 2

B.L. - 3 B.L. - 4 B.L. - 5

No. l

1 - 1

1 - 2 1- 3

1 - 4

No. 2

2 - 1 2 - 2

2 - 3 2 - 4

N::>. 3 3-1/

3 - 2

3 - 3

3 - 4

• • • • • rp

Initial water Effective Consolidation O:lntent - % Pressure - Kpa

.33.60 48

30.57 103 .

30.26 180 " 37.70 - 207

40.47 379

29.11 48 , 25.72 103 25-;47 207

26.32 379

40.00 48

28.24 103

31.00 207 39.54 379

22.90 48

28.00 103 27.34 207

28.59. 379

TABLE 4.7 TRIAXIAl TEST RESLLTS, fRa-1 CIU TEST. ~

"

J:+,;.. .. ~_...-.......,..ü'-~ '""'~

..

•

Strain ~ at Failure - %

. ,

1.25 0.70

1.67

1.75

3.00

1.90

1.50

1.55

4.50

1.00

1.59

1.59 2.33

1.67

2.72 1.41

3.78

\ .....

• •

Deviator Stress at Failure' - Kpa

D _

184 212

216

183

230

140

166

330

413

103

194

217

19B

1B5

205

254

333

•

Pore P,ressure Parameter - Af

.-'

0.095 0.246

0.270

0.713

1.040

0.155

0.300 0.151 .

0.520

0.200

0.235

0.536

1.37

0.029

0.234

0.462

0.700

61

• 1 ,

.....:1 (l)

! ~ î

~ . \ ':' \

'< i

";'

•

,

•

1.

l ".":' l <>c

1 1 ~

"

•

•

-, r

--------------- 79 - -1

TABLE 4.8 ~C' AND ,,~, VALuEs AS OmAl NEP FR(J.1 STRESS !?ATH ,

, j

1

SaI,!pl.e Cr (Kpa) ~' (0) . .

.BI,L. 65 to 45 16 f

"

No. 3 47 ,.

23 . , "

, No. 2 55 to 10 16 te 30

,

", .No~ 1 l5 30

1 ,f

<

-

1 , - v

- 80 -0 lA :r-

a 0 0 :r-

I Cl

a LA

'" t.n • t:l

,~a JI 0

:f' N1

• 0,..... . <.

0_0.. LJ'I

loL N \ \.J

• 0 Il..

~ Z

0 .... :I: c:J U

N < LU -'

• J:J LU 0::

0 0 LJ'I I.L.

LU r- 0:;

LU

0 ..J Q.

:E 0 <

J Cl (.1)

.- I.L. 0 - .. :r II'

t:1 :z::: ... é <

0-• '. .: .; . .. • • • • • LJ'I en .. ,.. ... ,.. .. .. '" ta

CI')

LU c:::

loi W W W ... ... ... ... ~ + e:. <d

1:] ... U)

t:J

Cl "'" -t 1{)

Cl ,t;:l Cl 0 t:l • • • • • .

0 1 .::r Ln

c:> -0 0 0 c ,0 0 U'\ CI Ln C N'1 N N ,.... ,..-

f)

u.. 0

(Vd)t) 0

'"

o ... > "

, .

~"-------"'-___ '1_1 .... , ••• , ••••••••• 11111 •• 11111111111 •••••• 'ÎIIi·llll!l~.,r. __ ._!IIl._"'J,'I'r._lIIIIIIIIIlliM1llilli.rwqiliil4.liIIIi_~--:;::"-~,-"''''''''''_···'"·

--------------------;;;-------------------- - -

- 81 -0

0 \J'\ :r

0

0 0

-(>--

t 0 \J'\ N1

0

0 t:I N"I

1-'.

0 -1 ,... « · c.n

, 0< C!) \J'\~

N~ Z -...., > 0

0 0- ~

LU cr.

c:::J 0::: c:::::I 'W N .... LL

<C c:::l

" \ . l't'\

LU

.... -1 Cl.. %: < ,," CI CI)

,;

• LL Cl 0 C .... :::t

1-

-- .. Ir t

.: .; ... • • •

< a.. Cl

• en Cl

CI)

UJ .. ... .. ... ... ... - -LfI Il::

l-CI)

Je + ta

• Cl ;:; • Cl .::r

CI C '0 • • • • • CI C CI CI C

• • Cl C C -t:l Lf\ C VI, CI VI u..

1 N'I N N .... ....

s ( V d jf)' 0

)

-~--

l~ ,f\ t1~ ... ,, ______ ---_. .. ..., ....... ~--~~--

r • )

- 82 -1f1 Cl

Cl ,( ~ IJ\ ::r

Cl Wt

Cl d

"""' -.- Cl ... N

LU

Cl LI....

• CI • Cl Z IJ\ <

0 N1

"""' Cl N

Cl ~

• Cl en 0 :;)

N1 0 :x: 0... 0:: ,

0 0 ,... :E: • ,<t: 0 <-

"~ • IJ\ Q,. C!)

N ~ Z

"'" ->. -;

0.- 0 !.J

0 :E: • LU

t:l et:

'\,. a 0:: , N LU .r'\. f-i' LL.

~ 0

• ... C .-1

lJ'\ LU ([

..J • 0... ~

Cl < l, en -

• e u-a 0 - :x:

1» f-- .. <

Cl 0...

• en .. ,,; . Cl en -• • • lJ'\ LU - - ... '0:: .,. .. - ~ ... ... ...

~ ... " .... l \ U)

0 JI( of. 1:8 Cl LI'\

.-t. e -

i:J 0 c::I C c J:J -=-c::::J • • • . . . , • :0 0 c- C C .;

.C:L~, c:::J CoD -0 10 ,1 "

- l.f\ Cl 1.1\ C Ln LI-;tJ"I N N - ~

) ( Vd~) 0 c.:.> ' ..

; "-

~, .' ~

O J-1 1

1 ? ,;

'\ .. <5F~' ., ,. ... l~~ ____ •• -- .... _ ... ,_ ... ~~~ k~ ~

# C lJ'\ • :r

j. ..

~ c .. .. 0 , . Cl

, ,- :r \ " ....

':. C

C I.f\

"" ., " 0

0 ON C

t-

"" -tI) • 0

CIl ,... :;:)

• 0 o < ::: l/'ILQ. Ng '-' :E:

Ci.. ex::

• 0 (!) :z

t:;J -C > ...... ,

N 0 ::::: 'i:ü c:::

0 a: • ...,., IJ.J 0 t-l/'I LL. ,. ~ c:t::

N

'. C LU ..J • C Q.

:z: C ct ~

(.1)

/, LL. - .. r 0 C

::t: ~ .: .: .

0 t-• • < a-a .. I.f\ ... .. .. Q.. .. III ... ... .. '" en ~ .. -]( + ta en

LU 0 Il:: , t-..... Cl (.1)

J ,

0 C t:I 0 0 t:J t.C • • • •

~ C C C 0 t:J Cl C C LI' Q LI' C lJ'\

'- N'1 N N -. ,... ~ ( V d~ ) 0

t.!)

\' -u.. 0

~

iF

t .. '

() ~,

"., , r' J

..... 'If". __ * li ,. ..... - -. " -'t ... , , .. ,,'!IL-.,.,....,.to. .............. 'Oo/i .. _~;t" ~ , \

./1

,

c:

•

•

, .

- 84 -

"{so.o· , lIE ml.', , .

\ ,

+ Tin .f. 2 t 1

)( 1In Il. 3 ,-if-' • lIS., ••• L! LfDO. CI t-

" .~ A "n Il.

l?

