CA2051024A1 - Variable conductivity trafficked surface for permafrost regions - Google Patents
Variable conductivity trafficked surface for permafrost regionsInfo
- Publication number
- CA2051024A1 CA2051024A1 CA 2051024 CA2051024A CA2051024A1 CA 2051024 A1 CA2051024 A1 CA 2051024A1 CA 2051024 CA2051024 CA 2051024 CA 2051024 A CA2051024 A CA 2051024A CA 2051024 A1 CA2051024 A1 CA 2051024A1
- Authority
- CA
- Canada
- Prior art keywords
- permafrost
- value
- season
- construction
- layer
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
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- Road Paving Structures (AREA)
Abstract
ABSTRACT
Road and the like construction on permafrost is improved by the inclusion of a variable heat conductivity (K) layer between the permafrost and the trafficked surface. The result is a lowering of the mean temperature of the permafrost itself over several years until a lower equilibrium temperature is reached then with the use of merely an insulating layer as in conventional construction.
Road and the like construction on permafrost is improved by the inclusion of a variable heat conductivity (K) layer between the permafrost and the trafficked surface. The result is a lowering of the mean temperature of the permafrost itself over several years until a lower equilibrium temperature is reached then with the use of merely an insulating layer as in conventional construction.
Description
~102~
VARIABLE CONDUCTIVITY TRAFFICKED
SURFACE FOR PER~IAFROST REGIONS
BACKGROUND OF THE INVENTION
Field of the Invention The present invention relates to road construction in general, and in particular to road and the like construction in cold and permafrost regions. More particularly still it relates to layered construction wherein one of the deeper layers under the trafficked surface exhibits relatively variable heat conductivity (K) from summer to winter. As a result, the annual mean temperature of the underlying permafrost layer is lowered, in contrast to merely decreasing the amplitude of the normal seasonal temperature variations which occurs with insulating or heat-sinking layers.
The construction of engineering structures such as roadways and airstrips on permafrost may lead to long term warming of the natural subgrade. The consequences of such warming are particularly debilitating in the vast regions of ice laden discontinuous permafrost which are characte~ristic of the major zones of northern habitation and industrial activity, such as the MacKenzie Valley of the Canadian Northwest Territories and Central Alaska in the U.S.A. In such soils, melting (permafrost degradation) leads to continued settlement and distress to the embankment structure.
VARIABLE CONDUCTIVITY TRAFFICKED
SURFACE FOR PER~IAFROST REGIONS
BACKGROUND OF THE INVENTION
Field of the Invention The present invention relates to road construction in general, and in particular to road and the like construction in cold and permafrost regions. More particularly still it relates to layered construction wherein one of the deeper layers under the trafficked surface exhibits relatively variable heat conductivity (K) from summer to winter. As a result, the annual mean temperature of the underlying permafrost layer is lowered, in contrast to merely decreasing the amplitude of the normal seasonal temperature variations which occurs with insulating or heat-sinking layers.
The construction of engineering structures such as roadways and airstrips on permafrost may lead to long term warming of the natural subgrade. The consequences of such warming are particularly debilitating in the vast regions of ice laden discontinuous permafrost which are characte~ristic of the major zones of northern habitation and industrial activity, such as the MacKenzie Valley of the Canadian Northwest Territories and Central Alaska in the U.S.A. In such soils, melting (permafrost degradation) leads to continued settlement and distress to the embankment structure.
2 ~ 2 ~
These are also the permafrost areas with the greatest extent of existing roads and airfields. If the recently suggested climatic warming predictions for -the North are verified it wilL be essential to provide cooling, and not merely insulation, to protect the existing infrastructure.
Pr-ior Art of the Invention The mechanical strength of frozen soil or permafrost is typically greater than its unfrozen ~0 counterpart. Also a frost susceptible soil will tend to heave when it freezes and settle when it thaws. Hence, considerable effort in the engineering of northern infrastructure has in the past been, and will continue to be, directed towards avoiding seasonal thaw of frost lS susceptible per~nafrost, thereby, taking advantage of increased strength values for design purposes, all the while precluding damaging thaw settlement effects.
Currently accepted construction techni~ues in permafrost regions consist of building gravel embankments whose thickness is chosen to be greater than the anticipated depth of annual thaw. In some cases layers of rigid polystyrene insulation are included within the embankment for the purpose of limiting seasonal tilaw while maintaining embankment thicknesses within acceptable limits.
