/Q40?“

A srunv or THEPHYSICAL AND ENGINEERING BEHAVIOUR

OF COCHIN MARINE CLAYS

A thesis submitted byBABU T. JOSE

in fulfilment of the requirementsfor the degree of

DOCTOR OF PHILOSOPHYOF

COCHIN UNIVERSITY OF SCIENCEAAND TECHNOLOGY

SCHOOL OF TECHNOLOGYCOCHIN UNIVERSITY OF SCIENCE AND TECHNOLOGY

COCHIN - 682 022

1989

CERTIFICATE

This is ix) certify that tflua thesis entitled"A Study of the Physical and Engineering Behaviour ofCochin Marine Clays" is a report of the original workcarried out kn! Shri Babu THJose, under nqr supervisionand guidance in School of Technology. No part of thework reported in this thesis has been presented forany other degree from any other University.

—Dr.K.K.Punnoose

(Supervising Teacher)Professor of Civil Engineering

rothamangalam, M.A.College of Engineering1 .November 3, 1989 Kothamanga am

DECLARATION

I hereby declare that the work presentedin this thesis is based on the original work doneby me under the supervision of Dr.K.K.Punnoose,Professor of Civil Engineering, M.A.College of Engineer­ing, Kotharnangalam, in School of Technology. No partof this thesis has been presented for any other degreefrom any other institution.

Cochin 682 022 BK§fi«T.JOSENovember 3, 1989

ACKNOWLEDGEMENT

I wish to place on record my profound sense ofgratitude to Prof.(Dr.) K.K.Punnoose, M.A.Co1lege of Engi­neering, Kothamangalam for his inspiring guidance andconstant encouragement during the various phases of thiswork.

I am deeply indebted to EuuA.Sridharan, Professorof Civil Engineering and Head, Mechanical Sciences Division,Indian Institute of Science, Bangalore for his valuableadvice, untiring enthusiasm and unstinted support throughoutthe course of this work. His contributions to the develop­ment of the geotechnical laboratories where this work wascarried out will be gratefully remembered.

I thank Dr.K.G.Nair, Professor and Head, Departmentof Electronics, Cochin University of Science and Techno­logy, most sincerely for help and guidance during theinitial period of the doctoral work.

My sincere thanks are due to Shri Benny MathewsAbraham, Lecturer, School of Technology for his understand­ing and cooperation at the different stages of this work.

The help and assistance rendered by the staffof the geotechnical laboratory is gratefully acknowledged.

I am grateful to the authorities of 1Departmentof Science and Technology for the financial assistanceduring the period of this investigation.

Babu T.Jose

Chapter I

Chapter II2.1

Chapter III3.13.23.3

Chapter IV4.14.24.3

CONTENTS

INTRODUCTION

REVIEW OF PAST WORK

Cochin Marine ClaysPhysical PropertiesConsolidationLime Stabilisation of Soft ClaysElectrical Resistivity of Soils

MATERIALS AND METHODS

IntroductionField Collection of SamplesPreparation of Samples for LaboratoryTestsAtterberg LimitsGrain Size AnalysisConsolidation Tests on CochinMarine ClaysDetermination of Free Swell IndexOther TestsIdentification of Clay Mineralby X—ray DiffractionStabilisation of Marine Soils

PHYSICAL PROPERTIES

IntroductionAtterberg LimitsShrinkage Limit

Page

l314

22

3O

36

4046

49

52

57

59

79

85

88

94

99

lO4l24

4.44.54.64.74.84.94.104.11

Chapter V

Chapter VI

Grain Size DistributionActivity of Cochin Marine ClaysFree Swell IndexOrganic Matter and Carbonate ContentEffect of WashingEffect of SoakingEffect of SaltsShear Strength as Related to WaterContentDielectric Properties of Pore Fluidand Index Properties

CONSOLIDATION CHARACTERISTICS OF COCHIN

MARINE CLAYS

IntroductionAn Outline of the Test SeriesCompressibility of Marine ClayCompression Index and Its ReliabilityEffect of Duration of Loading onCompressibilityPreconsolidation PressureConsolidation Characteristics ofCompacted Marine ClaysInfluence of Dielectric Constant of PoreMedium on Engineering Properties

ENGINEERING BEHAVIOUR OF LIME TREATED

MARINE CLAYS

IntroductionSelection of a Suitable StabilisingAgentPhysical Properties of Lime TreatedSoils

Page

127

148153160162

165

168

170

189

.198199

201

223

250272

293

304

322

325

331

Page

6.4 Compressibility Characteristics ofLime Treated Soils .. 335Chapter VII ELECTRICAL CHARACTERISTICS OF MARINE

CLAYS7.1 Introduction .. 3907.2 Resistivity Measurements on CochinMarine Clays .. 392

Reliability of Resistivity Measurements.. 4067.4 Relaxation Time and DielectricConstant of Pore Fluid .. 4167.5 Resistivity as an Indication ofLime-Soil Reaction .. 4217.6 Relationship Between Resistivityand Shear Strength .. 4267.7 Resistivity by A.C.Measurements .. 428

Chapter VIII CONCLUSIONS .. 433Appendix I REFERENCES .. 451Appendix II LIST OF PUBLICATIONS FROM THESIS .. 467

Chapter I

INTRODUCTION

The growth of Indian port cities over the lastfew decades has been phenomenal and Cochin is no exception.

With the increase in population, housing and constructionof various facilities have been a problem with urbanisation.Having exhausted all the trouble free hand, man is nowon the look cum: for techniques tx> improve areas whichwere originally considered uninhabitable. Thus studieson the nature and engineering behaviour of soft clayscovering long stretches of coastal line and Inethods toimprove their geotechnical properties have been of greatrelevance, of late.

The peninsular region of India consists ofnearly 6400 kms of coastal line. The coastal belt startingfrom Rann of Cutch on the western side to Calcutta onthe eastern shore liner is almost completely covered bysoft highly compressible marine clays (Fig.l.l). Problemsarising out of the high compressibility’ and poor shearstrength have thrown considerable challenges txa the geo­technical engineers.

I

§+_

/.6"

MARINE oeposnsI

500 km_]

Fig. 1.1. DISTRIBUTION OF MARINE CLAYS IN INDIAN PENINSULA.

The aim of the present investigation is tostudy in detail the physical and engineering behaviourof the marine clays of Cochin. While it is well knownthat the marine clays have been posing numerous problemsto foundation engineers all along, the relevant literaturereveals that no systematic and comprehensive study hasbeen attempted to date.

There have been innumerable problems connectedwith settlement <1f structures founded CH1 these soils and

with embankments enui deep cuttings for both railways andhighways. The Indian marine clays are pleistocene torecent in origin, considered to be young and were depositediJ1 salt or brackish water" environment (Narasimha FHflD &

Kodandarama Swamy, 1984; Mohan & Bhandari, 1977). Ithas been established that the physical characteristicsof offshore deposits are essentially time same ans thoseof comparable terrestrial deposits (Noorany £9 Gizieuski,1970). Hence the knowledge gained and data generatedcould be extended to foundations of <offshore structurealso. With time present hectic activity iml oil drillingin chug) sea, this assumes importance. The present workenvisages a systematic study of the engineering behaviourand electrical characteristics of Cochin marine clays

together‘ with their physical properties. The: knowledgegained is suitably used to improve these properties withappropriate additives.

The contents of the various chapters are brieflydescribed below.

Chapter II presents a detailed review of therelevant literature bringing out the limitations thatexist in the present knowledge and focusses attentionon the scope of the problem.

Chapter III deals with the materials and methodsused imx the investigation. It describes III detail themethod of collection of samples from far flung locationshi Greater Cochin area. The various tests carried outare described in detail with procedures followed.

Due to the peculiar nature of marine clayswherein the geotechnical properties are significantlyaltered, by drying in almost all tests for physical propert­ies, special care has to be taken to arrive at meaningfulvalues. The Indian Standard Specifications ck) not dealwith the special attention required by marine clays especiallyduring preparation of samples. I.S.Procedures, if followed

as such, can ‘yield highly’ erroneous results iJ1 case «ofmarine clays. This aspect has been well brought out whilediscussing the procedures adopted for each property. Modi­fications or amendments required in case of each experimenthas also been presented, highlighting the need for each.

It was noticed during the preliminary experi­ments that ‘drying’ and methods of drying considerablyinfluence the physical and engineering properties of theseclays. Hence care was taken to study the various chara­cteristics under three initial conditions viz. moist,air dried and oven dried. How samples are prepared underthese three initial conditions for each test is describedin detail. Preparathmi of 'washed' samples and ‘soaked’samples for different tests is also dealt with.

The significant role, the dispersing agentplays in case of marine clays while carrying out the hydro­meter analysis runs been brought out. While <fliscussingthe consolidation tests (N1 marine clays, the improvementsthat can be made in conducting the test have been pointedout. .A different loading pattern, which ii; simpler, hasbeen adopted for the consolidation tests. The limitationsof the existing log 1: and .HE methods for determination

of coefficient of consolidation have been brought out.The rectangular hyperbola method suggested by Sridharan et al.(1987) has been discussed in detail.

It has already been pointed out that I.S. pro­cedure jknr free swell index can yield misleading resultseven in case of ordinary soils. In case of marine claysthe problem becomes more complex as drying of samplesalters its swelling characteristics. But Indian Standardsinsist on 21 dry specimen. for the ‘test. The proceduresuggeted by Sridharan et al. (1985) was found to be moreappropriate for marine clays, which was followed throughout

Attempts were made to improve the strengthcharacteristics of marine clays with 18 different additivesas listed in this chapter. Lime was found to be the mostsuitable stabilising agent. The procedure adopted forpreparatbmi of quick lime enui of stabilised soil samplesfor different tests is also presented.

Chapter SUI deals VHJX1 the physical propertiesof Cochin marine clays. The results of the index propert­ies vis-a-vis the initial condition cnf the samples. arelisted in detail for the first time. Tests on Atterberg

limits and shrinkage limit have yielded good ,correlationbetween plasticity index and liquid limit, liquid limitand clay content and shrinkage limit and clay content.

How the initial conditions of samples caninfluence the grain size distribution is also discussed.As marine clays mostly exist in the form of flocs, disper­sion of clay is very important in hydrometer analysisof marine clays. Through a: series of tests using eightdispersing agents, it has been proved that the I.S.recommend­ation is also the most suitable one for marine clays.

Through the conventional activity chart, Cochinmarine clays could be classified ‘active’ while moistand 'inactive' after drying. Free swell index could becorrelated with clay content and liquid limit. The influenceof pore fluids of different dielectric constants on thephysical properties such as liquid limit and free swellindex have been discussed in detail.

A significant finding reported iJ1 this chapteris the correlation between shear strength and water contentratio (which is the ratio of natural water content toliquid limit of the soil) which exist for the marine clays.

Excellent linear correlations could be obtained betweenwater content ratio and logarithm of shear strength witha high correlation coefficient even with marine clayscollected from locations, EM) kms apart, because they areof same geological origin. Similar correlations couldbe obtained for other soils also. More potential usesof these semilog plots between 1' and WCR are indicated.

Numerous consolidation tests conducted on these

clays could bring out many features of the compressibilitycharacteristics <1f Cochin marine clays ixu particular andother soils imm general ens discussed iJ1 chapter V. Theeffect of air drying and oven drying on the consolidationbehaviour has been brought out. The reliability of thecompression index CC in the determination of total settle­ment has been discussed pointing out that the CC values,as suggested by Indian Standards yield very high settlementvalues which are very rarely realised in field. The slopeof the e — log p curve in the region of consolidationpressure of 140T/m2 cm: 8OT/m2 need not ‘represent thecompression of the clay layer in field. Highlightingthese, a new ‘method called segmental compression indexmethod has been suggested for the calculation of consoli­dation settlements.

It has been shown in this work that durationof application of consolidation pressure influences theresistance tx> compressibility developed knr marine claysconsiderably. The development cnf this resistance duringsecondary compression has been well substantiated. Reboundcharacteristics can be indicative of bond strength developed.

An important offshoot of the long series ofconsolidation tests is the development of a new techniquecalled ‘log-log method‘ for the determination of preconsoli—dation pressure. It has been shown that the value ofpc can be obtained with greater ease and accuracy fromthe point of intersection of two straight lines drawnthrough the initial and final points in 51 log e-log pplot. The advantages of this method over the existingCasagrande method could be turmght cum: by comparing the

pc values obtained and the actual preconsolidation pressureat which the samples have been consolidated and unloaded

to seating load. The prior knowledge of pc of sampleshelped to establish the credentials of the new method.

The desirable changes brought in by air dryingof marine clays can be taken advantage of in the constructionof pavements and enbankments. It has been brought outthat the compressibility and strength characteristics

10

of air dried Cochin marine clays got vastly improved.This introduces the possibility of using this clay afterair drying. Particle aggregation by oven drying is almostirreversible.

As part of basic studies, experiments werealso conducted ‘with four fluids of cdifferent. dielectricconstant. The results clearly indicate that the clayminerals in Cochin marine soils is of most montmorillonite

type.

The engineering behaviour of lime-treated marineclays is discussed in chapter VI. Eventhough the chemistryof the lime stabilisation is rmn: fully’ understood, thefactors which can be the reason for the gain in strengthare discussed along with the contradiction that existin the findings of the different workers. Rather thangoing imnxb the complex reactions, the investigations havebeen directed to result oriented study on the improvementsin physical properties and compression behaviour.

After 51 preliminary study (N1 the developmentof shear strength over a period of one month, on treatmentwith 18 different additives, lime was identified as the

11

most beneficial one. Six percent kn! dry weight of limewas found quite adequate and a smrength gain as high aseighteen times has been achieved.

Eventhough the effect on liquid limit has beenerratic, plastic limit readily increased with lime treat­ment which brought down the plasticity index. The compressi­bility characteristics improved significantly with limecontent and curing gmuiod. Deformation of treated soilsreduced tx> 20-25% CHE compression cm? the untreated clay,

for pressures lower than the bond strength (quite analogousto preconsolidation pressure) developed during curing.Lower percentages of lime were found to register a fasterrate in gain of bond strength. While the value ofde/d(log p) decreased with time of curing and lime content,coefficient of consolidation also was found to decrease.

Chapter VII presents the electrical characteri­stics of Cochin marine clays. Investigations have beencarried out tn) measure electrical resistivity with varia­tions in water content, density and physico—chemicalenvironment. Since interpretations CHE field resistivitymeasurements are based on the absolute resistivity ofthe individual sxfid. layers, the laboratory determination

12

of these values are important. It was found that resisti­vity measurements are dependent on sample dimensions and

hence a standardisation of the test is essential.

Polarisation of water molecules by the soilinterferes with resistivity measurements to a great extentquestioning the validity of measurements and measuringtechniques. The need zflmr taking iJux> consoderation thedipole moment enui dielectric constant of tflna pore fluidis brought out. Still the potential of resistivity measure­ments as an easy and rapid technique to give an insightinto the geotechnical properties of soils is highlighted.The superiority of resistivity measurements with A.C.supply is discussed in this chapter.

Chapter VIII gives a detailed list of conclusionsdrawn from the various investigations carried out in thiswork.

Chapter II

REVIEW OF PAST WORK

2.1 COCHIN MARINE CLAYS

Most of the Greater Cochin area consists of marine

clays which are known for its high compressibility andpoor shear strength. The depth of the soft layer is consi­derable, often extending txn 30 tx> 40 metres. Hence it isnot economically feasible to replace them by better material

King (1884) perhaps was the earliest to reporton the geology of the area as part of his studies on mudbanks off the coast of Cochin and Alleppey. Accordingto him, 2500 years back, the sea washed upto the high rangesof Western Ghats. The land between the Western Ghats and

the present coastal line nuns once well above the sea andwas subsequently submerged. It was uplifted again byvolcanic action auui again partially covered tn! sea water.The uplifted area includes the coastal belt (10 to 30 kmwide and about 150 km long) starting from Crangannore atthe north to Quilon at the South. Most of Greater Cochinis situated in this belt.

13

14

Failures of embankments and bridge foundationsconstructed on these soft marine deposits have been reportedby Ramanatmalyer (19660. While Chekkidikad bridge failedwithin an year of construction due to differential settle­ment between central pier and abutment; the Chanthathottambridge failed by differential settlement of piers. Rotat­ional failure of embankments in Cochin Bye Pass could bestopped only with extensive berms.

Marine deposits can be found all along the coastalbelt cxf Indian Peninsula. Narasimha Rao andKodandaramaswamy (1984), based on investigatiomson samplesfrom Cochin and Madras, have drawn some useful conclusions

on Indian marine clays. Indian marine clays are depositedat high water contents close to liquid limit giving riseto poor consistency and high void ratio. The soils havehigh colloidal activity and are low to medium sensitive.

2.2 PHYSICAL PROPERTIES

Jagadish Narain and Ramanathan (1967) were perhaps

the earliest to observe the physical properties of marineclays in Kerala. Amwording to them, the marine clays ofthis region undergo irreversible changes in plasticitycharacteristics. Air drying was found to cause formationof aggregates, which was considered responsible for thechange in plasticity.

15

The phenomenon of reduction in plasticity ondrying has been attributed to dehydration of hydrated iron/aluminium sesquioxides and «of time halloysite Inineral, byFrost (1967). He brings out the significant changes duringoven drying and indicates the importance of carrying outtests (N1 soil ixm its natural state. Organic matter andcarbonates are recognised as major cementing agents contri­buting txb particle aggregathmi and reduction in Atterberglimits upon drying (Rao et al., 1989). They indicate thedominance of calciunn and ‘magnesium ions :hi the» exchange

sites and presence of a high salt concentration (9.4 gm/litre) which facilitates strong interparticle attractionand a close spacing of the particles. In their study theyhave ruled out the possibility of coulombic particle-cation­particle linkage. According tub them, time aggregation ofparticles and variations in plasticity characteristicsis due to cohesion from surface tension forces arisingfrom capillary minisci formed between the particles atthe boundaries of the soil specimen during drying.

Atterberg limits have been in wide use for pre­liminary soil classification. Seed et al. (1964) presentedan exhaustive work dealing with the fundamental aspectsof the empirically defined values. Sridharan and Rao (1975)discuss in detail the mechanisms controlling the liquid

16

limit of clays. Atterberg limit tests are analogous toshear tests, The results obtained by Casagrande (1958)and Norman (1958) by the use of direct shear and vane shearapparatuses, respectively, indicate that the strength atliquid limit is of the range 15-30 gm/cm2.

The shear strength must be due only to the netattractive forces of the particles. Seed (1964) suggestedthat the liquid limit depends on the interparticle forcesand therefore on the surface characteristics of the soil.But Warkentin (1961) interpreted liquid limit as the dist­ance between particles or units of particles at which theforces of interaction become sufficiently weak to ;alloweasy movement of the particles or units relative to eachother.

In case» of normally consolidated 1narine clays,Skempton and Bjerrum have found that there is a well definedcorrelation between Cu/p and plasticity index and any devia­tion from this relation can be considered as a test forsampling disturbances (Bishop & Henkel, 1962). ‘A similarcorrelation has been suggested for effective angle of shear­ing resistance ¢ against plasticity index where ¢ reduceswith plasticity index (Bjerrum & Simons, 1960).

17

Narain anui Ramanathan (1970), while <discussingthe» geotechnical properties of the marine clays fromKuttanad area, focusses attention on the peculiarity ofthe soil where there is a variation in properties causedby air drying. The liquid limit considerably reduced onair drying; They established that air drying caused form­ation of aggregates and this was responsible for theirreversible reduction in plasticity. They’ also provedthat correlation of the type proposed by Skempton andBjerrum cannot be considered as valid for clays where changes

in soil structure are predominant. They also showed thatthe mechanical properties are dependent (N1 soil structurewhich is a function of interparticle forces as well asparticle size and arrangement.

Most of the soil testing is of either an inferen­tial or an environmental nature. An inferential testingprogram is one in which the properties are not directlymeasured but inferred through empirical correlations. TheAtterberg tests, proposed by Atterberg (1911), was intro­duced into soil mechanics by Terzaghic (1925). Casagrande(1958) perfected and standardised it as a percussion test:which became the most inferential soil test with wide uni­versal acceptance.

18

Soil with water contents an: their liquid limitsas discussed earlier, possess definite but small shearingresistance which was successfully measured by many(Youssef et al., 1965: Hajela & Bhatnagar, 1972). Theflow index obtained from the liquid limit test can be usedwith advantage for determining other properties such asplastic limit. The one point method has received ‘wideattention as a simple procedure. The cone penetrationmethod is, lfl some cases, especially’ those lfl which ‘thepore fluid zhs other tfluni water, very convenient comparedto the percussion method. The validity of the cone penetra­tiLH1 test has been studied iJ1 detail tn! Karlsson (1961)and Clayton and Jukes (1978).

Based on the same reasoning, the possibilityof developing the (NH? point method for time cone penetra­tion method of liquid limit has been successfully examinedby Nagaraj and Jayadeva (1981). They have shown that ifCasagrande percussion apparatus is used.

wWI. - l—K(log N - log 25) (2.2.l)

Another expression for determination of liquidlimit by one point method is of the form

W <—”— )‘’C (2.2.2)—— - 2

19

Mohan and Goel (1959) have shown that the varia­

tion in d\ is less than 1% for the range of N between 20and 30.

The drawbacks of time percussion test, such asdifficulty in cutting a groove in soils of low plasticity,and the tendency of soils to slip, have been overcome inthe cxnma penetrometer test. Nagaraj enui Jayadeva (1981)have developed a one-point method which can be used fordetermining the liquid limit from cone penetration test

wL = w/0.77 log D (2.2.3a)

wL = w/(0.65 + 0.0l75D) (2.2.3b)

Several attempts have been made to link plasticityindex with liquid limit through empirical relations(Casagrande, 1948; Dersseault & Scafe, 1979; Seed et al.,1964: Wroth 5; Wood, 1978). ‘All these relations have beensuggested on the presumption that plasticity index andliquid limit are fundamentally independent parameters.After examining the data of 520 samples and plotting ona plasticity index vs. liquid limit graph, Nagaraj andJayadeva obtained a linear correlation

PI = O.74(LL - 8) (2.2.4)with a correlation coefficient of 05957.

20

They have also shown that plasticity index andliquid limit are not independent parameters but the formeris directly related to the liquid limit water content.

Attempts have been made to correlate Atterberglimits with surface area, cation exchange capacity, swellingbehavioury California Bearing’ Ratio, compressibility’ etc.and to use alternate test methods like the cone penetrationmethod (Uppal & Aggarwal, 1958), the dye adsorption method(Ramachandran ex: al., 1963), tflua vane shear method(Darienzo et al., 1963) and the soil moisture tension method(Russel et al., 1970). But it remains a fact that investi­gations on the physical mechanism governing the liquidlimit of a soil have been very limited.

Sridharan et al. (1975) have investigated indetail the possible mechanisms governing the liquid limitof kaolinite and montmorillonite types of clays. To alterthe force fields governing the particulate system, sixorganic fluids and water ‘with ‘wide ‘variations jfl theirdielectric properties have been used in the investigation.The cone penetrometer method was chosen for the study asit was found convenient especially with organic pore fluids.Their investigations showed that for kaolinite, a non­expanding lattice type cnf clay, the contribution due ‘to

21

diffuse double layer is insignificant and the liquid limitis primarily governed by the shearing resistance at theparticle level. Hence emu increase iml dielectric constantreduces the liquid limit. In case cnf montmorillonite,the liquid ljmfii: is governed knr the shearing resistance.Being an} expanding lattice type of clay, the contributionfrom the diffused double layer overrides and primarilygoverns the liquid limit.

Studies by Sridharan et al. (1988) on kaoliniteclay showed that the liquid limit of these clays has nocorrelation with the percentage of clay size fraction.The liquid limit of kaolinite is not a function of diffusedouble layer thickness.

The shear strength of fine grained soils is largely

dependent on their water content, W0. Wroth and Wood (1978)gave ea linear relationship between xv and the undrained

shear strength Cu in the following equation

w + A log Cu = constant (2.2.5)where A is a constant.

But the result obtained by Skempton and Northey(1953) indicated that the ‘relationship> between time water

22

content or liquidity index IL and Cu is not a straightline CH1 a semilogarithmic plot. Inn: both agreed that theshear strength of a soil at plastic limit is 100 timesthat at its liquid limit. According to Wroth and Wood(1978) in the cone penetration apparatus the plastic limitvalue corresponds to the water content which permits apenetration of 2 mm, which is too low to be achieved. Thishas been overcome by making use of a plot between liquidityindex and penetration wherein the point representing theplastic limit is obtained from the intersection of twolines (Harrison, 1988).

2.3 CONSOLIDATION

The most important bench mark in the studieson consolidation was set by Terzaghi in 1923, eventhoughsome aspects of consolidation such as pore pressure dissi­pation was understood even during Sumerian civilisation(Kerisel, l985). In the last 60 years considerable workand progress have been achieved to improve our understanding

of clay behaviour. But it has to be conceded that under­standing tine problem fully has run: been achieved yet andsoil engineers even now are wondering whether there isa combination cxf primary enui secondary compression duringprimary consolidation.

23

The basic and most general equation for onedimensional consolidation can be written (Berry & Poskilt,1972) as

dev = l+e° E. ( 5.. EE')aE— rw dz l+e dz (2.3.l)

where

gv = vertical strain2 = depth related to initial thicknesst = timeeo = initial void ratioe = present void ratiok = permeability

Qw = unit weight of wateru' = excess pore water pressure.

The marine clay of eastern Canada, called Ledaclay, covers the broad, highly developed regions of Ottawaand St.Lawrence river valleys. One of the notable featuresof this marine clay was an unusually sharp change in compre­ssibility' at time preconsolidation load, vflUxfi1 results inextremely high compression indices. Hamilton and Crawford

(1959) have investigated this clay in great detail anddrawn many useful conclusions. The result showed that

24

the size of load increments do not affect the e - log pcurves. A method was developed to determine the end ofprimary consolidation under a load increment. A rapid methodcalled controlled strain type of test for preconsolidationwas perfected during the studies on Leda clay.

In 1979, Butterfield reported that for soft soils,the log f vs. log p relations could be represented by astraight line im1 the range cm? normal consolidation wheref is the specific volume defined as f = l+e. Oikawa (1987)extended these studies through investigations (N1 a widerange of soils with natural water content varying from25-941% and natural void ratio ranging over (DX7 to 17.The results showed that time log if - log E) curves areessentially composed of two segments of straight lines.The stress at which the two line segments of log f - log pcurves intersect agrees well with the cmmsolidation yieldstress which is obtained from the graphical method proposedby Casagrande.

Through a series of consolidation tests onWhangamarino clay, Newland and Alley (1960) could arriveat definite trends involving parameters like pressureincrement ratio, thickness of sample etc. They showedthat when time rate curves are plotted in terms of change

25

in void ratio vs. the logarithm of time, the slope of thesecondary tail is independent of ea wide range of factors.For a given duration of increment, the ratio between thevoid ratio change occurrhug as secondary compression, andthe total consolidation in the increment decreases, ashigher pressure increment ratios are used. They have pointedout that considerable shortening of standard consolidationtest, without loss lfl accuracy, may Ema obtained tn! usingmuch larger pressure increment ratios and restricting theduration of increments to the time necessary for the comple­tion of primary consolidation.

In case of marine clays, the electrolyte concen­tration of free pore water can vary. Mesri and Olson(1971) have shown that kxflfli the electrolyte concentrationin the free pore water and the pH do not influence theconsolidation curves CHE calcium montmorillonite. Consoli­

dation tests in which organic fluids were used demonstratedthat swelling of montmorillonite is caused by eitheradsorption of the pore fluid or formation of diffuse doublelayer.

2.3.1 Constant rate of strain tests

In the last inn) decades, numerous constant rateof strain tests (CRS tests) have been performed on natural

26

soils at ‘various strain rates. CRS studies (H1 easternCanada clays tux Crawford (1965), Vaid en: al. (1979) andLeroueil et al. (1983), on Swedish clay by Sallfors (1975),on Belfast clay by Graham et al. (1983) are well accepted.All the tests sfimwv that the strain rate influences thecompression curves of clays. At a given strain, the higherthe strain rate, the higher the effective stress.

Constant rate of loading tests (Jarret, 1967),stage loading tests (Larsson, 1981) and controlled gradienttests (Leroueil et al., 1983) confirm the important effectsof strain. In stage loading tests, such as the conventional24 hours oedometer test, it is possible to characterisetwo different phases primary’ and secondary. Eventhoughvarious definitions have been given iknr these two phases(Bjerrum, 1967: Leonards, 1977), the definition of Crawford(1985) is most suitable. .According to him "during theso called primary phase, the permeability cnf the soil isthe predominant factor controlling the rate of volume changeand during the secondary phase, it is the resistance ofthe structure that determines the rate".

In a constant rate of strain test, the stress­strain curve depends on the strain rate used. Data compiledby Leroueil et a1. (1983) for eastern Canada clays show

27

that the preconsolidation pressure dobtained in CRS testsis on average 28% higher than that obtained in conventionaltests. Holtz et al. (1986) have found similar resultson very stiff Montalto de Castro clay.

2.3.2 Compression index

Compression index (as, which is time slope of theplot of <2 - 1og E) curve, represents tflua compressibilityof the soil. To have an independent method of estimation,many investigators in the past have empirically linkedthe compression index with the inferential and state para­meters; of the soil (Hough, 1957: Oswald, 1980: Koppula,1981). Since the state of soil in nature is varying andcomplex, a unique- CC equation is not tenable. Furtherthe empirical CC equations which have no scientific basiscan be used only in specific soil states.

Nagaraj and Eminivasa Murthy (1986) have cmiti—

cally examined the known empirical compression index equa­tions ix) identify their possible scientific basis. Theyhave also tried tn) define time soil state :h1 which theseequations can be used. For this they have used the rationallygenerated compressibility equation (Nagaraj & SrinivasaMurthy, 1983) which is based on the Gouy Chapman diffuse

28

double layer theory and is applicable to normally consoli­dated saturated uncemented soils. Their study has indi­

cated that the (e/eL) — (R-A) relationship is more generaland unique than the d - (R-A) relationship. The parameter

eL inherently accounts for the variation in physico—chemicalenvironment in addition to the specific surface of thesoil. Two compatible compression index equations ie.,

CC = 0.234 eL and CC = 0.39 e have been rationally derived.

For saturated normally consolidated clays, the

compression index, CC is the slope of the straight lineportion of the e - log p curve. Among the various corre­lations available iJ1 published literature relating compre­ssion index and liquid limit water contents, Skempton's(1944) relationship is time most widely’ accepted. Heobserved that for samples selected at random, from differentparts of the ‘world, where» the initial moisture contentswere at liquid limit water contents all points are locatedclose to the line which is represented tn; the equation

CC = 0.007(LL — lO) (2.3.2.l)

The classical Gouy—Chapman diffuse double layer

theory, has been effectively used by Nagaraj and SrinivasaMurthy (1983) to evolve a generalised e — log p relationship

e

L= 1.o99—o.2237 log p (2.3.2.2)

29

The involved microparameters, specific surfacesand half-space distances between clay platelets are success­fully replaced by easily’ measurable Imicroparameters suchas liquid limit water contents and insitu void ratios inthe development of the above equation.

The relationship between CC and soil compressi­bility is not a direct one, and wrong conclusions are easilydrawn about the relative compressibilities of soils by

comparing values of Ca: or liquid limit. Thee manner inwhichs CC is presented implies that soils with high valuesof CC naturally have high compressibility. For a liquidlimit of 200, CC = 1.33 and for 100, the value of CC = 0.63.Comparing these two CC values one would think that theformer will be twice as compressible as the latter.

The expressions for consolidation settlementis

S : pO+L.-“P1+e lO—"”’—— (2.3.2.3)o powhere

S = settlement (m)

H = thickness of clay layer (m)

e = initial void ratio at pressure pop = effective overburden pressure

Lgp = the pressure increment.

30

It is evident from this expression that the soilparameter indicating compressibility is c

l+eO and rufl: CCalone. Saxena et al. (1978) define CC/l+eO as compressionratio.

Wesley (1988) has examined tflme relative signi­

ficance of CC, CR and mv as measures of compressibilityand their relationship to Atterberg limits. The investi­gations were based on samples from three soil groups-­sedimentary clays, tropical red clays and volcanic ashsoils. The results showed that remoulded soils undergoingvirgin consolidation, the compression ratio CR (or m )vis 23 better indicator <1f soil compressibility. For un­

disturbed soils, the recompression ratio EH2 = (CS/l+eO)is a better indicator of in situ compressibility than CR.

2.4 LIME STABILISATION OF SOFT CLAYS

Eventhough the use of lime dates back to Romans,the first attempt to improve soil by lime was perhaps madein 1924 lfl the state (Hf Missouri as ani experiment onconstruction of a road using hydrated lime (Uppal & Palit,1964).

Clayey soils can be stabilised by the additionof ea small percentage of ljmmu It enhances many cm? the

31

engineering properties of the soil. Generally the amountoflime required to modify a clay soil varies from 1 to 3%,while that required for cementation varies from 2 to 8%(Bell, 1988). Montmorillonite clays xxxxxnui more readilyto lime treatment than kaolinites.

When lime is added to clayey soils, calcium ionsare combined with clay minerals which leads to an improve­ment imm soil workability. There is eni immediate increasein plastic limit and a decrease in liquid limit. The optimumlime content which produces maximum plastic limit is calledlime fixation point. Lime in excess of this is used forcementation process and increases the strength of the soil.

When lime is used to stabilise clay; it formsa calcium silicate gel which coats and binds the lumpsof clay together and occupies the pores in the soil. Thegel then crystallises to form an interlocking structure.

The quantity of lime needed is related to theclay mineral content. Ingles and Metcalf (1972) suggestedthat the addition of upto 3% lime would modify silty clays,heavy clays and very heavy clays. While 2 to 4% was requiredfor the stabilisation of silty clay and 2 to 8% was proposedfor stabilisation of heavy and very heavy clays.

32

D1 most cases the effects of lime on pdasticityof clay is rmnxa or less instantaneous (Bell, 1988). Asexplained by Davidson and Handy (1960) calcium ions fromlime causes a reduction in the plasticity of cohesive soils,so that they become more friable and more easily worked.Very small quantities of lime only are required to bringabout these changes in plasticity. Tests carried out byU.S.Bureau cmf Reclamation indicated tflun: the addition of

4% lime reduced plasticity index (Hf clay from 47 to 12%(Anon, l975). However iJ1 case cflf kaolinite clays, limemay sometimes increase the plasticity index.

Mateous (l964) showed that the minimum amount

of hydrated Jimmy required tx> be added tx> montmorilloniteclays for maximum increase in plastic limit is given by

PL _ % 2 microns clay(max) _ 35 + 1.25 (2.4-1)

The addition of lime to clayey soils reducestheir potential iknr swelling. With small additions highcalcium hydrated lime is more effective than other hydratedlimes. Quick limes appear to be more effective than hydra­ted limes as far as improvement of shrinkage characteristicsare concerned (Anon, 1975).

33

Compared ix) cement stabilised soils, compactionof lime treated soils is more tolerant. Not only is delayless critical, so also is compaction moisture content.In other words, lime treatment flattens the compactioncurves. This ensures that a given percentage of prescribeddensity can be achieved over a much wider range of moisturecontent.

The addition of lime increases the optimum moisturecontent and reduces ‘maximunl dry" density’ for" the same

compactive effort (Bell, 1988). However the strength gainin the soil normally will more than compensate for changesin compaction optima, EHK3 they should run: be regarded asdisadvantageous.

The strength of lime soil mixtures is influencedby several factors such as soil type, type of lime and.amount added, curing time, moisture content, and timeelapsed between mixing and compaction (Ingles 5; Metcalf,1972). Soil mixed vdifim low lime content attains maximumstrength in less time than that to which a higher contentof lime has been added. Strength does not increase linearlywith lime content and in fact, excessive addition of limemay reduce strength (Bell, 1988). The optimum lime content

34

tends to range from 4.5-8%, higher values occurring insoils with higher clay fractions. This decrease is becauselime itself has neither appreciable friction nor cohesion.

Of late, lime column technique has been introducedas a foundation improvement technique in soft clays. Limecolumn (xvi be used txa support light tun medium structuresin soft clays. Somayazulu et al. (1984) carried out detailedmodel studies (N1 lime columns shi test tanks vdth. pilesof 50 mm diameter and 300 mm depth, in soft clay at amoisture content close to liquid limit. The results indi­cated that lime column foundations can tackle severalproblems in clays. Lime seeps from the columns intosurrounding soil. There is considerable reduction inplasticity index and significant increase in particle sizedue to aggregation.

The reactivity of Japanese marine soils to limetreatment is quite high as evaluated by unconfined compress­

ive strength qu (Terashi et al., 1977). Deformation modulus,E50, which is the secant modulus at qu/2 and strain atfailure show that the residual strength at failure is verylow and the strain at failure is small. These indicatethe brittle nature of the treated Kawasaki marine clay.

35

The treated marine~ clay’ behaves .like EH1 overconsolidated

soil due to the development of shear strength by bonding.

Engineering properties of lime treated soilshave been studied in detail by highway engineers for baseor sub—base material. For the application of lime in found­ation engineering, development cflf deep ix: situ mechanicalmixing method has been very helpful. This method is calledthe deep lime mixing method or D.L.M. method or D.M. method.

The machine consists of one steel pipe and several shaftsfor mixing blades. (Chemical agents in slurry“ form aresupplied into the ground by pressure through small flexiblepipe.

Another machine has been developed in Japan(Yamanouchi, l978) for lime stabilisation upto a depthof 1.3 metre while travelling at a speed of 50 to 200 mper hour. In order txa facilitate travel CH1 soft ground,the machine is given 51 caterpillar made (ME wooden planksfor lowering the contact pressure 1x3 0.1 kg/cm2. IX testroad stabilised with lime using the above machine was375 m long with six kinds of sections, heavily instrumentedwith settlement meters, inclinometers, earth pressure cells,and pore water pressure meters. The road was subjected

36

to repeated truck running reaching 30,000 repetitions.The stabilised bed withstood the test well and provideduseful data for analytical studies.

Since the use of lime stabilisation in foundation

engineering is closely linked with machinery for deep limemixing, the development of such machinery is equallyimportant.

One of the major field trials ever undertakenin India to stabilise marine clay was at the Outer Harbourin Visakhapatnam (Natarajan et al., 1982). The site ofthe ore handling yard underlain by 12 metres of soft marineclay cxf very lxna shear strength enui high compressibility,was stabilised using sand drains and sand wicks preloadedwith embankments. But the reasonable period of preloadingin stages txa develop strength TX) store E9 metres of ironore was as long as 4 to 5 years.

2.5 ELECTRICAL RESISTIVITY OF SOILS

One area where the electrical resistivity ofsoil 113 of paramount importance is 1M1 the interpretationof results from electrical resistivity ground surveys(Higginbotham, 1976). Other areas of relevance includeapplications txa non-destructive testing <1f concrete piles(Mccarter, 1981); the grounding characteristics of

37

transmission tower foundations: electro-osmotic drainingand consolidation of clays (Butterfield & Johnson, 1980).

Variation of electrical resistivity of soil withmoisture content has kxxxi the subject of little investi­gation (Mccarter, 1984). At low moisture contents, resisti­vity decreases rapidly with increasing’ moisture content.Studies on remoulded Cheshire clay showed that resistivityis a function of

a) Moisture content

b) Air—void ratio

c) Degree of saturationd) The fractional volunme of water ix) the soil

which is defined as the ratio of the volumeof water zhi the sample to time total volumeof sample.

The results indicated that resistivity vs. fract­ional volume cnf water relationships have been establishedfor two different clays over a practical range of moisturecontents, and aa unique relationship> exists: between. theseparameters for each clay.

The Offset Wenner System cnf vertical electricalsounding has been developed to reduce the spurious effects

38

on sounding curves which are produced by near surface varia­tions imm ground resistivity. Barker CHNMB) demonstratedtuna high quality wenner apparent resistivity’ curves (unibe easily obtained in engineering site investigations.The new system eliminates the electrode spacing errorsand increases productivity.

One of the problems faced by the geophysicalengineers is the selection of the appropriate choice ofinterpretation method. There are ea number of techniquesavailable but no single method can be considered fullysatisfactory. Kate and Khichchu Mal (1983) have shownthat Moore's cumulative plot ‘method is nunxe reliablecompared to other methods.

Murthy and Chandra (1981) have investigated theuse of electrical resistivity method for foundation analysisEventhough it is 21 quick method, they are of the opinionthat only the general character of the soil can be estimatedand it has to be supplemented by subsoil borings.

From the electrical resistivity survey of anunstable slope~ at Simla, Malhotra (1981) showed thatresistivity results match very well with other geophysicalsurveys.

39

When an impulse of alternating current is appliedto a clay-water-electrolyte system, its response can bemeasured jfl terms of aa resistance R anui a capacitance C.Capacitance can be expressed in terms of dielectric constant,

which ix; the ratio CH3 the measured capacitance tn: thecapacitance of vacuum. The dielectric constant in the6 8radio frequency range of lO txb M3 Hz is referred to asapparent dielectric constant

e‘: 223. (2.5.1)A60

where

d = the length of sampleA = cross sectional areago = dielectric constant of vaccum

(8.85x1o'14 farad cm-1)

Arulanandan and Smith (1978) have shown thatE’ is 51 function of frequency. The difference of 6} bet­ween the frequencies 3xlO6 Hz tub 75xlO6 Hz ii; referredtxa as dielectric dispersion A.€' (Fernando en: al., 1977).Lie can be made use to identify the clay mineral, estimateclay content and water content, cation exchange‘ capacityetc. (Fernando &: Doshi, l984). According ix) Arulanandanet al. (1973) the value of dielectric dispersion can beused to characterise clays without destroying or separatingthe soil mass into different sizes.

Chapter III

HATER IALS AND METHODS

3.1 INTRODUCTION

The aim of the present study has been to investi­gate in detail the physical properties and engineeringbehaviour of the deep marine clay deposits covering extensiveareas in Greater Cochin. Since a comprehensive study wasintended, the results will be more reliable and findingswill have wider acceptability if sampling and testing coveran area as extensive as possible. Further in an investi­gation as envisaged herein, the test results can crystalliseand converge txn well—substantiated conclusions only if thesoils collected have the same geological origin and identicalphysico-chemical environment which controlled the sediment­ation process. When the former calls for as extensive anarea as possible, the latter tends to confine to narrowlimits. The ideal extent lies in between "where samplingis done over an area as large as possible without’ causingserious losses in uniformity of samples, leading to disper­shmi of results. Hence the significance in the choice oflocations from which samples are to be collected cannotbe overemphasized.

40

41

Samples were collected from seven locations spreadover Greater Cochin area. The sites are:

l. Munambam

2. Parur3. Cheranelloor

4. Elamkulam

5. Maradu

6. Nettoor7. Kumbalam

The locations of these seven sites are shown inFig.3.l.l. While Munambenn is at the northern boundary:Kumbalam is the southern tip of Greater Cochin with a dist­ance of about 50 km between them.

The sampling locations were chosen after scrutini­sing as many soil investigation reports as possible and.after conducting a detailed reconnaissance survey. In almostall locations thick uniform layers of marine clays couldbe obtained only after 2 to 3 metres. Hence undisturbedand representative samples could be collected only frombore holes advanced by shell and auger method. Undisturbedsamples were collected from different depths to study theengineering properties. At Nettoor, thick layers of marine

Fig. 3-1-1 MAP OF 6. ER COCHIN-IOWING THE LOCATIONS.

43

clay were available at .shallow' depths. Hence sampling atthis site was done by open excavation.

It can be seen that sampling locations at Munambam,Parur, Kumbalam and Maradu were within a few metres of thesaline backwaters. Nettoor and Elamkulam were a littleinterior and Cheranelloor was almost a kilometre away fromthe backwaters. These locations helped to cover a widerrange of soil samples.

Soil profiles

Fig.3.l.2a and b show the soil profiles of thesix locations where samples were collected from bore holes.At Munambam the marine clay layer was encountered from8.0 tn) 14.5 metres from ground level. In Parurz the claylayers were met with between 5.5 and 13.5 metres. The claylayer at Cheranelloor was a thin seam just about a metrethick at a depth of 5 metres.

At Elamkulam, the marine clay layers were extremely

soft as indicated by the zero N value. The collection ofundisturbed samples met with some difficulties here as thesoft clays often failed to hold on to the sides of the sampl­ing tubes. The soil profile at Maradu shows medium stiff

.mm._Eom,._ dom J<U_&>._. E.\_.m .9...

__ 1..q u 2 K 1 ,:

ioumzxu N u z \ K\ooo3 ouifiuo E: \.. . \\ K

m u z m z to.>43 52% E \ q z \ ­

_ z - m

\ \M ><4u uz_m<: § %

a N u Z \\\ 1 m

N u zoz<m 53.5 H _..

.. ._.._ .. q

oz<m E

..H.. .. N

moofimz<Ezu m3._<a :<m_2<z:z .3 3 m

I» Q

4.

oum<:u

03 omfiomo Ed><._u 52.3 §><._u m_z_m<: §oz<m $23 Hoz<m E

.mm._EomE .__Om 4<u_n_>._...

w\\w\\HZ

34.... .m:

m H z

N n z\\H _ "2 Nm 2 Ko n 2 K/

., / ...

WI Mu /u.w.u:>o

:9.u.m.<: :<._3.2<d

1

Ac:

.:_ o

40 4mmnae

46

marine clay between 5.0 and 10.7 metres. At Kumbalam themarine clay deposit started at 6.5 ‘metres below «groundlevel.

3.2 FIELD COLLECTION OF SAMPLES

Considerable quantities of Samples were requiredfor the numerous tests carried out on soil samples collectedfrom seven sites as listed above. Undisturbed sampleswere collected for determination of engineering propertiesand representative samples were collected for index propert­ies. The procedure adopted for collection of samples isdescribed in detail below.

Since the top layers in almost all locations exceptNettoor consisted of sandy soils, thick layers cnf marineclay deposits were available» only’ at «depths varying from3 to 9 metres. Bore holes were taken to the clay layersfor collection of samples. Shell and auger method was usedfor advancing bore holes. The bore holes had a diameterof 150 mm. Casing pipes with an internal diameter of150 mm were introduced simultaneously with boring operationsso that the sides did not cave in and the loose soil couldbe taken out with auger or shell before a standard penetra­tion test was conducted or an undisturbed sample was

47

collected. Thus EH1 accurate logging cu? soil profile couldbe done. Boring operations were carried out as per thedirection given in IS: 1892-1979: Code of Practice for Sur­face Investigation for Foundations.

Representative samples were collected using anauger and immediately transferred to polythene bags withoutpermittimg any loss of fines or pore water. The polythenebags were sealed immediately and transferred to the labo­ratory on the same day where they were preserved under humidconditions.

Undisturbed samples were collected in samplingtubes (if 100 rmn internal diameter provided vdifil a cuttingedge. The inside diameter‘ of tflue cutting edge ‘was Ikepttwo percent less tfluul the inside diameter CM? the samplingtubes so tflunz the frictional drag Cfll the sample from thewall of the tube is reduced.

Since the marine clay samples were collected fromsoft clay formations, an area ratio of 7.5 percent wasadopted for time cutting edge. This jj3 sufficiently’ lessthan the maximum value of ten percent recommended for softand sensitive clays.

48

The samples collected in sampling tubes were trimmed

on both ends and immediately sealed with molten wax to suffi­cient thickness so that the natural water content, the fielddensity and the soil structure are kept intact. They werekept in sample boxes and transferred to laboratory on thesame day and preserved under humid conditions.

Bentonite slurry was never used during the boringoperations as it might contaminate the soil samples.

In case cnf the site en: Nettoor, thick deposits ofmarine clay were available at shallow depths. Therefore inthis case alone, samples were collected by open excavation.

The method of sampling from open pits was moreadvantageous as it ‘was cheaper and faster. More samplescould be collected from open pits than from bore holes.But since the water table in Cochin is very high (less thana metre in Nettoor area) dewatering had to be arranged duringsampling.

Since the top layers consisted of sandy clay depositsupto 1 In, top soil was removed upto this depth. The sampleCOlleCtiOn was done in three stages. At first, samples

49

were collected from ea depth of ]_ to 1.5 mm A number oflOO Imn diameter sampling tnflxxs were pushed ixnxn this layer

and samples collected and sealed immediately. Representativesamples were collected in polythene bags. The debris wasthen removed upto 1.5 rn and sampling was continued. Theprocess was repeated for the third layer from 2 m.