!;50.C1

- . ...;

~ ~OO. 0 -tn tn u.a

~:= 290.0 tn

cc: ~ t­<-..... 200.0 >­u.a Q

...J

f§ 150.0

"

100. 0

50. 0

~

o. Q

M

lA ~( ~J

W U

1

., ~ T/'

I!J Ji ~bo ~

~ ............ ...

~

)

1 ~

1

-~

r>

. ,

1

'. ~ ....

-:--r- ~ \2 ,

~ '-7\.

~ , -.... ... --- .~ . ,

.-. . -,

l \..,,'

0.00 T.OD Z.OO ~.OO ~.OO S.OO 6.00 AXIAL 51RAIN CPER CENT)

F~G, 4.17 STESS-STRAIN CURVES OF SAMPLE BEFORE LEACHJNG 1

. 1

"

,

7.'00

,

"Q' ~

•

,,.

"

• ..

• ...

1

J

o ..

o

• • J

liSO • o

Y)JO :0

550 .0

-e

. '

~ !OO. .-en en LW c:: .... 2?0. en

c:: = .... e ...... 2DO. > LW Q

.... e ~ 150. <

50.

O.

0

0

0

0

0

D

r:t.

(

- 85 -

.. TC" ••• 1 + 'Ill ... 2 X Tfll Il. ,5 Il TC., ... '4

. > .-/"

Ir

L 1

ft r ~ ,2 J

1 ~ ....

,

1 J /1/" .

J 1 0 V . -

\

. '

(\ Qt

) . , ,

,

" . , .......

~ . • I.-~ . \.. ~"

.. ...-i_

l .-~

~ I,...-W'

tMC;..~ -- 1

i'\. ,

"

"

.

. ,

~ -r-

.

\

!J.oo 1. 00 Z.OO 3.00 Y.OO 5.00 6.00 .AXIAL STRAIN (PE:R CENT) .

7.00

FIG. 4.18 STRESS-STRAIN CURVES OF SAMPLE 3 AFTER REMOVING J't

SALT J FROM «(lU) lRIAXIA~ TEST.

,

(

,

(

•

•

~ ...

1

)

n.

1

, \

\\' \

, 'J

, . ,

1 - 86 -

.. -

1.(50.0

Mt un Ir, 1 + TIlt Il, t )( !lIl .r. 1

YDO.O 1- If '"' Ir. ... '/~-: ./ /' 550.0

-< ~ 500.0 -en en La.! CE t- 250.0 , en .

0

0

0

'0. n~

•

"

/ lj ~

. , ~ If!

1,/

~

1 ,

%:

Il V

v 7~"'

.....

./: .,.

V -.

-

i

, ,

/ 1.-/

t

. / ~'~

~ ~ ~

" / V .

~ ,

\ •

~

-0

,

..,. tt

. ,~

~ .... --...-

,

, - .

, . . 0 • 0 D, 1 • DO 2 • DO' 5. 0 0 ~ • 00 5 • DO 6 • DO 7 • DO

, AXIAL 5TRAIN (PER CENT) ,,"" ~

FIG. 4.19 STRES~-STRAIN CURVES OF SAMPLE 1 AFTER REMOVING

AMO~PHOUS. AL~03 AN? FE2031 FROM (COD TRI'AXIAL TesT. t

, , ~ , .

1!' 1

,

•

•

•

l'

D

o

f)

o

'J ~~ ... t'

.... -c,

'4S0.C

'400.0

550.0

~ 500.0

en en Lt.I . a: ... en a: III

250.0

... t,

~ 200.0 > W Q

...1 -< ;: 150.0 ...:

100. 0 ,

50. 0

l' ,

)l1li "" Il. + ,.11 Il.

X '.11 Il. 1- • 'ft11 ...

,

,

\ .

.

f

.~ lI . ~V

87

11

, 1 S 14

. .

,

~

-"

V""

v ~ . te.

. ~

, ,

, ,

.~

~ .

.......

v " , .

. , " . -

~ .. v

, . -.

,

, . /

V- ,

1 . --. . " " " -

. J.

, ~ .

'1 Ir 1

. ~ -

)

~I ~ ~

!

f ' -

O. n ,

D.Oa 1. DO 2 • DO 5 • Q a ~ • DOS. 00 .6 • 00 7.00 A'q:AL STRAIN (PER Cr,NT)

STRESS,,;STRAIN CURVES OF SAMPLE ~. AF'T;~R' REMOVING

AMORPHOU,S SI02" ,FRor1 (CIU) TRIA~IAL TEST 1

FIG. 1'.20

• ;0 ,

, ' ~-- - ....,.._· ... -...._·~....-o< ..... 'r_v...i\i'It.I' ..... "'-....:, ..... ~ .. tt ... ,;'IJ< ...... '" _ ~_

" .

/

•

, ct' j I~' l \ ! ... "", ,', , ', ..... , ~ "

t "

(

1

~50.0

" ;DO.O

250.0

.... ::2DO.0 ~

I.U CIl: '~

en en15D.D I.U a:: c..

I.U CE

~1DO.D

.-.,TE + TE )( ·TE Ir TE

Tr .

..

.

L •

50.0

O. rB , 0 r

î

'\

"

88

-~T Nil. 1 liT Nil. 2

t> ' pT tJII. 5 >

IiJ NI!. '4 ;.

:T IJR 1:

" , ...,

~ ~

0 '-/ ~

~

l • il ~

1 "' 1

·r ~ ~ >{ -

/.~ -?\o

1--'"

/' t . ,

. -,

,f-/ 1-.-. . ,

" ,

""-------

DO 2.0D D Y.DO S.ClO AXIA~~RArN (PER CENT) 6.00 ' 7. 00 "

1

, FIG. 4.21 PORE PRESSURE DeVELOPMENT OF $AMPLE REFORE LEACHING.

•

•

»

• ;. 1)

o

? "

i

"'-

,,-

'/

, ,

- 89 -

1

~50.D - TE ~T He. 1 , • Te: ~T NIl. .2 . .,. )( TE T Ne. 5 Ir TE ~T NG. '4 ,

. .'

'250.0

,.... f' :200.0

. ~ - V "

. . ,/ <

:w ..., LU II:!:: :;)

Ul 111150.0 \.al 0::: c.. ...., 0:::

~IOD.O

50.0

V ~ . /

;1 V , .

j) /

!fL V

~ fltlf" .. ,

1 -, r

.' , -. ,

50'.0 D.DD 1. DO 2.00 5.00 4.00 S.OO

AKt~ STRAIN (PEP. Cr.tH)

FIG. 4.22 PORE PRESSURE nEVELOPM~NT OF SAMPLE 3.

. .

-

til' , la * t "ft .. bof j ~ ... ·~J.IW"_"""'''''' - .... - ...... - ~ .

+ i

.-

D ( .

...:.... ,

.. 0

.

.

" ,

po-

6.00 7.00

/l

r----:---------~--~--~~ ___ _

J

. "

•

t

550. D

1

5DO. D

2SD.D

, '

v'

.. 1

MT( ... TE )( TE • TE

.

" .1J2 -50.0

- 90

~T N' • , \

~T N'. 2 ~T Ne. 5 ~T NI. ...

,

, 4 - V '1 1 .j

~ ;

~

~

-7 ""'--'" ...--- -

c \f ,1

, , ... ~~ ,

J

, .

.

"

--"

~ ~ .

r-i

, . ,

•

,... ...-

~

,

---, .

1 . 0.00 1.00 2.00 5.00 Li.DD 5.0D 6.oD" 7.DO

AXIAL STRAIN (prR ~E~T) FIG. 4.23 PORE PRESSURE DEVELOPMENT OF SAMPLE 1.

c b

•

•

•

•

'. 0

o

o

'0

.. '. f

,,-

~

..

