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ALUR 1972-73

Stability of DykesEmbankments atMining Sites in theYellowknife Area

M. RoyP. LaRochelleC. AnctilCentre de recherches sur I'eauUniversite Laval

© Issued under the authority of theHon. Jean Chretien, PC, MP, Minister ofIndian Affairs and Northern DevelopmentlAND Publication No. QS-3037-000-EE-A1

This report was prepared under contract forthe Arctic Land Use Research Program,Northern Natural Resources and EnvironmentBranch, Department of Indian Affairs andNorthern Development. The views, conlu­sions and recommendations expressed hereinare those of the author and not necessarilythose of the Department.

ALU R 72-73-31

TABLE OF CONTENTS

LIST OF TABLES

LIST OF FIGURES

ACKNOWLEDGEMENTS

ABSTRACT

LEGEND

I. INTRODUCTION

II. GENERAL CONSIDERATIONS

2-1. Purpose of Mine Waste Embankments

2-2. Factors Effecting Stability ofTailings Embankments

2-3~ Methods of Design Analysis

i v

v

vii i

i x

x

3

3

4

6

2-3.1 Stability 6

2-3.2 Settlements 10

2-3.2 Seepage, Drainage and Water Bodies 14

III. DESCRIPTION OF SITES STUDIED

3-1. Location

3-2. Topography and Geology

i i

1 9

19

19

IV. RESEARCH PROJECT - GIANT MINE OF YELLOWKNIFE 23

4-1. Tailings System 23

4-2. Design of Dykes 23

4-3. Ground Temperature Observations 26

4-4. Thermal Regime 30

4-5. Settlement 32

V. RESEARCH PROJECT - COMINCO MINE 34

5-1. Tailings System 34

5-2. Design of Dykes 34

5-3. Ground Temperature Observations 36

5-4. Thermal Regime 38

5-5. Settlement 39

VI. DISCUSSION AND CONCLUSION 42

Stability 42

Settlements 44

Seepage 46

REFERENCES

iii

49

TABLE

I.

II.

LIST OF TABLES

Summary ground temperature installationsat Giant Mine.

Summary ground temperature installationsat Cominco Mine.

i v

PAGE

51

52

FIGURE

1 •

2.

3.

4 .

5.

6.

LIST OF FIGURES

Tailings disposal system of Giant &Cominco Mines of Yellowknife, N.W.T.

Giant Mine: General plan of tailingsdisposal system.

Giant Mine: Longitudinal profile oftailings disposal system.

Giant Mine: Grain size distribution ofmaterial in dyke No.3.

Giant Mine: Erosion resulting from waterseepage downstream of dyke No.2.

Giant Mine: Erosion resulting from waterseepage around a pipe incorporated in

dyke No.2.

PAGE

53

54

55

56

57

57

7 . Giant Mine . Dyke No. 3 ; cross sectionand instrumentation.

8. Giant Mine Dyke No. 3 ; location oftermocouple cables.

9. Giant Mine : Temperatures measured i nthe pond (GT 1)·

10. Giant Mine Temperatures measured in theground (GT 2, downstream of dyke No. 3 . ) .

11. Giant Mine Temperatures measured i ndyke No. 3 (GT 3)·

12. Giant Mine Isotherms between December1971 and March 1972 through dyke No. 3.

v

58

59

60

61

62

63

13.

14.

1 5.

16.

17 .

18.

19.

20.

21.

22.

23.

24.

25.

Giant Mine Isotherms between April andJuly 1972 through dyke No.3.

Giant Mine Isotherms between August andNovember 1972 through dyke No.3.

Cominco Mine General plan of tailingsdisposal system and drainage basin.

Cominco Mine Site plan showinglithological formation and the location

of instrument.

Cominco Mine Failure of the dyke byerosion during the thawing period.

Cominco Mine Dyke in construction onthe mining site.

Cominco Mine Cross section I-I andinstrumentations of dyke No.1.,

Cominco Mine Location of thermocouplesdyke No. 1.

Cominco Mine Termperatures measured inthe frozen ground (CT 2)'

Cominco Mine Temperatures measured inthe ground downstream of dyke No.1

( CT 1 ) .

Cominco Mine: Temperatures measured indyke No.1 (CT 3).

Cominco Mine Temperatures measured inthe pond (CT 4 ) .

Cominco Mine Isotherms through sectionI-I between January and April 1972.

vi

64

65

66

67

68

68

69

70

71

72

73

74

75

26.

27.

28.

Cominco Mine: Isotherms through sectionI-I between May and September 1972.

Cominco Mine: Isotherms through sectionI-I for October and November 1972.

Cominco Mine: Cross section II-II ofdyke No.1.

vii

76

77

78

ACKNOWLEDGMENTS

The present study has been greatly facilitated by a score of people

that it would be too long to name here. Nevertheless. we wish to

acknowledge. in particular. the helpful guidance and assistance of

officers from the departments of Northern Affairs and Energy. Mines

and Resources. in Yellowknife, N.W.T. Their constant help in

facilitating field trips and personal contacts is gratefully remembered.

Authorities from the two mines operating in Yellowknife. Giant Yellowknife

Mines and Cominco Con Mines, must also be thanked for their constant

cooperation in allowing researchers on their premises and bearing

with the inconveniences involved. We acknowledge also assistance

from the department of Environment Canada, in planning the program

and especially that of the Western Water Quality Station, in Calgary,

Alta., in providing with reliable and indispensable analytical services.

Finally we wish to recognize the assistance from researchers of the

University of Alberta.

vii i

SUMMARY

In this study, the major engineering factors relied to the

investigation, design and operation of tajlings embankments in

Arctic regions, are considered. Factors affecting stability of

tailings embankments and the methods of design analysis as stability,

settlement, seepage, drainage and water bodies, are discussed with

the considerations to the Arctic condition. Two mining sites have

been investigated to study the considerations on stability of dykes

embankments. The field investigations are located in Yellowknife

area, North of The Great Slave Lake in the Northwest Territories.

The following important points as tailings system, design of dykes,

ground temperature observations, thermal regime and settlement, have

shown that the design and construction of mine waste embankments in

northern regions must be approached in terms of the problems peculiar

to the extreme climatic conditions encountered in Arctic regions.

i x

LEGEND

INSTRUMENTATION OF TAILINGS DISPOSAL SYSTEMS

Giant bench mark ......................•.........•.

Comi nco Bench mark .............•..................

Gi ant pi ezometer ..........................•.......

Cominco piezometer

Giant thermocouple

New thermocouple cable Giant ....•.................

Cominco thermocouple ...•....•.....................

New thermocouple cable Cominco ..............•....•

Readi ng box ..•....................................

Thermocoupl e cabl e .•..............................

Dyke settlement gauge .................•......•....

"V" weir ...•......................................

Gi ant water outl et ...•.•..............•...........

Swi tch box thermometer .......................•....

Soi 1 thermometer ......................•...........

Water thermometer .

x

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I. INTRODUCTION

In order to establish mine regulations in the Northwest Territories,

a general engineering survey was undertaken in 1970 by the "Centre

de Recherches sur l'Eau" (CENTREAU) of Laval University on the

existing tailings disposal system located in the area of Yellowknife.

A major part of the objectives of the program was to undertake

studies for the design and operation of tailings disposal systems

in extreme climatic and permafrost conditions, and to develop

preliminary guidelines covering the design, construction and operation

of tailings dams. These guidelines may be placed into two broad

categories: guidelines concernina the safety of the dam and appurtenant

structures, and guidelines concerning the prevention of pollution.

Both types of guideline affect the design of the tailings embankment

facil Hies.

A good tailings embankment design must satisfy the basic requirements

of safety, poll uti on control, storage capaci ty and economy. To

achieve this, the design must be based on a thorough understanding

of both the geotechnical problems involved, and the requirements of

the mining development.

The purpose of the present report is to outline the major engineering

2.

factors that should be considered in the investigation, design

and operation of tailings embankments in Arctic regions. The

types of foundation, the stability of the dykes, the seepage and

the temperature regime in the dykes will be discussed from the

observations undertaken in the mines of Yellowknife.

It is not our intention in the present report to discuss at length

the problems associated with the design of tailings embankments, which

have already been treated in the "Mines Branch Technical Bulletin,

TB 145" (1972), and by Klohn (1972). However, we propose to

stress particular points related to the problems of construction

and operation of tailings ponds in Northern areas.

General considerations will be given in chapter II concerning the

problems of permafrost and of the freezing and thawing conditions

in the soils met in Arctic regions.

Field data obtained from the mining sites of Yellowknife will be

presented and discussed in chapters IV and V; these data concern

mainly design, settlement, seepage and thermal regime through dykes

under operation, at Giant Mine and Cominco Mine of Yellowknife.

3.

11. GENERAL CONSIDERATIONS

2-1. Purpose of Mine Waste Embankments

The purpose of waste embankments is the storage of solids.

However, tailings ponds usually must be used to store

temporarily a certain minimum volume of water for clarification

prior to reclaim for plant use or discharge to adjacent streams.

Usually~ the reclaim of water from tailings ponds will

requi re that a tai 1i ngs embankment retai n a certai n mi nimum

volume of liquid for sedimentation of the suspended solids.

Where tailings pond effluent would be a serious pollutant,

tailings embankments may have to be designed to retain as

much water as practicable. If this is not possible, it may

be necessary to treat the water prior to its release from the

pond.

In the Northwest Territories, where the climate is subarctic

in character with a long cold winter, a particular purpose of

the waste embankments is to accumulate water and solids during

the freezing period, or to operate all year round by an adequate

decantation system which can be operated in cold regions.

