PERMAFROST
AND THE ENVIRONMENT
IN ALASKA
U. S. ENVIRONMENTAL PROTECTION AGENCY
ARCTIC ENVIRONMENTAL RESEARCH LABORATORY
COLLEGE, ALASKA 99701
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PERMAFROST AND THE ENVIRONMENT
IN ALASKA
by
Frederick B. Lotspeich
Working Paper No. 18
U.S. ENVIRONMENTAL PROTECTION AGENCY
ARCTIC ENVIRONMENTAL RESEARCH LABORATORY
COLLEGE, ALASKA
Associate Laboratory of
National Environmental Research Laboratory
Corvallis, Oregon
Office of Research and Monitoring
March 1973
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A Working Paper presents results of investigations which are, to some
extent, limited or incomplete. Therefore, conclusions or recommendations
expressed or implied, are tentative. Mention of commercial products or
services does not constitute endorsement.
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ABSTRACT
Although permafrost is estimated to occur on about 20 percent of the
land area in the northern hemisphere, it is not a unique substance but
frozen, normal geologic materials. Permafrost is caused by the inability
of the geothermal gradient to supply heat rapidly enough to prevent deep
freezing when mean annual temperatures are below freezing. As most construc-
tion problems on permafrost are caused by melting earth materials, this review
describes how an understanding of the properties of elastics and principles
of soil physics can aid the construction engineer in evaluating factors and
predicting the behavior of thawed elastics. Texture and water content are
emphasized as being of overriding importance as elements that control how
melting elastics behave when thawed. During the construction of engineering
works on permafrost terrain thermal properties constitute an added, very
important element to be evaluated. The nature and properties of clastic
materials governs their thermal properties and a thermal analysis in advance
of a project becomes as important as other reconnaissance investigations.
It is the interactions of all elements that, when stressed by environmental
disturbances, cause a reaction. Computer modelling is now being used to
predict how these interacting elements react when various stresses are
applied. Several successful engineering works are cited as examples where
prior knowledge of clastic behavior and the employment of recommended
procedures have resulted in maximum stability while preserving environ-
mental quality.
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11
LIST OF FIGURES
PAGE
Figure 1 - Distribution of permafrost in Alaska (from
Johnson and Hartman).
Figure 2 - Typical temperature regimens in permafrost and
non-permafrost locales. Geothermal gradient is
exaggerated to improve clarity.
Figure 3 - Polygonal ground. This is the more common form of
patterned ground and represents resultant processes
that are characteristic of climates severe enough to
cause permafrost (Photo by Thomas Hamilton, Geomor-
phologist, University of Alaska).
Figure 4 - A pingo on the arctic slope of Alaska about 30 miles
south of Prudhoe Bay; this pingo is about 50 feet high
and about 200 feet in diameter at its base (June 1969).
Figure 5 - Massive ice in a road cut about 70 miles northwest of
Fairbanks (1970).
Figure 6 - Ice wedges and intercalated ice in a road cut near
Figure 5 ice content is estimated to be 40-60
percent.
Figure 7 - Frozen, unsaturated silt. Although this cut melted
on exposure, it remained stable because it was
relatively dry. Three to four miles south of the
Yukon River (1970).
10
13
14
15
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INTRODUCTION
Present concern given to the proposed trans-Alaska pipeline has focused
attention primarily on one factor of the Alaskan environment—the presence
of permafrost (this term was proposed by Muller, 1947, p. 3, for permanently
frozen ground). Permafrost is defined as perennially frozen earth material
resulting from continued cold climates; in Alaska it ranges in thickness from
zero at its southern boundaries to 1300 feet near Barrow. Frozen earth to a
depth of 5000 feet has been reported in Siberia. It must be emphasized that
permafrost is a condition of earth materials and is not a unique material in
itself; therefore, it is the cold environment that imparts unique qualities
to problems associated with man's activities in areas where permafrost occurs.
Because permafrost is frozen earth materials, properties of these materials,
when thawed, control most of the engineering behavior of thawed permafrost.
