A Review On Permafrost Geotechnics, Foundation Design and New Trends
A Review On Permafrost Geotechnics, Foundation Design and New Trends
A Review On Permafrost Geotechnics, Foundation Design and New Trends
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Abstract: Soil mechanics and geotechnical engineering that are used in mild climates are based on soil
temperatures above freezing point. When the temperature falls below freezing point, seasonally or during the
whole year, permafrost geotehnics application becomes necessary. Water phase change from liquid to solid
mutually induces frost heave and frost thaw as the main geotechnical problems in frozen soils. Permafrost
covers vast area of planet Earth, and therefore many types of structures are built in the permafrost conditions. In
this paper a comprehensive review on geotechnical problems and solutions for different types of civil structures
in permafrost has been performed. Structures that are discussed include shallow and deep foundations,
thermosyphones, roadways, railroads, bridges, and pipeline foundation. It was concluded that special
geotechnical engineering for permafrost projects is necessary to avoid main problems. Historical and new
projects are approval for existence of these geotechnical problems and necessity of mitigation methods for
future projects. Depending on type of project, active or passive cooling systems and thaw resistant techniques or
combination of all should be applied to build a stable structure in the permafrost regions.
Keywords: permafrostgeotechnics,thermosyphone, roadway, railway, pipeline foundation
I. INTRODUCTION
Practice of soil mechanics for mild climatesis established on soil temperatures above freezing point. In
permafrost regions, heat transfer as a main factor impacts freezing and thawing process in the seasonal
frost(Barker et al. 2013).Change of phase in soil water content from liquid to ice, and vice versa has significant
effect in physical properties of the soil. These properties are very sensitive to variation in soil temperature.
Considerable heaving by pore-water migration in freezing happens in addition to in-situ heaving phase change,
from water to ice (Barker et al. 2013).
Climates with temperature 0°C or below in the coldest month of the year is used to determine southern
border of frost in the cold regions of North America. Depth of seasonal frost incursion equal to 30 cm or more
below ground level, one time in every 10 years is considered a norm for detection of this boundary(Barker et al.
2013). The cold regions are classified into two types. A type, where the ground is frozen in a season only, and
other type lasts all year around.Also in other classification, the permafrost exist everywhere (continuous), or
permafrost exists just in some places (discontinuous). Usually, the mean annual ground surface temperature
should be lower than -2.7° C for maintaining permafrost condition(Barker et al. 2013). In non-permafrost
regions, depth of seasonal frost is defined as the maximum depth of freezing duringthe season. In permafrost
regions that frost lasts during whole year, active layer is defined as the maximum depth of thaw and, beneath
that, the ground remains frozen all over the year(Barker et al. 2013). Frost susceptible soils, controlled by
capillary rise and permeability, usually heave when enough water in the soil exists and expands due to the ice
formation. Generally, soils with more than 10 percent fine particles passing the #200 sieve can be assumed as a
frost susceptible soils considering following exceptions. In low capillary rise and high permeability conditions
similar to gravels, ice segregation happens; therefore heave will not occur. In other end i.e. in clays, capillary
rise is very high and permeability very low, so limited volume of water is drawn up into a clayey soil, and
limited ice lenses are formed in turn. Despite to the gravels and clays, silts with enough capillary rise and
permeability are highly frost-susceptible(Barker et al. 2013). The geotechnical characteristics of naturally frozen
soils are very important for northern civil engineering projects. The type of sampled frozen soil, the in situ
thermal gradient, the time and method of sampling, and transportation impactthe quality of frozen soil samples
for tests. Melt of ice lenses formed during frost heave, and pore water expulsion cause settlement. Also, shear
strength is lost in the soils which are called “thaw unstable” soils(Barker et al. 2013). Permafrost gets impact
from climate change, and human activity. They are controlled by variation in active layer thickness and
permafrost thermal gradient. Thawing of ground ice close to the permafrost table forms irregular and uneven
thaw settlement and thermokarst. These features induce great danger to infrastructures and structures, which are
laid on permafrost region (Nelson et al. 2002). Usually, the design procedure for foundation in permafrost area
is done by protecting permafrost from melt and controlled thaw after building the foundation. By protecting the
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permafrost from melt, the thaw settlement not only is avoided, high loading capacity of cold permafrost area is
applied in design too(Wei et al. 2002).