When the purpose of a waste embankment is to store solids,

D

the tailings embankments must be made relatively pervious.

However, the storage of solids and water requires the tailings

embankment to be relatively impervious.

The study undertaken in Yellowknife area, for instance at

Giant Mine and Cominco Mine, showed that the tailings embankments

built on these sites are of the pervious type. During the

winter, accumulation of ice and solids occurs in the ponds.

In these conditions, the accumulation of ice and solids requires

very large reservoirs to allow a continuous operation during

the long period of winter (7 to 8 months).

2-2. Factors affecting Stability of Tailings Embankments

The resistance to sliding along potential failure surfaces

within the embankment and its foundation is a prime factor

affecting the stability of an embankment. Shear strength

of the material, both cohesive and frictional, and the pore

water pressures at the failure surface, control the resistance.

Cracking of embankments, which is caused by differential

settlements, reduces the shearing strength along potential

failure surfaces.

In cold regions, where continuous and discontinuous permafrost

zones exist, the strength properties of frozen soils are

4.

greatly reduced following an increase in temperature and

when the soil is thawed, the strength may be lost to such

an extend that the foundation will not support even light

loads. Following thawing, fine-grained soils, which have

high moisture contents turn to a slurry with little or no

strength, and ·settlements and perhaps failures in foundation

and/or in the embankments may occur. Frost action in the

active layer, which freezes and thaws seasonally, may also

affect the stability of tailings embankments.

The following features of permafrost are significant in

construction of tailings embankments in Arctic regions:

a- the delicate natural thermal equilibrium is particularly

sensitive to the natural or man-made change in the surrounding

conditi ons ,

b- permafrost is relatively impermeable to moisture and,

c- the ice content of frozen ground is a most important

consideration. Fine-grained materials and organic materials,

which usually have extremely high ice contents and are

susceptible to freezing action, present the most severe problems.

As long as the water remains frozen in such soils, the ice

binds the individual particles together to produce a material

with considerable strength; when thawed, however, these soils

may change to soft materials with low or no strength.

5.

6.

2-3. Methods of Design Analysis

The methods of design and analysis for tailings embankments

including its foundation and abutments must meet the following

criteria:

i) The embankment and abutment must be stable and must not

develop objectionable deformation under all conditions

of construction and operation.

ii) Seepage through the embankment, foundation and abutment

must not result in piping, sloughing or solution of

material.

The approach to design consists in arranging embankment

materials in a tentative section with regard to strength,

permeability and economy, and performing some form of analysis

to estimate the stability of the proposed section under

anticipated loading conditions.

2-3.1 Stability

The result of a stability analysis is usually expressed

in terms of a safety factor, which is the ratio of

the average shearing resistance mobilized along a

potential surface of failure to the shear stress

acting along that surface and resulting mainly from

the weight of the material over that surface. The

results of the stability computations depend on the

shear strength selected, on the pore water pressure

acting along the surface and on different other factors

influencing the method used for computing the factor

of safety.

The current procedures used for determining the safety

factors of tailings embankments are based on the following

fundamental methods:

i) Method of circular arc.

ii) Method of planes or wedges.

iii) Method using combinations of arcs and planes.

As stability analysis is a procedure of successive

trials, a potential failure surface is first chosen and

the factor of safety against sliding along that surface

is determined. Different potential failure surfaces

are then selected and the analysis is repeated until

the most critical failure surface corresponding to

the lowest factor of safety is found. The factor of

safety against sliding along the critical failure surface

is the relevant factor of safety for the slope.

7.

The construction of tailings embankments on terrain

underlain by permafrost will often alter the thermal

regime to such an extent that melting of permafrost

may result. Some examples in which this phenomenon

has occurred are impounding of reservoirs, stripping

of vegetation and the effects of building foundations.

At a low rate of melting, the ensuing water will flow

from the soil at about the same rate as the ice is

melting. No appreciable excess pore pressure will

result and settl ement will proceed concurrently with

thawing. However, if thawing occurs at a faster rate,

excess pore water pressures may be generated, and may

andanger the stabil ity of the embankment. Slopes may

become unstable and tailings embankment foundations

may fail.

Frozen slopes, of course, have a high degree of stability

but the active layer, when thawed, may reach a delicate

state of equilibrium. Of greater consequence, however,

is the fact that if a surface disturbance results in

a deeper active layer, the newly thawed permafrost may

be less stable than the soil in the older active zone.

The stability of thawing soil is difficult to analyse.

8.

9.

In fine-grained soils where high ice content is

being thawed rapidly, the shear strength may become

negligible at different periods of thawing. As rapid

thawing usually does not occur under practical conditions,

it may be expected that some consolidation occurs as

thawing progresses with some increase in soil strength.

McRoberts (1972) suggested that quantitative stability

predictions may be made by investigating the effects

of excess pore pressures that result on the thawing of

frozen soils. The work of Morgenstern and Nixon (1971)

shows that the factor of safety against the excess pore

water pressures due to thawing consolidation and

resulting parallel seepage, is given by the following

expression:

F L [1 1~ 2~Jtan f= -y tan 8

where F = factor of safety

y I , Y = effective and total unit wei ght

e = slope angle

~I = effective strength parameter

= thaw consolidation ratioR =a

·2'ICVCv = coefficient of consolidation, and

with

a = rate of thaw, a constant in the

Newmann's solution.

This study indicates that any natural or artificial

change that increases the rate of thaw will contribute

to the slope instability and that the predominant

variables Whlch influence both the rate of thaw in

frozen soil and the rate at which the water produced

by thaw can be squeezed out of thawed soil, are of

fundamental importance in thaw slope stability.

Excess pore pressures and the degree of consolidation

in thawing soils are dependent principally on the thaw

consolidation ratio R. This parameter is a measure

of the relative rates of generation and expulsion of

excess pore fluids. As a first approximation, a value

of R greater than unity would appear to predict the

danger of sustaining substantial pore pressures at the

thaw front and hence the possibility of instability.

This analysis is capable of extension to a variety of

melting and loading conditions of practical interest.

However, considerable laboratory and field data are

needed to assess the practical limits to the application

of this analysis.

2-3.2 Settlements

The weight of a tailings embankment, together with that

10.

of the water reservoir overlying the upstream slope~

causes settlements in the foundation~ ranging from

a few inches at sites with hard rock to many feet

at tailings embankments underlain by thick deposits

of compressible soils such as clay and muskeg.

The magnitude of the foundation settlement will depend

on the height of the embankments~ the depth and

thickness of the compressible strata within the

foundation and their compression indices. The rate

at which the foundation settlements occur will depend

on: the magnitude of the change in vertical stress~

the permeability of the compressible material ~ the

drainage characteristics of the foundation and the

conditions prevailing in the foundation such as thawing

of frozen ground. Where finp.-grained soils with high

ice content are encountered in the zone of continuous

permafrost~ every effort can be made to preserve the

frozen conditions, and minimize settlements. In some

cases~ in either the continuous or discontinuous zone~

it may not be possible to prevent thawing of the groun9

during the life of the embankment and settlement must

therefore be anticipated and taken into account in the

design.

11.

As discussed in the previous section, the excess

pore water pressures generated in tailings embankments

by thawing will cause important settlements and

differential settlements may be aggravated.

A recent study by Morgenstern and Nixon (1971) has

shown that the excess pore pressures .end the degree

of consolidation in th~wing soils are dependent

principally on the thaw consolidation ratio R defined

by the following expression:

12.

R ex= 2VC;

where R is the thaw consolidation ratio

a is a constant determined in the solution

of the heat conduction problem, and

Cv denotes the coefficient of consolidation.

As a first approximation, a value of R greater than

unity would appear to predict the danger of sustaining

substanti a1 pore pressures and hence the possi bil i ty

of instability.

To prevent settlements, foundations and engineering

facilities in permafrost areas are usually designed to

preserve the frozen condition of the ground in order

to prevent thawing with potential settlement and

stability problems, and to utilize the relatively

high strength of frozen material. Where thawing of

the frozen ground cannot be prevented, the rate and

extent of degradation are factors that must be taken

into consideration in the design. The thermal interplay

between the atmosphere, the structure and the ground

are basic considerations in foundation design.

Preventing degradation and encouraging aggradation of

permafrost is accomplished by insulating the-ground

surface, isolating the structure from the ground, or a

combination of both methods. Fills or pads are widely

used not only for foundations but also to protect the

surface cover from disturbance due to construction

operations.

Lachenbruch (1959) has shown that the ability of a

fill to maintain the frozen condition in the foundation

material depends on its diffus tvt ty and thermal contact

coefficient and the contact coefficients of all underlying

layers which are sufficiently close to the surface to

produce appreciable effects.

13.

Because of the possible effects that thawing the

permafrost may have on the integrity of structures

and stability of the terrain, it is imperative that

engineers acquire the capacity to predict the

consequences of their activity on ground temperatures,

and develop design and construction techniques that

will be acceptable for permafrost areas.

2-3.3 Seepage, Drainage and Water Bodies

One of the most important considerations in the

design of dykes and tailings embankments for a given

site is the choice of a cross section in which the

seepage forces will be located so as to cause no

trouble, or will be controlled in a positive and

efficient manner.

Cedergrin (1968) specified that most failures caused

by ground water and seepage can be classified in one

of the two following categories:

i) Those which take place when soil particles

migrate to an escape exit, causing piping or

erosional failures;

ii) Those which are caused by uncontrolled seepage

pattern and lead to saturation, internal flooding,

excessive uplift, or excessive seepage forces.

14.

