Publisher’s version / Version de l'éditeur:
Endeavour, 23, 89, pp. 66-72, 1964-05
READ THESE TERMS AND CONDITIONS CAREFULLY BEFORE USING THIS WEBSITE. https://nrc-publications.canada.ca/eng/copyright
Vous avez des questions? Nous pouvons vous aider. Pour communiquer directement avec un auteur, consultez la première page de la revue dans laquelle son article a été publié afin de trouver ses coordonnées. Si vous n’arrivez pas à les repérer, communiquez avec nous à PublicationsArchive-ArchivesPublications@nrc-cnrc.gc.ca.
Questions? Contact the NRC Publications Archive team at
PublicationsArchive-ArchivesPublications@nrc-cnrc.gc.ca. If you wish to email the authors directly, please see the first page of the publication for their contact information.
NRC Publications Archive
Archives des publications du CNRC
This publication could be one of several versions: author’s original, accepted manuscript or the publisher’s version. / La version de cette publication peut être l’une des suivantes : la version prépublication de l’auteur, la version acceptée du manuscrit ou la version de l’éditeur.
Access and use of this website and the material on it are subject to the Terms and Conditions set forth at
Permafrost and related engineering problems
Brown, R. J. E.; Johnston, G. H.
https://publications-cnrc.canada.ca/fra/droits
L’accès à ce site Web et l’utilisation de son contenu sont assujettis aux conditions présentées dans le site LISEZ CES CONDITIONS ATTENTIVEMENT AVANT D’UTILISER CE SITE WEB.
NRC Publications Record / Notice d'Archives des publications de CNRC:
https://nrc-publications.canada.ca/eng/view/object/?id=f69708cf-4c0f-4d8b-9126-c43cb7b89a6e
https://publications-cnrc.canada.ca/fra/voir/objet/?id=f69708cf-4c0f-4d8b-9126-c43cb7b89a6e
Ser
fFrd'lN21t2
no. LT3
e . 2
BI,DG
PE,RMAF'ROST
AND RELATED
76 r ctlft 786?,u,
NATIONAL RESEARCH COUNCIL
CANADA
DIVISION OF BUILDING RESEARCH
ENGINEE,RING PROBLE,MS
by
R. J. E. Brown and G. H. Johnston
A N A L Y Z E D
Reprinted from
ENDEAVOUR, VOL. XXIII, No. 89, MAY 1964
B U I L D I N G R E S E A R C H
. L I B R A R Y
.
JUL 15 !964
N A T I O N A L R E J E A I ( ! H C O U N G I L
TECHNICAL PAPER No. I73
OF THE
DIVISION OF BUILDING RESEARCH
OTTAWA
MAY 1964
PRICE z5 CENTS
?ii:lf" ifi
clsTl / lclsT
lil||ur|luruiluLlul|urluurul
T h i s p u b l i c a t i o n i s b e i n g d i s t r i b u t e d b y t h e D i v i s i o n o f B u i l d i n g R e s e a r c h o f t h e N a t i o n a l R e s e a r c h C o u n c i l . lt s h o u l d n o t b e r e p r o d u c e d i n w h o l e o r i n Part, without permission o f t h e o r i g i n a l p u b l i s h e r . T h e D i v i s i o n w o u l d b e g l a d to b e o f a s s i s t a n c e i n o b t a i n i n g s u c h p e r m i s s i o n .
P u b l i c a t i o n s o f t h e D i v i s i o n o f B u i l d i n g R e s e a r c h m a y b e o b t a i n g d b y m a i l i n g t h e a p p r o p r i a t e remittance (a Bank, Express, or Post Office Money Order or a cheque made payable at Par in Ottawa, to the Receiver General of Canada, credit National Research Council) to the National Research Council, Ottawa. Stamps are not acceptable.
A c o u p o n s y s t e m h a s b e e n i n t r o d u c e d t o m a k e p a y m e n t s f o r p u b l i c a t i o n s r e l a t i v e l y s i m p l e . C o u p o n s a r e a v a i l a b l e in d e n o m i n a t i o n s o f 5 , 2 5 a n d 5 0 c e n t s , a n d m a y b e o b t a i n e d b y m a k i n g a remittance as indicated above. These coupons may be used for the purchase of all National Research C o u n c i I p u b l i c a t i o n s i n c l u d i n g s p e c i f i c a t i o n s o f t h e C a n a d i a n G o v e r n m e n t S p e c i f i c a t i o n s B o a r d .