Failure to understand how permafrost behaves, or neglecting to recognize the
serious consequences of failing to apply knowledge already known, can result
in engineering failure and serious water pollution caused by sediments entering
streams as uncontrolled melting progresses. Brown's recent book (Brown, 1970)
describing permafrost in Canada provides a good overall appraisal of problems
associated with it that are just as valid for Alaska.
The objective of this review is to describe some principles controlling
the behavior of elastics (fragments of earth materials), both under frozen and
thawed conditions, and to stress that an understanding of permafrost requires
some understanding of earth materials and soil physics. No attempt will be
made to introduce new material or to use rigorous mathematical treatment
proving credibility as this is available in the literature. The objective
is to render a practical explanation of permafrost and problems associated
with it, and remove whatever mystery may exist to those unfamiliar with, but
interested in, what it is, how it formed, and how it behaves.
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ORIGIN AND PROPERTIES OF PERMAFROST
Permafrost is a product of cold climate conditions; it covers about 22
percent of North America. These areas are generally divided into two zones,
continuous, about 2,950,000 mi2, and discontinuous, about 2,960,000 mi2
(Black, 1954). These will be defined later. Figure 1 shows the extent of
these zones in Alaska. Because the interior of the earth is hot and the
outer crust is cold, a temperature gradient exists called the geothermal
gradient that averages about 1°C/40 m (1°F/70 ft) of depth. However, within
the uppermost few hundred meters, the temperature is also influenced by
local climates and these layers will have different temperatures in the
tropics as opposed to polar regions. Moreover, other elements of the environ-
ment come into play near the surface such as vegetation, slope direction,
moisture content, and nature of the geologic materials that also influence
the near-surface temperature of earth materials. Permafrost develops when,
under a long continued cold climate, geothermal heat from the interior of
the earth is not supplied rapidly enough to prevent permanent freezing at
and for some distance beneath the surface.
Figure 2 is an idealized schematic diagram for a homogeneous material
that was first developed by Russian workers (Muller, 1947, p. 13) to illustrate
and explain some fundamental concepts concerning permafrost and its distribu-
tion. In Figure 2, the geothermal gradient is exaggerated to achieve clarity
and extends downward from point Z. Above Z, the extended line is the mean
annual ground temperature and is under the influence of seasonal variations;
this is true for any point on the earth, not just polar regions. With
seasonal warming the surface warms and the temperature increases toward E
to a maximum,then as cooling commences, the temperature decreases toward A
and reaches some minimum before the cycle is repeated. The magnitude of
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ENVIRONMENTAL ATLAS OF ALASKA
9/69
FIGURE 1
Distribution of Permafrost
in Alaska
SOURCE: FERRIANS
Generally underlain by
continuous permafrost.
Underlain by discontinuous
permafrost.
Underlain by isolated
:i:i:i:-:i:;:;:;> masses of permafrost.
n Generally free from
permafrost.
100 200 300
CO
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these seasonal variations is called the amplitude of seasonal temperature
variation and is transmitted downward with decreasing magnitude until some
depth is reached where these variations approach zero. This point, Z, the
depth of zero amplitude, is of fundamental importance in the behavior and
permanence of frozen ground. Surface disturbance may cause this point to
move up or down, depending on the temperature at that point.
Figure 2 also illustrates three hypothetical examples of how such a
diagram may be used. If the freezing line AB remains outside the curve (to
the left) for minimum temperature as the seasonal temperature reaches its
coldest, no ground freezing will occur at any season. Such conditions prevail
in warm climates such as the tropics except at high altitudes. If the freezing
line were at CD, it intersects the cooling curve and seasonal freezing would
occur. However, CD does not intersect the line of mean annual ground tempera-
ture below Z so no permanent frozen material is present. Such conditions
occur in all areas where seasonal freezing occurs to some depth and at
higher elevations of tropical climates.