Provisions for seepage control have two independent

functions: reduction of the loss of water to an

amount compatible with the purpose of the project, and

elimination of the possibility of a failure of the

structure from piping.

Control of seepage pressures and resulting erosion

are the important considerations for the stability of

tailings embankments. Regardless of the rate of

leakage, seepage pressures must be controlled so that

quick conditions and piping do not develop.

Pollution control requirements may necessitate the

use of special design features, such as impervlous

cores, cut-offs, blankets, etc ... to maintain the

rate of leakage from the tailings ponds within tolerable

1imits.

The position of the phreatic surface within an embankment

has a marked influence on its stability. If the

permeability of the bulk of the embankment fill is of

the same order of magnitude or is less than the tailings

adjacent to the embankment, drains should be provided

beneath the downstream shell of the embankment to

15.

lower the phreatic surface. The drainage system may

consist of granular blankets or strip drains.

The use of such drainage systems may be of a good

efficiency in most areas through Canada. However,

in Arctic region, it is not guaranteed that the same

systems may operate properly. Frost penetration below

the downstream face may reduce considerably the

effectiveness of drainage which may become blocked

by ice. The formation of ice and surface sloughing

with subsequent thawing may cause sink holes and"-

sliding of slopes. Even worse, they may create voids

in the embankment, which, if connected to the upstream

face, may result in concentrated seepage flows and

possibly lead to failures by piping.

The thawing effect of water is of particular importance

to the engineer in the design and performance of

structures that impound water, such as dams and dykes.

Due to the relatively high heat capacity and latent

heat of water, a large amount of heat can be transferred

from one area to another by seepage or stream flow,

or by evaporation and condensation. Because of its

16.

heat storage capaci ty, surface and subsurface water

exerts an important influence on the ground thermal

regime. Standing and moving bodies of water can

inhibit the formation of permafrost. Flooding or

ponding of water in areas underlain by permafrost

imposes a new temperature on the ground surface.

Thawing of the permafrost may occur as the ground

thermal regime adjusts itself to the new conditions.

In permafrost areas a thawed zone is always found

under 1akes and streams that contai n unfrozen water

throughout the year. Although such water bodies have

the greatest thermal effect on permafrost, small ponds

that freeze to the bottom each winter also influence

and modify the ground thermal regime. The thermal

effect of a water body can be felt not only below but

also to some distance beyond the waterland interface.

Where a thawed basin exists beneath a lake or stream

the boundary between the unfrozen and frozen materials

is usually found at or immediately adjacent to the

edge of the water. However, its location depends upon

a number of factors including the water depth, soil

type and thermal characteristics of the water and

soil. Examples of changes in the ground thermal

17.

regime under lakes and reservoirs in permafrost

areas have been reported by Johnston and Brown, 1964

and Johnston 1969.

Interruption of the natural surface and subsurface

movement of water may have serious consequences if

drainage is not considered or inadequate drainage

facilities are provided. The effects of even shallow

ponds as observed in tailings ponds of mines of

Yellowknife, which mayor may not freeze to the bottom

during the winter, must be recognized. Settlement and

stability are major considerations but, in addition,

the availability of moisture can introduce or increase

the detrimental effects of frost action on structures

and engineering facilities.

18.

III. DESCRIPTION OF SITES STUDIED

3-1. Locati on

The mining sites studied in the field investigations

described in the present report are located in

Yellowknife area, North of The Great Slave Lake,

along the Yellowknife Bay in the Northwest Territories.

The two mines are Giant Mine and Cominco Mine of

Yellowknife.

The Giant Mine, property of Yellowknife Mines Limited,

is on the north shore of Great Slave Lake (62 0 30 1 N,

114 0 21 I W) adjacent to the mouth of the Yellowknife

River, and approximately four miles north of the town

of Yellowknife (fig. 1).

The Cominco Mine is located a few miles southwest of

the town of Yellowknife (62 0 27 1 N, 1140 281 W) as shown

on fig. 1.

3-2. Topography and Geology

The topography of the Yellowknife District is typical

of the Precambrian Shield. Viewed from Berry Hill which

19.

is the highest topographic feature within the district,

the country is a peneplain strongly lineated by many

valleys and rocky hills. With the exception of the

lakes, the rivers and the organic deposits, the district

features a surface of a nearly continuous rock outcrop.

Exceptional opportunities exist for the observation and

the study of the complex g~ological features, due to the

fact that 1arge forest fi res have destroyed the once

existing moss, lichen, and tree growths.

The district was once severely glaciated during the

Plei stocene and errati c "roches moutonnees II, outwash sand

gravel plains, eskers, glacial lacustrine clays, and

other glacial features, are present in many areas. The

town of Yellowknife is built on a sand plain east of

Sand Lake, and the airport rests on the broad sand plain

south of Long Lake. The sand plain offers excellent

cons tructi on sites. Abandoned beaches are found 1ocally

throughout the area. These are located at least 240 feet

above Great Slave Lake in places and probably represent

glacial material that has been reworked by wave action.

Yellowknife is in a region of discontinuous permafrost.

According to Bateman (1949), permafrost is absent beneath

rock ridges or outcrop areas, but is generally present

20.

beneath deep overburden. He states that the depth of

permafrost, which in some areas goes to 280 feet or more,

is directly related to the thickness of the overburden.

The same author suggests that the permafrost may have

originated in late glacial time and was preserved by

the insulating cover of clay, sand and muskeg. He mentions

also that ice veins, filling cavities in late faults and

fractures, have been observed in the permafrost zone

down to depths of at 1east 250 feet.

All the consolidated rocks within the district are

Precambrian in age (Henderson, J.F. &Brown, I.C., 1966).

The oldest rocks, division A of the Yellowknife group,

are a success i on of mass i ve and pillowed andesite and

basalt flows with interbedded dacite flows, tuffs and

agglomerates. Some flows are pillowed and variolitic

along strokes for several miles and afford excellent

horizon markers. The rocks of division B comprise a

thick series of sediments including greywacke, slate

quartzite, arkose, argillite and phyllite. Near the base

of the series, dacites, trachytes, agglomerates and tuffs

are interbedded with some conglomerates and greywacke~

The regional climate, though naturally severe, is not

unpleasant. The summers are short, but warm, and the days

21 .

pleasantly long; temperatures occasionally reach the

high 80's; August is the warmest month with a mean

temperature of 60°F. The converse is true of the winter

months, with January averaging -20°F. The mean annual

air temperature at Yellowknife over the past 22 years

is 240F. Annual precipitation is low at slightly less

than 9 inches per year, of which approximately 5 inches

is rain.

22.

IV. RESEARCH PROJECT - GIANT MINE OF YELLOWKNIFE

4-1. Tailings System

The tailings disposal of Giant Mine is composed of a

series of three ponds which are separated by dykes.

Water outflows from pond 1 to pond 2 and from pond 2

to pond 3. The limits of the basin are well defined by

rock outcrops and partly by the dyke No. 3 as shown in

fig. 2. The drainage area of the tailings water shed is

about 0.165 square mile.

The flow direction inside and outside the tailings ponds

is shown in fig. 2. The water of the tailings is flowing

into the Baker Creek and then to the Great Slave Lake.

23.

Materials such as clay, sand and gravel, are the principal

constituents of the surface deposits met in and around the

tailings disposal system. The working of the system has

been previously described in the annual report LURE 3 (1971).

4-2. Design of Dykes

A longitudinal profile of the actual ponds created by a

series of rockfill dykes are shown in Fig. 3. It can

be observed that the dykes No.1 and No.2 have been built

over rock foundation, whereas the dyke No.3 has been

built over an old tailings deposit.

These dykes have been built of crushed rock from the mine.

The grain size distribution curve given in Fig. 4 gives

an indication of the size of rock used to build the dykes.

The dykes, constructed entirely of the same material, are

homogeneous dykes. Very low dykes are almost made of

homogeneous material, because their construction tends to

become unduly complicated if they are zoned. However, the

dyke may then have an internal drainage system.

The use of crushed rock dumped from trucks and leveled

by bulldozers with no compaction, resulted in a non­

homogeneous grain size distribution of the material. No

drainage system, such as downstream or blanket drains, has

been incorporated in the dykes.

Any homogeneous dyke with a height of more than about

20 to 25 feet should be provided with some type of drain

constructed of material appreciably more pervious than

the soil of the dyke. The purpose of such a drain is

twofold:

24.

a- to reduce the pore water pressures in the downstream

portion of the dyke and hence to increase the stability

of the downstream slope against sliding s and

b- to control any seepage water as it exists at the

downstream portion of the dyke in such a way that

the water does not carry away soil parti cl es of the

dyke.

The seepage through the deposited rockfill is dependent

not only on the coefficient of permeability but also on

local variations such as fissures and large void ratio

in the structure of the crushed rock. Where potential

seepage is important s such as with tailings embankments

retaining waters the possible existence of such fissures

and voids should be considered. They often occur in the

foundations at the contact surfaces between the embankment

fill and the underlaying foundation and abutments; within

the fill itself s in the form of segregated seams of stony

material between layers and at contacts between pipes

and walls incorporated in the fill. The photos shown

in Fig. 5 and 6 illustrate this type of problems met in

the operation of rockfill dykes of Giant Mine.

As no specific rules can be given for selecting the

inclination of the outside slopes of the dykes s the general

25.

procedure is to make a first estimate on the basis of

experience. Homogeneous rockfill dyke on stable foundation

is commonly designed with slope equal to the angle of

repose of the material. The slopes of dykes observed

at Giant Mine are approximately equal to the angle of

repose of the material used, i.e. crushed rock. The

behaviour of these dykes appears to have ample safety

factor against shearing failure of the slope.

