i •, .- -------- - aina publications serverpubs.aina.ucalgary.ca/gor/35082.pdf · alur 1972-73...
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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
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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
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i x
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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
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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
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TABLE
I.
II.
LIST OF TABLES
Summary ground temperature installationsat Giant Mine.
Summary ground temperature installationsat Cominco Mine.
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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
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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.
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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.
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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.
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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.
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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.
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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
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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.
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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,
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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.
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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.
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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
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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.
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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.
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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.
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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
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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.
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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
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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.
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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.
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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
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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
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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
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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.
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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
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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
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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
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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.
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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
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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:
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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
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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
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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
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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.
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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
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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.
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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.
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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
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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.
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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.
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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.
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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.
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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.
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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.
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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.
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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.
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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.
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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
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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
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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.
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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.
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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
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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
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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.
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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.
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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.
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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
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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
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•
~
•
o
•Yellowknife Boy
Iscale in miles
•
••
53 .
Fig. I -TAILING DISPOSAL SYSTEM OF GIANT S. COMINCO MINES OF YELLOWKNIFE, N.W.T.
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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
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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
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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 .
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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.
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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
~ ....... .-,..... .. ._..
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, 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
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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
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. >.~
.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
~
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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 )
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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
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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
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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
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'" \, 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
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[t~ Muskeg andpermafrost
Fig. 16 - COMINCO
MIN E' SIT E scole : I" ~ 50' - 0"
PLAN SHi~RMATION AN~WTING LITHOLOGICALSTRUMENTATION. ~E LOCATION OF
67.
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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.
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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
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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 )
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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 )
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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.;:;
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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 )
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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-
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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.
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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
![Page 88: I •, .- -------- - AINA Publications Serverpubs.aina.ucalgary.ca/gor/35082.pdf · ALUR 1972-73 Stability of Dykes ... in planning the program ... prior to reclaim for plant use](https://reader034.vdocuments.pub/reader034/viewer/2022051720/5a74f95c7f8b9a63638c1f17/html5/thumbnails/88.jpg)
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
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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.