The closest prior art known is United States patent 3,722,378 granted to John S. Best March 27, 1973. The patent pertains to trafficked surfaces built on 2~5~
foundations which rernain substantially undisturbed during seasonal climatic cycles, particularly in permafrost and near permafrost regions where considerable disturbance of the ground beneath foundations is otherwise common. The foundations include combinations of insulation layers, heat sinks and/or thermal bleeds which dampen and prevent the cyclic climatic seasonal variations from affecting the earthen support under the foundations, in both cut and fill sections, and in embankments and backfills adjacent the sections.
This prior art patent recognizes the problems associated with permafrost road construction and structure, and in particular recognizes that mere provision of an insulating layer above the permafrost layer is not sufficient. This and the proposed solution are discussed in conjunction with figure 2 of the patent, at column 29 line 59, as follows:
"Because of the sloping embankment 28 the insulation layer 18 extends downwardly along the embankment incline and a generally greater capacity (depth) of heat sink 20 is employed to achieve the desired effect. T~e purpose of section lO is primari]y to prevent permafrost 2~ from thawing during the summer months which would o-therwise occur during the summer climatic cycle. In some instances permafrost can melt to a depth of several feet, from solar heat. Such melting of permafrost ~9~2~
generally makes for a completely impassable condition. Section 10 prevents such thawing or can be used to control thawing where sorne thawing can be tolerated. The use of an S insulation layer alone is not practical in many places to sufficiently prevent such thawing. The present invention comprises in its preferred embodiment the combination of a heat sink with an insulation layer wherein the thermocell holds a trapped solution which is substantially frozen at the beginning of the summer season, whereby the heat of fusion of the solution then becomes addi-tional heat sink capacity, supplementing that of the permafrost supporting the same. The capacity of the thermocell heat sink is designed such that it will no-t achieve complete melting until the end of a summer season. Thereafter the winter season refreezes the heat sink solution such that it is ready again for the next summer season. The insulation layer on top of the heat sink prevents an undue quantity of heat from getting to the heat sink, permitting each to be of a practical design. However, during the winter season the insulation layer dampens the freezing effect of the colder season from regenerating the heat sink. But because in permafrost and near permafrost regions the winter season is so severe and longer lasting than the summer season, proper designing of the insulation layer still permits regeneration of the heat sink in the winter 2~5~2~
while preventing undue heat penetration during the summer."
The United States patent 3,722,378 is a generally useful background to the present invention and is incorporated herein by reference.
SUMMARY OF T~IE INVENTION
In its broadest aspect the present invention recognizes that it is not merely desirable to minimize the amplitude of annual temperature variations of the permafrost but to lower its annual mean temperature.
Such desideratum has been achieved by the inclusion of a variable heat conductivity (K) layer between the permafrost and the traeficked surface.
In a narrower aspect of the present invention, the variable K layer is more conductive of heat in the winter than in the summer.
In a narrower aspect still, the variable K layer has seasonally variable moisture content; dryer in the summer, and hence having lower K, and more moist in the winter thereby providing higher K due to its frozen water content.
The high K in the winter lowers the permafrost temperature because of the better heat conduction between the permafrost and the cold atmosphere. Thus, in many specific situations the annual mean temperature of the permafrost layer mav be lowered -from year to year as a result until it reaches a new equilibrium value.
20~2~
Thus, according to the present invention there is provided a permafrost road or the like construction of the type having a layered structure above the permafrost characterized by a variable heat conductivity (~) layer, K ~eing larger in winter than in summer.
The thermal conductivity K of a material is a quantifiable property which relates the propensity for heat to flow through the material under a thermal gradient. Thermal conductivity is the ratio of rate of heat flow to the thermal gradient and is expressed in units of W/rnK (~atts/metre-Kelvin).
The thermal conductivity of a wettable material varies as a function of moisture content, The thermal conductivity may also vary with temperature, notably if lS material structure or phase composition are affected.
The effect water has on the thermal conductivity of a base material to which it is added can be related to the relative ~hermal conductivity values of the constituents, i.e., adding water to a base material which is a poorer conductor than water will increase the thermal conductivity of the whole, Inversely, as this material dries out, it will become a better thermal insulator, Further, freezing a partially to fully saturated material will increase its thermal conductivity since water in the solid statP is a better conductor than in the liquid state. Hence, the thermal conductivity of a given material in a dry unfrozen state may be substantially less than that in the frozen saturated state.