For carrying out some tests, bore hole ‘water ‘wasrequired so that the salinity in the pore water is not dimi­nished knz the addition «of distilled water. The followingprocedure was adopted for collection of bore hole water.Tight—fitting casing pipes were introduced to the middleof the clay layer during boring. The loose material in thebore hole was removed by augers and the water was baled outcompletely using 51 shell. The nmmth cm? the bore hole wascovered and left for overnight. Pore water from the claystratum which oozed out during the night was collected thenext day and preserved in polythene bottles.

3.3 PREPARATION OF SAMPLES FOR LABORATORY TESTS

Based on the results of some preliminary tests forthe index properties of (Cochin marine claysq it was seenthat drying influences these values significantly. For acomprehensive study of the geotechnical properties of Cochin

50

marine clays, samples with four different initial conditionswere required for the laboratory investigations. They are:

1. Moist samples

2. Air dried samples3. Oven dried samples, and

4. Washed samples

When large quantities of soft sediments arerequired, the main problem faced is the lack of uniformityeven among the samples collected from time same «depth jfldifferent bore holes. Lack of uniformity in soil samplestested may seriously affect the correlation between indexand engineering properties. To overcome this difficulty,representative samples collected from same depth but fromdifferent bore holes of the same site were pooled togetherand rnixed thoroughly into ea uniform HESS enui repacked inpolythene bags. This is designated as the ‘moist’ sampleof Cochin marine clay. D1 order to study the propertiesof these clays without the marine pore water and excesssalts, representative samples were repeatedly washed inplastic buckets with distilled ‘water ‘taking extreme- carenot tn) lose any fines. Since» the entire clay fractionin case of Cochin marine clays exist in the form of flocs,the supernatant water above the soil being washed in plastic

51

buckets, was drained out by siphoning without any distur­bance to the soil suspension. This was repeated a numberof times. After a few washings it was observed at timesthat the colour of water turned light yellow and sediment­ation took more time. Samples washed like this were allowedto lose their water content by exposure to air till themoisture content became slightly above the liquid limitof moist sample. These samples are designated as 'washed'samples and are preserved in polythene bags in humidatmosphere.

To prepare ‘air’ dried‘ specimen, representativesamples were spread in large trays and dried under roomtemperature (30:4°C) and humidity (60:lO%) till equilibriumis reached which took about 15 «days. The lumps formedduring drying were broken by 51 wooden mallet. The sample:towards the end of drying were pulverised using a heavyhammer, and passed through 425 Inicron sieve ‘without anyloss of material.

‘Oven dried‘ samsples were prepared by dryingair dried samples in an oven at lO5—llO°C.

52

3.4 ATTERBERG LIMITS

IS 2720 (Part I) 1972, ‘Preparation of Dry SoilSamples for Various Tests‘ lays down the procedure forpreparathmi of samples for various tests. It also givesthe approximate quantity cnf dry sample required for eachtest. As per time code, the specimen required for liquidlimit iii 270 gm cm? air dried sample passing through 425micron sieve.

Since air drying brings in significant changesif} the plasticity CHE marine clays, the liquid limit fromair dried samples will show considerably low values. Henceair dried samples cannot be used for determination of liquidlimit. IS 2720 (Part V) 1970 indicates that wet soil alsocan be used for the liquid limit tests. To prepare samplepassing through 425 Ann sieve, the code recommends rubbing

the wet soil through a 425 um IS sieve until a sufficientquantity is obtained. The code observes that the resultsfrom the two procedures for preparation of sample- maydiffer. It accepts both values, perhaps on the presumptionthat the values may not differ significantly. But in thecase of marine clays this difference is considerable. Theliquid limit of marine clays reduces by 20-30% on air dryingand 40-60% on oven drying. Hence only 'moist' soil can

53

be used for the determination of liquid limit in case ofmarine soils.

To obtain the flow curve, the water content ofthe soil sample is varied usually by addition of distilledwater. In the case of marine clays the pore water issaline and the salinity can vary with the addition ofdistilled water. The salinity can be kept unaltered ifbore hole water is used for the tests. To examine theinfluence of this parameter on the liquid limit values,tests were conducted using both distilled water and borehole water. The results are presented in Table 3.4.1.

Sample of marine clay from Parur in the northand Kumbalam in south of Greater Cochin situated at a dist­

ance of around 40 km, were tested and results presented.They show that the values of liquid limit are essentiallythe same whether bore water is used or not. Hence thetests can be conducted using distilled water without anydiscernible error.

In the case of plastic limit, IS 2720 (Part I)1972 recommends 50 gm of air dried soil passing through

54

umumz mac: wuon

ow.¢ o.mH m.nm o.mm m.mm + Hflom umfioz An

uwum3 ©®HHfiuwfi©

mn.w m.mH 0.00 m.mm m.om + Hfiom umfloz Am emfimnesx .m

umumz mac: wnon

mm.¢ fi.m~ m.oo m.Hv o.moH + Hflom umfloz An

umumz fimaaflumfiv

wv.v v.Hm o.mm m.ov m.mm + Hflom umfloz Am pspmm .H

352 E; E Q; Q;

6?: fie: 3?: fie: fie:

.Zd3mm5um mmmxcflucm >ufioflummHm uflummam ©flSUwA wwamemm we wmwe coflumuoq .oz.Hm

mafia: WAGE mmom mo aommmm

H.v.m magma

55

425 gun sieve. For reasons mentioned above, 'moist' soilhas to be used for the test for plastic limit. The resultsof tests carried out with bore hole water are also presentedin Table 3.4.1.

Tests for Atterberg limits were conducted onair dried and oven dried samples also, dried as discussedearlier. The dried samples ‘were Inixed vn¢fi1 water to eawater content higher than liquid limit and preserved assuch without loss of moisture content for 24 hours to arrive

at equilibriunu The test for liquid limit was startedfrom ea water content which required around J1) blows only

for tflmegroove to close. The paste vuns then spread overglass plate tn) allow’ evaporation. This was tflmM1 mixedthoroughly for the next test. Thus all tests were startedon the wetter side of liquid limit.

3.4.1 Shrinkage limit

Aggregation of clay fraction into coarser parti­cles during drying influences the shrinkage limit also.Since a coarser soil fabric tend to increase the shrinkagelimit values, the shrinkage limit of marine clays increaseson drying unlike the Atterberg limits. The code for pre­paration of dry soil samples prescribes lOO gm of air dried

.56

soil passing through 425 micron IS sieve for this test.The effect of bore hole water on the test results is negli­gible as shown in Table 3.4.1.

The above discussions focus the attention onthe need for a specific mention in the Indian StandardCodes for determinathmi of Atterberg limits and shrinkagelimits making it mandatory to use ‘moist’ samples for thesetests in case of marine clays.

Tests were also carried out on air dried andoven dried samples for shrinkage limit. The dried sampleswere mixed with distilled water to a water content higherthan liquid limit and kept in ea glass plate covered ‘bya china dish for more than 24 hours to arrive at a uniformpaste.

3.4.2 Soaked samples

Both Atterberg limit tests and shrinkage limittests were conducted on soaked samples also. Samples ofmarine clay which were initially air dried or oven driedwere kept :h1 buckets filled with water to time top of the

57

5011- TheY were kept in buckets for over two years to checkwhether the aggregation will show any tendency to disinte­grate. If sum this vfidd. be reflected imm the values ofAtterberg limits. Hence tests were conducted (N1 soakedair dried and soaked oven dried samples.

3.5 GRAIN SIZE ANALYSIS

Grain size distribution is the most obviouslyaffected index property of Cochin marine clay during drying.Due to aggregation, a portion of the clay fraction is changedtn: silt size and aa portion of time silt size becomes sandsize. Hence grain size distribution tests on dried samplesgive anomalous results.

The code for preparation of dry soil samplesrecommends aux? dried samples for VMN: sieving eumfl for dry

sieving and hydrometer analysis specification warrantsthe use of soil sample oven dried for 24 hours at lO5-llO°C.For the «grain size analysis of rmarine clays, only _wetanalysis on ‘moist’ sample alone gives the correct results.

During the preparation of washed samples andsoaked samples, :U: was noticed that time supernatant waterover the soil was always clear. With ordinary clayey soils;

58

this portion was always filled ‘with colloids ‘which. willnever settle irrespective of the time allowed for sediment­ation. But lfl the case CHE soil suspensions (If Cochinmarine clay, the supernatant water was always clear. Thisabsence of cmdloids and very fine clay fraction indicatesthat iJ1 marine clays, tine clay fraction existed Mn thehymn of flocs. Thus compared tx> the normally encounteredclayey soils, the need cnf a deflocculating agent was morekeenly felt for marine soils.

Since the role of dispersing agent was moreconspicuous in the hydrometer analysis cnf marine clays:a series of tests were conducted to arrive at the mostsuitable dispersing agent and the optimum quantity of thesame. The different dispersing agents tried were

1. Sodium chloride

2. Sodium phosphate3. Sodium carbonate

4. Sodium nitrate

5. Sodium sulphate6. Sodium bicarbonate

7. Sodium hexametaphosphate

8. Sodium hexametaphosphate + Sodium carbonate.

59

The results and observations on these hydrometeranalysis are presented in section 4.4.1 in chapter IV.It was found that the standard dispersing agent, 100 mlof 33 gm of sodium hexametaphosphate + 7 gm of sodium carbo­nate 1000 ml of distilled water is the most ideal one forCochin marine clays also.

3.6 CONSOLIDATION TESTS ON COCHIN MARINE CLAYS

Consolidation tests CH1 undisturbed samples ‘wereconducted as gxmr IS: 2720 (Part XV) l965: Determinationof Consolidation Properties. Undisturbed ‘moist’ samplewas extracted from ]1K)1mn diameter stainless steel sampl­ing tubes. The first 3 txa-4 cm length of sample is cutoff and discarded as this might have been disturbed duringsealing with molten wax or during preservation by lossof moisture content. The bevelled edge of the consolidationring was then pushed into the samples being extracted fromthe sampling tube smufli that soil projects (N1 either sideof the consolidation ring. The sample :h5 then trimmedin level with the edges of the oedometer ring. The initialwater content of soil sample is determined from these trim­mings.

60

The oedometer rings. are 60 rmn in diameter" and20 nmm in height. The ring :h3 then introduced into theconsolidation test assembly’ with porous .stones (N1 eitherside. Filter papers were placed between the porous stonesand the soil specimen to prevent the soil from being forcedhfixa the pores cflf the stones. The cmmsolidation assemblywas tfluai positioned ix: the loading frame enui the speci­men was loaded vnifi a seatimg load of 0.0625 kg/cm2. Thesample was then inundated with water from a reservoir witha head of 50 cms.

Standard consolidation tests

Several series of consolidation tests were carried

out on samples (Hf Cochin marine clays varying differentparameters like duration of loading, effect of pore fluid,effect of mashing, etc. All these test results need tobe compared vniflm the results of ea standard consolidationtest, which had to be defined.

In the consolidation test which served as thereference test, the load increment ratio was kept at one.It was found that about two days were required for acomplete dissipation of pore pressure and for reachingan equilibrium void ratio tin: a particular loading stage.Hence the duration of the standard test for each load incre­

ment was kept at two days.

61

IS: 2720 (Part XV) 1965 recommends a loadingsequence of 0.1, 0.2, 0.4, 0.8, 1.6, 3.2 and 6.4 kg/cm2starting with ea seating load <1f 0.05 ibg/cm2. Eventhoughthis pattemi has a load increment ratio of one the loadingstages are a little odd figures especially when the e — log pcurve is plotted. Further, a loading of 6.4 kg/cm2 (64T/m2)is rarely realised as ea pressure increment in 51 clay layerin field. Considering these twK> aspects of time problem,a loading sequence of 0.0625, 0.125, 0.25, 0.5, 1.0, 2.0and <4J) kg/cm2 vans adopted for time numerous consolidationtests performed on untreated and treated specimens of Cochinmarine clays.

For each loading, dial gauge readings were takenat o. 1,, 1, 2, 3, 4, 5, 8, 11, 14, 17, 20, 30,40, 50, 60,80, 100, 120, 140, 160, 180, 210, 240, 270, 300, 330, 360,420, 480, 1440, 2880 minutes from the ‘time (Hf loading.Normally these values are chosen such that they give a uni­

form spacing of points for ft curves. But the rectangularhyperbola method was used to determine the coefficient of

consolidation Ck] throughout tints work. These timings forrecording the deflections were chosen to suit the rectangularhyperbola method. IX detailed discussion on the method and

its advantages over the existing two methods viz. ft methodand log t method are discussed later in this chapter.

62

Consolidation tests on remoulded samples

A number of consolidation tests were conductedon remoulded samples. Leonards enui Ramaiah (1959), basedon ea series <mf consolidation tests iJ1 clays remoulded atwater contents intermediate between the pdastic and liquidlimits, luui observed that E1 reduction lfl remoulding watercontent produces an effect similar to preconsolidationpressure iJ1 e - log E3 relationship. Hence tine initialmoisture content in all the remoulded samples was kept equalto liquid limit. Sample for remoulding was taken from thesame sampling tube close to the undisturbed specimen. Afterthoroughly working on the sample, it was hand remouldedinto the oedometer ring, taking care to prevent any entrap­ment <1f air iJ1 the specimen. Consolidation test Vmus thenconducted starting with a seating load of 0.0625 kg/cm2.

Consolidation tests on air dried and oven dried samples

Obviously consolidation tests could be carriedout only on remoulded specimens of air dried and oven driedsamples of Cochin marine clays. The initial moisture contentwas kept close tx> the respective liquid limit values ofair dried and oven dried marine clay samples which wereconsiderably lower than the liquid limit values of ‘moist’samples.

63

One of the parameters considered while runninglong series of the tests on untreated samples was the effectof duration of loading. While the duration given for eachload increment fin: the standard consolidation test nuns two

days, consolidation tests VMHK3 carried CNN: giving 1. day;

2 days, 4 days, 8 days, 15 days and 30 days for each loadincrement to study its effect especially on the developmentof higher cohesive strength during secondary compressionat each load increment.

3.6.1 Rectangular hyperbola method for determination of CV

Since settlement is one of the design criteriafor structures founded on cohesive soils, the consolidationtest is essential to ensure satisfactory performance ofthe structure. One of the important aspects of laboratoryconsolidation tests is the determination of coefficientof consolidation CK”. for predictimg the rate of settlementeventhough its applicability to field conditions is question­able.

Of the various methods for the <determination of

CV, Taylor's square root time fitting method and Casagrande'slogarithm CHE time fitting method are time most widely used

64

methods. All the methods for determination of CV are develop­ments of a comparative study of time t and deformation 6with the theoretical relationship between time factor, Tand degree (Hf consolidation U. A runv method called rect­angular hyperbola method developed by Sridharan et al.(l987)which was found simple and versatile has been used in this

work for the determination of CV. ‘flue data available fromthe numerous consolidation tests was taken advantage offor further study (Hi this method vis—a-vis Cochin marineclays.

The rectangular hyperbola method assumes that theTerzaghi's Lkfi? relationship can kxe taken as ea rectangular

hyperbola over a wide range of T. Hence a plot of % vs. Tgives ea curve upto [1 = 60% amui a straight line for60% < [J < 90%. The linear portion of the curve is givenby

T/U = 8.208 X 1O-3T + 2.44 x lO-3 (3.6.1.l)

and it has a correlation coefficient of 0.9999.

Fig.3.6.l.l shows a T/U vs. T plot for the theoreti­

cal curve. It shows that the ratios of the slopes M1 andM? of the lines joining the origin to the points corresponding

65

0-015 ' ‘ ' ' '‘Intercept C : 2-44 X103

» Slope M1‘: 2-031M+ 2 __3

T/U

.5

Fig- 3-6-1-1 THEORETICAL T/U-T RELATIONSHIP FROMTERZAGHWS CONSOLIDATION-(Rectangular!linear pore water pressure distribution)

66

to 60% and 90% consolidation respectively to the slope Mof the linear portion of the plot are 2.031 and 1.354 respect­

ively. This property can be used to locate t6O and tgopoints on an experimental curve. Similarly points correspond­ing to other degrees of consolidation can be found from

the ratio Mi/M which is termed the ‘A’ value. From thefigure 3.6.1.1

T/U = Mi.T (3.6.l.2)1/U = Mi

A = M./MlA = L <3.e.1.3>MU

For an experimental data plotted as t/(6 - 5i) vs. t:

t = m't + c‘ (3.6.l.4)Z6—Ji5

where :3i is the initial compression, m' is the slope ofthe linear portion of tflua curve» and <:' its the intercept

on the t/(5— ai) axis.

The equation of the line joining the origin toany point CH1 the linear portion of t/( 5- 51) vs. t gfltm

67

is given by

= Am't (3.6.l.5)where A is a dimensionless quantity and a function of degreeof consolidation U.

t = —__“_'__ (3.6.l.6)

C 2 TH2v tM'H2: ' (3060107)

ie. CV = Bm'H2/c' (3.6.l.8)where B = T(A—l) = C/M = 0.297. Thus CV is computed.

The rectangular hyperbola method for Ca] can claimmany advantages over the other methods. Some of the instanceswhereift method fails are:

1. When the ‘/7: curve’ does run: have and initial straightline but runs a continuous curvature preventing Lns from

drawing the line leading to the t9O point.

68

2. When the compression is low’ initially’ and rapid aftera certain stage.

3. When there is very rapid compression initially and almosta flat curve thereafter.

Similarly Casagrande's logarithm of time methodalso becomes ineffective in certain cases such as

1. When secondary compression ijs very large emui does not

yield a straight line failing to give the point tloo

2. In partially saturated soils, the initial portion maynot be parabolic and it becomes difficult to determine to

3. A longer duratbmn of consolidation test may be requiredso that the secondary compression portion is well defined.This slows down the tests.

The rectangular hyperbola method will yield resultsin any of the sfltuation listed above. This is illustratedwith some of the test results on Cochin marine clay.

69

Fig.3.6.l.2 shows the 6 vs. log t plot for thetest data on an undisturbed sample from Maradu at 9 m depthfor the pressure increment from 0.5 to 1.0 kg/cm2. Obviouslyit is difficult to get the point of 100% consolidation fromthe curve. The same data runs been plotted in Fig.3.6.l.3by Taylor's.ft method. It can be seen from the curves thatii: is difficult tn) draw ea straight line through ea set ofpoints at the initial portion as very few points fall ina straight line. But kn! rectangular hyperbola method the

value of CR7 can be easily arrived at without any ambiguityas shown in Fig.3.6.l.4. The value of intercept c is 0.068

and slope n1 is 0.00188. These give 51 value of (*1 as1.25x1o'4 cm2/sec.

When the Inethod ‘was first proposed tnz Sridharanand Sripada Rao (l98la), it did not consider values of theinitial compression. Later Sridharan et al. (1987) perfectedthe technique tx> include initial compression also. If c'and m' are the vertical intercept and slope of the straight

line t/(5-'9‘) vs. t taking into consideration the initialcompression also, it can be shown from a wide range of experi­mental results that

m'/c' = 0.809 m/c (3.6.l.9)with a correlation coefficient of 0.9944.

m>m:u . moTwu~.Tm.m.m:

oom.ooq..oom_

70

oom_n ooi

E33 o._ .. m.o

c_o.o

N

Ipmmo

:o<m<2.mh5 oom_

ooom

coo. _oom_

oo_

Amm::::; emzep

= ‘MP L '( 5U0!S!A!p)§ NOlSS3ticlHO'.)uWJZOO'

71

.u>m:u {_|% m; m.m OE

A.......::c_Ev .

com.

_ mH _ MV ?--;-,iJ§ M«HO O W mm0 w N

M1 «.ilIm!u .:; Ilui.:1 - oom_

W 0 _ 0/Aw 0 >H % W.71 1! ...L ,l% ow gem

or/.\

.r -- a 1 - -1 e o oo:

o

W O LM O D.:1!!! ..... Ill‘; 1 !

mE£3o._-m.o H a ._

Eo.m u IPQMD o 0-1: :o<m<: H mtm ila - F :luoom;w

a w9 wooom

72

; I I! SlTE- MARADU

---——-..;-. [___-_.--.DEPTH- 9.0m

p _-=o.5-r«okg/en? 3

0.6 ..._L ----._%.---- ’T‘—Z?Q>—1—

o.5~— - % ~

0.4 fi‘v i_\ .0.3 g _% ,I O-O68 i1 m = 000.188 ‘F I; !

u 5

1 L120 150 200 240 280 320t (minutes)

Fig 36-1-4 t/5-t CURVE.

73

The equation 3.6.1.6 gets modified tot = (3.6.l.l0)where K‘ = 0.809.

The value of CV can now be obtained from

B'mH2/c (3.6.l.ll)(3 llVR

where B‘ = BK‘ 0.241.

For 23 comparative study cnf the results given bythe three methods the consolidation test data has beenanalysed by all the three methods for undisturbed andremoulded samples. The results are presented in Table 3.6.1.1.

Due to the advantages the present method has;in comparison to the Taylor's and Casagrande's methods;the rectangular hyperbola has been used throughout thisstudy. However, for quite a number of cases the 5 — log tmethod also Inns been included especially for tflua determi­nation of secondary consolidation.

3.6.2 Preconsolidation pressure

The importance of an accurate determination ofpreconsolidation pressure of clay layers can hardly be

74

no.0 mm.o oH.H mo.H mm.H om.m o.wIo.mmm.o vm.o mo.H mH.H nv.H mm.m o.mIo.H

vm.o m».o mm.o mm.H II m©.H o.HIom.o E m Imn.o No.0 ©m.o II II II om.oImm.o swmumz

mm.H om.H mm.H m©.H m©.H vm.m o.vIo.mv>.H om.H H>.H mv.H ow.H m>.H o.mIo.H

©m.H mm.H mv.H wm.H »m.H ©v.H o.HIom.o E m.o ImH.H vo.H mm.H mm.H Hm.H mm.H om.oImm.o usumm

H>.H mv.o mm.H mm.H mm.H ©m.H o.v-o.mvm.H Hm.H w©.H HN.H mo.H mv.H o.mIo.H

oo.m ©o.H Hm.H No.0 wm.o wm.H o.HIom.o E m.mH Ivm.v mv.m ©H.v om.o m~.o mo.H om.oImm.o uzumm

vm.o No.0 @n.o mm.o HH.H »v.H o.vIo.mnn.o no.0 55.0 mm.o mH.a oH.H o.mIo.H

nm.o on.o wm.o vH.H mm.H mv.H o.HIom.o E oo.H IHo.H mn.o o».o »m.H mv.H mn.H om.oImm.o uoopuwz

©ocumE ©o:uwE

©o£umE.m.m u moa ©o:uwE w% ©oLumE.m.m u moa ©o:umE m%, AmEu\mxV

©m©H:oEmm Uwnusumaccb Q m:flHQEmm wo

. wusmmmum Lummo ©cm wufim

>

WDOEBMZ mmmme WEE wm mm:g<> 0 mo zomHm<mzoo

H.H.©.m magma

75

overemphasized as it helps to classify them into under con­solidated, normally consolidated or over consolidated clays.The engineering behaviour of clays is closely linked tothe state of consolidation. .As an offshoot of the severalseries of consolidation tests carried out during this investi­gation, a new method called log-log method, has been developedfor the determination of preconsolidation pressure.

The main problem with attempts to develop methods

for the determination of pc from tnudisturbed samples ‘wasthe non-availability of samples whose preconsolidationpressures are known beforehand. Eventhough there are differ­ent procedures proposed by various workers, their relia­bility could not be verified for want of a pmior knowledge

of pc. In this context, the attempt to prepare laboratorysamples for specific values of preconsolidation pressurehas been a success.

In log-log method, pc is obtained as time pointof intersection of two straight lines extended from thelinear portions on eithereyuj of the compression curve plot­ted to log scale on both axes. In order to check the validityof the pmoposed method, consolidation tests were conducted

76

on samples which were consolidated to known pressuresearlier. Tr> prepare smnfii specimens, remoulded samples <3fmarine clay were loaded in consolidation cells with theinitial water content equal to the liquid limit values,with a seating load of <3.0625 kg/cm2. The pressure ‘wasincreased iJ1 steps to Z1 kg/cm2 anui the load nuns retainedfor long durations such that the samples were fully consoli­dated at their known pressures. The load was then releasedin steps txb 0.0625 kg/cm2 Vdlfii the sample fully inundated

so that the Sample was. always fully saturated. A fullconsolidation test with a maximum pressure of 4 kg/cm2 wasthen conducted (N1 this sample preconsolidated txn l kg/cm2.The consolidation test data was plotted to get the e - log p

curve and pc was determined by the popular Casagrande method.The data was also plotted with both e and p on log scales:

pc was found out by the intersection of two straight linesfitted to the initial and final points on the log e - log pplot. Since the actual preconsolidation pressure was known,the results obtained from kxnfli methods could txa verified.

In all the cases it was found that log e — log p plots gavebetter values. Even tflua development CM? quasi preconsoli­dation pressure could be detected better by the log-logmethod.

77

Since the rmfifluxi was successful, ii: was verifiedwith marine clays from different sites and other types ofsoils also. The soils tried are:

1. Marine clay from Nettoor

2. Marine clay from Parur3. Red earth4. Black cotton soil5. Kaolinite

6. Marine clay treated with 3% lime7. Undisturbed samples from Maradu, Kumbalam

and Elamkulam.

Tests with these soils having wide and variedproperties helped tn) confirnu the ‘versatality anui accuracyof the runv 1og—l@g method. This iii further discussed insection 5.6.2.

Constant rate of strain tests

Constant rate (M5 strain tests cur CRS tests havethe advantage of completing the consolidation test at amuch shorter duration. The success of tflfljs test lies inthe selection of the rate of strain which will allow suffi­cient time for dissipation of pore pressure but at the sametime will help to complete the test at a shorter duration.

78

About ten CRS tests were conducted on samples from Parurwith three strain rates. The strain rates adopted were0.00192 mm/minute, 0.001414 mm/minute and 0.00065 mm/minute.

This has been further discussed in section 5.7.

3.6.3 Compaction characteristics

The changes that are caused by air drying andoven drying of marine clays improve their compaction chara­cteristics also. Since these changes are accompanied byconsiderable development in shear strength, detailed investi­gations were carried out (N1 the compaction characteristicsof dried samples of Cochin marine clay. Since the use ofoven dried samples in field application did not have anyscope, the studies were restricted to air dried samplesonly.

The water content dry density relationship usinglight compaction was obtained as per IS: 2720 (Part VII)1980. Air dried sample was compacted in the mould in threelayers, each layer being compacted with 25 blows from a2.6 kg rammer dropped from a height of 310 mm, distributeduniformly over the surface of the soil. The water content­dry density plot from the test gave the optimum moisturecontent and the maximum dry density that can be achievedin field.

79

Since the shear strength of these air dried compactedmarine clays showed considerable gain apart from improvementin compressibility characteristics, triaxial shear testswere carried out on samples prepared at maximum dry densityand optimum moisture content. These results can be usefulin the analysis of rotational base failure» and stabilityof slopes.

The water content—dry density relationship wasalso obtained as per IS: 2720 (Part VIII) 1983 for heavycompaction. The soil was compacted in five layers, eachlayer being compacted by 25 blows from a 4.9 kg rammer drop­

ped from 450 mm height.

The marine clay samples were first air dried andthen water was added to vary the water content to obtainthe compaction curve. The water content (mum be broughtdown kn! exposhxg the specimen ix) atmosphere starting from

natural water content. Compaction tests were done on suchsamples also.

3.7 DETERMINATION OF FREE SWELL INDEX

Free swell, as defined by IS: 2720 (Part XL) 1977is the increase in the volume of a soil, without any external

80

constraints, (N1 submergence zhi water; The test procedureconsists of weighing two 10 gm specimen of oven dry soilpassing through 425 micron IS sieve. Each soil specimenis poured into each of two graduated glass cylinders of100 ml capacity. One cylinder is then filled with keroseneoil and the other with distilled water upto lOO ml mark.After the removal cm? the entrapped air tnr stirring withglass rod or shaking, the soils in both the cylinders shallbe allowed to settle for a ndnimum of 24 hours, to attainthe equilibrium state cm? volume without any further changein the volume CHE the soils. The final volume cnf soil ineach cylinder is read. Kerosene, being a nonpolar liquid,does not cause swelling of the soil. The free swell indexis then calculated by

. Vd-VkFree swell index = V x lOO (3-7-1)k

Vd = volume of soil specimen read from the jar withdistilled water

Vk = the volume of soil specimen read from the jar contain­ing kerosene.

The present method or definition has some inherentdrawbacks even in case of cmdinary clayey soils as pointedout tn! Sridharan et ail. (1985). After ea detailed study of

81

nine natural soils, they reported that this definition cangive negative swelling index zhi certain cases. The detailsof tflma samples euui their sediment volume :h1 kerosene andwater are given in Table 3.7.1. With the exception of samplecollected from Gas Turbine Research Establishment (G.T.R.E.)

Campus which occupied ea high sediment volume ixu kerosenethan zhi water, all other soils gave 51 positive free swellvalue. X-ray diffraction spectra indicated that GTRE soilcontained only kaolinite. The free swell index test conductedwith pure kaolinite mineral gave a higher sediment volumein kerosene than imm water similar txn the observation inGTRE Campus soil. Thus it was proved that pure kaolinitemineral occupies a higher sediment volume in a nonpolarsolvent like kerosene than in water.

The above results point out the assumption thatthe level of 5: soil in kerosene graduated cylinder may beread as its original volume used in calculating the percentfree swell index does not hold good for soils containingkaolinite alone. Further, the presence of kaolinite insoils results in their occupying a markedly higher sedimentvolume in kerosene in comparison to other soils withoutkaolinite, suppressing their percent free swell values.Hence a redefinition of free swell index is warranted.

82

oo.m nm.»~@ o.om o.HH m.¢mH noon mucsmflcmm .mom.m mm.vHm o.mm m.oH v.@oH noon HH|mHHm:fl:mm .moH.m o.om o.Hm o.HH o.vm non- Humfifimcflcmm .»

muflc

oH.m o.ooH o.Hm m.oH o.ooH uofiflflpoeucoz usacm>mpmz .@om.H mo.Hm o.mH m.wH o.m» now: usfimeoo .mmn».H m».om mm.nH o.vH o.mn non- msaemu.um.H.H .v

®uflCOH.m.mwMOE

luCOE mvcm mcflume

mnm.H wH.@H mn.mH o.nH o.m» muflcflfiomx mpofimmcmz .m

msmemo

ov.H mm.om o.¢H ma mm muflcflfiomm .m.m.e.o .mmv.H Hm.mv m.vH o.mN sq muflcflfiomx muflcflaomx .H

Aemxuuv Awv Ameov Ameuv Awv

mwou

COfluflCflw®© mH uwm uwumz mcwmouwx HMMGCHE

3m: uwm mm mm xmbcfl cfl ®EDHO> CH ®ESHO> uHEHH xmao .oz

xwmvcw ._..Hw3m wwum H.m®3m womb ucweflmvmm ucmeflmumm Esvflq Hmdflucflum ._mflOm .._..m

Ammma .Hm um cmumncflum uoum<V

mm=g<> qqmzm mmmm mHmme az< mma«z ozc mzmmommm ZH mqHom ozc m»<qu mo mmzouo> ezmzHomm

H.b.m magma

83

During the discussions on preparation of moist,air dried and oven dried soils, it has already been pointedout that the clay content or the activity of a marine claysample ix; considerably’ reduced tux drying, due tr) aggrega­tion CH5 finer particles txn coarser grains. Swelling beinga result of a surface activity, a reduction in clay fractionor total surface area can considerably bring down the swel­ling potential of a clayey soil. Since drying is inevitablyaccompanied by aggregation in marine clays, use of dry soilspecimen as stipulated by I.S. Codes will lead to erroneousresults. ‘Table 3.7.2 gives the free swell index valuesof marine clay samples from different sites in Greater Cochinarea. The need for ea new method vans thus keenly felt incase of marine clay samples as in the case of kaoliniteclays. In this context the method proposed by Sridharan et al.(1985) as given below is more acceptable.

V

Free Swell Index = TE cc/gm (3.7.2)where V = the volume of ]L)<yn of soil specimen read fromd

the graduated cylinder containing distilledwater.

This equation defines free swell index as thevolume occupied by 53 unit weight cm? soil in water withoutany external constraint.

84

ma m.©H

mH mn.oN o.oH amHmne:x .o©H mH HH mH o.m smmumz .m

m.mH oN @H vN He: mnvv om.»m.vH NH m.NH NH cm.»

«H NH VH HN Hvwzmmzv om.HH

mH mH HH oN om.HH Magma .vmH ©H NH m.HN m.v uooHHmcmum;u .m

oH vH m.mH oN ow.vHvH ¢H an an oH.NHoH mH nu nu ow.HH

vH om.vH as us ow.oH emnemcsz .N

m.HH vH HH m.oH o.NNH mH HH wH m.H

oH NH oH NH o.H uoouumz .H

Aouv Auuv umum3 Huuv Auov uwum3mcmmoumx mwaaflumflw mcwmouwx ©wHHHumH©

Cfl wEDHO> CH.” wEDHO> Cw ®ED.__O> CH ®EDHO> AEV .OZomHH© cm>o @mHu@ uH< spams Ho coHHmuoH .Hm

mzoHa<uHmHommm

mmzH<amo N<AU mzHm<z ZHEUOU mo mmgmzcm mmHmo mo mmzaHo>

N.h.m wHnma

.m.H mam m<

BZMZHQMW

85

In the case of kaolinite soils, 10 gm of dry soilcan be weighted and then transferred to the graduatedcylinder. But since drying alters the swelling propertiesof marine clays considerably, only’ a known quantity of‘moist’ soil can be transferred to the jar. The dry weightof the soil specimen can later" be determined by findingout the natural moisture content of the 'moist' sample usedfor the test.

Thus due to the peculiar behaviour of marine claysupon drying, the Indian standard procedure cannot be adoptedfor the determination of free swell index of Cochin marine

clays. The definition proposed tn; Sridharan en: al. (1985)only’ can be adopted. This has time added advantage thatmeasurement lfl kerosene is eflihdnated. All the values offree swell index reported here are based on the definitionsuggested by Sridharan et al.

3.8 OTHER TESTS

The methods adopted for determinathmi of organicmatter, calcium carbonate, cation exchange capacity andpH value are given below.

86

3.8.1 Determination of organic matter

As per the procedure laid down by IS: 2720 (PartXXII) 1972 for determination of organic matter, the specimenrequired is air dried soil sample. The actual weight usedis determined tux an equivalent weight cmf soil oven «driedand weighed. cmn: of the two procedures recommended by theCode, the procedure where potassium dichromate was usedto oxidise the organic matter was used in the present study.The percentage of organic content was determined by thefollowing equations.

v = lO.5(l-y/X) (3.8.l.l)where

V = volume (ml) of potassium dichromatey = total volume of ferrous sulphate used in

the test

x = total volume of ferrous sulphate used inthe standardisation test.

Percentage of organic matter is given by

O.67w2VOM (% by weight) = —;—;——— (3 8 1 2)l 2 ' ° °

87

where w weight on oven dry basis (M5 the soil samples2

passing 10 mm IS sieve

wl = weight on oven dry basis of total soil sampletaken for the test before sieving.

w3 = weight (N1 oven char basis (Hf soil specimen usedin the test.

Tests were carried out with both air dried soiland moist soil. The» difference :h1 values obtained ‘wasnegligible.

3.8.2 Determination of calcium carbonate

The procedure for determination of calcium carbo­nate is given by IS: 2720 (Part XXIII) 1976. The carbonatecontent is determined by treating the soil with hydrochloricacid. The carbonate present III soil, percent try mass, isgiven by

Volume of 1N hydrochloric acid 100used for 5 gm of soil X 0.05 x —g— (3.8.2.l)

Here also the specimen recommended by code isoven dried soil sample» But moist sample whose equivalentdry weight was accurately measured was used for the test.

88

3.8.3 Determination of cation exchange capacity

IS: 2720 (Part XXIV) 1976 give two proceduresto determine the cation exchange capacity of soil samples.The method in clause 5 for the determination of cationexchange capacity treating metallic and hydrogen ions to­gether has been used for the determination of the valuelisted znu Table 4.1. Here also moist sample was used forthe tests. But tests with air dried and oven dried samplesindicated that the change in CEC values are negligible.

3.8.4 Determination of pH value

The pH value of the soil was determined usinga Systronics digital pH meter. The equipment was standardisedusing buffer solution of gfli equal to 9.2 anui the pH valuewas measured as per IS: 2720 (Part XXVI) 1973.

3.9 IDENTIFICATION OF CLAY MINERAL BY X-RAY DIFFRACTION

Concepts about clay structure took a new turnin 1923 Vduai Rinne iml Sweden ENM3 Hadding zhi Germany first

succeeded iJ1 obtaining X—ray <diffraction patterns cyf clayminerals (Sudhakar Rao, 1982). This work was rapidly followedby other studies which established that 51 great majorityof clays have well organised crystal structures.

89

The Bragg condition for production of a significantdiffracted beam is

n %_= 2d sin 0

where n is the order of reflection, ,\ is the wavelengthof the Xerays employed and G :hs the angle the incidentbeam makes with the set of planes that have the interplanarspacing d.

The first order basal reflections of the clayminerals are frequently their most important reflections.From the <geometry' of ‘the <iiffraction pattern. of 51 singlecrystal, information on the symmetry of atomic arrangementsas well as on size and shape of unit cell, can be gained.From the intensities of the diffracted beams, the positionsof atoms averaged over many unit cells can be calculated.

The main structural difference between the differ­

ent clay mineral species is the repeat distance perpendicular1x) the alumino silicate layers, often loosely referred toas the ‘layer thickness‘. Different clay’ mineral groupshave different layer thicknesses. This forms the basisfor identification cm? clay minerals in soil. However, thediffraction characteristics of clay minerals have considerable

90

similarities so that identification based on diffractiondata must be complimented by other studies.

3.9.1 Preparation of specimen for X—ray diffraction

For identification of clay minerals present inCochin marine clays, the clay size fraction was <givenstandard chemical treatment and analysed by X—ray diffract­ions as detailed below (Jackson, 1964).

Soil specimen from the Parur site was first washedwith distilled water so as to remove the free salts. Thewashing was persisted till the electrical conductance ofthe latter was close to tflun: of distilled water. Next thewashed soil specimen was dispersed by agitation in an aqueousmedium containing 0.4% of sodium hexametaphosphate (by weight)

as the dispersing agent (ASTM) 1972. The clay fractionwas separated tux sedimentation cxf coarser“ particles undergravity for 3.5 hrs at 25°C (Jackson, 1964). The supernatantcontaining the dispersed clay fraction was pippetted outand suspended in 50 ml solution of 1N sodoum acetate - acetic

acbd buffer of gfli 5 boiled gently for 55 minutes. Then10 ml of 1N magnesium chloride was added. The suspensionwas thoroughly mixed and centrifuged enui the supernatantliquid discarded. The clay fraction was washed once with

91

lN magnesium acetate and twice vnjfim lN magnesium chlorideto remove acetates which are <difficult to vnnfli out withalcohol. The clay was next washed, once with a small volume(10 ml) of water and then once in 95% alcohol. To solvatethe clay sample, lO% glycerol (by volume in water) was added

and mixed thoroughly’ to obtain ea smooth suspension. Thelatter was spread on a glass slide, allowed to air dry andits X-ray diffraction spectra recorded with Philips X-ray

diffractometer' using <3u-RX radiation (_A== l.54£) and DH.filter. The untreated silt and sand separates were alsoanalysed by X-ray diffraction.

3.9.2 X-ray diffraction analysis of Cochin marine clays

X-ray diffraction pattern (Fig.3.9.2) of the treatedParur clay fraction shows strong reflection around .l7.65Awhich is characteristic of montmorillonite, relatively weakerreflection was observed around 7.25£ typical of kaoliniteclay (Jackson, 1964). Additional reflections noted around3.58]: and 3.35}: can be attributed to kaolinite and mont­morillonite respectively.

It may be of interest to note that the methodof sample preparation has a profound influence on the result­ant X-ray’ diffractogram. For example, recording the 1£—ray

.zmm»~<a zo.»u<m%:o ><mux emgfim mm

Ammmmomov mm

o_ m. ow mm «m om cw

92

.1.

a , J

T%f_J”__jfM

;, _

M

-...-_._.::___:__..j_ -- __

.qoma

93

diffraction pattern of the oven dried and pulverised marinesoil specimen without prior fractionisation and chemicaltreatment led to diffused nature of the X-ray spectrum.In another trial the marine soil specimens was sieved througha B.S. standard 200 mesh sieve eliminating the sand fractionand the residual silt and clay fraction was subjected tomagnesium saturation and glycerol solvation as describedpreviously. The chemically treated silt and clay fractiondeposited on 51 watch glass Vuus oven dried and pmlverised.On recording the X-ray diffraction pattern of the abovepulverised fraction, major peaks around 17; and 7.2K corres­ponding txa montmorillonite anui kaolinite respectively weremissing. However the secondary peaks corresponding to mont­morillonite and kaolinite were resolved.

From the various trials, it is concluded thatfractionisation chemical treatment, followed kn! depositionemui air drying cnf the treated specimen on ea glass slide,is imperative tx> obtain reliable analysis cm? the clayminerals present in the marine clays. The diffused natureof the X-ray pattern in trial I and the absence of mont­morillonite and kaolinite peaks in trial II may be attributedto time presence <xf the coarser particles ixx the specimenwhich would dilute the overall clay percentage in the sample.Consequently as the X-ray diffraction method is not sensitive

94

enough to determine small amounts of clay when mixed withlarger amounts of other coarser" materials in the soil,failure to resolve the diagnostic peaks of the clay mineralsresults. Another possibility is that trials I and II involvedoven drying of the specimens. It has been observed thaton oven drying the marine clay undergoes aggregation, result­ing in formation of coarser particles, which are less sensitiveto X-ray diffraction analyses.

3.10 STABILISATION OF MARINE SOILS

As one of the main objectives of the study wasimprovement of shear strength and compressibility chara­cteristics of <3ochin marine clays, attempts were» made ‘toidentify a suitable stabilising agent for the clay and studythe improvement in the engineering properties of the treatedsoil. Twenty additives, as listed below, were tried onthe marine clay samples from Parur.

Sodium hydroxideSodium chlorideSodium silicatePotassium hydroxidePotassium chloridePotassium dichromateFerric chloride

CD\IO\U1J>-(JOI\)|-—'

O 0

Calcium hydroxide

95

9. Calcium chloride10. Calcium carbonate11. Calcium sulphate (gypsum)12. Sodium carbonate13. Sodium hexametaphosphate14. Potassium permanganate15. Magnesium chloride16. Aluminium chloride17. Industrial waste No.118. Industrial waste No.II19. Lime20. Cement.

It has been found that lime is the most suitablestabilising agent. The details of the various tests conductedand the results obtained from various additives are presented

in Chapter VI-Industrial wastes I and II did not show anypromise.

3.10.1 Lime treated marine clays

‘Moist’ marine clay Samples were treated with6% by weight of each of the above additives. The treatedsoil was remoulded into the moulds for laboratory vane shear

test. six samples of marine clay treated with each additivewas prepared. Three were tested on the seventh day andthe other three were tested after a rmnnflm in a laboratoryvane shear’ test apparatus. The average values CHE 7-day

96

and 30-day strength are presented in Table 6.2.1. Two indu­strial wastes from neighbouring factories were also tried.A comparative study of all the results indicated that limewas time most suitable stabilising agent lint marine clays.The increase in shear strength after a month of curing wasabout twenty’ times that cnf the strength <of tine untreatedmoist sample. For purposes of comparison the additiveswere tried on red earth also.

Specially selected uniform shells were used forpreparation of lime for stabilisation. The shells wereburnt to remove CO2 completely when they change to brittlewhite shells of calcium oxide which were preserved in airtight multilayer polythene bags. Just sufficient waterwas sprinkled over the lime shells taken from these bagson each day of preparation of lime treated samples, tillall the shells crumble to fine power which was then sievedthrough 2K3 425 micron sieve. This Inethod cnf preparationof lime was used because of its simplicity and ease withwhich it can be prepared for field application.

Once the most suitable stabilising agent wasidentified as ljmmn a detailed study cnf lime stabilisationwas taken Lqx Several series of consolidation tests were

97

run on lime treated specimens with varying lime contentsand curing periods. The lime contents selected were 3%,6%, 9% and 12%. Lime was added to moist soil and wasthoroughly mixed. The sample was then remoulded into stain­less steel rings of 100 mm diameter and 40 mm height takingcare~tx> see that air is not entrapped during hand mouldingthe soil into the ring. The rings are then covered withpolythene bags. They are then covered with thin circularG.I.sheets with diameter equal to the outer diameter ofthe rings. This assembly its again covered »n¢w1 polythenebags and tied with rubber bands. The specimens are thenkept for curing for various dirations.

Samples for consolidation tests are then takeninto the oedometer rings by pushing it slowly into the ringafter removing the polythene covers and G.I.plates. Consoli­dation tests are conducted on these samples cured for variousperiods.

The improvement in shear strength after 77 daysand 30 days of curing was measured by conducting laboratoryvane shear tests on treated soil samples. 'Moist' samplesof marine clay were mixed thoroughly with different additiveswithout changing the initial water content and filled in

98

the moulds of laboratory vane shear apparatus of size3.8 cm in diameter and 7.6 cm in height. The specimenswere kept for curing zhi air tight polythene bags in humidatmosphere. During the test, the vanes were gently intro­duced into the soil mass and kept for five minutes to allowfor dissipation CHE pore pressure, if aunn» before the testwas performed. IS: 2720 (Part XXX) 1980 was strictly followedfor the conduct of the test.

,.c«}w7 / *

Chapter IV

PHYSICAL PROPERTIES

4.1 INTRODUCTION

Marine clays formed by the sedimentation of claysoils in marine environments exhibit many unusual physicalproperties. They possess very high liquid limit and theirnatural moisture content is close to the liquid limit values.The most striking feature of the physical properties is thephenomenal changes that are caused by drying of the sample.In this chapter a detailed study of the physical propertiesof Cochin marine clays has been presented.

