Proceedings of the Thirteenth Muskeg Research Conference

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Proceedings of the Thirteenth Muskeg Research Conference

CANADA

ASSOCIATE COMMITTEE ON GEOTECHNICAL RESEARCH

PROCEEDINGS of the

THIR TEENTH MUSKEG RESEARCH CONFERENCE

7 and 8 May 1970

Prepared by

Miss J. Butler

TECHNICAL MEMORANDUM NO. 99

OTTAWA

(i)

FOREWORD

This is a record of the Thirteenth Muskeg

Res earch Confe rence, which was held in the Engineering Co mpl.ex of the University of New Brunswick, .:Fredericton!.._.Ne_w Brunswick,

on 7 and 8 May 1970. The Conference was sponsored by the

Associate Cornrnitte e on Geotechnical Research of the National

Research Council. A list of those in attendance is included in

Appendix ItA" of these Proceedings.

-TABLE OF CONTENTS

Thursday, 7 May 1970

Introductory Remarks • • • • • • • • " • • • • • • • • 0 • • • • • • • 0 • • • • • • • • iv

Keynote Address - Muskeg and Environmental Studies.

1. C. MacFarlane, National Research Council . . . • . . . 1

Contributed Papers

Shear Strength Characteristics and Structure of Organic Soils.

Z. S. Ozden and N. E. Wilson, McMaster University 8

The Vane Test in 0 rganic Soils.

R. P. Northwood and D. A. Sangrey 27

Muskeg and Environmental Studies: Part I Chairman: 1. C. MacFarlane

Prediction of Undrained Movements Caused by Embankments on Muskeg.

G.W. Hollingshead and G.P. Raymond . . . • • . . . 41 Muskeg and Access - The Need for Planning.

J. R. Radforth . . . • . . . •..

60

Muskeg Programme at Muskeg Research Institute.

N. W. Radforth . . . • . . . • . . • . • . . • . . . . .. 68

Friday, 8 May 1970

Chairman: R. A. Hemstock Contributed Papers

The Classification of Organic Soils in Canada. (Summary)

(i i i )

Friday, 8 May 1970 (Cont'd) Page

Postglacial Muskeg Development in Northern Ontario.

J. Terasmae ... . . • . . . 73 Paddy Production of Wild Rice in Muskegs.

J. M. S t e w a r t . . . 91 The Benefits of a Systems Approach to Resource

Utilization Studies.

A. T. E a s l e y . . . 98 Muskeg and Environmental Studies: Part II

Chairman: R. A. He rn s to c k

The Low Arctic En vironment and Primary Productivity.

R. W. Wein and L. C. B l i s s . . . 109 Methodology and National Muskeg Inventory.

E. Korpijaakko and N. W. Ra d fo r th 120

Muskeg Film - Muskeg Journey. 127

Appendix "A": List of Delegates Attending the Thirteenth Muskeg Research Conference.

INTRODUCTORY REMARKS

Dr. N. W. Radforth introduced Dr. J.O. Dineen, President of the University of New Brunswick, who warmly welcomed the delegates to the Conference on behalf of the University.

President Dineen had studied the programme of the Conference and made reference to the significance of the theme it

hoped to encompass. The growing concern for wise caretaking as

applied to our environment required urgent attention of scientists and

engineers. "Muskeg and Environmental Studies ", brought into a

common context, was appropriate for Canada especially in consideration of the vastness of Canada's peat deposits.

Dr. Radforth then called upon Mr. I. C. MacFarlane, Scientific Advisor of the Muskeg Subcommittee of the National Research

Council, to expres s the scope of the theme. He also reminded the

delegates that members of the Canadian - U. S. A. section of the International Society of Terrain-Vehicle Systems were present because of their interests in the theme pe rtinent to application of off -r o ad ve hides.

KEYNO TE ADDRESS

MUSKEG AND ENVIRONMENTAL STUDIES

1. C. MacFarlane

Introduction

It has been said that there is nothing so compelling

as an idea whose time has co rne , There can be little doubt that at this

particular time in history there is an unprecedented concern for the environment, for the effects on man of the pollution of the water, soil,

and air. This concern was aptly expressed by President Nixon in his

1970 State of the Union address when he said: "The great question of the 70's is: shall we surrender to our surroundings, or shall we make our peace with nature and begin to make reparations for the damage we

have done to our air, to our land, and to our water?" It is argued by

some (rather cynically, I feel) that this public and political concern is

only a fad and that the public will soon grow tired of it. Even if this be

so, I greatly doubt that in the future will s dentists and enginee rs (particularly the latter) be able to igno re the effect on the environment of their activities, no matter how desirable the end result from the point

of view of technological progress. This will arise both from moral

constraints as scientists and engineers become rno re aware and concerned about the side effects of their activities, and from legal restraints imposed

as a result of public pressure. Just this week, the Government announced

a land conservation program for Canada's North, which will include not

only land use legislation, but land use research as well. In Canada, therefore,

the time has corne for us to consider - and to consider seriously - the northern environment.

The subject of our deliberations for the next two days is "Muskeg and Environmental Stud ie s ", To channel our thinking on this very important topic, I have structured my brief introductory

remarks to first of all consider the subject of environment generally, then to talk about muskeg studies in particular, and, finally, to make a few comments on the interrelationship between the two.

Environment

Webster defines environment as "the surrounding conditions, influences, or forces that influence or modify; such as the

whole complex of cl irnatic , adaphic or biotic factors that act upon an o r g a ni s rn or an ecological co rnrriunitv and ultirn a.teIv d e te rrriin e its fo r rn and survival". The d e v e Io prnent of rnu s k.e g , for instance, is the result of certain e nv i r o nrn en tal conditions: high precipitation, low

evaporation, irnpe r vio u s soil or rock, poor surface drainage owing to

ins ufficient slope or uno rganized drainage sv s te rris , As peat a c curnu.l at.e s , a new e nvir o nrrie nt is established within the deposit which p r o rnote s

further a ccurnuIatio n , In the larger sense of the word, rriu s ke g itself is a very significant part of the overall e n vi r o nrn ent of the Canadian Arctic and the Subarctic, since it represents - at a conservative e stirna te - an area of 500, 000 square rnil e s ,

The word "e nvi r o nrnent" will represent different things to different people, depending upon their discipline, background

and training, as well as on their proposed use of the terrain. In his

encounter with the rnus k e g enviro nrne nt, the engineer is concerned with o ve r co rrri n g it or at least lTIaking the best of it. This rrray involve the de ve loprnent of vehicles to cross over mu s ke g with the rni nurnurn of d arna g e to the vehicle and to the terrain, the construction of roads, railways, hydro lines or other structures on or in it, digging drainage ditches, perhaps even of flooding it as a result of a hydro-electric

project. Most of his activities, in short, are irnpo s e d on the e nviro nrn ent

and will change it to a greater or lesser degree. So do those activities

of the agriculturalist and of the forester, who wish to change the rnu s k e g e nvir o nrrie nt to rnake it lTIO re productive. It is doubtful, however, if anyone today would suggest the rne a ns of a rne l io ration of the rnu s ke g

e nviro nrrie nt that was suggested at the 1956 Muskeg Conference:

"Since s o m et.hin g drastic is required to

arrest the a c c urriula tio n of peat, wishful thinking has turned to the possibility of a me l io r at io n through

broad e nvi ro nrne nta.l changes One such rne tho d

could be fire. . .. The use of fire either alone or in

conjunction with drainage and cultivation would appear to present great pos s ibiliti e s , It is true that only in very dry seasons that occur once in about 20 years is the peat dry enough to burn and that under these conditions the risk of burning large forest areas of s e ttl e merit and forest land is exceedingly great. Nevertheless, it appears that fire will b e co rne the

rno st practical tool in preventing the spread of

rnu s k e g conditions even though it cannot be used to reduce rriat.e ria.Il y the depth of peat on present rriu s k e g areas. "

3

-We can be grateful, perhaps, that this predictio n was not realized. On the other side of the coin from the users are the conservationists whose main concern is the preservation and

wise use of the environment. Historically, they have corne into

rather s harp conflict wi th the develope r , the engineer, and with

technological progress (so -called) in general. Another interested party

(who may actually be the conservationist) is the pure scientist, such as the botanist, pa lyno l o gist, e tc ; , who is concerned with the detailed

study of one or rrio re particular aspects of the env ironment. We will

be hearing something more from these people in the course of this Conference.

Implicit in the present-day environmental concept is the requirement for interdisciplinary co -operation and research and this is largely reflected by the establishment of environmental

institutes and similar groups on university campuses. The implications

are that the engineer, for instance, will have resources at his disposal to provide him with advice on the implications and possible effects on

the ecology by a proposed project. This has a profound significance

for the future, in view of what has happened in the past. What engineer,

for ins tance, would have ever imagined (let alone predicted) that the use of tracked vehicles for oil exploration in the northern tundra would have so upset the delicate ecological balance that it would lead, ultimately,

to a change in the migration pattern of the caribou? If nothing else is

learned from this, it is at least an object lesson of the scope of the

problem faced and of the need for interdisciplinary dialogue and co -o pe r a tio n. Muskeg Studies

It has now been 25 years since the National Research Council began to be interested in the muskeg problem, as part of the

terms of reference of the As sociate Committee on Soil and Snow Mec hanics,

which was established in 1945. Initially, the terms of reference of its

Muskeg Subcommittee were "to provide a useful interpretation of muskeg to assist military and civilian investigations concerning organic terrain." From the outset, the main thrust of the Subcommittee has been towards

the solution of engineering problems. This was simply because ther e was

a need (often an urgent need) for an answer to a particular problem at a

given time; this was where the action was. Its approach was a pragmatic

one. An examination of the Proceedings of the Muskeg Conferences (which

began in 1955 and were held annually through to 1966) will indicate that a great deal of time was devoted to discussion of the problems of off-road access (route planning, vehicle development, mobility and trafficability

a useful forum where such major problems were presented and discussed and it is believed that the Conferences contributed in part to a modicum of success in vehicle development and in design techniques for all classes of roads over muskeg.

In recent years, however, the emphasis has moved from the general to the specific, with regard to engineering problems. Much work is now being done on fundamental questions such as the response of the peaty material to compres sional loads, to s hear and

tensile stres ses, on hyd rology, thermal properties, etc. T his trend

has been reflected in recent Proceedings and, again, in the program of

this Conference. This will result, ultimately, in refinements to the

design of vehicles, of roads and other structures in contact with muskeg. Despite the heavy engineering emphasis, however, the Subcommittee has not lost sight of other aspects of the overall muskeg

problem. This has been partly due to the fact that the Chairman is a

palaebotanist and not an engineer. From the very outset as well, the

Muskeg Subcommitte, like its parent Committee, recognized the necessity

of an interdisciplinary membership. In recent years an awareness has

grown within the Subcommittee that it needed to broaden its perspective

in an official way. This led, late in 1967, to a special workshop meeting

of the Subcommittee at which it considered in detail its scope and terms

of reference. It was agreed that it should be within the scope of the

Subcommittee to encourage scientific and industrial research in muskeg

for the advancement of the country. It was also agreed that the relevant

fields of scientific research should include at least: hydrology, climatology,

palaeobotany, resource planning, conservation, geology, geography, palynology

and physics and chemistry of peat. Industrial research interests should

incorporate: remote sensing and aerial interpretation, vehicle access, agricultural and forestry development, fo res t products, mineral resource

exploration and development, peat products, road and railway construction

and relevant aspects of hydro -electric power development and of national

defence. Membership in the Subcommittee has been increased to assist it

to undertake this broader perspective. The Subcommittee is moving away,

therefore, from its heavy engineering emphasis without necessarily neglecting this very important part of its responsibility.

This new dimension for the activities of the Subcommittee was typified a year ago when, in conjunction with its annual business meeting, a seminar was held on Project TELMA which is concerned with the preparation of a world list of peatland sites of international importance to science and

within the promotion of their conservation. This trend towards interest in

5

-reflected in the program of this Conference as it has been in other Conferences.

Muskeg and Environmental Studies

Basic scientific research is very important to

gain knowledge of the principles governing accumulation and distribution of different peat types, and to interpret the history of types of peatland

environment. Peat deposits provide a fossil record of environmental

development, thus providing a historical background which helps to account for the present environmental status and to predict future

ecosystem changes as environmental factors are altered either naturally

or artificially. Investigation of these phenomena is not only a matter

of fundamental enlightenment but also relates to matters of national development.

A case in point was raised by Dr. N. W. Radforth in his keynote address to the 1968 International Peat Congress. He referred to the increasing need in North America for fresh water and

to the implication of water diversion schemes. Management of northland

water would be imposed on landscape in which about 70 per cent of the

terrain is organic. In these areas, muskeg is the retainer and the

delivery mechanism influencing the behaviour of the water supply. The question comes to mind of what happens to this environment when

drastic changes in the direction of water flow are imposed upon it. At

the present stage of development and of knowledge this is not possible to answer with any degree of assurance although this is the sort of question that we will have to be able to answer.

Fundamental research, if pursued on a broad and intensive basis, facilitates development of systems of access, mobility and transportation within the broad swath of difficult terrain known as

muskeg which sweeps across the central part of Canada. It enables

prediction to be made concerning best use of muskeg for agriculture, forestry, wildlife sanctuaries, and optimum production of natural

resources. It contributes to the under standing of the behaviour,

conservation and exploitation of our remaining water resources. It

also affords an approach to finding the best industrial use for peat and

peat products. In short, therefore, fundamental muskeg research

will contribute to the wise use of muskeg resources, will require inter-disciplinary activity, and will result in a better understanding of the environment.