- 91

~SD. D .TE "T N'.-~~" 1

TE ~T He, z , + x TE ~T HI, S

500.0 • TE ~T H', " \

25D.O

,

~ r-

V ,

-< a.. 2 DO .0 1 .. ,

~ -"" ~ a:: =' ~1 50.0

V ,

) {[J . •

w œ a.. w Q: CIl a.. 1 00.0

1 ~

~ /

li v .

50.0

0.0 ~ ~

.

,.. _. -

-50.0 D.OD

FI.G. 4.2l,

LJ -

,

\ , 1

1.00 2.00 5.00 ~.OO S.aD AXIAL 5TRÂ~IN (PER eEN'T)

f ' ,

'" ,

PORE PRESSURE DEVELOPMENT OF"SAMPLE 2. : \\ \

" ----- Hal "!/haq,., .. nllll!trrll'ltlllllliila.,_J>I!l<j~"'\"'/;"'1IIi1 Il • _.Ii.· . .. .,.... -~::

. ~

. ..

r ...... .' !

J ,

,

. .

n ' ,

r-

~

1,

6.00 . 7.00

•

f

•

• "

\ t.

'(

, , .

f

94

'" 4.2.4 Cornparison of Related Work

A recent ,study o~ sensitive clay from Outardes 2 has

shown 1nterest1ng results. Yong et al (19ryS) show that the

shear strenqth of the s01l from the same block s~ple de­

,creased when the amorphous iron and' alumina were' removed

by washing w1th 8NHCl followed by three wa&hings, with O.OSN , /

"' NeCl. They used remoulded semples te measure the remoulded

-~,

shear strenqth by a fall-cone test. Ill-' their wash1.nq pro­

cedure a11 the amorphous iron wes removed, whereas only 75%

of the total amorphous alumina waB removed. The strength

of this sample was extremely low 1n view of tl;le,near l1qu1'­

f1ed state. As shawn 1n Table 4.2 the amount of amorphous ,

alumina was very high in compar1son to the ameunt of alumina

of the samples 1n the present study.

The amount of the amorphous iron was almost the same.

The remQulded shear strength in this study decreased after , '1

1eaching a1rnost 16% of amorphouB iron and 6% of amorphous\

alumina. The remoulded sh~ar,strenqth decreased after leach-,

ing but the soi1 did not liqui fy. The pH =4. O":environment

of the soil in th~ present study prevented larger ,reductions

1n strength (Section 4.2.l)~.

"

Removal o,f amorphouB silica from the same s011 (Yong

et al, 1978) by wash1ng w1th sodium,hydroxide and heating

at 1000 for 5 minutes-and then treating with sodium chloride

to decrease the ~H, increased the rernouldèd shear strehgtp -

of the so11 as a result of reprecip1 taUon of silice.. The

Y' ,~

f"

"

, ,

1 0

1

~

/

,.

•

•

, •

•

1

o

()

93 .:...

amount of silic8 that was remov~ was less than 10% of the

- total arnount of silic8 (Table 4.2). Irl~the P~~dY .

it is d1fticult to co~nt on·th~'contribution of the amor-• , . Il·

. H pho~ s1lic8 to the strenqth asl the P did not change from

10.5 to lower value. The amount of silica, that was leache~,,-

from the 5011 was less than 2'. /

1

Synthetic 5011 was used by Suzuld and Yong (1978) when

different primary minerals were used· wi th different rnolar'

,ratios of amorphous ·material (~2P3/R203 +510 2 ) at the same

arnount of amorphous material. They found that the Plastic'!

limit, liqu1d limit and plasti~ index incr~ased witn an

1~crease ~n molar ratio hiqher th an 0.25. In the present .

study leaching of arnorphous iron did not greatly affect the ~

di~cussed properties (Section 4.2.1) whereas·the sensitivity ,

and the shear strength d~creased when the total amount qf

(

o -, •

arnorphous material at the sarne wateT content increased. These

observations were made in both studies. They found that the (

specifie surface area increased wi t~ th~ water content and . 1

amount of amorphous material. This' is the same observation

that Yong and Sethi (1978) had.

" The amount of amorphous material decreased wi th depth .

for two soils from St. Albans and Gatinèau (Yong and Sethi,

1978) 1 as the higher layer 1s exposed more to oxidation. The .. maximum variation wi thin 0 ~ Sm in a depth of 2. Sin below ,the

surface'wes found to be less than 3'. The block semple showed

'.

1 _,!,'f.otA~"" ____ '" ~ -, . ')

,--- ~-"·~'"_·""""''''''''_·_''''''''_.~_.'."""-",,,~ __ ~~'''~''-'I .. tf ... •

/'\

\ .

\

t

•

1

( r

•

1

II

,

2S .

20

>. 15 --;: ;: ëii

'1: • fi) 10 .

.5 •

o

.... '\

'\ "-

~""'." .... •. " ....

" " .'- ....

"D

....

"

• st. Alban

" Gatineau

'" " "

" '" " " " . .... , ~'\

'" Syi"''' "" 1 " • « ....

" .< "-.... Sy.~ ,

= .... ~. '" '\ .... ~~ , .", ,

'" " ....

5 10 15 20 lS

% Amorphous Material

FIG. 4.25 RELATIONSHIP BETWEEN' AMOUNT OF AMORPH6us MATERIAL

AND SENSITIVITY. (AFTER YONG AND SETHI'/1978).

,

/1,

1

l'

i - i

, 1 1'· ._~ !"PT ,.....-- ~ .. ..1.-. ..... 1 .... ....., .. I~"'*4_#Q» *95 _'! j 'it;r:p., . ~,.. ~..,.. _ ..... n .. ~~_

r

t.'

" •

1 1

(

'. •

o

o

o

"

95 • û . \ /

t ' ~ te)

, .

t

i . 5 .. • ... ... "" oC

~ . • ~

• 10 ~ . 1-., __ 1o>c~

n ~ .-deyw-iroc....-

.\tl

, ,

FIG. 4.26 COMPRESSIBILITY CURVES (AFTE~ KENNEy.I 1967) ,',

"

-.. .... ..

o

4

1 CI - '

= .. .. '. .. .. .. .. • •

• Q

It

FIG. 4,27

, ·r .. ~ ~ - -'~ 1-: .... - .l-v 1-

~. R0: ~\-~~ 1-

l'MTReATaD , ---- - - IOTA. o .... a • f-_._.- o. ••• c. • \ . ---- II-,.C' • ... \ 0

_ .. _ •• - 10'" + se Il.CI D , .\ \ 1\ ~, , \ - ,

\ . \1\,

1\ [~.\ ~ , f--

, . ~ 1''-'::;- .. I~' r-- .. - 1-- . I-f-

\ -_. . ~ .. :~ - - .. ~ .-rz .. r- -00:- -~:J' --~.- 1'--. 1--- ~ ,- .... f- -- fo--_ J -- 1'-

. , \

\ 1-.. - - ---...... . --.. . -.. - -- .... t . \ -- r--.. ~

1 , L-L.-

__ 1-

- 0.1 0.4 " • 4 • 10 10 'Rrt_c ('., •• ')

CONSOLIDATION TESTS ON CHEtlICALL-Y TREATED SPECIMEN'S . ,

(AFTER LOISELLE ET AL.l1971). 13

,..

"'~'--"---'. ,._ .... " ......... u'AlilflloV·~ ........ ;-~~..r~ ... W .. ~S~ .y:...... .-.t, ," ',.