Table 4.1 presents the physical properties ofsamples of marine clay deposits in their natural state andwhen they are dried by exposure to air or dried in an ovenat a temperature of 105-ll0%3. From the data given in thetable, it (uni be seen that both air drying and oven dryingsignificantly reduce liquid limit and free swell index con­siderablyu The oven dried samples have liquid limits inthe range of 40-60% of the natural moist sample and air dry­ing reduces liquid limit by 20-30%. The main reason attri­buted to this striking behaviour is the aggregation of parti­cles cu) drying (Ramanatha Iyer, 1966). .A similar reduction

99

100

A.oucooy

wsHm> umwoe :30 mufi we ucwoumm m m< *

An.~my Av.mny A~.m»y AH.©>y A».ony Am.mmy

o.~m m.ov ».mm m.vm o.mm o.mm cmflgm cw>o Aoy

Am.mmy Am.Hmy Am.mmy Ao.Amy Am.Amy

o.mm m.mv m.mm m.Av ».mm as mwfiuw ufim Anym.om m.mm m.mv m.m¢ m.~w m.mv Hflom umfloe Amy

Amy ufiefiH%oAummAm .m

Ao.mmy Av.mmy Am.~my AH.mwy Ao.owy *Am.mwy

o.om o.om m.om o.nm o.mm o.nm cmfluc cw>o Auy

Av.mmy Ao.o»y Ao.noy Av.Hmy Am.moy

m.mn o.moH o.m~ m.om m.nm nu omfiuc “Mm Anyo.om o.nmH o.moH m.mHH m.~mA m.©HH Hfiom umfioe Amy

Awy uflafia wflswfig .v

Awy ucwucoo

o.Hm o.nn o.mm o.mm o.¢mH o.mm muspmfioe Hmusumz .mov.H mw.A mw.H mv.H mv.A om.H Auuxemy mufimcmc Hmusumz .~om.~ mm.m ~o.m oo.m vo.m mo.m >pfl>mum ufiwfiomam .H

Amy Any Amy Amy Awy Amy Amy Afiy

o.oH o.m om.HA om.m o.A o¢.m Aey mcflaaemm mo gamma

.ozEmamnesm smumumz usumm uooaawcmuwco uoouuwz EMDEMCSZ coflumuoq ..__m

m»<qo mzHm¢z ZHEUOU mo mmaammmomm q<oHmwmm u<uHmwa

H.v magma

101

A.©ucooy

HmmvomAv.mmy

m.mH

Am.omy

H.mHm.mAvn.oAo.owy

o.vm

Am.wny

om.wvo.oo

OHowomAo.mmy

v.mH

Am.¢my

m.mHm.Hm»m.o

Am.mvy

m.mm

AH.mny

m.mmm.Am

mammNV

Av.moHy

v.H~

Am.mmy

m.omm.ommm.o

Ao.mmy

m.­Am.»my

».nmm.mo

Hmmvom

Am.moHy

m.om

Am.mmy

m.mAm.mHnm.o

A».omy

m.m~

AH.m»y

o.mmm.m~

amammv

Am.moHy

m.mH

Am.moHy

m.mHm.nAvm.o

Am.m~y

v.H~

Am.vmy

m.mwo.om

Ase mS.oAy

ma AWV QNHW UCQW Afldd

Ase mpo.oyvmoo.o.Ay

ow Awy wufim paflm AHA

Ase moo.ou.y

Nv Awy mwfim wmfiu AfiyHfiom umwoe Amy

cowusnfluumflw wuflm cwmuw

Ao.o~Hy

o.>m Cwflhfl cm>o Auynu nmfigc “am Anym.~m Hflom pmfloe Amy

Awy ufieflfi wmmxcflunmmo.o xmucfi >ufl©fl:vfiq

Aw.oNy

O.mH vmwuo cw>o ADVa- omfiuo pfim Anyo.Hn Hfiom umfloe Amy

.m.m.5Awy xmccfi wufluflummam .0

Amy

Any

Amy

Amy

Avy

Amy Amy

Aay

102

AH.mmy

mo.H

Am.mwy

mm.mon.vAm.»>y

om.H

Ao.wmy

mv.Hvm.HumummaHmavom

Ao.nmy

om.H

Am.mmy

~m.mom.m

Am.omy

mm.H

Ao.mmy

ov.Hqm.HmawmommaWVaw

An.vmy

vm.H

Am.omy

mm.mvv.w

Am.moy

mm.o

Am.Hmy

om.Hmm.HmmowmmomWVom

Am.omy

©©.H

Am.mmy

mv.mom.¢

Am.mwy

mm.o

Av.Hmy

nm.Hmo.mmmmmmmHmowmm

AH.mmy

om.H

An.~my

o>.Ho~.m

Av.mmy

vv.oAv.Hmy

mm.Hwm.Hummvmmmmmvmm

Am-mmy

ow.Hom.w

AEm\uuy

AH.mwy

mm.om®.Hmammmm

cwfiuu

cw>o Auymmfluc pflm AnyHHOW HMHOE Amy

Xwfififl HH03W wwum .HH

mwwuw cw>o Aoymmflum uflm AnyHwom HWHOE Amy

wmflmwuflmwwflm

>ufi>Huo« .oH

ocmm AAAuafim Aflfiwmfio Afly

flyycm>O Aoy

ccmm Afiflfiy

ufiwm Aflfiy

>mHo Aflycmfiuc ufl< Any

Amy

Any

Amy

Amy

Avy

Amy

Amy Afiy

103

mm.»oo.mom.»

om.nom.»om.o05.0

mm.mH

mm.mom.mov.o

om.mm

o@.nH©.>om.m

mm.»V0.5OH.©

mm.»om.oom.»

Awv mumconnmo EsfioamuwDHm> mmAwv uwuume uflcmmuoAH\mV >uflcfiHmm

.mH.vH.mH.mH

Amy

Awv

Aov

Amv

Avv

Amy

Amv

AHV

104

can be seen in the case of plastic limit as well as freeswell index. Nambiar et al. (1985) also have reported reduct­ion in liquid limit of fine grained carbonate soil from offwest coast, though run: significantly. Jagadish Narain andIyer (l967) reported significant reduction in the liquidlimit of Kuttanad clays on air drying.

But so far rm) systematic study runs been. carriedout (N1 the physical properties of Cochin marine clays withparticular reference txn initial testing conditions cnf thesoil viz. moist, air anui oven dried. Further experimentsare also conducted to investigate the effect of washing,soaking, addition of salts and other additives, organic andcarbonate content and grain size distribution on the physicalproperties of Cochin marine clays.

In this chapter an attempt has also been made touse liquid limit values to estimate the undrained strengthof Cochin marine clays having different moisture contents.

4.2 ATTERBERG LIMITS

Typical values <1f liquid lindt enui plastic limitof samples from different locations are presented in Table4.1. It can be seen from the table that 'eventhough the

105

locations from where samples were collected are .separatedby even more than 50 kms at times, the typical values ofphysical properties aux; quite consistent »n¢x1 one another.For moist samples the liquid limit varies from 83.5 to 175%depending upon the composition of the soil together’ withthe physico—chemical constituents. The values of the plasticlimit vary from 33.8 to 60% for all the clays tested.

Fig. 4.2.lapresents the liquid limit vs. pflasticityindex for the numerous soil samples tested in this investi­gation. Most of the points are close to the A—line.

But a statistical fit for the values obtained frommoist samples gives the relation

PI = O.62(LL -2.0) (4.2.la)with a correlation coefficient of 0.92.

Table 4.1 also gives the liquid limit and plasticlimit values for air dried and oven dried samples of Cochinmarine clays. As explained earlier, due to aggregation offiner particles to coarser‘ ones during drying, the claycontent reduces and this sum turn brings down the Atterberg

106

.:om 5.0: mom x.u_oz_ >:uZm<._n. 9, :23 3:63 .o_.m.q.m_.._

A .\. V :23 930:

SN cm. of o.: of 8. om om 3 o~ o

W 7 1 3omNmnod om

:..jr$.ouE o

\ \\\ M\o M F _\ _ _ _ _

om.

(‘/. )x3c1m )\i|3llSV'1d

107

limits. Fig.4.2.lb shows the plasticity chart for air driedsamples and Fig.4.2.lc is the plot for oven dried specimens.The plots give statistical fit as shown below:

PI = O.56(LL—l.6) (4.2.1b)

with a correlation coefficient of 0.96 for air dried samples

PI = 0.67(LL-23.5) (4.2.lc)

with a correlation coefficient of 0.89 for oven dried samples.

Fig.4.2.ld shows the relation between plasticityindex and liquid limit for all the three types of samplesput together giving rise to the statistical fit

PI = O.74(LL-23.5) (4.2.ld)

with a high correlation coefficient of 0.98.

Bjerrum (1954) reports the values of Atterberglimits for Norwegian marine clays. The liquid limit of theseclays varies over a range of 59.4 to 21%. A statistical

108

..__o.n. Om_mQ m_< mo... xm_oz_

>:u:m<#.._

E, :23 9:03 .n:.~.q .m£

A .\. :.z: 9303

o2 om: o: 2. co om cm on om ooomoqomom

ij T -—­

r-—————-«- r

00.

( ’/, 3x3CJNI /\.Ll3l.LS\1‘ld

109

..._ _om SEQ z..§o

mo“. xmoz_ >:u:.m<E 2, :23 9293 .£.~.q .9.._

AN .223 9:03

o.: of 9: om om. oq om

. o

__ fl

éééé Amen - 2

D

\n _ O.»

X mm.o£

\4(Am.m~..j:m.o "E om

_

om

( '/. )X3GNl Au3I1SV1d

110

.m:om DMEQ zm>o

oz< ofmo m_< .55: mob. V352. CC:m<#_ m> :2: 930....

..:.~..\ .9“.

AN 75:: 9:02

oom cm. of oi om. oo_ om om o

A W

OO

om:mo 25,0 0

m2: < X L

V mm.o u._ ouEo¢_< 4\\ :.....~L i.:.o "E dom 55: o

x\ F _

ON0x!

O@

OWco.of

( )x3oN.t A.Ll3[J.SV'ld

111

fit of the liquid limit vs. plasticity index gives the rela­tion

PI = O.795(LL—l7.2) (4.2.2)It can be taken that the slopes for both Cochin

marine clays and Norwegian marine clays are of the same order.For inorganic soils, the relationship of Casagrande plasti­city chart for inorganic soils lies above that of the relat­ionship obtained for Cochin marine clays and that ofNorwegian clays. This behaviour is possibly due to the pre­sence of organic matter in these clays.

Several attempts have been made to link plasticityindex and liquid limit treating them as independent para­meters (Nagaraj et al., 1983: Seed et al., 1964: Casagrande;1948). Apart from Casagrande's A-line which represents anempirical boundary between inorganic and organic soils therehave been other attempts to establish relations betweenplasticity index and liquid limit.

The popular relations are

PI = O.74(LL—8) (4.2.3a)(Nagaraj and Jayadeva, 1983)

112

PI = O.98(LL-27.5) (4.2.3b)(Seed et al., 1964)

PI = O.6l5(LL-9) (4.2.3C)(Schofield and Wroth, 1968)

These relations assumed importance as many engineer­

ing properties have been correlated to Atterberg limits;hi particular liquid limit enui plasticity index. It alsopermits field engineers tn) check; the suitability’ of anyborrow pit for appropriate construction material. With properjudgement Atterberg ljndts <xu1 be effectively used :h1 manygeotechnical engineering pmoblems. In view cnf its useful­ness this aspect of geotechnical engineering is activelypursued even rune as research topic (Sridharan et a1., 1986and 1988: Harrison, 1988).

The relation between flow index and plastic limitis shown 1J1 Fig.4.2.2a vfinxfix is represented km! a straightline]

PL = 0.473 (If + 65.9)

with a correlation coefficient r = 0.80.

PLASTIC LIMIT (°/.)

113

80 yl o MOIST SOIL

70 ll ——__I A AIR DRIED! D OVEN DRIEDf I' L60 % fl

: I ,——//////I50 ——-~ D %>I

A ‘T : ’i A A D ' EI I3o—£ID—I‘5~f+—-——~II : I2 0 ———~ D I ~ I

10 « — -———————-I

O O 10 20 30 A0 50 60FLOW lNDEX,h

Fig, 4.2.23. PLASTIC LIMIT vs FLOW|NDEX­

.392. 30: .2 $02. :_uEm<Z .n~.~.q m:

A.\. :moz_ >:u_»m<E

8. cm cm on om om 3 on om o. o

114

. ITv|l||l'll-‘x 0.

8:5 zw>o 0demo m_< c.:on... 5.0: o

7a

a

O _om0.»omom

‘I ‘xacml MO'l:.l'

115

Fig.4.2.2b shows the relation between flow’ indexand plasticity index for ‘moist, air“ dried enui oven driedsamples. These values give rise to a linear relationship

If = O.44(PI-5.30) (4.2.4b)with correlation coefficient equal to 0.91.

Tests to determine the liquid limit of a soil areanalogous to shear tests. The number of blows N of the cupin percussion testing is aa measure <3f time shear strength(Hf the soil, an: that water content. Nagaraj and Jayadeva(1981) have shown that time flow curves of cfifferent soilscan be generated using their respective liquid limit watercontents to obtain relationships of the form

E— = C-d log N (4-2-5)W

L

where W = water content

WL = liquid limit

N = number of blows

c and d are constants.

116

Fig.4.2.3a shows the flow curves. for" moist, airdried enui oven dried samples from Parur. When time watercontents are cfivided tux their respective liquid limits, inalmost EUJ. cases, the values fall into a straight line ora narrow band.

Fig.4.2.3b gives the plot between %— vs. log numberL

of blows for moist samples from various sites. A statisticalfit to the data generate a straight line,

= 1.42-0.305 log N (4.2.6)SIS

This has a high correlation coefficient of 0.97.

Thus it can be seen that equation 4.2.6 can beeffectively used for finding’ out the liquid limit ans onepoint method,

W

L - c—d log N

The values of c and d for Cochin marine clays are1.42 and 0.305 respectively.

Since the Atterberg limits are a measure of soilbehaviour characterised by the surface forces of clay minerals,

W/WL

117

:40 I I IIo MOIST sou.'20 A AIR DRIED

D OVEN DRIED

no

NV100#­ZL|.JF­Zo 90(.2

(ILLJF­<330 - - -»—- M R+

!7o — —--~——~6o______ _—— Q 3 -r ,3 G ‘H50 ‘I L ­I‘-20 I [A LD 0 A AL 1 *,_O0,.____, - D A D —-0 é) A :1 ‘

I080 1 1 40IO 15 20 25 30 35NO. or BLOWS

Fig z..2.3a. FLOW CURVES FOR SAMPLES FROM PARUR­

118

mmtm m:oE<> 29: mm:n_z<m 55: mo... mzéau zed .nm.~.q .9...

maoqm .._O Smzsz

on mm

‘M/M

8.oom.ooo._

_ 3.0” .

_m _ mom.o - ,3; L3 3 oi2<4<m::x ;V -g oNF

2<4:x2<4m j _

:o<m<2 4maxi o

m _. _m 4823

119

they should show 51 correlation with the percentage of clayfraction. Plots between liquid limit auui percent clayfraction are shown zhm Fig.4.2.4a4tnc: and 4.2.5 for rmoist,air dried, oven ckied Emmi all samples respectively. Theygive the following linear relations with clay percent c.

For moist samples

LL = 3.4(c-10) (4.2.7a)r = 0.83

For air dried samples

LL 2.50(c+1.20) (4.2.7b)r = 0.83

For oven dried samples

1.19(c-24.7) (4.2.7a)LL

r = 0.68

For moist, air dried and oven dried samples puttogether, the statistical fit gives the equation

LL = 2.94(C—4.0) (4.2.8)with a correlation coefficient of 0.95.

ugouna LMMT (Z ) G! O

120

I80

n5o~——w«w¢

:40

I20

C) O

60

40

2015

Fig. 4- 2-40­

— . - .___.—__j:___—._{u

. I

_ .__—....._.. ._-_j_ ..j_..___L..._jjj jg;

25 30 35 40 45 55CLAY PERCENT

LIQUID LIMIT vs CLAY PERCENT FOR MOIST SOIL­

)'/.

LIQUID LIMIT(

11.0

I20

LOO

121

I

LL = 2.5o(c+1-20) Ir = 0-83I20 I I »—— — -_ - I

010 15 20 25 30 35 40 45

Fig. 1.. 2. lob.

CLAY PERCENT

50

LIQUID LIMIT vs CLAY PERCENT FOR AIR DRIED SOIL­

f\

LFQUID LIMIT ( Z

122

I20 TI

too + —-~ ~w————~%

80 V60

F?1.0 T[LL =1.19 (C-1-24-7)

2o_— «¢—L—- - ’ —————­

o_no :5 20 25 30 35 40CLAY PERCENT

Fig» 1. 2.l.c. LIQUID LIMIT vs CLAY PERCENT FOR0 VEN DRIED. SAM PL ES­

LIQUID LIMIT( 7- I

123

130 I I 1 I I {o MOIST SOIL I I'60.. A A’ 00 O /CI OVEN DRIED O7.40 0 ,%I20 0I

T :I————-——+-~- * T‘

2015 20 25 3o 35 40 45 50 55CLAY PERCENT

Fgg. 4.2.5. LIOUID LIMIT vs CLAY PERCENT FOR MOIST, AIR DRIEDAND OVEN DRIED SAMPLES­

124

While it can be noted that the correlation coeffi­cient is very good for all the soils put together, for ovendried samples the redationship obtained is run: that satis­factory, since tflma r obtained zhs only 0.68. However, formoist soil one can get very good correlation between liquidlimit and clay percent, with more data. Since it is tediousand time consuming to obtain clay percent through hydrometer

analysis, correlation with liquid limit will be of <greatuse since we will always be determining liquid limit in anycase.

4.3 SHRINKAGE LIMIT

The shrinkage limit is quite high for moist sampleswhen compared to their liquid limits and plastic limits fromwhbdi one can infer that the moist clay consists of flocs.It has been reported (Lambe, 1958) that higher shrinkagelimit indicates flocculant fabric. Fig.4.3.l gives ea plotbetween the shrinkage limit and clay size fraction.

A statistical fit gives the relation

SL 3l.lO-O.276c (4.3.1)r = 0.83

szmummi id .3, :2: ,..3<xzExm ._.m.q .9“.

pzuummm >43

om oq om cm 0. O

125

a

SEQ zm>O DSE0 «.2 4sow 5.02 0

(°/. ).uwn 39v>+N1aH<5

5’ .% almm

126

cm.

F22: 036:

cm: 0.:

om.

m> i2: moizazm

Ax 5.23 9:03

o?

co

om

fin; ac

Oq

ON

/Qm_mO 295 DOm_mQ m_< <

.__om 5.0: O

.3 \.:.o I mfimm H S

Y

35

u‘.

m _ommmon

( ‘/.) uwm 39v>4NnaHS

127

By and large, the shrinkage limit got increasedfor oven dried samples. It is as ought to be since coarserparticles formed knr aggregation result iml higher shrinkagelimit.

Fig.4.3.2 shows tflna plot between shrinkage limitand liquid limit for moist, air dried and oven dried samples.Since aggregation during drying causes a reduction in liquidlimit, by the same reason the shrinkage limit should increase.Both these aux; well reflected iJ1 the figure. The equationfor a statistical fit for the data is

SL = 32.75-0.117 LL (4.3.2)which has a correlation coefficient of 0.95.

4.4 GRAIN SIZE DISTRIBUTION

Apart from the Atterberg limits, the effect ofdrying of marine clay specimens is most conspicuous on grainsize distribution as cxnl be seen from 51 number of figuresprovided in this section. ID: may be seen that aggregationtakes place at all size levels. Fig.4.4.la and b show typi­cal grain size distribution curves for 4 locations from which

128

samples were collected for the study. It may be mentionedhere that while carrying out the hydrometer analysis dis­persing agent was used as per IS:272O (Part IV) 1975.In spite of using dispersing agent and mixing the soilslurry thoroughly with stirrers, the aggregation resultingfrom air drying and oven drying could not be broken tofiner particles.

In order to study the grain size distributionof the clays with and without dispersing agents, a seriesof tests were conducted from samples from all the sites.The results of a typical test are presented in Fig.4.4.lcfor moist, air dried and oven dried soil from Parur site.It can be seen from the figure that the percentage of claysize fraction increases considerably with the use of dis­persing agents. In case cnf Parur soil tflue clay percentincreased from 36 to 44% for moist sample and for air driedsample the value increased from 7 to 29%. Similar resultshave been obtained for other samples. These results clearlyindicate that "under natural conditions, ea major‘ portionof the clay content is in the form of flocs whose sizeis larger than clay size. These flocs are not broken bythe conventional use cm? stirrers. Thus tine dispersing

129

.mm_>m:u zo_Sm:Em_o H5 z_<mo

.24 .4 at

A EEENE md_E<n_

9. 5. . 50.

5\O 1

u\uV o~

.\\.O. \4.\QO\\\.O

omEozm>o a T W _ \o:\\MM_\

omzmo E< a _ M \o\ b\\q /iom 55:0 W _ “\Q\ Jomfiow

T\Ox

mooj- xx“ E

uz<mmxu.m:m _ -om-o~

.\D\ D

xox

\ .\\\\d

‘O.\\Q \.d\.\Q.

53..

0\ \a\\\ \o oq

\

“¢\ \o\\o\

8:5 zm>o n \vA Q\\o

Dmzmo E4 6 . W fi\ 10$

gom 5.0: o

mootmz ..m:m H b\u\

1 omgoo.

130

.mm>m:u zo::mE$_o “Em z_<m¢ .£.: mm

AEEVmN_m m.3_E<a

0+0 5.0 _oo.o

A o

L

JON10¢

3&0 zm>o n M W W ­3:5 «.2 < -oo 4 o M.__om 56: o am

25<m::xm:_m

-8 no N59.0 4

omEozm>oa . _ J -oo

BEQ E< o A [ ­aom 55:0 1

om

:o<m<:” mzm

goo.

131

.mm>m:u zo::m_m$_n_ mim zzmo .u_..: .3

:55 min m3_E<a T

_b an m q m N o_o.o 5 m m m 50.0

.1; u

\n—.

Nbx

\% \W x

14¢! 1- L , 7+

M _ Aw M

“_ _ \\ n

.1‘ -._T. u f w ! .- .i\\I. r Lt IL\\o _ aw

_ \\Q

\ \xd \ \4\

\ \ \

x \I\ AX

\\L \ \l.V\\\

K \ \ \T\o\ \n\\4\ Jxxa %- \\ \\ \ mflv x

K \\ \\\.\._ \\n%

\ \\d Ox‘

\ \.I.. .||.J\|

;\ \§. \O\ O

\ xx \\ A 2 vomzmo zm>o n.

wk 1 x .Om

X o.K A : ZEEQ E4. 4«X A»zmo< mma 505;: gom 5.0: 0

.\ T- T! A .. Ewan zm>o _. om

\

. .. Swim m_< 4

A Hzuo< 35 1:2: dom 5.0: o .2:

EEE “Ea

2:i3Nl:l 24%

132

agents have a greater role to play in the grain size analy­sis by hydrometer method in case of marine clays.

4.4.1 Role of dispersing agents

Table 4.1 shows tine wide variations jfl indexproperties between initially moist and initially air andoven. dried samples. These results indicate tflunz marinesediments require special attention with regard txb testprocedures for index properties, as the initial state ofthe sample - moist or dry — yields results that are signi­ficantly different. This prompted further investigationsregarding the suitability of the normally accepted testprocedures for the determination of index properties ofmarine clays. Aggregation being the primary cause forall these changes during drying, studies on grain sizedistribution of marine clays merit special attention.Fig.4.4.2 which shows tine grain. size <distribution. curvesfor the initially ‘moist’ enui initially’ 'over\ dried‘samples underscores the necessity for the present investi­gation. They have been obtained by following strictlythe Indian Standard Code cu? practice, which ii; the sameas unified classification procedure, using soil sampleswhose equivalent dry weight is around 50 g. with lOO ml

133

.zo::mE5_o min... 2:33 ZO ozimo u_O CH7; .m..~..7m:

A EEENE M: SE5

9. mac 6. moo.o _oo.oo_come. 2 Bio zm>o , - ow

uooo 2 8:3 zm>o

QmEo ml A om

.__om Zcz

% V oq 7.H‘II: ommH

omono mom

oo_

134

of standard dispersing agent (33 g. cm? sodiunn hexameta—phosphate and '7 g. <of sodiunn carbonate in ]_ litre ofdistilled water). These curves are an: considerable var­iance with each other and the grain size distribution curvesof’ marine clay samples dried en: lower" temperatures Lairdried and dried at 60°C) fall in between these two curves.

Since» the entire clay fraction exists ixn theform of flocs, use of the type and quantity of dispersingagents plays 51 decisive role 2M1 obtaining the percent ofclay size. In this work the most suitable dispersing agenthas been identified and its optimum quantity has beenarrived at.

Dispersing agents

A series of hydrometer analyses on Cochin marineclays were conducted with different dispersing agents andquantities. ‘A deflocculating agent cxni either act em; aprotective colloid on the soil particle or alter the electri­cal charge on the particle to prevent the formation ofsoil flocs (Lambe, 1961). According to Lambe, two commonlyused <deflocculants Emma sodiunu silicate (water glass) andDaxad No.23 (polymerised sodium salts of substituted benzoidalkyl sulfonic acid). Lambe indicates that 2 <3: of a

135

freshly prepared 10% solution of Daxad No.23 has been found

satisfactory for many clays. Likewise one-half to one ccof Baumae' sodium silicate has been found satisfactoryfor most clay types. Sodium pyrophosphate has also beenused successfully. According txa Parcher and Means (1965)the same dispersing agent will not work for all clays,but sodium silicate can be ‘used successfully with manyclays and is quite commonly used. Sodium hexametaphosphate

is also frequently used as a dispersing agent.

More recently, Head (1980) states that numeroussubstances fmnma been tried for LMM3 as dispersing agents,

many of them very successfully for most soils. Accordingto Head, sodium hexametaphosphate is one of the most suit­able and convenient dispersants. The British standardrecommends 35 <g. cnf sodium hexametaphosphate with '7 g.of sodium carbonate along with distilled water tx> make1 litre <1E standard solution. The Indian Standard codeof practice recommends 33 g. of sodium hexametaphosphatewith 7 <3. of sodium carbonate in distilled water to make1 litre of standard solution. Both codes recommend 100 ml

of this standard solution for each experiment.

136

In this investigation eight dispersing agentseach 40 g. in one litre of distilled water were tried. Theyare:

1. Sodium chloride

2. Sodium phosphate

3. Sodium carbonate

4. Sodium nitrate

5. Sodium sulphate

6. Sodium bicarbonate

7. Sodium hexametaphosphate

8. Sodium hexametaphosphate + Sodium carbonate

Fig.4.4.3a and b shows the grain size distributioncurves along with percent clay size obtained using differentdispersing agents. It can kxe seen that time percent claysize varies from about 45% to 4% depending upon the typeof the dispersing agent used. To obtain percent clay size:material finer than 2 pm size (.002 mm) has been designatedas clay. Further, it can be seen that sodium hexameta­phosphate: + sodium carbonate, which has been recommendedby many, has given the maximum percent clay size.

137

.mhzmo< oz_mmmn_mE Lo SEE .om.q..~ .9,._

Ass; wim z_<mo

o_.o mod o_o.o moo.o _oo.o. o

\D

4 I mQEO;_Iu znaom D

.1: mE<zomm<u :_.:aom .. \! o.

2... E<:n::m zpaom 4 \

QQI \

+ mZ:n_mo:n_<E:<xm:.oom om m L234 oz_m..En_m_o 501:; o

A

:3 m:m<n_ H.531

lilxom

\\\\K

1

I

om

L

of

ti':'lNl:.l'/.

138

0_.0

?._.:E mdm z_<mo

m0.0 0.0.0

m _ I u»<In_mOIn_ zaaom I0 _ mC<m:z zaaom D

0 N m:<zomm<u_m zaaom 4N a I m:<:1mo:n_E m__2<x mr zaaom O

m m .. Emo<oz_mzm_n_m_o HDOTE2, O

N >m_u

magi aim

mood

_00.0

0_0.»o...owcm

00.

a3NI;i°/.,

.»zmo< ozafiama nE<oz<$ LO Swim .€.3.m:

AEEV mfim m:u_E<n_

139

070 m0.0 5.0 mO0.0 50.0

_ \ \4 SN

H 234 oz_mmmn_ma 501:2? x \

\»zmo< oz_m$n_m_o ::3< _ xx

mooCmz ..E._m _ \u 1

_\ 3

+

-3 -o~

-omIo«ZH.N3ud

Loo_.ow

9 \\.\ Hzmo<oz_mmmam_o 505:; o#234 ozafimma 1:: o

m:m<mHm:m

Lo?

140

In order to study whether the quantity of thedispersing agent runs any effect (N1 the percent clay size,experiments were conducted with different quantities ofthis standard dispersing agent.

Experiments without dispersing agents

In order to obtain more insight into the problem,experiments were also carried out without. any’ dispersingagent. Fig.4.4.4 shows some typical grain distributioncurves with and without. the ‘use cm? dispersing agent forthe marine clays from two sites of Cochin.

The test without dispersing agent showed thatafter two cnr three hours, the tuna porthmi was completelyclear enui devoid cnf soil particles indicating ea near totalabsence of colloids. There was a clear horizontal surfacedividing tine clean water above Emmi soil suspension below,slowly descendimg with time. In contrast, experiments onkaolinite and bentonite clays without dispersing agentsshow presence of colloids throughout the suspension. Therewas no clear supernatant water as was noticed for the marineclay.

141

Fig.4.4.5 shows the different stages of the soilsuspension in ea hydrometer ‘test cni Cochin marine» clay.Fig.4.4.5(b) shows the gfimmograph of ea hydrometer test onmarine clay using standard dispersing agent, after 4 hours.Eventhough there is sedimentation of grains, the soil sus­pension covers the entire volume even after the elapse ofdays, since time colloids will run: settle. Fig.4.4.5(c) and(d) show time stages after 4 anui 8 hours respectively forthe same clay where no dispersing agent was used. In bothcases, it (xvi be seen that time supernatant water isabsolutely clear of soil grains including colloids. Fig.4.4.5(a) shows the photograph of 51 hydrometer test (N1 abentonite sample without the LMM3 of dispersing agent after4 hours. .A comparison between bentonite ENM3 marine clayclearly shows that the entire clay fraction in marine claysexists in the form of flocs.

It can be clearly seen from Fig.4.4.4- that thegrain size distribution curves are entirely different forsamples with and without dispersing agents. This showedthat dispersing agents have a greater role to play in caseof marine clays. Since marine clays required more defloccu­lation or dispersion than other clays, it vuns felt thatthere is a need to determine the optimum quantity of thedispersing agent to be used.

7'9 5 "v.'°.°,." ''-.— -. - _. i- 'é,§.--’T..,.§J, *~.4r; '- ­

,, . ii .._-i._«"_¢4_-W. .'.- r:_ ­

EFFECT OF DISPERSING AGENT.

Bentonite without dispersing ogent._dfier 1. hoursMarine clay with dispersing agent _. after 4 hoursMarine clay wiihoui dispersing agent .. after 4 hoursMarine clay without dispersing agent-after: 8 hours

142

Optimum quantity of dispersing agent

Hydrometer tests were conducted with differentquantities CHE standard dispersing agent (33 gg. of sodiumhexametaphosphate 4- 7 g. CHE sodium carbonate iJ1 1000 Inl

of distilled water) varying from 0 txa 250 ml, using moistmarine clay whose equivalent char weight was about 50 gms.Fig.4.4.6 shows the plot between quantity of dispersingagent and clay size fraction. At or slightly above 100 ml;maximum dispersion of the soil particles as indicated bythe highest clay percent was achieved. It may be inferredthat beyond the optimum value, aggregation of clay particlesmay take place resulting in a reduction of clay fraction.Similar experiments for a montmorillonitic clay (black cottonsoil) showed that the changes in clay percent beyond 100 mlof standard dispersing agent is marginal (Fig.4.4.6).

Addition of dispersing agent is essential forobtaining the clay percent for marine clays in which clayparticles exist in the form of flocs. They have to be testediJ1 the natural moist condition without initially air/ovendrying. Tests with different dispersing agents clearlyindicate that the percent clay size can vary significantlydepending LqxM1 the type (If dispersing agent. The popular

143

SO I [' Ii z; \;‘s3 !5 o——% . f 5’ A w'. I

4 5 -~ —-Ar-—-« — ~«—— ——— 7- — — «,— - T*2 ' r !Im % I I ;U ‘ I35 I I % ’40 ——-- —r~-— — 5 T‘L 1 1 1' ;Z .5.4 g MARINE CLAYu

T A35 —? 7 A BLACK COTTONSOIL __I30 I IO 5 O I00 150 200 250QUANTITY OF DISPERSING AGENT(ml)

Fug 4-4-6 t EFFECT OF QUANTITY OF DVSPERSING AGEN T­

144

dispersing agent viz., the smandard solution of IE3 g. ofsodium: hexametaphosphate and '7 g; of sodiunu carbonate ixlone litre of distilled water, is found to be the most effi­cient one txb determine the cfljqz size fraction. lOO ml ofthis solution is found to be the optimum quantity of disper­sing agent which gave the highest percent of clay size.

4.4.2 Effect of increase of coarser fraction on physicalproperties

All the tests for physical properties so far weredone on samples obtained from field. These soils had arange for the percentages of sand, silt and clay as shownin Table 4.1. It is possible that marine clays with higherpercentages of sand or clay may be encountered during soilexplorations. In order tx><get an idea CHE the engineeringbehaviour of Cochin marine clays with higher sand or claycontents, four soil samples were prepared in the laboratoryfrom moist samples. Water in large quantities were addedto ‘moist’ soil 2H1 a bucket Ix and mixed thoroughly; Themixture was permitted to sediment for a few minutes so thatthe coarser particles settled at the bottom of the bucket.The supernatant solution was poured to another bucket B.

‘I45

o.mm mm.v mm.H o.m@ H.wH o.vw O.mHH ma om av Q Hflom cmucmeflcmm .mm.mm ©m.v om.H n.¢o m.mH m.mm m.moH om mm mw U Hfiom cmucmeflcmm .w

n.mv nm.m om.H m.mm m.om v.qm ».©m mm mm ow m Hflom owucmeflwmm .mm.mN wn.m mm.H m.Hm o.mm ».vm o.©m om om «N 4 Hflom cwucmeflcmm .m

u. mv.H nN.H m.mm m.mH H.mm o.mm mm mq ma mmfluc cw>o Aovan on.H mm.H H.om o.mH v.mm m.m@ om mm mm nmfluw ufim AnvH.vv mm.m mm.H v.ow v.om o.mm o.mm om mm mm umfloe Amy

flow HMHSHMZ . H

.mooH\vme

>uflummmu Aem\uuV Awv Awv Awv Awv Awv Awv Awv

mmcmcoxm xmwcfi xwwcfl uflEflH uflEHH uHEflH Ucmm uafim >mHU mwamemm mo .ozcoflumo HHw3m mmum >uH>fluu< >ufloflummHm wmmxcflucm uflummam wflzvflq coflusofluumflc mmflm cflmuo coflumfluummo .Hm

zoHe<azmzHomm wm amm<mmmm mmqmz<m mo mmaammmomm q<uHmwmm

H.~.v.v magma

146

The process was repeated with the soil—water mixture inbucket B and the solution above was poured to bucket C.The process was repeated once more and the finest soil wascollected iJ1 bucket EL After allowing sufficient time forsedimentation, four different soil specimens were obtainedin buckets A,B,C and D, by pouring out the supernatant clearwater without any loss of fines.

The index properties of the four samples are pre­sented in Table 4.4.2.1 The results clearly underscore thesoil behaviour discussed so far. The liquid limit increaseswith clay content. In soil A the clay content is only 24%and liquid limit is 56%. In soil D the clay content is49% and this increases the liquid limit value to ll3%.Corresponding variations in plastic limit and plasticityindex can be observed in’the Table.

The shrinkage limit decreases with increase inclay content. Hence the argument that higher shrinkagelimit indicates greater fraction of coarser’ particles isfully substantiated. The free swell index increase» from2.74 to 4.85 cc/gm. The cation exchange capacity signi­ficantly improves with increasing clay size fraction.

FREE SWELLINDEX (CC/9 )

LIQUID LIMIT( 7.)

147

Fig. 1.. 4. 2.1.

CEAYCONIENTIY->

EFFECT OF

5-0 I I /O1. 0-~—/R ' ’ ' ’ W /I3.0 /J,2 0 0.x

1-0

120 { W /¢_M_/I 00 "MW /30 r”’”"f““ ' T

I6 0 5502 O 35 40 "5IO 1 5 20 2 5 3 0

ER FRACTION.INCREASE IN COARS

148

The content of coarser‘ particles could .also kxaincreased knr adding ifixma sand ixl small quantities. Table4.4JLl’giva3the variation in physical properties on addition<1f fine sand. As expected the Atterbeng limits and freeswell index decreases with decreasing clay content.

Fig.4.4.2.l gives the ‘variation of liquid limitand free swell index with clay content.

4.5 ACTIVITY OF COCHIN MARINE CLAYS

To compare the clay fraction of «different clayminerals Skempton (1953) introduced the term activity whichis the ratio cnf plasticity index anui clay fraction. Itis found that with increasing activity, the cohesive compo­nent CH5 shear resistance increases whereas the fkictionalcomponent is reduced (Narain and Ramanathan, 1970). Gibsonhas studied the variation of cohesive and frictional compo­nents with activity (Trollope, 1960).

Bjerrum (1954) showed through his studies onNorwegian marine clays the usefulness of the average acti­vity for correlation with index properties. Fig.4.5.lashows the plot of plasticity" index vs. clay ‘percent for

149

moist soil. If the plasticity index and clay size fractionis plotted for a number of marine clay samples, a straightline can be drawn through these points and the origin.The slope of the line gives the average activity of theseclays. The average activity of moist soils is 1.63. Fig.4.5.lb shows time average activity lines lint air dried andoven dried soils.

Fig.4.5.2 shows the activity chart for moist,air dried and oven dried soils. The activity chart hasbeen divided into 'active', ‘normal’ and ‘inactive’ zonesas shown in the figure.

The activity of the moist samples range over 1.37to 2.47 which could be classified as active clays (Skempton,1953). Cochin marine clays become normal or inactive onoven drying. It. is needless tx> state that time colloidalactivity gets diminished on air and oven drying.

As it has been noticed in the case of liquidlhmflz vs. clay percent, one <xu1 get a unique relationshipbetween plasticity’ index and clay percent iinr moist, airdried enui oven dried samples altogether. Fig.4.5.2 gives

PLASHCITY INDEX ( x )

150

100

G) O

C3 O

xx 0

20

oO 10 20 3'0 40 5 5cCLAY PERCENT

Fig.£..5.1a:ACTlVlTY CHART FOR MOIST SOIL.

PLASTICITY lNDEX( Z )

I00 1 I IJ I gA AIR DRIED ;[3 OVEN DRIED :so I ,' |

50-——— — ~ =5‘ g5

1

7

2O

0

151

FIg.l..5.1b

30 50O ,___ 20

CLAY PERCENT

1 ACTIVITY CHART FOR AlR DRIED AND OVEN DRIED SOILS

152

.:u_<:u >:>_C< m.m..N.mE

_. zmummn. >45

ow om oq om om o. o

HMW_

M W

« -i-. H.-- .---I o. - -.-l-,- -.til.+W_-.- i!lI,ll!..-||.memo zm>o n. 1|nlI|;L

memo m_< qsow 5.02 0

cm

C)\T

0LDon8.

( /)x3cJNI /\.Ll3llSV"|d

153

this plot. The statistical fit for the data is

PI = 2.l2(C—ll.3) (4.5.l)with a correlation coefficient of 0.94.

4.6 FREE SWELL INDEX

Free swell of ea soil is defined (Indian Standard2720 (Part XL) 1977) as the increase in volume of a smdlwithout Emmi external constraint, (M1 submergence lfl water.The specimen for the test, as detailed by the code, islO g. of oven dry soil passing through 425 micron IS sieve.The~ disadvantages CHE this experimental procedure amui its

results have been discussed in detail by Sridharan et al.:(1985). The problems are much more complex in case of marine

clays as drying of the soil specimens would completely alterthe grain size distribution and activity of the soil samples.Hence the values of swelling index of the marine clay samplesreported ix: this work fumna been obtained tn! the proceduresuggested by Sridharan et al. (1985) where

V

Free Swell Index = —f% cc/gm (4.6.l)where V == the volume of ]L)<yn of soil specimen read fromd

the graduated cylinder containing distilled water.

154

Table 4.1 reports the free .swell index values asdefined by Sridharan et al. for samples from various locations.The equilibrhun swollen volume cflf the soil vdthout anyrestraint in distilled water was reached in about 7 days andthe dry weight was determined later’ as the experiment hadto be started with a ‘moist’ specimen whose equivalent dryweight was lO gm approximately.

The value was found to vary from 3.0 to 5.9 cc/gmfor" moist samples cnf Cochin marine clays. Similar ‘tests,carried out for kaolinite, and bentonite resulted in freeswell index values of 1.45 anui 6.7 cc/gm respectiveby. Asper their classification (Sridharan et al., l985) Cochin marineclays could be termed as moderately swelling.

Drying reduces the value of free swell index consi­derably. (M1 air drying the xnfihma for Nettoor clay reducesfrom 5.9 tun 2.2 cc/gnu (62%) and txb 1.5 cc/gm (74.5%) ‘uponoven drying. These values show that the swelling characteri­stics in case of marine clays can be brought down significantlyby drying. This fact can be taken advantage of in construct­ions on and with marine clay soils which has been discussedlater.

155

Fig.4.6.la and b give the relation between thepercentage of clay fraction and free swell. of’ moist soilsand free swell of all specimens respectively.

The correlation between liquid limit and free swellis shown in Fig.4.6.2a and b.

Statistical fits (EH1 be obtained for eitl the fourcurves and they are given below.

For moist soil

Free Swell = O.l2(C-1.2) (4-6-la)r = 0.89

For moist, air dried and oven dried soilsFree Swell = O.l3(C-9) (4-6-lb)r = 0.86

In terms of liquid limit values,

For moist soilFree Swell = 0.043(LL-1.7)

with r = 0.89

For moist, air dried and oven dried soils togetherFree Swell = 0.05(LL—24.4)

The correlation coefficient is 0.89.

156

.mmZn_z<m 56: mo; Hzmumma ><d m> xm_oz_ :.1.m>>m Mimi _2.o.q .m_.._

Hzmumma ><4U

On om om O4 Om ON 0. O

OM M .w .|...l : I o._

j _ 3M H 3_ 6 M.- o.m 3H ._ 7 T:._..uZ_.ou m.._:\ MIa.|||| if %- _ _..O_._:1; Iulnnlllolu XM_ 31Ilur%--:?i. -!1;.-].i: ti: Al -|ln O .m 5

, ll. . ||lO. wW I 0.5

u

.7 O _ O.m

157

gzuumma 2.3 mi, :oz_ ._._.u;>m Emu. Hf_o..?m_.._

pzmumma ><4u

o5 ow om oq om om o. o

% _ N o

__ H

11!: ..... W ..o_

W a W n

on U W D D MG G D 0%

n W . 0 W #0 M gsiillom

_ . _ ¢ 0 __ Q nG . _

_ _ q W0 o

7 mmguu. q »4 M w , :1 .I1oq

Amwuzeoumm W

7 4 ; J O .V.1I|u::- , ; - .;:I.om1 M ii om;:_zm>o nu .4ow

oEmo~:< q

; I .__om 5.02 o on

o@

( 5/3°)x3GNI113Ms 3333

158

.:om 35: mo; E23920: 3 Caz. imam H.:_.._..u$..\. am

A.\. V E2: 0503

8. of o.: of 8. om om 3 om o

o-r; IIITIIIII I‘ :a|'.II a In- |r1I-|| I _T1-I »

M

W .M0 _

:41 . 4 , we V ;I§Ia.o.~

[ O W ¢

o o

- - .II. in O . m

m@ou;

AIA 3.32.5.0 u $I|!...o..~I l|.|uI: 1-!:|! I :l|1o.m_, 1o.o;a+i. i -1 o. 5ca

(6/33) xacmn -1-13/ws 3:-12:13

159

.223 9:03

m>

xmoz_

44m3m mum;

A x :33 9:03

nm¢;flEw­

oom om. of oi oi oo. om

M

l_T»as--ii -I

W¢ 0

-- u +- éufl -1

% _ L oW I% <9 H

. .

A.i.:n._: mod" mu.

I! _,_

- I omio zm>o 0 ,Ii+V IL

SEQ E4 q

-1 .__om 5.0: o I ­

o _ .O » % W_ . o M __ r F

Qm

C?m9

\fC)LO

CD

0OS

( 5/3'->)x3c1N1 TIEMS 33:43

160

4.7 ORGANIC CONTENT AND CARBONATE CONTENT IN COCHIN

MARINE CLAYS

Studies on marine clay sediments from Santa BarbaraBasin (off Southern California) kn! Booth. and Dahl (1986)showed that good correlation exists between organic contentand Atterberg limits. The ‘Atterberg limits increased ‘withorganic content.

Nambiar et al. (1985) reported the aggregation pheno­menon of marine clays from investigations carried out on finegrained carbonate soils from off the west coast of India.The calcium carbonate content of this marine clay were veryhigh ranging over 47% tn) 55%. Since the above factors-—highorganic and carbonate contents—-could be the cause for aggre­gation, a series of tests were taken up to find out whetherthese influenced the changes in time physical properties ofCochin marine clays on drying.

The organic content of the soil can be removed bytreating with hydrogen peroxide~ and the carbonates can kxaremoved kn! hydrochloric acid. The moist clay samples were

treated with H202 and HCl and the treated samples were ovendried and the Atterberg limits and free swell index deter­mined. The results of these tests are presented in Table 4.7.1.

161

nu nu mm.H m.HH nu n.vm ow omfipm cm>o AnvH.> o.o mm.v ».om m.mN w.ow m.nm Hflom pmfloe Amy

Hum wcm momm :ufl3 cmummgu Hflom .m

nu nu o».H m.»H m.mH m.mm ow nwfluw cm>o Anym.o m.m nm.v N.mo m.mH m.mm mm Hflom pmfloe Amy

Hum cpflz mmummuu Hflom .~

nu nu mm.m m.mm m.mH m.mm ow mmfluu cm>o Aovnu nu mo.m m.Hm n.mH 5.5m mm cmfluu uflm Anvm.mH o.o mo.w ».mm ».o~ m.qw ooa Hflow pmfioe Amy

momm spas cmummup Hfiom .H

m.Hm Ho.m ww.v m.mo m.om m.mw mofl owpmmuuca

AWV W W W W

mmwmc aE@XUUg A09 A09 A09 Aov

uonumu uwuume xmwcw

EDHUHMU owcmmuo aHm3m mmum Hm um um uq wamemm wo cofiuafiuummo .Hm

BZMBZOU me<zomm<u OZ< UHZ<UmO mo eommmm

H.n.v wanna

162

It can be seen from the results presented in thetable that these two either do not influence the aggregationat all or they fail to make any discernible difference.

4.8 EFFECT OF WASHING

In order to study the effect of salt content alreadypresent in the natural moist soil, series of tests werecarried out on repeatedly washed moist soil. For thispurpose, large quantities of moist soil were taken in eabucket of 20 litre capacity and mixed thoroughly with largequantities of distilled water with a Inechanical stirrer.After thorough mixing, the samples were allowed to settledown for ea number CHE days. The clear supernatant liquidwas carefully siphoned out taking extreme care not to permitany loss of fines. In the initial few washings, the waterat the top was clear without the presence of any colloids.As the salt content got reduced by washing, more and morecolloids were released by deflocculation, increasing thetime for sedimentation. The washing was repeated till thesupernatant water is free of salts. The process took morethan 3 months. Series of tests for physical propertiesof such prepared clays were carried out.

163

Table 4.8.1 presents the test results on washedclay samples from Nettoor. It is seen that washing resultsin an increase ofliquid lindt tflunnfii not significantly. Theplastic and shrinkage limits also <get hmxeaaai marginally.The primary reason for increase is attributed to the changehi fabric from fflocculant to ea relatively less flocculantfabric. While discussing the mechanism controlling theliquid limit of soils, Sridharan and Rao (1975) have broughtout that relatively more flocculant fabric shows higherliquid limit. Bjerrum (1954) reports reduction if! liquidlimit values »n¢w1 reduction lfl salt content zfinr Norwegianmarine clays.

The free swell index of washed sample is less thanthat of natural moist sample, supporting the view that thewashed samples possess less flocculant fabric than naturalmoist samples. The marginal changes iJ1 the properties canbe attributed to less salt content of the <Cochin marineclay. It can be seen from Table 4.1 that the salt contentvaries from 5.9 to 7.3 gm/litre. In comparison the Nor­wegian clays are sflgnificantly affected kn! washing becauseof the high salt content in its natural state (Bjerrum,1954).

164

wmfim CHMMU

o».A mm.A mfi mm mm v.om m.Am m.vm m.mo mmflum cm>o AuvoA.m ©m.H ma vm om m.mA m.©v m.mm m.mm mmfluu uflm ADVm».v m©.H ofi Av mv m.Am m.m© n.mv o.moH Hflow umfloe Amy

Hfiom wmcmmz .m

wm.A mm.o mm ow mm v.Am m.Nm ».mm m.om wwfiuw :m>o Auv©m.m om.A om vv om m.om 5.5m m.mm o.mn mmflun uflm Anyvw.v mm.A ma mm mv m.om m.mo m.mv o.moA Hflow umfloe Amy

HHOM Hmusumz .H

Aemxuuv Aw wv wv Awv Awv Aw Awv

mmam mwam wmam

. . . uflefia xmwcfl

xwvcw .%“fl> mcmm uawm >mHnV mom mufiu uaedm uaedm .oz

coausnauumaw . . . .

HHw3m mmum IHuu< . . . Ixcflucm Iflummam uflummam ©wSUflA HHOW mo cofluafluuwmo .Hm

AAHOW msm<mV uzHmm<3 mo eummmm

H.m.¢ magma

165

It may be noted from Table 4.8.1 that in spite ofrepeated washing, the reduction in liquid limit of air driedand oven dried samsples are of the same order: thus reveal­ing that presence of excess salts is not the primary reasonfor aggregation.