To conclude my remarks, I can do no better than to quote a section of the recently -is sued report of the Science Council

on research in the earth sciences. This section relates to the role of the earth sciences in en vi r onrne nta l p r o bl erris ; it is both relevant to and SUITlS up what I have been trying to say.

llThe increasingly co mpetitiv e use of the land, whether

for rrii.n ing , agriculture, forestry, hydroelectric

develop-rne nt , industrial and urban d eve lopdevelop-rne nt, or recreation and nature conservation, neces sita tes judicious use of natural resources and d erria nds proper regard for pres erving the quality of the natural enviro nrne nt , The present public and political concern in North Arne r ic a about pollution of water and air, destruction of wilderness areas, urban sprawl and other factors

contributing to deterioration in the quality of rria nts

e n vi r o n rne nt is a sYITlptOITl of the acute need for rnuc h greater attention to the rriaria ge rrie nt of our natural

e n vi r o nrne nt and resources. Canadians not only face

the challenge of achieving effectively the accelerated growth of urban centres that will take place in the next few years, but are also responsible for the

d e ve Io prne nt and rna na ge rne nt of one of the largest virgin

wilderness areas r e rnaini ng in the world. A concerted

attack on thes e challenges and pro ble rns , although enci rcled by social, e co no rrri c and legal factors, rnu st be based

on objective, factual, scientific i.nfo r rna tio n concerning land or te r r a.i n vi nfo r rn.a'ti o n which is the essence of the solid -earth sciences.

Knowledge of the nature and behaviour of the land, which is es sential to effective land us e planning and rria na g errre nt

of land resources, is based upon sold -earth science

info r ma tio n concerning relief and l.aridfo r rns , surface and 'near -surface bed rock, unconsolidated earth rria.te ria l s ,

soils in the pedological sense, as well as water both in

and on the ground. Facets of geology, physical geography,

soil science and soil engineering are all involved.

In particular, Canada is currently facing a critical need for land use planning in the pe r rnaf'r o st and rnus ke g areas

of the Arctic. The rapidly increasing rate of petro l eurn

exploration is forcing the i.rnpl e rne nta tio n of political and technical decisions without an adequate background of

scientific knowledge and experience. The nurnbe r s of

7

-"At the federal level, only five persons are engaged in permafrost research, a phenomenon covering over

half of the country. The Science Council endorses

the conclusions of the Study Group that increased emphasis must be given to northern terrain studies.

"Greatly increased activity in all branches of environmental earth sciences is necessary immediately, including

appropriate attention to the social aspects of planning, especially as they relate to the protection of our

environment. The work already done must be rapidly

expanded upon firm scientific foundations, and aided by

all that res earch can contribute. Accordingly. as Canada

moves to investigate and solve the problems of the environ-ment' care must be taken to ensure that the environmental earth sciences are developed to play their proper role. "

SHEAR STRENGTH CHARACTERISTICS AND STRUCTURE OF ORGANIC SOILS

Z. S. Ozden and N. E. Wilson

Abstract

Shear strength characteristics of peat were investigated by a series of consolidated -undrained triaxial tests, with pore water

pressure measurements. Similar samples of peat were infiltrated with

paraffin to produce thin sections for microscopic examination. A correlation

between the macroscopic and micro scopic properties is dis cus sed.

*

-/ /

CARACTERISTIQUES DE LA RESISTANCE AU CISAILLEMENT ET STRUCTURE DES SOLS ORGANIQUES

Z.S. Ozden etN.E. Wilson

Les ca r a c te ristique s de la resistance de cisaillement de

la tourbe o nt ete determines

a

echantillons co nso l id es avec des mesures de pression interstitielles. On

a inje c te de la paraffine

a

d'0btenir de minces echantillons pour examen micros copique. L'artic1e

dis cute de la relation entre les p ro p r i.ete s macroscopiques et micros copiques.

9

-Introd uction

An understanding of the behaviour of the structure of peat under stresses can direct the application of Soil Mechanics principles

to peat. The structural similarities of peat to mineral soils, as well as

their differences, have been appreciated. Though more complex, peat

pos ses ses a structure, with particle sizes ranging from colloidal

ｳｩｺ･ｾ

to tree trunks all at various degrees of decomposition, all of various !

but organic origin. Under an apparent cosmos lies organization and

perhaps some discipline as implemented by Radforth classifications (Radforth, 1952).

Arno ng workers in this field, Hanrahan conducted laboratory triaxial testing of peat (Hanrahan, 1954); he carne to the conclusion that the shear strength of peat was mainly due to cohesion.

There we re others, however, who seemed to entertain the idea that its

strength was mainly due to the frictional component and MacFarlane

pointed out this controversy (MacFarlane, 1959); Pioneering work in

Canada (Adams, 1961) supports this latter point of view. This led Wilson"

and his associates to doubt the applicability of strength theories that have

been successful in determining the shear strength of mineral soils to pe atj thus they chose to investigate the strength of peat from a rheological

point of view (Schroeder and Wilson, 1962; Krzywicki and Wilson, 1964).

Yet each investigator was dealing with one kind of peat

with a unique structure. Peat should be treated as a unique material and

the testing techniques for each type of peat should be consistent. While

each investigation was useful for the accumulation of information, it was

necessary to accept the results cautiously due to the complex biological

origin of peat. This was the reason for controversial laboratory test

results.

It is logical that, in order

to

is necessary to find some common structural elements and concentrate

the attention on these. In other words, it is necessary to supplement

any investigation in shear strength with an investigation on a microscopic

scale as the constituents of peat range down to colloidal particles.

MacFarlane and Radforth report research where the effect of stressing on peat structure during consolidation is to be examined microscopically

although no results are given (MacFarlane and Radforth, 1964).

Microscopic examination and analysis of peat for

purposes other than engine ering have been utilized. In almost all cases

thin sections of peat were examined. One of the more significant was

for exam.ining the in situ arrangem.ent of peat by paraffin infiltration

(Radforth and Eydt, 1958). Stewart m.ade indirect use of cuticles in

exam.ination of peat (Stewart, 1960). Material and Investigation Techniques

Peat sam.ples were taken from. Copetown Bog in the

Wentworth County, Ontario. The surface vegetation is lEF-ElF

and--BEl according to the Radforth Classification. The sam.p1es were taken

from. two to three feet below ground level.

The peat was non-woody, fine fibrous, containing som.e

coarse fibres (Category No. 8 of Radforth Classification). The peat

sam.ples had a natural water content of about BQO.per:.c:ent, a specific

gravity of 1. 57, 96 per cent organics and a pH value of 4.5. Sam.ples

for testing were preconsolidated in the 1.5 inch diam.eter stainless steel

cutting tubes driven into the block sam.ple. The sam.ples were then

transferred to the triaxial cham.ber for further consolidation.

Difficulty was encountered at the consolidation stage.