/'\

1

•

(

,

1 »

•

t

t

o o

- 96 -- .

the same behaViO~,~U~ the vari,ati?n was m';ch ~gger 'with-

in 7.Sem .{Se~tion 4.~~Fig. 4.2 ows the relationship be-, ..

twee~ the ~mount of amorphous m that ., 1 " ;'

was :~bserv ... d by Yong a~d Sethi, (1 ". :~~ .... ' ~; recé~~:study could, fit in with this relationship.

of the

,

Kenney -(1967) and' LOisel~e et! al (19,71) conducted a ... ,

leaching test to rem9ve amorphous material from the soil. o ...

The EDTA tias u~ed t'o remove -amorphous irone ~eir resul ts

_ from the consolidation tes~ ar~ shown in Figs. 4.26 and

4.27. These results have been discussed in Section 4.2.2. , .

Further, this study has shown that the amorphous iron .. plays an "imp?rtant ro1e in the cementin~ b'onJ of the c-..lay

e from Outardes. 2. Bu~,,, the pH environment may control th'e

behaviour of this cementation bond. '"

4.2.5 Theoret\Çal Analysis and General Discussion

The clay particles interact through:-,

~ 1) the ~yers of adsorbéd ·water . < •

~ ~) the diffuse ion la~ers, and , -

3) through minera1 contact in ce tain particular ,/L;

casep.

The adsorbed water on surfaces of the particles will

èause repulsion between the cl,al' particles as the water , ' l .

mo1e~ules'adsofbed on t~e s~face force' adjacent particlès J'.

spart. The water will aet also when osmotico8ctiv!ty of the

ion o~curs. Th~s behaviour accounts for swelling.

..

(

)

-

- 97 -

The diffuse 10n layers theory considers the clay par­

ticle as a simple charqed plate 'for which the cation from the / .

pore water interacts between two clay particles. The cations

'" are not aIl he Id in a layer riçht at the clay surface, but are

present at sorne average distance from the surface. Alexander

and Johnson (1~49) used Stern1s model of a fixed positive

layer'?ext to the surface throuqh which the potential drops

l1nearly with distance. Beyond the Stern f1xed layer is the

-diffuse layer; which 1s sirn1l~r to the Gouy model through

wh1ch the p~~en~ial drops almost exponentially with distance.

pennef (1965) used this theory to study the sensitivity in

Leda clays •. .­'.

~

The cial particles could be bonded by chernical bonds \

such as those existing in crystals or by the weaker, inter-

molecular Van der Waals bond. Since aluminurn, iron and . oxygen are component atoms of.)he Cl~y ~rystal, chemical

bonds, can be easily fQrmed~n the oxides precipi.tate be­

tween part1cXes. Calcium or magnesium carbonates along with "f

organic matter also precipitate betwèen particles, forming

bond$ from one particle to a~other (Soderrnan and Quigley,

1965; Colon, 1966; Quigley and Thompson, 1966). \

\

The important forces of repuls~on and attraction deter-

mine the clay particle arrangement or fabric, together ~ith

sant and silt size. The edge to edge and face to e~~é 'ior7es

",.twill create the floccul;:lted state between the clay fabric

units and the clay particles, and the face to face arrangement

~---_.--,M~~l~ __ .'~'''FT.'''" •• ''''l_~_~f_.~·.~~~.~_a __ ' ______ .~ __ ._._~~ .,..~ ",~~'~MoJ~t"~'''<''-''''''~''l' "" .. -< _-.p.~"

,. , . ..,/)

--

, "

•

(

1

•

, 1

1

1

- 98 -

will cause the soil to disp'erse and exhibit a weà~et strength

behaviour. The dispersivity and the flocculation stete will ~

change to.sorn~ extent by cHanginq:-

1)

2)

3)

4)

the~tJconcentration in the pore water

exchange ble ions

raising pH to prevent positive charoes and l'

lowering pH to increase posit~ve'charqes, and

water content.

By add1ng salt the forces of 1nterpârticle,attraction 1n­

crease and cause the clay to flocculate, (Penner~965~

, Torrance, 1974)~

Leaching of salt from Outardes 2 clay did. not s1gn1-, . \

f1cantly affect the undisturbed soil properties. As 1t was

shown 1n Chapter 4, the Pc value, and CI parameter and the

sensitiv1ty were not affected by leaching of salt. The low

salin1ty ofth~ Canaè1an clay wàs estab11shed earlier (Penn~r, (

1965: Torrance, 1974: Soderman and QUigley, l~65). The salt

conten~ of the soil from Outardes 2 was found to be less th an

'1 gr/liter •. Skempton and Nortqey (1952) reduced.the salt

content of Scandinavian clay from 12.6 gr/liter to 2.2 gr/

liter bY',leach1ng with. distilied water. During the leaching .. ,

they observed a s11ght increase in sensit1v1ty. Bjerrum and

Rosenqvist (1956) reduced the salt cont~nt of artific1ally

sed1mented mater1al from 35 gr/liter to véry low values·~ The

sample thus leached exh1b~ed lawer shear strenqth and higher,

.. 11

•

•

,

•

o

>

o

Do,

(

sensitivity. Bjerrum (1967) ,presented the rf)!lsults of ~n • ,

oedorneter leaching experiment in which the pore water salt

concentration was reduced from 21 gr/liter to 1 gr/liter.

Increases in the compressibility were observed as a result of

leaching. Kenney, (1966) treated the sample with potassium

chioride. The high concentration of potassium chloride used

caused the development of quasi-preconsolidated pressure and

a decrease in the compre'ssibility.

The leaching of salt in' the present work shows sorne

effect on the re~oulded soil prpperties. The liquid limi~ .

increased 'and so the plastic limit~ by rernoulding, the clay

is more dispersed and the soil particle can retain more wa­

''\,..rter. The flocculation of the natural Boil from Outardes 2

(Dascal and Hurtubise, 1977) s~ems to be controlled more by ,­

the cementation bond than by the' salt. Eut when the 5011 was

remoulded after leachi,ng, the leaching of salt showed more

influence on the mechanica1 behaviour of the soil. The Cc

and'the ~I increased as the so1l was more dispersed after

rernoulding •

The effect of the pH on the liquid limit of two SOiid t(

minerals wa~discussed by Warkentin, (1961). Kaoloni te (,~on.

swelling mineraI) showed high values for liquid limit whe H the clay had P of 4~ ,The soil was flocculated in an edqe

to face arrangement whiëh resulted in a hiçh interaction vol­

ume (Schofield and Samson, 1954). When the "pH of the kaol-. on~te was 10, the liquid limit was low. In a dispersed state

\

~U;O--"~_V/f1ll~,~"..-v""r$'Û'H/'[_'rb )uWaf'l!'b\ ;(',p 1fr"~~~~~~"~"'~"'~'*--~--- -.....-.......... { .. -... ........ "' ... ;;-........ 1 . '1......... .~ ('f

. ./Ï

/

, '

I(

•

,

•

•

1 t

1 ,

c.

J

100 -

the interparticle resisting movement 1s the tepulsion be-

tween partic1es which keeps them in a more parallel arrange­

ment with low' int'raction volume •. ,

The pH = 10.5 that wes used"in this study to leech amor- " 1 r-...,

phous silica increased the neqati ve charges 'on the clay sur"-4!...

face. This fa ct changed the natural arrenqement of the Boil

from flocculated to dispersed and it resulted in a decrease

in the liquid limite These results agree with the decreas,

in the undisturbed strength properties: the Pc reduced and~ ,... '" the C' decreased in the soil with the high water 'content.

The dispersivity of the semples with the,pH= 10.5 environ-

ment caused the sample to be more compressible and for the

same reason the 9' value, because the particles have hiqh

sliding surface when the s01l i8 dispersed. The effect of

the amorphous silica could not be observed, as the dominant , H

factor in these samples was the ~. In samples~with ~lower • _. H

water content 2-2 and 2-3 (Section 4.2.3), the P = 10.5 has

a smaller ef~ect but because only a small amount of amorphous

silica was leached, no change in the C' and 9' was observed.