Study of permafrost geotechnics includes different topics. In this paper, a review considering new
trends in foundation design especially pile foundation, thermocyphones, road and railway, and pipeline
foundationare presented.
Fig. 1 Large differential settlement in a structure in permafrost region, Fairbanks(Modified after Clarke, 2004).
The SEF idea can be simplified by modeling a foundation as a beam system or a cantilever mode by
using reinforcing steel in the bottom and top of the SEF footing (Fig. 2). Load disturbance resulted from thaw
strain are located under them(Clarke, 2004).
Fig. 2 SEF system in a) Footing mode, b) Beam mode, c) Cantilever mode(Modified after Clarke, 2004).
Pad and post is another permafrost foundation system with lowest price that includes a concrete or
wood pad located on the ground or hidden under the ground (Fig. 3). The structure is maintained on a system of
rigid beams. These beams avert excessive racking of the structure during settlement or re-leveling. A free air
space under the structure is provided by columns that thwarts melting of the frozen soils and can be covered by
some ornaments or decoration(Clarke, 2004).
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Fig. 3An example of pad and post system(Modified after Clarke, 2004).
Beside adjustable foundation designs other foundation systems which are common in permafrost areas
are slab-on-grade, crawl space, external support, and basement foundation systems(Clarke, 2004). Slab-on-grade
foundations are getting popular in Canada, especially in rural, northern and First Nations housing (Fig. 4). This
system provides a cost and energy-effective, and durable foundation. Positive aspects of this system can be
summarized as: reduction in the potential for soil moisture and pressure problems by building it in a grade level,
and reduction in cost of heating air by removing the basement option(CHMC 1998).
Fig. 4A schematic and a real example of insulated Slab-on-grade foundation(Modified after CHMC 1998).
To avoid or reduce the potential for frost heave and settlement, foundations must be emplaced on an
undisturbed soil that does not have any organic matter. A slab that transfers the structure loads to soils
underneath is used. Another point is insulation for heat flow, providing desirable heat for occupants inside along
with frost protection. Design in permafrost areas should use some methods to retain the ground in frozen status
rather than unfrozen. Also, air, soil gases and water leakage into the home should be prevented (CHMC 1998).
One of the refrigerated spread footings applications can be spread footings with a
grade beam or post and pad foundations. They are usually less expensive than the slab-on-grade
or pile foundations. This refrigerated foundation can employ an insulation layer on the tope of cooling system to
decrease heat flow from the ground surface and lower cooling load requisite. Mechanical refrigeration or
thermosyphon can be used for refrigeration in this foundation(Clarke, 2004). Refrigerated on-grade foundations
are usually employed in sites with heavy floor loads. Examples could be warehouses, garages, reservoir tanks,
industrial complex. Components of the foundation usually are concrete slab, a layer of bedding sand, a layer of
insulation, a system with piping for refrigerating, and a non-frost susceptible pad over the soil in the site.
Usually a membrane is used to prevent the insulation layer degradation by leakage or spill of petroleum or its
products(Clarke, 2004). The best design method for this type of foundation is obtaining optimized design and
material in foundation using numerical methods. Active systems, and passive systems have been used
successfully in permafrost area projects. Active systems were methods that used a vapor-compression
(mechanical) refrigeration (in airport buildings of Barrow and Deadhorse, Alaska) and cooled liquid where the
liquid was pumped and cooled by ambient air in a fan coil unit (in vehicle maintenance shop at Dalton highway,
Alaska). Passive system were equipment such as air ducts (in a fabrication shop of Sohio in the Prudhoe
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Fig. 5 Slurry pile with Polyethylene film around it (Modified after McFadden, 2004).