Line EF introduces some new elements to this description because it shows
\
the various relationships in a permafrost locale. Line EF, the freezing line,
now moved to where it intersects the warming curve near its extreme seasonal
amplitude, also intersects the geothermal gradient at some distance below the
surface at F. Under this circumstance, permafrost would extend to F or a
depth of about 190 feet on the scale shown here. All temperatures along the
geothermal gradient are below freezing and become colder with decreasing
depth. Point G on line EF is where the freezing line intersects the seasonal
warming curves and marks the maximum depth of seasonal thaw. The distance
between E and G is the thickness of the active layer or the layer of
seasonal freezing and thawing, in Figure 2 it is about 1 meter (3.3 feet)
thick. At Barrow, in northern Alaska, permafrost extends to 400 m (1300 feet)
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COOLING
A C
WARMING
E
o
2
N
MEAN
ANNUAL
GROUND
TEMP
B
'ACTIVE LAYER
UJ
UJ
U.
Q.
UJ
O
h-50
h—1OO
—ISO
20O
^250
GEOTHERMAL GRADIENT
Figure 2
Typical temperature regimens in permafrost and non-permafrost locales.
gradient is exaggerated to improve clarity.
Geothermal
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and the active layer is thin; as the southern boundary of permafrost is
approached, point F on the geothermal curve gets closer to the surface and
the active layer is thicker because more seasonal heat is available to thaw
the subsurface materials.
Temperature at Z, the level of zero amplitude, is fundamental in pre-
dicting and understanding the behavior of frozen earth materials. When the
temperature at the level of zero amplitude is several degrees below freezing,
depth and stability of permafrost is increased. Should the line EF shift
nearer Z, that is, the temperature at Z increase, depth and stability of
permafrost will decrease. It is under this latter circumstance that surface
disturbances can seriously alter the permafrost regimen because it is then in
tenuous equilibrium without the added stress of disturbance of an environ-
mental factor. It is the temperature at point Z that is used to define the
boundary between continuous and discontinuous permafrost and ranges from about
-12°C at Barrow to 0.0°C at the warmer boundary of permafrost.
A prominent surface manifestation of permafrost, as evident from the air,
is patterned or polygonal ground (Figure 3). In these patterns, the lines
ranging in length from 10-100 m (33-333 ft) are usually ice wedges with the
thin edge downward and are the basis for the classification of permafrost
by Pewe (1963). These wedges are actively forming in areas of continuous
permafrost which, according to Pewe, only occurs when the ground temperature
is colder than -5.0°C at the level of zero amplitude. Ice wedges are not
actively forming in the zone of discontinuous permafrost where the tempera-
ture ranges upward from -5.0 to 0.0°C at the level of zero amplitude. Ice
wedges are common in the discontinuous zone but result from former climates
colder than at present. Patterned ground may be present without ice wedges
in areas where thawing, resulting from recent warming climates, caused the
ice to disappear but preserved the patterns; Pewe refers to these as fossil
ice wedges.
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Figure 3. Polygonal ground. This is the more common form of patterned ground and represents resultant
processes that are characterized of climates severe enough to cause permafrost.
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Theoretical treatment of heat transfer physics based on these basic
concepts has allowed construction engineers to compute the behavior of
permafrost under specific treatments. By these calculations, they are able
to predict how much fill is required to preserve permafrost during construc-
tion activities which use geologic materials for foundations. Using such
theoretical treatments, engineers have concluded that in areas of continuous
permafrost it is economically feasible to preserve permafrost by placing
gravel pads or road overlay directly on undisturbed surface materials. Con-
versely, in areas of discontinuous permafrost, with its higher temperature,
even in the frozen state, it is not economical to prevent thawing by fills of
natural materials, and other means to induce stability must be used. Experi-
ments using artificial insulating materials appear promising, and pilings
embedded in permafrost for buildings and other structures have long been used
in Alaska, Canada, and Russia. To be effective, pilings must be properly
installed or repeated freezing and thawing of the active layer can "jack"
them out of place and seriously disturb the supported structure. With proper
design and construction procedures, these methods produce stable but costly
foundations, compared to warmer climates. These additional costs are the
price that man must pay when he brings his exotic way of life into this cold
environment, if he is to successfully cope with these environmental conditions.