An examination of Fig. 7 shows that the dykes are built

from the old upstream construction type of tailings dams.

This type of tailings dams does not meet conventional

requirements for slope stability, seepage control (internal

drainage) and resistance to earthquake shocks.

4-3. Ground Temperature Observations

A complete description of instrumentation installed in

the dyke No.3, the tailings deposit and the ground

downstream the dyke has been described in previous annual

reports LURE 3, 1970, 1971. A summary of field installations

is shown in Table I and Fig. 8 of the present report.

Variations of temperature with respect to depth and

26.

time were observed for more than two years, and the

configuration of isotherm curves in the ground and in

the dyke are obtained from temperature readings. This

provides the opportunity to present a general view of

the total fluctuation during complete cycles. The

temperatures confirm that below a certain depth the mean

annual temperature is just above 32°F. During summer,

the surface warms up between 60° and 68°F. reaching its

maximum temperature usually in July or August, while

during the winter months the ground surface temperature

decreases to a minimum occurring in January. From Fig. 9,

10 and 11, we can observe the variations of temperature

registered by thermocouple cables GT, GT 1 , GT 2 and GT 3

shown in Fig. 8. The shape of the curves indicates that

there is a large difference in the temperature gradient

of the ground during warm and cold seasons. Snow cover

and frozen ground properties influence the rate of change

in the temperature gradient.

Temperatures observed on this site indicate that the

ground temperatures are oscillating with the air temperature

but at a smaller amplitude as depth increases. Measurements

made with thermocouple cable GT 2 shown in Fig. 10 indicate

that the mean annual temperature in the ground (old

tailings downstream of dyke) is about 32°F and is almost

27.

maintained constant below a depth of 20 feet. This

shows that below this depth, ground is permanently

frozen. Also between 4 and 20 feet, the change in the

temperature gradient is approximately zero under the

effects of the cold period, while large change is

observed under the effects of the warm period.

Thermocouple cable GT l is recording the temperature in

the waste deposits under water. The monthly variations

of these temperatures are presented in Fig. 9. These

results provide the opportunity to present a general view

of the total fluctuation during an annual cycle. The

temperatures indicate that under a depth of about 16 feet,

the tailing is continuously in unfrozen condition. A

small variation between 33 to 40 0F has been observed above

a depth of 22 feet, for an annual cycle. Between 0 -

6 feet, the temperature follows approximately the air

temperature at the surface of water, while in the upper

part of the tailing (between 6 to 16 feet) the temperature

decreases below 32oF. during the cold season and increases

during the warm season. Ice cover formed on the complete

depth of water and the frozen tailing underneath insulate

and preserve the unfrozen state of the ground.

28.

The thermocouple cable GT 3 installed in the dyke No.3

up to a depth of 37 feet below the crest of the dyke

has provided temperature data. Monthly temperatures

throughout the dyke obtained from these observations

are shown in Fig. 11. The results are similar to those

previously described for the tailings zone. Generally,

the temperature gradient decreases with respect to

depth according to the season. Below 22 feet, the

temperature is almost maintained constant with a time

lag in the temperature fluctuation relatively to the

surface temperature. It can be observed that during

the cold season, the temperature in the upper part of the

dyke decreases below 32°F without, however, reaching

the air temperature. The non-uniform temperature is then

influenced by the heat transfer in the rockfill mass.

These temperatures indicate that during winter, seepage

flow may be active in the dyke below the depth of about

22 feet. However, from Fig. 9, it is observed that no

more water is available under the ice cover in the pond

so that no seepage flow is taking place. Temperature

observations in the ground downstream of the dyke confirm

this result. Seepage flow from the pond may be active

only up to November or December. However, it should be

29.

mentioned at this point that the same situation would

not prevail if the depth of water in the pond would

have been greater.

4-4. Thermal Regime

Monthly isotherms for the three thennocouple cables

GT l , GT 2 and GT 3 placed along cross section perpendicular

to the dyke, have been interpreted from the temperature

observations and are shown in Fig. 12, 13 and 14.

The temperature pattern across the section of the dyke

varies with time according to heat losses and heat gains

due to variation in air temperature and in seepage

conditions.

The progression in the heat losses during the cold season

is very well illustrated in the monthly isothenn curves.

The formation of the ice cover is initiated during October

in the pond and downstream of the dyke. In the meantime

the permafrost may be observed to progress in the ground

downstream of the dyke. A continuous ice blanket in the

dyke is formed during January and a confined seepage flow

may be maintained for a certain period under that blanket.

30.

Later in the cold season~ the permafrost surface rises

in the ground and coalesces with the ice blanket which

had been thickening since the beginning of the cold

season. The isotherm curves of May 1972 (Fig. 11) show

a frozen ground up to the surface. This implies that

no seepage flow may be possible under that condition.

However~ it is difficult to assume that every year the

conditions are the same and that seepage flow is impossible

all year round. From the isotherm curves~ one can

observe that the ice cover increases downward in the

pond so that towards the end of the cold season~ no

water is available between the surface of the ground and

the ice cover. When this condition arises~ it becomes

evident that the confined seepage flow may not be maintained

all year round.

All interesting that these results may be~ they cannot

be generalized to every winter and every dyke in the Northern

area. The coalescence of the permafrost table with the

ice blanket depends upon many factors which have to be

fully appreciated when the design of a dyke is agreed

upon. Obviously the presence or absence of seepage plays

a major role in that phenomenon and is itself influenced

by the depth of water in the pond and by the freezing

index of the area. However, a proper use of heat transfer

theories may lead to realistic forecast.

31.

4-5. Settlement

Bench marks and gauges were installed during the summer

1970 in order to measure settlement of dyke No.3.

Details of the gauges have been reported in LURE 3, 1972.

The presence of tailings deposits underneath the dyke

should normally result in a large amount of settlements

in the foundation. The fill which consists of crushed

rock leveled by bulldozers does not contriJute appreciably

to the observed settlement which is mainly the result

of the consolidation of the foundation material. In May

1972, two years after the installation was completed,

level survey indicates a maximum settlement of about

8.5 inches. Comparatively to the settlement of about

6 inches reported in the 1972 report, the settlement

observed during the last year is not very significant.

Due to the fact that the dyke has been built during many

years and that no observations of settlements were taken

before 1970, it is very difficult to interpret that

behaviour since large settlements may normally be expected

to take place during construction and immediately after

in the following years. There are two possible explanations

to that behaviour. One being that the settlement of 2.5

inches observed during the last year corresponds to a

32.

secondary consolidation which is bound to decrease

during the coming years. However, it is also possible

that, depending on the yearly average temperature,

the permafrost table is more or less affected and

will appreciably influence the observed settlements;

if this so, the settlements might be erratic from one

year to another.

33.

V. RESEARCH PROJECT - COMINCO MINE

5-1. Tailings System

The tailings disposal system of the Cominco includes

a series of lakes, the first of which, Pud Lake, is

located just a few hundred feet from the mill (Fig. 15).

This area presents the same geomorphological aspects

as those found at Giant Mine with respect to the

general shape of the sedimentation basins, i.e. the

lakes are surrounded by rock outcrops. However, a

slightly flatter topography has been observed with more

frequent muskegs and blue grey clay deposits. Permafrost

occurs generally in and underneath the muskeg.

Between Kam Lake and Pud Lake, there is groundwater

exchange through a low muskeg valley. Cominco Mine

Company has cut off the valley to prevent the mill and

waste water from flowing to Kam Lake.

5-2. Design of Dyke

The actual ponds created by rock outcrops and dyke are

shown in Fig. 15. The dyke is built of crushed rock

from the mine. Due to the inaccessibility of the site

34.

by heavy equi pment duri ng summer, the dyke has been

constructed during wintertime over the ice and snow.

The material was simply dumped by trucks on the site.

The rock material composing the dyke is non-homogeneous

and the size of crushed rock varies from 0.25 inch to

12 inches.

In the deeper part of the valley, a dyke of about 5 to 8

feet high above ground surface lies on weak foundations

and is about 70 feet large at the crest. Where the dyke

lies on permafrost foundations, the width at the crest

decreases to 10 feet. A plan view of the dyke No.

and of the permafrost and unfrozen ground areas is

given in Fig. 16; this figure illustrates also the

superficial geology around the site of the dyke.

Fig. 17 shows by photo a partial view of dyke No.1

after the thawing period of last spring. The size of

crushed rock used to build the dyke is illustrated and

it can also be observed from that photo that the material

is non-homogeneous. That photo illustrates the failure

of the dyke by erosion during the thawing period. In

that period the pond size was too small to accumulate

water resulting from the thaw and erosion was initiated

35.

on the crest of the dyke up to complete failure by

a large breach.

Fig. 18 illustrates a dyke under construction on the

site. No preparation of the site and no study were

undertaken to investigate the soil conditions underneath

before the construction started. As mentioned above,

the crushed rocks were dumped by trucks over the ice

and snow cover.

5-3. Ground Temperature Observations

Four thermocouple cables were installed at the Cominco

Mine since summer 1970 in the drilled holes, as indicated

in Fig. 16 and 19,

the thermocouple cables CT 1 and CTz are located

downstream of the dyke: CT 1 is placed in the zone

of unfrozen muskeg and clay, and CT 2 close to CT 1

but in the permafrost,

thermocouple cable CT 3 is located in the dyke, and

the thermocouple CT 4 in the tailings disposal (Pud Lake).

Data on thermocouple lengths and respective positions

are given in Table II and Fig. 20. Complete informations

36.

on the instrumentation were presented in previous

reports LURE 3, 1971 and 1972.