4.9 EFFECT OF SOAKING ON DRIED SAMPLES

To explore the possibility of the initially air/oven dried soil regaining their original properties priorto drying, the samples were tested after soaking them inwater for different periods. The results are presentedin Figs.4.9.l and 4.9.2. Although the liquid limit steadilyincreased with duration of soaking, it could not reach itsvalue corresponding to that of original moist samples.It could attain cnflqr about 80% (H3 its original value forinitially air dried samples and 62% for initially oven driedsamples even after soaking for 2 years. Correspondingly:the plastic limit of initially air dried sample increasedfrom 35.3 in) 39.5% on soaking. D1 case of initially ovendried samples, the value increased from 33.7 to 36.5%.

It can be seen from Fig.4.9.l that the bulk of theincrease ix: the value» of .liquid limit enui plastic limittakes place within the first 3 tun 4 months. The increase

166

.C_2_._ u:m<._n_ a C23 0503 ZO oz:..<om .3 Bm..E.h:.m..~ .9...

$23 n_o_mmn_ oz_x<om

O00. com 8. om O _ m _

omI oq

CE: u:m3n_ aom $.62 ._<m:Ez

M

omomonJ om

3:2: u:m<._n_ V 2 4

I A :2: 930: V 8.5 zm>o q om

MA _. .2: u:m<E .. . 2 0:3: 9303 V Bio E4. o

maxi “Ea

w.iV.lI ; F A . V 3.

2.2.3503 .__om 55: :E2<z

O:

(7. nuwn 3liSV'1d /uwrl OIflOl'1

167

coo _

.xmoz_

oom

.:m_2,m HE zo oz:_<om no CHE m.m.q.m:

A $35 Eozba oz_x<om

O0. Om O_ m _

o._.n.._o.~mao.m

ow_IQZm>O 4

ma

omio m_< o

mDm<n_ _m:m

- u. !- O..V

.:Om F902

(5/33)X3CJN| TIBMS 3353

168

thereafter is marginal. Hence it could perhaps be surmisedthat aggregation is almost an irreversible process.

The variation in the free swell index value for24 months duration of soaking is shown in Fig.4.9.2. Freeswell index increases with soaking period and time rate ofchange is higher than that of Atterberg limits.

4.10 EFFECT OF SALTS

It is possible that addition of salts like sodiumchloride and calcium chloride can kmnne marked changes inthe physical properties of these marine clays. In orderto get a gnxfliminary information on this, index and otherproperties were determined with different percentages ofsodium chloride and calcium chloride salts. For these;the moist soil was mixed thoroughly with 5 to 20% by dryweight of sodium chloride and calcium chloride salts andthe physical properties were determined. It is seen fromTable 4.10.1 that addition of salts reduces the liquid andplastic limits. While the reduction in liquid limit ismarginal (138 to 122%) for the addition of 20% sodium chloride,

the reductbmi is quite considerable (138 txa 102%) for theaddition of 20% calcium chloride. The effect of salt con­centration fun; been explained kn! depression <1f electrical

169

om.m II II II ©.NH o.mo o.vm o.moH ©v.m magma wow AmNH.m II in II o.vH o.mm 0.0? o.mmH mo.m maomo wofi Am©H.v ma mv om v.¢H o.wm 0.5V O.HmH mm.~ «Homo wm AH

mcfipoasu esfloamo + Hfiom umfloz .m

on.m In In nu H.om m.mm o.mm m.mmH mm.m Humz wow Ammm.v In In In w.mN o.nm o.mv o.mmH om.m Homz wofi Ammmé wm mm 3 ma: o.om «.8 oéfl ofim Smz wm S

mm.v vm mm vv m.wH o.om v.mw o.wmH wnfluofigo esflcom + Hflom umfioz .mom.m am am mw om.nA o.om m.~v m.nmH mn.m Hflom umfioz .H

Asm\ooV Awv Awv Awv Awv Awv Awv Awv

QNHW wmflm mmflm xmwcw

xwwcfi vcmm uafim >mHu wmm >ufiu uflEfiH UHEMH >uw>mum

HHw3m wwum coflusnfiuumflv wmwm CAMMU Ixcflucm Iflummam ufiummam UfiDUflA ufimflummm umwu man we coflumfluomwo .Hm

Auaom mooaamzv mmaammmomm g<uHm»mm Z0 mau<m mo maummmm

H.oH.v magma

170

double layer (Olsen & lfiesri, 1970; Mesri & <Dlsen, 1971:Sridharan & Jayadeva, 1982). In this case also the reductionin liquid limit could kn; attributed ‘to time depression <3fdouble layer because of increase in salt concentration(Sridharan & Rao, 1975).

Table 4.10.1 also presents data (N1 shrinkage limitand free swell index. The shrinkage limit with sodiumchloride ans additive runs shown significant increase, whilecalcium chloride as additive does not show much variation.Further there is 51 marked reduction in free swell indexwith time increase iJ1 salt content. This can kn; attributedto deflocculation and aggregation of particles. The slightincrease in silt size and sand size content supports themarginal formation of aggregation due to addition of salts.

4.11 SHEAR STRENGTH AS RELATED TO WATER CONTENT

In Greater Cochin area the layers at shallow depthshave their natural nwdsture contents quite close tx> theirliquid limits. The» clay deposits below’ vary’ widely inconsistency upto 40 to 50 m where good load bearing stratumcan kxe met with. While large kfitflm rise buildings arenecessarily founded on these strata over 40 to 50 m below,

171

structures of lesser height are supported by friction piles.D1 order ‘U3 design these friction pales, ii: is essentialto cget EU] accurate assessment cyf shear‘ strength <1f thesemarine clay deposits. Since the consistency of the claylayers varies widely, the estimation of shear strength canbe done cnflgr through shear strength tests (N1 numerous un­disturbed samples. Since this is a tedious and time consum­ing process, the need for a faster and easier techniquefor estimation of shear strength is keenly felt by <geo­technical engineers handling foundation problems in softmarine sediments all over the coastal belt in Indian penin­sula.

Even during the soil exploration, it was foundthat collection of undisturbed samples of extremely softclays was a (difficult task, as the sampling tubes couldnot hold the samples due to its poor adhesive strength.At the same time it was found far easier to collect repre­sentative samples, though disturbed, with the help «ofmechanical means smufli as augers. D1 this study on Cochinmarine clays efforts were made to develop correlations bet­ween the index properties of clayey soils and shear strength.The results of the investigations to predict shear strengthof Cochin marine clays based on their natural moisture

172

contents area presented ixx this section. The applicabilityof the results were tested for other soft fine grained soilsof high liquid limit.

4.11.1 Water content ratio

The shear strength. of clayey’ soils its dependentcni its water content. Any increase ix) water content isnecessarily accompanied by a reduction in cohesion or shearstrength. But an: the same xunxm: content, different soilshave different shear strength, as shown ix) Table «4.ll.l.The table gives the shear strength values of five differentsoils whose natural water contents vary from 100 txz 106%.Eventhough the natural water contents are in the same narrowrange, the marine clay from Maradu in Cochin has the lowestshear strength of 0.0175 kg/cm2, while bentonite has a shearstrength of 0.115 kg/cm2. Thus if the nmatural moisturecontent alone its taken as time basis, the shear .strengthbehaviour looks highly erratic.

Eventhough ea comparison between natural moisture

content and shear strength does not indicate any possibilityfor a correlation between the two, incorporation of theliquhfl limit values into time analysis shows some definite

173

Table 4.11.1

NATURAL WATER CONTENT AND SHEAR STRENGTH OF CLAYEY SOILS

S1. Soil Natural Shear Liquid WaterNo. water strength limit contentcontent 2 ratioW (%) (kg/cm ) WL(%) W/WL

1. Cochin marine clay 105.9 0.021 118.3 0.90(Parur)

2. Cochin marine clay 105.7 0.0175 105.7 1.0(Maradu)

3. Cochin marine clay 105.8 0.0236 119.1 0.89(Elamkulam)

4. Bentonite 104 0.115 307 0.345. Black cotton soil 101 0.021 103 1.0

174

trends. Tabbe 4.llQl also shows the liquid limit valuesfor the soils listed. It could be clearly seen that forthe same water content, the shear strength is directly pro­portional tn) the liquid ljmfii: values. Thus ii: is obviousthat shear strength values can show regular and consistenttendencies only if it is correlated to natural moisturecontent along with the respective liquid limits. A newfactor called ‘Water content ratio’ defined ans the ratioof natural moisture content to liquid limit is introducedhere txi obtain 51 regular correlatbmi with shear strength.Obviously shear strength is inversely proporational to watercontent ratio (WCR) though not linearly.

Significance of water content ratio

The utility and versatility of the proposed watercontent ratio zhs well brought out knr figures 4.ll.l.l and4.11.1.2. The shear strength at different water contentsobtained from laboratory vane shear tests on remoulded repre­sentative samples of Cochin marine clays collected fromtwo sites are given in Fig.4.ll.l.l. Eventhough the twosites are within Greater Cochin, the sampling locationsare separated tnr 35 km. But the clays are (M5 the samegeological origin. Samples from Kumbalam had a liquid limit

175

of 98% while Parur sample had a liquid of 118%. The samplesgive two separate curves as shown in Fig.4.ll.l.l. Thesetwo curves do not help us to establish any correlation bet­ween shear strength and water content.

Fig.4.ll.l.2 gives a plot between shear strengthand WCR for the two samples. It can be seen from the figurethat the two curves merge into one single curve indicatingthat good correlation zhs possible- between shear strengthand water content ratio.

The liquid limit value of any clay is dependenton the clay mineral and the clay content of the sample.As the clay content increases, liquid limit also increases.Similarly clays containing montmorillonite clay mineralwill have a higher liquid limit than kaolinite clays. Boththese have sdgnificant influence CH1 the shear strength ofclayey soils. But the influence cnf both are convenientlyincorporated by normalising the water content by expressingit as a ratio of natural moisture content and liquid limit.

A semilogarithmic plot between shear strengthand water content ratio can give a better correlation betweenthe two as shown in Fig.4.ll.l.3. The data from Fig.4.ll.l.2

176

.oZ<m pzmfizou $23 9, Eozmmfi Efizm m._.:.q .9;

:>\>> o_:.E Hzfizou m.u:<>>

o 9. ac m.o éo 9o mo so m.o

% o.o

!- 3.0

/ O

/,V

9/ moo

/////

T f.om__ m:m<a o »(.om¢

mm :<4<m::x u .

x Aom . qwo

.

g mac

(aw >/5>t)HL9N3a1S z-.w3Hs

177

gzmfizou E:<3 2, :Sz....;:m m<H.:$ 2:; .3

AN V hzflzou mmzis

of

o _ o: co. 8 pm on om om oqo

o//

/O/ I..nI.I)II/

« /or I////y

/ fix cod.

/i/

M an 8.0

//

5 C..u , w/ V, S o a// Su, m‘I. , 3-1! ,, 2 o Mm__ z:m<a o / mmo zqimzax u ,, 1Q , Om.O\/A x V Sm , MA .: 29:33 -23 ,, /3

.

. qwo wz

mac

178

are plotted in Fig.4.ll.l.3 with shear strength on loga­rithmic scale and water content ratio on natural scale.Excellent linear relationships have been obtained for thetwo soils. They also have almost the same slope. Experi­mental data cum two ‘more samples (Hf Cochin marine clayscollected from tun) other sites viz. Maradu and Elamkulam,

are also plotted in Fig.ll.l.3 which gave the same slope.

Fig.4.ll.l.4 shows the semilog plot between watercontent ratio and shear strength values of the same foursamples of Cochin marine clays. It can be seen from theplot that a linear correlation could be easily obtainedbetween water content ratio and shear strength for Cochinmarine clays, though the clay percent and liquid limit valuesof the individual samples are different. A statisticalfit to the experimental data gave the following expression.

WCR = 0.231-0.414 lOgT (4.ll.l.l)with a high correlation coefficient of 0.987.

Correlation between liquidity index and shear strength

Attempts have been made by earlier workers tocorrelate shear strength with liquidity index of clays.Plots between these two for different clays collected from

.o_Zm E328 E23 3 Eozmmfi mfizm 3.: 4‘. .9...

A 5&3 0 15255. Ebzm

179

0m.

? .

mo.

_0.

4 «.0

:<5x:<._m

L

10.0; «.03.? ob

O

-- .. 0 0 J «.0

E <._<m::x

00; no 01

@

: _

2073.004

©

0«.00.00.00;

OlJ.VH J. N31 N03 H3.LVM

180

O4

.923 m_zE<z 2:68 mo; 53 m> :Bz..#:m m<m:m

A~c::axv:»ozmmHm m<m:m

qee_¢.mm

om ow mo. . . A90

:§;fl £:§fl 2

M M j _ _ % F "

1 . Tl. W * I!

WM MW % . . _

_ W. _ _ mmmAuu_

+;+ .:q.o.._mm.ou 53!? - Yo

M _ WW M _ _ _

__; + ..f{ ---i!il1o¢

:<4<m::x u » W:o<m<: 4 M

:<4:x:<4m om:m<m o

zo:<uo4 -pmm W__ __ 5 _ M

°OlJ.Vti l.N3iNO3 HEILVM

181

literature are given in Fig.4.ll.l.5. Eventhough Wrothand Wood (1978) proposed a linear relationship between thesetwo: plots in 2Fig.4.ll.l.5 clearly indicate that this isfar from reality. Leroueil et al. (1983) gave the followingexpression

(c ) = 1 (4.11.1.2)2

(IL - 0.21)

which is not a simple linear expression as claimed by them.Further, correlations with liquidity index involve the deter­mination cnf plastic limit iJ1 addition tx> liquid limit. Yetthe liquidity indices for the various samples cnf Cochinmarine clays are plotted in Fig.4.ll.l.6 from which it canbe concluded that the relation between liquidity index andshear strength is not linear. Thus the method of correlat­ing shear strength with water content ratio is simpler andhas great potential for design applications.

4.11.2 Correlations for other soils

The method proposed can be acceptable only ifthe correlation suggested is xmfljri for other clayey soilsalso. Laboratory vane shear strength was found. out forthe following four soils by varying their water contents.

182

.x moz_

>_._Q_DO:

m>

A N529: 18235 mfizm

Eozmgm mfizm

5 .:.q .9“.

O.— O—. mO. $ . —O. mOO.. o

M #M _ W_ j

1 & I... ILT- I alomo

J M -w-Ito,wo

W . W %

% _ W M -¥-Jm--.J o 9 o

_ _

M --|m OO.—

r . k _

mi "SEE .. om Eoamoo .. M [

vi mm §S<m::x _. E zm><4m:m a It w:_.--%7I_.| W or

mo. 852: 4 I 2829 a W _ _ H

a: £393 0 om zoEoI o _ . 32.: .mE__m:o$: %

. . -. , E A E.oL: % oi

4» am W , N _ :§L,,,,

, _ _“ _ _

j T % 3_ _ % F _ A

of

XHGNI A.L|OlflO|'l

.m><d uz_m<: 2:58 .. :SzmE._.m Eizm 9 V352. >:Q_DG: f._3.9...

183

Ame <3 E5235 mfixm

cg om. or mo. 5.

€ d a g a : _ _ % 5

M . , __.... : . _ M

Ww W. 0. ll V - T. ;l.Jo~.o

M V OD . n

1 _

W _ lnO_<. ¢ N

w 1!, I ..I won w, T: :¢ra;%;:I.o€o

_ M 4 _D _

L I 0 M .

.1; W W _ T D

. F % M on onm:m<a o W N «own W:<4<m::x u L H W

1!‘... _D .-I nll ill .

3o<m<: 4 _N oofi omo

. _ 4a

:<4:x:<4m o H u o

1 Ir H M W zltoo;

4 zo:<Uo4 -mmm M % Mu:Ho.

M H W __ _ . . ._ H ~ W , _ r H

X3ClN| ALIOIHDIV

184

l. Bentonite

2. Black cotton soil

3. Red earth (passing through 425 microns sieve)

4. Kaolinite

The results are plotted in Fig.4.ll.2.l. In thesecases also, linear relationships could kxe obtained betweenshear‘ strength Emmi WCR. Fig.4.ll.2.2 shows time liquidityindex xui. shear strength relations for time same four soilsshowing rm) uniqueness. .A comparative study cnf these twofigures underscores the superiority of the proposed correla­tion for shear strength.

The plots in Fig.4.ll.2.l indicate some morepossible uses for these correlations. While kaolinite clayhas time least slope for the 1j- WCR plot, the bentonitehas the maximum slope with other soils falling in between.The variation in slope indicates the possibility of identi­fying the clays cnf similar‘ geological origin and similargeotechnical behaviour using these plots. Clays withkaolinite mineral (such as red earth) will fall in the regionwith flatter slope, while soils containing montmorillonitemineral (such as Cochin marine clays) show a steeper slope.

185

.m:om _.zH.EH.rE_o mob. mu; 9, p H §.:..N .3

A ~E:9::Szm«:m z<m:m

of om. 3. mo. 5.

4 a A

m:zo:$m:_ ,

-1 .m.OA_O.O

.vIo| . r . ‘olllil

M %M _ %T.__om ,

zotou vafimfi‘ ,1­

_M__

_ W

04

Ol LVH LNEHNO3 HELLVM

186

om.o

mdom HzE..mt_o mo“. $02. C530: 2, PM ~33 mi

$539: 1523.5 mfizm

9.0 8.0 S.o

o3- 1 1|: :3- V 2.0, %%%%%%% % so

/7/

/ ., 3.0

/o/

5 .230: < 1

_/,-|- rue I

utzohzmmo / om.o

:»m<m ammo

sow zoC8 64.6 o W . ,

4- N, -W._Lr.ll-I:--_ "IA |i|II|I1OO.—

_ M MW _ _

XBCJNI ALIGIHOIW

187

The possibility of correlating water content ratios withcompressibility has been investigated (Nagaraj & Murthy,1983 and 1986).

Table 4.11.2 shows the shear strength of differentsoils at their liquid limits and plastic limits. The valueof shear strength at liquid limit is reported to vary inthe range of 15 to 30 g%cm2 (Sridharan & Rao, 1975). Thepresent investigations show tfluflz it varies from 11) to21 g/cm2. At plastic limits, shear strength varies from180 to 600 g/cm2. In case of Cochin marine clays, the shearstrength ranges over 14 tun 19 g/cm2 at liquid limit and380 to 540 g/cm2 at plastic limit.

The above discussions show that a good correlationcan be established between the natural water content andshear strength cnf the clay. Water content ratio providesthe relation between the two. Good linear correlation couldbe established through semilogarithmic plots between watercontent ratio and shear strength. The slope of the straightlines can help tun identify the cflay nuneral. Thus watercontent ratio can tn; a simple and useful factor to assessthe shear strength of soft layers.

188

Table 4.11.2

SHEAR STRENGTH OF DIFFERENT SAMPLES OF CLAYS

S1. Soil type L.L. Shear strengthNO‘ <%> (kg/cm2>AT L.L. at P.L.

1. Bentonite 429 0.013 0.262. Black cotton soil 100 0.021 0.603. Kaolinite 47 0.0105 0.184. Red earth 51 0.021 0.215. Cochin marine clay

(a) Parur 118 0.014 0.43(b) Elamkulam 119 0.0157 0.54(C) Maradu 106 0.0175 0.41(d) Kumbalam 98 0.019 0.38

189

4.12 DIELECTRIC CONSTANT OF PORE FLUID AND INDEX PROPERTIES

Eventhough Atterberg limits were originally devisedfor classification, its utility and significance in geotechni—cal engineering steadily increased as more and more soilproperties such an; surface area, cation exchange- capacity,swelling behaviour, California Bearing Ratio, compressibility,shear strength, compaction etc. were correlated to them.Since the dielectric constant of the pore medium exercisesconsiderable influence on the shear strength of the soilthrough variations in the thickness of electrical doublelayer, the consistency limits of fine grained soils shouldbe influenced by their values. Eventhough Kinsky (1971)reported that there is a tendency for the liquid limit valuesto increase with Cheflectric constant, the values reportedhas considerable scatter. Judging from the behavioural patternin other properties, this correlation should have been moreregularu Studies on <Cochin marine clay using differentdielectric liquids helped to confirm the correlation betweenliquid limit and values of dielectric constant.

Liquid limit tests were carried out in Casagrandeapparatus or cone penetrometer using the following six fluids.

. Carbon tetrachlorideEthyl acetateAcetoneMethanolDimethyl sulphoxide

O\k.J'l-I5-U)l\.)IA . Water

190

To obtain the influence of the above organic fluidson liquid limit value of Cochin marine clays, ‘moist’ samplesshould have been used. But since :H: was found difficultto obtain ‘moist’ samples in which the marine pore watercould be completely displaced with these organic fluids bycirculation or permeation, oven dried marine clay sampleswere used for carrying out the tests for liquid limit. SinceCMHH1 drying considerably’ influences tflue physical propertiesof the soil as discussed earlier, this change is bound toinfluence the liquid limit values and correlations couldbe different from Vflun: they really ought to Ema But sinceX-ray diffraction studies have already indicated the typeof the basic clay mineral in Cochin marine clay to be mont­morillonite this variation could tn; considered while inter­preting the results.

Table 4.12.1 shows the properties of the cmganicfluids used for the ‘test euui the ‘values of .liquid limit.Since it Inns been reported that tflua mechanisms controllingshear strength are different for montmorillonite and kaoliniteclays, tests were carried out on those clays also to obtaina comparative study with Cochin marine clays.

Since some (M3 the pore fluids used are volatile,it was difficult to find out the liquid limit value usingCasagrande's apparatus. The liquid limit tests using

.AmmmHv uwmuwnmmflwz ccm Awomav ummwz uflwmmav cusncmmz Eouw vmuumaaoo mum mmfluuwmonm GHDHM mce «

191

o.mH mH.Hmm o.m¢m mm.H mm.mnH o.m© mH.H mm.omH o.mv v.om vm.H mmm.o umumz .©

mwflxocmasmHwnume

oH.m In II In In In In In In m.wv om.m ooH.H ufio .mmm.H om.mmm o.mo om.H mv.mmH o.ow ~m.H vo.mvH om.Nv mo.mm v@©.H um». Hocmcpmz .w

oH.m om.mom o.mo om.H m.mmH o.mv om.H om.mmH o.oq on.om m>.m mm~.o m:oumu¢ .m

wumuwum

nu nu nu n nu nu u nu un mo.o Hw.H mmm.o Hwcum .m

wwfluoanuumuuwu

o©.m HH.mmH o.mHH om.H mm.mvH om.ow on.H mm.onH o.moH wmm.m o mmm.H conumo .H

3; A.» 13 E; Q; 13AEm\uuv Amflmmn Amflmmn AEm\uuv WHWMD mflmmn AEm\uuV Amflmmp Amflmmn

xmwcfl .Ho>V .u3V xwwcfl .Ho>v .u3V xmwcfi .Ho>v .u3V

HHm3w uaeaa uaeaa Hawzm uaeaa uaeaa aamzm uaeaa uaeaa

. . . . . . . . . . . . Pcmmwmwcnumv 9

85 mmaflmmnvvficmflswfl wmufim EEUS 3&3 8%.. 2:63 3&3 .1 oi Lcmeoa CUES 323 .ozu. u m >mHo wcfizwu cwcuoo mumcwaomm IMUGHGHO «waomflm «wufimcwm muom .Hm

muaom mo mmaammmomm u<uHm»mm QZ< mQHDAm mmom mo az<amzoo oHmaumqmHo zmmzamm zoHa<qmm

H.NH.v magma

192

pore fluids other than water were carried out by cone penetro­meter; The ‘water content that will permit a penetrationbetween 20 rmn amd 30 mm was determined and liquid limit was

found out from the equation

WL = wd + 0.0l(25—x)(wd+l5) (6.8.l)

where WL = liquid limit of the soil

wd = moisture content corresponding to penetration x

x = depth of penetration of cone.

Fig 4.12.1 gives the plot between the liquid limitof oven dried Cochin marine clays and <flielectric constantof the pore medium. The liquid limit values were calculatedby volume basis as the unit weight of the pore fluid usedwas different from one another. The water content by volumebasis is defined as the ratio of the volume of fluid to thevolume of solids expressed as a percentage.

The figure shows tflmn: while the liquid limit ofbentonite increases significantly with the dielectric constantof the pore fluid, that of kaolinite shows a decreasing tend­encyu The liquid limit cnf oven dried <Cochin marine clayshows 53 tendency tun increase vniflu increase lfl liquid limitbut considerably lower than the increase shown by montmorillonite.

193

The behaviour of bentonite and kaolinite which representtwo different types of soil structure has been explainedvery well by Sridharan and Rao (1975).

Mechanisms controlling liquid limit

Both attractive and repulsive forces of an electri­cal nature exist between clay particles (Kruyt, 1949; Lambe,1958: Rosenquist, 1955). The ‘primary’ parameters aaffectingthe electrical forces are the distance of separation of theparticles and tflue dielectric constant cm? the medium (Kruyt,1949; Davies, 1965: Lambe, 1958). The electrical attractiveforces vary inversely with the dielectric constant cnf thepore medium and tflua repulsive forces increase directly withdielectric constant (Sridharan, 1968: Sridharan & Rao, 1971,1973, 1975). An increase in attractive forces increasesthe shear strength while an increase in repulsive forcesdecreases the shear strength. Consequently, an increasein the value of dielectric constant shoulti be accompaniedby a decrease in shear strength.

Liquid limit is essentially a test for shearstrength. It is the water content or fluid content at whichthe shear strength is around 15-30 gm/cm2. Therefore anincrease in dielectric constant should bring down the liquid

194

limit value. But from Fig.4.l2.l only kaolinite followsthis dictum. In case of montmorillonite and oven dried marine

clay, the liquid limit increases with dielectric constant.

The peculiar behaviour of montmorillonite hasbeen well explained by Sridharan and Rao (1975). Other factorsremaining same, the thickness of diffused double layer variesdirectly with dielectric constant of pore medium (Lambe,1958). Eventhough there is 53 reduction jfl shear‘ strengthwith E , the increase in thickness of diffused double layeris more predominant. Thus the liquid limit of clays of themontmorillonite type increases significantly with

It can be seen from the figure- that oven «driedmarine clay occupies a position in between kaolinite andmontmorillonite. The liquid limit of oven dried Cochin marineclay tends to increase with dielectric constant, but thevariation is not significant. Eventhough Cochin marine claysare montmorillonite clays, because of its formation in salineenvironment it undergoes considerable changes on air or ovendrying. Due to aggregation of the finer particles, the thick­ness of the double layer of oven dried sample is not as largeas time moist marine clay. Thus, eventhough, tflme plot foroven dried marine clay shows an inclination for higher values

1

LIDDID LIMIT (VOLUME BASIS- °/.)

195o Do I ’I C] BEN TONITE j 7900 ''-——“——‘ro T» o MARINE CLAYI OVEN DRIED) IA K AOLI NI TE I800- II RI I' ! I

700 _4—« ------—-- -— -­

6oo___

500 ————‘——~ ~

z. oo ~E——­

30o _- , I2 oo _D__#%##,fl _ -_Iv T‘100D ID 20 3o 1. D so so 7o so

___, DIELECTRIC CONSTAN T

Fig. 1.12.1 LIQUID”­ LIMIT VS DIELECTRIC CONSTANT

196

for liquid limit with increasing values of E 1 the variationis quite subdued.

Fig.4.l2.2 shows the free swell index for bentonite,kaolinite and oven dried <3ochin marine clay, in cdifferentorganic fluids with varying dielectric constants. Bentoniteshows a free swell index as high as 19.0 in water and aslow as 2.6 in carbon tetrachloride. The variation in kaoliniteis very low. Oven dried marine clay shows similar tendenciesas bentonite tun: the variation its far below the free swellindex shown by bentonite.

FREE SWELL INDEX (cc/ g )

20

I8

16

14

12

TOT

197

Fig. 4.12.2

I I II ;__ D - - . «I II ID BENTON I TEo MARINE CLAY . I(MOIST SOIL) I I0 MARINE CLAY( OVEN DRIED)A KAOLINITE I— I I I-_..__._ —--~T--— — iI I II I I = I—————I~ —— ~ — ——-—+— »+«EE——I I I I II I I Ii I____-- I I - —— lfiI II I ' II.__—______ 4 I- ---—»-——--E» — 4' —I---—I OL ———— + — — ~— — -——— T»-— ——I I 'D D _.AL _ _ _ _I __ __ _ _ 1

O__ ._—— —-8_——-- —-" ‘'''I'' -;_/E_)_ P %-E

O 10 20 30 40 50 60 7O 80DIE ELECTRIC CONSTAN T

FREE SWELL INDEX vs DIELECTRIC CONSTANT.

Chapter V

CONSOLIDATION CHARACTERISTICS OF COCHIN MARINE CLAYS

5 . 1 INTRODUCTION

Consolidation has been a major concern tobuilders for 51 very long time. Kerisel (1985) reportedthat 6000 years ago, Sumerians built Ziggourats — embank­ments to support temples — on the soft soils of theEuphrate valley. One (M3 the temples, the white templeof Eridou, has now its foundation 12 m below the street.Since that time, a great number of structures settledand suffered damage. with the rapid industrialisationseen during the last few decades and consequent urbanisa­tion, it has become necessary to occupy lands that wereearlier avoided and marshes considered unsuitable forhabitation. Thus the spate CHE buildings (N1 soft soilsmultiplied.

Another consequence of industrialisation isthe increasing demand for water, which is often takenfrom the subsoil. The consolidation of marine deposits

198

199

in coastal cities like Tokyo, Stockholm, Shanghai, Veniceetc. has caused some settlement problems (Leroueil, 1988).Yamamote (1977) estimates that in Japan 1200 square kilo­meters of valuable land has submerged below the sea level.Vast stretches of areas in the coastal belt of Kerala,with deep formations of marine clays, pose serious problemsto the geotechnical engineers. Hence the compressibilitycharacteristics of marine clays is of great significance.

The consolidation test provides basic informa­tion (N1 the compressibility characteristics <1f soil. foruse in computation of the magnitude and time rate ofsettlement resulting from cnma dimensional consolidation.To improve the applicability of the test results, theseries of tests planned should simulate as closely aspossible the conditions which exist for an element ofthe prototype in the field. To achieve this objective,the series of consolidation tests planned should takeinto consideration as many parameters as possible whichinfluence the volume change behaviour of fine grainedsoils.

5.2 AN OUTLINE OF THE TEST SERIES

In an extensive study of the compressibilitycharacteristics cnf these marine deposits, several series

200

of consolidation tests have been carried out to accommodate

the implication cnf various parameters like time effect ofdrying of marine clays, duration of load increments,accurate assessment of preconsolidation pressure, etc.Since the engineering behaviour‘ of’ montmorillonite soilsis governed by the physico-chemical environment than thesoil fabric (Sridharan 5; Rao, 1973, 1975: Sridharan. &Jayadeva, 1982: Kinsky ea: al. 1971: Mesri & Cflson, 1971)the dielectric properties of the pore fluids exercise signi­ficant influence on the compressibility characteristicsof these clays. Leaching of marine clays can alter thephysical and engineering properties of marine deposits(Bjerrum, 1954). An attempt has been made to study thegeotechnical behaviour of Cochin marine clays in the back­ground of the above aspects.

As indicated earlier, several series of consoli­dation tests have been carried out to study the consoli­dation properties of Cochin marine clays. A number of testshave been carried out on untreated marine clay samplesand the remaining were conducted on clays treated withadditives.

201

5.3 COMPRESSIBILITY OF MARINE CLAYS

Several series of consolidation tests were carried

out (N1 saturated undisturbed samples from Parur, Nettoor,Maradu, Kumbalam, and Munambam as per standard procedure.

The procedure for determining the one dimensional consoli­dation behaviour has been described in detail in chapter IIIIn order to obtain "remoulded" samples, soil taken outfrom the same sampling tube, was worked on thoroughly andhand remoulded into the consolidation ring without permit­ting any change in natural moisture content.

For" the ‘present series, a lxmui increment ratioof one has adopted and the samples were inundated ‘withbore hole water. I\ duration of tuna days was given to allsamples for each load increment unless mentioned otherwise.

Fig.5.3.l shows typical e — log p curves forthree undisturbed samples from Kumbalam, Elamkulam andMaradu. The samples were collected from depths of 9.5,4.5 and 9 metres respectively. The curves show preconsoli­dation pressures consistent with the depths. .Fig.5.3.2shows the e — log p curves for two undisturbed samplesfrom Nettoor; The upper curve has a load increment ratioof one. For the second curve the sample was loaded with

202

smaller load increments to arrive at the preconsolidationpressure more accurately. The curves are more or less para­llel indicating that the load increment ratio of one can describethe compression of marine clays satisfactorily.

The e - log p curve for the remoulded sample isalso shown in the figure. A comparative study of the curvesshows that remoulding destroys the bond strength completely.At higher’ pressures both undisturbed and remoulded samples

almost merge at a void ratio nearly equal to 0.4 eo whichagrees well with Schmertmann's (1955) observations.

Fig.5.3.3 shows some typical e — log p curves ofundisturbed samples obtained from three different locationshaving different liquid limits. The ratio of initial watercontent (Wi) to liquid limit (W) is approximately 0.9 forL

these curves. It may be noted that the curves are placedin the order of their liquid limits and they tend to mergeat higher pressures. Efig.5.3.4 shows another pair of

e - log E3 curves with WE/WL nearly equal to CL7. In bothcases higher plasticity curves are placed above those withlower plasticity (Lambe, 1958).

IS:272O (Part XV) 1965: Methods of test for soils-—

determination of consolidation properties, gives the method

.m

5&3:5: 9: a .mm:mmmmn_

0..

Q Oo_...u

H mam

0..

.21..

203

n Nwf _ _ _-i1r aw V. -- 1+: WW T J1- u w -- - H - T -­

M MW_

, _ M

/ n

’(||.| |uL_.| r Incl ITIJI- 9 I * ll. ...'uI|-I.­

/ _

/

/ W

I ,.

._ u/ r;

M J;_ /

r H _ W

If I Y .4! gr I ||':.\.iT- I a

. O,/O/I

W _. _ I

_ I

:3 I 5---? m 15% b; - ­

# _ . AV;

% _ _ _ _ /0;

_ .

_ . _ _

+ I- rnr fi-T!-_1--. I 1- -1.

I

._ ..... _.--___._____r-....

_.__V­-_+__ j_ -4 ..-.__. ._ ___r_.-—_..--­I

T

.T'-.Jfi in - ­

4 . .

_.,__. -__. -' .. .. .»

.__. -j__.j.

. I. u

_M_

33:02”; OSmmimazs o

2 575%.:

. mooFmz-mEm

Ill‘

|l||+

5.0o._m._.

QN‘-0NC?m

V.‘on0;»3on

a 'OliVz-J CJIOA

204

smaller load increments to arrive at the preconsolidationpressure more accurately. The curves are more or less para­llel indicating that the load increment ratio of one candescribe the compression of marine clays satisfactorily.

The e - log p curve for the remoulded sample isalso shown in the figure. A comparative study of the curvesshows that remoulding destroys tflue bond strength completely.At higher pressures both undisturbed and remoulded samples

almost merge at a void ratio nearly equal to 0.4 eo whichagrees well with Schmertmann's (1955) observations.

Fig.5.3.3a shows some typical e - log p curves ofundisturbed samples obtained from three <flifferent locationshaving different liquid limits. The ratio cnf initial watercontent (wi) to liquid limit (w) is approximately 0.9 forL

these curves. It may be noted that the curves are placedin the order of their liquid limits and they tend to mergeat higher pressures. EigJL3.33 shows another pair of e — log p

curves with wi/w nearly equal to 0.7. In both cases higherL

plasticity curves are placed above those with lower plasticity(Lambe, 1958).

IS: 2720 (Part XV) 1965: Methods of test for soils ­determination (ME consolidation properties, gives tflue method

205

.mm>m3 a a2.» ..<u_n_>._. omém am.

Aassmx: a mmammmma

e m N o.. 5 m q n 9o 5 m .. m N 5.o.1- ! III llls! .1: LI. ..- nlll | 1| 1| 1

ql.OW :0.

__F -- E , J M 1.10..

W w% M

f « 27 %

_ \;m_loco.W RN.

m+ . _mm:---:a[I-u.I% o.m

W dow 2322:: a

iom mam: q ma

% /A32 iom mooCuz o

2% 5.;

'3 0lJ.VH G10/\L

206

.m E326 a ms;

4<uE>p

Aaezmi n. mmam mmmn.

..m.m.m .95

o._ q n N 9.0 5 m q m N 5.

HI @._

mmGH

lI-l:. r! if ii. N I ©.N

m

.r 2

/I T $rr 39

M. f -- --lTr;%.I om

_

j _ ..

- Lf ...... -.i|.}-!- m.m

M

W _ [

T +l'.1l‘ 4.||..Il-|.

/ % .__om «SEE <

M /o/ W .__om moofimz o_

in ._#|1 » _..;..

E _ 1 fi mu: _ _ L

_ _ ._ _ ~ _

9’Ouva mo/x

207

to determine CC. According tx> the code, "the initialcompression curve would be found to be a straight line atpressures above a certain value. The slope of this straightline portion of the curve shall be reported as the compressionindex C ".c

The code tacitly assumes that the portion of thee - log p curve after the preconsolidation pressure, pc isa straight line. But when one considers the numerous consoli­dation curves obtained in the present investigation, thee - log E3 curves very rarely is linear after pc. The slopeof the curve varies and quite often there will be a reversalof curvature also. Thus by the value of compression index,as defined by the code, one cannot describe the rate of changeof void 1mnflx> with increase ix: pressure. To overcome thisanomaly, the compressibility characteristics can better bedescribed by the slope of the e - log p curve for differentpressure increments. This slope is given by de/d(log p) forthe pressure increment. Throughout this work, the natureof compression curve has been described by the new factor

de/d(log p) rather than CC as it described the compressibilitycharacteristics cnf marine clays enui other soils better than

the conventional compression index, CC.

208

2-00 _-____. .._

N _ __ "i /JLeo _.w__ /I-40 ___--- .-_. . v ———1

A o KUMBALAM 9-Sm /fO.

on '20, A ELAMKULAM I.-Sm B.9

., Q MARADU 9-Om1 1-00 ­U

‘U

___ _ __o-eo——-—~+ —

o.z.o____w

o.2o————».—« -1., /;0

0-000'10 050 1-0 2 5-0PRESSURE p (kg/cm )

dz/d (log p) vs PRESSURE.

...#5mmmEn_ 9 J H §.m.m .3

ANESEZ umammmma

om o._ 3 m8 3 moo

209

Jo;% o .N

—-.- :—-___..—j—.— I. _

:<3x:<$ Q23%. 23 x O

-vl|ll||I'.|.

x)/«D07...

( 393/umz

oso.m

210

The ratios of de/d(log p) were calculated fordifferent pressure ranges starting from the lowest value andare reported in Fig.5.3.4a. .Although by convention, the

compression index Ca: is meant txa represent the straight lineportion of the 623- log E) curve, here the de/d(log p) valueshave been calculated for lower pressure ranges also in orderto study this behaviour. It can be seen that for undisturbedsamples, for pressure ranges below the preconsolidation pressure,the de/d(log p) values are low. The undisturbed samples haveyielded larger values of de/d(log p) at higher pressure ranges.Its implications have been brought out in section 5.4. Fig.

5.3.4b shows the variation of CV values with respect to pre­ssure increments for undisturbed samples from Kumbalam andElamkulam. The curves show higher values en: lower pressureranges and a minimum between 1-2 kg/cm2. The values pick

up thereafter. But, in general, the behaviour of CV withpressure has been erratic.

5.3.1 Effect of drying of compressibility

It has already been discussed at length in Chapter IVthat air drying or oven drying has significant influence onthe grain size distribution of marine clays due to the aggre­gation of finer particles into coarser <grains. The ‘valueof liquid limit reduces considerably. The aggregation of

211

particles due'to air drying and oven drying brings in signi­ficant improvement in the compressibility characteristicsof air dried or oven dried marine clays. Through a seriesof consolidation tests, it has been shown that the value of

compression index Cc is brought down by drying.

Fig.5.3.l.la shows the e — log p curves for un­disturbed, remoulded, air dried and oven dried marine claysamples from Nettoor collected from a depth of 1.5 m. Whilethe remoulded sample was subjected to consolidation at thenatural moisture content, the initial moisture content ofair dried and oven dried samples was kept below, but closeto, their respective liquid limit values. It can txe seenfrom the figure that the ea-— log p curves for air dried andoven dried specimens are considerably below the curves forundisturbed and remoulded samples. Fig.5.3.l.lb shows thesame set of curves for specimens from Parur from a depth of13.5 m. The pattern is quite consistent with the previousfigure.

The improvement in compressibility characteristicsis fully reflected in the values of de/d(log p). Fig.5.3.l.2shows the variations of de/d(log p) for the four specimens.

212

.m..:E5 a mo_-~

AMSEZ umsmmmma

< m N O;

5

4<u:m>»

m

<

m

Ufffim

N

.D_h_

V: .1: ­

_.___._j_

V

m.oo._9QN

omio zm>o nmemo E4 4

omnzaozmz 0ommmifloza o?cm+.£%3 lm 00: 5...“: _m

LO

(No.mma

9 OILVH GIOA

213

.mEE:u a mo_.;. .:3_&: ;:._.m.m .3

¢.E.2mxZ wmammmma

o.m o. _ o_.o moo

3 OIIVH OIOA

vmtu cm>O DDe _.:u.._m 4u....u_3oEo_ O_umn.:.:m_Uc: O

mamé - Ema. IE5

214

d_c/d(log_‘p)

('3 ti:

SITE: PARUR(Depth I3-Sm)

o UNDISTURBED

o REMOU LDEDA AIR DRIED:1 OVEN DRIED

C?on

COMPRSSION INDEX

C? o L‘ dw

0-2

0-10 0-50

Fig. 5-3.1.2 '

1-02

PRESSURE P( kg/cm )

dc/d(lo9 :2) vs PRESSURE­

5'0

-4 2

, Cv xlO(crn I Sec-)

8SJTEPARUR (Depth -I3 -5m)

0 UNDISTUR BED

7 o REMOULDED IA AIR DRIED g‘

I

6 D OVEN DRIED J

COEFF. OF CONSOLIDATION

215

0'0 0-50 1-0 2PRESSURE p( kg/cm )

Fig-5.3.1.3 CV vs PRESSURE.

216

While maximum value of de/d(log p) for undisturbed sampleis 1.17 for time stress range 1.0-2.0 kg/cm2, the same forair and oven dried samples are 0.615 (0.5—l.0 kg/cm2) and0.438 (2.0—4.0 kg/cm2). These factors have kxxnm taken fulladvantage of in the studies on compaction of Cochin marineclays ‘which will be <discussed later zhi this. chapter. Thevariation in coefficient. of consolidation for time same setof samples is brought out in Fig.5.3.l.3.

Consolidation tests on samples from other locationsgave similar e — log p curves.

5.3.2 Compression index

It is well known that as liquid limit increasesthe compression index increases. Higher plasticity curvesare placed above those with lower pdasticity (Lambe, 1958).

The relationship between CC and the liquid limit (LL)

CC = 0.007(LL - 10) (5.3.2.l)for remoulded soils is one of the most widely quoted relation­ships in soil mechanics literature.

217

But there are quite a few vmmkers (Saxena et al.,C

1978: Oikawa, 1987: Wesley, 1988) who feel that Egg repre­osents the compressibility characteristics of fine grainedsoils better.

Fig.5.3.2.l gives a plot between de/d(log p) ofundisturbed Cochin marine clays and the corresponding liquidlimit values (ME moist samples for time pressure increment of1 to 2 kg/cm2. A statistical fit for the values plotted givethe equation,

de/d(log p) = 0.011 (LL — 24.8) (5.3.2.2)

with a correlation coefficient of 0.61.

Fig.5.3.2.2 shows the relation between dekflloggfland LL for the pressure increment 2 to 4 kg/cm2

de/d(log p) = 0.0ll(LL — 20.6) (5.3.2.3)

with a correlation coefficient = 0.65.

de/d(l09 P)1+ eo

To examine the superiority of the factor

compared to de/d(log p) alone, to represent the compressibilitycharacteristics of Cochin marine clays, the corresponding

218

(:2... 0.30: m>

A

3 ms;. u. u..:

Z..m.m am

4.. H223 Q50:

om: 8 _. O.» _. oi Ooh om Ow 04 on

o

O

o T : a , - oq.o

o # o o o o\V@ $..Z...j:_o.olamo:32.

an» x « 8.0

O

I%--l§T.!V Arllljofi_. i ofTfiz- j - xi.’ ~Eu\9_ o.m-o._ u a -,oo.m

_. Smézma 2: H 5n_z<m

of”

(d 501) 9/29

219

9.2: 9303 .3 Zoo: n\~o m.m.m.m .m:

Ts; :23 9:0:

o2 8. oi or 8. 8 8 8 om

To0

3.2 u..::o.ou Zoo:n?u

Q N

m1¢-:-- 7 » {Isa

_ Q

\ G M

r _ 7.] N213 o4 now u 0.

ommE:55z: H mEz<m

04.00 mo2..ofSeoi

( d 601) P/3P

220

data have been plotted in Fig.5.3.2.3 for a pressure incrementof 1 to 2 kg/cm2. The statistical fit for the data is givenbelow.

deidilzg 9) = 0.0028(LL - 37.7) (5.3.2.4)O

This has ea correlation coefficient cm? 0.651 which

is higher than the correlation coefficient for the relationbetween de/d(log p) and LL.

The relation between de/d(log p) and LL for remouldedclay is given in Fig.5.3.2.4. The equation for the line is

de/d(log p) = 0.0087(LL - 12.6) (5.3.2.5)

where r = 0.76.

It can be seen that the undisturbed. sample hasgiven a comparatively lower correlation coefficient with alot of scatter of points. This is possibly due to the non­uniform conditions of the undistirbed samples. On the otherhand, because of the uniformity of soil samples, the coeffi­cient of correlation l£3 higher’ for tflua remoulded Samples­It may be noted that the de/d(log p) - liquid limit relation­ship obtained lint both undisturbed anui remoulded samples isabout 20-25% higher tflun1 those suggested kn; Terzaghi (1948)

221

.0 m> OIIIII.|.u:_.._. D

. u . . .. _

$23 93 3 Aamo:uZ:u m mmm L

A .4. V :23 220:

com om: of o.: of 8. 8 8 S 8 o

8.0 _ o.o

@ \

_ OOK P P\l .6

:0 ;- A%;.-i-- %- :--i--%T---!ll omo MAU H ._ .0o o oui E mo. u M:.2..jZ8o.o H u +

U Om.O O2

illofio1 :1 N5 U \ 3 o.m..o.. u a omxo

Bméimazs ..m:n_2<m

222

oom

.:z_._ 9203 .2 Aamoluxi. 2 mm .9...

A .\.; :2: 93,0...

09 of 0.1 om. oo_ om 8 3 cm oo

@ w a _ \:

IIII- I -l1O.u.O

_

% . ._

ufia moi v\uU 8.0om;- fi ¢:-V!Iom._

1 - 4 iJ N513 o.m:o._ u a Jooa

H _

__ 303025 ..m#§<m

_ o.~.~

(C1501) P/2p

223

and Skempton (1944) for undisturbed and remoulded claysrespectively, possibly due txa the excessive compression offlocs present iJ1<3ochin marine clays. TNM2 fact that floccu­lation in Cochin marine clays is of a very high order hasbeen brought out in the section of hydrometer analysis.

The de/d(log' p) and liquid limit values for tflueair and oven dried samples are presented in Fig.5.3.2.5 withthe linear relationship

de/d(log p) = 0.0084(LL — 5) (5.3.2.6a)r = 0.92

Fig.5.3.2.6 «gives the ode/d(log _p) - liquid .1imitrelation for all samples combined. The equation is

de/d(log p) 0.0075(LL - 17.8) (5.3.2.6b)r = 0.70

The liquidity index for these clays varies over arange of 0.46 to 0.87 indicating that these clays could betaken as medium to very sensitive as per Bjerrum's classifi­cation (Bjerrum, 1954).

5.4 COMPRESSION INDEX AND ITS RELIABILITY

The compression index Ca: is one cnf the best knownparameters jfl Soil Mechanics. The relationship between void

224

.52: Q_Dd_._

m> flame: Uxuu

A .7 5.23 9:02

0.: om. oo_

om 3 3

m.~.m.m 5:

om O

fix

\

U ad E

3.0 u .Am:j:8o.ou A a mo: 2 3

0.0oso

3P

0 mo

dfioy)

Om;

N

Qm_m_D zm>o DSEQ m_< a.