In the zone of continuous permafrost, the ground is unfrozen only under
specific conditions. All ground is frozen regardless of slope direction or
altitude except under large lakes or rivers. Brewer (1958) places lakes and
rivers into two depth classes, those 0.6-1.0 m (2-3 ft) and those 2-3 m
(6-9 ft). Shallow lakes and rivers [less than 2 m (6 ft)] freeze to the
bottom each winter and are underlain by frozen materials. Deeper waters do
not freeze to the bottom and are underlain by unfrozen material. Heat flow
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calculations suggest that deep lakes wider than twice the depth of regional
permafrost are underlain by unfrozen material to the bottom limits of perma-
frost. Such lakes, therefore, form vertical chimneys of thawed material and
may be a source of potable ground water. A similar circumstance is present
in deep rivers whose active flood plains are two times wider than the depth
of permafrost. Instead of chimneys, unfrozen material beneath rivers consists
of channels bordered by permafrost and may act as subsurface streams with
gradients similar to those at the surface.
Similar relationships hold in the zone of discontinuous permafrost.
However, as temperature of the frozen material rises, slope direction and
elevation become important and south facing slopes may be unfrozen. Many
recently snifted river-meanders in this zone remain unfroze, whereas adjacent
portions of the flood plain may contain permafrost. Vegetation in this zone
may frequently be used to delineate unfrozen ground and commercial white
spruce is usually restricted to unfrozen slopes and thawed portions of flood
plains.
Minor topographic features in permafrost areas, but interesting because
of their origin, are "pingos," an Eskimo word for low hill. Pingos are conical
hills ranging in height from less than ten to one or two hundred feet and up
to 600 feet or more in diameter. They are covered with a thin layer of soil
but the interior is nearly pure ice. Their location and mode of formation
are believed related to active ground water movement. On the arctic slope
they occur on flat terrain (Figure 4) but in the discontinuous zone they
usually occur in valleys and many have melted sufficiently to form small
circular lakes.
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Figure 4. A pingo on the arctic slope of Alaska, about 30 miles south of Prudhoe Bay; this pingo is
about 50 feet high and about 200 feet in diameter at its base.
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PROPERTIES OF THAWED MATERIALS
Two papers summarizing many of the engineering problems caused by
permafrost are those by Pewe (1966, revised from the earlier 1957 version)
and a recent discussion by Ferrians, et al. (1969). Pewe cites many examples
of failures of engineering works, and probably presents one of the most balan-
ced appraisals of permafrost and how it affects life in the north. Ferrians,
et al. presentation was in response to the controversy associated with the
proposed pipeline to transport hot oil from Prudhoe Bay on the Arctic coast
to the deep-water, ice-free port of Valdez in Southcentral Alaska. Their
discussion presents many of the problems caused by improper or insufficient
attention to consequences of melting permafrost and cites most of the litera-
ture describing the theoretical basis for calculating heat flow and rate of
melting under prescribed conditions. However, neither Pewe's nor Ferrians'
work stresses the importance of how the nature of unconsolidated clastic
materials controls their engineering behavior when thawed.
Basically, two procedures can be followed when dealing with permafrost as
an engineering problem: (1) use the frozen material as a foundation by pre-
serving its frozen strength, called the passive method; or (2) permit melting
to occur, then design with thawed or imported materials, after excavating
thawed material, called the active method. Passive methods are usually superior,
especially in continuous permafrost; however, in the zone of discontinuous
permafrost extreme care must be taken to prevent thawing because of the higher
temperature of the frozen materials. Refrigerated pilings have been designed
that may be used in either zone, where the structure warrants the added
cost, and offer a satisfactory solution to achieving maximum foundation
stability in permafrost terrain.
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TEXTURE, WATER CONTENT, AND STABILITY
As discussed in the introduction, permafrost is not a material but a
condition of normal geological materials and it is the properties of these
materials in the thawed condition that are the concern of construction engi-
neers. Texture, or particle size distribution, is the overriding property
controlling the stability and bearing strength of a thawed material. Some
related factors of texture are pore size, total porosity, degree of sorting,
packing or particle arrangement, and shape. Well rounded alluvial particles
pack differently than weathered rock in situ, and pore size and channels will
also differ. Frozen, fresh bedrock usually does not change properties when
thawed. A material dominated by a large percentage of one particle size will
transmit or retain water much differently than one with a wide range in par-
ticle sizes, where large pores may be filled with smaller particles. All of
these physical properties influence the quantity of water held in a material,
the rate at which liquid water moves, and the eventual strength when thawed.