Piles in permafrost should be designed in such a way that piles keep the settlement in acceptable range.
Meanwhile, applied load should not be more than the short term adfreezestrength of the pile-soil contact(Nixon
1978).
There are different terms which are used for cooling system of piles to prevent thaw in warmer times.
Thermal pile, or thermosyphon or thermosiphon, or thermopile or thermoprobe or heat pipe or heat tube or
thermotube are used interchangeably to address this foundation system (Clarke, 2004). Design usually take into
the account the tangential adfreeze strength at the soil-pile interface, which is maximum stress that creates
failure of the adfreeze bond between the pile and the frozen soil.In this method settlement allowance during
service life is not considered, however settlement can be limited by applying higher factor of safety. A method
for rational consideration of settlement exists. In this method the creep of ice-rich frozen soil is approximated
using a constant creep rate during service life(Nixon 1978). Then, the creep law, or flow law, is applied in a
mathematical model for the pile, pile-soil contactand the adjacent continuum. Finally settlement rate by
applying a known pile load is calculated through a solution.
A research on adfreeze strength of different piles in permafrost conditions using Ottawa sand as the soil
material was conducted (Fig. 6)(Parameswaran 1978). It was concluded that the maximum adfreeze bond
strength happens in uncoated wood piles (B.C. fir and spruce). However, adfreeze bond strength in concrete
piles were lower than wood; it was higher than steel and coated piles. Application of coating material such as
creosote, paint, and etc. decreased adfreeze bond strength significantly. From low to higher values of adfreeze
bond strength, following piles were sorted in order. From painted steel pipe in the lowest rank, to the creosoted
B.C. fir piles, unpainted steel H-sections, cylindrical section, concrete, uncoated spruce, and uncoated B.C. firto
higher and the highest value(Parameswaran 1978).
Fig. 6 Depicting different types of forces on a pile foundation in permafrost environment (Modified after
Parameswaran 1978).
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Gravels and boulders are a porous media with very effective natural convection in winter and only conduction in
warm seasons. These material if combined in grooves with specially designed piles (Fig. 7), thawing in the
frozen soils can be avoided (Li and Xu, 2008).
Fig. 7 Special designed concrete pile with grooves(Modified after Li and Xu, 2008).
In winter time, in the grooved concrete pile surrounded with gravel and boulder size grain, cold air
moves downwards and chills the adjacent soils. In summer time, lower part with colder air has higher density
than warmer air at the top which prevents convection. Heat exchange in conduction mode happens in negligible
amount.It was observed that with using the specially grooved pile, the refreezing time for adjacent soil is
decreased around 40% in comparison to normal piles(Li and Xu, 2008). Permafrost table will increase because
of more cold air penetration and thawing settlement will decrease. In turn, bonding strength will increase
leading to 16% increase in bearing capacity in 10 m long pile with 1m diameter comparably. With stable frozen
period, the frost heaving force is decreased by 80% (Li and Xu, 2008). In lateral loading of piles, pile fixity near
the bottom of the active layer is considered for permafrost soil conditions. Experiments in permafrost showed
that laterally loaded piles will typically bend near the top of the frozen surface. They show higher resistance to
thelateral loads during short-term loading cases(Nottingham and Christopherson1978 ).
Also creep settlement rate calculation for piles in saline permafrost using following equation obtained from the
non-linear creep law can be obtained (Nixon and Lem 1984;Nixon and Neukirchner 1984).
3( n1)/2 aB an
ua (1)
n 1
a = Pile displacement rate
Where u
a = Pile radius
a = the applied stress on the pile shaft
n = Creep exponent
B = Creep coefficient
Settlement of courthouse building in Alaska using above equation estimated the general rates of creep
in piles closely(Miller and Johnson 1990). Sensitivity of obtained rates to small changes in temperature was
more than data reported by authors of equation (1).