Observations on the variations of temperature in soil

and water with respect to depth and time are quite

similar to those discussed for Giant Mine and the

interpretation is much the same.

The results obtained by thermocouple cable CT 2 located

in the ground outside the pond indicate permanent

permafrost in that area, the temperature is maintained

just below 32°F all year round, as shown in Fig. 21.

Measurements by thermocouple cable CT 1 (Fig. 22)

located in the ground downstream of the dyke indicate

a uniform temperature of about 30 to 320F during the

cold period and an increase in the temperature in the

first 10 feet during the summer period.

Fig. 23 shows the variations in temperature through

the dyke. One can observe that the temperature varies

with the air temperature with respect to depth and time.

It is interesting to note that the temperature decreases

below 32°F on the total depth of the dyke, which

37.

indicates that no seepage takes place during a part

of the cold season.

The temperatures registered in and below the pond is

shown in Fig. 24. Below a depth of 8 feet, the

temperature is maintained over 32°F all year round.

It can be noted that at the end of the cold season,

all water was frozen in the pond which implies that no

water was flowing under the ice cover at that time

and that seepage was thus impossible.

5-4. Thermal Regime

Monthly isotherms for the four thermocouple cable

installations CTI' CT 2 , CT 3 , CT 4 , placed along a

cross section more or less perpendicular to the dyke,

have been plotted from temperature observations and are

shown in cross sections in Fig. 25, 26 and 27.

As in the case of Giant Mine, the temperature pattern

is varying with time and is fluctuating in response

to the heat exchanges. It can be observed that in the

muskeg, clay and permafrost, the heat transfer is

slower, comparatively to that in the rockfill dyke.

38.

On the other hand, the temperature fluctuations

recorded in the dykes follow promptly the environmental

air temperature and the seepage water temperature.

Under the pond and the dyke, no permafrost has been

observed during the two years of observation. At the

beginning of the cold season, the ice cover forms

from the surface in the pond and in the upper part of

the seepage flow through the dyke. Later a confined

seepage flow may be maintained if water is still

available in the pond, which is shown by the monthly

isotherm curves of January and February 1972. However,

the isotherm curves of March and April 1972 show the

closing of the lce cover downstream from the dyke. This

implies that the confined seepage flow may be maintained

under the ice cover for a certain period or stopped

by the formation of ice in the total depth of the pond.

A complete cycle of the frozen and thawing period is

illustrated in Fig. 25, 26 and 27.

5-5. Dyke Settlement

Observations of the movements of the dyke have been

made by means of the bore holes and of a level survey

39.

on three settlement gauges. These gauges are

placed mainly on the centerline of the dyke built

over the unfrozen muskeg at about 100 feet intervals.

Along the cross section I-I, the large settlement that

has occurred in the unfrozen muskeg foundation may be

noticed in Fig. 17. It is estimated that, before the

dyke was built, the top elevation of the muskeg was

574 feet. Thus, the settlement at present is about

8 feet on the centerline of the dyke and it is not yet

compl eted.

Measurements taken on each settlement gauge after two

years and referenced to temporary bench marks established

on rock outcrops indicate that a vertical movement

varying from 0.65 feet to 0.94 feet depending on the

location of each gauge has taken place during that

time.

In fact, the volume of rock used to build the first

dyke at the beginning of the mining operation has just

compensated for the compression of the muskeg under the

weight of the rock material which was transported during

subsequent years to maintain the dyke crest at the

elevation of 579 feet.

40.

On the contrary! along cross section II-II (Fig. 26)!

the dyke built over muskeg and permafrost is still

stab1e. No appreciable settlement was encountered

and the permafrost table which has not been affected

by the dyke still constitutes a solid base foundation.

This may be explained by the absence of seepage through

the foundations in this section of the dyke where the

initial level of the surface is higher than in section

I-I. This implies that permafrost may be preserved

in the ground when no seepage takes place! or else

that seepage plays a major role in the melting of

permafrost under dykes.

41.

42.

VI. DISCUSSION AND CONCLUSION

The observations made during the present research project have shown

that the design and construction of mine waste embankments in northern

regions must be approached in terms of the problems peculiar to the

extreme climatic conditions encountered in these areas. The construction

of structures involving water bodies and seepage is bound to affect

the ground thermal regime and produce variations in the elevation of

the permafrost table. Although the precise behaviour of a dyke on

permafrost is difficult to predict, it is possible to define the main

factors which have to be taken into account in order to insure that

the structure will be stable and will fulfill its puroose.

Hence, the design and analysis of the tailings embankments and of

their foundations and abutments have been considered in the present

report under the different aspects of stability, settlement and

impermeability as they may be influenced by the presence of water

bodies and by variations in the ground thermal regime.

Stabi 1ity

The construction of tailings embankments or dykes on terrains underlain

by perma f rost will often alter the thermal regime to such an extent

that conditions of instability may result in the slopes or in the

43.

foundations. This occurrence will depend on the type of soil, its

ice content and the rate of thaw of the permafrost.

The rapid thawing of a soil with a low permeability and a high ice

content may temporarily cause a large increase of the water content

resulting in a build up of pore water pressure and a significant

decrease of the shear strength; such conditions may lead to failures

in the slopes or foundations. However, if the rate of thaw, the

permeability and the ice content of the soil are such that the water

produced by melting ice drains rapidly enough, the decrease of shear

strength may be prevented.

The dykes at Giant Mine and Cominco Mine of Yellowknife are built with

crushed rock having a very high permeability; hence no instability

conditions may develop in the slopes of the dykes due to pore pressure

build up. As for the foundations, it has been observed that the

permafrost table was affected by the seepage; however, no instability

conditions developed since the dykes were built by stages over the

years allowing sufficient consolidation to take place so that the

shear strength was kept well over the critical stresses.

Hence, when building a dyke in the North, it is essential to insure

that the pore water pressure build up following the thawing of the

permafrost in the foundation or of the seasonal frost in the slopes

will not result in instability conditions. This may be insured by

44.

a proper choice of dyke material, by an efficient control of seepage

in order to keep the permafrost thawing rate to a minimum, and by

a rational choice of the geometry of the slopes so as to keep the

stress level below the anticipated strength of the thawing soil in

the slopes or in the foundations.

Settlements

The settlements which are expected to occur during and after construction

of embankments depend usually on the compressibility of the soil in

the foundation or in the embankments. In most cases, the compressibility

of the fill material is fairly low so that the settlements observed may

be attributed to the presence of compressible soils, especially clayey

or organic deposits, in the foundations.

When such structures are built in northern areas, they usually rest

on foundations of permanently frozen soils with compressibilities which

are low and will remain so as long as the soil stays in a frozen state.

However, if the permafrost table is affected by the structure resting

on the surface in such a way that the soil thaws in the foundation,

considerable settlements may result depending on the ice content of

the soil; the settlements may be of such a magnitude that the tai 1ings

dykes may develop leaking problems which may lead to piping and

destruction of the structure.

45.

The dykes which have been observed in Yellowknife are built with

crushed rock and it is estimated that the compressibility of the

rock fill did not contribute appreciably to the over-all settlements

measured. Whenever the permafrost was affected by the structure and

especially by the seepage in the foundation~ considerable settlements

resulted where fine or organic soils were present in the foundation.

The major part of these settlements usually takes place during the-

first year following the construction of the dykes. If no seepage

is produced in the foundation the settlements are small or negligible.

Both these cases were observed in Cominco Mine: a certain length of

the dyke where seepage was observed to take place in the foundation~

has undergone very large settlements whereas in other parts of the

dyke~ where the permafrost foundation was not affected by seepage,

no movement could be observed.

Hence, when tailings embankments are built in northern areas on

permafrost foundations, 1arge settlements may be expected to take

place; the magnitude of the settlements must be estimated on the basis

of the ice content and of the compress i bi 1ity characteri s ti cs of the

thawed soils if a proper design of the dykes is seeked in order to

insure that they will fulfill their role as water and tailings

containers.

46.

Seepage

A proper operation of a tailings pond requires the confinement of

a body of water of sufficient volume so as to insure an efficient

sedimentation of solid particles before the waste water exists from

the pond. Both the surface of the pond and the depth of contained

water is of importance. The dykes must then be built in such a

fashion as to insure their impermeability to water under normal

conditions of operation. There are many possible techniques available

for achieving that purpose (see Mines Branch Technical Bulletin, TB 145,

1972). The design of tailings dykes for seepage control is pertinent

not only to northern areas but to any other regions and follows from

good engineering practice. Obviously, if the seepage through the

dykes is not under control, neither is the pollution downstrean of

the dykes.

In Yellowknife, the dykes are built with crushed rock; the resulting

porous material incorporates fairly large voids which allows important

leaks to develop in many places. As a consequence it was found

difficult and even impossible to build up a body of water of sufficient

volume for a proper sedimentation of solid particles to take place.

The evaluation of the volume of water to be stored in the pond must

take into account the fact that an ice cover forms rapidly at the

47.

beginning of the cold season, thus hampering the exit of water from

the pond and resulting in a cumulation of the effluent from the

plant in the form of ice layers.

It has been observed in the dykes at Yellowknife that at the same

time that the ice cover is forming in the pond, an ice blanket also

forms in the downstream face of the dyke. The seepage will then

be confined between the ice blanket and the permafrost table; that

situation will prevail until the bottom of the ice blanket progressing

down into the soil coalesces with the permafrost table, at which time

any seepage will be prevented. From the isotherm curves obtained,

it has been observed that the end of seepage coincides with the

time when the ice cover reaches the bottom of the pond so that no

more free water is available.