It was found that, because drainage was only from. the bottom. of the

sam.ple, by the tim.e pore pressures fell close to zero within the aarnple ,

the bottom. of the sam.ple was stronger than the top due to its lower water content; because of the length of drainage path, the bottom. of the sam.ple

experienced m.ore secondary consolidation than the top. This gave rise

to a non-hom.ogeneous sam.ple which prom.oted failure at the top half of

the sam.ple during shearing. To overcom.e this effect, drainage from.

the top as well as from. the bottom. was tried. This procedure was

dis continued because the pull by the plastic tubing used to drain the sam.ple from. the top gave ris e to som.e eccentricity along the length of the sam.ple

before shearing started. The non-hom.ogeneity of this peat was such that

eccentricity of the sam.ples was com.m.on; during shearing that sam.e

eccentricity grew larger and the sam.ple failed by buckling. This is

significant in that it gives a false value of the stress that the sam.ple can

carry in the field. Finally, side drains cut from. filter paper were used

to obtain a relatively uniform. sam.ple with regard to its water content after consolidation.

A constant displacem.ent rate of O. 009 in/m.in. (or about O. 32 per cent/m.in. ) was us ed during all tests.

Strength Test Results

A series of consolidated undrained tests with pore

11

-and pore pressure diagram is shown in Figure 1. The pore pressure parameter

B was calculated by raising the cell pressure and recording the pore pressures

induced. After each increment of cell pressure, ten minutes were allowed

for the pore pressures to reach equilibrium. The values found are in the order

of O. 9 - 1. O. The pore pressure parameter A_f, calculated by dividing the

pore pres sures (at maximum deviator stress es) by the maximum deviator stresses, lie in the range of 0.44 to 0.84; these values fall in the range commonly associated with normally consolidated clays.

Figure 1 indicates that the peat has a stable structure under static loading over large strains (i. e. in excess of 20 per cent strain). It is seen that the induced pore pressures follow, in general, the shape of

the deviator stress curve and both cu r v e s retain their values without substantial

change with increasing strains. For most of the tests, the induced pore

pressures a revin excess of 90 per cent of the cell pressures. Similar res ults

have been reported elsewhe re (Adams, 1961; Hanrahan, 1954). In spite of

these high pore press u r e s , the relatively low A values further substantiate that peat has a stable structure over large ranges of strain induced by static loading.

Mohr circles, in terms of total stres ses, are shown in

Figure 2A. Maximum deviator stresses were taken as the failure criterion.

An approximate envelope drawn for these circles indicates a cohesion intercept of O. 05 kg. / cm2 and an angle of s hearing resistance of 180 _•

Figure 2B shows the results of the tests in terms of

effective stresses; the approximate envelope indicates a cohesion intercept of

0.05 kg. /cm. 2 and an angle of shearing resistance of 460 •

The high angle of shearing resistance appears to indicate a

strong material. Due to the high pore pressures induced,

s

ma gni tud e and, therefore, the mobilized strength is small. In the case of

complete drainage, a relatively high strength is obtained and succes si ve

deformations result due to the great volume of water that is expelled. These

results are further substantiated by the vector curve plots.

The stress history and behaviour of the sample as it is loaded and brought to failure can indicate the structural properties of the soil. Graphs can be constructed by plotting the history of shear stresses and normal stresses on the incipient failure plane from the beginning of the test to failure.

A vector curve is a plot of shear stress versus effective normal stress on the incipient failure surface; the vector curve is shown

in Figure 3. The behaviour of the peat under load indicates that the pore

water pressures generated by the shear stresses have the consequence of reducing the effective normal stresses on the failure surface; the sample fails at a low strength due to the pore water pressures generated within it.

It can be seen that the cu r v e s for the shear strength tests consistently go towards the left, the origin of the graph; similar curves for drained

material would go upwards to the right.

When strain contours are superimposed on the vector

curves, these can be utilized to predict the approximate magnitude of

strains to be expected during loading. This feature is especially useful

with peat as it serves for both the drained and the undrained cases. It was shown that peat has a stable structure over long ranges of strains induced by static loadings which suggests the necessity of including

undrained movements as a design criterion even in short-term (undrained) loading conditions.

Influence of Cyclic Loading

Pore water pressures generated by shear stresses can be very significant to failure in the case of cyclic loading (Glynn, Kirwan

and Wilson, 1968). Structural breakdown of the fibres and cell walls takes

place as the strain increases with each load application. During the cyclic

loading, major inelastic deformations occur and the peat rapidly deteriorates. For this type of loading, there is a transition point, or

"thres hold stress", where major inelastic deformations begin to occur with associated effects on pore water pressures and resilient modulus. Under low stresses, the resilient modulus is essentially constant (Figure 4)

and the soil is capable of withstanding 1,000 stes s applications. At slightly

higher stresses, the modulus decreased rapidly after approximately 50 applications; at this stage, there is a corresponding marked increase in

pore water pressure. It was hypothesized that the rapid increase in pore

water pressure, as the permanent deformation effects become more

significant, is due to the breakdown of the fibres and c e l l s within the peat

which releases trapped water into the void spaces. It has the consequence

of producing rapid permanent deformations as the effective stresses are reduced and the peat behaves as if there was a sudden increase in water content.

The permanent deformation is not very pronounced until the threshold stress has been approached and, consequently, the peat can

withstand many stress applications. This behaviour has been noted in

the field (Hanrahan, 1964) where it was reported that a roadway embankment was satisfactory until it was used for heavy traffic.

Microscopic Analysis

To examine the effect of s hearing on the structure of peat

13

-along desired planes and examined under a microscope capable of utilizing

reflected light. This approac h was dis carded, however, because of

technical difficulties; the surface of peat, being irregular and dark-coloured,

absorbed the light. An electron microscope has too great a magnification

for this purpose. It was, therefore, decided to conduct examinations using

thin sections and transmitted light. Section Preparations

First, a freezing technique was tried. The sample was

fro zen and thin sections were cut using a microtome. Sections, however,

crumbled and did not retain their original arrangement. Gelatin embedding

accompanied by quick freezing was also discarded for similar reasons. A method originally used by Eydt (1956 and 1962) was modified for the

purpose. Peat cubes were infiltrated with paraffin wax from which thin

sections Were obtained. These were mounted on glass slides and examined

under transmitted light (Ozden, 1967). Microscopic Examination

The pore water pressures generated during the shear of the peat do not allow the peat to mobilize a high shearing resistance.

The term "fibrous interlock" has been used to describe the internal shearing

resistance. In the case of complete drainage, a high shearing resistance

could be obtained provided the large deformations associated with volume changes could be tolerated.

Under application of stress, the individual fibres and particles experience changes in structure and orientation; Figure 5

diagrammatically illustrates the behaviour of two fibres. Pro gressi vel y,

the fibres are forced closer together reducing the void space; as the contact between the fibres increases, the cell structure of the fibres

changes. Figure 6 shows some typical microscopic sections examined

during the research.

The water in the peat can be generalized into four categories:

The first category is the loosely held water in the voids enclosed by what can be considered as the solid constituents of peat.

The second category is water within voids in the solids. For example, water within the void portions of roots, hollow stems, etc. This water is more firmly held than the water in the voids in between the solid constituents.