PERMAF'ROST AND RELATED
ENGINEERING PROBLEMS
Permafrost and related
engineering problems
R.J. E. Brown and G. H. Johnston
Roughly one-fifth of the world's land area is subject to permafrost, that is, perennially frozen
ground. It is particularlv important in the Soviet Union and in Canada, each of r,r'hich
has roughly
half its territory affected. Permafrost not only poses
questions of great geophysical interest but
pre-sents the civil engineer with many exceedingly difficult problems. This article reviews the principles
governing the distribution of permafrost and some of the ways of overcoming the diffrculties.
The term'permafrost' was coined in rg43 by S. W. Muller, who used it as a convenient short form of 'permanently frozen ground' [r]. It describes the thermal condition of earth materials such as rock and soil when their temperature remains below o'C continuously for a number of years, which may be as few as two or as many as tens ofthousands. In recent years, however, it has been realized that permafrost is not necessarily permanent. Changes in climate and terrain can cause the permafrost to thaw and disappear, and the term'perennially frozen ground' is now used instead of'permanently frozen ground'.
Permafrost underlies 20 per cent of the world's land area, being widespread in North America, Eurasia, and Antarctica. In the northern hemisphere, it occurs mostly in Canada and the Soviet lJnion, each country having about one-half of its total land area underlain by it (figure S) [e, g].
The origin of permafrost is not well understood, but it is suspected that it first appeared during the cold period at the beginning of the Pleistocene. During subsequent periods of climatic fluctuations, corresponding changes have occurred in its extent and thickness. It is known at present to be diminishing in some areas and increasing in others.
Distribution of permafrost and thermal considerations In the northern part of the area shown in figure 3, permafrost is continuous, but further south it is discontinuous. In the con-tinuous zone, it occurs everywhere under the ground surface and may be hundreds of metres thick; in the discontinuous zone, permafrost exists in combination with areas of unfrozen material (figure r). In the southern area of the discontinuous zone, it occurs as scattered patches and is only a few metres thick. The thickness of permafrost at any particular point is determined by the close and complex interaction of a large number of climatic and terrain factors. The most important of these factors are air temperature, relief (slope and aspect), vegetation, drainage, snow cover, and soil tlpe.
Above the permafrost is a surface layer of soil or rock, called the 'active layer', which thaws in summer and freezes in winter
(figure z). Its thickness depends on the same climatic and terrain features as affect the permafrost. The thickness may vary regionally from several metres in the southern fringe of the dis-continuous zone to only a few centimetres in the north of the continuous zone. Local variations in terrain factors may cause
R. J. E. Brown, M.4., Ph.D.
Was born in Toronto in 1931 and educated at the University of Toronto and Clark University, Massachusetts. In 1953 he ioined the National Research
Council, Canada, and has since been attached to the Northern Research G r o u p , S o i l M e c h a n i c s S e c t i o n , D i v i s i o n o f B u i l d i n g R e s e a r c h . A g e o ' g r a p h e r , h e h a s b e e n c o n c e r n e d w i t h m a p p i n g t h e d i s t r i b u t i o n o f p e r m a ' frost in Canada and investigating the physical factors affecting this' G . H , J o h n s t o n , L S c .
Was born in 1927 in Winnipeg and is a civil engineering graduate o{ the University of Manitoba. He is attached to the same group of the National Research Council as Dr Brown, and has been particularly concerned with s i t e i n v e s t i g a t i o n a n d c o n s t r u c t i o n t e c h n i q u e s i n p e r m a f r o s t a r e a s a n d th e effect of permalrost on ongineering structures.
66
Figure 1 Typical vertical distribution and thickness of permaf rost.
the active layer to vary in thickness from less than one metre to several metres within any one area.
In permafrost regions, the mean temperature decreases steadily from the ground surface to a depth ranging approxi-mately from Io to 30 metres. Below this depth, the temperature increases steadily under the influence of the heat from the Barth's interiot. After a timeJag determined by depth and local conditions, fluctuations in air temperature during the year produce corresponding temperature fluctuations about the mean annual ground temperature to depths of some 2o metres. The amplitude of these fluctuations decreases with depth to less than o'roC. The depth at which fluctuation becomes imperceptible is called the 'level of zeto annual amplitude', Below this, ground temperatures change only in response to long-term climatic changes extending over centuries.