From this one can assume that leaching of lese than 2.0% of

amorphous silica did not affect the Pc' liquid limit, plastic

~imit and sens1tivity.

The undisturbed strenqth properties, Pc ' C' and sen­Î

sitivity, of the samples after leachinq amorphous iron and

amorphous alumina were reduced. The pH: 4.0 environment in-

•

•

•

J

,

•

J

" '

- 101

creased the positive charge of the clay surface and caused "

more flocculation, but it seems that the effect of amorphous

material was more dominant and the undisturbed properties,

the Pc and CI and sensitivity, decreased when the cementation

bond wes broken rather than increased under low pH. Th~ loss

in strenqth of these s~mPles emphasizes the britt1eness o~

sensitive clay (Townsend, 1969; LeRoche11e and Lefebvere, 1971)

due to the amorphous iron and amorphous alumina. The decrease .

in the sensitivity was expected as the surface area was de­

creased by leaching of amorphous material (Yong and Sethi,

1978~ but the liquid limit did not change much and even in-

creased s11ghtly in one sample rather than decreasing (lower l

surface area). The reasonlmay be the low pH wMich created

more edge to face and,edge to edge arrangement while the soil '-.J

was remoulded. The plasticity index increased slightly and

there was no effect on the C value. c

The plastic limit of the soil depends more on the size

and shape of the particles ~on the surface area. That

might be the reason for the small changes in the plastic l1mit

of samples that were leached with the buffer solutions.

It was shown th~t three factors affect the strength

properties 9f the soil from Outardes 2 to sorne extent; the salt

conte?~, the pH environment ~nd the amorphous material.' Among

The pH these, the l~aching of salt is of minor importance. 0 f

plays an important role in the strength properties but the

bri ttle behaviour 1s accounted for by the amo'rphous iron,.

. /1

, ,

\ < t.

r l': r'

•

1

• f

•

1

a

"

102

\ .

CHAPTER V

CONCHUSIONS,

~ The sensitive clay from Outardes 2 River in Ouebec, .'

Canada has britt1e behav!our as cementeç clay. One of the

most significant cementinq age~ts was found to be the amor-

phOU8 irone

The.meohanioal properties of the S01l were affeoted by

Ieaching. From this study several'conclusions can be made:

Removal 0 f 15,; of tge Fe203 and 5~ of alumina, , /"

when the total amount of amorphous i ron in t"6'e 1 1

1

soil was 3. 45~ and the total amount of arnorphous'

A1 203 was almost 1.O~ (~ection 4.2) 1 decrease~ f.. J

the P value of the 80il by more th an 1/3 of the c ~ ,

Po valu~ of the unleached ~am~le (Table 4.6)., :r

The e-10g P of the two sample~ II ~d III; exhibit f. ' '

non-cemented clay be~aviour (Sf!ction ~" 2 • 2) as

the sharp break in both samplesd1sappeared with

the reduction in the Pc' rrhe P~ = 4.0 environ­

ment of the soil should cause flocculatlon (Section " i" '

, 4 of' 5) and consequently an 1nore,ase in; Pc value.

Therefore, one wes led to attribute the reduct10n in

the Pc to the léaching of arnorphous ~ate,rial rather

than to the low ~~o The sensitivity increased 1.

by more than 2 ti;mes a.s a result of l~eaChing Fe203 \, N ~

• 1

•

•

•

o

o

i! ,

103

and A1203 and there was no siqnificant change J

in th~ consistency which could be affected by

" . the lOI< pl! .(5~W4.2.1). 02) Remov:p::l 2~ sil1ca wa,s not as significant as

. H the h gh P environrnent of the soil. The reduc- '.

,tion in the Pc value by 50% the Pc value of the

sample before leaching (Table 4.6) was due-to dis­

persion rather than to the amorphous material

(Section 4.2.2) as the high pH incre~ses the

negative charge on the clay particles. The sen­

siVity of these samples was very low ~nd it was

unmeasured by the fall-cene test. The sample ex-

hibited a very low remoulde~ strength and it

liquif1ed in the natural water content. ,The

plast~ lirnit and liquid lim1t decreased as did

the plastic index (Section 4.2.2). 'Consequently

the ~ompressibility increased.

3) The shear storength parameter C.' and ~' from CIU /

test changed ,after leaching yith a buffer solutton H of P = 4.0. Rernoval of lO~ Fe2~3 and l.5~ A1 203

decreased the C' value by more than 3 times the C'

of the unleached sampleT consequently the V' in­

creased (Table 4.8). The mater1al lost sorne of its

... ~" -~ .......... ,~,

\

•

,

1

•

f;

,

'c;.'

.'

, 4)

- 104 -

., britt1e behaviour under 10w ~onfin1nQ pressure

(Section 1. 3) .'

The ;a ~ lo.s)environment leeched just 1.2~ of amorphous silice. The strength properties

H ' were governed by the high P rether then by the

amorPhous silice (Section 4.2.5). The Triaxial

test gave two en~e1opes (nonhomoqeneity of the

soil s-ample). The samples with the high water

content lost cohesion by more than 3 times and

consequént1y the ~I increased. The other two

samples did not show siqnificant changes in the

cohesion and ~I (Table 4.8).

. ,

5) Leaching of salt did not show signifieant chan~es

in the Pc,iJ Cc" ~' of C' as the salinity of th1s

so11 was found tdil be low. It seems that thi JI"

mechan1cal properties depend less on the ~eaching

of salt than on other factors (Section 1.3) •

6} The J:)onhomogeneity Of the so11 samp1~ made it"

more difficult to look on other mechaniea! changes

in the soi1 resul tinq from leaching such as pore',

s~ze dis~ribut1on, grain-size distribution and X­

Rey diffraction •

o

'·"-"-"'-~I·~III_.I.I •• II.I.I __ .UI.f_.a.tI.4_'_._I_l_R'2--_~

, -1

!

•

.' •

•

•

•

•

"

- 105 -

APPENDIX l

LITERATURE 'REVIEW

1-1 Definition of Sensitivity.

The sensit1vity of clay 1s defined as the ratio between

the undrained shear strenqth of the soil and the undra1ned

remoulded strength of the soil (Terzaghi , 1944).

The term "quick clays Il 1s used to denote a clay of such

h1qh sensitivity that it behaves as a viscous fluid in the liT

remoulded st~te. ) '

Clays of sensitivity between 4 to 8 are , , ~

defined by Rose~qv1st (1958) as very sensitive. ,

~he sensitivity of the clay that-was used in this study

was found to be 8.5 (Table 4.1).

1-2 The Causes of clày sensitivity

It is very important to differentiate between phys1ca~

and physico-chem1cal mechanism, when considering the factors

which lead to the sensitivity of clay. One must 1nclude these 4'

factors that depend only upon physical interference between

the clay particles, resulting either from the types and size ~ ~

,'--- .

r

~.~.--_. __ . ,-- -

"

1

/Î '

r

( (

(

1

•

1 1

l

,

- 106 -

of 'partioles or the boundary conditions. In the s~cond group ~

one should consider l~aching, rupture of the cementation

bonds, ion exchange' and weathering, and addition of dispersing

agent~. )

The undisturbed fabric of sensitive clays is composed ,

of floccu~ated assemblag~~ of clay particles ~ domains

(Rosenqvist 1953: Mitchell l~56, Wu, 1958). The result of

the observation by Quigley and Thompson (1966), while using

X-Ray diffraction, showed ~irectlY the f10cculated nature

of the undisturbed clay fabrit.