E13 o.mIo._ u a

(

5:: 9:0: 3 2 mo. V13 £..m.m .mm

A.>:_2_\. 930...

225

09 of o.: of oo_ om 8 oq on c

j \ O

O P P

\I Gd

<n%

o~.o... . _ 80

..jZ3o.ou 3 mo: u\~u

Jo:of

SEQ zm>o Domzmo E4 a

om_oSozmE o co.m

ommmfmazs o~51? o.~..o._ u a

oim

(d 601)p/2p

226

ratio e and logarithm of consolidation pressure p for ordinaryclays can be represented by a straight line in the range ofnormal consolidation. This property of ordinary clays hasbecome cnua of the most sacrosanct empirical relationship andperhaps it has been used so widely regardless of its reliabi­lity or applicability. The linearity of the e — log p relation­ship has been questionable especially in case of sensitiveclays, organic soils and peats (Oikawa, 1987).

The relationship between CC and the liquid limit (LL)

CC = 0.007(LL — 10) (5.4.l)for remoulded SOi1s_ gained acceptability eventhough its suit­ability txb all situations (especially iJ1 case CHE soils withhigh liquid limit) is not unquestionable (Wesley, 1988). Theformula for the consolidation settlement as per’ IS: 8009(Part I) 1976 is

CC.HiS = rre—1°91o

O

+ / )° AP (5.4.2)P

(p

o

It is evident from this expression that the soilparameter indicating compressibility is CC/(l+eO) and notCC alone. Comparison of compressibility would be better madecum the basis cnf the compression ratio CC/(l+eO) rather thancompression index CC (Saxena et al., 1978).

227

The variation of compression index de/d(log p)with respect to change in effective stress for undisturbedsamples from Parur at a depth of 6.5 m is shown in Fig.5.4.l.The plots show a tendency for the value of de/d(log p) toincrease upto pressures between 0.5 to 1.0 kg/cm2. Relationsbetween de/d(log p) and pressure are given for’ differentdurations such as 1 day, 2 days, 4 days, 8 days, 15 days and30 days. After 0.5 to 1.0 kg/cm2 the behaviour does not followany regular pattern. The value (Hf de/d(log gfl tends todecrease at higher pressures for longer durations of stageloadings. The reason for this has been attributed to thedevelopment of bonds between the clay particles, discussedin section 5.5.

It has been already indicated that the compressi­bility' behaviour ii; significantly’ influenced tax the initialvoid ratio CHE each loading stage auui compression ratio mightrepresent the compressibility characteristics better thancompression index CC. In order to examine this, the compressionratio de/d(log p)/(l+ei) has been plotted against log p for1, 2 and 4 days duration in Fig.5.4.2 and for 8, 15 and 30days in Fig.5.4.3. It can be seen that straight lines couldbe fitted in all the six cases in these two figures if thecompression ratio value for the first loading stage viz.

228

_#5mmmEn_ 3 E mociuu

TE .9“.

$529: a wmammaa

o.m o _ 8.0 9.0

. o.o

23.1: \I ' ‘ I ulu L: X \% C

\“\‘

xx T\

,,_\ m_\

V \\ \ R

4

( \

3.0

on I q 0

I m —. 4 N C

m 0 _ 0Sin V 6m 35: Smzo:<m:o -23 zo:<m:o -2 >m

Em o H IE8 .m:m<m H mtm

(d 6o1)p /zp

229

o.m

_~+_

.mE:mmmEn_ m >

A amo:u\~u ~qm.9m

C529: mmsmmmma

o._ omo o_.o

fio

nw\\ D

\ \

9 \\\ &

\\\ q \ 8

\\n

K“?

\

\. 32.5 q 0

m.o

3:3 N 4>wu — O

Emb H Emma I1a|i

m:m<n_ ..mEm

«.0

!z+L.(dfionp/an

OILVH NOISSBHCIWOD

230

Oh

_u + P

.mm:mmmmm m>

Amchzmxv mmammmmm

o; omgu

Aamozuxuu ”mEsm.9m

owo

\\\H\x\\\\

m>mU om Iwxmu m_4m>mv m 0Em.o Hzhmmom:m<a ”.w:m

__

ToW0

CMLVH NOBS3HdNO3

mo

'2 —+ L(d 5°l)P/7P

#0

231

0.0625 kg/cm2 is left out. Since this point is influencedby the initial compression of the sample and mechanical adjust­ments of the loading system, its omission may not interferewith the general behaviour pattern. It can also be notedthat the slope of the straight line decreases with increasein the duration of stage loading.

Fig.5.4.4 shows the variation of de/d(log p) withp for the same duration of stage loading for undisturbedsamples collected from Parur at ea depth of 13.5 nu It canbe seen that the plots present a highly erratic behaviour.But the compression ratios for time same plotted zhi Figs.5.4.5 and 5.4.6 show, uniform correlations. These figuresclearly indicate that it zhs the compression ratio

de/d(log p)/(l+ei) which is more reliable in the study ofcompressibility characteristics than the compression indexde/d(log P).

Fig.5.4.7 shows the de/d(log P) - log p plots fora series of consolidation tests carried out on four differentspecimens of soils which were originally consolidated at asustained pressure of l kg/cm2. The pressures were thenreleased and full consolidation tests were carried out onthe samples preconsolidated at l kg/cm2. The failure of the

232

Qmpmmmfi T, An. mo. V u?u

A~Eu\mxva mmsmmmmm

_3.m .9...

om o._ om.o o_.o

A w _ _ _ _ _ ©o

om n .w 0 .

®—. ‘ ® Q u|l:IIl--_w.I|.|I|Iu 1 I ll

m o _ o W

33.3 33.3

2 o_:E:o -%m zozéao Lmm I. -1- ­

E mim _-I.T.._mo £553 .. mtm

IIII I'

._____W._‘P:2::—q———— —--— -­

T

I /V/\

(d f>o1)p /2p

233

o.m

. umammmza

..v.

>

_~_F

Zmo:u?u

$629: a mmsmmmzm

9.3

.9“.

o._ { om.o So

a % ..o

_ M D_ M M o_ % <

m>mU a D fi|wTV. P ul---+V

m>mU N < \>mU _. O

rCm.m_...IH&mQ .r

EEE .. m:m \ u\

\\ \

\\

xx \

M \ %

mow‘ 2

__% W

OILVH NOlSS3HdWO3(d501)p/an

234

on

.E..5mmmEn_ m>

ANE U 5: n_ mmawmma

mo

0;

.~+_

Aamo_:_.\~u

0.3 mm

Am>mU om Im>mu m. 49:3 m 0Ema _%:n_uomaxi ..m:_m

I_¥

To~.Om.o

52 +1(d 501)r>/2P

«.0

OILVH N Ol‘SS3HdWO3

235

o.m

..uE:mmmEn_ 9, Zmozuwu 5.3.3

Ame imia mmnmmmmm

o._ m.o

T I 3 KW luq

—.O

0.0owo

,_._._-__ __j..p. ._.j-———- - jj’_ .‘...__.___:._é_

0908.0

I_.m<m cum Dm:_z:o<x Gflow 20:8 53m oA mtm mooCmz:<dmz_m<: o

N633 _ .9 Stajomzouoz< 3 Z Bnsaozmm H Bn_:.<m gom

_

om.o

O;om;0.»...00..

(d 6o: ) p/an

236

.m_m:mmm_E m> An mo: U\uv w.q.m .m_.._

o.m ANE Em: Q mmmpammmma Om.o To

‘ % -A % o.o

W §T T {u om. oV II |r.-I-%t--:-% f+._1!;-- “Val? I %|l| O.u.O

W

M fi _

Ta] - - 8.0

_ w_ T /1!! _ ll PW 18.0 U. m>m u om 0 .mw>mU m_ D d

1 ,Il-- |J m>mU P G O.— /\

m>mu N O

.. mom NE U 2.; _ om;

Z. Bz_<5:m oz< 0..omtazomou .fi Z SoSo:mE

><.U mzE<: H mizfi sow Isl. 3;

P

Ow;

237

fabric of the soils is clearly shown by the sudden increasein the value of compression index de/d(log p). Fig.5.4.8presents another smm.<Jf curves between de/d(log gfl and log pfor marine clay samples preconsolidated at l kg/cm2 for differ­ent durations. The variation CHE de/d(log EH is similar tothat in Fig.5.4.7 except that the final value of de/d(log p)tends to be almost same.

5.4.1 Prediction of total settlements from compression index

The determination of allowable soil pressure isone of the most important aspects in the practice of geo­technical engineering. The allowable soil pressure is directlyrelated tn) the permissible settlements cflf the structure andits foundation. This necessitates an accurate assessmentof the rate and magnitude of the consolidation settlementof a foundation due to the compressible layers beneath thefoundation, under any load.

The process of determination of allowabsle bearingpressure involves the determination of tflma following para­meters.

a) Compression Index, CC

b) Preconsolidation Pressure, pc.

238

While the I.S.Codes (IS: 1904, IS: 2720 (Part XV):IS: 8009 (Part I)) specify various methods and proceduresto arrive at the above values and compute the quantum ofsettlement leading tx> the estimation cnf allowable soil pre­ssure, quite often ii: is observed that the actual settlementdue tn) consolidation its considerably less tfiuui the predictedsettlement.

The city of Cochin and its suburbs consist of deep

deposits of highly compressible» marine clay ‘with Ck: valuesaround 1.5 and natural moisture content very close txn theliquid limit. It has been often observed that almost allthe structures, founded on spread footings or raft foundationsinvariably show actual settlementafar below the computed values.Since the actual settlements were significantly less thanthe computed values, designs based on geotechnical principlestended to be on the uneconomical side whereas foundationsprovided as per thumb rules proved more economical. Thesefindings prompted the present study’ which shows that thereexists a need for a relook into the code provisions to redefinecertain terms and amend certain methods and procedures sothat the settlement computations are more realistic and designsmore economical.

239

The parameter, which controls the total settlement,

is the compression index CC. The total settlement is directlyproportional tx> this value. CC its defined (lfh 2720 (PartXV) as ‘the slope of the straight line portion of the curve’(e - log g3 curve). In order txa obtain 51 realistic pictureof the problem, undisturbed samples were collected fromKumbalam, Cochin, the soil profile of which is shown inFig.5.4.l.l.

Fig.5.4.l.2 shows 51 typical e - log 5) curve foran undisturbed sample cflf Cochin. marine clay collected froma depth CH5 9.5 metres. As per time definitions (IS: 2720

(Part V)): the value of Cc is l.69.

As per IS: 8009 (Part I), ‘Code of Practice ofCalculation of Settlements of iFoundations - Shallow Found­ations', for ea clay which is rufl: precompressed, tine totalsettlement is calculated from

H pO+£Jp)_ _ tSf — Soed — l+e CC log(——E——— ) ) (5.4.l.l)o o

where Sf = final settlement, mSoed= settlement computed from 1-D consolidation testH = thickness of soil layers, m

240

A_

/ aooLxfizlixx llgljpfl H“_ '1 00lg 10"‘ J] 3 ‘L50

SAND

Y : 1.809/CC

'1oo

CLAY

Y: 1.509/cc

60: CC::I"H.OO

SAND

Fig 5.4.1.1 FOUNDATION DETAILS WITH SOIL PROFILE.

.J§oz_ zoammxizou #:z.h§o.“_W S3 .9...

C5 9: Q maammwaa

2 8.0 as $0

« .fi of

. __

/ -,. % O:

_ " M %

241

_w % 8..OQN,;.:,..wu- / % W 93

5.? «mo / M _

JD

.— 3. N

. ./

/ 2. .. oomomm

/

3 Own 010/\

242

eo = initial void ratio

po = initial effective pressure at mid height of layers:kg/cm2 . 2,;p = pressure increment, kg/cm .

Field compression curve developed from the laboratory

curve for time above soil sample, yields a Ca: value of 1.99for the clay of ordinary sensitivity, as per Appendix C ofIS: 8009 (Part I).

For a 10 m square structure resting on a mat found­ation the effective overburden pressure is 0.8 kg/cm andincrease ix: stress x;p == 0.246 kg/cm2, an: the middle of theclay layer for a foundation pressure of 8t/m2. The totalsettlement calculated from the above expression is 25.25 cm.

As per IS: 1904-1978 — ‘Code of Practice for Struct­ural Safety of Buildings: Shallow Foundations‘, the maximumpermissible settlement for a reinforced concrete structurewith raft foundations resting on plastic clay is 10 cm. Thus,as per code provisions, the allowable soil pressure is farless than 8t/m2. This, from experience, is far from reality.The allowable pressures obtained from codes are considerablylower than values that can be permitted judging from field

243

experience. Thus strict adherence to the codes yields a highlyuneconomical design iJ1 case of time highly compressible Cochinmarine clays.

5.4.2 Segmental compression index

Since field observations in almost all cases showthat the codal provisions yield unrealistically high values

for CC, it is felt that the value of CC needs a redefinition.Further, CC at present is taken as the slope of that portionof the e — log p curve where the soil is subjected to compress­ive stress of the order of 40 or 8Ot/m2 which is rarely exper­ienced iJ1 actual practice. The initial portion (Hf thee - log ;3 curve, especially that ruxur the insitu stress;describes the compressibility characteristics of the clayin that pressure range better than the portions of the curvein the vicinity of stresses of 40 or 8Ot/m2, which at presentis taken as the measure of compressibility characteristicsof the clay, irrespective cnf the stress range or stress in­crease. This, ii: is felt, is unrealistic ENM3 is the reasonfor the high values of total consolidation settlements computedfrom code provisions.

The true representation of the consolidation ofthe clay, when subjected tn) an increase iJ1 pressure ;;p is

244

given by the portion of the curve between the abscissas poand g%) + /_p (Fdg.5.4.l.2). The slope of the line joiningpoints (e I p ) and (e, p +ygp) can give a better represent­O O Oation of the field compression of the clay. The slope ofthis line, called the ‘segmental compression index‘, Cé, is avariable quantity whose maximum value will always be lessthan C .c

In the ea - log E) curve~ shown :hi Fig.5.4.l.2 forthe stress range cm? 0.8 kg/cm2 to CL8 -+ 0.246 kg/cm2, thesegmental compression index works out to 0.64, which is consi­derably less than time original value of 1.99 from the fieldcompression curve. The total settlement, with the new value

for CC works out to 7.61 cm only. The estimation of thesettlement could be further improved by dividing the thicknessof the compressible medium into a number of layers and taking

!

corresponding CC.

Thus a bearing capacity of 8t/m2 which was notpermissible according to I.S.Code provisions zhs well. withinpermissible limits as per the new method. As is clearlyevident, segmental compression index method will give morerealistic and economical designs.

245

Fine grained soils, under constant pressure,can develop bond strength. This will be reflected in thevalue of preconsolidation pressure as quasi preconsolidationpressure. For foundation loads, which induce a. Lvp withinthe quasi preconsolidation pressure, the consolidationsettlement will txa very’ marginal. This :hs truly’ repre­sented by the segmental compression index approach where

the (3%: will be almost equal tx> the slope CHE the tangentat po.

It is evident that C'C is a quantity which variesbetween the slope of the tangent to the e - log p curve

at po and the compression index (SC. Fig.5.4.2.l givesthe variation of <3”: with increase iJ1 the value of _g_pfor an cwerburden pressure CM? 0.8 kg/cm2. It shows that

C'C reduces after a certain value of -’_p(2 kg/cm2). Thisis due to the reversal of curvature of the e - log p curve.For computation of settlement, where the increase in stressis more tfluni the fr p corresponding to time peak value of

C'C, the peak value may be used in the settlement comput­ations.

Fig.5.4.2.2 shows the percentage variation of

the ratio of settlements calculated using CC and C'C respect­ively. It can be seen that for lower values of gx p, the

246

I ‘ I T T I I2-0+ -1‘-—COMPRESSlON |NDEX Cc*1'99

/"'?o\(3% ‘-0 41-51? 1U

L.)O

SEGMENTALoz CIJMPRESSION \NDEX cc:‘UL.)"‘g 1 1 1 1 1 10 0-4 08 1-2 we 2-0 2-1. 2-8 32

A P (kg/cmi)

A-PVARIATION OF cg AND CC WITH

247

mid om:<o3omz8E>o mo... J _.3.mum_n_

_,.E._<um co: mmammwma .. .UL CC W

-:II_uIIll1. 1.IInILo..S.o

///

/ AOU m./ UVH./ Ou x ..

x

2

.a< 3 mi. ”m.3.m.mm

Fc._u\m3_C ad

mm

no

11

2:,0?52ommoomomm

(°/.)oo1 x,s/9

248

settlement as per I.S.Codes is about 332% of the value

given tnz C'C. The difference drops xmnqz fast and comesto a steady state for higher values of flip.

5.4.3 Settlement of overconsolidated clays

Fig.5.4.3.l shows the procedure for determiningthe compression indices for over consolidated clays asper Appendix C <1f IS: 8009 (Part I). Ku represents thelaboratory curve. The portions between po (effective over­burden) and pc (preconsolidation pressure) is the recompress­ion curve. The line kxfl is drawn through k) parallel tothe laboratory rebound curve cd. ba'cf is treated as thefield compression curve from which mv is calculated.

Settlement sf =_A.p.mV.H (5.4.3.l)

where mv = coefficient of volume compressibilityH = thickness of compressible stratum, m.

The procedure does not elaborate on the comput­

ation of mv from the field compression curve- and lacksclarity.

Winterkorn and Fang (1975) give a better treat­ment of the problem wherein the total settlement is assumed

249

to consist of tn«> parts —- Se and SC. Se gives therecompression settlement upto the preconsolidation pressure

pc, computed from the settlement equationH P_ cSe - TIEO Ce log1O( 53- ) (5.4.3.2)

where Ce is the slope of the recompression curve. Similarlythe consolidation settlement from the virgin portion ofthe e - log p curve,

Ht p + pSC = l+e CC loglo (‘ o ’ ) (5.4.3.3)pc

Total settlement S = S + S (5.4.3.4)f e cIn case of the proposed segmental compression

index method, such ea separation of time total settlementinto two parts is not envisaged, as the segmental compre­ssion and ‘virgin compression portions CHE the e - log pcurve» Hence a differential treatment to overconsolidatedand normally consolidated clays ‘may run: be necessary incase of the suggested method.

In conclusion, it can be said that consolidationsettlements computed by I.S. procedures tend to overestimatethe settlements of foundations resting on clayey soils.

250

This is chm; to an overestimation of the compression index,

CC irrespective of the stress range. The segmental compress­ion index method where C'C is selected based on the insitustress and stress increase, will give more realistic values.Since tflue I.S.Codes tend tub overestimate time consolidation

settlements rendering foundation designs uneconomical, thereis 23 need for 51 revision of time codes incorporating theabove suggestions.

5.5 EFFECT OF DURATION OF LOADING ON COMPRESSIBILITY

The effect of duration of loading on the compressi­bility characteristics cm? cohesive soils runs not ‘receivedmuch attention from the research workers in <geotechnicalengineering, eventhough stress-strain behaviour of sensitiveclays runs been studied iJ1 detail tn! Bjerrunu (1967) andMitchell (1970) during their studies on Norwegian quickclays and cemented Leda clays found in eastern Canada. Untilrecently it was generally considered that the influenceof time effects <M1 the stress-strain behaviour <1f claysis relatively not very significant. Investigations on un­disturbed and remoulded samples of Whangamarino clay byNewland and Alley (1957) tend to agree with the above hypo­thesis. But findings of Hamilton and Crawford (1959) duringtheir investigations (N1 Leda clay onfirm that factors such

251

as duration, load increment ratio etc. influence the compressi­bility characteristics. Through ea series (Hf tests onremoulded samples, Richardson and Whitman (1963) demonstrated

that tflua time dependency cnf both preconsolidation pressureand undrained shear strength was significant.

The volume change that takes place under constanteffective stress is called secondary compression. Duringsecondary compression, a cohesive clay‘ develops increasedstrength and reserve resistance against further compression.The behaviour‘ of the clays and the Inechanism controllingthe one-dimensional secondary compression have been explained

taking into consideration the inter-particle attractiveand repulsive forces, by Sridharan and Sreepada Rao (1982).The reserve resistance against compression developed duringsecondary compression increases with the tjmma of sustainedloading since the amount of secondary compression alsoincreases. Ihi this section it. is proposed tx> investigatethe time effects on the compressibility behaviour of Cochinmarine clays.

5.5.1 Consolidation tests and results

A series of consolidation tests were carriedout on marine clay samples from Parur at depths of 6.5 an

252

10.5 m, 12.5 m and 13.5 m. Tests were carried out at dura­tions of 1 day, 2 days, 4 days, 8 days, 15 days and 30 days.The load increment ratio VNMS kept uniformly at 1.0. Eachsoil specimen was loaded upto 4.0 kg/cm2 starting from aseating load of 0.0625 kg/cm2.

Compression index, coefficient cyf consolidation,permeability and secondary compression were calculated at

each loading stage. Ck] was calculated tn! the rectangularhyperbola method in every case (Sridharan. & ‘Rao, 1981:Sridharan et aflJ,l987). The results are pmesented in theform of a series of curves.

Almost all the consolidation tests have beencarried out cum undisturbed samples to take into considera­tion time normal variations that (EH1 occur even lfl case ofsamples taken from the same depths from closely spaced boreholes. Consolidation tests on remoulded samples would havegiven more consistent results as the initial void ratioof all the specimen could be made uniform (close to liquidlimit). The interference from the effects of preconsolida—tion pressure of tfima undisturbed samples could also 'havebeen avoided. But to study the field behaviour of the marineclays more closely, tests were carried out cm Lnmflsturbed

253

samples collected and preserved as explained in chapter III.The studies in this work are based mainly on natural depositswhich are believed to form the most reliable basis for ageotechnical treatment, even if the results may be encumberedwith some scattering due to Ihnfl< of homogeneity’ of thenatural clays (Bjerrum, 1954).

Fig.5.5.1.1 and 5.5.1.2 show the relationship

between e/eo enui log E) for tax) soil specimens from Parurcollected from 13.5 rn and 6.5 m respectively. The loadingduration for each stage of loading was kept at l, 2, 4,8, 15 and 30 days. Since the initial void ratio of thespecimens varied from 3.063 to 3.642, pressure was plotted

against e/eo so as to normalise the effects due to the varia­tions in initial void ratio to some extent.

It can be seen from the curves that eventhoughthe pressure intensities are sustained for a longer duration,the corresponding deformations do not increase as one wouldhave normally expected. In fact the equilibrium void ratiofor the curve for durations of 15 days and 30 days are higherthan the average values of void ratios. These plots clearlylend support txn the hypothesis that the shear strengthcomponent cnf coheshmi is increased VHMH1 the pressures are

allowed for longer durations.

254

.mm3mmuma m> o~\o ecwm.m;

A .:u\mxva umnmmmma

m

cm o.. . Bo o5 mo.o

: a ::i . fl :;

_ W W ._. _ J E . _ H _

H u , _ _

w

- - - - 1 W %i4va1I.omog,T;l§

M M_ _

fl - 1- II -- 1.1% iiluomo

r_ _ Wmoo.m om u u _ _

-/

I N3. m m_ 4 .l? . x .--llOm.O

mom.m m o

woma a D _

r 1; --;oo¢

_qTm m a

mofm _ o .

r Amxmuq T: -s:;;:.un L

ou ~zm:umsgo<o4 Jom oo._

mozozziso -z>m M

,:m.m. rhino .m3m<a“HE;m W _ M L L .

_ r _ F . _r V r _ » - r Vr r V.

255

mmommmma ..,..> oi» ~.$.m a;

£539: a mmammmmm

om o._ omo 9.0 mos

H @ # :i§__ 4 9:130

_ M _ _ u u _ M _ W L _ _ _M 4 M J M _ _ J % M

7-,‘ . J - -l- “+I% Ear %a-LOm.ON ; W 3.0

./ 7l.. - - I. 2.0 A

fl H /, . fl W ...% 2 _ , % o W ? W o

I ./ . M W

; u . .-u _ , -Tio®o

amog om - // _ _ %

. C _ _

Zoe m. 4 . _ _

hmme m o 11 f _ / TL owe

mfg q u i

N C 4 . CWL_m.~ > _ o .

Am 2: -- -f. - 4+; - I _ Loo. F

ow Em_:mSz_ 9:5 Sm M _ “

mo zo:<m:o -23 W F . _ % ‘

Em.m ”T_._.n_mn_ \¢:m<n_fl.:_m 9 E __ __ .

256

In order to bring out this phenomenon with greaterclarity, the deformation in number of divisions have beenplotted against time (N1 logarithmic scale ix: Fig.5.5.l.3and 5.5.1.4. The former shows Q3 - log t relationship fortwo undisturbed samples ihxmi Parur collected from ea depthof 13.5 In, for time pressure increase ifixxn 0.0625 to0.125 kg/cm2. In this pressure range, the deformation fora duration of two days is less than the deformations obtained

for 30 cknmm Such behaviour has already been reported forlower ranges of pressure (N.S.Murthy, 1986). But a pressureincrease from 2.0 to 4.0 kg/cm2, the deformation. for .30days consolidation is considerably below that <1f 2 daysconsolidation (Fig.5.5.l.4).

To substantiate this behaviour further, thedeformation of two samples from Parur, from a depth of 6.5 m,have been plotted in Fig.5.5.l.5 for the pressure range0.25-0.50 kg/cm2. The deformation for two days consolidation

which starts with 51 lower value initially, overtakes theother. In Fig.5.5.l.6 the deformations for 30 days durationis consistently and considerably lower than the other.

Eventhough such a behaviour has been predictedby some of the earlier workers (Richardson & Whitman, 1963:

Perloff and Ostenberg, 1963), some other investigators

257

.mm>m3 # mo. I w m.$.m .9“.

comooqoom

OON

‘MP 1(su0!S!A!p) /°NOlSS'1tldWOI)

NE u\m.$fi.o-mSo_oua

m 33 om aimo N o

OOP

Em._.m_ HI_.n_..._omam: Hmfim

UJUJZOO =

OOOF OO— O— —

Amm3c_EV . mi;

258

.mm_>m:u . mo. -w .Z.m.m .9“.

_. .M7M___

~Eu\9_.o.To.mua

inn cm a

m>mD

N O

p_m.m_

m3m<a

uzwamomp_m

oooom oooo_ OOOF

Amo.:c:tv .

oo_

mzr_

oohcomcomcos

oomcomoo_

om

’(Su<>sswp ) P NOISS3HdNO3Lwwzo0o= NP

.323 H mo_Aw m._.m.m .9“.

259

m.5\3om.o-m~on Q “m>m.b Om D "

m>mU N OE Wm “Emma

magi pm:._m

08 m 80.9 89 o? 9

?..,.SEE: m2:

o8ooqoomcomO0.

= -Asp L ’(suo!swp) ,0NoIss:1ac1wo3wwzoo-o

260

mEu\3o..To.~u Q

m>oU om Dm>oU m 0Em.w.:ȢmoESE .. mtm

ooo om OO0.0_.

mmiau

..mo_ - 0 $3

Aw.3C_C._ V.

.m.mm

8.m2:

9

ooh5 IE. - cooooqcomcom8.om

L (SU0!S!A!p)j> NO|'SS3HdWO3WUJZOO O = ‘MD

261

reported results txa the contrary (Grahmans, Grooks & Bell,l983). But in the case of Cochin marine clays durationof each loading stage has remarkable influence on the volumechange behaviour and the increase in strength is much morepronounced tflun: those reported if: the literature (Sangrey,1972: Lo & Martin, 1972).

Another set (Hf plots between compression g; andtime in minutes are given in Figs.5.5.l.7a,b and c in supportof the above. Fig.5.5.l.7a shows the a-— log t plot fora pressure increment of 0.5-1.0 kg/cm2 for ea remouldedsample from Parur for durations of 2 days and l5 days. Herethe compression for 15 days is more. But for the next load­ing stage of l.O-2.0 kg/cm2 the compression for ]£3 daysduration is lower than that for 2 days duration during theprimary consolidation. as shown :h1 Fig.5.5.l.7tn The :finalcompression is almost equal in both cases. But in Fig.5.5.l.7c,the total compression for 15 days duration is less ‘thanthat for 2 days duration. These three plots clearly bringout the development of strength during secondary compressionjmm the case cnf samples consolidated ikn: long duration. Inthe case of pressure increment of 0.5-1.0 kg/cm2, the totaltime available for consolidation for sample with 22 daysduration, before current pressure increment was 6 days viz.

262

.mm>m:u W mo_-w

..oZ.m.m .9“.

NEE? O... .. m.o Hmmcm: mmmtm

._m_>.m.c_ m>mU m. _mm.cmEEuc_ U....o._ 4._w>E.c_ mxmn N .mm.cmEmbc_ Umo._ O.58.? .. Emma

A EEK V omoéozmm Sn_:<m sow

898 80.9 89 00. V 0.

322__EV . mi;

comom»o83oomOm_.

wwzoo-0 = -Mp L ’(5U°!‘5!/\!P ) PNOISSEHMWO3

263

.mu>m:u . mo_-w

Eu_.m.m

.m_1._

com

.%au\mxAvm-o;Hmoz<m mmmmhm .!t¢­

.m>EE_ m>mU m— F. m.cmEmCc_ Um0._ 4332:. m>mU m .m m.cmEmbc_ Um.o._ O

.1c.omg: H xhmmo Tux

g m:m<mv omo4:o2mm

————-—+——-w-—-—-—%—- -—» «— «~­

Bn_:<m sow

coo? 89

Am.23c_ Ev .

om;oomQ3

mi:

mu; zoo.o = -Mp L ’(‘5U0!S!/\!P)f NOISSZ-h:IdwO3

£04

.m..:E3 1.3. m

._m>.m.c_ .w>mU 5 .m m.cmEu._uc_ Umg G._m>EE_ mxmu m 2,”. £cmEwbc_ Umg 0

~63? 0,.» uoa .. omcm. mmwbm

E om .9 “IE3

?Sm<n:8o5o:mE H m#_:<m :om

89

A.wm:..c_Ev .

u:.m.m .9“.

M22.

8.

0.

00moicooomqcomom...

wwzoo~o= mp l ’(suo!swp) /0NOlSS3tidWO3

265

2 days such for the load increments of 0.0625-0.125,0.125-0.25 and 0.25-0.5 kg/cmz. In case of a sample with15 days duration the time available was 45 days. But thecurves show that the second sample has not gained strengthduring these 4&5 days compared tx> the first sample. But inthe next plot Fig.5.5.l.7b the deformations are almost equalfor the load increment of 1.0-2.0 kg/cm2. In the next figure(Fig.5.5.l.7c) the gflxm. for lfi days duration consistentlyshows compression less than that for 15 days. This perhapsshows that the development of shear resistance duringsecondary’ compression. takes place- after ea certain Ininimumpressure only.

It has already been shown in the earlier discuss­ions on Figs.5.5.l.3 to 5.5.l.7c that soil specimens subjectedto pressures for longer durations develop shear strengthwith respect to time. If it is so, the magnitude of primaryconsolidation for an increase in pressure should be lessin case of specimens subjected to longer durations as thesoil has become less compressible due to gain in shear strength.Therefore the primary consolidation expressed as ea ratioof total consolidation should show a decline with respectto time.

266

In Fig.5.5.l.8 the ratio PC/TC, where PC is theprimary compression and ‘TC iii the total compression foreach stress increase, has been plotted against pressureintensities, for undisturbed marine clay samples from Parurcollected from a depth of 6.5 metres, for durations of1 day, 4 days and 30 days. It can be seen from the plot

that the value of PC/TC decreases with duration. It alsoshows a similar behaviour with higher effective stresses.

When the primary compression shows 21 reductionwith respect to total compression, there should be a comple­mentary increase in the secondary compression. Fig.5.5.l.9shows a plot between the ratio of secondary compression

(SC) and total compression (TC) and the effective stress,for loading durations cflfjl day, 4 days and 30 days fromconsolidation tests on undisturbed samples from Parur at6.5 m depth. The plots show a regular increase in thevalue of SC/Tc with duration. The increases in the valueof SC/TC with respect to stress increase is marginal.

A close study of the figures discussed aboveshows that the amounts of initial and primary compressionsobtained for the different durations are in opposite direct­Aion to that of secondary consolidation. There is a signi­ficant reduction in the values of initial and primary

267

o.o_

on

.mm:mmmma m> A:\w;

o..

m+mm.mm

Ame 2 m ._ a mmnmmmmm8.0

0... O

3.0m>mu on I 3.0

m>o_u 4 D>mv — 0

68¢ “rims .o

m:m<o_ H utm

O50om.ooo.ooo;

31/°d

268

om

. mmammmma .u.> U» \ um

m.Z....m .9...

CEBV: a mmsmmmma

o._.

om.o

m><o om Iwin 4 D><O F0.:mo”I»amomam: “min

0.20

+

'9'

:o-—- T... _.. . ._

‘V

T

I

Iu|.|'!1|u |l . ‘ . I vs

r11

o .N . oomo8.o

269

compression with increase in duration of load at a givenpressure increment, while the reverse is true in caseof secondary compression.

Eventhough there» have been contradicting’ con­clusions by research workers on the development ofstrength with duration of loading and consequent reductionin primary and total compression, this has been wellestablished by the present series of tests on <3ochinmarine clays and by earlier workers (Leonards & Ramiah,1959: Bjerrum, 1967; Allam & Sridharan, 1979). The cohesive

component of shear strength is likely ix) be improvedby growth of cbulombic particle—cation—particle linkagesand \Hn1 der waals bonds, while fabric changes occurringduring secondary compression further improve the resist­ance to compression.

5.5.2 Rebound characteristics of consolidatedmarine clays

It has now become an established fact thatmarine clays develop strength and resistance to compressi­bility when they are subjected to effective stress forlong durations. This has been attributed to the increase

270

in the number of contact points between clay particleswhich increases the cohesion component of the shear strengthis iJ1 plastic clays (Bjerrum, 1967). If this increasein strength is reflected in the soil fabric and if thisstrength gain due to development of bonds between clayparticles, has some sort of permanance, it will try toretain its soil structure even when the load is removed.Of course there will be an inevitable elastic rebound:but the soil structurte may’ manifest its strength gainthrough its rebound characteristics. In order to explorethe possibility of such a volume-change behaviour uponremoval of pressure, the rebound or swelling of. theconsolidated specimens of marine clay was studied indetail from the results of the consolidation tests.

Fig.5.5.2.l shows the plot between the reboundof undisturbed marine clay specimen from Parur collectedfrom a depth of 6.5 m. They have been consolidated upto4.0 kg/cm2 with a load increment ratio of 1. The durationof each consolidation pressure increment was chosen as1 day, 4, 15, and 30 days. The rebound of these samplesin number of divisions when the pressures were reducedfrom 4 to 0.0625 kg/cm2 has been plotted with pressurefor various durations. ‘It can be seen that the rebound

271

om

mmammmma 9, azaommm ....$.m.m_u_

$523 V a umsmmmma

O.— Om.O o_.o m0.0. 0

%

- I w of. OON

//.//.

flu///U.

/ com

o / /.4.w>uU om I

m>oU 2 4 M

w <

m>oU v D _ 00

>8 _ o

Eom.m” IE8 W A com

m_.E<n_ “min. _ M

oom

UJLU zoo-0: ‘Mp L ’(SU0!S!/UP) CINHOGI-It!

272

was maximum for samples consolidated with duration of1 day and minimum for the duration of 30 days with theother two (4 days and 15 days) falling in between inthat order.

5.6 PRECONSOLIDATION PRESSURE

The consolidation test provides basic inform­ation on the compressibility characteristics of soilsfor computations of the magnitude and time rate of settle­ment resulting from one-dimensional strain. The twomost important consolidation characteristics viz. compre­ssion index/coefficient of volume decrease and coefficient

of consolidation are significantly influenced by pre­consolidation pressure. An important aspect CHE deter­mination of the magnitude of settlement is the realisticestimation of the pmeconsolidation pressure. Casagrande(1936) defines preconsolidation pressure as the "largestoverburden in which the soil had once been consolidated".

But a soil may show a preconsolidation pressure higherthan the maximum past pressure. This difference is attri­buted to the ‘bonds formed due to long term secondarycompression, aging and other physico-chemical factors(Leonards & .Altshaeffl, 1964; Bjerrum, 1967). A soilmay show a preconsolidation pressure caused by a variety

273

of factors including overburden pressure that may ormay not have reduced due to erosion, desiccation, tempo­rary overloading, sustained seepage force etc. (Leonards,1962).

It is generally accepted that an accurate deter­

mination of g%: is the most important step in predictinglong term consolidation settlements and analysis of shortterm stability problems (Jamiolkowski et al., 1985).The major variables that can influence the measured pcvalue are sample disturbances, test equipments and pro­cedures to obtain the compression curve, environmentalfactors and the interpretative techniques used for theestimation of the preconsolidation pressure.

5.6.1 Methods available for determination ofpreconsolidation pressure

One of the earliest and most widely used pro­cedure is the method proposed by Casagrande (1936). Theother tun) methods are ‘those of Burmister (1951) andSchmertmann (1955). Jamiolkowsi et al. (1985) <discussat length the mechanism of the preconsolidation pressureand also opine that time most popular‘ method still isCasagrande's empirical construction technique. According

274

to Leonards (1962), as there are rm) reliable methods forthe determination of the in situ preconsolidation pressure,no suitable criteria exist for appraising the relativemerits of the various methods that have been proposed for

determining ;%y As 23 corollary txa the detailed investi­gations carried out for the study of the consolidationcharacteristhms of Cochin marine clays, 51 new method hasbeen developed and its reliability tested in this work.

The Casagrande construction involves selectingthe point corresponding to the minimum radius of curvatureon the reloading curve, drawing horizontal and tangentlines at this point and bisecting the angle between them,then projecting back the straight line portion of the curveto intersect the bisector of the angle.

In Burmister's method the sample is reboundedas soon as the compression curve reaches the straight lineportion and is then reloaded. The characteristic trianglethus formed is then transferred to the first loading curveby trial and error "giving more weightage to the verticalleg than the horizontal leg". The procedure is obviouslycumbersome and time consuming.

275

D1 the method suggested knz Schmertmann, the labo­

ratory loading, rebound and reloading procedure is the same

as Burmister's method. An assumed value of pc is chosenon a line drawn parallel to the mean slope of the rebound

curve through the point (eo, po) which are in situ void ratioand overburden pressure. This pc point joined to the pointcorresponding 13: 0.42 eo cum the compression curve 515 theassumed virgin curve. The reduction in void ratio Ale, bet­ween the assumed virgin curve and the laboratory curve isthen plotted against log EL The procedure is repeated for

different assumed 3%: points and virgin curves anui the mostsymmetrical void ratio reduction pattern is chosen for pc.

While in <3asagrande's method, there could bepersonal errors involving tine choice cnf the minimum radiusof curvature, the other two methods are basically trial anderror procedures with their inherent drawbacks. The mainlacuna in assessing the validity of any of the above pro­cedures is the non-availability of the real value of pc tocompare with. The series cnf tests CH1 Cochin marine clayswith long durations of loading helped to evolve a new methodcalled log—log method for time determination cnf preconsoli­dation pressure.

276

5.6.2 Preconsolidation pressure by log-log method

In this .method, Ex: is obtained as time point ofintersectbmi of two straight lines extended from the linearportions (N1 either end (M5 the compression curve plotted tolog scale on both axes (Fig.5.6.3.2). After running severalseries of consolidation tests with varied parameters suchas soil type, sustained pressure, duration of sustainedpressure, it has been confirmed that the log-log method issuperior to all other existing methods.

The validity of the log-log method has been veri­fied knr conducting 51 series cnf consolidation tests whereina pre—knowledge of the preconsolidation pressure was madeavailable. This was achieved by consolidating the saturatedsoil samples from slurry level (initial water content nearlyequal to their liquid limits) to a pmedetermined consolida­tion pressure for sufficient time. The specimens were thenunloaded to a nominal initial load and then reloaded muchbeyond the predetermined sustained pressure. Thus the initialportion of the recompression curve upto predetermined sustainedpressure is the overconsolidated portion and the portionbeyond this ix; the ‘virgin compression line. Use CHE thisrecompression line to check the validity of any method of

277

determining pc will have the distinct advantage of a priorknowledge» of the preconsolidation pressure. The validityof the log—log method is examined in detail below.

5.6.3 Test results and analyses

Tests were conducted in standard oedometer setups (N1 eight different soils with widely varying compressi­bility characteristics with their liquid limits varying from47 to 137%. The soils used were of different origin, fiveof them being Cochin marine clays one is black cotton soilfrom Benihalla in Karnataka State, a red earth from KeralaState and a typical kaolinite clay from Karnataka State.The physical properties of these soils are listed in Table5.6.3.1. They are highly sensitive to air/oven drying. Hencethey have been determined on natural moist samples.

Typical ea - log 5) curves from consolidation testsare shown in E1g.5.6.3.l. The same results are plotted inFig.5.6.3.2 taking logarithmic scale for both void ratioand pressure. Straight lines cxuu be readily fitted to theinitial and final portions of log e - log p curves, the pointof intersection of which agrees well with the value of theprevious sustained pressure which can be taken as the ;%:

.278

UCM ...__M um CMMMLUHHWV m\uu ca Ummmwumxw .H®_.m OCHMDMMGE M CH ®ED.mO> ucwefluwm :w:o3m map ma HH 3..

NH

Aswmumz uwuflmv

mm om om.o m.Hm o.mm o.mm o.nmH wmfiu mcflume cflcooo .m

Aemflsxemfim "mgflmv

5 nw ow mv.o v.mH m.vm m.ov o.moH mmfiu mcfiums cficuoo .»

Aamamnesx uwuwmv

5 nw ow mv.o ©.mH v.mn o.ow o.omH wmfio wcflume cfisoou .0mm mm m mH.H m.om m.mH m.vm o.»v muficflaomm .mmm «m wv om.m H.nm m.»H m.mm m.mm cuumm cwm .vw om mo om.m o.m m.mm m.mm o.mm Hfiom coupon xumfim .m

Ausumm uwufimv

mv mm mm oo.v H.mH m.mm m.mm o.vm >mHu mcflume cflcuoo .m

Auoouuwz nmuwmv

om mm mv om.v 5.5a m.om m.nw o.vmH >mHu wcflume cflcooo .H

$3 1: >5 5.63 3; C3 C3 3:

vcmm uawm mam *xw©cfl f¢;~wmm §$¥:>uflo uflefla ufiefifi .ozcowusnwuumfln wmflm cflmuo HHGBW mwum Ixcflucm Iflummam oflummam ©wDUHA max» HHOW .Hw

mmaammmomm q<uHm»=m

H.m.o.m wanna

279

A.oucoov

mH.N :1 NN.N mm.N ma oo.N .. .mHmv.N In oN.N mm.N N oo.N .. .NHoH.H oN.H vH.H om.H ma oo.H .. .HHma.H oN.H wH.H om.H ma oo.H Nflom couuou xomam .oH

ow.H an oN.H om.H N oo.H nuumo mom .m

mo.H oH.H mo.H mN.H N oo.H Awuflm usummv

wmao wcflume Cfl£UOU .wwO.H oH.H mH.H oH.N ma oo.H .. . .5

oH.N mo.H mo.H mH.H N oo.H ummu mmouAmuflm noouuwzv wmau mcfiume

cflcoou cmmfisoemm .0oH.N mN.N oN.N mv.N ma oo.N .. .mma.H mN.H NN.H om.H om oo.H .. .voN.H mH.H mH.H mm.H ma oo.H ~. .moH.H oH.H mH.H om.H » oo.H .. .N

Amuflm uoouuwzvmmao wcflume

mo.H mo.H mo.H om.H N oo.H cflnuoo wmcfisoewm .H

23 AC :3 5 :1 A3 ANV A3

uofim uofla uoam cocums

Q moHINw4 Q moanawq Q moanwmoa wwcmummwmu Amwmwv ANEu\mxv

Eouw A Eu\mxV musmmmum cofiumvflaomcouwum wofluwm wusmmmum .02N cmcflmumsm vmcflmumsm HMOM we mQ>B .Hm

moomamz azmmmmmHn was wm mm:q¢> Um mo zomHm<mzou

~.m.o.m magma

28H)

on.o©©.o~m.o

on.o05.0mm.o

m».omo.omo.HNN.No©.Hmm.HwN.Hom.Hom.mom.moo.mmo.Hmo.Hmm.mom.m

wm.o©o.ooH.H

mamamammmmmammmm

Awufimsvmumzv wmau mcflumeCfl£UOU Umnusumflnca

Amuwm EMHDMEMHQV >mHoQCMMQE cflcoou wwnusumflwca

AwufimEMHMQESMV wmfiu wcfiumecwzuoo wmnusumfiwcawsflfi we nuflzUwumwuu >mHu mcwumz

xxxxxx

mafia wm spa;Uwumwuu >mHu wcflnmz

xxxxxxxx

w#HCHHOMM

xx

aHOw COHHOU MUMHQ

.mm.>N.om.mm.vm.mm.mm.Hm.om.mH.wH.nH.©H.mH.va

E

at

:3

A3

A3

281

taking into consideration the quasi-preconsolidation pressurealso. A series of much tests have been carried out and theresults are presented in Table 5.6.3.2.

Leonards and Ramiah (1959) report that fine grainedsoils develop quasi preconsolidation pressure (N1 sustainedloading for long durations. Allam and Sridharan (1979) havebrought cnn: the significant increase ix: strength cnf soilsconsolidated. to different aging periods. Keeping this inview, samples were loaded to predetermined pressures startingfrom slurry condition and kept for long durations, were un­loaded and then reloaded. The duration of sustained pressurewas varied from 2 to a maximum of 96 days.

Table 5.6.3.2 also contains results obtained withvaried duration of sustained loading. Fig.5.6.3.3 showstypical test results of a marine clay specimen kept for aperiod of 90 days under a sustained pressure of 1.0 kg/cm2.The existence of the quasi-preconsolidation pressure is evidentfrom the illustration. Fig.5.6.3.4 presents the same dataof the recompression curve in log—log scale. The intersectionof straight lines drawn through the initial and final portionsof the curve results in a pressure of 1.22 kg/cm2 as against

282

com

.mm:E:u a 9: nu 4<u_n:C _.m.w..m .9“.

§Eu\9:a mmammmmn.

8.. one So

VI/ll

J]m:z_..o<x 4sow zoCou 54.5 o

Amcm mooiuzv

><d uz_m<: ziuou 0

920 ~ ooaua omzztmsmE US; ofi manmmmaa omz::m:m

oc.>LD_O

oo..-10.:ofo:cosoohown

a ouva CJIOA

283

.m..i/may a mo_

L. woo. .Zu_.n:C 63m .9...

AmEu\mv:a maammmma

.o.m o._. 8.0 oeo mod

.mm.o

w:z:o$. q

M ,

, sow zoiou 54$ 0 ‘co;

3:5 moohfizv A><..u mz_m<: ziuou o .oo..mO

_

_ m><o~ ooama omzzfimsm .oC

. -3; HA mmammmaa omz_<B:m 1mo._W.

‘r "P

m . . a

.om _ flop _

.ome

. 55.

W .o.Z rm. _

.23 @

m

_ wom F .Om.—

" _

_ .

W _ _ @

. _ _ W 10;

_ _

_ M _ .35A W M _ ¢ rom m

_[ b H ~ 7 _, F r 9

284

.mm>m:u a mo. Ia

Ame VB x Z mmnmmmmn.

m_m.m.m .3

2 coo one 8.0

L % % i % ow.o

_ _ W U j _ _

. . . . _

. '+| 1 ii. W _ W

_ W_ U

/ _

.1 ;--iIl ;r;Lf 7 no o 9.

QHYII 1%

min. om mo... = _ < T» « ooa

33 54528 3/ _ y %m/ M W _ _

1 _. VA/.4: ...I-Ii....l'..I|1T|_ ....¢.,.-. .+I.l - T. C ®via:

m><o 2? ooiua Sz_<$:m _

m, . W W ial /1 oma

Nei .\_ S .mE:mm.#_n_ Bzztmam W W H ///o

_ __. H M

3:3 mootwztid uzasz sow é _ L_%

, _ ooa

8 OLLVH OIOA

285

om

.mm:.Ed a mo_ I N m2

0+

q.m.m.m .9.._

me u\ 3 E waammuam

8.0 9.0

a fl

143.,

9:3 om ooiun. om.z_<53m

mEu.::_ o._ mmammwma owz_<5:m3:5 moofiuzv ><._u mzE<z H.:Om

o:o....._ofo:

I V1Ix!UT

ofom;ooa

a ouvu OIOA

286

the sustained pmessure of ILA) kg/cm2. The increase of0.22 kg/cm2 could only be attributed to the bonds developeddue to aging under sustained load. More of such resultscan be seen in Table 5.6.3.2.