2 ~
BRIEF DESCRI~TION OF THE DRAWINGS
The preferred reference of the present invention will now be described in detail in conjunction with the annexed drawings, in which:
Figure 1 is a schematic representation of the layered construction of road construction, including one shoulder, on a permafrost foundation;
Figure 2 is an alternative construction to that shown in figure 1 using a high conducting fin at the shoulder;
Figure 3 is another alternative using a wick--type : geofabric at the shoulder;
Figure 4 is an alternative construction using geotextile wick at the shoulder;
Figure 5 is a computer simulation slowing -thermal : 1~ behaviour of permafrost roads constructed using a normal : insulation layer;
Figure 6 is a compu-ter simulation showing thermal behaviour of permafrost roads constructed using a heat-sink layer; and Figure 7 is a computer simulation showing thermal behaviour of permafrost roads constructed using a variable K layer according to the embodiments of Figure 1 to 4.
2 ~ 2 ~
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
Referring to Figure 1, which shows a transversal half section including one shoulder (hatching has been omitted for clarity), a sub~rade or permafrost layer 10 has a layer 11 of coarse grained material such as gravel S laid on top. On top of layer 11 a variable K layer is constructed which cornprises an impermeable membrane 12 on top of which is a layer 13 consisting of a free draining porous thermal insulating strands, pellets or the like such as superexpanded polystyrene beadboard pellets manufactured by BASF and identified by it as drainage board. Extruded polystyrene strands or flexible polyurethane foam are also useable. On top of the layer 13 there is another coarse grained layer 1~
such as gravel, which provides the top surface layer of the road construction. At the shoulder, zones 15 and 16 are constructed of conventional insulating materials having conductivities not significantly dependent on temperature . Zone 17 at the shoulder is a continuation of the variable K layer 13 and, due to the provision underneath of the insulting zone 16, follows more closely the atmospheric (air) temperature, thereby allowing it (zone 17) to block drainage of the layer 13 as temperatures drop at -the beginning of winter. The water retained in the layer 13 therefore freezes and causes the layer 13 to become highly conductive in contrast to its previous low conductivity in summer.
In order to aid the draining blockage provided by the zone 17, an improvement is added as shown in Figure 2, wherein a highly conductive fin or heat pipe 18 is 2 ~ 2 ~
g provided to conduct heat ~rom close to the road surface down to the zone l7. The in 18 is perforated at its base (between the layer 13 and the zone 17) in order to continue to allow drainage of the layer 13 in summer.
The fin 18 could be rrleta1~ or totally made of or include wick-type geofabrics in conjunction with perforations to enhance blockage.
Figure 3 shows an embodiment wherein the shoulder drainage/blockage is achieved by means of a wick-type geofabric layer 19 delimiting the variable K layer 13 at the shoulder, and freezing due to its proximity to the top surface thereby blocking drainage.
In Figure 4, the variable K layer 13 continues down the shoulder of the embankment, but is interrupted by lS geotextile wick barriei^s 20 and 21, which freeze due to their contact with a similar barrier 22 that is close to the exposed embankment shoulder 23 and the atmospheric cold air in winter.
Figure 5 shows the result of a computer model simulating equilibrium thermal behaviour of permafrost construction using a conventional insulating layer in place of the variable K layer 13. The dotted curve F
shows the protile after the first five years, while curve E shows the profile of temperature vs. depth after equilibrium has been reached.
In Figure 6 the thermal behaviour simulation is that using a heat sink layer rather than an insulating 2 ~ 2 ~
layer as in Figure 5. As may be seen, the thermal behaviour is quite similar at a depth of lm down to 8m, where the equilibrium temperature is slightly above 0C.
Figure 7, on the other hand, shows the results of simulation using the variable K layer 13 of the present invention, where at 8m depth the equilibrium temperature is below 0C, with an improved (lower) temperature profile above, including a lower temperature than surface temperature in contrast to the results of the simulation as shown in Figures 5 and 6.
These are also the permafrost areas with the greatest extent of existing roads and airfields. If the recently suggested climatic warming predictions for -the North are verified it wilL be essential to provide cooling, and not merely insulation, to protect the existing infrastructure.
Pr-ior Art of the Invention The mechanical strength of frozen soil or permafrost is typically greater than its unfrozen ~0 counterpart. Also a frost susceptible soil will tend to heave when it freezes and settle when it thaws. Hence, considerable effort in the engineering of northern infrastructure has in the past been, and will continue to be, directed towards avoiding seasonal thaw of frost lS susceptible per~nafrost, thereby, taking advantage of increased strength values for design purposes, all the while precluding damaging thaw settlement effects.
Currently accepted construction techni~ues in permafrost regions consist of building gravel embankments whose thickness is chosen to be greater than the anticipated depth of annual thaw. In some cases layers of rigid polystyrene insulation are included within the embankment for the purpose of limiting seasonal tilaw while maintaining embankment thicknesses within acceptable limits.