A situation is then reached when no more water is flowing out of the

pond neither by seepage nor by surface flow, so that the mine effluent

will have to be stored in the pond in the form of ice layers during

few months. If the usable storing volume of the pond is not

sufficiently large, the dykes may be overflown by layers of iced

effluent with undesirable consequences at springtime when the ice is

melti ng.

It has also been observed that, at springtime, the melting mine

48.

effluent is straming at the surface of the ice cover through the

pervious dykes without having properly sedimented its solid oarticles;

in this situation, the pond does not fulfill its purpose.

Hence, it seems quite obvious that in order to make an efficient

sedimentation pond, it is necessary to build a reservoir of sufficient

volume with dykes sUfficiently impervious to contain the effluent

of the mine plant during the cold season. In order to calculate the

required volume, many factors have to be taken into account including

problems of heat t rans.ter' as discussed in the present report. All

the observations made during the research program tend to show that

mine waste containment systems should be built with impervious dykes

if efficient pollution control is required.

There are many techniques available for insuring imperviousness of

dykes even if large settlements are to be expected. However, due to

the special conditions met in northern climate, it might be worthwhile

to study new methods which might have economic advantages over known

techniques. One of them being the use of peat as impervious core or

blankets in the dykes. Peat has the advantage of being a very common

material in the north; it is fairly impervious when compressed and

has thermal properties which might be used with profit in the geometry

of dyke in cold climate. Some more research should be done on this

aspect of the problem.

REFERENCES

Lachenbruch, A.H. (1959). "Periodic heat flow in a stratified

medium with .appl i cation to permafrost prob1ems". U.S.C.S.,

Dept of Interior, Geol. Survey Bull. 1083-A, Washington, U.S.A.

Morgenstern, N.R. and Nixon, J.F. (1971). "0ne dimensional

consol i dati on of thawi ng soi 1s ". Canadi an Geotechni ca1 Journal,

Vol. 8, No.4, pp. 558-565.

McRoberts, E. (1972). Special contributions; Proc., Can. Northern

Pipeline Res. Conf., Nat. Res. Council of Canada, Assoc. Comm.

on Geotech. Res. Tech. Memo, 104, Ottawa (NRC. 12498).

Bateman, C.D. (1949). "Permafrost at Giant Yellowknife". Trans.

Royal Society Can. 3rd Ser., ·Vol. 43, Sect. 4, pp, 7-11.

Johnston, C.H. and Brown, R.J.E. (1964). "Some observations on

permafrost distribution at a lake in the MacKenzie Delta,

N.W.T., Canada". Journal Arctic Inst. of N. Amer., Vol. 17,

No.3, pp. 164-175.

Johnston, C.H. (1969). "Dykes on permafrost, Kelsey Generating

Station, Manitoba, Canada". Can. Geotech. Journal, Vol. VI,

No.2, pp. 139-157.

49.

Henderson, J.R. and Brown, I.C. (1966). "Geology and structure

of Yellowknife greenstone belt, District of MacKenzie".

Geol. Surv. Can. Bull. 141.

Mines Branch Technical Bulletin, LB. 145, (1972). "Tentative

design guide for mine waste embankments in Canada".

Klahn, E.J. (1972). "Design and construction of tailings dams".

elM Transactions, Vol. LXXV, pp. 50-66.

50.

0DEPTH OF * ELEVATION TOTALw

CABLE-l

GroundTOTAL DEPTH

LENGHT OFLOCATION-l

THERMOCOUPLE POtNTS BottomN!! i5! surface OF THERMO ~

(f) or water of cable CABLEz ( ft. ) COUPLE CABLE- surface ( ft. )

GTTI,I,2,3,lLl,5,6,7,8,9,10,566.00

xGT1 12-09-70 594.00 28 280 c 0

12,14,16,18,20,24,28 0 .0

E s:E ~

GTT, 594.00 593.00 I0 ·i X18-07-71 0.9,1 253 U III 0

CD

GTT2 ,-2,-1,0,[TJ,2, 3,4,5,6,7, C>x Z

GT2 17- 09-70 8,9,10,12,14,16,18,20,22, 571.00 541.00 30 206 c 000 .0

GIANT DYKE N23 26 30 E <tE

s: w0 ~ a::

GTT2 18-07-71 0.9, I 571.00 570.00 I 174 u ·iIII z

0GTT ,-3,-2,-1,1IJ,1,2,3,4,5,6, :E

GT3 19-09-70 7,8,9,10,12,14,16,18,20,22, 608.26 569.26 37 53 c x :E0 00 .0

26,30,37 E uE s:

o0 -GTT3 18-07-71 0.9,1 608 .26 607.26 I 13 u .~

* Depth below original ground surface. Negative sign indicates above ground surface.

IIJ Represents thermometer for comparison point.

GTT Represents the new thermocouples cable installed in summer 1971.

Table I -SUMMARY GROUND TEMPERATURE INSTALLATIONS AT GIANT MINE

aDEPTH OF '* ELEVATION TOTALw

...J TOTAL DEPTHCABLE ...J Ground Bottom LENGHT OF

LOCATION <:{ THERMOCOUPLE POINTS surface OF THERMO-N!! I- CABLEU>( ft. )

or water of cable COUPLE CABLEZ surface ( ft. )--2,-1,0,1,2,3,4,5,6,7,8,9.10.

CTr I I, 12, I 3. 14 , 15,I 6.00 , 18 ,19, 574.69)(

10-09-70 550.69 24 143 c 00 .0

20,CTT1 E s:E 0-CTTI 57.4.69 573.69 I 1210 .~17-07-71 0.9, I U III

o .1/2, 1, 11/2, 2 ,3,4,5,6, 7, )( XCT2 15-09-70 577.59 555.59 22 189 c 0 0

8,9,Io,I2,rn,I6,I8,20, CTT20 .0 mE s:E 0 o0 - Z

CTT2 COMINCO 17-07-71 0.9, I 577.59 576.59 I 168 o .~

aIII<:{

DYKE WCTT3 ,20, 18,16,[I], 12,10,9,8, 0::

578.97 554.97 24 104)(

CT3 N!!I 20-09-70 c 0 Z7,6,5,4,3,2,1,0 0 .0E 0E .r. ~00 - ~

CTT3 17-07-71 0.9, I 578.97 577.97 I 80 o "3 0III U

CT40, 1,2,3,4,5,6,7,8,9,10,12,14,

576.25 546.25 30 128)(

25-09-70 c 016,00 ,20,24,28, CTT4 0 .0

E s:E 00 ~

CT T4 17-07 -71 0.9, I 576.25 575.25 I 99 u 3III

* Depth below original ground surface. Negative sign indicates above ground surface.

[I] Represents thermometer for comparison point.

CTT Represents the new thermocouples cable installed in summer 1971.

Table 2 -SUMMARY GROUND TEMPERATURE INSTALLATIONS AT COMINCO MINE. U1N

•

~

•

o

•Yellowknife Boy

Iscale in miles

•

••

53 .

Fig. I -TAILING DISPOSAL SYSTEM OF GIANT S. COMINCO MINES OF YELLOWKNIFE, N.W.T.

os

...

I

I BOO4~01e ,n feet

o

YELLOWKNIFE BAY

d 10 Iheions are refereThe eleva" G. nt mines.Note n of 'aoriginal pia

-~-~==~=~~~~:::-::POSAL SYSTEMOF TAILING DIS

I --====~~====-===============~~ GENERAL PLANT MINE,Fig 2 - GIAN

'27109/72

610

600

590

-s: 580C.Q)

a

570

PRELUDE ROAD

I,.. _1000'

Crushed rock

DYKE No:! II

..14 ~1800'

Crushed

DYKE No:! 2

I"1 4

I1

1

60520 .

t~1800'

DYKE N ~ 3I

.. I

III

~'

Crushed rock

550o 100 200 300 400 500I I, I I, I , I

Hor score , ff.

Fig. 3 -GIANT MINE. LONGITUDINAL PROFILE OF TAILING DISPOSAL SYSTEM. (See figure N!! 9)

23/12171

U"1U"1

mesh number mesh size

8 12

20030060 100

I~ 2 2Y 3 4

2010626.2

100 60 40 30 20 16 12 10 8

.1

200

.06

.. leve 4 '8 2 4 2 '2

/'/

/(~

//

I

rIJ

II

(

//

~~

w---- - - 1- - ~ ~ ~ ~- -IIII L IddIII I I I II I Ii I I I I I I I 1,1 I I I ,I ,I I

10

o.02

30

20

70

80

60

40

90

....Q)

c 50

~o

diameter ,mm.

sand grovel rock

fine I medium I coarse fine I medium I coarse

Fig. 4 - GRAIN SIZE DISTRIBUTION OF MATERIAL IN DYKE N~ 3 .

Fig. 5 Giant Mine - Erosion resulting from water seepagedownstream of dyke No.2.

57

Fig. 6 Giant Mine - Erosion resulting from water seepaqe arounda pipe incorporated in dyke No.2.

100I

Hor. scale, ft.

20 40 60 80I ,I I I

oI

TAILING DISPOSAL PLATFORMIIIIIIII

DYKEIIIII

630

620

610TC

600

~590s:a~ 580

570

560

550

540

Fig. 7 -GIANT MINE, DYKE N~ 3, CROSS SECTION AND INSTRUMENTATION

(See legend page no. x )<.nex>

23/12/71

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

, RB

GTzGTTz

GT3 GTIGTT1

PLAN

F:g. 8' GIANT- MI NE I DYKE N2 3 I YELLOWKNIFE IN. W.T

LOCATION OF THERMOCOUPLE CABLES

(See pOQe no )(.. for leQend)

CROSS SECTION

GTI

o

6050

'Y.L

II

t

~I,

40

.1

~,~

\

: T\T,r;'

I: ~ I \ • i: /., i I ,'.