PUsch (1962, 1966' conclud~hat edge ~o edge linkage

appeared of greater importance in the fabrics than.those o

[

studied by Rosenqvist (1959) 1 where edge te face waS the

dominant association. 'Thua, any flocculated s~ate may be ~ ,

present in sensitive clay. "Remoulding sens~tive clay causes , "

a change from one of the flocculated fabrics ta a deflQc-.. culated state. Tarzaghi (1925) 'was one of the first to look

on the changes in clay :prope\r~s caused bl" disturbance.

Casagrande (1932) explained marine clay sensitivity on ~ .

'the basis of a load carrying skeletons consisting of highly

.. '.

- ,

,

l

•

,

»

J

o

..... I.M ........... .... ,. ...... 1"

•• ~ ..... 10· ..... 1

107

" , rI~ 1.1 STRUCTURÉ OF SENSITIVE CLAX (AFTER CASAGRANDE 1 1932L .

\

,-

1-

1

et • ,

, (

FIG, 1.2

...

-

\ , , ../ . \ \ 7

1 '\ ....

,

RELATI N BETWEEN SENSITIVITY AND SALT {

C9NC€Ni RATJON, Sor·tE NORWEGIAN CLAY DEPOS ITS 1

,1

. • , .. ''Ï'

(

(

• . ,

1

1

,

1

.. ,. ,

- 108 -

~

compressed "bound cla ~ ',"

trapped between silt and fine 1

... ~

sand particles (Fig. l during consolidation which creates

deposition 9f. flo culated clay particles and coarser silt

'~d d . 'an san gral.n in the marine (salt water) environment.

causes flocculation of the clay and 1

simultaneous disposition of clay, si1t and' sandr'at a high "

void ratio. A drop in sea level or rise in land levei causes

leaching by fresh water, ,and as a result, salt will be removed

from" the pores. This kind of 1eaching will cause high sensi-~ !

tivity in clays (Bjerrum and Rosenqv1st, 1956) as indicated

'in Fig. 1.2.

1-3 Leaching

Removal of amorphous material by leachipg may change . sorne' of the mechanical propertie~ of -sensitive clay. Natural

cemèntation increases the resistance of a soi1 to deformation.

When breakdown of the cementation does oeeur, the magnitude

and rate of subsequent deformations are ~ar~ especially

\ when aecompanied by an increase in pore water pressure.

The cementation bonds are considered to develop during

deposition of clay (Crowford, 1963) and are a result of the

, ,existing chemieal environment, both past and present. A '/

il..

"

----:-.F7------'""iîf"l,,~,r-----..--------~---~-----.

f

, ." •

1 Y

1

,

o

109

change in th~ pH, of~he en'ironment by rainfall might

disl;S0tVe the amorPhous~c9mpounds such as Fe203,/~l'203' Si0 2 or CaO in the natural cemented soil and the c~menta-

tion~on~ may bréaki or, re-preciPit,.ti~n of amorphousJ

~,

new', ce~enti~ bond. A Q

compounds such as silica can build a

As a' result, ,an increase :i.n strength will occur. '"

An experiment that ha~ been done by L~e (1960; showed 1

, 1"

that all the natural soils which have aggregated fines con-o ,

taining.pne or more of carbonates, iron oxides and organic ,1 ~

matters can 'forro smaller or larger plastic particles .. He

had done sorne experi~enis on compacted silt and also silt ,...( J'

treated with lime. ~he cementation bond caused by the lime • increased tJ;le effective angle of internaI friction from 370

to 450 (Fig. I.3 ) ..

~

A Ieaching experiment was londucted by Ke~ney (J .. 967) on

clay from thetteast,"Coast of Labra~or, .Canada. ~~ clay was

originally a marine depgsit, and the smail salt concentratiBn .

in the pore fluid iSleviderice that the clay has been leached.'

The sail which was extremely homogeneous was leached by EDTA 't&

solution and sea water • The Pc vaf.ues and éompressibili ty

. were observed after treatment for the. ]?urposes of comparison

wi th the sample before treatment (Fig. I.S ) .

_ ..... ·~~'-~~)Ml,fle: ••• lfG •• 'F • ... ~~ ... ~~~_...Ji.... __ :.-_. ~ ,

l ,

j

, , '.'

..

,

" ,

•

,.

.,

t

1 , ' ,

1 ----- ' .. - --"-._----"-_.- .

110 -

Leaching by EDTA ,removes cementing agents such as

carbonate oxides and(iron oxides.

:7 1

t'+,eatment

in the soil~

sea water increases the salt ~ontent

o·

A bomparison of the-d sample bef.ore· and after leaching 1

shows that rernoval of iron by ~DTA decreases the Pc value

of the soil, increasihg the salt dontent by sea water treat~ 1

)

ment"increases the P value of tne samp~e • c

~' b ',1 EDTA was also used by Loiselle et" al (1971) to remove

" q cementing agents from the clay of outardes 2, the area from

..; l '

~

1,

which the S9il sample was used for the purposes'of this work.

The oementation agents in this clay were Fe203 and A~203'

calcium carbonates or gypsum. Among these, the iron oxides

• are the most important. The salt concentration of this c~ay , ' is weak, as a result of leaching in the geological past.,

... Figure I.4 shows the leaching curve of this clay.

.,.. -, c-~

l

\rr;be wit1 NaCl sample was pretreated 0.6 gr/liter and

then with EDTA. NaCl followed for a secqnd time. Changes 1

in the mechanical properties were observed. The P value c , ~ ,

increased by treating the soil with sea water. Removal of ., iron oxide by EDTAfresulted in a decrease in the P value c

, of the natural soil.

1

"

, !

-

e.

. '

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

-'111 \

0'

\

In the two cited works of Kenney (1967) and Loiselle

(1971), the EDTA soluti~n wa; used to lèach Fe203 and A1203;

their result showed that the EDTA removed the amorphous iron ,

f

compound. The EDTA solution that was 'used by thern is organic;

theJ:;'efore;' ft is possible that the EDTA solution may precip-

itate in the soil to creye a new bond. For this reason,

the EDTA solution is not used in this work as a leaching

solution (Section 3.1.2). 0

~

\

..

trI F

( (

, '

" ,.

,

u,".!

(

l

t

(

t

1 l-f [

, ,;;U;~}tfllWfo~lo>I:fy..~~)"""""''}f.~.(~'1t'jlitl'''~t>-g ... ~~~~~~ ...... _. _____ .! ... ___ ~ _ _ .. _

) ~ ' '1 :; .. .... •

" .. .. .. • "

~} ~-

FIG. 1.3

, .

•

o

, 1

"i 10 \.~

•

0 0 1 •

."'CTlVI CO.'~ID&TIO. """1II1It , ... , •• ',

, . CE~ENTATION AND EXCHANGEABLE

(AFTER LAMBE~1960).

L'

o

"

, \

IONS ON STRENGTH PROPERTIES' (-

\

-0'" .:. .. -.. j .~ .. , •

•

•

•

,

•

o \

0,

- 113 ____________ . __ ~.D~'~. ____________ +-__ ~,~.---------.~.~~.~.O=---------------~

~

_---- ~o .. :v:""'f" :.._-- - --- , •••• ] t c ___ ._._ •• c ..... ""

c ••• &"&L'I""

-----.... OI"n.Ulaf _··-----"1 .,.

'-1>0 ~ __ ~~~ _____ -L ________ ~ ____ ~~ _____ ~ ______ ~.~'~~ _______ ~

.~

-i ~ ..