The settlement patterns related to salinity of soils were from ground temperature changes(Miller and
Johnson 1990). Soil surrounding upper half of the pile had lowersalt content, while the soil around lower half of
the pile was highly saline. In early summer the creep movements were small, but when the lower portion
became warm due to salt existence, expected bearing capacity was not obtained and high creep rates occurred.
By start of winter the upper portion of the pile becomefrozen and the creep stopped (Miller and Johnson 1990).It
was concluded that salt contents must be taken into account in the design step of pile foundations in permafrost
conditions. The frozen soils creep are considerably sensitive to the pore fluid salt content and change in
temperature. Test for detection of pore water salinity must be taken necessary in a routine investigation(Miller
and Johnson 1990).
Piles can behave differently under seismic loading in permafrost regions. A series of shaking table tests
for scale model of pile foundation in frozen soils were conducted (Wu et al. 2012). It was found that dynamic
loading causes the frozen soil foundation in scale model present a temperature rise response. Shear deformation
response in dynamic loading for the foundation showed clear resonance characteristics with dominant
frequencies that were all above 15Hz. The reinforced soil did not show any resonance, and dominant frequency
for that was in high frequency domain(Wu et al. 2012). Also,ice layers in permafrost had impact on the
acceleration, dynamic earth pressure, and displacement reaction, considerably. Increase of temperature changed
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the seismic response of permafrost layer and pile foundation, and a heightening of acceleration input increased
the response values(Wu et al. 2012).
2.2.Thermosyphon
Thermal pile can be defined as a pile with natural convection or forced circulationcooling system that
transfers heat from the ground to the air(Johnston 1981). These thermal pile systems can use coolant circulated
in the tubes, cold air blown to the pile by fluids or air convection. Also, there is a two-phase mutual alteration of
vapor and condensate for that system.Thermosyphon usually is made from two-phase system,a pressure vessel
filled with a singlecompound under pressure. This compound that can be propane, carbon dioxide, ammonia
existsin liquid and vapor phases which are cyclically transformed to each other by absorbing and releasing heat
(Clarke 2004).Thermosyphon cooling system was applied in Alaska in 1960 and was noticeably employed with
over 120,000 thermosyphons installation on the Alaska pipeline in 1975 (Heuer et al. 1985). The early
thermosyphons were made from vertically sealed tubes in the ground with surficial radiators. An example of
passive cooling system and its structure by using thermosyphone in foundation of oil tanks in Alaska can be
seen in Fig.8(Zarlinget al. 1990).The vertical thermosyphon evolved to usual sloped evaporator thermosyphon
or (Sloped-TF) in 1978 (Fig.9-b) and then to the flat loop thermosyphon (Fig.9-c) (Holubec 2008).Application
of different thermosyphones can be as follows (Holubec 2008):
I) Thermoprobe in designation and deescription too can be used for keeping ground frozen around piles or
keepingground frozen around structures.
II) Thermopile in designation and description can support structures on piles installed in frozen ground.
III) Sloped-Thermosyphon-Foundation in designation which is described as sloped evaporator pipe under slab-
on grade foundations can be used to keep ground frozen below slab on grade foundation.
IV) Flat-Loop-Thermosyphon-Foundation in designation which is described as flat loop evaporator pipe under
slab-on grade foundations can be used to keep ground frozen below slab on grade foundation.
Fig.8 Typical thermosyphone structure installed in Alaska(Modified after Zarlinget al. 1990).
Four figures below (Fig. 10) show different types of thermosyphone in practice. Flat loop
thermosyphone was tested in comparison to sloped-TF in Winnipeg in 1993-1994, during winter time. It was
observed that flat loop-TF could freeze 1.4 times the volume of soil compared to the sloped-TF.