I :.':' ~ " I

I ···-:r:y: , ~ /\,"' .'.\ i \ I

I\,\\\.. . i /I \i\~\. 1/ i./

<

20 30Temperature, 0 F

10o

December 4, 1971January 15,1972February 26,1972March 4, 1972April 29, 1972

May 14, 1972July 29, 1972

August 5, 1972

September 9, 1972

October 21, 1972

-10

v'------~

';r-- -- --- -- J:1

~ ... _.._.._... -<>

0-"-,,-,,-,, - ..-0

0· ..·- ...... · .... ·..·· ..····0

*.. _._._._. *

~- ------ - - ---@I

lr-._._._._.-.---6.

f:!.---.---------D.

.~----e

Fig. 9

-GIANT MINE' TEMPERATURESMEASURED IN THE POND (GTd

-20

4

2

12(f) -t- -- ~

(f) .c14

0 0..0.. <1l

W 00

16<.9z-l<{ 18t-

o-l 200(f)

22

24

26

28

. >.~

.v-~

'>~.;:: -::::--.:.,,::- - - - - );""'---+--~----+-~""::':'-\-:01~+-------f---.!--~"£"- ---"::' -----I --- __

0"170 -'6050

\.\

rI

?,

40

m· if .'/Ojl!!:/ I11.1./1 J jj

TV! Tj/rIII!' 'f~;.I I' ,'./: , j

T! v:; " .'

'illl

ftjJ' i n.rijl: 'i

., .II 'j' .':. :

oJII,I, ,.

~l.,I, i'III'IP~:,I;iliil

30 I.. 32°F20Temperature, OF

............. • <, -... . -'...... - 1 i._· .-- .-.- ....;::.:~ --" '.. .. ' .., ....~----- '--. .........-- ,)....!.. , .---.. ~~ --.~ .

- ------~ ........,U .:....., .

10o

December 4, 1971

January 15,1972February 26,1972

March 4,1972

April 29 , 1972

May 14. 1972

July 29, 1972

August 12,1972

September 9, 1972

October 2 I , 1972

•

•

-10

- GIANT MINE: TEMPERATURESMEASURED IN THE GROUND( GT2, downstream of dyke Ng 3)

Fig. 10

v- - - - - - - - - -"V

(>-... _ ... _ ... _ ...(>

•.- --------.A-·_·_· _._.-4

l:r---------l:>.

0-.. _ .. _ .. - .. --0

0 .. · 0

*_._._._._*

-20

6":''''

2 ;~;.~>

., 14...,.';+1:+.-+------I---------i-----+------I--------iHlIl:»~ ~+_----_+-----+_----_l£. ':',::'.'

~ 16Pg·;,:..;;~·:1-~--I---------I-----~-----I__--...,...--_+_-----t-.,t+e"<>__+-----+_-----__+----______l

8~o-lo

(f)

I-(f)

oQ.Wo

t:>Z-l

~

7060504020 30Temperature, ° F

10o-10

::OJ -- ~_A --- II .- » *.~:Q

~Wr I t:r--~~ .:::- --. T - - -6 ~:.;~ I""-A.~ <, --'- 1 0 : <\ ~'- ,

pp> --.. -.6:.:......-. ---- ~ '«,

y*.~:(5---~-: ---. f *~'9~

< '{~: <, I~ < *,,-~--. ---, 11

i~""':'- --.. J < ,11' l~.:~. I o ~~'1 *<, j ",'" ",

~

,"-

I ~, , "'\.

i<{

,o J *

it 1 \ /~ j

~j"IT

\1 <: /

t ~}.

?~0:1 ~, (\'~;8i ~'",

*""'''''~

I • • December 4 1971 · \ \. " / ,, . , ,I.: \ ,

·:-.;:1 E-------. January 15,1972!~

\ \ YI I

~, I

A-·_·-·_·'" February 26,1972 ~ ~ ''9 y;II ,." , I . I

I6-------6- March 4 1972 · ~ \ .

, . I I, , I

0-"-"-"-0 April 29 1972 I ~ \" ' i Y I

i~t~I,

4 * sr14 1972

,0 ..............·..0 May , ,· I.· : ,,*_._._.-7(. July 29 , 1972 I ~ L i J / _tfl ,,

... • August 12, 1972 II YI"l" / / I,''"::..!i: i ni\'l, /i .I ,

~'1------'1 September 9 ,1972

,

<r... _..._... -<) October 21 1972 Iaw/..iV' .qf

:~.\~.: ':~,

32°F-1-::. :.:~:~ 1

24

12

16

4

8

~ 20a.Qlo

--

~

uo0::

~ 28(f)

o0-w 32o<..?Z

-l 36<l:f-

oWI(f)

:::>0::U

o

40-20

Fig. II - GIANT MINE: TEMPERATURES MEASURED IN DYKE N2 3 (GT3 )

v///////,

----

-- -

rozen

Frozen

rozen

~ 40·-~--------I-----t

L------

//

/(

/

' ............. .,.-;~.

/'

32°

JANUARY 15,1972

MARCH 4,1972

FEBRUARY 26,1972

590

56

Frozen

610

600DECEMBER 4, 1971

-"'.580

tGlo

Frozen

T < 34°

rozen 0 20 40 60 80 100I I I I I I

~ ~ Horizontal scale, ft.

Fi g. 12 - G I A NT MI NE: ISOTHERMS BETWEEN DECEMBER 1971 AND MARCH 1972TH ROUGH DYKE N ~ 3

64.

100I

Horizontal scale. ft.

20 40 60 80I .• I , I , I

_--------1- 85°

v///////,

°

roz en

W/,fi

T< 60°

re zen

_------ 36°-+__---1

o,

------35° --------+--

_------------- 35°

_--------------- 40°-+----,

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

Frozon

rOlen

roren

82°

APRIL 29,1972

JUNE 3, 1972

JULY 29, 1972

MAY 14,1972

T< 80°

~------+_600

Fig. 13 -GIANT MINE ISOTHERMS BETWEEN APRIL AND JULY 1972 THROUGH

DYKE N° 3

65.

~////////.

40°-/-----

W//i

T>600

o 20 40 60 80 100, , 1 I I I

Horizontal scale, ft,

---------- 40°--I------t

_----------45°

,.:r-----..2 ::-- -- 35° --

:r-------------- 50°--1-------------- 45° ~=::t======1

""r-,1.11----- ------ 4 0 °

--

2

AUGUST 12, 1972

610

SEPTEMBER 9,1972

OCTOBER 21, 1972

rozen

~40

NOVEMBER 25,1972

59

-.... 580

tQl

o

t--------1r 50°

L------------t-- 40°

.---------jr---- 35°

T « 40°

Fig, 14 -GIANT MINE: ISOTHERMS BETWEEN AUGUST AND NOVEMBER 1972 THROUGHDYKE NC? 3

'" \, 1, I

, __----, I

........ _--... ..... -------,,/OF YELLOWKNIFEI

.-

IIIIII

I,.,",,---

/

(\ .... ............. ,

""\\\I,

I

/;,-, ;'I ...._/

200 400 600 800 1000 feel

SCALE

66 .

Fig. 15 -COMINCO MINE. YELLOWKNIFE. N.W T.. GENERAL PLAN OF TAILING DISPOSAL SYSTEM AND DRAINAGE

BASIN.

23/12/71

[t~ Muskeg andpermafrost

Fig. 16 - COMINCO

MIN E' SIT E scole : I" ~ 50' - 0"

PLAN SHi~RMATION AN~WTING LITHOLOGICALSTRUMENTATION. ~E LOCATION OF

67.

68

Fi g. 17 Com1nco Mine - Failure of the dyke by erosion duringthe thawing period.

Fi g. 18 Cominco Mine - Dyke in construction on the mining site.

PLATFORM PUD LAKE DYKEIII

II

CREEK1

24.00' ~54.971

~:~////////,

590

580

570

s:...a.CDo 560

550

540

oI

20 40 60I I I

Hor. scale ft.

80I

Fig./9 -COMINCO MINE, DYKE N~ I ,CROSS SECTION I-I AND INSTRUMENTIONS

(See legend page no. Xl)23/12/71

CT4

20 40I

o

CTTICTI

21:'0"

I at 4-0

CROSS SECTION

CTT2 ' "CT2~ ot 0-6

8 at 1'-0"22'_0" +

21 at I'- d' 6 Iat 2'_0"

~-n-rrI-rrrr:Trfrt~rrfrjlrh-r.,-r-n;-·l

590PUD LAKE

CTT4 II

580I

CT4 II

570 lOot 1'.:·0"

-+560 30"-0" 5 at 2'-0"

• iOI4'-0"550

*~I at 2'-0"540

Scole

Fig. 20 -COMINCO MINE, DYKE N~ I ,YELLOWKNIFE, N.WTLOCATION OF THERMOCOUPLES(See legend page no.x )

70605040

II:

: i,:II

\ I' To; : .I \ I~. : iILl. 1i

\ I I" ;:I I j!' :\ j": \ Ii '.1. i I

, 'T r:\ j\ i;\. J '{

\,\

20 30Temperature I 0 F

'.\\

'.

