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PRO CEEDINGS of the
THIRD CANADIAN CONFERENCE ON PERMAFROST 14 AND 15 JANUARY 1969
" " 1
,..../"
PREPARED BY R. J. E. BROWN
TECH1\[ICAL MEMORANDUM NO. 96
OTTAWA SEPTEMBER 1969
FOREWORD
This is a record of the Third Canadian Conference on P'e r m a-frost which was neld at MacEwan Hall, The University of Calgary, on
14 and 15 January 1969. The Conference was sponsored by the Associate Committee on Geotechmcal Research of the National Re s ea r cn Council. A list of those in attendance is included in Appendix "A" of these pro-ceedings. Approximately 370 pe r son s attended the Conference from Canada and the United States including delegates from tn e Yukon and Northwest Territories, and Alaska.
Tne overall theme of tne Conference was concerned with permafrost problems related to the mining and oil and gas p r o du ctio n industries. Papers from both Canada and the United States considered various aspects of these problems in the permafrost region of Nortn America. The first session, under the cnairmanship of Dr. R. M. Hardy, Dean of Erigi ne e ring , University of Alberta, Edmonton, Alberta, included papers on the distribution of permafrost in Canada, permafrost problems in iron mining at Schefferville, P.Q., site investigations at potential mine sites in no r tn e r n Quebec and Baffin Island, and blasting frozen ground with compressed air. The second session was cnai r e d by
Mr. L. Samson, Terratech Limited, Montreal, P. Q., and three papers on experiences with permafrost at mines in northern Canada were presented. The Chairman of the third session was Mr. R. A. He m sto ck , Imperial Oil Limited, Calgary, Alberta. Papers were presented on po s s i.bl.e p r ob l e m s with pipelines in permafrost regions, considerations of heat transfer in soils for design and performance of engineering structures, velocity of compressional waves in. porous media at permafrost temperatures, and permafrost aspects of oil exploration in northern Alaska after the Second World War. The Chairman of the fourth ses sio n was Dr. W. O. Ku p s c h , Director of the Institute for Northern Studies, University of Saskatchewan, Saskatoon, Saskatchewan. Papers were presented on permafrost pr:)blems in oil and gas exploration and production, thermal erosion problems in pipelining, and techniques for setting drill rigs on piles and cementing well casing in permafrost.
The documentary film of construction on permafrost in the U. S. S. R., presented to the Division of Building Re search, National Research Council, by the Soviet Ambassador to Canada, was shown. Of the fifteen papers presented at the Conference, thirteen are reproduced in their entirety in these proceedings and two are presented in summary or abstract form.
TABLE OF CONTENTS
Introductory Remarks Permafrost in Mining
(i
v )1. Di stribution of Permafrost in Canada by R.J.E. Brown, Division of Building Research, National Research
Council, Ottawa, Ontario 1
2. Permafrost in tile Knob Lake Iron Mining Region by B. G. Thorn, McGill Subarctic Research Laboratory,
Schefferville, P. Q. . . 9 3. Experience with Engineering Site Investigations ln
Northern Quebec and Northern Baffin Island by L. Sam son and F. T'o r don , Terratech Limi ted,
Montreal, P.Q. 21
4. Blasting Frozen Ground with Compressed Air by
J. McAnerney, 1. Hawkes and W. Quinn, U. S. Army
Terrestrial Sciences Center, Hanover, New Hampshire 39 5. Experience with Permafrost in Gold Mining by
G. H. Espley, Giant Yellowknife Mines Limited,
Yellowknife, N.W. T. 59
6. Mining Experience with Permafrost by R. J. Kilgour,
Discovery Mines Limited, Discovery, N.W. T. 65 7. Design and Construction Problems at the Clinton Mine
of Cassiar Asbestos Corporation Limited by
J. G. Drewe, Cassiar Asbestos Corporation Limited,
Clinton Mine, Y. T. . 71
Permafrost in the Oil and Gas Production Industries
8. Some Possible Problems with Pipelines in Permafrost Regions by T. A. Harwood, Defence Research Board,
9. Thermal Design in Permafrost Soils by H. R. Peyton
University of Alaska, College, Alaska. . . .. . . 85 10. Velocity of Compressional Waves in Porous Media at
Permafrost Temperatures by A. Timur, Chevron
Research Company, LaHabra, California. . . l2J 11. Permafrost and Pet 4 by J. C. Reed. Arctic Institute
of North America, Washington, D. C. . . .. . . 121 12. Permafrost Problems in Oil and Gas Exploration and
Production by J. C. Sproule, J. C. Sproule and
Associates Limited, Calgary, Alberta. . . 129 13. Thermal Erosion Problems in Pipelining by
T. G. Watmore, Imperial Oil Limited, Edmonton,
Alberta. . . ... . . 142 14. Techniques for Setting Drill Rig Piling and Surface
Casing under Permafrost Conditions by J. S. Dier,
Mobil Oil Canada Limited, Calgary, Alberta 163 15. Cementing Well Casing in Permafrost by
R. C. Cameron and G. A. Welsh, Dowell of Canada.
Dow Chemical of Canada Limited, Calgary, Alberta.. 174 Film - "Construction on Permafrost" . . . 187 Appendix "All - Li st of Those Attending Third Canadian Conference
INTRODUCTORY REMARKS
Mr. T. A. Harwood, Chairman of the Permafrost Subcommittee, Associate Committee on Geotechnical Research, National Research
Council, welcomed delegates to the Conference. He noted the expanding development of permafrost investigations in Canada during recent years. Approximately 180 delegates attended each of the two previous permafrost conferences held at Ottawa, Ontario, in April 1962 and Edmonton, Alberta, in December 1964. The pre sence of twice as many people at the Third Canadian Conference on Permafrost in Calgary from all over North America indicated the rapidly growing interest in this subject and the importance of it on r e source development in the North.
Mr. Harwood introduced Dr. A.W. R. Carrothers, President of the University of Calgary, who welcomed the delegates on behalf of the university. He expressed his pleasure at the selection of the Conference site because Calgary is the oil capital of Canada and the university is also developing an intere st in the North, particularly in the fields of archaeology, economics, engineering, environmental sciences, geology and sociology. He has also a personal interest in the North, having served as Chairman of a Commission to advise the Government of Canada on the development of government in the Northwest Territories. It was at this time that he first observed some of the problems cause by perma-frost during his travels in northern Canada. Dr. Carrothers remarked that the delegates were meeting to discuss what is basically an engineer-ing problem - the relationship of permafrost to the minengineer-ing and oil and gas production industries. He asked that the Conference keep in mind the fact that people constitute one of the major resources of the North.