It is well known that addition of lime increasesthe strength of the soil fabric at the same water content.Further, due to pozzolanic action, the sample gains strengthwith ‘time. Fig.5.6.3.5 shows ‘typical results <1f Cochinmarine clay treated with 3% lime and with four differentsustained periods viz. :2, 7, 15 Emmi 60 days. Becauseof pozzolanic action, the increase imm preconsolidationpressure over and above the sustained pressure is evidentfrom the curves. Fig.5.6.3.6 presents the same resultsin the log-log plot. It is clear that there is a substan­tial increase in E%: due to the duration of the sustainedloading. Thus xmhfli the addition of Jimmy increase ix:bond strength with aging is quite significant. The resultsare presented in Table 5.6.3.2.

Fig. 5x;3,1 presents typical e - log E3 curvesobtained from consolidation tests on three undisturbedsamples cnf Cochin. marine clays. The correspondinglog e - log p plots are shown in Fig. 5.6JL7. It is clear

2-20

1-80

140

3-80

(3-40

3-00

*2-20

r-1'80

E1-1.0

3-80

3'40

‘P2 .20

*1-80

4-40

I

3-00

-2- 20-2- 60

.1 .20 +­

*1-1.0

3-80

T

(3-40

1~3-oo

~2'60~

T

I

fi(-3

0.05

287

0 -10

sou MARINE cLAv+3l LIME2

SUSTAINED PRESSURE‘-H9/Cm

O 2 daysA 7 days

SUSTAINED PERIODD ,5 days

00 60 days.

0.50 1.0 50PRESSURE p (kg/cm?)

Fig 5-6.3.5 c — log p CURVES­

om

288

.mm>Ed a 931 u mo. o.m.m.m .3

§Eu_5v:a mmammmma

o._ 8.0 ore 8.0

a

mic om n

J. 9,8 9 o ooEH.E

_ 929 5 o omz_<5:m

mic N o

m.E.uE.x o._.. mapmmwaa 82.45%

. m::.>m+

Gcm mnaqnz ><d mzE<: H sow

@ _mw w_@ .

fl (AT fl T

. @ M

u hcr mm

.8;.2;3..

.2;

3..3.. .oo.~.om._ .o_.~63 5352. 52a2 .o§.02 .02

.o§@.02

.o.u._..om._.3:.05;.3.am...oo.~.om.m.om.m5:.03

a ouva CIIOA

289

»O._& a mo_ sumo. L.m.m.m .9“.

“me U \ 3 E maammmma

. f --_1IlJ.ow.o

/ _

Jw -..-,: --i!l:- foo _

omm 3o<m<z Ow.A oo.m :<4<m::x o

?£oz_._a:<m .3;fl I .3;__ _ ,8;

If .

_ oz,/a/JJ .3 N

_ 1111 I70

_ . J. 7 _ _ .o~.~v ,o:..,lT!17A¢!.+fI:¢:l-?,7+-o ,3 N.3 m.%I|Il}.l|ulLr.|...|..fil|||.|.é|‘|.l|...-l?rr|||n|||||||‘ILII? fl? T

OILVH OIOA

290

from the figure that the estimation of pc is quite simpleby the lxm;-— log method. These results are also includedin Table 5.6.3.2.

A detailed comparative study between the pcval ues given by the log-log method and the popularCasagrande method are also presented in Table 5.6.3.2.The superiority of the log-log method over the conventionalCasagrande method is evident from time fact that resultsof log-log method are closer to the sustained pressurethan those of the Casagrande method. It is further under­scored by the consistent increase in the quasi-preconsoli­dation pressure with increase in duration of sustainedperiod, while the increase in erratic in the case ofresults from Casagrande method.

5.6.4 Superiority of log-log method

The Casagrande method pmoposed ixn the thirtieshas been the only method in practice for the past half.a century ix: spite cflf certain inherent drawbacks. Even­though there have been sporadic attempts txa develcm> newmethods, these procedures could not earn wider accepta­bility as they were time consuming and cumbersome. Theyalso lacked precision and clarity.

291

The present series of tests clearly showed thatthe proposed 'log—log' method runs considerable advantagesover the existing methods for the determination of pre­consolidation pressure. Since the tests were designedto give 51 pre—knowledge of tfiue preconsolidation pressure,the results yielded by Casagrande method and log-log method

could be compared with actual values of pc. A comparativestudy indicates that the results by the Casagrande method

were higher than the actual values of pc. This has impli­cations on the unsafe side.

As shown knr Fig.5.6.4.l, tine quasi—preconsoli—dation pressure increases with the period of sustainedloading. While the log-log method clearly brought outthis established fact, the results from the Casagrandemethod were erratic.

The greatest advantage of the log-log methodis perhaps the elimination of errors due to personal judge­ment, as the preconsolidation pressure its obtained fromthe intersection of two straight lines while the selectionof the point of maximum curvature plays a key role in theaccuracy of the results given by the conventional Casagrandemethod. Thus tflua proposed log-log rmfifluxi is superior tothe conventional methods iknr determination CHE preconsoli­

dation pressure.

292

.oz_o<o4 3 zoF<m:n_

3:2: 954 82.453

.3, an 3.m.m .mw_

no 2o_:E:o

om oo om 9 o

‘ _ ' lllui ­

ooxflz mozqaoqmad Q_

8:32 02.09 o

1» Tie--- ha- in 1 ­

2:O Som.o 93 .3

(_Lu3/Bx) 3d 3tiflSS3tid NOl.LVO|'1OSNO33t1d ‘*'—~

293

5.7 CONSOLIDATION CHARACTERISTICS OF COMPACTED MARINE CLAYS

Along the coastal belt of Indian Peninsula,long stretches such as Rann of Kutch in Gujarat, Calicutto Quilon in Kerala, and Visakhapatnam and its suburbsin Andhra, have deep deposits of marine clay which posenumerous problems to embankments constructed for highways

and railwayeu Embankments built over‘ soft marine claysoften failed by rotational failure through base. Vastareas of shoulders or berms had to be constructed to pre­vent this failure which proved to be expensive. Henceimprovement. of engineering properties cnf marine clays aasa base material and also as a construction material willnecessarily form a part of a comprehensive study of theengineering behaviour of Cochin marine clays.

It has already been discussed in great detail,the enormous changes, that are brought in by air dryingand oven drying of marine clays, in their index propertiesand consolidation characteristics. The aggregation offiner particles into coarser grains brought about duringdrying improves the compressibility characteristics ofmarine clays as shown by Fig. 5,7,2, The compressibilitycharacteristics are considerably improved. The compressionindex of the air dried soil is 0.91 and oven dried soilis 0.42 as against 2.55 of the moist soil. Hence if themarine clay layers at the top is air dried by exposure

294

to sunlight, its gains in engineering properties couldbe taken advantage of as 51 base course since the consoli­dation settlements are considerably reduced. Since airdrying the top layers during summer by ploughing or similarmeans will be cheaper compared tn) the ‘usually expensivestabilisation techniques, air drying can provide a cheapmeans <1f improving time geotechnical properties cmf marineclays.

Once the engineering properties of marine claysare improved by air ckying, it can also be thought of asa possible construction material for the embankments. Hencecompaction characteristics of the air dried marine claysamples were investigated and the results are presentedbelow. Studies on oven dried samples were not taken upin detail due to their limitations regarding the feasibilityin field applications.

Compaction studies were carried out on soilsamples from Parur. The clay content of the original moistsample was 48%. (N1 air‘ drying, the fraction less than2 microns dropped to 33% anufl oven drying brought down thepercentage of clay size to 13%. The corresponding increasein coarser fractions can considerably alter the compactionand shear strength characteristics of Cochin marine clays.

295

Table 5.7.1 presents the physical properties of the marineclay samples used for the investigations.

Compaction was carried out as per proceduresdescribed in chapter III. Fig.5.7.la shows the dry density-­moisture content relationship for air dried and oven driedsamples for both standard Proctor test and modified Proctortest. Fir air dried soil the maximum dry density achievedwas l.33 gm/cc: at an optimum moisture content of 30.4%for standard test. For the modified compaction the corres­ponding values are 1.56 gm/cc and 23.2% respectively.

For the above tests, the samples were firstair dried anmi compacthmn was done (N1 air dried specimens

by adding water to them. In order to find out whetherthe compaction characteristics will be similar in natureif the moist specimens are dried to the respective watercontents instead of air drying first, another series ofcompaction studies were conducted with both the .standardand modified procedures. CNN; results of these tests arepresented in Fig.5.7.lb. Eventhough the results are highlyerratic without showing any peak cn: optimunn value, thisprocedure» of drying the samples was also adopted for afew investigations as the latter was more economical andless time consuming.

296

Table 5.7.1.

PHYSICAL PROPERTIES

31. Physical property Moist Air dried Oven dried0. soil so11 soil1. Liquid limit (%) 131.5 94.5 62.02. Plastic limit (%) 53.9 45.2 40.53. Plasticity index (%) 77.6 49.3 21.54. Shrinkage limit (%) 18.1 18.8 19.25. Grain size distribution

Clay (%) 48 33 13Silt (%) 34 47 55Sand (%) 18 20 32

DRY DENSI

1.6 0

1-50

1-20

1-10

1'00

297

Fig.

I

I

I

III

I

MODIFIED PROCTOR TEST

0 OVEN DRIEDA AIR DRIED

5.7.I.a

I STANDARD PROCTOR TEST

0 OVEN DRIEDA AIR DRIED

25 3OMOISTURE CONTENT (°/.

35

COMPACTION CURVES.

I

1.0

)

45

DRY DENSITY (9 /cc)

298I II

1.60 PM +3-.-- _ _W____._SAMPLE-' MOIST SOIL

' O MODIFIED COMPACTION1'50 ii " ‘I “‘ "“jj—""I" 9 STANDARD COMPACTION. O : Io ' I I0 , I .mo ——-N—«- «N

‘ 5 I—,--— fl‘ O ;.. C1-20 =f

I o. .T10-——. *‘—1f-‘ -_ _ -.­I

100T0 T5 20 25 30 35 1.0 A5MOISTURE CONTENT (°/o)

Fi9« '5.7.1.b : MOISTURE CONTENT vs DRY DENSITY­

299

Consolidation tests were carried out on samplesprepared an: Proctor density (both standard enui modified)and the results are presented in Fig.5.7.2. Since thesamples prepared at optimum moisture content and maximumdry’ density’ were only’ partially saturated, the~.specimenswould swell on inundation with water. To accommodate this

possible swelling sample thickness was restricted to 1.5 cminstead of the usual 2 cm, for all the consolidation testsusing dried samples. A comparative study of the e - log pcurves for tflua moist soil an: original void ratio and airdried samples at standard and modified Proctor densityreveals the significant reduction in compressibilityachieved through air drying. The figure also shows thetest results CH1 samples dried to optimum moisture contentfrom moist state.

To bring out the remarkable reduction incompressibility obtained through air drying, deformationvs. time zhi minutes tuna been plotted iml Fig.5.7.3. Itgives the relation between and time for the stress in­crease of 0.5 to 1.0 kg/cm2. The deformation for moistsample after 1440 minutes is 580 divisions. For air driedmarine clay, given standard proctor compaction and modifiedproctor compaction, the corresponding values are JAM) and53 respectively. Thus the marine clays which pose numerous

2

VOID RATIO

2 .

0-05 0-10

300

PRESSURE p (kq/c m2 )0-so . 1.0 . 5-c40 O MOIST SOIL AT LL­

2.00

1.80

1.60

1.40

1.20

1.00

0.8 0

0.60

0.1.0

AIR DRIED AT LL­

MOIST SOIL AT STANDARDPROC TOR DENSITY­

AIR DRIED SOIL AT STANDARD:PROCTOR DENSlTY- ;

AIR DRIED SOIL AT MODIFIEDPROCTOR DENSITY­

MOIST SOIL MODIFIED PROCTORDENSITY­

5.7.2 2-109 p CURVES.

301

.mm>m:u a mo. ..m H .03 .9...

ooh

«JmQ8 dH3Azo_C<a:8 moCoan_ %37.50: V SEQ m_< a oom WO)A zo_S<n_28 mofivoma Mom<oz<S: memo E< 4 ooq Mommmffozs o m.U

meim; o.. .. 8.0 M Q 6

com ..

m...com A__OO0Zoo. m.m

88 ooo F com 2: om

O_. m —

Ap..:£:EEV .. M2:

302

problems to embankments by excessive settlement can beimproved remarkably tn! an inexpensive ‘treatment like aairdrying.

The values of de/d(1mg p), CV and C! are givenin Table 5.7.2 for undisturbed, air «dried and compactedat standard proctor density, air dried and compacted atmodified proctor density, moist soil dried to standardoptimum moisture content and moist soil dried to modifiedoptimum moisture content.

5.7.1 Shear strength of compacted marine clays

Improvement in compressibility characteristicsalone will not make the air dried marine clay a good constru­ction material for embankments unless ii: is accompaniedby considerable improvement iJ1 shear strength. Since theaggregation cyf finer particles imnxn coarser fractions canimprove the shear strength of air dried specimens of marineclays, a series of triaxial shear tests were conductedto measure the shear strength parameters viz. cohesion Cand angle of internal friction ¢, which are presented inTable 5.7.2.

303

.nDumm Eoum mmaaemm umwoe we >uflmcm@ >u© wcm ucwucou musumfioe Hmusumc wnu mum mmwca «

m.vm mv.H m.mm mv.H @m.H N.mm cofiuumaeou uouuoum wmflwflcoecw>flm wcm ucmucou musumfioa

EDEfluQO ou wmfluw Hflom umwoz .m

m.wm mm.o m.mm ©H.o mm.H ¢.om coflpumaeoo cumccmum

cm>wm vcm ucwucou wusumfloe

EDEwuQO ou wwwuw HHOM HWHOZ .v

n.mm oH.H ~.mm vm.o ©m.H m.mm cofluommeoo cmflwficoz I

mmflum ufi< .m

n.m~ mm.o m.mH H~.o mm.H w.om cofluummeoo cumwcmum :

cmfluc ufla .mm.m mo.o m.o no.0 m».o * mm* mfimemm wmnusumficco .H

Auuxemv Awv

Amwmummwv AmEu\mxV Ammmumwvv AmEu\mxv >u«w ucwucoo.3 .o WE U Icw© >u© musumwoemmmuum w>wuomwwm wnwumemumm wmmuum Hmuoa Esewxmz EDEfiuQO

mumwu umwcm Hmwxmfiue

mumme cowuummeou

wamemm mo cowumfluommo

WBWMB m<mmm A<HN<HmB oz¢ mamma ZOHBU<m2OU mo measmmm

~.n.m magma

.oz.Hm

304

5.8 INFLUENCE OF DIELECTRIC CONSTANT OF PORE MEDIUM ONENGINEERING PROPERTIES

It is well recognised that the engineeringproperties of clays are dependent (N1 the interaction ofthe clay particles with fluid contained in their pores(Sridharan, 1968; Sridharan & Rao, 1970, 1971, 1973: Kinsky,1971). Most cm? the geotechnical properties can kxe linkedwith the electrical double layer of cflays. The structureof the electrical double layer“ is «determined "to ea greatextent by the polarity of the pore fluid. This can beexpressed in terms of the dielectric constant of the bulkmaterial. In case of marine clays which will be fullysaturated the kmLH< material is ea two-phase medium. Thedielectric constant of a dry silicate mineral is around4 and that of water is about 80. The large differencein values clearly indicates that it is the dielectric con­stant of the pore medium which controls the behaviour ofmarine clays emufl their properties Vflflxfix are dependent onthe value cflf dielectric constant. The equivalent thick­ness of the electrical double layer can be related to thesquare root of the dielectric constant.

To study the effects of the dielectric constantof different liquids on the engineering properties of clay,

305

Kinsky et al. (1971) carried out a series of experimentson the hydraulic conductivity of cylindrical samples usingorganic fluids such as dioxene, ethanol, dimethyl sulphoxide,formamide and water. The value of dielectric constantranged over 2.2 (dioxane) to lO9 (formamide). The clayused was Wyoming bentonite in which montmorillonite repre­sented 98% of clay minerals.

The hydraulic conductivity or coefficient ofpermeability of Wyoming bentonite samples 1 cm in heightand l0 cm in diameter was lO-8 cm/sec for water. Whendioxene whose dielectric constant was 2.2 compared to 80for water, was used the permeability increased to lO-4cm/secWhen water was allowed to flow again through the soil,instead of dioxene, the permeability was unchanged forone or two days. But after a few days the value of per­meability slowly came down very close to the original valueof 10-8 cm/sec.

The variation of permeability could be wellexplained tn! the dielectric property’ of time pore fluid.When a high dielectric fluid like water was used the thick­ness cflf double layer increased amui the permeability’ wasIUMM. When dioxene was allowed to permeate through the

306

sample, the thickness of double layer reduced considerablypermiitting free drainage. The permeability values forother organhic fluids increased inversely proportionalho the dielectric constant. Permeability of clayey soilscan be increased by a number of order of magnitude as thedielectric constant is decreased.

When water was allowed to pass through a soilfully permeated with dioxene, the value (Hf k did not in­crease appreciably for a number of days. But when forma­mide was allowed to flow through the sample, the permea­bility readily decreased tx> l0—7 cm/sec. This indicatesthat the reaction of different organic fluids with clayspecimens are at different rates.

To study the effect of different pore fluids(N1 the electrical double layer, 51 series of consolidationtests were carried out (N1 oven dried samples (Hf Cochinmarine clays. The samples were initially’ loaded tn)0.25 kg/cm2 from a seating load of 0.0625 kg/cm2. At thispressure, the following fluids were circulated for a numberof days.

307

Pore fluid Dielectric constant1. Carbon tetrachloride 2.2842. Acetone 20.703. Methanol 32.634. Water 80.4

After obtaining full saturation with the new porefluid, the coefficient of permeability of the samples weremeasured. Fig.5.8.l shows the plot between coefficientof permeability and head causing flow for the four fluids.It can be seen that carbon tetrachloride gives the highestvalues of k and water gives the lowest values for differentheads. The permeability values given by acetone and methanolfall in between in tflue order of their dielectric constant.The slope of the straight lines giving k value for variousheads, increases with decreasing dielectric constants.

Since water has time highest dielectric constant,ii: has maximum thickness for tflma electrical double layer.This restricts the cross sectional area available for flow.In case (ME carbon tetrachloride, since dielectric constantis only 2.284, the double layer thickness reduces and con­sequently increases the flow rate.

'7

308100 VSAMPLE = UNDISTURBED _.[ . _.

I50 0 WATER F-“Y ' """1 A METHANOL “—“‘

D ACETONE _ ._A ' CARBON TETRACHLORIDEL’W

EU

S?

X

'\>- 5'—

3'55<(Lu

20:Lu0.

Ln.0u_'L1...‘E3’ A //9-’r//73“U 10 r’ -__~r-~ , ———.-.— — .—__ .__.+--_-.__-_.__-_._—..—. —-—- —r—-- ' ~ - ~[ %1-._.­. J0 5° 30 40 so so 70 so so

HEAD h ( cm )

Fig- 5.3.1 HEAD vs PERMEABlLlTY­

309

5.8.1 Use of dielectric fluid to study compressibilitybehaviour

Sridharan and ‘Venkatappa Rao (1970, 1972, 1973)have shown that there are two mechanisms which control the

volume change behaviour of fine grained soils. In the firstmechanism, where the compressibility of a clay is primarilycontrolled tnr the shear resistance at time near Contactpoints, volume changes occur’ by shear" displacements. Inthe second one the compressibility is governed by the longrange electrical repulsive forces, primarily from the doublelayer. It is possible to find out which mechanism is appli­cable to a particular type of clay by conducting a seriesof consolidation tests wherein the shear resistance of theContact points cm: the electrical repulsive forces can txecontrolled. By reducing either of the above, if the compre­ssibility could be increased the mechanism by which thecompressibility of the clay is regulated could be identified.

The effective stress concept of Terzaghi is repre­sented by

= _2 " U (5.8.]...].)where = effective stress

’ = total applied pressureu = pore water pressure

310

This could explain many of tin; phenomena associated ‘withthe strength enui compressibility characteristics (Hf soils.But it fails to explain some of the features in the strengthcharacteristics of clays as the equation assumes that thereare only two external forces acting on the soil grains viz.total stress G1 and hydrostatic pressure u.

But it has been well established that both attract­ive and repulsive forces of an electrical nature exist bet­ween clay particles. Repulsive forces are primarily attri­buted to an interaction between double layers (Lambe, 1953,1958: Seed et al., 1960). Repulsive forces are proportionalto the dielectric constant of the pore medium (Bolt, 1956).

The attractive forces can be contributed by vander Waals' forces (Sridharan & Venkatappa Rao, 1973), Londondispersion forces, coulombic attracthmi and hydrogen bonds(Lambe, 1953; Rosenquist, 1955). Some of these forces areinversely proportional to the dielectric constant of themedium and the distance between clay particles (Davies,1965). Considering all these forces Lambe (1960) proposeda generalised equation

+ R — A (5.8.l.2)

311

where

9 = total stress2: = mineral to mineral contact stress

am = fraction of the total inter particle contact areaA = total interparticle attraction divided by total

interparticle contact area

R = total interparticle repulsion divided bur totalinterparticle contact area

i‘ = equivalent pore pressure.

This equation can be rewritten as effective stress

<3" = =C’::am + R - A (5.8.]..3)

As per the equation effective stress increases with repulsiveforces and decreases with attractive forces. This doesnot auger well with common concepts. Hence Sridharan (1968)

rewrote this equation as

E" = gaam =<s‘4Bw - Ea - R + A (5.8.l.4)where

-E = effective contact stress5‘ = external applied pressure

‘SW = effective pore water pressure*5‘ = effective pore air pressure.

312

This equation shows that the effective contactstress is proportional to (A—R). It is difficult to assessquantitatively the exact values of the attractive or repulsiveforces. But it is quite possible to regulate them by control­ling the dielectric properties of the pore fluid. Sincea study of this nature will help to identify the mechanismwhich governs the compressibility characteristics of Cochinmarine clays, a well—designed series of consolidation testsinvolving change in pore fluid properties at various stagesof the consolidation tests were undertaken.

5.8.2 Consolidation tests with different dielectric fluids

To find out the mechanism which controls the volume

change behaviour of Cochin marine clays, series of consoli­dation tests were carried out on oven dried samples of Cochinmarine clays from Parur. In all the tests the load incrementratio was kept at one. A duration of two days or the timerequired for the completion~ of primary consolidation waspermitted iknr each load increment. Extreme precaution wastaken to avoid errors due to side friction and air entrapment.Care was taken to minimise evaporation loss of pore fluidfrom the top of the cell and from the burette or reservoir,containing the fluid.

313

The following organic fluids were Lnnxi for theconsolidation tests on the oven dried marine clay specimens.

Pore fluid Dielectric constant1. Carbon tetrachloride 2.32. Ethanol 28.03. Methanol 32.64. Methanol + water 56.55. Water 80.4Since there was considerable difference between

the values of dielectric constants of water and the organicfluid. close tn) it (methanol) another <flielectric fluid xmasprepared by waxing equal volume of methanol and water andits dielectric constant was assumed as average of the values(Kinsky et al., 1971).

The specimen for consolidation tests using differ­ent organic fluids consisted of oven dried samples of Cochinmarine clays packed dry into an oedometer ring. The thicknessof the specimen was kept as 1.5 cm leaving a gap of 0.5 cmfor possible swelling of time dry’ marine clay vfluni it isinundated with the pore fluids of varying dielectric constant.After the samples have undergone the full swelling under

314

a seating load of 0.0625 kg/cm2, consolidation tests wereconducted to find (nu: equilibriunl void ratic> for eachpressure intensity.

Fig.5.8.2.l shows tflua plots cflf the consolidationtest results. The change jfl thickness of time specimenexpressed as a percentage of the original thickness(Jgfl%£999has been plotted against consolidation pressure for thefive dielectric fluids. The curves exhibit a regular patternin that the compression curve for the liquid with the highestdielectric constant viz. water, is the lowest and the curvesfor the fluid with the lowest dielectric constant, viz.carbon tetrachloride is the highest. The three other curvesfall imm between with time increasing values <yf dielectricconstant from tun) to bottom. When time maximum compression

of carbon ‘tetrachloride ii; 7.5% only, time compression forthe marine clay specimen mixed ‘with ‘water :n3 as high as24%. Thus the curves clearly show that the compressionof the oven dried marine clay increases with the value ofdielectric constant.

The relation between the equilibrium void ratioand the consolidation pressure is given in Fig.5.8.2.2.At the seating load, the sample washed with water has shown

315

.C3_m_mmmEn_2ou zopzfimzou uECH._._m .0 L0 Sit N —.~.m.m .mm

~ fl _ _ _ ~ i- _ _ A mm

_ #3 mH.:<>> 0

_ J _ 9% . mE<>>+._oz<xEz 4 .

1|- O.mm .#OZ<I_.m:2 O W om

o5: ._Oz<IE e

E2: >5“. mzE<z..:om

1

O

(°/.)OOl x

owe 9.0 mod

A NE: SE wmammmmn.

maaofu m ... <Em:. zommfi M D _

:.I -1 -!-!. e 3. ._Omu m F H V933. -:>m H

316

.mm>Ed a mo. -u «gm .5

$629: a mmsmmmmm

o.m O.— on...o o_.o moo

O50

m...:<>)

omo

mm: <>>+._OZ<I.bmZ

._OZ<I._.m:2

._Oz<T:.m < oma

..EEo¢C<mE» zomE<u u

o_:4u 4om2>m

oo._

AQMEQ 5:: ><dmzE<2;_om

.9

2 ouva cno/\Om...o:

317

maximum swelling and therefore has the highest void ratio.The void ratio of this specimen is higher than all othersamples till a pressure of 0.5 kg/cm2 is reached, The samplewashed with carbon tetrachlorhme has the lowest values ofequilibrium void ratio for the pressure intensities upto0.5 kg/cm2. As dielectric constant of pore fluid increases,the thickness of electric double layer also increases.The ea - log E3 curves show that ii; is the repulsive forcesthat govern the compressibility of Cochin marine clays upto0.5 kg/cm2. The behaviour is similar to that of montmorillo­nite clays.

After a pressure of 0.5 kg/cm2, the compressibilityincreases with dielectric constant (If the pore fluid. Thisindicates that the mechanism of development of shear strengthchanges to the one in which attractive forces dominate.The shear strength now its improved tnz the reduction indistance between the clay platelets (Sridharan & Rao, 1973:Sridharan & Sudhakar Rao, l985). This behaviour is similarto the pattern followed by kaolinite clays where the shearresistance and volume change behaviour are governed byfactors like

i) frictional resistance

ii) clay fabriciii) attractive forces arising from physiochemical

mechanism (Sridharan & Sudhakar Rao; 1985).

318

Thus the pressure-equilibrium void ratio curvesof oven dried samples (Hf Cochin marine clays exhibit apeculiar‘ behaviour‘ wherein. at lower pressures, the ‘volumechange behaviour is governed by repulsive forces and athigher intensities of pressure, the attractive forces dominatethe shear resistance.

This change in the p attern of volume change beha­viour’ might tn; due 13) the aggregation caused tar drying.It may be noted that the oven dried marine clay was closerto the kaolinite clay in the plot between dielectric constantand liquid limit (Fig.4.l2.l) and dielectric constant. andfree swell index (Fig.4.l2.2).

Incidentally it may be of interest to note thatwhile Terzaghi's effective stress concept fails txn explainthe contradictory behaviour of two basic clay minerals underidentifical physico-chemical environment, the hypothesesput forth by Sridharan and Rao (1978) is able to fully explainthis curious behaviouru This highlights the need for awider acceptance for the new relation for effective stress.

The variation of de/d(log p) with pressure fordifferent dielectric fluids is shown iJ1 Fig.5.8.2.3. The

319

mmammmmn. 9 E mo:u?u

Ameimi a mmsmmmmm

om O... m .0

$235:; + ..Oz<I._- M2.52 <15:._OZ<I_.m

mo_mod<mh: zommfi D

9:: Jom-:>m><.C mz E32 SEQ zm>omEz<m m.~.m.m an

2.0

o.oowo

om.o D3lD:omo U06d3.0 (

om.o8.0oh 0

320

value of de/d(log p) is minimum for carbon tetrachlorideand maximum for water. It steadily increases both withconsolidation pressure and with dielectric constant of pore

100 B plotted influid. Dielectric constant e; vs. HFig.5.8.2.4. As indicated by the previous figures, compressi­bility increases with respect to pressure as well as withdielectric constant of pore fluid.

The swelling characteristics of the oven driedmarine clay it; brought out tnr the rebound characteristics(M3 the consolidated samples shown iJ1 Fig.5.8.2.5. Figureshows the rebounded cnf the consolidated specimens when thepressure was reduced in steps from 4 kg/cm2 to the seatingload of 0.0625 kg/cm2. The highest rebound is shown bywater‘ and lowest is tn! carbon tetrachloride. ifima volumeincrease is proportional to the value of dielectric constantof pore fluid indicating that the increase iml volume isdue to the higher thickness of the electrical double layer.

924528 u_EH._d E 9, Immnn H q.~.m.m .9“.

Q o

pzfimzou u:.._Z5m_o

om om 2 8 om 3 om om o. O

321

T WT

mm.o-m§.o O

_ $539: SmM W, L mmpmfii -2>m

M E A SEQ 22,3

id M232: .. sow

OFm.

o; u o.m 0

0; I omto

a om

521

on

.mm:mmmma

m> ozzommm

m.~.m.m .9...

feimx E umsmmuma

o._ 8.0 oeo mom

om

M oofi

53;; o

E:<3:oz<:E: 4 .o..._

4oz<:»u: 04oz<:»m d

ma_mod/ES: zommfi a oo~

9:: Smzaw j %

.><d mzE<: ammo zm>o” Suzi _ _ H

% _[lon.._~

(SNOISIAICJ )C1NflO8 35I

U-“J-' ZOO'O"' '/\|C] L

Chapter VI

ENGINEERING BEHAVIOUR OF LIME TREATED MARINE CLAYS

6.1 INTRODUCTION

The use of lime as a stabilising agent dates backto the early Romans who used it in the construction oftheir roads, especially the famous ‘Via Appian'. Thisroad has given outstanding service since its constructionand is still maintained as a traffic artery (Leonards,1962).

Clay minerals carry regular negative charges ontheir surface and to a large extent are responsible forimparting plasticity tn) the soil sample. Such soils havebeen successfully stabilised with lime which decreasesthe plasticity of the soil. Lime stabilised soils findwide application in subbase courses in highway and airportpavements and as foundation bed for buildings.

Although the details of the chemistry of limestabilisation is not yet fully understood (Thompson, 1966)

322

323

the improvements in engineering characteristics of thelime stabilised soils are attributed to

i) cation exchangeii) flocculation

iii) carbonationiv) pozzolanic reaction

The general order of replaceability of the commoncations associated with soils is given by the lytropicseries (Grim, 1953) Na+.L. K+ 4. Ca++ Mg++. Any cationwill tend to replace the cation to the left of it and mono­valent cations are usually replaced by multivalent cations.The addition of lime supplies an excess of Ca++ and cationexchange will occur.

The addition of lime txaaa fine grained soil causesflocculation and agglomeration of the clay fraction.Electrolyte content (Hf pore fluid influences the activity(Herzog & Mitchell, 1963).

Lime, especially when the soil is exposed to atmo­sphere, reacts with carbon dioxide and forms relativelyweak cementing agent of calcium carbonate.

324

The pozzolanic reaction is the reaction betweensoil silica and/or alumina and lime to form various typesof cementing agents. ‘These reactions are considered asthe major contributing factor to strength development inlime soil mixtures by quite a few workers (Thompson, 1964:Eades, 1962: Narain & Singh, 1966). The complexity ofthe whole process is brought out by the hypotheses proposedby the following workers for the nature of soil—lime reaction(Humad, 1987).

1. Miller and McNicol (1958) suggested formation of CaCO3from Ca(OH)2.

2. Galloway and Bucharan (1951) advocated cation exchange.

3. Arba (1948) proposed formation of calcium alumina silicatecomplexes from added lime and the free silica and alumina.

4. Laguros et al. (1956) proposed flocculation as a resultof decreased potential.

5. Clare and Cruchley (1957) suggested flocculation dueto proton transfer and subsequent binding by Ca++.

As the main objective of the present investigationson lime treated marine clay specimens are improvements

325

in shear strength and compressibility characteristics ofthese soft clays, prime importance was given to measurementof shear strength and compressibility characteristics ratherthan going into the details of the reactions caused by variouspossible stabilising agents. About ]i3 different additiveswere tried and the improvement in shear strength was studiedby laboratory vane shear tests. This series of tests clearlyindicated that lime was the most suitable stabilising agentas far as marine clays are concerned. Hence detailed investi­gations were carried out on the potential of lime as stabilis­ing agent for Cochin marine clays.

6.2 SELECTION OF A SUITABLE STABILISING AGENT

In an attempt to identify the most suitable stabilis­ing agent for marine clays, the following additives weretried on ‘moist’ marine clay samples. Two industrial wastestried did not show promise.

Sodium hydroxideSodium chlorideSodium silicatePotassium hydroxidePotassium chloride

1.2.3.4.5.6. Potassium dichromate7. Ferric chloride8. Calcium hydroxide9. Calcium chloride0. Calcium carbonate

326

11. Calcium sulphate (gypsum)12. Sodium carbonate13. Sodium hexametaphosphate14. Potassium permanganate15. Magnesium chloride16. Aluminium chloride17. Lime18. Cement

Each cnf the above additives was mixed with ‘moist’

soil at a rate of six percent by weight. The weight ofadditives to be added was determined by comparing with equi­valent dry weight of the ‘moist’ sample. The sample wasmixed thoroughly and transferred to vane shear moulds. Thespecimens were then subjected to laboratory vane shear testafter curing for one week and one month. Three specimenswere tested each time and average value was taken for theshear strength. The shear strength values after one weekand one month gave a comparative evaluation of the potentialcflf the additive as ea stabilising agent. The results arepresented in Table 6.2.1.

The» table also «gives the .Atterberg limits andshrinkage limit of treated soils found out immediately aftermixing. Out of the 18 additives tried, lime, calcium hydroxideand cement showed very impressive gains in strength. Sodiumsilicate, potassium dichromate and aluminium chloride gave

327

mmm.o mm¢.o ©.mH m.mm ofloo In moo.o wv.om m.oo mmH w©flxou©>L esHmmmuom .m

mmo.o HoH.o om.Hm o.mm .m.mm mHH.o vmo.o mm.mm m.mv m.HoH wHmoHHHm e:Hcom .wIn Hmo.o oH.mH m.mm o.mm :1 @mo.o ov.mH H.©v mHH mnHHoH;o esHmom .mo»m.o Lmfic >pm> om.vH m.mm m.vo :1 mvo.o mH.mm mm m.oNH w©flxon©>£ esHmom .mvoo.o Hmo.o m.mm II m.mv nmw.o o>m.o om.qm mm nvH meflq .H

II mNo.o H.nm m.mm m.mm ©mo.o omo.o oH.o~ ©.mm m.omH mmummuuca

ANS S3 8: A9 A3 At A8 A2 A3 A2 A3 A3

Lucoe xwmz

£5: H H83 H E E E H H8. H SH E E E

pom Cwuso pom mmusu o o o wmusu wwuso o o o

A Eo\mxV uflefia A Eo\mxv uflefla

N mom HHHEHH HHEHH N was. HHEHH HEHH .ozLumcmuum umwnm Ixcflucm uflummam UwSUflA cumcmuum nmmcm Ixcflucm oflummam ©HDUfld uamm .Hm

cuumm cmm wmmo wcwume CMSUOU

meqammm same m<mmm mz<>

H.N.® wHnma

A.©ucouV

Aesmmmmvmumnmasw

In In In In In mmo.o mvo.o In In In esflufimu .mH

mumconumo

In 4| In In In In mmo.o In In In esfiufimu .HH

wwflnoacu

In In In In In nn vwo.o In In In esflufimu .oH

8 w©fixou©>L

n nn nn nn nn nn mmm.o mmA.o nn nn nn esfluflmu .m

mcfluoasu

In nn v.vH In m.ov «no.0 Amo.o In m.wm mmfl ufluuwm .m

mumeoucuflw

owo.o mmo.o o.Hm ».©m nv »mA.o omo.o mm.mm m.om oofi esflmmmuom .5

wwfiuoaco

In Hmo.o om.mH m.om om nn mmo.o mm.mm m.mm omfi asflmmmuom .©

Ami AH: Ac: A3 A3 A5 A3 A3 A3 A2 A3 AC

II In an In In omm.o nmH.o II II II pcmemu .wH

mwfluoacu

us In In :1 II Hno.o Hmo.o In In In E:flcflE:H< .nH

wvfluoacu

1- an .. u- I- o¢o.o Hmo.o nu .. us esflmmcmmz .oH

9

M wumcmmcmeumm

II In In an In vmo.o mmo.o II II In Esflmmmuom .mH

wumconumo Esfimom+ mumcqmoca mume

In In In In In mmo.o mvo.o In In In umxmc esflmom .vH

wumconumu

II In In nu In Nwo.o mmo.o In in In esflcom .mH

Away AHHV Aofiv Amv Amv Anv Aov Amv Avv Amy Amy AHV

330

marginal increase iJ1 shear strength. Others did run: havemuch effect on the strength of marine clays.

Lime showed the highest promise as ea stabilisingagent. Within one week, the gain in strength was more than10 times. After one month curing, the shear strength wasabout 18 times the original strength.

For a comparative study of the action of the additiveon a non-marine soil, the same .additives. were added tosamples CHE red earth »n¢m1 a consistency close txn that ofCochin marine clays. The gain in strength due to additionof lime was nmrginal in case cm? red earth. But sodiumhydroxide and potassium hydroxide registered good gain instrength during the first week. But the strength was foundto lose with time. Since other additives did not showpromise with Cochin marine clays, they were not tried onred earth.

Cement also gave very encouraging results as astabilising agent for marine clays. However further studiesin the direction of improving the shear strength andcompressibility characteristics of Cochin marine clays wererestricted to lime only.

331

6.3 PHYSICAL PROPERTIES OF LIME TREATED SOILS

In most cases, the effect of .lime CH1 plasticityof clay is more or less instantaneous (Bell, 1988). Calciumions from lime cause a reduction in plasticity of cohesivesoils and make them more friable and more easily workable(Dandson 6; Handy, 1960). Only’ very’ small quantities oflime are required tn) bring about these changes inplasticity (Bell, 1988).

The addition of lime increases the plastic limit.Eventhough the variation of liquid limit with increase inlime percent is run: very regular that cnf plastic limit isa steady increase. This brings down the gflasticity indexaccompanied obviously by a reduction in plasticity.

Studies on tflua effect of lime (N1 liquid limit ofdifferent soils give conflicting results. Investigationsin India on black cotton soils showed a rise in liquid limit(Uppal & Bhatia, 1958). Similar observations have beenmade by Spangler and Patel (1949). But Clare and Cruchley(1957) feel that the influence on liquid limit is more complex.

In case of Cochin marine clays the effect of limehas been erratic. The physical properties of lime treated

332

In m.mm m.»© o.mo m.wmH mcucoe ©©.© m.mm o.mo o.on vvfi mnucoe mH.n H.mm 0.05 o.©n ©vH mgucoe m~.n n.mm m.mn H.mn >vH space Hm.» n.mm o.n© o.nn vvH mxmmz m©.> m.Hm mo o.mm mvH xwmz Hn. o.om m.m» ».oo mvfl mxmm m

m.w m.mm o.»@ m.Hw m.wmH >m© o w .m

m.n o.om m.m» m.qm vmH space H

m.o m.mm m.mm w.om vvH xmmz H m .mov.o om.om m.mn m.©m mmH II o .H

Aemxuov Awv Awv Hwy Aw

xmocfl uHEHH xwocfl uHEHH uHEHH coflgmm mafia we

HHm3m mwum mmmx:HuLm >uHuHummHm uHummHm GHDUHH mcHu:u wmmucwuumm .oz.Hm

usumm nwuHm

mw<qo WZHm<Z ama<mma WZHA mo MHHEMWQOKQ q<uHmwmm

H.m.® wHDmB

333

H.© m.o@ o.©m o.©m mmH mzucoe 0m.© o.om m.nm o.mm m.mvH mcpcoe m«.0 o.»m o.mm m.vm m.mvH mgucoe NH.> n.mm m.N@ m.om mvH gucoe H

H.w m.nm N.m~ m.m© NVH xmmz H NH .m

m.© m.mm m.vo m.on HVH mcucoe ©H.© ~.mm ©.N> van vvfi mcucoe mH.w m.ov m.ao n.om mqfi mgucoe No.m m.mv m.mm 5.0» ©mH space H

n.n ~.mm >.Hn m.mm m.nmH xmmz H m .mov.© om.om m.m» m.©m mmH II o .H

Aem\uoV “$3 Awv Awv Awv

xmmcfi uHEHH xmocfl uHEHH uHEHH coflumm mEHH mo

HHw3m wwum wmmxcHn:m >uHuHummHm oHummHm UHDUHH mcHu:U mmmucwuumm .oz.Hm

~.m.m mHDmB

WAHOW ome<mme MZHH mo mmaemmmomm q«oHmwmm

334

soil for various lime contents and cdifferent periods ofcuring are presented in Tables 6.3.1 and 6.3.2. It canbe seen from ‘Tables 6.3.1 and 6.3.2 that liquid limitinitially increases with time and then decreases. Withtime there is a general decrease in plasticity index whichis seen for all percentages of lime. For both 9% and 12%of lime the shrinkage limit significantly increases withtime whereas for 6%, shrinkage limit increases significantlywith time initially and then marginally decreases.

The ‘variation of liquid limit with increasee inlime content for curing periods of 1 week, 1, 2, 3 and 6months can be seen from the tables. It can also be seenfrom the tables that only very low percentages of limeare required for the changes in Atterberg limits whichis in agreement with the findings of Sherwood (1967). Theplasticity’ index ‘tends txa decrease Vwflfli increase zhm limecontent.

Compared tt> the Atterberg lindts, tflue variationin shrinkage limit is nmnxa steady’ with increase iJ1 limecontent as shown by the tables. The shrinkage limits tendto increase with lime content. This could perhaps be attri­buted tx> flocculathmi and agglomeration (Thompson, 1966).The free swell index increases initially but on curingthe value slowly decreases.

335

6.4 COMPRESSIBILITY CHARACTERISTICS OF TREATED MARINE CLAYS

The selection of the most suitable stabilisingagent for Cochin marine clays was mainly done based on thedevelopment. of shear strength of ‘treated samples Ineasuredby the laboratory vane shear tests. There has been a pheno­menal increase in shear strength of marine clays with limetreatment. But ii: had to kxa verified whether these gainsin strength are accompanied by an improvement in compressibi­lity characteristics since excessive consolidation settle­ment was the major concern of the foundation engineers deal­ing with Cochin marine clays. In order to verify this andallied properties, a series of consolidation tests werecarried out on marine clay samples treated with differentpercentages of lime and cured for various periods.

Fig.6.4.l shows the compression curves for un­disturbed, remouldad and lime treated marine clay sam.plesfrom Parur site collected from a depth of 7.5 m. Thecompression curves of treated soils are above the curvesfor untreated samples eventhough the initial moisture contentof treated soil was lO6% compared tn) 87% of undisturbedsample. The compressibility characteristics improve ‘withtime as shown by the upper curve when the sample was curedfor one month before the test, compared to the lower curvefor which no time was allowed for curing.

336

.mn._>m:u zo_mmmEn_zou _..$.mm

SE3 Ezozsmzz

03 .5 q 1:; 32mm: 0

W - mo, AozE3ozE2:

M °:::3oE<mE aZ Bafiozmm q% -:rl mm Smmsfiozp o

$2520 V A o m

$25.02

4<Ez_ ME: m:n_2<m -23

~

Ems .. IE3 mDm<& ..m:m

o.m O... 8. o

$549. E mmammmma

om.cm0.»omom

('1. )OOL X Hv

337

The improvement in compressibility characteristicsare more conspicuous at lower pressure levels than at higherpressures. For time consolidation pressure CH5 0.25 kg/cm2,

the 3% value is only 4% compared to 12.5% for the remouldedsoil. The comparison has been drawn with remoulded marineclay as the treated soil gets thoroughly remoulded during

mixing with lime. But at a pressure of 4 kg/cm2 9%-valuesare 33% for treated soil cured for one month and 42% forremoulded soil.

Fig.6,4.2a shows the compression curves for limetreated soils cured for ‘various durations of 23 days, «oneweek and two weeks along with the curve for undisturbedsoil. It can be seen from the plots that the compressibilitycharacteristics steadily improve with curing period. TheAH values at 0.5 kg/cm2 for the specimen cured for 14 daysis only 3% compared to 14.5% for undisturbed sample. Thisindicates that time consolidation settlements will tn; only20% of the settlement that may be realised in case of un­treated soils. But at higher pressures, for example at4.0 kg/cm2, the corresponding values are 38% and 28% whichrepresents a settlement ratio far’ below tflua earlier pairof values.

338

A study of the four curves show that, the stabi­lised soil develops a preconsolidation pressure (bond strength)slightly above (JAB kg/cm2. Till this point the Hmgnitudeof compression is insignificant. Once the consolidation

pressure crosses this pc value, the settlements for treatedsoils tend in) increase. It can also kxe noted that the

portions of the compression curves after this pc value aremore or less parallel. These results perhaps indicate thatthe consolidation settlements from 23 treated soil VHJJ. be

considerably less than that of untreated soil if the totalpressure po +.Ap are kept well below the pc values developedthrough stabilisation.

It can also be seen from the curves that whilethe behaviour cnf untreated soil present a gradual failure,more elastic iJ1 nature, time compresshmi curves cxf treatedsoils give a picture of brittle behaviour.

Fig.6.4.2b, c and d present the compression curvesfor lime percents of 6, E) and 12%. The plots confirm theearlier findings.

Fig.6.4.2d gives the compression curves for 12%lime, for curing periods of 0 day, 8 days, 1 month, 3 months,6 months and 18 months. It can be seen that there is a

339

.mm>m3u zofimmmizou o~..$.9.._

O mmi?) N a H 3.

Em; — G .

93 m 4o.n:<m_Ez: o

.3 H EH28 m2: o m

omo_oo.m o._ omo oeo mod

Ame V7.3: n. mmpmmmma

340

.mu>m3 zo_mmmmn_:ou..§..$ .3

mxhzoz m DIHZOE — Gm><o N 4oz::: 20 0Dm._.<mm:.ZD O

4.? 53.28 m2:

om

mmammmma

owomowonomo.

(°/.)0oL>< Hv

341

.mm>m:u zo_mmmmn_zou

u~..$.m_.._

om

o._

_ _ # é

E M _ m

_ _ flBE: IHZOE m_. xSE3 :20: 0 I

‘ SEC 520: m D oq

SE3 IFZOE h 4SE3 «Em; F 4

om

oz::2 zo 0Q5352: 0

.5 m zm zoo m:>:._

»-V%%-%.f;v A omS

_ H

J:/. /

on._.o 9.0 moo

£5 1?. V a mmnmmmma

(°/..) OOLX Hv

342

.853 zo_mmmEz8 H 3.3 .3

on

o._ V

-- - fiii .!fiu---A -­

:4SEC WTFZOZ 9 x

HEB mT:.ZO2 o

DBEG E202 m I<

QmmDu I._.zO2

B5: 55:

o? 2

—

— 402:22 Z0 09.:<mEz: O.. ._. Z5. zou mi:

Owomoq

/8. .o

$.E:3E mzammmma

//}

WWV....

J!

E -._

,0/O/YE

.nu|.||‘nlIH‘ i .

OWO

Om

~l/

omO—

(°/.)O0L x

8.0

HV

343

steady increase ixm preconsolidation pressure developed withtime allowed for curing, as indicated by the shift of thepoint of maximum curvature to the right.