These factors are taken under consideration by the material specialist and
geological engineer when using soil mechanics during the locating and design
of engineering works.
Moisture content, which in permafrost is frozen, is another very important
factor that determines the behavior of unconsolidated earth materials. Ice
in permafrost takes many forms. It may be massive (Figure 5), as in wedges,
and be nearly pure ice; it may be intercalated, lenticular seams or horizontal
masses up to several feet thick (Figure 6); or it may be fine interstitial
ice partially filling pores (Figure 7). Massive and lenticular ice causes
the most serious problems because of the relatively high water content and
volume occupied by ice which drains upon thawing. Massive ice of any form
is usually associated with fine materials (silts and clays) and is rarely
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Figure 5. Massive ice in a road cut about 70 miles northwest of Fairbanks.
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Figure 6. Ice wedges and intercalated ice
40-60 percent
in a road cut near Figure 5; ice content is estimated to be
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Figure 7. Frozen, unsaturated silt. Although this cut melted on exposure, it remained stable because
it was relatively dry. Three to four miles south of the Yukon River (1970).
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encountered in sands and gravels, probably because coarse materials drain
better and remain dry above a water table.
All frozen materials retain their stability and bearing strength when
thawed if their water content is low. Once melting starts and continues,
as under heated buildings or a warm pipeline, transfer and disposal of water
becomes a vital problem when water content is high. Rapid melting without
proper water disposal causes severe thermal erosion and instability, therefore,
the problem exemplifies itself through two facets, temperature control and
moisture movement. Rarely do sand or gravels lose their bearing strength when
thawed if their moisture content is below saturation—such events might occur
when these coarse materials are saturated and frozen below a water table. It
has long been known that airfields built on coarse subsurface materials were
stable even though the construction disturbance caused permafrost to thaw.
Structures using coarse materials for foundations should be stable even when
the ice melts and drains away because their ice content is usually less than
100 percent of the pore space.
Frozen silts, with moisture contents well below saturation, if free from
massive ice, retain their bearing strength when thawed. It is when water
content, in the form of ice, approaches or exceeds total pore space that
instability becomes a problem. Evidence that thawed silt can be stable is pre-
sented by a section of experimental pipeline at the University of Alaska. A
600 ft. aluminum pipe, four feet in diameter, was buried in frozen silt and
heated by hot air at 160°F. Soil moisture content at time of installation
was well below saturation, ranging from 20 percent to 30 percent by weight.
After several months of operation no signs of instability appeared, even
though a thawed zone up to 18 ft. from the pipe developed. Even with this
evenly distributed heat in the pipe and with 4 feet of backfill with frozen
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silt removed during excavation, the surface froze during winter under a
moderate snow cover. Silts even with a high percentage saturation, gain
strength rapidly when the water is removed. Personal observation of slurry-
like silt on a new road excavated through permafrost indicates that this fine
material rapidly changes in properties after thawing and draining.
Pore size is also important because clastic materials coarser than silt
have pore spaces and interstices that are larger than capillary in size, hence,
cannot retain water against gravity above a water table. Capillary rise of
water is nearly impossible in coarse materials, possibly being a reason why
massive ice seldom occurs in these materials. Water may be transfered within
a clastic material in two states, vapor and liquid. Ice cannot move except
to deform under load but can sublime and move as a vapor. Liquid water moves
chiefly by gravity and has limited lateral or upward movement. Stratification,
sometimes within narrow textural ranges, may significantly influence liquid
water movement. A stratum of fine material overlying a stratum of gravel must
be nearly saturated before water moves downward into the coarse material, in
accordance with the soil physics outflow principle. Thus, alternating layers
of coarse and fine materials behave quite differently from a homogenous mix-
ture in their water transmitting properties. This may be a partial explanation
for the usual occurance of massive ice in silts and clays but which is seldom
found in sands and gravels.