ïIO~---~--_~------_I~------~------~~~~---~------_I_------­ , ,: . .... 1 -

fi ••• _ ...... --- -.... ,e , . -. "

~ • ~ Ir

> Cl---~~--~--~---~---------I~--~~~ _______ -4--______ .~~ __ -L~, ________ ~ uo ;: l ' ;; u w :, ~ .. -'- :. : ,.,-' . ----: ~ / __ • 1

,~. 1 .. __ --- .. ---- ... -~ 1 II----I---t-,.'---/f--'~- ._ ::::::=:=: .. - ... -._- --:-;-.. _-, ]--_ • .,;'-~..:

... AI

;- --- .. ""'-.~ __ ...L.._...L...:. • .: ... ;.:~~:..:-:':'"' - or: .-~ 0 • ~O .0 - 10 lolO ISO .. 0 Il. 140

1

FIG. 1.4 CONTROL OF EDTA,TREATMENT (AFTER LOISElLE ET AL J 1971).

1:1: J

H:jJ 1 : li' :-~l-;:Z'-' li:1 ,E j i­

• r ~ " ,- 1

1 ... ' · j/ ., , ........... ,

• • i · ! •.

E .' ./.:-1

• •

/ '<;,

----- .. -.-- 4::~ c. ~ .. -.-

1

.. • Il ~ U; • ; l

1 i i : 1 , 1

~::=: . 10 .-;

" " ,

f'

FIG. 1.5 LEACHING TEST PROCEDURE USING EDTA (AFTER KENNEY J 1967). "

. Jtt:""" s .~_4"",""""-"'-~'" ~ ~'"f'. ~--~---'--~-"""''''''''''''''»'o<'''''~''-''' <""".' ... ~ ...... ~.: ""6

/"1.

, \

)

c

a ~

1

.1

1

1

114

APPENDIX II "

" EXPERIMENTAL p'RO:œnURE

1

II-1. Deter.mination of Amorphous Material

1

II.1.1 Segalen Method

r-' , 500 mgr. of ov\n dried sample

~' were mixed with 40ml.

of SN Hel at room tempe~ature and shaken for 30 minutes in

L.

a shaker to remove amorphous iron and alumina. The suspension , 1

was centrifuged and the sup~rnatant li<[uid was collected.

The sample was then washed with 40ml. of boiling O.SN NaOa " '

for 5 minutes to dissolve the amorphous alumina and silica

compounds. The suspension was centrifuged, and the supernatant (,

liguid was collected. This procédure was repeated 8 times

until the arnount of iron, alumina and silica in the supernatant

~iquids were low and relatively co~stant. The amount of Si02 ,

Al203 and Fe203 were determined colorimetrically. The

following identification method was used toOdetermine the

amount of amorphous material after washing by the Segalen

rnethod.

i al

1 1

1 ~

•

•

•

•

1

o

o

o

o

115

ILl. 2 Identification of Amorphous Silica ,(Vionovi tch, 01966)

1. 10ml. of the supernatant liquid was transferred to

a IDOml. volumetrie flask •

2. lml. of ammonium molybdate 'reagent solution was added.

The contents of the flask was stirred for a while, .

and the flask was allowed to stand for 10 minutes.

3. 4m!'. of tartaric acid (10%) solution was added,

while stirring the contents o~ the flask.

4. lml. of reducing solution was added.

5. Distilled water was added to make lOOml.,uand the , 1

flask was allowed to stand at least 30 minutes.

6. The percent transmission at wave length 730mp was

deterrnineâ using standard curve.

II.l.3 Identification of Iron (Vionoviteh, 1966)

1. S to lOml.\ of's~ple was withdrawn and transferred

to a IOOml. volumetrie flask.

'1 ~,2. Sml. ammonium ehloride was added.

'\ ~ -_ .. _, .............. su.' ........... _ ... ., __ ._' __ ..:_~ ... - ..... , ........ M - ...... __ ... _,., ____ ---

\\'\i~ 1 ~ ·----------.... I~,.t ~ _ .. 1~ .. ~ - -""" •• 'tl'" ", /'\

l'

• Ir

r

(

•

l '

•

1

3. Gml. of sulfoscyclic acid wasi added, stirring the

conte~ts o~ the flask until a pink colour appeared.

4.

6 •

II.l. 4

The least amount of ammonium hydroxide, just enough

-to change the pink colour to yellow was added.

~

The contents was mixed well and distilled water L

added to ma~e lOOml.

1

The percent transmi~sion at wave length 420 mp

was determined by using standard'curve.

Identification of Alumina (Mc1ean, 1965)

1. 3 to lOml. of sample was withdrawn and transferred

to sOml. volumetrie flask.

2. 2ml. of iron dompensatin~ reagent was added, stirring

the contents of the fl~sk.

...

3. Sml. of thioglycalic acid was add~d •

4. Sml. of 0.75% erochrome cyanine Rdye was added.

5. H lOml. bf ammonium acetate, adjusted at P .6, was

added.

-

•

•

•

fi

•

•

•

,

- 117 -

1

6. Distilled water to make SOml. was added, and thé' w

,Ji

flask wa~ allowed to stand for 20 minutes.

~ ~). 7. The percent transmission at wave length 535 rnp w~s

determined by using a standard curve.

II.1.5° Identification of Amorphous Material from Leaching Test

The above procedure was used tQ identify amorphous

silica and amorphous iron (Vionovitch et al, 19~6). The ~

amoun~, of amorphous alumina was determined by different

agents as the identific'ation of the alumina was influenced ,

by the pH environment. The method was applied as the amorphous

alumina had higher oco~entration (Hill, 1966) by leaching

in comparison to Segalen method. In this procedure three .. agents were"used and different transmission wave length

as described below:-

l. l-4ml. of the effluent r-~

from the leachi'ng experiment.

2. 2ml. of 0.1% erochrome cyanine Ryde was added. 1}

'" " 3. 2m1. of 2% mercapto acetic acid was added.

~,

•

" ..

'-'~""'~Ifil"# l' IlliCh " .:-, ------~-~~--~ .. ~,\ltW\i'ti..,.\l."\:I'f .. ,.~ .. ' "f

, ./Î

r

(

•

•

,

1

- 118 -

4. 2ml. of ammonium acetate, adjust.ed to pH: 7.5

was added.

5. Complete to SOml. with distilled water and heat

for 30 seconds.

6. Use blank solution by adjusting hydrochloric acid

to pH.4.0 and adding it, instead ~f as in step No. l.

" 7. The percent transmission at wave length 595 mp

was determined by'using standard curve.

II-2 Determination of Pore Fluid Chemistr~ (

(' II.2.1 Saturation.Extract Method

400gr. of soil was mixed with water anQ stirred with

'" a spatula. At saturation, the soil paste glistens as it

reflects light, flows slightly 'when the container ia tipped )

and slides freely and cleanly off the spatula. The sample ,

was left overnight. The soil was transferred to a filter l

)

tunnel with à filter paper in place and vacuum was applied

until air began to pass through the filter (Richards, 1954). 1

.;

The extractant solution was determined by absorption Spectro-

photQmeter.

,l

•

•

•

o

o

o

o

o

1

.... ~

~ ~ .......... ~ ~~--- ,--_ .... -..._ ..... """'" .....

,\

- 119 -

.11.2.2 Ratio Soi1:Water Method

~.

In order to find the amount of salt present in the soil,

different soil to water ratios, ran§ing from 0.033 t6 0.5 can

be used. The ratio of 1:10 was used in this study (Fried

and Borshaft, 1967). The mixture was centrifuged and the

amount of cation was determined by absorption spectrophotometry .

11-3 Sensitivity and'Atterberg Limit ~

The samples were taken from the same cells that were

used for consolidation to observe the different properties

of the soil a~ter leachirig in comparison with the soi1 before

leaching. Properties such as 1iquid limit' and plastic limit

were calculated following -the procedure of A. Atterberg •

..