Mr. Harwood expressed the regrets of Dr. R. F. Legget,
Director of the Division of Building Research, National Research Council, for not being able to attend the Conference. He was for 22 years
Chairman of the Associate Committee on Geotechnical Research, formerly called the Associate Committee on Soil and Snow Mechanics. This Com-mittee has sponsored many geotechnical conferences through its Sub-committees on Soil Mechanics, Snow and Ice, Muskeg, and Permafrost. Mr. C. B. Crawford, Head of the Soi l Mechanics Section, Di vision of Building Research, succeeded Dr. Legget as Chairman of the Associate Committee in 1967. He expressed Dr. Legget' s regrets at his una voidable absence and delivered the following message from him to the Conference delegates:
I'It is a matter of the keenest personal regret that I cannot be with you in person to bring you the greetings and best wishes for this meeting from the Di vi si o n of Building Research, National Re search Council. I had looked forward so keenly to attending the conference,
especially since it deals with a subject which is of great personal interest to me. This has proved impossible, however, and I must send you this message from the Division in this way. From the start of its work in 1947, the Division of Building Research has app r e cia te d that it had special responsibility with regard to
research work into the problems of permafrost in northern Canada. Our studies started with the survey of building foundations right down the valley of the MacKenzie River carried out by the late John Pihlainen in 1950. From that time on we have always had members of our staff spending full time on these special northern problems. Although we have not done all that we would have liked to have done, I venture to think we have been able to make some contribution to the development of the knowledge necessary for the opening up to industry of our vast northern territory. Our list of publications, copies of which are available for you, will show you what we have tried to do in putting into convenient written form information based on our own researches, and those of others relati ve to all aspects of northern building.
Perhaps you will allow me to invite your special attention to two notable publications of 1968. First, our first full report on the performance of the dykes at the Kelsey Power Plant by
Mr. G. H. Johnston and, secondly, the Permafrost Map; many of you have this, developed by Dr. R.J. E. Brown. Each of these publications records the results of many years of work by my two northern colleagues who are with you at your Conference. All of us appreciate the special importance of the subject which you will be considering at the Conference, a matter which your Chairman, Mr. Harwood, and I have discussed on several
occasions. We know something of the problems and I am sure that my colleagues who are with you will have a much better appreciation of what is involved by the time your deliberations of these two days come to an end. In keeping with our overall
responsibility to assist the construction industry in this country in all its phase s , the Division of Building Re search is most anxious to work with the industries here represented to seek further solutions to the problems that have to be faced in connection with your northern development work.
Unfortunately for us our offer of assistance has to be seriously qualified because everyone present will know that the Government of Canada last year imposed the strictest controls on all federal expenditures and restricted the additions of more members of staff to all federal agencie s including the National Re search Co u ncil., Accordingly, we cannot add any members to the staff of the Division, beyond our establishment of 244 as it was on
2 March 1968. Our budget is seriously limited in keeping with this overall government policy. May I make very clear that this state-ment is made not as one of complaint but as one of fact. We accept the conditions under which we have to work willingly but you will see the difficult position that it places us in when we receive requests such as are almost certain to arrive as a result of your deliberations.
Anticipating such requests we have been c on sid.e r i n g what sugges-tions we can make for working with you in the critical months ahead. May I outline two suggestions, which will, at least, be an indication to you of our good will and of our keen desire to work with all who are concerned with the development of the North. 'I
Dr. Legget remarked in his message that, in the first place, the facilities of the Associate Committee on Geotechnical Research can be made available. Mr. Crawford commented on this later. The second suggestion concerns relations between the Division of Building Research and industry as exemplified currently by arrangements with the steel and concrete industries. Each of these industries has a Fe1LJw who is riow
"vo!'King with the Division, as if he were a member of staff, with all its facilities available to him, while being paid by the industry concerned and working in a special field of research of direct interest to this industry and mutually agreed upon. The industry pays the Division a small overhead. The result is a very economical way of doing research for an industry, utilizing all tn e facilities of the Division but wi thout adding to its establishment. Dr. Legget assured delegates that he would be happy to make similar arrangements in other fields such as those represented at this Conference if it would be appropriately useful. Dr. Legget concluded his message by expressing his wishes for a suc-cessful Conference and he looked forward to hearing ab o ut the meeting from his colleagues who are present.
Mr. Crawford continued from Dr. Legget's remarks by pointing out that there are a number of people on staff at tne Division of Building Research, in addition to Mr. Johnston and Dr. Brown, wno are knowledge-able in scientific fields closely allied to the problems which will be dis cus sed at the Conference. Although the Di vi sion staff and budget are fixed, some effort can be directed to these problem s if they are defined and arrangements advanced to give them priority over existing work.
Mr. Crawford explained the organization and operation of the Associate Committee on Geotechnical Research and its subcommittees which are quite separate from the Division of Building Research. When the National Re search Council was established in 1916, it had two
A grant system was established to fund research in universities, and this has continued to the present time. In the year just ending it has amounted to approximately $60, 000, 000. It has been increasing annually at the rate of 30 to 40 per cent in recent years although this next year will have a very modest increase. Secondly, a system of associate committees was established to coo-ordinate research and these have continued to the present; there are now 45 of these associate committees, one of which is on geotechnical research. They range from dental research to bird strikes on aircraft. Any group of people who have a technical problem and can convince the National Research Council that it requires stimulation and co-ordination can arrange for the establishment of an associate
committee. They do not require much money but they do bring together considerable competence. The money is mainly the input of competence to the deliberations of the associate committee, as seen at this
Conference.
In the mid 1920's, the National Research Council Act was extended to include its research laboratory effort and the Division of Building Research is part of that effort. The Associate Committee on Geotechnical Research was established in 1945. As mentioned previously Dr. Legget was its Chairman for 22 years, and thus he has had a very great influence on developments in this field. The function of the Associate Committee on Geotechnical Research has been defined as follows:
liTo co-ordinate and stimulate research on the engineering aspects of the terrain of Canada, and for this purpose four subcommittees have been set up - Soil Mechanics, Muskeg, Snow and Ice, and Permafrost. These subcommittees have as their purpose to define
problem areas in their assigned fields, advise the Associate
Committee on research needs, follow through actively in promoting research and as sisting in the application and publication of the research results".
The Permafrost Subcommittee was established in 1960; it has been instrumental in two previous Canadian Conferences as well as the Third Conference currently in session. It was also involved in the International Permafrost Conference at Purdue Uni ver sity in 1963.