The third catego ry is the water that constitutes the

rna te ria l itself. The constituents of peat, being of biological origin,

are co rnpo s e d rnai nly of water. Water, therefore, fo r ms an integral

part of what is considered to be the solid constituents. This water,

held in the cells, for instance, can be expelled under certain ranges ofJ

stress.

The fourth category of water is the colloidal water.

It could be expected that the constituent rna te r ial s which

fo r rn the peat would change under stress. It was expected that the slope

of the envelope would not be a straight line as different constituents of

the peat yield and deteriorate. Consequently, the selection of an angle

of s hearing resistance and a cohesion intercept rnay be rather arbitrary..

The rni c r-o s co pi c exarninati.on showed the amo r phous

granular rnate ria'l to be the rno st co mmo nl y encountered ele me nt that

fo r me d the structure of this peat. These generally ranged fro rn 0.1 to 5

mic ro ns . Therefore, a high colloidal activity is probable. A unique

property of colloidal particles is their large surface areas. As, in general,

organic colloids have a high affinity for water, the colloidal pheno me non

rnay be the chief cause of the high water content of peat.

For the peat types examined, the rni c ro s co pi c exarnina tio n

showed a high density as well as a fairly high fibro sity ratio. The fibrous

axes were rno s tly non-woody. These fossilized organs formed an impo r tant

part of the structure of the peat and rnay act as the supporting rne di.a for

the structure.

The rna in body of the cells were identified as being sedges.

The lack of ITlOSS cells was probably due to their being less resistant than

sedge-type cells and not due to their original abs ence. There was a general absence

of leafy tissues which rnay also be due to me chani.c.al breakdown as well as bacterial action.

The cherni cal nature of m Lc ro nodul es is a d ete r mini ng factor in their colloidal activity; the general behaviour of the structure will not be only colloidal as fossilized plant organs d ete r rni ne the fibrous activity. The behaviour of the fibres in turn is partly de te r mi ned by the be haviour

of their cell structure. For instance, the strength of the fibres is influenced

by the amount of water expelled frorn these cells under stresses. In any

case, significant changes in the structure can be expected (both in relation

to colloidal activity and the behaviour of mac rocor gani srns ) as water is

15 -Wa ter Content Relations hips

A unique relationship between water content and

co rrrpr e s s i ve strength exists for the peat tested (Figure 7). For clays, the s a me relations hip has been shown to be repres ented by a single

straight line (Henkel, 1960; Casagrande and Rivard, 1959).

The shape of the curve indicates that less water is expelled fr o rn peat for an increase in strength (after a threshold stress range) than from clayey soils. The rnic ro s c o pi c e xarrii na tio n has shown this to be due to different solid-water phase relationships that govern

the structure of peat under stresses than those for rnirier al soils. Water

fo r ms an integral part of even what is no r rna l l y considered to be the

solid constituents due to their biological 0 rigin. As water is expelled

under stres s e s , solid constituents of peat undergo changes. In other

words, the original rn a te r i a l does not r ernai n the s arn e . This is why the Mo hr -Co ulo rnb strength criterion, so successfully applied to rni n e r al soils, which aSSUITles a straight line relationship (envelope) for the

aarne rna te r ial can only be applied to peat with the reservation that it is only an a pp r oxi rna tio n to a curved envelope.

Conclusions

The rni c r o s co pi c exarrrina tio n has shown that various

categories of water are held in different ways within the peat. The water

content is the controlling factor 0 ver the s hear strength of peat. As so l.id> . water relationships for peat are different f ro rn those for mineral soils,

a straight line strength envelope is only an a.ppr oxi rna tio n to the true envelope. The shear strength tests, with both static loading and cyclic loading, have shown that the pore water pressures generated during shear d efo r rriatio n s have a significant influence on the u l tirriat e failure conditions for the peat.

It has been shown that the peat can corrrpe ten tly support loads under static

loading pro vided the thres hold stres s has not been exceeded under dynamic

loading. In other wo rds, the structure is the controlling facto r ,

AcknowledgITlents

This research work was conducted by the senior author, under the direction of the junior author, as part of the graduate prograITl

in the Faculty of Engineering at McMas ter Uni vers ity. The as sistance

and en cou ra gernent of Dr. N. W. Radforth are sincerely appreciated. The

research was supported by the National Research Council of Canada and the Defence Research Board of Canada.

REFERENCES

Adams, J.1. Laboratory Compression Tests on Peat. Proceedings

Seventh Muskeg Research Conference, National Research Council (Canada), Associate Committee on Soil and Snow Mechanics, Technical Memo randum No. 71, pp. 36 - 54, 1961. Eydt, H. R. N. An Introduction to the Study of the Structure of Muskeg.

Unpublished. M. Sc. Thesis, McMaster University, 1956.

An Assessment of the Component Tissues of Peat in their

-In Situ Arrangement. Unpublished. Ph. D. Thesis, McMaster

University, 1962.

Glynn, T. E., R. W. Kirwan and N. E. Wilson. Measurements of the Dynamic

Response of Peat Subjected to Repeated Loading. Proceedings

of the Third International Peat Congress, Canada, 1968.

Hanrahan, E. T. An Investigation of some Properties of Peat. Geo te chni que ,

Volume IV, p. 108, 1954.

Krzywicki, H. R. and N E. Wilson. Viscosity Measurements to Determine

the Shear Strength of Peat. Proceedings of the 10th Muskeg

Research Conference, National Research Council (Canada), Associate Committee on Soil and Snow Mechanics, 1964.

MacFarlane, 1.C. Guide to a Field Description of Muskeg. National

Research Council (Canada), Associate Committee on Soil and Snow Mechanics, Technical Memorandum No. 44, 1958.

and N. W. Radfo r th, A Study of the Physical Behaviour

---

Proceedings of the Tenth Muskeg Research Conference, N. R. C, Ottawa, 1964.

Ozden, Z. S. An Investigation on the Shear Strength Characteristics of

Peat. Thesis submitted to the Faculty of Graduate Studies for the Degree Master of Engineering, McMaster University, 1967.

Radforth, N. W. Suggested Classification of Muskeg for Engineering. The

17

-Radforth, N. W. and N. R. N. Eydt. Botanical Derivatives Contributing

to the Structure of Major Peat Types. Canadian Journal

of Botany, 36, 1958.

v Schroeder, J. and N. E. Wilson. The Analysis of Secondary Consolidation

of Peat. Proceedings of the Eighth Muskeg Research

Conference, National Research Council (Canada), Associate Committee on Soil and Snow Mechanics, Technical Memorandum No. 74, 1962.

Stewart, J. M. Cuticle in 0 rganic Terrain as Applied to Copetown Bog.

Unpublished. M. Sc , Thesis, McMaster University,

Hamilton, 196O.

Thaler, G. R. Assessment of the Components of Mineral Peat in their

In Situ Positions Utilizing Thin Sections. Unpublis hed.