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Fig. 10a)Thermoprobes (in Joe Lake, MB) for highway stabilization (Courtesy AFC), b) Thermal piles
( in Manitoba DC Line, Courtesy AFC), c) Sloped thermosyphon foundation (inRoss River, YT), d) Flat loop
thermosyphon Foundation (in Airport maintenance garage, Inuvik, NT, (Courtesy AFC) figures from (Modified
after Holubec 2008).
After this performance, it started to widely use in Canada and Alaska from 1994 due easier installation
and good performance (Holubec 2008). Hybrid system can be composed from flat-loop TF, enhanced by the
addition of mechanical cooling system to accelerate and increase the rate of cooling. The hybrid system includes
a cooling coil around the verticalevaporator pipe. The coil is connected to a refrigeration compressor (Fig. 11).
Themechanical cooling part becomes active in warmer air temperature that condensation of thecarbon dioxide in
the pipe gets difficult(Holubec 2008).
Fig. 11Hybrid thermosyphone installation in Inuvik hospital (Modified after Holubec 2008).
Fig. 12A schematic depiction of wintertime pore-air circulation in an ACE (Modified after Saboundjian and
Goering 2003).
B analysing temperature data (Fig. 13), it was concluded that control section was colder at the
embankment centerline, but warmer in the side slope region(Saboundjian and Goering 2003). It was observed
that insulationlayer in control section can reduce the annual temperature in soil beneath the embankment
centerline. Although, considerable yearly thaw was happening in the side-slope region inside the foundation
soils under the control section. Thaw in control section side-slope resulted in major distortion and shoulder
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rotation, while no sign of distortion at either shoulder of ACE embankment was observed (Saboundjian and
Goering 2003).
Fig. 13 Positions of thermistors in strings A to C in control section and strings D to K in ACE located within
and below the embankments (Modified after Saboundjian and Goering 2003).
Three types of passive cooling methods were applied in Thompson Drive in Alaska to control the
thermal stability of permafrost beneath the highway(Xu and Goering 2008). These methods were ACE layers,
ventilated shoulders using crushed rocks and boulders, and two-phase hairpin thermosyphons. The hairpin
thermosyphons (Fig. 14) is a novel design that keeps both the condenser and evaporator concealed under the
ground surface. Older models of road thermosyphons use air-cooled condenserswith finned heat exchangers
reaching above ground surface in contact withfree air. By using hairpin design, problems such as high-cost of
air-cooled heatexchangers and the safety and esthetic concerns are avoided. Heat flux and temperature data
obtained from the hairpin thermosyphons confirmed its efficiency for eliminating heat from subgrade soils
underneath the embankment(Xu and Goering 2008).
Fig. 14 Hairpin thermosyphon condensers used in Thompson drive, Alaska (Modified after Xu and
Goering2008).
A review on different methods and their costs in stabilizing roadbed in permafrost areas was performed
(Regehret al. 2012). These methods were classified to four categories: (I) methods thatcontrol roadbed thawing;
(II) methods thatcool the roadbed; (III) methods thatinsulate the roadbed;
and (IV) methods thatreduce roadbed fill weight.
Two types of techniques for category (I) were suggested. Prethawing or thawing before construction of
an embankment by removal of the topsoil and vegetation, and exposing underneath permafrost was one of those
techniques. Thawing after construction of road embankment by embankment widening and snow removal
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another technique(Regehret al. 2012). Six methods in category (II) were found, which are used broadly to cool
the roadbeds and are well documented especially in Qinghai-Tibet Railway. These techniques include (a)
reduction of solar radiation by different covers; (b) construction of air convection embankments; (c) utilization
of ventilation ducts; (d) application of thermosiphons; (e) application of heat drains; and (f) methods to control
heatconduction. One or combination of above methods can be used to achieve desirable results too (Regehret al.