Mr. Crawford suggested that the Associate Committee can provide assistance in three ways. The first is by organized discussion. The National Research Council, although funded by the Government, is not a department but a fairly independent agency. It has been quite
successful in bringing together many people who represent various fields of interest and combining their knowledge for the common benefit of the profession. This is accomplished by holding conferences and
subcom-mittee meetings. For example, the Snow and Ice Subcommittee examined snow removal and ice control which is a multi-million dollar problem in Canada. A small group was brought together under the auspices of this Subcommittee, exchanged ideas, defined the factors that most influenced the cost, and prepared a manual of recommended procedures which is now widely used to the benefit of Canada and elsewhere. This sort of situation could apply to the Permafrost Subcommittee also. Secondly, the Associate Committee on Geotechnical Research can promote research by adding its influence in various ways to organizations and individuals. Thirdly, it maintains links with the Division of Building Research where most of the Secretariat is located, thus providing good two-way commu-nication between the Associate Committee and the Division.
2 (Summary)
The theme of this Conference is concerned with permafrost problems related to the mining and oil and gas production industries. The purpose of this paper is to set the stage by describing some of the
characteristics of the permafrost region of Canada. In 1967 a
perma-frost map of Canada was published in colour jointly by the Division of Building Research, National Research Council, and the Geological Survey
of Canada, Department of Energy, Mines and Resources. Copies of the
map can be obtained from either of these agencies.
This map shows the extent of the continuous and discontinuous
zones and their relations to the climate and physiographic regions. The
distribution of permafrost at high elevations in the Cordillera in British
Columbia, south of the discontinuous zone is also shown on the map. A
table listing ground temperatures and thickness of permafro st for 24
locations in northern Canada is included. Explanatory notes
accompany-ing the map describe the nature of permafrost and its relation to climatic and terrain factors.
A diagrammatic profile of permafrost through the continuous
zones in Canada is shown in Figure 1. (Note that thicknesses of the
permafrost and active layer are shown in metres.) Permafrost is several
hundreds to more than 1, 000 feet thick in the continuous zone and the
active layer is generally 1 to 3 feet thick. Southward in the discontinuous
zone, the permafrost is interspersed with areas of unfrozen ground. In
the northern part of this zone, permafrost is widespread varying in
thickness from about 50 to 200 feet. In the southern part of the zone,
termed the "southern fringe", permafrost occurs in scattered islands ranging in size from a few square feet to several acres, and varying in
thickness from a few feet to a maximum of about 50 feet. The active
layer is thicker than in the continuous zone and it does not extend
every-where to the permafrost table. Figure 2 shows typical profiles in the
continuous and dis continuous permafro st zones.
1S e e Appendix "A" for affiliation of authors of papers.
2Information in this paper is contained in various papers bv the authors which have been published by the Division of Building Research, National
Research Council, Ottawa, Ontario, Canada. Copies can be obtained by
The ground thermal regime (Figure 3) is an important aspect particularly because the definitio n of permafrost is based on temperature referring to ground which remains below 32°F continuously for more than one year. This is the minimum length of time required for frozen ground to be considered as permafrost, or perennially frozen ground. At the other end of the time scale is permafrost which is thousands of years old and hundreds of feet thick. Fluctuations in air temperature during the year produce corresponding temperature fluctuations about the mean annual ground tempe r atu r e to depths of about 20 to 50 feet. The amplitude of these fluctuations decreases with depth to less than 0.1 of. The depth at which fluctuations became imperceptible is called the "level of
negligible annual amplitude" or "level of zero annual arnp l.itu de ", Below this, ground temperatures change only in response to long-term climatic changes extending over centuries. The ground temperature in the perma-frost and below increases steadily under the influence of the heat from the EarthIs interior.
Tundra polygons (Figure 4) and pingos (Figure 5) are among
the most distinctive permafrost surface feature s in the continuous zone. Po l ygon s attain sizes of 50 to 100 feet in diameter and the marginal fissures are frequently underlain by vertical ice wedges extending to depths of tens of feet. Pingos are conical hills up to 100 feet or more in height containing a core or plug of massive ice. They may be either the closed system type usually associated with old lake beds in the continuous permafrost zone or open system type associated with groundwater move-ment through unfrozen ground in the discontinuous zone. Ice wedge
polygons are also found in the discontinuous zone but they attain their greatest development in the continuous zone.
Surface permafrost features are not as distinctive in the dis-continuous zone although some terrain patterns atte st to the presence of permafrost. Figures 6, 7 and 8 are vertical, oblique and ground photo-graphs in an area of widespread discontinuous permafrost. Unfortunately the distribution of permafrost is not usually delineated so readily from surface terrain features. In many parts of the di s c ont i nuou s zone, the permafrost does not have any surface expression and its presence can onl y be inferred or ascertained by sub surface field investigations.
In the southern part of the discontinuous zone, where perma-frost occurs in scattered islands, the most distinctive permaperma-frost feature is the palsa (Figure
9).
These peat mounds have a core of permafrost with a peat cover. They are found in some peatlands and peat bogs southward to the southern limit of the permafrost region.Ground ice is an important component of permafrost occurring widely in many forms in overburden and bedrock (Figure IJ). Ice forms
include segregated ice, forming discrete layers or lenses, pore fillings which cement or bond individual soil particles, intrusive or injected ice formed by freezing of injected water, vein or wedge ice in thermal
contraction cracks, and buried ice including snowbanks, glacier ice, and ice on water bodies. The existence of large masses of ground ice is immediately evident where such features as pingos and ice wedge polygons occur. Many areas where ground ice occurs, however, may not exhibit any surface manifestation and its presence can only be inferred from the type of earth materials.
As the mining and oil and gas production industrie s expand their activities in the permafrost region, knowledge of the distribution of permafrost and features associated with it is assuming increasing importance. The following papers describe various aspects of explora-tion and producexplora-tion affected by permafrost.
* *
*
*
* *
Discussion
Mr. B. L. Odo m asked if there is a maximum depth below which one would not expect to find large masses of ice in the ground and if this is so, what determines this depth? Dr. Brown replied that his colleague, Mr. P. J. Williams, Division of Building Research, National Research Council, Ottawa, Ontario, published a paper on this subject entitled "Ice Distribution in Permafrost Profiles", Canadian Journal of Earth Sciences, Vol. 5, No. 12, Dec. 1968, pp. 1381-1386. In this paper Mr. Williams analyzed soil samples from the Mackenzie River delta comparing field observations of ice segregation in the samples with theoretical calculations of maximum depths at which ice segregation and lensing would occur. He found that the quantity of ice in the soil
diminished with depth and below relatively shallow depths of perhaps 1J
to 15 feet little ice was present. This is a situation where there is a slow but steady accumulation of sediments over many c e n tu rie s . A different type of situation exists in northern Baffin Island where there are extensive deposits of glaciofluvial sands and gravels. Massive
blocks several tens of feet thick to depths of 80 feet or deeper have been encountered in drilling for engineering site investigations as described in Mr. Samson's paper. This ice might be buried glacier remnants or formed by injection of water prior to freezing. The distribution of ice in the ground in permafrost regions appears to depend to some degree on the type of material and the mode of deposition.