Figures 6.4.3a, t3 and <: present emu interestingbehaviour exhibited by treated soils which was noticeablewhile comparing vane shear strength values also. Fig.6.4.3ashows the compression curves for lime percents of 6, 9 and12 for ea curimg period cm? 1 week. Highest resistance toconsolidation is exhibited by 6% curve with 12% curve keepinga low profile. Fig.6.4.3b gives the compression curvesfor specimens cured for three months where all the threecurves show more or less similar consolidation settlements.

Fig.6.4.3c shows the ‘Q; vs. log p plots forspecimens treated with EL S9 and 12% lime and cured for sixmonths. Here the specimens treated with 12% lime occupiesthe highest position with 9% and 6% curves falling belowin that order. This indicates that the process of stabili­sation is faster when the lime content is less. As thelime percent is increased the rate of chemical reactionis much lower and it takes much longer to gain strength.This phenomenon has been observed zhi comparative studies

344

om

. we/Ed zo_mmm_E:8 H uni .9;

4.. m_..5. m

o\o ® 0

P2528 mi: Jomzfi.

Em; _ oozma ez_m8

om.o A NEu\@.C a mmsmflmm 9.9

.

_W_W+______ _ _ ,_ __ ... ._._, r . if ~—————--—:­I

3.0

001H\7

345

.mm>m3 zo_mm.“En_28.. £33 .5

.\..§o\o@do w

HZMFZOU mg: Smz>m

WIHZOZ m .. DOEME oziau

W :Lon 3 8.0 o_.o

A N519: a mm:m..,H:E

V00L x

m o.o

346

.m.m>m3 zo_mmmE:8 5.3 .3

4.. E u

or m o If 1 I1

or o o

.. O m

zm 2

F _. ou mz: 2>mmzkzoz o .. QOEmE ozzpu

H

1 F - if

é -l_+|'-I-- r"T-:­

W

on o._ m.o mo.o

ANEXQZQ mmsmmumm

ommmom

HV

m_.

OOL X

Op

347

involving varying percentages of lime content and samecuring period.

Fig.6.4.4 shows the ratio of deformation oftreated samples and deformation of untreated remouldedsamples for ea lime content cm? 9%, for samples cured for1 week, 1, 2 and 3 months. It can be seen that the ratioof lwitreated/zmwuntreated is very low for lower consoli­dation pressures enui the ratio increases with intensityof pressure. The change lfl rate cnf increase it; around0.5 kg/cm2 as pointed out earlier. This may correspondto the preconsolidation pressures developed during curing.

6.4.1 Variation of de/d (log p)

Fig.6.4.l.la shows the values of de/d (log p)for various curing periods for samples treated with 6;9 and 12% lime for a pressure of 0.0625—O.l25 kg/cm2. The

conclushmi that lower percentages of lime treatment showa faster rate in strength gain is confirmed by the plotsin this figure. The value of de/d (log p) is as low asO.l for a specimen with 6% lime without any curing. Inthe case of the specimen treated with 12% lime the valuefor de/d (log gfl is as kflrfl1 as 0.64. The value for 9%

348

. @5552: 1.6

cm 2 8.0 9.0 moo

\\O

\\

%.I]%,d m.L o_. .a ,JON

M2 _

, omf 1% h oq

_WIHZOE m o _

9.3.202 N D _ m Om

IHZOZ _ a W

Em; _. o llom

ao_$n_ oz;:C Aom W-23 “

ME

_

4° 0

H 2528 m2:

GBLVBHLNDx Hv(°h)OOlG3.LV3H.L H V

349

lime falls in between. The de/d (log p) value for thesample treated with 12% lime slowly reduces for lnbghercuring periods ‘ultimately reaching 21 steady’ valuer belowthe curve for 9% lime content.

Fig.6.4.l.lb shows the same plots for thepressure increment from O.25—O.375 kg/cm2. It can beseen that the curves are closer to each other for curingperiods longer than 90 to 100 days. But in Fig.6.4.l.lcthe values of de/d (log p) for 6% lime are the highestfor‘ the pressure increment. of 2.0-4.0 kg/cm2. Thede/d (log gfl values for €¥% and 12% ljmma fall below theplot for 6%. The variation in de/d (log p) values withcurimg period its very marginal compared tub the previoustwo sets of curves.

It has already been pointed out that thecompression curves of treated soils indicate the develop­ment of a preconsolidation pressure (bond strength) around0.5 kg/cm2. The consolidation settlements Emma very lowwhen the pressure intensities are lower than the precon­solidation pmessure developed. The de/d (log gfl valuesare very low for the pressure increments of 0.0625 to0.125 kg/cm2 and 0.25 to 0.375 kg/cm2, as shown in Figs.6.4.l.la and b. The same figures show very high values

ooEmn_ ozE3 2 2mo:u\...n 2._..$.m_u_

Aiou V oozfii ozE3

350

of of oi oi o9 om 8 oq om o

a o.o

a

_ uO_..O

W

L, i owoV} W j g... O3

_ _

_ w

Wor C a

or a q l i T - 3.0

.4. w 0

% I , omo

pzurgou m2_._ Smzfi _ MEu 9. m~_.o:m$o.o Ha .

7- , } , _. -- - om.o

fl M _ _ _

_ W W - _ 050

(d5°l)P/3P

351

.oo_En_ ozisu ms Zmo:.o\Nu

A Z .3 .9?

7.3:... VQOEME ezisu

Owfi of 0.2 om.

00..

8

.<.. m—

o\o m G4. o W o

T‘.

#2528 923% ._Om2>m..I ll. ul||.1

NE V1.1 m.o -mt...on a

_ _

-————o

0.0cm. 0

O~.T0

CnoC

(d 5°1)P/3P

352

.oo;mE OZEDU m>

O®—

A m>d_uv

of 0.1 03

ha mo_Vu\uu

ooh

:;.€o

ooEmn_ oz E3

om

8

ON. 0

_

,__H_

_

w

% eu\\\\;

fl _

a +1 U. 1-! u .

o\o D +.> m a Wo\o ® 0 d

Em: zou E23

Smzrw

N

c:\9_©q-Q~ua

__

of8..co.m

(d5W)P/5P

353

for de/d (log p) when no curing is allowed for the samples.The de/d (log p) values are high in such cases as there

was no time for the bond strength to buibd up. Once pcvalues are built up with curing period, the values ofde/d (log EH drop down txb steady low values. But once

the pressure increment is higher than the maximum pcthat can be developed for the given lime content and periodof "curing allowed, de/d (log gfl shows ea regular‘ steadyvalue irrespective of the curing period as shown by Fig.6.4.l.lc. Thus an accurate assessment of preconsolidationpressure that can develop for a given lime content andcuring period is essential before designs involving stabi­lised soils, are taken up for field applications.

Fig.6.4.l.2a shows the plot between de/d (log p)and curing period for marine clays stabilised with 6%lime for tflue pressure range CHE 0.0625-0.125 kg/cm2,O.25—O.375 kg/cm2 and 2.0-4.0 kg/cm2. Fig.6.4.l.2b givesthe same relations for 12% lime. Both these figures arein agreement with the findings from Figs.6.4.l.la, b and c.

The variation of de/d (log p) with the percent­age of lime added to the soil is given in Fig.6.4.l.3for three pressure increments. The curing period allowed

354

A

.ooEmm OZEDU .u.> An moZU\uU

“ion V ooima oz_m:u

of of o.: 0: oo_ cw om oq om o .

D o o

Ar

III? +‘II|:|- I - -- .|'uJ.Om.O_ «zn---:-.§,-- if - .- ::_V|u|-- -.M ..

_ %

E M - 4 so

o.q u o.~ omivo - m~.o -<% mm_.o-m$o.o D

M

__ A metm: Aom% MEDWWMZQ .53_+ .\.w E328 22:

¢ _ I _ in

355

.ao_$n_ ozE2u 2, E mo:o\~u £....$ .9“.

7933 no.5; ozE3

ow _ of o.: 2 _ o9 8 8 3 om o

o[% , omo

,l... _T o.so

WM

tofu

cg u o.m O

I Q ll- .mE.o-m$o.o u M§.E:.:: :51 i J

H.E:mmmE :23.5 .2 2528 m2:

flA T,_w_

T-.1.-.

.....W._.

0.»;Se

356

2-00

1 J CURING PERIOD-.1MONTH' i SYM PRESSU E1_8O __jL BOL (kg/cm )

g D O-0625-O-125E5 ‘ ~ 5 - ~501.60 _ _h__a ; A O 37 OE? 2.0 - 4-01 -1 0 _.E EME - - ,.-_:___~

1.20 E“ '“ ~——*1-00 ‘+- ­0- rE A gV 0-80» E1} ~ A « —— —-—+‘U

‘:7U O-60*“ ~ —~—

O.4Q4___

O-20 E-E —-—~O-O — T0 2 A 6 8 10 12

LIME CONTENT (°/. )

Fig. 61.-1-3: dc/d ( 109 D) vs LIME CONTENT.

357

was one month. These curves give some useful informationregarding the most ideal lime content. For a pressureincrement of 0.0625-0.125 kg/cm2 for 3% lime the valueof de/d (log p) its about 0.49. When ‘the ljmma contentis increased, the value of de/d (log p) decreases andreaches a ndnimum value an: 6% lime content. For higherlime contents the value for one month curing increases.Since de/d (log gfl is directly proportional tn) consoli­dation settlement, the consolidation settlement of treatedclay layer which can be given one month for curing willbe least for a lime content of around 6%. Lower lime content

will obviously give a higher value of de/d (log p). Limecontents higher than Efls can give 51 lower value forde/d (log p) provided a longer duration can be permittedfor curing.

Similarly for a pressure range of 0.375 to0.5 kg/cm2 time lowest value CHE de/d (log gfl is given bya lime percent of around 9 for a curing period of onemonth. Since the lowest value of de/d (log p) has a bearingon the preconsolidation pressure developed through stabi­lisation, a higher lime content. is required tx> developthe higher pc within a month to meet the higher pressure.

358

This shows that studies of this nature will help to optimisethe lime content for parameters such as pressure incrementand period of curing.

The relation between de/d(log p) and consolida­tion pressure are shown in Fig.6.4.l.4a for a curing periodof one week. The values increase with pressure and thenstart dropping down. The higher lime content gives highervalues of de/d(log p). The reasons for this have alreadybeen discussed. Since the rate of development of shearstrength is inversely proportional to the lime content;the sample with 21 lower lime content will show’ higherstrength cn: lower «de/d(log gfl for" short curing ‘periods.Here the curing period was only one week.

How the de/d(log p) curves will change thetrend is shown by Fig.6.4.l.4b where the samples havebeen allowed to cure for 6 months. Here the sample with12% shows the highest strengttn or lowest values forde/d(log p). The figure also indicates that the differencein resistance to deformation between 6% and 9% is muchhigher than the difference between 9% and 12%.

dc/d(log p)

359

1-80

1-60

CURING PERIOD-/IWEEK

1.4ObO 6'/, LIME9/. LIME

D 127. LIME1-20 ._I1-oo§— —

O.3O[_ -._0°600.40 —---4O-20

1'

|0-0 1050 1-0 500-10 2PRESSURE p (kg/cm )

Fig. 6-A-1-Ac: dc/d(l0g p) vs PRESSURE­

361

The variation of de/d(log p) with pressureis presented im1 Fig.6.4.l.5 fin? five samples which havebeen cured for 1 week, 1 month, 3 months and 6 months.The plot for a sample for which no curing was given isalso given Lhi the figure. A comparative study cm? thecurves in the higher pressure region, show that the valueof de/d(log p) is least for the sample for which no timewas given for curing. The values cm? the sample curedfor 1 week is the next lowest. The curves for the samplescured for l, 2 and 3 months are very close to each other.Here a lower value for de/d(lmg p) does not show higherstrength. For 51 sample which has run: been permitted tocure, no preconsolidation pressure has developed. Hencethe e - log p curve will not show any sharp variationin slope.

In Fig.6.4.2c the curve for remoulded sampleshows a very uniform slope throughout. Hence its de/d(log p)is the lowest. The sample treated with lime and for whichno curing was allowed, has the next least compressionindex as well as de/d(log p). The next sample has aslightly higher value for de/d(log p). Hence for a treatedsample which has developed some bond strength will show

362

2 -O ILJMECONTENT: 6] I ' ;CLHNNG REmoD: 1 V‘ //L1-6 -—+ 3. 0 C10 y it 1 /O 1 we e k I 11-4 I; 1 , ,A 1 month g 1 §

A1-2 D 3 months 1 1 i- MQon A 6 months 13 1.0 1 ~ 1 /-/ Iv 13 .'N O-80_—— 1"0 2

0 '60 ~—-~——RR»~R——!r R;1 /0-1. 0 1 / —/‘/,/ // 10.2 0 ‘~ H-.. ;D - 1 110-00-10 O -50 1-0

PRESSURE p(kg!cm2)

1ag.e4+5 dc/d(lo9 R) ‘us PRESSURE­

363

low values of «de/d(1og p) at lower pressures and highvalues at higher pressures.

6.4.2 CV and Cde for lime treated clays

As lime stabilisation causes flocculation oraggregation of finer «grains, the permeability increaseswith cmring. This has been shown by the curves in Fig.

6.4.2.1 where CV has been plotted against curing periodfor 6, E9 and 12% of ljmma As expected CV has been foundto increase with time.

Fig.6.4.2.2 shows the variation in CV withincrease in lime content. The value increases upto about8% and decreases. A possible explanation for tffljs canbe the clogging of voids by the products of stabilisation(Brandl, 1981). By lime stabilisation the mineral parti­cles are cemented within the soil-lime mixture. The fineskeleton is embedded partly within the gelatinous inter­mediate mass. Hardening products of the binder grow intothe voids of time soil aggregates, changing’ the ‘voidstructure» This can bring down time value of coefficientof consolidation or permeability.

364

com

.oo_EE .uzE:u 3 J E..$.m:

A 3:2: ao_$n_ wz_Ed

om: of oi om. Q2 om 8

,1'|r4.‘_vI‘n‘|N|||,' I |vx.TI"'.|n|'

\I

% -- w

E. Dxa G3 0._OmH2528 “.2: 23

me. 30¢ - ca H Q

C?l\

C?00

Qcn

0.0_0.20.s.D

("->v3'5/ZUJ3)'7_OL X “D NOILVGHOSNOD 3033301)

-z.

COEFF. or-' CONSOLIDATION cv x 10 (cm?/sec-)

7-0

ch (5

U1 0

7°

9’ o

M O

c’)

365

i= I1

CURING PERIODS 1 MONTH

smess RANGE -. 2~o- L-Okg/cm?

+ LJ IA 6 8 10 ‘I2LIME PERCENT

Fig. 6-4.2-2 CV vs LIME PERCENT.

.ooE.nE ozE:u 9, 3; m.m..$.mm

Am.>UUV oo_mun_ GZEDU

O+&~ of 0.: ON_. OOF Ow O0 04 ON

. 4; A .

_ ____..__—————

366

_ O

_ M_

1!- - » V 7-1 pzmtzoumzj Lgmm

aim; o..7o.m H a

_ _ fl _

oC?(V

O('7

O\T

1.13L0

U 7Q.00 C?of) ~

OL x 3*’ 3 ’Nouvc1nosNo3 AHVCINODES so 3:130)E­

COEFF. OF SECONDARY CONSOLIDATION c 46 x 1O'3

367

'1?-O ]O A1o.o_ _ __I CURING PERIOO-. I MONTH

STRESS RANGE: 2-O-L-O kg/Cmz8-0;. I I I6-0;»­

4.0;I2-05 Ik i0 1 J I lO 2 z. 6 8 10 T2UME PERCENT

Fig. 6.4.2.4 C“ vs LIME PERCENT

368

As the newly formed chemical bonds betweenthe grains become harder anui harder, the coefficient ofsecondary consolidation should increase. Hence Cue shouldincrease vflifli curing periods and time consolidation ‘testresults also show the same trend as in Fdg.6.4.2.3. Fig.6.4.2.4 shows the variation of Cde with lime percent fora curing period of one month. C,» reduces with lime content.cg:

6.4.3 Development of bond strength

Fig.6.4.3.l presents an interesting featureof stabilising process when lime is added to Cochin marineclays. It shows the plot between preconsolidation pressureor the bond strength developed and lime content for fourcuring periods, viz. 1 week, 1, 3 and 6 months. The curvefor 1. week duration shows that imm case of samples curedfor ]. week, the highest strength, 0.76 kg/cm2, is givenby 6% lime. A lime content above this shows a reducedstrength. A higher lime content will certainly give astrength higher than 0.76 kg/cm2. But it has to be givena longer duration for curing. It shows that if the curingperiod that can be allowed before a stabilised soil isused for EH1 engineering application, if; only cnue week,the optimum lime content which gives maximum strengthis 6%. Similarly the optimum lime contents for l and

369

T 1 7W I ‘CURING PERIOD ¢1-40 0 1 WEEK .__4'A 1 MONTH

3 D 3 MONTHSE moi” 1 o» 6 MONTHS _ "J!K 9 I ! ;O‘ ‘ ‘ f I_~z I ! 5V 1009- E —-— —~ ——§; ‘ . g080;. .. - . .. AO-60j— — _ _5 .

i' 0O-loOi— J —— - ——O3

00 1 1 I J I JO 2 A 6 8 10 1?LIME CONTENT(°/o)

Fig. 6'4-3-1 pc vs LIME CONTENT.

370

3 months of curing are 7% and 9% respectively. In caseof samples cured for six months the optimum lime contentis more than 12%. This shows. that depending upon thetime available, one cxui design ea stabilised sxflJ_ whichwill give time highest shear strength with least limecontent for a given curing period. These curves are ana­logous to compaction curves where optimum lime content,preconsolidation pressure and curing period have respectiveanalogies in optimum moisture content, maximum dry density

and compactive effort.

The development of preconsolidation pressurewith respect tn: curing period ‘for ljmma contents cyf 6%;9% and 12% are shown in Fig.6.4.3.2. It can be seen fromthe graph that 6% picks up a smrength of 0.76 kg/cm2 onthe 7th day whereas the strengths developed by 9%‘ and12% of lime are 0.44 kg/cm2, 0.36 kg/cm2 respectively.After six months of curing 12% occupies the highest posi­tion anui the other lime contents follow iJ1 that. order.This again proves that lower lime contents gain strengthfaster than higher percentages of lime.

371

.ooEmn_ ozizu 9, ua ~.m..s....ma

Aiouv oops: ozzsu

om Ow— 0.1. Omp OO.— cm Ow 0.» ON

m M , ,_ é _ . . d1 H , _ V

N: DII: E Q

No 0

HZMHZOU M2:

....-_j._j__. ._j.—-——~—-:——r --A - '-­

oweO90om. OOO.—

0.»...

“d 3:1 nss I-ltld Nouvcmosuoaaad

372

6.4.4 Duration of load increment

Fig.6.4.4.la, b and c show the compressionvs. log p curves for 2%, 4% and 6% lime. The first pair

of curves show £%-- log E) relation for tmna lime—treatedsamples with no curing for two loading durations of 2days and E3 days. The second figure shows similar curvesfor 4% lime. Both show that the curve for 8 days durationhas undergone greater compression than that for 22 daysdurathmi. This is contrary to the results of consolida­tion tests on untreated samples (Hf Cochin marine clayswherer the strength improved with duration especially’ athigher stress levels. In case of lime treated marineclays such development of strength is not available.The strength gain is due to bonds developed between grainsdue to physico-chemical action of lime, which is unaffectedby loading stage or loading durations. Fig.6.4.4.lc showsthe 9E vs. log p curves for two samples with 6% limeH

content cured for 1 rmnnfin Eventhough the loading dura­tions were different, the curves are very close to eachother indicating that duration of loading has little effecton strength gain.

6.4.5 Comparison with other soils

For a comparative study of the improvementin compressibility characteristics between Cochin marine

373

I

.mm:mmmma m>.AmWn n:¢;?o.m£

M W _

L . ML 4<>mmH7: m><o m F<m::o<o4Au.:is+ 1Auo

4<>m.n:z_m><o N Z oz._a<o4 o

%w+|, Aozzza ozvxmukzmpzoumzi. _uw om v

m:m<n_ ..mZ_m W

xw _ %L o u L_ _ _ WM W . M )M H _ ./. W. w + f rnfi O m.. (x

MH E .

I T r on

W Mn _ _

lif . , . W W , or

W _ M .W _ _

_ _ ~ _ _ oom o._ om.o . mod

.Eu\mx Q mmsmmmma

374

.mE:mmmEn_ m>

: .. n 3..$.m:_

I G

. : _ fl 2

. M _

_

II .1 , In I1

W M 4<>mEz_ 9,5 9 .2 oz_o<9 4 ow

4<>m.“:z_ 9,5 N Z oz_o<9 o

GzE3 ozv? #2328 ms: J,lo m

ESE H utm H W

. __ o q

_ _ W V...M _ m

. . _* Ifilom- »|lON

on o._ om.o moo

AEu

N

375

I

|L|d|_... ;_.,3.o .m_.u_

.nE:mmH.En_ m>

;_<>mHz_ mica »< oz_o<o4 Q4<>mm:z_ 9:3 m._.< 02.0404 0

rhzoz h n::mma oz_m:uNo H hzmhzou m2_4z:m<m “m»_m

. _.___ -..‘_. _.._. 1-.--.. - ._ - ..-.-..

cmmmom

H vHXm. LOO7/o_ ,x

nym

Am:u\mxVa mmnmmumm

a,moo

376

clays and black cotton soil, the compression curves areshown in Fig.6.4.5.la and b. Eflg.6.4.5.2 shows the rela­tion between de/d(log EM and log E) for time two soils.The figures indicatee that the effect of lime (N1 blackcotton soil is much more pronounced than on Cochin marineclays.

For all the discussions so far, the resultsfrom tests carried out on lime-treated samples from Paruronly were considered. To verify whether the findingsare equally applicable to samples from other locationsin Greater Cochin area, typical compression curves forlime—treated samples from Kumbalam and Maradu are pre­sented in Figs.6.4.5.3b and c for untreated samples, samplesimmediately after mixing and samples cured for l weekand l rmnnfiu The curves are in good agreement with eachother.

To study the development of bond strength undercontinuous strain, consolidation tests were conductedon twM> samples, keeping tflue total time» spent the same_The first one was not given any time for curing, but moreduration was allowed for each load increment. In ‘thesecond, sample was allowed to cure, but the duration foreach load increment was reduced so that both tests took

377

.mE:mmmmn_ m>

fl , _. fl A 2

M

.:¢m zPL8 54.3 o +1 S

.,.m:m<n: >433 m_:E<:o

xmmz, h ..ooEmE OZEDU om

3 Hzwtzou m2:

9-411 9

_

_, omoo

OOL X’ HH V

378

.mE:mfl.:E 3 .3 ..f.m..$ .9...

_ _ _ q _« Om

% . r k m_ B W

jom zofiou 53m o 1 mm

W_ E:m<n:..><d mzE<: o M_ _

%- !%vi- + mzhzoz N . o H v/ M . oima ozE3 W om H

_ M _

W o \q #2528 M2... w.W. é _ fl _ ,2 )M W ._ W . /_ M A C

1|: W 4 w 1119

r V Tu.» J. m

, W % W W

H L o9.0 moo

mmammmma

379

...E:mm.n.Ea 3, Zmolutn 2.3 .9“.

A Eu\mxva mmammmma

om N 3 owe oco

oweo.so

PE .0W

W -:|l.om.o

W m% _ . 5, dat dom zofiou 5<4m o I iiowo C

?5¢<n: ><.U mzE<: o

i xH,;>TooEma ozE3 11% 1o:

.3 Lzfzou m:>:._

om;

380

on

n.E:mmmmn_

0..

I

T, unlql ..um.m<.o an

E.zo:_ ac”. Sago 4Ems. mom amaze Gm::.$ I_._>> 02:22 Z0 0

BS5523 sow ._rm_O2 O

m:m<n_ ..mEm

no

5 moo

A NEURV: Q mmammmma

OJHH(Z )OOl><

.mm:mmmmn_ m> nuI‘. ..nm.m..».w .9...

381

Id

oq_, Ezoz _ mom Bmauu mm

M M _ xmu>, _ mow ommzu 4 ,% M ”£4:N@::3oZ§:zoo w

W 3E<mEz: V jom 562 o I om

M 2<4<m::x” mtm v

Hmm “H

Xm0ii: - 11., om x,W Z_ c

1 Ayfiw w o_

W . % W M _

Hfl . _ H IL

_ _ _ H_ W _“_ J _ _ +

% 4 _x_ . __ _ '_'.,”lh Oom o_ m o owe moc

Am:u\mxVa mmammmma

.m¢3mmmEn_ m> IHIQ‘ um.m.q.w .9“.

382

_ , _ 2

_ é

_ W m M

7 . W .T . . f I flw mm

H .V M .

r _ F _

:»zoz_ mom QME3 n om

imzi mom SEC 4

mi... 3 1:3 oz_x_: zo o H vSm:aEz::_om 5.0: o mm H

:o<m<2.. mtm xcm m

3o.mocm 9 m o oeo 3.0

Ameimi a mizmmmi .

383

the same time (45 days). The compression curve for boththe samples emu; given in Fdg.6.4.5.4. The sample whichwas not allowed to cure showed greater compressibilityindicating that the development cnf bonds VHHN1 the soilis subjected to pressure is less than that when the soilis allowed to cure free of pressure.

6.4.6 Effect of sustained loading

One cm? the aims cnf this investigation was tostudy the engineering behaviour of Cochin marine clayswhen they are subjected to constant pressure such as froma building. It has already been shown that untreatedclay develops strength when they are subjected to sustainedloading and the resistance to compression considerablyimproves with the duration of loading in consolidationtests. In case» of treated marine soils, the durationof load increment does not have any influence on the develop­ment (Hf bond strength. Ihi order tn) study time behaviourof stabilised soil beds under sustained loading, a seriesof consolidation tests were carried out to assess thedevelopment of preconsolidation pressure. Fig.6.4.6.lshows the e»- log p curves for two samples remoulded attheir respective liquid limits mixing with 3% and 6% lime.

384

.1 I I

: _fi fl _ ow

_

I L 353 Ezo: : w

#552. «:3 N Z oz_g<o._ 4 _ om

_

A ozizu oz V

. :11 4<>E:z_ 925 m 2 oz5<S o 3

T pzutzou M2: H W

+ om x. m. M 0V - om X

, W. o.

I.

% % /T C O

om o._ 8.0 9.0 3.0

Amei 9. V a mmnmmmma

385

.mm:E2u Q

o._

mo_-~

2.3

AmEu\mx V

.9...

mmammmma

3

.[l ' .

m>mU m.

.. com E owzgmsm

ms:M23

xmoxmo~,,S\9: Hmmammmma Szémam

.3 F4. Bofiozmi ..m::<m

go .1of03ooa.

.-_ r___._..._ __

oim2;

_-__4r__..__. . _ .

P"

own

3 OILVH CHO/\

386

In the oedometer ring the samples were kept at a pressureof 1 kg/cm2 for 15 days. The pressure was then releasedto seating load of 0.0625 kg/cm2 and a full consolidation

test was run to determine pc. Both the curves show thatthere is increase in the preconsolidation pressure byO.25—O.3 kg/cm2 in each case. It may be noted that higherlime content does run: show higher strength ans one would

normally expect. This may kxe perhaps due tn) the shortduration where samples with low lime content will be moreactive.

Fig.5.6.3.5 shows the ea — log g3 curves formarine clay samples mixed with 3% lime. They were consoli­

dated under a sustained pressure of 1 kg/cm2 for durationof 2 days, 7 days, 15 days and 60 days. The four plotsshow that there is a regular increase in preconsolidationpressure and it is proportional to the period of sustained

load. When the increase in pc for 2 days loading is hardly0.2 kg/cm2, the same iknt 60 days duration is 0.6 kg/cm2.

The increase in g%: from sustained pressurte consistentlyincreases with duration of sustained loading.

Fig.6.4.6.2a and k) shows two ea - log E3 curvesof samples with lime contents of 6% and 9% cured for

387

EE3 a mo. - u om.m..$ .9“.

A~Eu\9:a mmamflma

o. m o._ om. o 9. o moo

owm

_

1lL« Loin

H mizoz 9 mo... W

mizoz w QOEME ozE3 ._ filo?”

m_Z3 .3 + 3.3 mzE<2 ..m:a2<m

omaoo.mxii, owmI, »s:1185cam

3 OlJ.\/H CIIO/\

388

cm

m>m2u a mo_-~

o...

n~.m..%w

.m_n.._om . oaS\9_E mmzmmmmm

9.0

9:20: o mom

N

Eu\mx m.o

WIHZOZ 0

_.< Bz_<B3m

QOEMQ oz E3..,:>:._ Na + ><d mzE<z m.Iz<m

. ll.

9:om:O omomm85can

3 OLLVH CIIO/\

389

six months. Then they were consolidated for six monthsin an oedometer ring under a stained pressure of 0.5 kg/cm2.The load was then released to seating load and full consoli­dation tests were conducted. The two e - log p curves

show that there is considerable increase in pc. The totalcompression for 6% lime is much more than the totalcompression for 9% lime.

Chapter VII

ELECTRICAL CHARACTERISTICS OF MARINE CLAYS

7.1 INTRODUCTION

In recent years, geophysical methods of exploringthe subsurface Punna gained momentum imm geotechnical feasi­

bility studies encountered in civil engineering (Mitra,1984: Murthy 5; Chandra, 1981). Among various geotechnicalmethods available, electrical resistivity survey’ has beenvery popular as ea rapid and relatively inexpensive method.Eventhough its earlier applications were more in searchof metals and minerals, of late, geotechnical engineershave been taking advantage of the versatality of the technique(Malhotra, 1981: Raman, 1984; Rao et al., 1987: Ravindranath

et al., 1983). Geophysical measurements essentially involvesearch for time subsurface kn! physical measurements fromthe earth's surface. The two geophysical methods whichare of maximum use in engineering studies are electricaland seismic prospecting techniques.

In resistivity prospecting, direct current isimpressed into the ground through a pair of metallic electrodeswhile the potential difference between two other intermediate

390

391

points is measured. From a knowledge of the electrodeseparation, potential difference anui current, tflue apparentresistivity can be calculated. If the ground is homogeneous,this is time true ground resistivity. Since ea homogeneoussubsurface is very uncommon, it is the weighted averageof the resistivities of the formations through which currentis passed, that one gets from an electrical resistivitysurvey. It is from an analysis of the variation of thisquantity vdiflm change jfl electrode spacing enui position thatdeduction about subsurface cxn1 be made. Hence interpret­ation techniques are equally important in a successful sub­surface exploration by any geophysicals method (Kate &Khichchumal, 1983).

The popular methods that are used for interpret­ation of the resistivity’ data. for arriving an: the soilprofiles are

i) Moore's Cumulative Plot with Hummel's Extension

ii) Direct slopeiii) Inverse slopeiv) Barnes layerv) Master curves

392

The values of the apparent resistivity obtainedby any one of the above methods are then compared withstandard absolute resistivity values txn recognise the typeand depth of the various layers.

While significant work has been carried out inconnection with field oriented studies, no information isavailable vdlfli regard tx> its usefulness im1 the laboratory.In this chapter an attempt has been made to investigatewhether this technique could be used advantageously to relateit with engineering properties.

7.2 RESISTIVITY MEASUREMENTS ON COCHIN MARINE CLAYS

The resistivity survey provides the values ofapparent resistivities. Resistivity soundings provide the-values cu? apparent resistivities Pa in aa layered systemat known depths. However the values of absolute resistivitiesare required txb identify tflua various layers ix: subsurfaceprofiles. The apparent resistivity at any depth is a funct­ion of absolute resistivities and thicknesses of variousstrata in the subsoil through which current passes. Hencethe value of absolute resistivity is essential for purposesof correlation between field resistivity measurements andgeotechnical properties of Cochin marine clays.

393

The absolute resistivity of soil is the resistanceoffered to the flow of current by a soil cylinder of unitcross sectional area and unit length (Chauhan & Kate, 1983).

where

Q = Resistivity of the soil (ohm-cm)R = Resistance offered by a cylindrical soil specimen

(ohms)

A = Cross sectional area of specimen (cm2)L = Length of the specimen (cm)

Laboratory results on electrical resistivitystudies have been scanty. Preliminary results on the effectof density and moisture content on resistivity of soilshave been presented by Chauhan and Kate (1983). A criticalexamination of the’ limited available data showed that itwas desirable to investigate the electrical resistivityof Cochin marine clays. Since these tests are very simpleand least time consuming, any correlations between theelectrical resistivity and other engineering propertieswill be of immense help. With this in view, studies wereinitiated with regard txa the electrical resistivity chara­cteristics of Cochin marine clays.

394

Laboratory tests

The experimental set Lu) tc> measure tflue absoluteresistivity of clays consists of a simple perspex mouldof size 11 cm x 41 an x 8 cmn Well polished copper platesof size 3.9 cm x 3.9 cm and 1 mm thick are used as end plates.Oven dried marine clay sample was remoulded into the perspex

mould at the desired water content and density. The requireddensity was achieved by static compaction. One end of theconnecting wires was welded to the face of the two copperend plates, and the other end of wire to a highly sensitivemultimeteru The sample is kept in the upright positionand a nominal weight of 0.2 kg was kept on the top of thetop copper plate in order to ensure perfect contact betweenthe soil anui the copper plate. The self weight cm? thesample and the nominal weight ensure good contact at thebottom.

In the case of undisturbed samples no mould wasused. The resistivity of the undisturbed sample was measuredby keeping the undisturbed sample <iirectly (N1 the bottomcopper plate and the top copper plate along with the nominalweight was placed on the top of the sample. For undisturbedspecimen, the size used was 3.8 cm diameter and 7.5 cm height.

395

Fig.7.2.l presents the plot between dry densityand resistivity of oven dried Cochin marine clays for variousmoisture contents. Since the value of resistivity was foundto vary from 800 ohm-cm to 5OOxlO3 ohm-cm, the resistivity

was plotted to log scale. The curves show sharp variationsin absolute resistivity’ for variations iJ1 dry’ density’ aswell as moisture content. Fig.7.2.2 shows the relationsbetween resistivity and nmisture content for cfifferent drydensities. Since both curves have regular patterns, theycan be utilised where density measurements have to be takenat short durations. It may be noted from both the curvesthat the changes in resistivity for normal changes in densityand moisture content is of a very high order. Since densityalso represents the porosity and hence the volume of mediumof separation, the resistivity is strongly influenced. Hencesuch sharp variations can be expected.

For purposes of comparison, results have alsobeen obtained CH1 partially saturated kaolinite clay samplesat different moisture contents and dry densities. The resultsare shown in Figs.7.2.3 and 7.2.4.

7.2.1 Effect of sample dimensions on electrical resistivity

Resistivity measurements reported so far by variousworkers are rmmwmlly (N1 small cylindrical specimens. For

RES|ST|V|TY(k...n..Cm)

396

500 —Y——— — T SOIL MARINE C.LAY_ ’ 1 (oyen;Lr:ed)' I ” CURVE MOISTURE CONTENT__ D __ NO- ( °/. )Q) 1 5I , _ ____,__I Q) 2 O‘ @ 2 51 ”. -———-~— @ 3 5

50 E-—-E

10 :1‘

5 1.

E

1.0 _0.5 D .0.50 0.60 0.70 0.80 0.90 1.00 1.10

DRY DENSITY ( gmlcc)

Fig. 7. 2.T RESISTIVITY vs DRY DENSITY.

7.20

RESISTIVITY ( k..n..c rn)

1000

S00

10

1.0.

0.5

397

[ I [ MARINE CLAY} E SOIL (oven dried)” : T CURVE DRY DENSITY— i 1 + -~ -~+—~ NO- (gml cc)‘0 9 K 0.60’ ‘— 0.70__ 0 0.80g 0.90§ 1.00P:00 1.10;_l._

LI

T"

10 15 20 25 30 35 40MOISTURE CONTEN T( °/.0 )

Fig. 7.2.2 RESISTIVITY vs MOISTURE CONTENT.

SOO

RESISTIVIT (k.n.Cn_1_)

C) O

0.50 070

Fig. 7. 2- 3.

398

SOIL

O80 O90DRY DENSI TY(g

RESISTIVITY vs

KAOLINITE

MOISTURECON T EN T(°/

RVE

100 110m/ cc)

DRY DENSITY­

120

RESISTIVITY (k. .n.-cm)

399

500 _ ’___-E ....,.._._E..E____ _ ; SOIL KAOLINITE__E CURVE DRY DENSITYNO- (gm/cc )‘ ° E‘ W Q) 0.60Q) 0.70X Q) 0.80‘O0 *0 ; E @ 0.900 ' 1.00

5 10 15 20 25 30 3 5MOISTURE CONTENT ( °/. )

Fng_ 7. 2.1.. RESISTIVITY vs MOISTURE CONTENT.

400

fine grained soils, measurements on such specimens can giverepresentative values. But in geophysical exploration,where the resistivity methods have maximum applications,the absolute resistivity cnf soils with coarser grains alsowill have to be determined so that an accurate interpretationof the field test data is made possible.

In order to find out the influence of sample sizeson square pmismatic samples, resistivity measurements werecarried out on samples of different areas of cross section. 2and lengths. The areas of cross section chosen were 16 cm ,36 cm2, 64 cm2 and 100 cm2. The lengths of samples testedwere 2.5] 5.0] 7.5] 10.0] 12.5] 15.0] and Cm.The tests were carried out on oven dried marine clay sampleswith different water contents. The results are presentedin Figs.7.2.l.l to 7.2.1.4.

Fig.7.2.l.l shows the plot between lengths ofsample and resistivity of oven dried specimens for fourareas of cross section for a water content of 40% and drydensity of 1.2 gm/cc. It can be seen that the value ofabsolute resistivity tends to decrease with length of thesample. The rate of change is faster for shorter specimensthan for longer specimens.

RESISTIVITY (k-.fi.—cm)

401

J

— _ SOIL '. MARINE CLAY(OVEN DRIED)L E.” MOISTURE CONTEN T = 40 ‘lo

100

SYM- 2ABQL AREA OF C'S'( Cm )

._s@o\1‘­

O

A

C]

O

0 2.5 5-0 7-5 10 12-5 15 17.5 20LENGTH OF SAMPLE (cm )

F-"lg. 7.2.1.1 RESISTIVITY vs LENGTH OF SAMPLE.

SOO

U3 0

(K.n.—cm)

RESISTIVITY

10

50

1-0

0-5

Fug.

402

SOIL MARINE CLAY (OVEN DRIED)

MOISTURE CONTENT: 25 °/o

2SAMPLE AREA OF C'S- ( Cm

4 X6

8

a

5

7.2.1.2

7-5 10 12-5 15 17-5LENGTH OF SAMPLE ( cm )

RESISTIVITY vs LENGTH OF SAMPLE­

)

10-0

5.0

b RESISTIVITY (k._n.. c m.)

403

SOIL I MARINE CLAY(OVEN DRIED)MOISTURE CONTENT‘. 40 °/oSYMBOL LENGTH OF SAMPLE(cm)

2-5

5-0

0-510 2o 30 40 50 60 70 80 90 I00CROSS SECTIONAL AREA (c m2)

Fig. 7.2.1.3 RESISTIVITY vs cnoss SETIONAL AREA­

RESlSTlVlTY(k..n..-cm)

500SOIL MARINE CLAY(OVEN ORIEO)MOISTURE CONTENT -. 25 °/.

SYMBOL LENGTH OF SAMPLE(cm)O SA TO

100T5

50

10

5-0

1-0

0-5

CROSS SECTIONAL AREA (cm?)

Fig. 7.2-1.4 RESISTIVITY vs AREA OF CROSS SECTION­

0 25 50 75 I00

405

Fig.7.2.l.2 shows the variation of resistivitywith length of sample for the different areas of cross sectionof oven dried marine clay samples for a water content of25%. Here also the 9 values decrease with length of specimen.

Figs.7.2.l.3 and 7.2.1.4 show the relation betweenabsolute resistivity and area of cross section for fourtypical lengths. The water content in Edg.7.2.lg3 is 40%and 7.2.lw4 is 25%. The curves show that the resistivityvalues increase with cross sectional area.

Since the values of absolute resistivity are depend­ent on the dimensions of the sample, in case of squareprismatic specimens, there is ea need for standardising thesample dimensions. One possible suggestion could kxe thatthe sample size of 37.5 nm1)< 75 mm, which is the standardsize, may be adopted.

7.2.2 Resistivity of samples and dielectric constant ofpore fluids

The resistivity of the soil is aalso ea functionof the dielectric constant of the pore fluids. Fig.7.2.2.lshows the relation between the fluid content and the resisti­vity of oven dried marine clay collected from Parur site

406

fnmn a depth CM? 7.5 metres. The variation of resistivityhas been plotted against the fluid content for a dry densityof 1.2 gm/cc. For four pore fluids viz. carbon tetrachloride,acetone, methanol and water; The values indicate that theresistivity of ea soil decreases as the dielectric constantof the pore fluid increases. In the case of acetone, methanoland water the edectrical resistivity of the clay decreaseswith time fluid content an; expected. But for carbon tetra­chloride the resistance increased with higher fluid contents.

For purposes of comparison, resistivity studieswere conducted on kaolinite and bentonite. The resultsare presented in Figs.7.2.2.2 and 7.2.2.3.

It may be mentioned here that among the four differ­ent dielectric fluids used the thickness of electrical doublelayer is maximum for water and least for carbon tetrachloride.This may be possibly the reason for their relative positionsof the different curves.

7.3 RELIABILITY OF RESISTIVITY MEASUREMENTS

At present absolute resistivity P of a soil sampleis determined tnr finding (mm: the resistance P2 of specimen

RESISTIVITY (k-J1-Cm-)

1000

500

100

50

‘J0

1-0

050

407

SOIL: MARINE CLAY(OVEN DRIED)

10

Fig.

CARBON

ACE TONE

TETRA CHLORIDE

METHAN 0L

WATER

20

7.2-2-1

30 40 50 GO 70FLUID comI:m(°/. )

R ESISTI VITY VS FLUID CONTENT.

80

RESISTIVIT (k-.rx.c m.)

10

Fig.

20

408

7.2.2.2

30 40 SO

SOIL: KAOLINITE

D CARBONT ETRA CH LORIDE

A ACETONE

o METHANOL

. WATER

so 70 soFLUID CONTENT( °/o )

RESISTIVITY vs FLUID CONTENT­

RESBTHHTY (k.JLLnm)

20a)SOIL : BENTONITE

U CARBON TETRA CHLORIDE /31000­A ACETONE /0 METHANOL /500 ff

% é // :I I100~——___* 00000 W ,0 00] 1

::;;$’ :_:;:““$“” ’j I

_ _ _____, T __ _’{ __ __T __1 , IT'>\ 0 I$410 M__;\ 1 E, T5 \n g

\ av — +—— 0 ~

mo10 20 30 40 50 60 70FLUID CONTENT( °/o )

Fig. 7.2-2-3: RESISTIVITY vs FLUID CONTENT­

410

of length L and area of cross section A by the equation(Chauhan & Kate, l983).

(9 = R'A° (7.3.1)It has been already pointed cmnz that the ‘value

of Q is not a constant as it should have been if it werea property of the material viz. soil. But it has been shownalready that the value of 0 depends on the length of thesample and the area of cross section. This expression givesthe absolute resistivity cm? a conducting medium. Soil isa particulate medium and the resistance offered tn! soil,even if fully saturated, is considerably higher than thevalues normally permitted iknr conducting media. Thus thestudies on the electrical characteristics of the soil treat­ing it as a dielectric medium will be more meaningful. Theresistivity measurements on a dielectric medium has veryserious limitations. The fact that soil is more a dielectricmedium than ea conductor can kn; brought out by 51 series oftests on soil specimens.

In 21 conducting medium, the ‘value CHE resistanceis ea constant and it (uni be measured instantaneously. Butin the case of soil, the resistance is found to vary with time.

411

Fig.7.3.l shows a curve Bl which is a plot ofthe resistance of aa bentonite sample having 10 cm1>< lO cmcross section and 2 cm height. It had a water content of200%. When a direct current was passed through the soilspecimen the first reading indicated ea resistance (ME 120ohms. The value of E2 was found tx> increase with time andafter about l2O seconds it reached a peak value of 150 ohms.

Curve Bl ii; the plot cm? the readings. when the directionof the current was reversed by interchanging the terminalsfrom the d.c. supply, the value of resistance instantaneouslywas found to drop to just 40 ohms from l5O ohms. The value

was then found to increase with time aSshown by curve B2.The maximum value of resistance in both direction is foundto be almost same.

Curve M1 in Fig.7.3.l shows the plot of the resist­ance values with respect to time for a marine clay specimenof 4 cm x 41 cm x 7.5 cmu The maximum value of resistanceobserved was 660 ohms which took about 330 seconds. When

the current direction was reversed abruptly, the resistanceshown by the multimeter was as low as 60 ohms. The valuethen improved with time in about 620 seconds and reacheda maximum of 630 ohms.

.u:_» m> muz<»m_mm¢ ..m~.mm

A mucouumv u2_r

com co. om

co,oom

412

oom

-———j -—1r-—-—-j-- - ---—----~ ~--1 -­

ooq

.. . D

_ _ N _ M .

H.” .7 v A .. .: .v V V ...II I w v .. . u. _ .: .|I.||

_ . _ . . _ _ . V _.

_ % - . ., _ _.

. . H . .

W . . _ . _

_ . _ . , _

___

N _ com

;<4u E:m<2.. 2w 2.m»_zchZflwu mm w_m

.%- § Vynloom

( SL1“-4°)El3N‘v’.L€lS3tJ

413

These tun) experiments show tflmm: the resistivitymeasurements of soils treating’ it as E1 conducting mediumhas serious limitations. The change in resistance withrespect to time is due to the polarisation of water moleculescaused by the direct current. As the current flows throughthis medium, resistance ii; built up. When the cfirectionis reversed, tflua water molecules being 51 dipole take sometime to reorient themselves. Therefore the initial resist­ance on reversal of direction of flow of current is verylow. Ins the material gets polarised and reoriented theresistance increases. The time taken tn! the material forcoming back tun normal orientation knr itself is called therelaxation time. when current is passed in the oppositedirection the relaxation time is can: down. Thesee obser­vations clearly indicate that soil should preferably betreated as a dielectric medium than a conducting medium.

The effects of polarisation is brought out bytwo cycles of direct current flow in Fig.7.3.2. When directcurrent was applied, a plot between resistance and timewas obtained as curve lJ The initial reading was 180 ohmsand it reached the maximum value of 445 ohms in 60 seconds.

When the current was reversed, the resistance readings withrespect to time gave curve 2. Immediately after the reversal,the resistance was as low as 120 and it reached 440 ohms

.m:2:. m> mazfimmmm

.AmncouumV

oom om

N: .9“.

m2:

414

.5 me x am: ..mN_m4. NOF Emfizou mE3m_o:

A Smifimazi

.23 mzE<z H.:Om

VI‘

oo_comoomcomcom2:

( SuJu0)3:>Nv1SIS3u

415

in 180 seconds. When the current was again reversed plot 3was obtained and (M1 the fourth test, reversing the flowagain, curve 41 was obtained CH1 plotting time readings. Thisclearly shows that soil is 51 dielectrdx: mediuni which canbe repeatedly polarised in either direction. These testsindicate that the resistivity measurements and the correlationsbased (N1 them are run: unquestionable due txa the anomalyin the basic assumption that soil can be treated as a conduct­ing medium. Hence the possibility of making use of thedielectric medium for interpretation of geotechnical propert­ies of Cochin marine clays need to be explored.

Whenever there is flow of current in one direction

water molecules get oriented in the direction of the field.This is called dielectric polarisation. Since the materialhere is loosely bound, these polarised dipoles get reoriented

according tx> its relaxation time. This reorientation canbe attained faster if ea reverse field ii; applied. At thistime ii; results ill a large displacement current and hencea reduction in the resistivity. This explains the phenomenonobserved. The relaxation time is inversely proportionalto dipole moment.

416

7.4 RELAXATION TIME AND DIELECTRIC CONSTANT OF PORE FLUID

It has already been shown that resistivity byd.c. measurements are not very reliable as they are dependenton the polarisation of the pore fluid contained in the soil.Since polarisation is influenced by «dipole ‘moment of ‘thepore fluid, the latter can influence the resistivity values.

To examine this possibility, two- specimens wereprepared by mixing carbon tetrachloride and water with ovendried marine clay. Since carbon tetrachloride has zerodipole moment, the resistance should show a reading whichis run: time dependent. Si nce water has ea dipole momentequal to 1.84 debyes, it should show a relaxation time.