2012). Category (III) can be applicable by insulation that made from polystyrene or polyurethane foam. The
insulation material is emplaced near to the surface of the roadbed in a layer form. To apply category (IV)
strategy, light weight fill material withlower density than typical soils and rock and even as low as 12 kg/m3 can
be used. The light weight fill material could be expanded polystyrene (EPS) blocks, foamed (or cellular)
concrete, rubber tire fills from shredded or crumbed tires, and organic fills (peat) or combination of them
(Regehret al. 2012). It was concluded that cost of above improvement techniques includingtransport costs
changes in different geographic and climatic conditions.Betweenmethods to cool the roadbed, air convection
embankments and ventilation ducts had lower capital costs. Installation of reflective surfaces and shoulder
ACEs had lowest life-cycle cost perspective(Regehret al. 2012). Generally techniques to controlthawing,
insulate the roadbed, and reduce roadbed fill weight had lower capital and life-cycle costs than roadbed cooling
techniques. Sometimes do-nothing procedure compared to above techniques can be considered by taking
different strategies cost, and expected serviceability into account(Regehret al. 2012).
Fig. 15: Different cooling methods in Qinghai–Tibet railroad project. a)Shading boards; b) Rock-based
embankment; c) Embankment with temperature-controlled ventilation ducts; d)Thermosyphones(Modified after
Wei et al. 2002).
Fig. 16 Different configurations for crushed rock embankment in QTR project. (a&b) Crushed rock
embankment; (c) crushed rock revetment; (d) crushed rock U-shaped embankment(Modified after Cheng et al.
2009).
foundation. Piles were installed open-ended to depths of 18 to 21 mfrom the ground surface passing frozen silt
and resting on a sandy layer(Krzewinski and Ross 2013). Capacities of piles in ice rich soils relies on several
factors such as temperature, rate of loading, ice content, and soil type. Axial capacity of piles were formed from
arrangement of the adfreeze bond laterally from pile perimeter and an end bearing in the sand layer which were
smaller comparably (Krzewinski and Ross 2013).
Lateral capacity of piles were calculated considering two scenarios by using a non-linear material
properties and p-y curves, a mutual relation between soil reaction (p) and lateral pile deflection (y). Two
considered scenarios were: a) a completely frozen layer in the height of winter conditions, and b) when the
thawed active layer is in its maximum thickness in late fall(Krzewinski and Ross 2013).Thermosyphons were
mounted inside 6 out of 12 piles, and inside 4 out of the 6 piles at abutment, alternatively. Radiators were
installed horizontally (Fig.17) with some slope on piles while thermosyphon condensers had 6 m2 condenser
area.It wasconcluded that this railroad bridge was first in its own to use thermosyphons for passive refrigeration
of its foundation and surrounding soils(Krzewinski and Ross 2013). Good performance for the bridge after
construction was reported.
Fig.17 Thermosyphone condenser installation on bridge pier piles (a: courtesy of Arctic Foundations Inc, and b:
courtesy of Alaska Railroad Corporation’s)(Modified after Krzewinski and Ross 2013).
Construction of dry bridges in total length of 125 km were reported in QTR project (Fig.18)(Wei et al.
2002). Piles of 1.2 m in diameter were installed in 25–30 m depth from ground surface that produced a robust
foundation with deformations of less than 2 mm (average) and 5 mm (maximum) after operation.
Fig.18 An example of dry bridge in Qinghai–Tibet Railway (QTR) project(Modified after Wei et al. 2002).
Dry bridges can act as a shade and reduce the ground temperature in combination with air flow below them.
They can tolerate heavy loads and create required stability in sensitive permafrost. Wild animals can easily pass
railroads or highways (Wei et al. 2002).