RESOLUTE OWT (74·01
NORMAN WHlS NWT HAYRIVER NWT
(650II) (61-hil
UNFROZEN GROUNO (TALlK)
Fig. 1
TYP1CAL VERT1CAL 01 STRI BUTION AND THICKNESS OF PERMAFROST
Typical vertical distribution and thickness of permafrost.
tOfllT INUOUS lOllC DISCONTINUOUS 1011£ TYPICAL PROFILES IN PERMAFROST REGION
Fig. 3 1 ＬＬＢＬＬＭＬｾ Maximum f/onlhly : Melin Temperature I I I Ｏｾｌ･ｶ･ｬ of Negligible [ __ I Annuil! Amplitude I ｾＲＰ - 50 fl I ! Permafrost I I i
TYPICAL GROUND TEMPERATURE REGIME IN PERMAFROST
Typical ground temperature regime In permafrost.
Fig. 4 Aerial view from about 1, 000 feet of tundra ice wedge
polygons, 50 to 100 feet in diameter, in continuous
permafrost zone near Tuktoyaktuk, N. W. T. The cracks
or fissures are underlain by wedge-shaped masses of ice up to 3 feet wide extending to depths of 10 to 20 feet.
Fig. 5 Aerial view fr orn about 800 feet of a pingo near Tuktoyaktuk,
N. W. T., near the arctic coast, east of the Mackenzie River
delta, in the continuous pe r rnaf r o st zone. This pingo is about 13
a
feet high and has a crater on the s urnrnit, It is located in a lake bed and has a core of rna s siv e ice.Fig. 6 Aerial photograph (scale - 1. 6 inches: 1 rni l e ) of terrain near
Gi l Ia rn, Manitoba, on Nelson River in northern part of discontinuous
zone where pe r rna fr o st is widespread. Light-toned areas are
forested peat plateaux with pe r rnafr o st about 80 feet thick. Dark
Fig. 7 Aerial view from. about 400 feet of terrain shown in Fig. 6. Forested peat plateau with perm.afrost at top of photograph. Wet, sedge-covered depression with no perm.afrost in m.iddle of photograph.
Fig. 8 Ground view of terrain shown in Fig. 6. Man is standing on
peat plateau underlain by pe r ma fr o st, Wet sedge-covered
Fig. 9 Mature pa l s a (peat mound) in southern fringe of discontinuous
permafrost zone near Great Whale River, P.Q. The peat is 3
feet thick overlying silty clay soil. The depth to permafrost
in the pal s a is about 1 1/2 feet. The permafrost in the paIsa
is probably between 10 and 20 feet thick. No permafrost occurs
in the surrounding terrain.
Fig. 10 Massive horizontal layers of ground ice in perennially frozen
soil face exposed by landslide. The ice is protected from melting
by overhanging vegetation. This exposure is located in a soil slump
at the base of the Richardson Mountains which flank the west side
PERMAFROST IN THE KNOB LAKE IRON MINING REGION B.G. Thom
This paper presents in outline the programme of exploration used in mapping permafrost III the Knob Lake (Schefferville, P.
o.:
mineregion, and the techniques used by the Iron Ore Company of Canada (IOCC) to overcome problems of mining in permafrost areas.
Permafrost in central Labrador-Ungava occurs as discontinuous bodies of various shapes and sizes within the upland terrain above
approximately 22JO feet in elevation. In most mine areas of tn e Knob Lake district, frozen ground is absent. At two locations shown in Figure 1, Ferriman and Timmins, permafrost presents, however, a problem to mining. The active layer (seasonal freezing and thawing) varies from 5 to 10 feet in depth, and if there is no permafrost below tnat layer then the groundwater circulates freely in aquifers. Particularly under exposed windswept ridges, free of tree cover, permafrost or
perennially frozen ground can extend to depths of 250 feet. These perma-frost bodies are commonly elliptical in cross-section and are elongated parallel with rock strike and ridge crest trend. Ground temperature s vary from 25 to 32 of, and vertical isotherms at the freezing point parallel the slopes of ridges indicating sharp plunging boundaries to the permafrost (Figure 2). Tnese boundaries often transgress rock types, and appear to be in close adjustment with surface climatic and vegetation conditions. Occasionally, pods of frozen ground are encountered at
depths of 150 to 200 feet. These may be relics of colder climates during the Pleistocene.
EXPLORATION IN PERMAFROST
Exploration methods can be divided into three phases: short-term, intermediate and long-term. Aspects of each phase may occur concurrently in any given area. Short-term investigation of permafrost conditions over a period of one or two years takes place at the early stages of development of an area to be mined. Seismic and resistivity surveys used to determine depths to bedrock and water table respectively can also detect the upper permafrost table in many places. Seismic
velocities and resistivity values often dramatically increase in perma-frost. There is a 20-100 fold increase in resistivity of altered Iron Formation upon freezing (Bacon, 1957). Seismic velocities of frozen altered rock are frequently similar, however, to values in unaltered Iron Formation. Difficulties of interpretation obviously arise and other techniques are needed.
Test drilling may show signs of permafrost, but because mud is commonly used as circulating fluid, it is rarely possible to see ice in the recovered sample. Coring has not proved to be succe ssful in Knob Lake ores. It is considered vital to any assessment of ice structure, water content, rock strength, etc., that good cores be obtained. Shallow test pits through the overburden frequently reveal permafrost if under-taken from August to late October. Back hoes are unable to cut into frozen ground without blasting. On many occasions, te st pits have been terminated before the bedrock has been encountered.
Since geophysical methods and trenching only define the perma-frost table, other techniques must be used to provide information about the geometry of permafrost. Temperature measurements in drill holes have been widely employed for this purpose at Knob Lake and elsewhere. Thermocouple cables containing 12 sensing junctions set at different
depths have been installed, and the temperatures read at frequent intervals inside small shacks using a portable potentiometer, or a Speedomax
recorder mounted on a sledge. At one mine area (Timmins 1), the cable s were lowered into oil-filled holes cased with plastic tubing. At other sites, h owe v e r , it has been just as economical to backfill the holes with sand, and although the cables were lost, the expense of casing was avoided. Furthermore, there was a risk of water penetration into the oil which may permit temperature migration in a vertical direction. Readings of ground temperature are used to construct isotherms along section lines. An example from the Ferriman area based on work completed in 1962 is shown in Figure 2. This section indicates the existence of cold "cores" beneath the ridge crest and an area of unfrozen ground (talik) in a poorly drained depression between two permafrost bodies. Temperatures
obtained in the vicinity of Timmins 1 (Holes 2, 4, 6, 7 and 8) and Timmins garage site (Holes 9 and 10) are listed in Table 1.