There is a broad relationship betineen mean annual air temperature and mean annual ground temperature [4]. Observations at various places have shown that the mean
o N o r m a n W e l l s H a Y R i v e r (65 N) (61 N) C o n t i n u o u s z o n e ( U s u a l l y e x t e n d s t o permaJrost table) D i s c o n t i n u o u s z 0 n e
7-,:F
r
{ 'r C/a. \ !ac.kenziel?2 q€t1
S c h e f l e r v il l e A p p r o x i m a t e S o u t h e r n o f C o n t i n u o u s P e r m a f r o s t A p p r o x i m a t e S o u t h e r n L i m i t o f D i s c o n t i n u o u s P e r m a f r o s t 120'E 90'wannual air temperature is less than the mean annual ground temperature by about 2 to 5oC' depending on local conditions; the overall average is about 3'C. This difference can be attributed in part to heating of the ground surface by solar radiation and the insulating effect of snow cover. For example, the mean annual air temperature at Resolute, Northwest Territories, in the continuous permafrost zone, is - r6'r'C and the mean annual ground temperature is - re'8"C. Thompson, Manitoba, in the discontinuous zone, has a mean annual air temperature of about -4'C and a mean annual ground temperature in the permafrost of about - o'soc.
Over a long period of time, a change in the mean annual air temp€rature can result in a significant change in the extent and thickness of permafrost. Geothermal gradients ranging from about r"Cl zo m to r'C/l 6om--depending to some degree on the type of soil or rock-have been observed in permafrost regions in Canada, Alaska, and the Soviet Union, A change of roC in the mean annual air temperature, for example, could result, over a long period of time, in a change of IoC in the mean annual ground temperature. This would cause a change in permafrost thickness of approximately eo to 16o metres.
The age of permafrost may differ considerably lrom one
Figure 3 Map showing distribu-tion of permafrost in the
northern hemisphere, and position of places mentioned in text,
60"w
portion of the permafrost region to another' depending on geological history and variations in climatic and terrain factors in space and with time. For example, permafrost in unglaciated portions of Canada, such as the Western Yukon Territory and the northwest portion of the arctic archipelago, may be several hundred thousand years old, having formed at the beginning of the Pleistocene, before the continental glacia-tion. In the remainder of the country, covered by ice, it is unlikely that existing permafrost formed until after the final retreat of the ice sheet, ten to twenty thousand years ago. In areas inundated by postglacial lakes and marine transgression, however, permafrost formation would not have begun until these bodies of water receded, several thousand years after the ice retreated.
An estirnate of the time required to forrn thick rrasses of permalrost can be obtained by simple calculations if some assumptions are made. For example, it can be calculated, on the basis of simple conduction theory, that at Resolute about ro ooo years was required for the ground to freeze to a depth of 3go metres, the present estimated ttrickness of the permafrost. A more precise estimate would have to take account of such factors as the latent heat of fusion of ice, proximity of the ocean, 67
fluctuations in mean annual air temperature since the initiation of permafrost accumulation, and changes in terrain conditions. Nevertheless, the above value must be of the right order of magnitude.
Terrain influences
Although climate controls the broad pattern of permafrost distribution, other factors are necessary to explain Iocal variations. Climatic differences alone do not explain the varia-tions in thickness and temperature at depth in neighbouring areas of the continuous zone that have similar mean annual air temperatures. Nor do they explain the patchy occurrence of permafrost in the southern fringe of the permafrost region. These variations in permafrost occurrence appear to be governed predominantly by local variations in micro-climate and such features of the terrain as reliet drainage, vegetation, snow cover, and soil type.
Relief influences the amount of solar radiation received by the ground surface. In the discontinuous zone, this may result in permafrost occurring on north-facing slopes but not on ad-jacent slopes facing south. [n the continuous zone, permafrost tends to be thicker, and the active layer thinner, on north-facing slopes. At high elevations, permafrost can occur in temperate and even tropical regions because of the reduction in air temperature with altitude.