\\~

iIi

'.\,\

10o

December 18, 1971January 22, 1972February 26,1972

March 4, 1972

April 29 I 1972May 8,1972

July 29.1972

August 5 I 1972

September 16,1972

October 21 I 1972

-10

0"'-",-,,0

6-----6

0- .._ .._ ..-0

00··············.0

*_._._.*

• •.------..a-·_·_·-a

. .,'1-----"1

O~..,.----r------,.....-----,.....--l;P----t----IIIO--D/C-"''''----,r-------r------r------­1,1III

r-....' ,.2 I'

~\_/~/ \,/

II4,IIII61=i-----+-----+-----t-----¢--+------.t-e.~tJ;_l~----I_---~----_+----_1

1

IIF=8 1 -.

r­1=III- 10~;;;;t_---_f_----_+-----+-------:,r-I---e:_......._-----+_----_+_----_J.----_____l

-- 1-

=====0. =QI 12~=I_----l.-------I..------+_-----l_4_-___I~JlM_-----_+-----__l_-----.J_----___I

0 ====14~

======

16=~===18 ;:::::;;;;;;;;;======

20~======;22 ....... J.- ........ -l- --L. ---' --IL.- J.- ....L.- -'

-20

>­<l:...JU

Fig. 21 -COMINCO MINE: TEMPERATURES MEASURED IN THE FROZEN GROUND (CT2 )

80706050

/!!:'/' /1* ~ )(.'\ . " r[\ lU /)

30 40Temperature, ° F

~1'1'\ .. 'f / "'1" )('.. t <}

iLl. ~ ,

I !:~ ,~,~

\ ! I

I-------'~\ ; ----f--------+------+-------l-------1

32°F *9

I-----~ rr

~ II", !,; ~;

1------1= i!i.'!'I '''':t: ~.i ;:"

• • December 12, I 97111---- - -- ... January 15, 19721a.-'-'-'-'-6 February 26,1972

0-,,-,,-,,-,0 April 29,19720 ..··· ....·..··· .... 0 May 8, 1972*_._._.* July 29,1972

'" '" August 5, 1972\1-- -- - -.sy September 16,19720-.._ .. _ .. <) October 21,1972

0 10 20

a :\: r11 Ii

1=:=I------I------.1-------+-----t :n.{f :,'~I i'l.{j

01- .... ,,1,-1

/ ,-/',,-

o 2J _ 1

W -,'~ l/..... j

(J) 1'// ,.... /

:::> <, ~ \~ 4 1/ \

..... /~

" \- ,r .v-~I=

II~=8_==::::::::::=0-==- =- =~ =s: 2.=.-0.. =Q) ==0 E

4->- =<t =..J ==u

:1======2O~========

22124

-10

Fig. 22 - GOM INCO MINE:. TEMPERATURES MEASURED IN THE GROUND DOWNSTREAM OF DYKE N~ I (CT,l.;:;

7060

/'(

50

I/-.... .... -- .~"'I'

~-r"""" .., ,i *;, -- ,.

I t~

*'..0'

40

II

Y

l~\..\

cr ?II

y

'D. I'I

'to"

i

.'I .. .,..i.-..i-> 1

'\... I

I

i

,y'ef'J

30

\\

\\'.\

\\

Y';'" Y ~Y

r ' I ~ '. : : 11:'/I I' \.. 'f'!! . ;'

.V

2010

.>1-

o

December 18, 1971January 29,1972February 26,1972March 4, 1972

April 29,1972May 15, 1972

July 29, 1972

August 5, 1972

September 16,1972

October 21, 1972

0·· .... · .. 0

\/------\/

-10

0- .._·-0

~------~

!p----'"*_._.-. *

.... _.-._.-...• •.------11

'7\\-,

,\ 1/\-\7'.,',

R7iI~ ~\

/ , I

\'\ "~ - \

~~

===============~

0

2

~

0 400::

0 6w:I:(J)

:::>0:: 80

- 10......c-a.w 120

(9

IW~ 14(J)

:::>~

16

>- 18<I:...J0

20

Temperature, 0 F

Fig. 23 -COMINCO MINE:TEMPERATURES MEASURED IN DYKE N~ 1 (CT3 )

7060504020 30Temperature 1°F

I

10o-10

'\"" "',,~~~ *\*~------'o-~ , '; J ~

\ ... / ,\.- ...- '" \ ,. '>;;,/ "-.. :--".

': ri I',*

\I \ .. " - -

1 \,,~ I.' "~.~ , I

}·;i·(. ': " '1' "'1 I

7(-

;;M~; q ~l~ ~Q:\v *"I \ : 1.' ,\. .1 .')j ; )" I .1,

:~~.~;""\., -'k~ '1l / ~

[n."~ '.' -: I

'*\1 .,: '.,I::.,,' : '"" ,( ~"" ~

is· r""-.:;...... ",\'~""~,

--.*h -'I '~¥\ .*-'-'~ . ··~.·1 \, '~,

~ I ......,.

F= I 7.1 ;;

~'(dF= I '1 \ . \f== / • 0 \ , .1r== ' \: \ . / I

~ / to .I~ J- / '1= I T \\ ~ 1> /i== ' ., 'I I

i== I I \: ' I ~ I

F= ., \II I

1. " .:I

~ I "J. .1.1F= I ~ T i '~. I ff==

I I: ,

f== I: ~ j I

1= • () December 18 1971 ' ./

F=I 1 II lLiL.--------1lJ 29 11972~ January I , If rr1=== Jr-.-._.-.o- February 26,1972 I I ./

f== : I' If== . \: .. : •~ ~----'-6 March 4 1972 i I . ~ !: ,::::::::: , ,

= 0-"-"-',0 April 29, 1972 ! I Ii. .' i= I, .! I':= 0 .. · ...... · .... 0 May 15 I 1912 I li'i= i

.. :'"F== ; Iii "~ *_._._.* July 29 19721= , I T ·'T, I

~ August 12,1972 I:: I• V I I ,1,1,

i,

"'l'\1------J:;; Septem be r 16,1972 , it'0-"'-,,,-,,0 October 21 1972 I Hi'

====, I iI~,= i

/

#,:=::::::=~=== I I !f, i

:=::::::=I ,/,,;

=! F' 24 -COMINCO MINE: TEMPERATURES I ii'== Ig. ,=:::: MEASURED IN THE .POND (CT4 ) flJ= I I= ;l,"== 32°F i I 11':::::::: i

, .=

16

26

18

24

22

20

28-20

>­<I:...JU

o

....-

10

~ 14a.Q)

o

4

6

12

a::wI- 2<{

~

a..wo

oZ...J

<{ 8I-

75880

JANUARY 15, 1972

580-n -

32 rozen /'

JO v ;.::,. ;;,>./. .

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

--~

........-... ....,................................................<'...~~.~~

570- t---+-----~~:::::~~-.---."......

Pormafroll

1--+_--- 40°-----

580-

540­

Depth. ft.

FEBRUARY 29, 1972 )J-

.......rozen

.......... . '.......

I-----"_-----I~ 40°- -----.Permalrol

-,

MARCH 4,1972

___ IT

-- --- .....

Frozen

Pe r", afroll

'3Zo~ .. •.... 0.. - ....... - . ...........

."..,

<,<,

-,\

\

...... .......... .

"

.... .t-------lf-- 3!5 °-

"

APRIL 29,1972 n-r C 3!5°_D=::--==-------------J/32°

32° Frozen

~ ~~.W$ '////// ~///... ,Horizontol scole, ft.

80

er,n.afrOII

604020o

........... tV

'-'-,­-,

-,

""

.'

., ~.~~.~.,.;_;.:: . • . ~z~.~ ~..

! I

Fig. 25 - COMINCO MINE: ISOTHERMS THROUGH SECTION 1-1 BEETWEEN JANUARY

AND APR IL 1972.

IB90

MAY 27, 1972

890-

.

l!I60-

JULY 29, 1972

J-------+--- 400

AUGUST 26.,1972

........ ..

n-

//

""

n-

-----

./........._...

. .. .... ... ~ .

/L

Aerma frost

Permafrost

76

~ -+ -_- ----- 40°

SEPTEMBER 16,1972

400 _

--o

I , I , Ieo

Fig. 26 - COMINCO MINE: ISOTERMS THROUGH SECTION 1- I BETWEEN MAY AND

SEPTEMBER /972

77.11"'0

OCTOBER 21, 1972

880-

I---+-- 40°

HO-

!l40- ",

Depth. fI,

NOVEMBER 26,1972

~ Frozen32°

n-

.............'

' .....................

n--

.......'" '

.. - .­.. '..'..

,,/ ..

Permafrost

Permafrost

...-.. , ,-................ ­".'.. '

........".. '......... ",.'......,.'

......... . ........................ . ............ .

_...

oI

Horizontal scole, ft,20 40 60

I t I , IBO

I

Fig, 27 -COMINCO MINE: ISOTHERMS THROUGH SECTION 1-1 FOR OCTOBER AND

NOVEMBER /972

NW SE

574.21H --

13 572 56574.16

H -­"57285

574.11H -­

9572.78

575.28H--

' 573.99

PUD

~'i'TlOlt>(j/·" f I I mlTflTl

57474 ~HG~ H5

580

575 -

570

565

!~ 560~

555

550

545 ~ Permafrost

l~pDo:;:r,;:1 Crush rOCk

540fZ§t!\~~ Toihn9 deposits

l;r:lt",.1 Muske9

E3 Clay

fZlZ27LZ! Bedrock

H~ Ground level

1~ Perrnctrost levelII

~open ditch

........ Io 10 15 20 30

Horizontal scoIe.1M'

Fig.28 -COMINCO MINE, YELLOWKNIFE ,N.W.T. ,DYKE Nil ,CROSS-SECTION n-II.