Studies by Annersten (1964) in the Ferriman mine area in 1961-62 showed a correlation between the minimum depth of snow on ridge crest sites and the presence of permafrost. To further test this correlation and thereby determine whether snow depth is a useful tool in permafrost mapping, snow courses were established across areas where thermocouple cables were located. At Timmins 1, during the winter of 1967-68, snow stakes eight feet high were placed at 200 foot intervals along lines 500 or 1000 feet apart (Figure 3). These stakes were read at least once each month and after major snow and wind storms. Snow depth and density varies with relief, aspect and vegetation. Thick permafrost (200 feet) is probable in areas with less than a maximum of 16 inches of snow during the coldest rnoritn s of January and February. Figure 4 depicts the seasonal snow cover for two courses located 1000 feet apart at Timmins 1 orebody. Very cold ground temperatures prevail at drill Hole 8 (see Table 1) whereas at Hole 7 in a sheltered vale the ore was
not even frozen at a depth of 10 feet. Using the temperature and tn e snow data, a map of the proposed Timmins 1 mine area was constructed to show probable permafrost, marginal permafrost (31-32OF), unfrozen and unknown areas (Figure 3).
Vegetation reflects long-term climatic effects and in an area of discontinuous permafrost may act as an insulating agent and thus reinforce the effect of snow. Therefore, a map of vegetation which emphasizes the structural properties of the plants can assist in the understanding of permafrost distribution. A map of vegetation should also include coverage of local drainage conditions and frost heave
features (e.g. polygons, stone stripes, etc.). In the Timmins 1 area, the distribution of tundra-like vegetation or rock desert closely agrees with areas of highly probable frozen ground (Figure 3). Stony earth circle s are very characteristic of such surfaces. Poorly drained, boggy areas and surfaces covered by a dense growth of ground birch are more likely to be unfrozen in this region.
At the moment, therefore, short-term permafrost investigations at Knob Lake involve the analyses of seismic and resistivity geophysical data, examination of test pits, installation of thermocouple cables to depths of 50 to 300 feet, and snow and vegetation mapping. Without core drilling these data can only be used to prepare a preliminary estimate of permafrost conditions to be encountered in mining.
Intermediate range work involves the continued monitoring of thermocouple temperatures over a period of 2 to 5 years. This is mainly to examine changes in ground temperatures within the zone of annual fluctuation (30 to 50 feet). Work of this nature continues at F'e r rirn an at thermocouple cable sites established by Annersten in 1961 (ibid).
Analysis of such data eliminates seasonal effects in what could be a
critical zone for shallow pits and for surface construction. Snow surveys have not been carried on for more than two years at any Knob Lake
permafrost site. It may be advantageous to survey small areas over periods up to 5 years to eliminate seasonal differences.
There are two further programmes which have as yet not been attempted at Knob Lake, but which will receive some attention in the future. Both studies could be completed in 2 to 5 years. The first is a detailed appraisal of the structure of permafrost in any given rock type. This work by necessity has to be undertaken in an operating pit. Here the relationship between ice structure (in pores, lens or massive), water
content, bulk density, strength properties, fracture pattern, lithology and mineralogy can be assessed. Preliminary studies in the Retty pit in March, 1968, showed considerable differences in ice structure in two rock units differing in lithology and joint pattern. The more massive and
open jointed sil.ic a-ca r bonat e iron formation contained ice lenses one inch or more thick, whereas the porous, altered ore was well bonded by minute crystals of ice in pore spaces. At any given depth there was no tempera-ture difference between rock types, but differences in ice types and
moisture content have an effect on ease of extraction (see below).
The second type of study which is envisaged in the future is a detailed analysis of the energy balance in areas that are perennially frozen. It is necessary to know more than just the ground temperature gradients in order to determine if any given occurrence of permafrost is in equilibrium with the present environment. The input of solar energy into the ground should be measured and this should be equated with loss of heat to the atmosphere. In practical terms this study required the installation of radiation equipment and temperature sensing devices above ground level. A study of this type is being planned for the Timmins 4 mine site.
Long-term objectives include the continued monitoring of thermal r-e g irn e s at selected sites for an indefinite period. It is possible that
s ubtle changes in climate will be reflected by changes in the temperature of the permafrost at depths of 5J feet or greater. More important from a mining point of view are attempts to modify the ground temperature
regime by artificial means. Perhaps the most practical technique involves the construction of snow fences in an attempt to increase the insulating snow cover and thereby reduce the loss of heat from the ground during the winter. Efforts of this nature in the Ferriman area in the 19501s were
unsuccessful as the programme had only short-term objectives. A tenta-tive plan has been drawn up to construct snow fences of various experi-mental designs on an orebody which will probably not be disturbed for 10 or more years. Also important from a long-term point of view is the possibility of controlling ground and surface water systems near perma-frost areas. Drainage diversion or dam construction may be other ways of modifying thermal regimes, and thus alleviating, in part at least, some of the problems of mining permafrost ores.
Many of these short, intermediate and long-term objectives are to be undertaken at the Timmins 40rebody. In October 1968, nine
thermocouple cables were installed and ground temperature measurements have commenced. A 150-point snow course in the form of a 2JO foot grid has also been established. Geophysical surveys were undertaken in the summer of 1968 (Seguin, 1968), and research on the mechanics of stony earth circles has commenced at one site near Timmins 4. Figure 5 illustrates the extent of operations at Timmins 4 as of January 1969.
MINING PROBLEMS
There are three main problems in mining frozen iron ore In the Knob Lake region;
1. Blasting
Where the water content exceeds 10 per cent, ice crystals and lenses absorb a large proportion of the energy generated by each blast. This results in incomplete rupturing of the pit face which in turn sets in motion a vicious circle of events which are summarized in Figure 6 (Ives,1962). Far more explosives are needed to reduce frozen ore to the required state than is the case with unfrozen ore. Cost of blasting is more than doubled as a denser drill hole pattern is employed, as well as more explosives (a slurry mixture and not simply AN.FO). Friction of the drill bit on frozen material causes the sides of the hole to melt and slump. The resultant reduction in hole depth and diameter causes
uncertainties in correct location of explosives (Ives, 1962). More details on the problems and techniques of blasting in Knob Lake ores are con-tained in a recent paper by Lang (1966).