Fig.7.4.l shows the resistance of a sample ofoven dried marine clay mixed with 10% of carbon tetrachloride.The dimensions cm? the sample were 4 (fin x 4-<nn x 7.8 cm.When the direct current was passed for the first time, plot

F1 was obtained. It showed a steady value equal to 80 kilo­ohms immediately. When the supply was reversed the resistanceshowed a value of 61.5 kilo—ohms. When the supply wasreversed again, the resistance was found to be 51 kilo—ohmsamd the resistance was found tub be only 41 kilo—ohms whenthe direction was changed again.

417

88

009

.m2_._.

oom

9 muzffmmz ._4~.mE

33.03.: M2:

OO_ om OF m

.moEoEu<EE zomzfi No.34; m~._On_A uozu 5:3 ><._u mzE<2 ..H:n:z<m

(°"'U"")[) EJDNVLSISEH

418

As expected there was rm) relaxation time 1H1 anyof the four tests. Fig.7.4.2 shows the resistance vs. timefor three samples with the same dimensions. The first samplewas prepared by adding carbon tetrachloride and, as notedearlier, the reading showed an unchanged resistance ‘withrespect to time as shown by curve 1. When current was passedthrough EH1 oven dried marine clay vdth 51 water content of20%, the initial reading was 360 kilo-ohms. The value steadilyincreased and reached the maximum value in about 180 seconds.

Curve 3 shows the resistance vs. time plot for a sampleof oven dried marine clay with a water content of 40%.The initial reading was 55 kilo—ohms which increased tothe ‘maximum value cyf 2OO kilo-ohm zhi 600 seconds. Thege

curves show that the polarisation is caused by the dipolemoment (M3 the pore fluid. Further, the figure also showsthat the relaxation time is higher for a sample with higherwater content.

Fig.7.4.3 shows the plot between resistance andtime in seconds for ea sample with water content CM? 20%.When the current was passed in one direction, the variation

of resistance with time is given by plot Fl. When the currentwas reversed the plot between resistance and time curve

R1 was obtained which showed a higher maximum value.

.mz_._. 3 uuz<»m_m..:_ aqs mm

A mucouomv m2:

419

89 com o9 om o. m _o

_ _

11\¥wrT .V

M TVQ\ 4 »g oo_

;\ W ”

M i

fl V ; - Loom

H W M H_ . 3W . U . w Ba T T _ T T . ..v *1 r, rl. % r :1 1| 1 I B_ _ _ _ D

_ _ _ J % \\4 ,1 (

¢ ; M H % _ _ . 5 !%--|\oo.f.M 3. o.fiEH.:z8 H.E:5_o2Em:§> @ (

@ 00m

202 “EB 28 $25.02 E53;

W mo;::zu<mhwp zomm<u Amv

_ cow

_ W o_:4m m o .02

M W m a m>z:u

_ _

% _ _ Aum_:ucm>ov><quH::m<: m4a2<m

420

m2: .2, .nSz<»m_mum 6.: .9“.

Amncoumi mz:

OOF cm

H z.u;z8 m:E:m_o:W52; 93.: mmoa92; $>oZ<3 mzE<: L323

('suJu0)33Nv1SlS3a

421

When the current was reversed again, which was

the first direction of flow of current, curve F2 is obtained.When the current was again reversed, plot R2 is obtained.It may be noted that the time to reach the maximum valueof resistance either iJ1 the» forward, direction or iml thereverse direction is more or less unique.

Eventhough polarisation has been pointed out asa drawback of the resistivity measurements using directcurrent, this property perhaps could kn; made use cm? fordetermining the water content of soil samples. As resisti­vity values are influenced by both dry density ‘and watercontent, it is difficult to establish ea correlation withany one of the parameters independently with the prevailingpractice. But the relaxation time is dependent only onwater content and this could perhaps be developed and per­fected as a quick method for determination of water contentespecially in field control of compaction.

7.5 RESISTIVITY AS AN INDICATOR OF LIME-SOIL REACTION

Resistivity measurements of lime treated specimensshow spectacular increase in resistivity values for a shortspell after mixing with lime. Fig.7.5.l shows the resisti­vity of three lime treated specimens of Cochin marine clay

422

from Parur from a depth of 8 nmmres, treated with 6% lime.The samples prepared for unconfined compression strengthhad a diameter of 38 mm and height of 75 mm. The resistanceof the specimens was measured with the help of a multimeteras indicated in section 7.2 The values of resistivity measuredfor 20 days from the date of mixing are plotted in Fig.7.5.l.Resistivity of all the three specimens sharply increasesinitially and comes to a more or less regular value by thelOth day. , +Lime stabilisation is ea process by which the Na+ . ++ . . .and K ions are replaced by Ca ions. The affinity ofa clay for reaction with lime is called the lime reactivityof the clay. The lime reactivity is a measure of the poten­tial of the soil to react with lime and the gain in strengthis proportional to lime reactivity.

Lime reactivity is defined by Thompson (1966)as the difference between the maximum compressive strengthof the lime treated soil with the strength of the untreatedsoil. A better definition for the term would have beenthe ratio of the maximum unconfined compressive strengthor laboratory vane shear strength of the treated sampleto that of the untreated sample.

423

.DO_mwn_ ozaau m> >:>:m_n.mE

éiou Eoxmi ozE:u

Es

an

ON 3 N_. mm .w 0 OON

_

7 _% A; : l

i - uinufllii 00 m

lit: 4a!uu E: Y il - EIL

/4% rill: I ul-J 4 slim I a-::Q~mwooo._

E m:n:2<m DC m:n_:<m 4F m._n:2<m O

Q23 .5. o + ><..umZ_m<2 55: ..mE2<m

L—._--fir.

OOO‘Ncoon

coca“

(wa—wu0) ALHHLSBBH

424

At present the lime reactivity of a soil can bedetermined only by the destructive test of a series of treatedsamples, varying parameters like lime percent and curingperiod. Since we have tr) allow sufficient time for curingthe specimens, the series of tests will take considerabletime. Instead, resistivity measurements can be adoptedfor assessing the potential for lime to react with soil.

It can be seen from the figure that the resistivityof all the samples was around 900 ohm-cm initially. It shootsupto even 5000 ohm-cm and drops to steady values by the10th day. The ‘variation lfl resistivity for time last lOdays 513 marginal. The sudden variation imm resistivity isdue to the complex chemical reactions between lime and soiland hence this can be utilised to measure the lime reactivityof soils. It has the added advantage that it ijsaa simplenon-destructive test which effects considerable saving inthe number of samples to be prepared.

Fig.7.5.2 shows the resistivity’ - curing periodrelationship for two samples of Inarine clay treated ‘with3% lime. The samples were 75 cm long and 3.8 cm in diameter.

As imm the ‘previous case time value (if resistivity’ sharplyincreases on the first day and comes back to steady valuesafter nine days.

RESlST|VlTY(0hrn-—c m)

425

50,000

SAMBLE MOIST MARINE CLAY

+ 33/‘. LIME

0 SAMPLE I

“W00 A SAMPLE 11

1,000

300 0 4 8 12 16 20CURING PERIOD I days)

Fig. 7-5-2 2 RESISTIVITY vs CURING PERIOD’

426

7.6 RELATION BETWEEN RESISTIVITY AND SHEAR STRENGTH

Resistivity measurements, if perfected by detailedinvestigations, can be of great help .in the determinationof geotechnical properties. The greatest advantage of theresistivity method it; that it :h3 a non—destructive testingmethod, which can make considerable saving :h1 the~ numberof samples used for strength studies. To explore this possi­bility, attempts were made to study the development of shearstrength of lime treated specimens.

Moist soil from Parur was treated with 6% limeand the samples of 75 mm length and 38 mm diameter wereprepared and kept for curing; Three samples were takenat regular intervals and their resistivity was measuredand shear strength determined. Fig.7.6.l shows time plotbetween the resistivity (M5 the samples and shear strength.For the first few days the samples showed very high resisti­vity and a regular correlation could be obtained after afew days of curing.

It can be seen from the graph that the resistivitydecreases or conductivity increases with strength. Thisis quite understandable as the conductivity can increase

+:ozmE5 mfixm 9, :_>:m_mmE I: .9...

C613 V :SzmEB admin

427

8.0 owe owe 8.0 o3 omo omo o..o oooo

O

/.O

1 com

1/O/1

A]

[V 0093/SH.Mcom:AmU;8 wommau a m2_4 q_msm 1:; 8n:3o:m:.._ 0 (

amm~_3m_oz: o oom:

><:_u mzpzz S52 M sow

. s f oom_

0

v OOON

428

as more and more bonds are developed within the soil mass.Since the study was not persued further, firm conclusionscannot be drawn at this stage. But there is considerablescope for further work in this direction.

7.7 RESISTIVITY BY A.C. MEASUREMENTS

It has already been pointed out that the measure­ment CH3 resistivity vn¢fi1 a multimeter using direct currenthas certain inherent drawbacks due to polarisation. Thereading itself takes some time to stabilise and the resisti­vity in the opposite direction is very low initially andtakes considerable time to reach a steady reading. Thisvalue will normally’ be» at considerable ‘variance~ with theoriginal resistivity measured. Thus the resistivity measure­ments can be considerably influenced by the passage of directcurrent prior to the test as the water particles with dipolemoment might have oriented themselves in such a way to in­crease the value of resistivity or decrease it.

The variation in the resistivity value due tod.c. measurements can be avoided by measuring the resistivityagainst alternating current. Due to the frequency of osci­llation, there will not be any polarisation and consequentvariation in resistivity.

429

To study the advantages of resistivity measurementsusing a.c. and to compare the results of both measurementson the same sample, a circuit was designed where both a.c.and d.c. <xnflri be passed through time soil and resistivitycould be measured. Fig.7.7.l shows the circuit adopted.

Soil sam ple was taken in a container with a squarebase of 6 cm x 6 cm and a height of 6 cm. Both ends werecovered with copper plates. To ensure the contact betweenthe top copper plate and soil, the plate was loaded by apply­ing a contact pressure CHE 2O gm/cm2. The resistance ofthe sample xuus found cum: by nmasurimg the voltage acrossthe end plates and the current passing through the sample.

By Ohm's law

R = 31 (7.7.1)I

where

R - resistance of specimen (ohms)V — voltage (volts)

I - current (amperes)

Resistivity =

430

m4az<m

.:om

.:<mo<:.

mOh<H:220uJ2

::uEu Ex .3

mumaom

9

431

The results of aa typical test it; given iJ1 Fig.7.7.2. Resistance against a.c. supply was found to be aconstant equal tx> ll.32 kJL cm for 51 voltage CH3 8 V. Thesupply was then changed to d.c. using a commutator and theresistance ‘was lneasured taking readings every IU5 seconds,for five minutes. The resistance values were found to besteady tux this time. The plot E? in Fig.7.7.2 shows the1

Variation of resistivity with respect to time. The direction

of the d.c. was then reversed and plot R1 represents theresistivity values for a «duration of five minutes. Theresistivity was found to increase marginally. When thedirection was reversed again,the value was very low initially.But it steadily increased to about three times the original

value. Curve lag shows these variations. Curve R2 3H3 theresistivity time plot obtained when the direction was reversed.

Curves F3 and R3 are the plots of resistivity values obtainedwhile changing the direction of the direct current.

These curves show that there could be wide variations

in the value of resistivity measured by tdirect currentwhereas the a.c. measurement gave very steady values. Sincepolarisation influences tflma values significantly, resisti­vity measurements using alternating current will bepreferable.

432

ME: 3 C_>:m_mHE..mee .mm

Tmflssev . mi;

m q m m _ lo?

aw T 4 \

:1 L L7 g

5 w fl Lu LT

. ,

L A

Elem

M _

1, 1 - mm.m_ om

_ M W W . mhzmzmiamfiz mm .3

m I W q.a

u. ._

. M »zm_:H.E:m<m: .u.< *

_ .\. Sgzflzou “E350:

W _.- Amman 25/S

_ _ ><d m_zE<2 ;_om

Oq

( w3"u'~>1 )A’_I.I/xuslszlu

Chapter VIII

CONCLUSIONS

Based cw: the detailed investigations carried outin this thesis, the following major conclusions have beenarrived at.

Marine clays, well known for its high compressi­bility and poor shear strength, cover extensive areas inGreater Cochin enui these clays are cm? the same geologicalorigin as indicated by the similar results obtained fromsam ples collected from locations separated by as much apfifty kilometres.

Extreme care has to be taken in the preparationof marine clay specimens for different physical and engineer~ing properties. Since Cochin marine clays are susceptiblefor significant changes in test results depending upon theirinitial condition, it must be stated that all the propertiesneed to be investigated under natural moist conditions.

Drying before carrying out any test either inthe oven cn: under atmospheric conditions will significantlyaffect tflue properties. pFor example liquid limit and cflay

433

434

content reduce significantly by drying. While plasticlimit and free swell index decrease upon drying, shrinkagelimit marginally increases. These changes are attributedto aggregation of particles on drying.

Since the initial conditions of the sample signi­ficantly influence the test results, initial conditionsneed to be specified for carrying out Atterberg limits,shrinkage limit, free swell index and grain size analysistests. Suitable amendments should kxe incorporated inthe I.S.Codes so that marine clays receive special attentionduring preparation of samples.

Since all the clay fraction in an marine soilare likely txa exist imx the form cnf flocs, deflocculationis more important compared tn: other clayey soils. Testswith eight different deflocculating agents showed thatthe dispersing agent (Sodium hexametaphosphate 4- Sodium

carbonate) recommended kn? I.S. Code is tflue most suitableone for Cochin marine clays also.

While determining’ the value- of coefficient of

consolidation CV, it was found that the rectangular hyper­bola method is time most versatile. There were instances

435

where both Taylor's and Casagrande's methods coduld notbe used whereas rectangular hyperbola method could beused without difficulty.

Careful examination of X-ray diffraction patternsindicated that the primary clay mineral in Cochin marineclays is montmorillonite. Some secondary peaks showthe presence of traces of kaolinite also.

Air and over drying prior to testing broughtabout notable changes in the physical properties of Cochinmarine clays. Upon oven drying, the liquid limit reducedby 42-58%, plastic limit by 12-30% and free swell indexby 65-77%. The clay content reduced by 9-33% on airdrying and 45-55% by oven drying.

The following useful correlations were obtainedbetween index properties for 'moist' samples of Cochinmarine clay.

PI = O.62(LL - 2.0)r = 0.92

PL = O.473(If + 65.9)r = 0.80

436

LL = 3.40(C - 10)r = 0.83­

SL = 31.1 - 0.276 Cr = 0.83

Free Swell = O.l2(C - 1.2)r = 0.89

0.043(LL — 1.7)r = 0.89

Free Swell

where

PI = Plasticity IndexPL = Plastic Limit

LL = Liquid Limit

SL = Shrinkage Limit

Similar correlations have been obtained forair dried, and oven dried soils and for all three typesof samples put together.

Investigations (N1 washed samples indicatedthat reductions in salt content increases the liquidlimit and plastic limit marginally. Clay content andfree swell index also increase to a limited extent.

437

Soaking the sample for about two years showedthat the .Atterberg limits increase vHIk1 soaking. Butthe liquid limit of oven dried marine clay could increaseonly tn: 62% of its original liquid limit of moist clay.A similar increase was noted in case of plastic limitalso. But the increase in free swell index was moreappreciable.

A very useful correlation could be establishedbetween shear strength and natural water content of Cochinmarine clays which could be extended to other soils also.Vane shear strength of Cochin marine clays at liquidlimit water content was 14 to 19 gm/cm2. A unique relat­ionship as shown below could be obtained between shearstrength and water content ratio (ratio of naturalmoisture content and liquid limit) of Cochin marine clays.

WCR = 0.231-0.414 log‘?

r = 0.987

This relation for clays of same geologicalorigin will be useful as the shear strength can be esti­mated from natural water content and liquid limit withoutgoing zhi for time consuming shear tests. Similar semi­logarithmic relations could kxa obtained for other soils

438

also. The slope of the lines can give more informationabout the behaviour of the soils as kaolinite soils havea flatter slope than montmorillonite soils.

Dielectric constant of the pore fluid influencesthe liquid limit and free swell index values of the soil.For montmorillonitic clays the liquid limit and freeswell index increase with the increase in dielectricconstant. Kaolinite clays show emu oppositer behaviour.Oven dried marine clays show a behaviour similar to mont­morillonitic clay eventhough it is very much subduedas the soil has been oven dried.

The long series of consolidation tests helpedto bring out the compressibility characteristics of Cochinmarine» clays. As; test results, especially ‘those ‘takenfrom greater depths, indicated that the preconsolidationpressure obtained was consistent with depth, the Cochinmarine clays can txe classified as normally consolidatedclays. IN: has been found that Vfluxi clays of differentplasticity are subjected to consolidation tests, thee - log p curves arrange themselves in the order of theirliquid limits.

439

It has been shown that initial drying of soilimproves the compressibility characteristics of marine

clays considerably. The value <1f compressbmi index CCor the value de/d(log p) which is defined as the slopeof the e — log p curve for any particular pressure incre­ment, it; brought down kn! initial drying. The value ofde/d(log EH got reduced tn) around 50-55% fin: air driedsoils and 35-40% for oven dried soils.

Correlations have been obtained betweende/d(log p) and liquid limit values of undisturbed andremoulded specimens for two different pressure incrementseventhough the correlation coefficients are not of ahigh order. (Hue values of de/d(log p) are about 20-25%higher than those suggested by 'Terzaghi (1948) andSkempton (1944) for undisturbed and remoulded claysrespectively. This is attributed to the compressionof the flocs.

The liquidity index for these clays Varies overa range of O.46»tx> 0.87 indicating that these clays canbe taken as medium to very sensitive as per Bjerrum'sclassification (Bjerrum, 1954).

440

Many workers have suggested that CC/l+eO, calledthe compression ratio, can represent the compressibility

characteristics (Hf clays better, compared ix) CC alone.The present results also indicate that compression ratiovaries linearly with log p. The value of de/d(log p)decreases as duration increases.

The CC values obtained from consolidation testsfor Cochin marine clays, around 1.5, is quite high andtotal settlements computed based on this value are consi­derably higher than tflue actual settlements realised inthe field. It has been shown that this is due to anoverestimation of Cc by I.S. method. A new term calledsegmental compression index, Cé defined ems the slopeof the segment of the e - log p portion between theabscissa g%) and po +-.D\p, gives more realistic resultsfrom the equation for settlement. Another advantagewith segmental compression index method is that a settle­ment of over—consolidated clays can be determined inthe same way whereas the method suggested by I.S. Codeis cumbersome and time consuming.

The resistance to compressibility was foundto increase with duration of the load increment. Reserve

strength was found to develop with secondary consolidation.

441

For' the same ppressure, especially en: higher" pressures,e - log p curves with longer duration show higher equili­brium void ratio, indicating development of resistanceto compressibility under long duration of constant stress.At lower pressures the effect of duration is marginal.

When duration increases, the ratio of secondarycompression to total compression increases as expected.

The rebound curves obtained during unloadingto seating load, folltwz a regular pattern wherein thetest with longest duration shows the minimum reboundand the (NH? with shortest duration occupies the highestposition. This might be the result of stronger bondsdeveloped during consolidation for longer duration.

One of the major findings from the studies onconsolidation is the development of a new method for

determination <3f pk” called the log - log nnethod.Casagrande's method for pc involves personal judgementof point of maximum curvature. The other two methods—­Burmister's and Schmertman's--are cumbersome and time

consuming. Compared to these three, the log - log method,

where value of pc is obtained from the intersection of

442

two straight lines drawn through the initial and finalsets of points plotted in log — log scale, is far simplerand more accurate. The success of the proposed methodlies imm the development of ea technique tn: obtain the

actual value of pc for purpose of comparison with thevalue obtained from log - log method.

The significant improvement iJ1 compressibilitycharacteristics due to air drying can be taken advantageof in the construction of embankments and formation ofcuttings and subbases. The shear strength also improvesby air drying and this provides a cheap method to improvethe geotechnical properties of marine clays. For Cochinmarine clays the optimum moisture content is around 30%and maximum dry density obtained is 1.33 gm/cc.

Studies on the compressibility behaviour ofoven dried marine clays using pore fluids of varyingdielectric constant indicated certain interesting featuresin case of oven dried samples. Attractive and repulsiveforces exist an: microlevel and time former controls thecompressibility of kaolinite while the latter is responsi­ble for the resistance to compressibility offered by

443

montmorillonite. Consolidation tests with differentpore fluids indicate that oven dried marine clay samplebehaves like a montmorillonitic clay during consolidationtill 0.5 kg/cm2 and like a kaolinitic clay for pressuresabove 0.5 kg/cm2.

After having studied the physical and consoli­dation characteristics of Cochin marine clays, successfulattempts were made to improve their engineering properties.Out of eighteen different additives tried, lime was foundto be the most potential stabilising agent. Shear strengthtests CH1 samples treated with different percentages <3flime showed that 6% was the optimum lime content. Withinone weak of curing the shear strength improved ten foldand after a month it improved by about eighteen times.

Physical properties of marine clays were foundto improve considerably kn! lime treatment. The liquidlimit was found to behave a little erratically but plasticlimit was found to increase from 56.5% to 83% after one

week. The reduction in plasticity index makes the samplesless compressible but more friable. Test results onphysical properties agree with the findings (ME Sherwood(1967) that only small percentages of lime are requiredto bring these changes in physical properties.

444

The shrinkage limits tend to increase withlime content which could kxe attributed to flocculation.

The free swell index increases from 6.4 to8.3 cc/gm on mixing with lime. But on curing, the valueslowly decreases.

Through a series of consolidation tests, ithas been verified whether the phenomenal gain in strengthdue to lime treatment is equally valid for the compressi­bility behaviour of Cochin marine clays. The compressioncurves for treated soils are~ above» that for ‘untreatedsoil. They arrange themselves with the specimen withmaximum period of curing, occupying the highest position.

Due tx> the development cnf bond strength which

will. be seen as 51 preconsolidation pressure E%: in thee - log p curves, the compression at lower pressureswill be £5 to 1/3 (N3 the actual compression without the

additives. But once the applied pressure crosses pczthe compression of treated soil will be about 80% ofvalues for ‘untreated soils en: higher" pressures. Thusconsolidation can be considerably reduced by keeping

the maximum applied pressure lower than the pc valuedeveloped.

445

The consolidation curves also show that thetreated soil present a brittle behaviour while the un­treated soil fail graduallyy. For specimens cured forlonger periods, point of Inaximum curvature znu thee - log E3 curve gets sfldfted txb the right indicatingthe development of bond strength with period of curing.

It has been shown by both laboratory vane sheartests and consolidation tests that the rate of developmentof bond strength in treated soil is inversely proportionalto the lime content. Eventhough higher lime contentswill show higher maximum strength, the lower lime contents

will show a faster rate of development of strength.

The value of de/d(log p) decreases with increas­ing curing period and becomes steady after about 80 daysof curing. Etm‘ a specified curing period and stresslevel, there is a unique lime content which gives thelowest value for de/d(log p). When the curing periodis short, lower lime contents will show lower de/d(log p)values as they have a higher rate for development ofshear strength. But. for‘ longer" durations de/d(log p)is inversely proportional to lime content.

446

Coefficient cxf consolidation, CV, increaseswith curing period iknfi all lime contents. But for’ aspecific curing period and stress range, there is anoptimum lime content which will give the maximum value

for CV. The reduction in (R, with higher ljmma contentmay be explained by clogging of voids by the reactionproducts formed. The secondary compression coefficient,C,» decreases with increase in lime content and curingperiod.

For a given curing period, there is an optimumlime content which will give maximum bond strength. Boththe optimum value of lime content and correspondingmaximum bond strength increases with curing period.

The lime reactivity of black cotton soil ishigher than that of Cochin marine clays.

Unlike untreated marine clays, the bond strengthdoes not increase with longer durations allowed for eachload increment. Bond strength does rufl: develop ‘underconstant strain. But under sustained pressure thereis an increase in preconsolidation pressure or bondstrength proportional to the sustained period.

447

Eventhough electrical resistivity surveys arevery popular as a geophysical method, resistivity measure­ments have not been fully exploited by geotechnicalengineers in spite of the fact that it if; a quick andinexpensive method. Since in geoprospecting the measure­ments give cnflqz the weighted average resistivity of thedifferent layers, soil profiling can be done only throughcomparison with absolute resistivity values of the indi­vidual layers. Hence laboratory measurement of absoluteresistivity is important.

Laboratory measurements of resistivity is donewith the help of a multimeter. Satisfactory correlationshave been obtained for water content and dry «density.As expected, the resistivity reduces with both watercontent and char density. The reduction its faster withmoisture content.

The limited literature (N1 resistivity measure­ments in the laboratory shows that there are no standardsprescribed for the soil specimens used for measurements.But this is important as the sample dimensions influencethe resistivity values considerably. From 23 series oftests, it has been shown that resistivity reduces withlength of the sample, while it increases with area of

448

cross section cyf sample. Thus the ruaxi for standardi­sation of the test specimen has been brought out, sothat the data generated can be compared with other data.It is recommended that ea standard size cxf 37.5 Imn indiameter and 75 mm in length may be adopted.

It has been shown that the resistivity of asoil sample is also a function of its pore fluid. Usingfour pore fluids viz. carbon tetrachloride, acetone,methanol and water which possess a wide range of valuesof dielectric constants, it has been brought out thatthe resistivity reduces with fluid content in case <3facetone, methanol and water. But with carbon tetra­chloride the resistivity was found to increase.

Literature shows that time resistivity measure­ments in the laboratory are done using the equation

But resistivity obtained from this equationis not a unique value. This may be due to the fact thatsoil is not a conducting material but a particulate medium.

449

Studies (M1 the characteristics of time soil treating itas a dielectric medium will be more meaningful and theresistivity measurements using the above equation haveserious limitations.

Through a series of time vs. resistance plots,it has been shown that resistivity measurements areconsiderably influenced by polarisation of water moleculescaused tax the direct current. The ‘resistance tub flowof current in either direction its also different fromeach other. The time taken tn! the molecules to orientthemselves is called the relaxation time and :U: isinversely proportional tx> the dipole moment of the porefluid.

For pore fluids with zero dipole> moment, therelaxation time is zero. Hence for samples with carbontetrachloride as pore fluid, the resistivity valuesinstantaneously show the maximum value of resistancewithout any time lag. Samples with «other gxnxe fluidstake some time to show the maximum value of resistance.Eventhough polarisation or relaxation interferes withthe resistivity measurements with direct current, thefact that ‘relaxation time ix; proportional tn) the fluid

450

content can possibly txa made ‘use cxf for ‘water’ contentmeasurements.

When lime is mixed with moist marine clay;the chemical reactivity generated indicates the possibleincrease in strength that can be gained by lime stabili­sation. The intensity cflf the reaction between lime andsoil can be measured by the resistivity which gives somepeak values during the initial period.

Similarly in case of lime stabilised soils,bonds are developed during curing and this reduces theresistivity. Instead cxf determining tfima shear strengthby destructive testing of a large number of specimens,it might kn; possible tn) monitor time gain lfl strengthby measuring the resistivity.

Since polarisation, which interferes withresistivity measurements, is caused by direct current,it can be avoided by a.c. measurements as shown by thetest results. The directionality of measurements isalso avoided. Hence a.c. measurements will be morereliable and faster.

REFERENCES

Allam, M.M. and Sridharan, A. 1979. The influence of

aging on the shear strength behaviour of two fine grainedsoils. Canadian Geotechnical Journal, Vol.16, No.2.

Anon 1975. Earth Manual. U.S.Bureau of Reclamation,

Washington, D.C.

Arulanandan, K. et al. 1973. Significance of Magnitude ofDielectric Dispersion in Soil Technology, Highway ResearchBoard Record 426.

Atterberg, A. 1911. Uber die Physikalische Bodenuntersinchungund inber die plastizitut der Tone. Int. Mitt. Bodenk 1, 10.

Barker, R.D. Resistivity Sounding in engineering investi­gations with offset wenner Technique. Geotechnique, Vol.38,No.3, pp.355-366.

Bell, F.G. 1988. Stabilisation and treatment of clay soilwith lime. Ground Engineering, Jan. pp.10—15.

Berry, P.L. and Poskitt, T.J. 1972. The consolidation ofPeat. Geotechnique, 22: pp.27-52.

451

10.

11.

12.

13.

14.

452

Bishop, A.w. and Henkel, D.J. 1962. The measurement of

soil properties in the Triaxial Test. Edward ArnoldLtd., London.

Bjerrum, Lauritus. 1954. Geotechnical Properties ofNorwegian Marine Clays. Geotechnique, 4: pp.49-69.

Bjerrum, Lauritus. 1967. Engineering Geology of Norwegian

Normally consolidated marine clays as related to settlementsof Buildings. 7th Rankine Lecture, Geotechnique, No.2.

Bjerrum, L. and Simons, N.E. 1960. Comparison of shear

strength characteristics of Normally consolidated clay.Proc. of ASCE Research Conference on shear strength ofcohesive soils, Colarado.

Buisman, A.S. 1936. Results of long duration settlementtests. Proc. Ist Int. Conference on SM & F.F. Cambridge,Vol.I. pp.1o3-1o7.

Burmister, D.M. 1951. The Application of Controlled TestMethod in Consolidation Testing. Symposium on Consolidation

Testing of soils, ASTM Special Technical Publication, 126.

Butterfield, R. 1979. A Natural Compression Law for Soils.Geotechnique, Vol.29, No.4, pp.469-480.

15.

16.

17.

18.

19.

20.

21.

453

Butterfield, R. and Johnson, I.w. 3980. The influence ofelectro-osmosis on metallic piles in clay. Geotechnique,30, No.1, 17-38.

Casagrande, A. 1936. The determination of the Preconsoli­dation Pressure and its Practical significance. Proceedingsof 1st ICSMFE, Cambridge, Mass. Vol.III.

Casagrande, A. 1948. Classification and identification ofsoils. Transaction ASCE, Vo1.113, 1948, pp.901-930.

Casagrande, A 1958. Notes on the design of the liquidlimit device. Geotechnique, Vol.8, pp.84-91.

Clayton, C.R.I. and Jukes, A.w. 1978. A one point conePenetrometer liquid limit test. Geotechnique, 28, No.4,pp.469-472.

Crawford, C.B. 1965. The resistance to soil structure toconsolidation. Canadian Geotechnical Journal,Vol.II,pp 0 0

Darienzo, M, and Vey, E. 1955. Consistency Limits of Clayby Vane shear method. Proceedings of H.R.B. Annual Meeting,Vol.34, pp.559-566.

22.

230

24.

25.

26.

27.

28.

454

Davidson, D.T. and Handy, R.L. 1960. Lime and Lime

Pozzolana in Highway Engineering Handbook. Ed. By Woods,

K.B. McGraw Hill, New York, pp.23-98.

Dusseault, M.B. and Scafe, E. 1979. Mineralogical andEngineering Index Properties of the Basal McMurray

Formation of Clay shales. Canadian Geotechnical Journal,Vol.16, No.2, pp.285—294.

Fernando, M.J., Burau, R.G. and Arulanandan, K 1977.

A new approach to determination of Cation Exchange Capacity.

J1. of Soil Science Society of America 41: 4.

Frost, R.J. 1967. Importance of Correct pretesting,Preparation of some tropical soils. South East AsianRegional Conf. on Soil Engineering. Bangkok, pp.43-53.

M.J. and Doshi, S.N. 1984. Application OfFernando,

Dielectric Constant Measurements in Geotechnical Engineering.Indian Geotechnical Journal Vol.14, No.4.

Graham, J., Grooks, J.H.A., and Bell, A.L. 1983. Timeeffects on the stress-strain behaviour of natural softclay. Geotechnique, 33 : 327-340.

Hamilton, T.J. and Crawford, C.B. 1959. Improved deter­mination of Preconsolidation Pressure of a Sensitive clay.ASTM Special Technical Publication No.254, pp.2S4-270.

29.

30.

31.

32.

33.

34.

35.

36.

455

Harrison, J.A. 1988. Using the B.S.Cone Penetrometer forthe determination of Plastic limit of soils. Geotechnique,Vol.38, No.3, 433-438.

Head, K.H. 1980. Manual of soil Laboratory Testing,Vol.1, Pentech Press, London.

Higginbotham, I.E. 1976. The use of geophysical methodsin engineering geology. Ground Engineering, 9, No.2,

Hough, B.K. 1957. Basic Soil Engineering, New York,Ronald.

Ingles, O.G. and Metcalf, J.B. 1972. Soil Stabilisation,Butterworths, Sydney.

Jackson, M.L. 1964. Soil Clay Mineralogical Analysis.Symposium on Clay MineralogY. Visginia Polytechnic

Institute. C.I.Rich and G.W.Kumze, Eds. University ofNorth Carouno Press. NC. pp.245—294.

Jamiolkowski, et al. 1985. New Developments in Field andLaboratory testing of soils. Proc. of 11th InternationalConference on S.M. & F.E. San Franscisco. Vol.1, pp.57-153.

Jarret, P.M. 1967. Time dependent consolidation of asensitive clay. ASTM Bulletin T(7): pp.300—304.

37.

38.

39.

40.

41.

42.

456

1961.R. Suggested improvements in the liquidKarleson,

limit test with reference to flow properties of remouldedclays. Proc. 5th Int. Conference Soil Mech. Paris Ipp.171-184.

Kate, J.M. and Khichchu Mal. 1983. Comparative study of

resistivity interpretation Techniques. Indian GeotechnicalConference, Madras.

Kerisel, J. 1985. Histoire de lingenierie geomecaniquejirsqua 1700 Proceedings. 11th International Conferenceon Soil Mechanics and Foundation Engineering - San FranciscoJubilee Vol. .pp.3-90.

King, W. 1884. Consideration on the smooth water anchorages

on mud banks of Narrakkal and Alleppey on the Travancore

Coast. Records of the Geological Survey of India. Vol.XVII,Part 1, 1884, pp.14-27.

Kinsky, J. Frydman, S and Zaslavsky, D. 1971. The effectof different dielectric liquids on the engineering propertiesof clay, Proceedings of Fourth Asian Regional Conference onSoil Mechanics and Foundation Engineering, Bangkok, pp.367-372

Koppula, S.D. 1981. Statistical Estimation of compressionindex, ASTM Geotechnical Testing Journal., 4, No.2,pp.68—73.

43.

44.

45.

46.

47.

48.

49.

50.

Leonards,

457

Lambe, T.w. 1951. Soil Testing for Engineers. JohnWiley & Sons, Inc. New York.

Lambe. T.W. 1958. The structure of compacyed clay.Journal of SM & FE, Dn, ASCE 84 : 2 : pp.1-34.

Larsoon, R. 1981. Drained behaviour of Swedish Clays,Swedish Geotechnical Institute, Sweden, Report 12.

G.A. 1962. Foundation Engineering. McGraw HillBook Company London.

Leonards, G.A. 1977. Panel Discussion. Proceedings ofInt. Conference on Soil Mech. & Foundation Engineering,

Tokyo, Vol.3, pp.384-386.

Leonards, G.A. and Altschaeffl, A.G. 1964. Compressibilityof clay, JSMFE, ASCE, No.SM 5.

Leonards, G.A. and Ramiah, B.K. 1959. Time effects in the

consolidation of clay. Symposium on Time Rates of Loadingin Testing Soils. ASTM, Special Technical Publication 254.

Leroueil, S., Tavenas, P. and Lebiham, J.P. 1983. Propertiescaracteriques des argiles de lest du Canada. CanadianGeotechnical J1.2O : 681-705.

51.

52.

53.

S4.

55.

S6.

57.

458

Leroueil, Serge. 1988. Tenth Canadian GeotechnicalColloquium: Recent Developments in Consolidation of

natural clays. Canadian Geotechnical, Jl.25, pp.8S-107.

Lo, K.Y. and Morin, J.P. 1972. Strength anisotropy andtime effects of two sensitive soils. Canadian GeotechnicalJ1.9, 261-277.

Lowe, J.O., Jonas, E. and Obrician, V. 1969. Controlledgradient consolidation test. J1. of Soil Mech. and Found.Engg., Proc. of ASCE, Jan. 1969, pp.77-97.

Mateous, M. 1964. Soil-lime records at Iowa StateUniversity. Proc. ASCE Jl. Soil Mechanics and FoundationDivision, 90, SM 2, 27-153.

Malhotra, B.R. 1981. Electrical Resistivity survey of anunstable slope at Simla. Indian Geotechnical Conference,Hyderabad.

Mccarter, w.J. 1981. Resistivity testing of piled found­ation. Ph.D. Thesis, University of Edinburgh.

W.J. 1984.Mccarter, The electrical resistivity charact­eristics of compacted clay. Geotechnique, 36, No.2, June,pp.263-267.

58.

59.

60.

61.

62.

63.

64.

65.

459

Means, R.E. and Parcher, J.N. 1963. Physical Propertiesof Soils. Charles E Merrill Book Co., Columbus, Ohio.

Mesri, G. and Godlewski, P.M. 1977. Time and Stress

Compressibility Interrelationship. ASCE J1. of Geo­technical Engineering Division, 103 (GT8) pp.417-430.

Mesri, Gholamresa and Olson, Roy, E. 1971. Consolidationcharacteristics of Montmorillonite. Geotechnique, Vol.21,No.4, pp.341-352.

R.J. 1970. On the yielding and mechanicalMitchell,

strength of Leda Clay. Canadian Geotechnical Jl.7, pp.297-312.

Mohan, D. and Goel, R.K. 1959. Correspondance. The one

point method of determining the volume of liquid limit ofa soil. Geotechnique, 9, No.3, 143-144.

Murthy, A.V.S.R. and Chandra, Deep. 1981. Use of electricalresistivity method for foundation analysis. IndianGeotechnical Conference, Hyderabad, pp.45-49.

Nagaraj, T.S. and Jayadeva, M.S. 1981. Re—examination ofone point Methods of liquid limit determination. Geotechnique,Vol.31, No.3, pp.413—425.

Nagaraj, T.S. and Jayadeva, M.S. 1983. Critical Reappraisalof Plasticity index of soils. J1. of Geotechnical Engg.Vo1.109, No.7, pp.994-1000.

66.

67.

68.

69.

70.

71.

460

Nagaraj, T.S.and Srinivasa Murthy, B.R. 1983. Rationalis­ation of skempton's compressibility equation. Geotechnique,33, N00Nagaraj, T.S. and Srinivasa Murthy, B.R. 1986. A criticalreappraisal of compression index equations. Geotechnique,36, No.1, pp.27-32.

Narain, J. and Ramanathan, T.S. 1970. Variation ofAtterberg Limits in relation to strength properties ofhighly plastic clay. Jl. of I.N.S. of SMFE, Vol.9,No.2, pp.117-128.

Narasimha Rao, S. and Kodandaramaswamy, K. 1984. Geo­

technical Properties of Indian Marine Clays. IndianGeotechnical Conference, Calcutta.

Natarajan, T.K., Murthy, A.V.S.R., Tolia, D.S. and Rao, E.S.1982. Performance of test embankment on treatment of marine

clay Deposits. Proc. Seventh S.E. Asian GeotechnicalConference, Nov. 22-26, Hongkong.

Newland, P.L., and Alley, B.H. 1960. A study of Consolid­ation characteristics of a clay. Geotechnique, 10, No.2,pp.62—74.

72.

73.

74.

75.

76.

77.

78.

461

Norman, L.E.J., 1958. A comparison of values of liquidlimit determined with Apparatuses having Bases of differentHardness. Geotechnique, Vol.8, pp.l-8.

Oikawa, Hiroshi. 1987. Compression curve of soft soils.Soils and Foundations. Vol.27, No.3, pp.99-104, Sept.1987.

Oswald, R.H. 1980. Universal Compression Index equation.

Jl. of Geotechnical Division, ASCE, 106, pp.1179-1199.

Perloff, w.H. and Osterberg, J.O. 1963. The effect ofstrain rate on the undrained strength of cohesive soils,Proc. 2nd Pan American Conf. Soil Mech. Brazil 1, pp.103-128.

Ramanatha Ayyar, T.S. 1966. Strength characteristics ofKuttanad Clays. Ph.D.Thesis. Dept. of Civil Engineering,University of Roorkee.

Rao, S.M., Sridharan, A. and Chandrasekharan, S. 1989.

Influence of drying on liquid limit behaviour of a marineclay. Accented for publication, Geotechnique.

Ramanchandran, V.S., Kacker, K.P. and Rao, H.A.B. 1963.

Determination of liquid limit of soils by Dye Absorption.Soil Science, Vol.95.

79.

80.

81.

82.

83.

84.

85.

86.

462

Richardson, A.M. and Whitman, R.V. 1963. Effect of

Strain rate upon undrained shear resistance of a satur­13, pp.310—324.ated remoulded soft clay, Geotechnique,

Russel. E.R. and Mickle, J.L. 1970. Liquid limit valuesfor soil moisture tension. Jl. of soil Mech. and Found­ation Division, ASCE, Vol.96, pp.967-989.

Sallfers, G. 1975. Preconsolidation pressure on softhigh plastic clays, Ph.D. Thesis, Chalmers University ofTechnology, Gothenberg, Sweden.

Sangrey, D.A. 1972. Naturally cemented sensitive soils,Geotechnique, 22, pp.139-152.

Saxena, S.K., Hedberg, J. and Ladd, C.C. 1978. GeotechnicalProperties of Hackensack Valley Varved Clays of New Jersey.

Geotechnical Testing Journal, 1(3) pp.148—161.

Schmertmann, J.M. 1955. The undisturbed consolidation of

clay. Trans. ASCE. Vol.120.

Schofield, A.N. and wroth, C.P. 1968. Critical State SoilMechanics. McGraw Hill, London, England. pp.1S1-161.

Seed, H.B., Woodward, R.J., and Lundgren, R. 1964. Claymineralogical aspects of Atterberg limits. Jl. of soilMech. and Found. Enqg., ASCE, Vol.90, SM 4.

87.

88.

89.

90.

91.

92.

93.

463

Skempton, A.w. 1944. Notes on the compressibility ofclays Q.J.Geolo. Soc. London, 100, pp.119-135.

Skempton, A.w. 1953. The colloidal Activity of clays.Proc. Third International Conference on soil mechanics

and Foundation engineering, Zurich, Vol.1.

Smith, R.E. and Wahls, H.E. 1969. Consolidation underconstant rates of strain. J1. of soil Mechanics andfoundation Division, Proceedings of the American Societyof Civil Engineers, Vol.95, SM 2, March 1969, pp.519-539.

Somayazulu, J.R. Ramesh, N.V. and Narasimha Rao, 8. 1984.

The use of lime columns in soft clays. Indian GeotechnicalConference, Calcutta, Vol.1.

Sridharan, A. and Jayadeva, M.S. 1982. Double layertheory of compressibility of clays. Geotechnique, Vol.32,NO.2, pp.133-144.

Sridharan, A, Murthy, N.S. and Prakash, K. 1987. RectangularHyperbola method of Consolidation Analysis. Geotechnique,37, No.3, 355-368.

Sridharan, A. and Rao, G.V. 1973. Mechanism controlling

volume change of saturated clays and the role of effectivestress concept, Geotechnique, Vol23, No.3, pp.3S9-382.

94.

95.

96.

97.

98.

99.

100.

464

Sridharan, A. and Rao, G.V. 1975. Mechanisms controlling

the liquid limit of clays. Proceedings Instanbul Conferenceon S.M & F.E., Vol.I, pp.75-84.

Sridharan, A. and Sreepada Rao, A. 1981. Rectangularhyperbola fitting method for one dimensional consolidation.

ASTM Geotechnical Testing Journal, 4, pp.161-168.

Sridharan, A., Sudhakar, M.Rao and Murthy, N.S. 1985.Free swell index of soils. A need for redefinition.Indian Geotechnical Journal. Vol.15, No.2, pp.94-99.

Sridharan, A., Rao, S.M.and Murthy, N.S. 1988. Liquidlimit of kaolinite soils. Geotechnique, Vol.38, No.2,pp.l91-198.

Terzhagi, K. 1925. Introduction to Brdban Mechanik aufBoden - Physikaliches Grundlage, translated by A Casagrande,

In. From Theory to Practice, by Bjerrum, L et al. 60,New York J. Wiley.

Terashi et al. 1977. Fundamental properties of Lime treatedsoils. First Report. Report of Port and Harbour ResearchInstitute.

Uppal, H.L. and Agarwal, H.R. 1958. A new method for

determining liquid limit of soils. Road Research Paper19, Delhi,pp.1—25.

101.

102.

103.

104.

105.

1060

107.

465

Uppal, H.L. and Palit, R.M. 1964. A resume of limestabilisation with particular reference to the effectsof lime on the Physics and Chemistry of soil. IndianRoads Congress, Jl. Vol.XXV., No.2, pp.203-212.

Vaid, Y.P., Robertson, P.K. and Campanella, R.G. 1979.Strain rate behaviour of Saint Jean — Vianney Clay,

16, pp.39-42.Canadian Geotechnical Journal,

warkentin, B.P. 1961. Interpretation of upper plasticlimit of clays. Nature, Vol.190.

Wesley, L.D. 1988. Compression Index: MisleadingParameter . Journal of Geotechnical Engineering, ASCE,VOl.114, No.6, June, 1988.

winterkorn, H.F. and Fang, H.Y. 1975. FoundationEngineering Handbook. Van Nostrand Reinhold Co.

wroth, C.P. and wood, D.M. 1978. The correlation ofIndex properties with some basic engineering propertiesof the soil. Canadian Geotechnical Journal, Vol.15,No.2,Yamamoto, S. 1977. Land subsidence in Japan. JapaneseSociety of Soil Mechanics and Foundation Engineering

Tsuchi - to - kiso, pp.13-19.

108.

109. Youssef, M.S.,

466

Yamanouchi, T. et al. 1978. A new technique of limestabilisation of soft clay. Symposium on soil rein­forcing and stabilising techniques, Sydney,pp.531-541.

El—Ramle, A.H. and El-Demery, N. 1965.

Relationships between shear strength, Consolidation,liquid limit and plastic limit for remoulded clays.

6th Int. Conf. Soil Mechanics Instanbul I,PI'OC.

po.126-129.

Australia,

I.

APPENDIX II

LIST OF PUBLICATIONS FROM THESIS

PAPERS PUBLISHED

Babu T.Jose, Sridharan, A. and Benny Mathews Abraham.

(1987). "A Study of Geotechnical Properties of CochinMarine <2lays", Marine~ Geotechnology, New ‘York, Vol.7,No.3, pp.l89—209.

Babu T.Jose, Sridharan, A. and Abraham, B.M. (1988)."Physical Properties of Cochin Marine Clays", IndianGeotechnical Journal, Vol.18, No.3, pp.226-244.

Babu T.Jose, Sridharan, A. and Abraham, B.M. (1989)."Log-log Method for Determination of PreconsolidationPressure", ASTM Geotechnical Testing Journal, Vol.12,

No.3, pp.230-237.

Babu T.Jose, Sridharan, A. and Abraham, B.M. (1987)."Engineering Properties of Cochin Marine Clays and itsStabilisation with Lime", 9th South East Asian Geotechni­

cal Conference, Bangkok, Thailand, pp,5_115 to 5-126,

Babu T.Jose, Sridharan, A. and Punnoose, K.K. "Geo­technical Properties and Electrical Characteristicsof Cochin Marine Clays", Institution of Engineers——National

Convention of Civil Engineers--Annual Paper Meeting,Calcutta, Jan.l8-20 (1990).

467

468 —­

II. PAPERS COMMUNICATED

1. "Determination of Clay Size Fraction of Marine Clays",

Communicated to ASTM Geotechnical Testing Journal,Philadelphia.

2. "Variability of Geotechnical Properties of MarineClays due to Test Techniques", Communicated to Marine

Geotechnology, New York.

3. "Low Cost Ground Improvement Techniques for Construct­

ion of Highways over Soft Marine Deposits", Communi­

cated to Ground Engineering, London.

4. "Prediction of Shear Strength of Clayey Soils basedon Natural Moisture Content". Communicated to Geo­

technique, London.

5. "Prediction of Settlement of Foundation — The Needfor a Relook into I.S.Code Provision", Communicated

to Journal of Institution of Engineers, Calcutta.

6. "Improved Methods for Estimation of PreconsolidationPressure", Communicated to Geotechnique; London.

7. nReSiStiVity Measurements in Geotechnical Engineering":

Communicated to Indian Geotechnical Journal,New Delhlv