M. Sc , Thesis, McMaster University, Hamilton, 1964.

*

-Dis cus sion R. Dubas:

Discuss the sampling techniques, size of sample, and the possibility as well as the effect of sample disturbance on the test results.

AuthorsI Reply:

Field samples were taken at a depth of 2-3 feet by driving

sharpened 4" diameter cutting tubes into the ground. Triaxial samples

were then obtained by driving 1.5" diameter thin-walled tubes into the

field tubes. An examination of the interior of the samples by freezing

and cutting showed that the disturbance was small. (Ozden, 1967).

P. Yurkiw:

*

-Was the cyclic loading used a function of time - that is regular time intervals - or was the pore pressure allowed to return to a constant once load was released before load reapplication?

AuthorsI Reply:

Cyclic loading was a function of time - 10 stress applications per minute and a pulse duration of 0.6 seconds; details

are shown in Figure 3 of Glynn, Kirwan, and Wilson, 1968. During

the cyclic loading, the pore pressures returned to a steady value between

stress applications.

*

-F. A. Gervais:

(i) You mentioned critical nature of threshold stress. Have you in fact done any field work - such as instrumentation - to verify your conclusions?

(ii) What type of pore water pressure device was used -"Springed" Mercury Pot?

Authors' Reply:

(i) We have not performed specific field tests related

to the concept of threshold stress. Other research work, however,

substantiates the concept (Hanrahan, 1964; Wilson and Krzywicki, 1965; Raymond, 1968).

(ii) Pore water pressures were measured by transducer.

*

-J. Hosang:

(i ) In the discussion of repeated loading on the peat

specimens, the re was shown to be a very significant difference in

behaviour of the peat under a loading difference of onl yIp. s ,1. How

important would specimen variation be in explaining the difference in behaviour?

(ii) Could fatigue have contributed to the behaviour variation?

AuthorsI Reply:

Sample variation can be significant for peat and, for this reason, the same sample was used for the test at both stress levels.

19

-The peat sample was initially subjected to 1, 000 stress applications

of a deviator stress of 5.

a

was increased to 6 -0 lb. /sq. in. ; failure o c cu r r ed after 80 stress

applications. As the pore pressure generated by the lower stress level

had stabilized after 120 applications, it is unlikely that the cyclic loading history caused failure under the higher stress level; failure of the sample is very definite and could be attributed to fatigue or breakdown of the fibrous interlock (Glynn, Kirwan and Wilson, 1968).

-N

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27

-THE VANE TEST IN ORGANIC SOILS R. P. Northwood and D. A. Sangrey

Abstract

In situ vane tests were carried out in a nurnbe r of different rnu s ke g deposits to exarnirie the rne c ha ni s rn of failure and

the effect of variation in vane size and speed of testing. The failure

rrie chanis rn in peat was found to be s irni la r to that in soft clays. The apparent shear strength varied with vane size but was independent of

testing speed. There was an o pti rnurn vane size of 10 CITl d iame te r .

Block s ampl e s were obtained fr o rn one site for laboratory vane tests to investigate anisotropy in the strength of the

peat. In situ tests for anisotropy using vanes of varying shape co nfi rrne d

the laboratory results, and showed that strengths on the vertical plane could be 100 per cent higher than those on the horizontal plane.

- ':::

-TESTS AU SCISSOMETRE VANE, DANS DES SOLS ORGANIQUE

ResuITle

R. P. Northwood et D. A. Sangrey

Des essais in situ au s cis sorriet r e vane ont ete effe c tue s dans plusieurs de pot s de rno s k eg d iffe r errts afin drexarrrin e r I a rne cani s rne

de rupture et lteff et produit par des variations de la grandeur de la vane

et la vitesse des e a s ais , Le rne c ani s me de rupture de la tourbe s 'est revele entre s ernbl.abl e

a

la vitesse dtes s ai , La dirrie ns io n o ptimum de la vane est 10 CITl de d iarn et r e .

Les blocs echantillons ont ete 0 btenu d 'un endroit pour

des e s s at s en laboratoire, afi n de d e te rrriine r anisotropie dans la force

de la to u r be , Les es sais in situ pour 1 'anisotrophie en utilisant des vanes

de diff e r ente s dIrnerisio ns ont co nfi r me Les r e s ultats de laboratoire, et

ont rrio rrt r e que les forces de Le plan vertical pouvait ｾｴｲ･ plus de 100

pour-cent superieur

a

-Introd uction

The field vane test is us ed extensi vel y for the determi-nation of the s hear strength of peat in highway and railroad construction.

It is a simple and relatively inexpensive test which generally gives

satisfacto ry results. There are, however, some factors peculiar to

organic soils which make the test results more difficult to interpret

in these soils than in soft inorganic clays. These factors have been

raised in various publications and are the subject of study in this paper. In an investigation into pavement performance over muskeg in Northern Ontario, MacFarlane and Rutka (1962) showed that in some peat deposits the apparent shear strength measured with

the vane varies with vane size. They used standard vanes, with vane

height equal to twice the vane diameter, and found that in several different deposits the apparent shear strength increased as the vane size decreased.

Helenelund (1967) carried out tests in a very fibrous

peat, also using standard-shaped vanes but with varying numbers of

blades. He showed that there was an unusual failure mechanism in

this type of peat; there being no well-defined failure surface. The

peat tended to squeeze out between the vane blades during the tests and to rebound on further rotation, giving more than one peak strength value.

Finally, there is evidence that some peats show anisotropic strength behaviour (MacFarlane, 1961) and this may also affect the apparent strengths measured with standard vanes.

Muskeg Deposits and Apparatus

In order to obtain more detailed information on the above factors, a program of vane tests was carried out in three areas of muskeg

terrain in Southeastern Ontario during the sum.m.er of 1968. The organic

soils were of varying types, and details of their properties and classifi-cations are given in Table 1.

At Sydenham the soil at one metre depth was a mossy peat strongly reinforced by larger fibres derived from roots and the remains

of large woody plants and bus hes. Below the peat, at 3 metres depth,

was an organic marl with no significant reinforcing fibres. At Mer Bleue

the peat was similar to Sydenham with a mossy matrix but with much weaker reinforcing fibres, derived from the remains of small plants. The peat at Lyndhurst was woody and consisted of branches, twigs and roots from large trees in a matrix of partially decomposed leaves and small plants.

29

-The "Jonell and Nilsson" Swedish vane apparatus used

in the investigation is illustrated in Figure 1. The apparatus consists

of a heavy duty portabl e bo ring rig with a sys tem of hand cranking fo r

inserting and withdrawing the vane. Torque is applied to the rods by

hand through a variable geared loading device in the vane head, which also contains pressure sensitive recording paper on which a record

of torque and rotation are inscribed during the test. The vane is

attached to the rods by a slip coupling which allows rotation of the

rods through 15 degrees before torque is applied to the vane. By this

rne an s the torque due to rod friction in each test is recorded, and may be substracted fro m the peak torque rn ea s u r e d .