2. Removal of Ore from the Pit Face
Large blocks often originate from a frozen pit face. These are either pushed to one side to thaw out, or broken down by percussion. Congestion of the pit floor may result. Secondary blasting leads to an uneven pit surface hindering the movements of the shovel. In the screen-ing plant the frozen blocks of about two feet diameter are difficult to break down, because of their hardness and elasticity. This results in inefficient reduction of ore to required sizes and increased cost of maintenance of equipment.
3. Transportation to Blast Furnace
Frozen ores are frequently above the critical 14 per cent water content and therefore need to be dried out in the drying plant at Sept Lle s , P.O. before loading into ships. T'h awi n g en route to Sept Lle s or in the ship results in t'sticky" ores which are difficu1t to remove from the rail car or ship hold.
These problems have all been overcome to the point that
frozen ores are mined. Blasting, thawing, crushing and drying problems, however, produce higher rnini n g costs. Therefore, in the discontinuous permafrost zone, it is important to define the areas of frozen ore so that pit designs and mining schedules can be organized more efficiently.
REFERENCES
1.
Annersten, L. J. Investigations of Permafrost in the Vicinity of Knob Lake, 1961-1962. In J.B. Bird, editor, Permafrost Studies in Central Labrador - Ungava, M cGill-Sub-Arctic Re search Papers No. 16, 1964, pp.5l-l43.2. Bacon, L. O. Report on Resistivity of Iron Ore Samples as Related to Permafrost Conditions. Iron Ore Company of Canada, Engineering Files, 1957.
3. Ive s , J. D. Iron Mining in Permafrost, Central Labrador - Ungava: A Geographical Review. Geographical Bulletin, No. 17, 1962, pp. 66-77 . 4. Lang, L. C. Blasting Frozen Ore at Knob Lake. Canadian Mining
Journal, Vol. 87, 1966, pp. 49-53.
5. Seguin, M. Geophysical Reports, Summer, 1968. Iron Ore Company of Canada, Engineering Files, 1968.
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EXPERIENCE WITH ENGINEERING SITE INVESTIGATIONS IN NORTHERN QUEBEC AND NORTHERN BAFFIN ISLAND
L. Samson and F. Tordon
Subsurface investigations were undertaken in permafrost areas in connection with the engineering design of two potential major mining developments in the eastern Canadian Arctic. These are the Asbestos Hill and the Baffinland Iron Projects (Figure 1).
Asbestos Hill is located in the northernmost part of the Province of Quebec, 30 miles from Hudson Strait in the continuous permafrost zone. The project is owned by Asbestos Corporation Limited and included in the initial plans, provisions for a mine, an adjacent treatment plant to produce 100, 000 tons of asbestos fibre annually, a nearby townsite for an initial population of 500 people, a 40 mile gravel road from the Asbestos Hill plant site to Deception Bay, an inlet of Hudson Strait. where a wharf and storage facilities were proposed (Figure 2). Site investigations required for foundation design of the various buildings and facilities of this project took place intermittently between 1962 and 1964.
The Baffinland Iron Development is located at Mary River in northern Baffin Island, 30J miles north of the Arctic Circle, and is the property of Baifinland Iron Mines Limited. Engineering site investiga-tions were carried out in the Spring of 1965 for a preliminary design and feasibility study. In its present layout, the project consists of mining and crushing facilities at Mary River for an initial production of
2, JOO, 000 tons of high grade direct shipping ore per year, a townsite for 1, 000 people, a 60 mile railroad, a wharf, extensive storage and
reclamation installations at Milne Inlet (Figure 3). GENERAL SITE DESCRIPTION Asbestos Hi 11
The Asbestos Hill area is a gently rolling plateau having an average elevation of 1,500 feet above sea level, with the highest hills reaching slightly over 2,000 feet. The area is underlain by metamorphic rocks generally exposed but occasionally covered by a thin veneer of overburden.
Asbestos Hill is nearly 300 miles beyond the treeline and vegetation is restricted to tundra communities (Maycock and Matthews, 1966). The climate is characterized by a long, cold winte r , The
estimated mean annual temperature is 17°F, with extreme temperatures rarely exceeding 70°F in summer and -40°F in winter. The average air freezing and thawing indices are approximately 6,300 and 1,000 degree days (Fahrenheit) respectively (Thompson, 1963). Near the coast, tne air temperature is somewhat milder. Records taken in 1962 and 1963 show mean annual temperatures of 17°F at Deception Bay, and 13 of at
Asbestos Hill. Annual precipitation is low and totals about 14 inches, including 6 feet of snowfall.
Under natural land surfaces permafrost was found in all drill holes and test pits put down at various sites of the project. The tempera-ture of the perennially frozen ground measured by thermocouples installed in a few drill holes at Asbestos Hill is 19 ° to 20 of below the 50 foot depth. Ground temperature measurements taken at Deception Bay show the
permafrost to be about six degrees warmer (25 ° to 26 OF), a difference which may be attributed partly to the different climatic environment, as mentioned previously, and to the proximity of the bay water. From the ground temperatures, the total thickness of permafrost is estimated to exceed 900 feet at Asbestos Hill. The depth of the active layer, measured at several locations in late August and early September 1962, varies
generally between 3.5 and 4 feet and occasionally reaches 4.5 feet in well drained granular (coarse-grained) soil.
Mary River
The area investigated in the Mary River district is located in a large valley leading to the coast, a drop of approximately 600 feet over a di staric e of 6J miles. This valley appears as an unconformity between Precambrian rocks on the Northeast, and Paleozoic sediments on the Southwest. In the valley itself, there is occasional relief of a few hundred feet, but adjacent hills often show local relief of 1,500 feet.
The valley and surrounding area are practically devoid of vegetation, with only moss and grass patches and very few low shrubs, and have a semi-arid climate with an average annual precipitation of 6 inches, approximately half of which is snow. Maximum temperatures seldom exceed 60 of, with minimum daily temperatures occasionally in the -50°F range. The nearest meteorological station at Arctic Bay, N.W.T.,
150 miles west of the site, indicates air freezing and thawing indices of about 9,900 and 800 degree days (Fahrenheit) respectively, with a mean annual tempe rature of 7 of (Thompson, 1963).
Ground temperature measurements at Milne Inlet give a tem-perature of 11°F at a depth of 50 feet. In view of this low ground tempera-ture, it is possible that the permafrost could extend to depths exceeding
1,000 feet. The active layer ranges from less than one foot under organic cover to approximately 5 feet in granular soils and averages 3 feet.
ICE DISTRIBUTION IN SOILS
Determining the ice content in permafrost soils was one of tne primary objectives of the s uo su r Iac e investigations at both project sites. Visible ice in the undisturbed samples was carefully recorded and
moisture (ice) content was determined for many samples. One particular observation drawn from the analysis of these results is the difference in the occurrence of ice between various types of soil deposits.