The use of the fall-cone tests to measure the sensitivity

of.the soil be~ore and after leaching was found, applicable,

using the Banslor (1957) procedure for these tests. The 1

undrained shear strength of the undisturbed and remoulded

soil were determined and these values were used to find'the

sensitivityof the soiltbefore leaching and after léaching. ~

/

,_._. -------y, ' '-'~/7/ < \ -- ~"-:==-_" ......... r [..-, --_._, .... ~ -~ --~~r ..

J

"

f ]

(

(

<.

1

- 120 -

II-4 ~Conso1idFtion Test

The samples which were 3.Blcm. in height wete' used

,lor. the consolidation 'test,. The contro11ed gradient te~t

was conducted on the 6 leached samp~nd another sample " .

before leaching, in order ,to observe the influênce of ca.

leach~ on the P value and the.compressibility. c

1

~he test was performed on a t~in cylindrical specimen

identical to that used in the conventional consolidation .

tèst. Drainage was-'tn the axial direction and only to the j

upper fàce of the specim~n. At the bottom face a small and

constant hydrostatic excess pressure of 2.49Kpa was maintained

by graduallyapplying axial load to the specimen. Under

these boundary conditions a parabolic pattern of hydrostatic

e~ess pressure develbps which varies from the hydrostatic

excess pressure maintained at the bottom of the ~pecimen to 1

zero at the upper face. A data equisition system was . ./

1 "

connected to the apparatus 50 that readings of strain and

stress could be taken in millivqlts and then transformed

b~ using a calibration factor into ·k.g.m. units.

A great advantage of the test is that the coefficient '-~

of consolidation can,he computed simply' and directly without

. ,

: f _ .. t ,. .Ri,II 4 t. ;:, . ri a.et.z. 1 .....

"

~

•

•

o

o

o

·9 24

_.. -\- -.

- 121 \

" l

) l' i' ,

resorting to curve fitting schemes . such as Taylor's square .

root of uime or Casagranda's log of time schemes used in

connection with conventional tests. Also, an unlimited

number of points may be obtained for plotting of curves •

Il-S Triaxial Test

The triaxial ~est after leaching was used on ce~l~.l, / (ll

-2,3 and on the sample before leaching. The tr iaxial appar-

atus was described by Bishop and Benkel(1962). ~he type of

test that was condqcted on the saturated samples was the "

'consolidated-undrained test.

First, the test was run on the 'sample befor~ leaching

in order to choose the strain rate that will be used e~ually

through, all the tests, and the applied confining pressures.

Each leaching cell 'whic~ was,lO.16cm. in diameter and 1-.,

7.63cm. in heigh~ wa'S' triIl\l1tladt9, 4 samples, of 3. 56cm. in

, diameter so that the standa~d teSt could be 'a.pplied. '

On th~&~~ype o~ test a back pressure was applied on the ,4'

samples to get fUlly-saturated samples by measuring the 'B'

, p~râ.meter using the rormula:AU-BAP 3: f

)

, "

- ......... ~-_ .... ~~~~.t;.&t...,,~"-<.J...lit; ~ _~, t /Î ' \

•

"

, .

rr:--, --~-~--_. --~---

1 " ", .«1,~ \'1 •• r,"''''' t~ )',.......~".;l"'}~~ .... t<I~"""''''''tloI'''i'" 1<f~"'M""fr~*,rr .,-., _~.r .. ",...~)t'l"'M"._,,,,,,,~~,,,,_.,,,.,,~,,,~. __ ,

011.

•

»

•

"

Il+"

122

, '

'\. The samples were allowed to cons'olidate after ,full

-saturation under a cell press,\re P3. Then the sample, was

Sheared under undrained conditio~s by applying an axial

load in a constant sttain rate. The pore pressure during

- " the test was measured by a transducer and was ~ecorded

'~gainst time. Another recorder measure~ the applied load

versus displacement •

j!

,To give 'si~e draina?e during consolidation, a filter

paper was used. The sample' had drainage at the top, at the

bottom an~ from the sides 'during consolidation.

CI- As a resul t of these tests, the strength parameters C' ~ ..

and ~. could b~ observed on the samples before leaching

compared with the samples after'leaching.

1

) r

)

, \

/

-'- , - ""..:"~"",,,ai •• T.ll111l -------~---... 4M',~"._J_I'IIII •• pl!Jl!fl ... 1l.i1 ---.... , ... ygM._-""I"III!._;1 ___ .. .'1l11f'W1""Ui11tlllilillrili.jjI-/ ,,'>

1 "-, f

,

•

•

,

v

, ~, ... -,

.~."

_ 123 _ 'ftJ

/

APPENDIX III

TEST RESÛLTS

~

III-i Grain Size Distribution b

• <> Grain size distribution curves were plotted from the

standard Hydrorneter test for the different samples. From ,

these curves one can learn about the variation in the block

sample as discussed in Section 4.1. " ~ .

1 The' leaching experirnent affected the grain size distri-

bution curves but the di fferences will not be discussed here .. as t~ soil sample was not homogeneous. It· seems tl)at tl}e big-"

differerces are due more -to the variation in the block sample

than to leaching. 'From Fig. lI'I.l ohe can see the grai'~ size J.

',' distribution of the 7 sarnples which are described in Table 3.1. ,

o

'Sample ln has the lowest Clay content 23%, whereas the highest

clay content, 44%, 1s found in Sample 3I

• The sample before

leaching falls between these two extreme curves. \

FiÇfUre III. 2 shows the grain size distribution of Samples

l,2 and 3 (Table 4.7). sample 1~2 shows the lowest clay con­

tent (15%). The highest clay co~tent (35~) is found in

Samp1es 2-1 and 2-4. The sarnples wi th the higher clay content ~> '

can retain more wate·r and this correlates with the grain size

distri.bution resul ts.

, 1 rj 1

1 li l '

, .

.. ~.-..;>- ~,x'ii tr'.1' .... ~~r ___ ..r.~.""_-._..-"'<""_, __ ) ,.,.

, .~

, c

.~~" ... j -~ ~~

1 ~

" .~

";;"

f

'" ,

j

,.

i"

;,

·n '"

\-\' '

~ "~_"~:- '" ",,:" ,:-~f,;;~~;~:j,~~'1.

.... l'"'l ,.., .,

" n ~ f'"'I ~ 1

)

~

• 100..-. !'; 1 l ' . l Clay :;;A;

SUt

~

•

".

~

!'

~..., 3D

2]; ...... < > ....

ç.

o-Sampre before ~~eaching -

b-Samples ~ .1n~

A-Samples '21:.20

• -Samples lx 1 3a

"<" ..

~9 ~ .....

B.L. . .......,:

'.

-

~.

201 lit ~ 1 1 1· ~ . 1

0.1 r nn1 0.001 Oiameter -mm

. ~

FIG, I1Ll r,RA~~-SIZ"E DISTRIBUTION CURVES OF SAr1PLÈS.I AFTER CONTROL GRADIENT TESTS.

G /J____ '

'>

"'-

l ' ... II.)

"'"

.;;>

'II 4' ,g, .. , ~~

' ..

î 1 l J

:-: .

i i: 1

'. / L

T }

"

... "", '''-\ t '." ~ 1

'-."" .. ~ :, ~"_ i :,~'>-

,.~ ...

~ ';:.,

""~ !,,:r

- _.

)

t J ,

o ; -

/ /

"

... ~

"

-"

• .. • • ......

'" î;

,-1

1 ! 1 901 1- 1 Clay

so:

~

1 1: QI

~ QI

CL 3(1

~

'" _ B.l.-2

-'

1-2 ...

"

(

~

o-Sample before leaching

ô-Sample 1-2

&.-Samples;2-1.2-2,2-3,2-4

e-Sample 3-2

~_ 2-1

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