A series of vanes of standard shape with four blades was built for tests to investigate the effect of variation in vane size. Vane d Iarne te r s were 5 CITl., 6.5 CITl., 8 CITl., 10. 5 CITl., and 13 CITl.

A 45-degree vane of the type used by Aas (1967) for anisotropy tests

in clay was also built. All the vanes were made of very high tensile

steel and had low area ratios for rni ni murn soil disturbance during insertion.

Testing Procedures

P'r e limi na r v tests were carried out at Svderiham and Lyndhurst to d e te r rrii ne a suitable testing speed for tests in peat. The ti rne to failure in a series of tests was varied between a few seconds

and two to three hours. It was found that within the lirnits of accuracy

of the test in peat, there was no noticeable variation in apparent strength

with test speed (Figure 2). Since excess pore water pressures are surely

generated in the failure zone, such behaviour can only indicate co mpl et e drainage, an i.rnpo s sibi.lity for the fastest tests, or else an effective

stress shear strength for peat which is constant in the range of low no r mal

stresses. In this pr'o gr arn a standard test speed of 0.4 degrees/sec. ,

was chosen, since this speed was rno st convenient for use with the

Swedis h apparatus.

At least four tests were carried out with each vane

within a Hrnited area at each site. The tests were repeated at 2 or 3

different depths and the horizontal 'and vertical distance between adjacent

tests was rriai ntain ed at one rne tr e where pes sible. Many of the tests were

extended beyond the peak value of torque up to 360 degrees of rotation,

to d e te rrnine if rno r e than one peak value of torque was obtained. A few

tests were carried out close to the surface at each site so that the rne c ha ni s rn of failure could be ex.arrri.ne d visually.

f'ro m the peak torque with a correction for rod friction. The peat was as s um e d isotropic and a failure surface with a height and diarrie te r equal to that of the vane blades was a s s urn ed .

Effect of Vane Size

Helenelund (1968) considers the strength of undisturbed

peat to be derived both fro rn the fibre strength and fro rn the strength

of the peat rnatr ix . Due to their very low densi ty, the peats tested in

this pr o g r am exist under very low effective stresses. For this reason

the strength derived f ro rn frictional behaviour must be low and the rnain

part of the peat strength rriust be derived fro rn fibre interaction. This

strength, which is independent of no r m a l stress at low effective stresses,

is derived fr o rn interaction between the rnain reinforcing fibres of the

peat, and fr orn s irni la r interaction between the srnal l e r , finer fibres

in the peat rriat r ix, The preliITIinary tests carried out at varying speeds

co nfi r m this strength behaviour. The strength appears to be independent

of the degree of drainage, or pore water pressure, and therefore cannot be of p r edo rrii na.n tl v frictional nature under low effective confining stresses.

The results of individual tests in the peat at Svde nharn

are shown in Figure 3(a). There is a lower lirni.t to the apparent strength

at around 0.11 Kg. /sq. CIn which represents tests where the reinforcing

fibres have the least influence. The peat rria trix strength is probably

close to this strength but slightly below it. The test results are scattered

and the scatter increases with decreasing vane size, since individual reinforcing fibres have rno r e influence on the s ma l.l e r varie s , Any given reinforcing fibre requires the s a rne stress on the failure surface to break

it or pull it out whether the vane is large or srn a.ll , This stress is, however,

large co rnpa r ed with the stress required to shear the rna trix and the reinforcing fibre increases the apparent strength obtained fro In the

srnal le r vane by a greater percentage than that fro rn the larger vane. The

effect is dependent on the spacing of the reinforcing fibres relative to

the vane sizes used. When the vane size used is large enough to ensure

that a representative nurnb e r of reinforcing fibres is sheared in the rna jo ritv of tests, the scatter of results is s mal l and the average is representative of the average strength of the peat.

Figure 3(b) shows the rne an values of the apparent

strength in the peat at Syd e nharn and the statistical standard deviation

f'ro rn the rne an , The 10.5 CIn vane shows a low scatter of results with

a rn ea n strength of 0.15 Kg. /sq. CIn which represents the average

strength of the peat derived fr o rn the fibre and rnat r ix strengths. At

vane sizes below 10.5 CIn the vane is too s ma l l to effectively give a reasonable average strength, and the standard deviation increases

31

-site it was found to be irnpo ssible to insert the 13 CIT1 vane by no r rna l

rne an s , due to the high fibre strength, down to one rne tr e depth. The

single result was obtained by preboring a hole, and represents the strength in a slightly disturbed condition.

The rne an apparent strength values at Sydenharn do

not lie on a SIT100th curve, probably due to variations in peat strength

within the test area, but the general trend of results is sirrii.la.r to

other sites. Figure 3 shows the rne a n apparent strengths at seven

locations in Eastern Ontario. In the organic rna r l at 3 rnet r e s depth

at Syden harn there are no reinforcing fibres, and, consequently, no

variation in measured strength with vane size. At Lyndhurst and

Mer Bleue the results follow the same pattern as those in the peat

at Sydenham. The mean strength remains constant for the larger

vanes but below about 8 to 9 cm diameter the measured strength tends

to increase as the vane size decreases. The percentage increase in

apparent strength with the smaller vanes becomes larger as the mean strength increases, and the mean strength at these sites increases as

the strength of the reinforcing fibres increases. There were no problems

in the use of the 13 cm vane at Lynd hurst and Mer Bl.e ue , and the standard deviation of the results with each vane at these sites decreased as the vane sizes became larger in a roughly linear relationship.

MacFarlane and Rutka (1962) published apparent shear strengths obtained in a muskeg deposit with different sizes of vane. A typical result has been plotted on Figure 4 for comparison purposes.

The results from the two larger vanes are close to the pattern of results at Sydenham but the results from the small vane seem unusually high. MacFarlane and Rutka suggest that their unusual results may be due to

rod friction, dial error or peat structure. Since the increase in apparent

strength with the smallest vane is higher than the increase due to structure in other peats, it seems probable that the high result is due to

under-estimation of the effect of rod friction.

In the three deposits tested, the rrnrnrnurn vane

diameter for consistent results was about 8 or 9 crn.. , but it is possible

that in other types of peat the rnirrirnurn diameter might be higher.

Since a 13 ern. diameter vane is difficult to insert in some types of peat,

the optimum vane size for general use in peat is about 10 ern (or 4 inches

diameter.

Anisotropy in Peat Strength

A 45 -degree vane (Aas, 1967) was manufactured to

in an isotropic soil. Comparison of the results from these two vanes at Lyndhurst showed that the ratio of the apparent strength with the conventional vane to that with the 45-degree vane varied between 1.1

at one metre depth to 1. 3 at three metres depth. Since the conventional

vane measures strength mainly in a vertical plane, whereas the 45-degree vane measures the strength in two directions at right angles, it seemed likely that the peat at Lyndhurst was stronger in the vertical direction than in other directions.

To verify the abo ve results, b10 ck samples were taken

from the peat at one metre depth for laboratory tests. A small laboratory

vane was inserted into the peat in the vertical and horizontal directions

and at 45 degrees to the vertical. The results showed that the strength

measured by the vertical vanes was 45 per cent higher than that measured by the horizontal vanes and that the strength on the inclined plane was

midway between the horizontal and vertical strengths.