At the Asbestos Hill mill site and townsite, bedrock is covered with 5 to 10 feet of residual soil consisting of sandy and silty gravel with many boulders. Large ice content is present throughout the pe r rn af r o st
portion of this deposit in the form of non-visible ice, minute ice crystals and ice formations sometimes a few inches thick. The ice content of many samples is given in Figure 4 and illustrates the large and variable amount of ice in this overburden. The soil matrix of this deposit
(exclusive of gravel sizes and boulders) is found to contain an average of 65 per cent of ice by volume, of which 35 per cent is estimated to be excess ice. The engineering implications are evident by the large
settlements that would be caused by the thawing of tnis permafrost. For thi s reason, it is recommended to preserve the permafrost conditions within the townsite by providing natural ventilation under the heated
buildings together with adequate insulation on the ground surface bymeans of a clean gravel pad of 4 feet minimum thickness.
A somewhat different ice distribution pattern was observed in a till deposit present at or near ground surface in the Deception Bay area. In the upper 15 feet below ground surface the till contains fre-quently visible ice in the form of ice lenses and ice crystals contributing to a high ice content as illustrated by several moisture content deter-minations ranging from 7 to 131 per cent by weight (Figure 4). At a depth of about 15 feet, the moisture content falls markedly and remains
practically constant below this depth as observed in all 5 boreholes where thick till was found. The measured ice content of many samples
range s from 4 to 19 per cent with an average of 11.2 per cent (Figure 4) and is comparable to the moisture content of fully saturated unfrozen tills. These observations indicate that the till below approximately
15 feet contains very little or no excess ice.
In the marine clay deposit at Deception Bay, ice segregation occurs in the form of irregularly oriented ice formations ranging from hairline to five inches thick with well bonded frozen clay between the segregated ice. The moisture (ice) content of random samples of frozen clay ranges from l7 to 76 per cent, with an average of 32.5 per cent (Figure 4). This average moisture (ice) content is comparable to the natural moisture content of the unfrozen clay of the same deposit found
below the bay where the clay is soft and normally consolidated. In the upper seven feet or so, however, the frozen clay has a much higher ice content as illustrated by a few test results. It is therefore inferred that no moisture has been added to the clay during freezing below a depth of about seven feet. The scattering in the moisture content of the frozen clay is considerable, however, and reflects the non-uniform distribution of ice in the soil which is corroborated by the volume of visible segre-gated ice in the clay estimated to vary between 10 to 30 per cent. This system, consisting of an ice phase and a frozen soil phase without the addition of any outside water, is the result of moisture migration within the soil mass during freezing. Upon thawing, it is expected that the strength properties of such frozen soil would decrease considerably and may be several times less than those of the same soil not subjected to freezing. Large settlements would also take place mainly because of melting of the segregated ice.
The Mary River site is located on a relatively flat area under-lain by an extensive glaciofluvial deposit exceeding 100 feet in depth and consists of strat.ified sand and sandy gravel with random cobbles. This frozen soil shows little visible ice segregation, generally in the form of srna l l crystals, thin ice coatings and a few thin ice layers. Moisture (ice) content tests of many samples taken at various depths in the deposit give fairly consistent values without noticeable variations with depth. The higher half of the moisture content values are comparable to the moisture content of the same soil fully saturated and in the least compacted state.
It is expected therefore that upon degradation of tn e permafrost this sand and sandy gravel deposit will experience relatively small settlements due to melting of the segregated ice and densification of the granular soil whi c h is loose after thawing.
At the same site, rectangular polygons, approximately 50 feet or more in diameter, cover the terrace and are particularly prevalent near large bodies of water. The presence of ice wedges associated with the surface polygonal pattern was explored at a short distance from a lake (about 150 feet) by two vertical drill holes. One drill hole was located at the centre of a polygonal trench and a second hole at the edge five feet away. The f'ir st hole encountered ice between depths of 5.7 and 74.6 feet, and the second one between 19.0 and 76.1 feet. A 6 foot deep test trench dug subsequently at the borehole locations showed that the width of the ice wedge is approximately 1.5 to 2 feet at the top and increases by a few inches within the depth of the test trench. These limited field observa-tions indicate the presence of unusually deep ice wedges.
ICE IN BEDROCK
The proposed Asbestos Hill mill area has 5 to 10 feet of over-burden overlying a chlorite-sericite schist bedrock having a welkleveloped
schistosity with a dip varying from 45 to 90°. Discontinuities in bedrock, such as points, open bedding plane s and irregular breaks are filled with ice, either with or without soil inclusions. Such ice formations were carefully sampled in six boreholes drilled with refrigerated drilling fluid in an area of about 600 by 800 feet. The ice layers are generally a frac-tion of an inch thick except in the upper five feet of bedrock where larger ice layers up to about two inches are present (Figure 5). The amount of ice decreases with depth and becomes small below the depth of about five to seven feet. Borehole M-218 having a somewhat higher ice content is located in a zone of more shattered bedrock (Figure 6).
T his unexpected pre sence of ice in bedrock has a significant effect on the foundation design of the production plant buildings which would normally be founded on bedrock because of the building sizes and loadings and the shallow depth to bedrock. In the initial plans, the pro-duction plant complex having overall dimensions of 450 feet by 220 feet, incorporated a number of related units such as the mill, maintenance shops, garage, warehouse, power centre and storage. The mill building was a lO-storey structure, whereas the other units were one to two storeys high.
The pre sence of ice in bedrock has led to the following founda-tion design considerafounda-tions. First, the production plant complex has b e e n relocated to avoid the zone of more shattered bedrock with larger quan-tities of ice found in the area of borehole M-218. The production plant warehouse which is a comparatively light structure is actually built on footings resting on a compacted clean gravel pad, five to nine feet thick and placed on the bedrock surface. Provisions are made to level the building columns if necessary to accommodate settlements as much as a few inches. A similar approach was envisaged for other light buildings designed to accommodate some settlements. Heavier buildings, such as the mill building with column loadings of the order of 300 tons and
machinery that cannot tolerate nor accommodate minor settlements, were to be founded in bedrock at a level where predicted settlements from the thawing of permafrost are within acceptable limits. Such safe foundation level was to be defined following more detailed subsurface investigations in these areas to determine the actual ice distribution in bedrock. From the preliminary information available and described previously, a satisfactory foundation level may be obtained at a depth of about 7 feet below the bedrock surface.