Vegetation affects permafrost in various ways, One [S] is by pro'uiding resistance to heat flow by conduction. By transpira-tion, it draws water from the soil, which is thus depleted of the heat held by the water. Furthermore, the process ofevaporation (including that due to transpiration) withdraws heat from the surrounding atmosphere and from incident solar radiation. In the present context, mosses and lichens are particularly significant. Mosses are strongly hygroscopic, but can lose moisture rapidly and in large quantities. Lichens, however, have very dry surfaces at all times, even when lower layers near the soil are very wet; possibly they protect the soil against heat gain more by an insulating process than by one of evaporative cooling. It is possible, however, that rapid evaporation or diffusion exchange of water vapour from the wet basal layer to the atmosphere above the lichen may contribute to low soil remperatures and a high permafrost table. The underlying peat, fcrmed from the accumulation of decomposed vegeta-tion, also influences the heat transfer between the atmosphere and the soil beneath.
Snow cover influences heat transfer between the air and the ground and hence affects the distribution of permafrost. The snorvfall regime and the time that snow lies on the ground are critical factors. A heavy fall of snow in the autumn and early winter will inhibit winter frost penetration and the formation of permafrost. On the other hand, a thick snow cover that persists on the ground in the spring will delay the thawing of the underlying frozen ground.
Drainage and the existence of large bodies of water greatly influence the distribution and thermal regime of permafrost. There is almost always a talik (unfrozen zone) beneath water bodies that do not freeze to the bottom. The extent of this thawed zone will vary with a large mrmber of factors-area and depth of the water-body, water temperature, the thickness of winter ice and snow cover, the general hydrology ofa lake, and the composition and history of accumulation of bottom sedi-ments [6]. A large body of water increases the geothermal gradient arorrnd its borders [7]. For example, the influence of the ocean is of interest near its edge, where it depends upon the magnitude of the temperature difference between the land surface and ocean bottom, the thermal properties of the ground 68
materials, past changes in climate, and the history of marine transgression and shoreline emergence. Theoretical considera-tions of ground temperature observaconsidera-tions at Resolute, where permafrost is 39o metres thick at the settlement about r.5 kilometres inland, suggest that permafrost does not exceed 3o metres beneath the ocean bottom at points more than a few tbousand feet offshore.
Bare soil and rock have considerable influence on the tem-perature of the ground, because of their ability to reflect solar radiation. Reflectivity values in the range of re to 15 per cent for rock and r 5 to 30 per cent for tilled soil have been observed. There will also be different evaporation rates and intakes of precipitation.
In the southern fringe of the permafrost region, most of the perennially frozen ground is confined to peat bogs. The thermal properties of the peat are to a great extent responsible for the formation of permafrost in this type of terrain; changes in the extent of permafrost are also largely dependent on changes in the thermal properties of the peat. The mechanisms which cause the formation of permafrost in these bogs are associated with variations in the heat e>rchange at the surface of the moss and peat. When dry, peat has a low thermal conductivity equal to that of snow (that is about o'ooor7 cal/cm'C sec). Peat can absorb large quantities of water; when wet, its thermal con-ductivity is greatly increased. lJnsaturated peat has a conduc-tivity of about o.rno7 calf cm"C sec, while that of saturated peat is about o'oor I cal/cm"C sec. When ftozen, its thermal con-ductivity is many times that of dry peat and approaches the value for icel saturated frozen peat has a conductivity of about o'oo56 cal/cmoC sec. During the summer, a thin surface layer of dried peat having a low thermal conductivity prevents warming of the underlying soil. During the cold part of the year, the peat is saturated from the surface, and when it freezes, its thermal conductivity greatly increases. Because of this, the amount of heat transferred in winter from the ground to the atmosphere through the frozen ice-saturated peat is greater than the amount transmitted in the opposite direction in sum-mer through the surface layer of dry peat and underlying wet peat, A considerable quantity of heat is also used during the warm period to melt the ice and to warm and evaporate the water. The net result is a loss ofheat, and conditions conducive to the formation of permafrost.