Transfer of water in the vapor phase may be important in permafrost
terrains because colder materials cause lowered vapor pressures and water
vapor moves from warmer to colder materials. Thus, during winter, moisture
is transferred upward because surface temperatures are lower at that season,
condensation and freezing of the vapor then occurs near the surface. This
may be one reason why the percentage of ice is greater near the soil surface.
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Water vapor may move in any direction in response to a thermal gradient,
and in artifically melted materials, may move downward or laterally to con-
dense at the thawed-frozen interface. Such phenomena could cause drainage
problems with hot pipelines on sloping terrain, especially in areas of deep
silts. Transfer of water released by thawing is an important consideration
when predicting or estimating strengths and stability of thawed materials
derived from permafrost.
The movement of liquid water in clastic materials has received much
attention by soil physicists and materials engineers and the principles of
movement are well established. If failures are to be avoided in permafrost
terrains, disposal of meltwater becomes all important, because frozen layers
may prevent downward movement of liquid water. In warmer climates, excess
water usually percolates downward to enter and be included in groundwater.
Many times this is not possible in frozen materials and other provisions to
dispose of water must be planned. Where permafrost occurs as massive ice,
or large percentages of lenticular ice, thermal erosion can be serious if
melting is not controlled. It is not the water movement that erodes, it is
the removal of large volumes of ice that causes cavities to appear with highly
turbid meltwater.
Liquid water released by thawing may move upward only in fine textured
elastics and then very slowly. For elastics coarser than sands, water must
move downward under the influence of gravity; if an impermeable layer is
encountered, lateral movement is possible as hydraulic head provides the
energy to move, as governed by the Darcy law. Any engineering structure
that acts as a continuing source of heat such as a hot pipeline must remove
water, which will move in response to gravity and thermal gradients or
laterally downslope on a frozen layer. It is unlikely that much will be
lost to the atmosphere as evaporation because gaseous water moves in response
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to a thermal gradient, and the pipe is warmer than surrounding material
Water must move downward or laterally to colder surfaces where it will
condense and freeze at the cold edge of the thawed envelope.
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TEXTURE AND HEAT TRANSFER
Physical properties of clastic materials strongly influence the rate of
heat transfer mainly by controlling water content and its movement. Since
thermal relationships are so important when dealing with permafrost ter-
rains, an understanding of how physical properties influence heat movement
becomes necessary. Many factors influence heat transfer: temperature,
moisture content, porosity, texture, mineralogy, shape of particles, and
degree of packing (Kersten, 1949). Of these, moisture content and porosity
are the most important and both are strongly influenced by texture. For dry
materials, gravels are better thermal conductors than fine materials. How-
ever, under the natural environment most materials are not dry and the presence
of moisture increases thermal conductivity. High total porosity--silts are
higher than gravels—inhibits heat transfer under dry conditions; however,
even small amounts of water greatly increases it. The insulating efficacy
of dry silt was strikingly evident during operation of the hot pipeline
test referred to earlier. In this test it was noted, after several months
operation, that as soon as a thin envelope of dry silt developed in contact
with the pipe, the rate of heat transfer slowed significantly. However, when
this material was rewetted during breakup the original thermal properties of
the silt returned. A clastic material consisting of one grain size conducts
heat more slowly than one with a wide range of sizes; conduction occurs at
contact points of the material. Thus, it becomes apparent that a complex
system of interrelated factors are operating to influence thermal conduc-
tivity.
Since thermal phenomena are so important for most engineering works on
permafrost, a thorough thermal evaluation of a proposed construction site
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becomes mandatory. Once the thermal regimen is established, knowledge of
controlling factors of clastic materials may be applied to engineering
studies. Thus, another environmental element is added to the already com-
plex system that engineers must consider when planning engineering works in
cold climates with permafrost.
Although each of these topics has been discussed separately, they do
not operate in isolation from one another but by complex interactions which
make accurate predictions difficult. Only by previous knowledge, gained
through thorough reconnaissance of physical factors, thermal regimen, and
moisture content, can reliable predictions be made on how a given structure
will perform. Designers can produce a final structure that will serve its
designated purpose, with minimum damage to the surrounding environment,
if due regard is given to each controlling factor.