PERMAFROST IN RIVER BEDS
Subsurface investigations at three river sites on the Asbestos Hill Project have disclosed the presence of permafrost at shallow depth below the river bed. At the site of a proposed water storage reservoir,
two miles from Asbestos Hill, a small river about 125 feet wide flows between rocky banks, on as much as 60 feet of granular alluvium. Bore-hole results and ground temperature rnea s ur e rn e nt s show that the river bed is perennially frozen below depths of six to nine feet. Thermocouple readings taken in late August 1965 in the centre of the river are given in Figure 7 and show the ground tempe rature at tne depth of 50 feet to be 26D F .
This ground temperature is somewhat warmer than the ground farther from the river (190 to 2JoF at Asbestos Hill mill site) and reflects
most probably the local influence of the river water on the ground thermal regime. The climatic conditions of the region are responsible for tile wide fluctuations in the river flow ranging from peak floods during the snow melt season in June to zero discharge in the winter. Indeed, field observations in March 1963 showed that the river was frozen to the b o tto rn , including the active la.yer of the river bed.
The presence of permafrost in the river bed raised particular problems for permanent water supply installations at this site. The possibility of using groundwater is of course eliminated. A water reser-voir of adequate storage capacity may be created by building a small dam a cr os s the river. The design of such a dam founded on permafrost.
how e v e r , will have to accommodate the expected settlements resulting
tram the thawing of the thick alluvial deposit caused by the impounded water. Design considerations will also be required to prevent seepage through the foundation material which is very pervious in the thawed state.
Permafrost was also encountered at two other river sites investigated for river eros sings. At Deception Ri ver, permafrost occurs at a depth of about 12 feet and the ground temperature measured 40 feet below the river bed is 24 of. At Murray River, permafrost was encoun-tered below the river bed during a site investigation in early June, and observations made in late winter 1966 showed that the river was frozen to the bottom.
PERMAFROST UNDER THE SEA
An unusual occurrence of permafrost was observed under the waters of Deception Bay which is approximately 10 miles long by 1.5 miles wide. In connection with the development of harbour facilities. the bay bottom subsurface conditions were investigated at various sites on the periphery of the bay a short distance offshore (about 50J feet from the high tide line). Sixteen sites were tested, most of them with one or two boreholes, to depths ranging from 40 to 70 feet below the bottom of the bay and generally located in areas of about 35 feet of water at low tide. No permafrost was found within the depths of investigation except in two areas.
At one site, two boreholes located 600 feet apart have encoun-tered permafrost at depths of 33 and 38 feet below the bottom of the bay. At both boreholes the permafrost table coincides with the upper contact
of a sand stratum underlying a marine clay stratum. A third borehole put down on the tidal flat to a depth of 45 feet and well into the sand stratum did not meet any permafrost.
At another offshore site, three boreholes spaced 600 feet apart and located in about 35 feet of water at low tide reached total depths of 60 to 70 feet below the bottom of the bay. Permafrost was encountered at one location at a depth of 32 feet, again at the contact between an upper marine clay and a lower sand strata. No permafrost was found in the other two boreholes.
It is assumed from rudimentary temperature measurements of the soil taken by inserting a thermometer in freshly recovered samples that the ground temperature below the bay is close to 32of. Tempera-tures slightly below 32 OF produce frozen conditions in the granular soils but may not do so in the marine clay mainly because of the clay particle sizes and the salt content of the pore water. Limited tests show that the salt content in the pore water varies between 5 and 10 grams per litre. A small depression in the freezing point of the clay moisture may explain the presence of the permafrost table at the lower contact of the clay stratum overlying a sand deposit at all three locations where permafrost was actually observed below the bay.
Isolated patches of permafrost also occur under the sea water at Milne Inlet in the area of investigation for the proposed wharf, where soft marine clay overlies till and bedrock. From a total of 22 boreholes located over generally 10 to 60 feet of water at low tide and reaching as much as 80 feet below the bottom of the bay. permafrost was found at only one borehole. At this location, permafrost is present in the clay stratum at a depth of about 40 feet and consists of ice lenses and ice
crystals within sections of unfrozen clay. The temperature of the unfrozen clay, measured by inserting a thermometer, is 30°F.
During the month of August 1965, the depth of thaw at the high tide line was found to be approximately two feet. Within five feet of the water at low tide, the depth of thaw was found to range from 11 to 15 inches.
These observations indicate random islands of permafrost under the bay waters. The properties of these islands of permafrost are quite different from the permafrost found on the adjacent land and are comparable to the discontinuous permafrost found much further south. This frozen soil would be highly susceptible to relatively minor thermal disturbance and may have serious consequences on construction of har bou r faci li tie s ,
SAMPLING TECHNIQUE
On both project sites, satisfactory samples of frozen soils and frozen bedrock were obtained by core drilling. Other methods, such as drive sampling and test pitting were used in some cases with limited success. Air photo interpretation of terrain conditions was particularly useful for the selection of the road location as reported by Mollard and Pihlainen (1963).
Drilling Equipment
The basic drilling unit consisted of diamond drill with a
hydraulic head having ample capacity to drill holes to the required depths of up to 100 feet. Pumps used for the drilling wash fluid had a rated capacity of 1000 gallons per hour at 250 p.s.L and proved to be adequate for "B1
! size holes and the limited drilling done in "N" size.
Coring equipment consisted of double-tube swivel-type and rigid-type core barrels, the best results in all types of frozen material e nc currter ed being obtained with the swivel-type core barrel. Most of the drilling was accomplished with a five foot BXL core barrel (nominal core diameter of 1 5/8 inches); high recoveries were generally obtained and did not warrant a larger coring size. Indeed, with the colder ground temperatures at Mary River, it is felt that "A" size double-tube swivel-type core barrel could have functioned with some success. The standard core spring functioned satisfactorily in all types of frozen soils.
Coring Bits
The choice of bits to core permafrost is a function of the type of overburden. Carboloy bits (tungsten carbide) are suitable for fine-grained soils but were found unsuitable for granular materials. The merit of carboloy bits stem s from the high footage per bit and the r e suiting economy in fine-grained soils. High footage in fine-grained soils was also achieved with diamond bits and it is felt that carboloy bits should be
restricted to sites known to have substantial fine-grained soils.
Two types of diamond bits were tried: the bottom discharge and the normal bevel wall bits. Initially it was felt that the bottom dis-charge bit would be preferable because of the reduced contact of the
drilling fluid with the core sample and the expected lower sample disturb-ance. No improvement was detected, however, in the quality of the sample with this type of bit, and the logical choice fell on the more durable bevel wall bit. The bottom discharge bits may however yield better samples in areas where permafrost temperature is only a few degrees below freezing and wash fluid contact with the core is critical. Two types of diamond