This thermal mechanism does not cause the permafrost to increase in thickness indefinitely. Rather, a quasi-equilibrium is reached whereby the downward frost penetration is balanced by heat transfer from the unfrozen ground below. The thermal sensitivity of this permafrost is vividly demonstrated by its rapid thawing when the overlying moss and peat layers are removed,
What has been said above relates to the southern fringe of the permafrost region. Further north, the thermal properties of the peat and other terrain factors assume a relatively minor role and the thermal properties of the ground as a whole, together with the clirnate, become dominant. Variations in thermal properties such as conductivity, diffusivity, and specific heat affect the rate of permafrost accumulation. For example, the thermal conductivity of silt is about one-half that of coarse-grained soils and several times less than that of rock. Variation in thermal properties alone will not, however, necessarily ;:r.:t,
t" differences in permafrost thickness within a particular
Engineering considerations
Permafrost is an important consideration in engineering work in the Far North. Although frozen soil provides excellent
Figure 4 Differential settlement of warehouse on mudsill surface loundation, caused by thawing of the underlying permalrost containing large quantities of ice, Hay River, Northwest Territories, located in the discontinuous permafrost zone. Seotember 1962,
Figure 5 Massive ice deposits in exposure of perennially lrozen stony fine-grained soil, The site is on the west side of the Mackenzie River delta, located in the continuous permafrost zone, May 1954.
Figure 6 Construction of airstrip by 'insulation technique'. Placement of thick (2'5-4'5 m) crushed-rock fill on undisturbed surface vegetation cover for runway at Inuvik, July 1958,
Figure 7 Extensive ground slumps caused by melting of massive ground ice deposits in the tundra, near Tuktoyaktuk, on the Arctic coast iust east of the Mackenzie River delta, located in the continuous permafrost zone. Aerial view looking north from an altitude of about 3(x)m, .luly 1960.
Figure 8 Polygonal patterned ground in the tundra, located a few miles south of Tuktoyaktuk. The polygons are about 15-30 m in diameter, Aerial view from an altitude of 450 m. July 1960.
Figure 9 Pingo 100 km north of lnuvik. T h i s is a b o u t 2 0 m h i g h w i t h p o l y g o n a l markings on its lower slopes. Aerial view from an altitude of 60 m. September 1 957.
\i
I
bearing for a structure, it may when thawed Iose its strength to such an extent that it will not support even light loads. Sub-stantial settlement can occur when frozen foundations thaw, and differential movements usually result in serious damage or even complete failure of the structure (figure 4). The detri-mental effect of frost action in the active layer, which alter-nately freezes and thaws annually, has to be considered also. Structural movements sufficient to cause damage can result from the heaving of frost-susceptible foundation soils. To ensure satisfactory structural performance, special steps, such as reducing the depth of frost penetration or replacing such soil with material in which ice accumulation will be minimal, must be taken. Three features of permafrost are significant in engineering construction:
(r) Permafrost is particularly sensitive to thermal changes. Any natural or man-made change in the environmental con-ditions, however slight, will greatly affect the delicate natural thermal equilibrium.
(z) Permafrost is relatively impermeable to moisture. Drainage is vital, therefore, because all movement of water occurs above the permafrost; in northern areas, surface water is conspicuous despite the generally low precipitation. If natural drainage is impeded, or proper drainage structures are not provided, construction operations can be seriously complicated by intensified frost action during the winter and accelerated thawing during the summer.
(3) The ice content of frozen ground is a most important consideration. Solid rock, gravel, and sand usually contain little or no ice at temperatures below o'C and few difficulties are encountered in building on these materials, Most problems arise with fine-grained materials and organic materials such as peat, which usually have extremely high ice contents and are susceptible to frost action. As long as the water remains frozen in such soils, the ice binds the individual particles to-gether to produce a material with considerable strengthl when thawed, holvever, these soils can change to a soft slurry with little or no strength.
The ice in perennially frozen materials can occur in a number of forms: as coatings or films on small particles, stones or boulders, or as inclusions in the cavities in the soil. Such occurrences are normally observed in coarse-grained soils. Ice may also take the form of layers or lenses ranging from hairline sizes to several metres in thickness, and in this form is generally found in fine-grained deposits (figure 5). All forms can occur within the same material; in some cases, silty soils for example, the volume of ice may be as much as six times that of the soil. Some of the more spectacular ice deposits are found as large blocks or wedges in frozen ground.