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SOME EXAMPLES OF CONSTRUCTION PROJECTS ON PERMAFROST
Many examples, both good and bad, can be cited of engineering works on
permafrost; only a few good ones will be mentioned here. Engineers can use
principles illustrated in Figure 2 as the basis for calculating and evaluating
design criteria for a given project. A good example of such treatment is that
described by Peyton (1969) and points out the necessity of having certain
required information before design can start. A good theroetical prediction
of thawing caused by a hot pipeline is given by Lachenbruch (1970) and illus-
trates the complexity of the system under study. Lachenbruch discusses the
role of water but his treatment of its movement under implied conditions is
not as thorough as his thermal analysis. In designing the Trans-Alaska
pipeline, hundreds of man-years have been expended in data gathering and
engineers are using computer models based on these data to solve many problems;
however, much of the input to the computer is based on the principles and
interactions of factors discussed in this review.
Passive methods of construction are used in Arctic Alaska for drill rig
pads and roads by providing enough gravel fill to preserve permafrost. The
Naval Arctic Research Laboratory at Barrow is built on wooden piles imbedded
in permafrost to maintain the foundation strength of frozen gravels. An
example of a major construction project on permafrost is that of the research
community of Inuvik on the MacKenzie River delta, Northwest Territories. It
was decided to use passive construction methods and support all structures on
piling. Careful planning and scheduling of operations consisted of: mini-
mum disturbance (all clearing was by hand), restriction of traffic to thick
gravel pads and roads, and installation of piling deep enough and early
enough to permit complete freezing before any load was placed on them.
(Johnson, 1963). Results are outstanding, with no serious failures after
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ten years. Although every effort is made to route highways on coarse materials
to utilize their superior foundation properties when thawed, some sections must
cross frozen silts. Therefore, some sections of highways built in the zone of
discontinuous permafrost are expected to be unstable for several years where
they cross areas of high-ice, silty materials as the thermal regimen shifts in
response to increased thermal inputs from the new dark surface.
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SUMMARY
The presence and need for developing natural resources existing in
northern North America has focused the attention of engineers and scientists
on gaining a better insight of permafrost properties and how it behaves as an
engineering material. This review gives a brief, nontheoretical description
of permafrost in its various forms, and has, as its primary objective, a
discussion of properties of clastic materials in their thawed state and how
these influence stability and bearing strength as applied to engineering prob-
lems in very cold climates. Attention is drawn to the requirement that to
understand the environmental behavior of permafrost, it is vital that the
mechanical properties and extent of clastic materials be known prior to design.
Water relations are always important controls over engineering behavior of
clastic material. In frozen materials,moisture relations are critical and may
make the difference between success or complete failure of engineering works.
Temperature as a factor seldom requires serious attention by designers in
temperate regions; however, in permafrost regions, detailed thermal analysis
becomes an overriding consideration of success is to be assured.
A final conclusion is that, without detailed consideration of materials
extent and properties, their water content and predicted behavior as its phase
changes from ice to water, and thorough thermal analysis, any proposed project
may fail. Complicated as these interactions become, failure to properly
evaluate each in its role as a factor can only cause additional failures.
Modern computer technology has provided planners with a mechanism of testing
various models, what remains now is to gather sufficient data from intensive
reconnaissance to avoid overlooking some vital factor. Prior to computers,
handling of extensive data was limited because of ponderous hand calculations
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and some factors may not have received sufficient attention. That day is
fast vanishing, and even though more intensive field exploration generates
huge quantities of data, they can now be handled by computers; such treatment
should result in superior engineering works with minimum damage to the
environment.
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REFERENCES
1. Black, R. F., "Permafrost--A Review," Geol. Soc. Am. Bull.. 65:835-855.
1954.
2. Brewer, Max C., "Some Results of Geothermal Investigations of Perma-
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U.S. GOVERNMENT PRINTING OFFICE: 1973-797-816/14 REGION 10
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