If

conventional to 45 -degree vane strength of 1. 1 corresponds to a vertical

to horizontal strength ratio of 1. 45, it may be inferred that the vane

strength ratio of 1.3 at three metres depth corresponds to a strength

in the vertical direction about 100 per cent higher than that in the ho rizonta1

direction. This result is of considerable significance since it was not

readily apparent, from examination of samples taken by a peat sampler, that the peat strength behaviour was likely to be highly anisotropic. Examination of block samples, however, showed that the general trend was for branches and twigs in this peat to lie horizontally, and it seems

probable that this trend also existed in the finer material. In contrast to

the behaviour at Lyndhurst, the field vane tests at Mer B1eue showed that the peat at this site was almost isotropic in its strength behaviour. Hence, it can be seen that anisotropy may lead to problems in the inter-pretation of results from conventional vanes, and that these results should be used with caution especially if no detailed examination of the peat

structure is made. Mechanism of Failure

Visual examination of tests carried out close to the surface at all three sites, with a range of vane sizes, showed that there

was a cylindrical surface at failure in all tests. The highly disturbed

area of the failure surface was about 2 nun. wide. There was no evidence

of any squeezing out of the peat between the vane blades, although some compression occurred at the leading edge of each vane and a slight gap was noticed behind the trailing edge.

The torque -rotation curves for the tests at all sites showed that the torque rose smoothly to a peak at about 40 to 60 degrees

33

-rotation and then dropped slowly. The torque continued to drop

smoothly through as much as 360 degrees rotation with no evidence of secondary peaks, except for occasional tests where the vane hit a

large root or major obstruction. All the peats tested were fibrous

to s o m e extent, and the peats at Mer Bleue and Sydenham had a high

fibre content (F₂ on the von Post scale). The tests published by

Helenelund (1967) which showed secondary peak values of torque, were carried out in a peat COITlPO sed almo st entirely of fibres (F 2 - 3 on the von Post scale).

The above results indicate that peats rna y have a high fibre content and still show a no r rnal failure rn e c hanis rn , It appears that the only tests in which an unusual failure rne c hanis rn will occur are those in which almost the entire structure of the peat is

corripo s ed of the larger types of fibres. If an apparatus similar to

the Swedish apparatus is used, the record of torque against rotation gives an irnrnediate indication of any unusual failure rn e c hanis rn and, where this occurs, the results should be treated with caution.

Conclusions

The series of tests described in this paper have yielded further i.nfo r rna tio n on SOITle factors which affect the interpretation of

vane tests in organic soils. The following conclusions have been drawn

from the work:

1. The speed of vane testing in peat has little

effect on the rn ea s u r e d strength because the strength is essentially constant in the range of low effective no r m al stresses.

2. There is an o ptirnum vane size for tests in peat of about 10 CITl d ia me te r by 20 ern high (or 4 inches

by 8 inches). Srnal le r vanes tend to give higher

average strengths due to fibre effects, and larger vanes rriay cause practical difficulties in insertion. 3. Anisotropy in strength behaviour is of considerable

significance in some Canadian peats, and conventionally

shaped vanes rnay not record the average strength of

the peat.

4. Unusual rrie c ha ni s rns of failure in the vane test probably occur only in peats which are co mpo s e d alrno st entirely of larger fibres.

REFERENCES

Aas, G. Vane Tests for Investigation 0 f Anisotropy of Undrained

Shear Strength of Clays. Proceedings of the Geotechnical Conference, 0 slo, Vol. 1, p. 3, 1967.

Helenelund, K. V. Vane Tests and Tension Tests on Fibrous Peat. Proceedings of the Geotec hnical Conference, 0 s l o ,

Vol. 1, p. 199, 1967.

Compres sion Tension and Beam Tests on Fibrous

Peat. Third International Peat Congress, Canada, National

Research Council, 1968.

MacFarlane, 1. C. and A. Rutka. An Evaluation of Pavement Performance

Over Muskeg in Northern Ontario. U.S.A. Highway

Research Board Bulletin 316, p. 32, 1962.

Aspects of Research and Development of Roads Over

Organic Terrain in Japan. Canada, National Research

Council, Associate Committee on Soil and Snow Mechanics, Tech. Memo. No. 71, p. 149, 1961.

*

-Dis cus sion G. Hollingshead:

(1) You mentioned three peats, two of which were fibrous

and one amorphous. Which of these were tested for anisotropy with

the lab vane?

(2) Would the small size of the lab vane be a significant factor with regard to your conclusion concerning anisotropic strength? Authors' Reply:

(1) The laboratory vane tests described were carried

out on the peat from Lyndhurst. Due to the small size of the laboratory

vane, it cannot be used in many fibrous peats. The fibres in the peat

matrix at Lyndhurst, however, were generally short in relation to the

vane size. Furthermore, the laboratory tests were used only to confirm

35

-(2) No absolute values of strength were measured using the laboratory vane and the results were used only to compare strengths in different di r ec tioris ,

-

-F.A. Gervais:

(1) What is the ratio of vertical to horizontal vane shear strength?

(2) Do you use this average value along the slip circle when designing?

Authors' Reply:

(1) The ratio of vertical to horizontal shear strength is discussed in the section on anisotropy.

(2) An average value of shear strength should be acceptable

for most design purposes but this will depend to some extent on the shape

of the likely failure surface. The average strength of the peat may be

obtained by the use of a 45-degree or similarly shaped vane, or by

calculation from the results from two vanes of different height to diameter ratios.

-Table 1

Sydenham

Radforth Classification BDF

von Post Classification ｾ B₃F

2 R2VI

Density 1. 1 gm/cu. em

Average Moisture Content 700%

Mineral and As h Content 150/0

Lyndhurst Mer Bleue

AF EI

H 3_s"B3 F l R IV 3 H3B3F2R2Vl

1.1 gm/cu. em 1.1 gm/cu. em

600% 800%

37

o

•

•

o

•

-

-

.

•

o

i ·

2

_I

_{(0;----'1---'---}

I I

ｾ］ｾｾ］Ｚ［Ｚ］］ＭＧＭｔＬＭｮｮＭＭＧＭｔＧＢＢＢＢＧＢＭ

_a

I

.1

ｾ

I

-o

SYDENHAM I METRE (PEAT)

• SYDENHAM 3 METRES (MARL)

.1

I

10

TEST SPEED (DEGREES PER SECOND) LOG SCALE

:s

I

I

I

_A

6.

LYNDHURST 2 METRES (PEAT)

o

LYNDHURST 3 METRES (PEAT)

,

,

.1

I

10

TEST SPEED (DEGREES PER SECOND) LOG SCALE

ｾ

<t

.2

w

ｾ

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.

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Z

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FIGURE 2

INFLUENCE OF TESTING SPEED ON THE APPARENT SHEAR