Site investigations
Stereoscopic examination of air photographs, together with a knowledge of the local climate and geological historn can pro-vide much useful information for a preliminary appraisal of an area. Surface features provide reliable indications. For example, beaded or 'button' drainage, thermokarst topography (thaw sinks), 'drunken' forest (that is, trees at various angles), solifluction lobes or terraces, frost mounds, patterned ground
[B], and 'pingos' all indicate permafrost or intensive frost-active conditions (figures 7-g) [g]. The ground will contain large amounts of ice, and is potentially unsuitable for building. Selected areas, subdivided. on the basis of similar terrain characteristics, are then examined in the field to check predic-tions made in the initial survey and to gather and correlate information on soil and permafrost conditions.
Field investieations to determine the extent and nature of
permafrost are most important, particularly in the southern fringe of the permafrost region, where frozen ground is found in scattered patches and is near thawing. Variations in the depth of the permafrost table and the thickness of the permafrost over a potential site are determined during this survey. In the discontinuous zone, the depth to the permafrost table can vary from about o.5 to 3 metres and the thickness of the perimafrost from less than r to about r5 metres. In the continuous zone, the variation in the depth to the permafrost table is usually less, only about o.5 to r'5 metres, and the relatively mihor variatibns in the great thicknesses of permafrost are of little pragtical significance.
Field studies must include a programme for examining and sampling subsurface materials in situ. This work, like the perma-frost observations described above, can be carried out by ,1 probing, hand augering, or power drilling methods [ro], or by fii the excavation of test pits. Determination of ice content is parti-ff cularly important. For example, at Aklavik in the Mackenzie f Delta, the top 3 metres of perennially frozen silt were found to contain 6o per cent ofice by volume. The serious engineeiing implications are evident, for if this frozen soil thawed there would be a settlement of t'B metres in the top 3 metres. : Ground temperature measurements are also an inportant part of these studies. This is particularly critical in.1he southerrt fringe area, where the permafrost temperatures are within oire degree of zero, Further north, the ground temperatilres are several degrees below zero-for example, below -5"C on the arctic coast-and consequently severbl degrees of wariming can be tolerated without adversely affecting the strength of the foundation soil.
Design and construction
When general site conditions have been evaluated, further detailed investigations are'normally reqdired at the locations of individual structures. The results of these will indicate the approach to be taken in foundation-design and the con, struction techniques to be used. These are rirsually considered under one of the following headings:
(r) Neglect of permafrost conditions. : . (e) Preservation of frozen conditions for the life of the structure,
(3) Elimination of frozen condition or material before building.
(4) Thawing offrozen ground with expectation ofsubsequent ground settlement; foundation design takes the expected movement into account.
Perennial freezing can be neglected when engineering works are sited on well-drained coarse-grained soils or bedrock, an{ conventional design and construction are possible. Ii.l the zone of continuous permafrost, particularly where fi ne-grained soils with high ice-content are encountered, every effort must be made to preserve the frozen condition. In the discontinuous zone, it may be convenient to remove the frozen material by thawing or excavation and to replace it with well-drained material not susceptible to frost action; standard foundation designs can then be used. For some structures, in either the continuous or discontinuous zones, it may not be possible to prevent thawing of the ground during the life of the structure and settlement must therefore be anticipated and taken into account in the design.
Preservation of the frozen condition c4n be accomplished by either ventilation or insulation construction techniques; the former is commonly used with heated buildings. Foundations are well embedded in the permafrost, and the structure is raised above the ground surface to permit circulation of air
beneath to minimize or prevent heat-flow to the frozen ground. Pile foundations placed in steamed or drilled holes have proved well suited to this method, and have been used exten-sively in northern Canada and elsewhere [r r].
Where pile placing may be difficult, as in very stony soils, alternative foundation designs may prove more economical. Insulation to prevent thawing of the underlying frozen material may be achieved by placing a gravel blanket on the surface of the ground on which the structure is to be erected. This method is generally limited to small cheap buildings that can tolerate some movement.
For the construction ofhighways, railways, and airstrips [rz], where the ventilation technique cannot be applied, the insula-tion method must be relied on (figure 6). Normally, filI methods are used throughout, and disturbance of the surface cover is kept to a minimum. Cuts through hills are avoided where possible. Proper drainage must be provided to prevent accu-mulation of water, which would thaw the underlying perrna-frost, and the formation of icings', which can block a road during the winter.