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pipeline(Oswell 2002).The pipeline below freezing point keeps stability of permafrost slopes, and enhances
buoyancy control and restraining the pipe by the frost bulb around the pipeline. The geographic location in
which the pipeline set-up changes from below freezing point to above freezing is called the “last point of cold
flow” usually lies in transforming zone from permafrost to non-permafrost zone(Oswell 2002).The transition
zone can be detected by geophysical, and geotechnical investigations. With mentioned transition, frost heave
and thaw settlement problems should be considered simultaneously. Mitigation techniques for thaw settlement
and frost heave can be different based on project and time of identification. In design step, re-routing is one of
the best methods to avoid those hazards. Excavation and filling with thaw stable materials, insulation, pipe
temperature control,ground water control and support above ground surface are some preventive methods for
thaw settlement and heave frost (Oswell 2002).A numerical modelling was conducted to study thermal effects
under permafrost conditions in the Chinese–Russian crude oil pipeline(Zhang et al. 2010). Two types of
transfer, conventional pipeline burial mode and pipeline on aboveground embankment were modeled. Two
methods for thermal control e.g. bare and insulated pipeline along with three climate conditions were
considered. In climate conditions average ground surface temperatures of −0.5, −1.0, −1.5 °C, along the pipeline
in the next 50 years period were applied in modeling(Zhang et al. 2010). It was concluded that in all the climate
conditions and the thermal control methods in buried pipeline mode the permafrost table goes down constantly
after start of pipeline usage (Fig.19a). Although,in aboveground embankment pipeline, permafrost table under
embankment rises in the first decades, then goes down when operationtime goes further (Fig.19b) (Zhang et al.
2010).
Fig.19 Progress of thaw plugs under bare and insulated pipeline in mean ground surface temperature of −0.5 °C
a) under buried pipeline b) under embankment pipeline(Modified after Zhang et al. 2010).
It was also concluded that in the embankment mode by thermal control methods, thawing of permafrost
can be prevented in the service life of the pipeline. However, in usual buried pipeline method, the thawing of the
permafrost cannot be prevented in all the assumed climatic and insulation conditions(Zhang et al. 2010).
Backfilling with non-frost-susceptible soils, and/or utilization of thermosyphons in the buried pipeline method is
recommended in the warm and ice-rich permafrost conditions to guarantee pipeline stability (Zhang et al. 2010).
Takashi’s equation [Eq. 2] for frost heave prediction and numerical modeling to evaluate the maximum bending
strain and stress for structural design was used for pipeline structure (Kanieet al. 2006).
100 0 U0
0 1
U [2]
Numerical modeling by above equation predicted frost heave withreasonable accuracy.It was
concluded that load intensity from frost heave can be assumed with a constant distribution along the pipeline in
non-permafrost area(Kanieet al. 2006). In non-permafrost end, Takashi’s equation with two dimensional
analysis of heat transfer can predict frost heave in freezing season. The distributed load (Fig. 20) which was
calculated with two dimensional analysis of heat transfer but without considering creep effect demonstrated
good concurrence with the observed results in reality(Kanieet al. 2006).
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40
-20
-40
-40 -35 -30 -25 -20 -15 -10 -5 0 5 10 15 20 25 30 35 40 45
Distance from the boundaryin m
IV. CONCLUSION
Permafrost areas cover close to a quarter of earth surface and many projects have been or will be
constructed in the permafrost. From a comprehensive review on geotechnical problems and solutions in different
civil projects in permafrost regions (e.g. building foundation, roadway, railroad, and pipeline) following
conclusions can be drawn. A special geotechnical engineering for permafrost projects is necessary to avoid main
geotechnical problems. Historical and new projects are approval for existence of these geotechnical problems
and necessity of mitigation methods for future projects. Depending on type of project, active or passive cooling
systems and thaw resistant techniques or combination of them should be applied to build a stable structure in the
permafrost regions.These techniques will be functional by following considerations: reduction of solar radiation
by different covers, lowering of pore space occupants temperature or soil temperature by refrigerating,
enhancing air convection, utilization of ventilation ducts, heat drains, thermosiphons, reduction of heat
conduction, and using of thaw stable fill materials. Each or combination of above considerations can be applied
in permafrost projects depending on project type, requirements, and budget.
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