Excavation of frozen ground can be difficult and costly because normal excavation techniques are much less effective in permafrost. For some structures' however, it may neverthe-less prove economical to excavate the frozen soil, replacing it with material not susceptible to frost action on which the foundation can be built.'fhis method is particularly applicable in the southern fringe area. Again, adequate drainage must be provided to take care ofseepage water. The procuring oflarge quantities of fill for road and airstrip construction presents its own problems; suitable sources must be located, cleared of vegetation, and allowed to thaw well in advance of construc-tion operaconstruc-tions.
Permafrost complicates the provision of water and sewer services [r3]. Only limited year-round sources of water are available because many lakes and streams freeze to the bottom during the winter, and water-bearing strata are only occasio-nally encountered in permafrost. Normal methods of sewage disposal into the ground are generally prohibited because of the imperviousness of the permafrost. Distribution systems are generally located in insulated boxes (utilidors) on or above the ground surface because of problems resulting from excessive thawing of the frozen ground by the contents of the pipes or, conversely, freezing of pipes if they are placed in the active layer or in the permafrost.
The thawing effect of water on perennially frozen ground becomes particularly critical when dams and dykes are con-structed on permafrost and large areas are covered by im-pounded water Ir4]. The rate at which thawing will take place and the depth to which thaw will penetrate beneath the water and the water-retaining structures are of prime importance in the design of their foundations. According to circumstances,
underlying frozen ground can be excavated and the structure placed on bedrock; the frozen condition can be retained by natural or artificial refrigeration; or the embankment can be built up as settlement occurs when the permafrost thaws.
Conclusion
This necessarily brief review of the properties and behaviour of permafrost indicates its great significance in the development of the extensive territories in which it occurs. Not only do severe climatic conditions complicate all constructional work, but buildings may have to rest on foundations having properties quite different from those encountered elsewhere in the world. Empirical methods, assisted by growing knowledge of funda-mental principles, have led to much progress but further studies are urgently needed to extend those already made, mainly in North America and the Soviet Union'
Acknowledgments
The authors wish to acknowledge many useful discussions with Dr R. F. Legget and Dr N. B. Hutcheon, respectively Director and Assistant Director of the Division of Building Research, National Research Council, Canada. This paper is a contri-bution of the Division of Building Research and is published with the permission of the Director'
References
[r] Muller, S. W, 'Permafrost or Permanently Frozen Ground and Related Engineering Problems'. U.S. Arm2, Strategic Engng' Stud2 62, tg4g.
[z] Hopkins, D. M., Karlstrom, T. N. Y., et al. Geol. Suru, Prof' PaPer 264'F, Washington, t955.
[3] Shvetsov, P. F. (Editor)' Ocrroerr feorpzonorzrz (udpsno-roae4errze) (Fundamentals of Geocryology (permafrost) )' I. Academy of Sciences of the U.S.S.R., Moscow, I959. [4] Brown, R.J. E. Arctic, t3, 163, 196o.
[5] Legget, R. F., Dickens, H. 8., and Brown, R.J. E. in'Geology of the Arctic', Vol. rr, p. 956, University of Toronto Press, Toronto, 196I.
[6] Johnston, G. H. and Brown, R. J. E. Nature, Lond., rg2, z5t,
r 9 6 I .
Lachenbruch, A. H. Bull. geol. Soc. Amer., 68, I5I5' I957. Washburn, A. L. Ibid., 67, Bz3, t956.
Sjtirs, H. Endeanour, zo, zr7, tg6,t'
Hvorslev, M. J., Goode, T. B. Boyd, W. K., and Lange, G. R' 'Core Drilling in Frozen Ground'. Seventh Annual Drilling Symposium. University of Minnesota. 1957. Pihlainen, J. A. Proc. Amer. Soc' ciu. Engrs, (Soil Mech. Dia')'
8 5 , S M r , r , 1 9 5 9 .
ttl
tBl
tgl
I r o ] I t r ][rz] Linell, K. A. Ibid., (Air Transp. Diu,),83, AT r, I, 1957' [r3] Dickens, H.B, Polar Rec.,9,4zt, r95g'
[r4] Lewin,J. D. Pubt. Wks, N-T.,79, No. 5, zz; No.6,33; No' 7' 57, r94B'
A list of all publications of the Division of Building Research is available and may be obtained from the Publications Section, Division of Building Research, National Research Council, Ottawa, Canada.