The closest prior art known is United States patent 3,722,378 granted to John S. Best March 27, 1973. The patent pertains to trafficked surfaces built on 2~5~
foundations which rernain substantially undisturbed during seasonal climatic cycles, particularly in permafrost and near permafrost regions where considerable disturbance of the ground beneath foundations is otherwise common. The foundations include combinations of insulation layers, heat sinks and/or thermal bleeds which dampen and prevent the cyclic climatic seasonal variations from affecting the earthen support under the foundations, in both cut and fill sections, and in embankments and backfills adjacent the sections.
This prior art patent recognizes the problems associated with permafrost road construction and structure, and in particular recognizes that mere provision of an insulating layer above the permafrost layer is not sufficient. This and the proposed solution are discussed in conjunction with figure 2 of the patent, at column 29 line 59, as follows:
"Because of the sloping embankment 28 the insulation layer 18 extends downwardly along the embankment incline and a generally greater capacity (depth) of heat sink 20 is employed to achieve the desired effect. T~e purpose of section lO is primari]y to prevent permafrost 2~ from thawing during the summer months which would o-therwise occur during the summer climatic cycle. In some instances permafrost can melt to a depth of several feet, from solar heat. Such melting of permafrost ~9~2~
generally makes for a completely impassable condition. Section 10 prevents such thawing or can be used to control thawing where sorne thawing can be tolerated. The use of an S insulation layer alone is not practical in many places to sufficiently prevent such thawing. The present invention comprises in its preferred embodiment the combination of a heat sink with an insulation layer wherein the thermocell holds a trapped solution which is substantially frozen at the beginning of the summer season, whereby the heat of fusion of the solution then becomes addi-tional heat sink capacity, supplementing that of the permafrost supporting the same. The capacity of the thermocell heat sink is designed such that it will no-t achieve complete melting until the end of a summer season. Thereafter the winter season refreezes the heat sink solution such that it is ready again for the next summer season. The insulation layer on top of the heat sink prevents an undue quantity of heat from getting to the heat sink, permitting each to be of a practical design. However, during the winter season the insulation layer dampens the freezing effect of the colder season from regenerating the heat sink. But because in permafrost and near permafrost regions the winter season is so severe and longer lasting than the summer season, proper designing of the insulation layer still permits regeneration of the heat sink in the winter 2~5~2~
while preventing undue heat penetration during the summer."
The United States patent 3,722,378 is a generally useful background to the present invention and is incorporated herein by reference.
SUMMARY OF T~IE INVENTION
In its broadest aspect the present invention recognizes that it is not merely desirable to minimize the amplitude of annual temperature variations of the permafrost but to lower its annual mean temperature.
Such desideratum has been achieved by the inclusion of a variable heat conductivity (K) layer between the permafrost and the traeficked surface.
In a narrower aspect of the present invention, the variable K layer is more conductive of heat in the winter than in the summer.
In a narrower aspect still, the variable K layer has seasonally variable moisture content; dryer in the summer, and hence having lower K, and more moist in the winter thereby providing higher K due to its frozen water content.
The high K in the winter lowers the permafrost temperature because of the better heat conduction between the permafrost and the cold atmosphere. Thus, in many specific situations the annual mean temperature of the permafrost layer mav be lowered -from year to year as a result until it reaches a new equilibrium value.
20~2~
Thus, according to the present invention there is provided a permafrost road or the like construction of the type having a layered structure above the permafrost characterized by a variable heat conductivity (~) layer, K ~eing larger in winter than in summer.
The thermal conductivity K of a material is a quantifiable property which relates the propensity for heat to flow through the material under a thermal gradient. Thermal conductivity is the ratio of rate of heat flow to the thermal gradient and is expressed in units of W/rnK (~atts/metre-Kelvin).
The thermal conductivity of a wettable material varies as a function of moisture content, The thermal conductivity may also vary with temperature, notably if lS material structure or phase composition are affected.
The effect water has on the thermal conductivity of a base material to which it is added can be related to the relative ~hermal conductivity values of the constituents, i.e., adding water to a base material which is a poorer conductor than water will increase the thermal conductivity of the whole, Inversely, as this material dries out, it will become a better thermal insulator, Further, freezing a partially to fully saturated material will increase its thermal conductivity since water in the solid statP is a better conductor than in the liquid state. Hence, the thermal conductivity of a given material in a dry unfrozen state may be substantially less than that in the frozen saturated state.
2 ~
BRIEF DESCRI~TION OF THE DRAWINGS
The preferred reference of the present invention will now be described in detail in conjunction with the annexed drawings, in which:
Figure 1 is a schematic representation of the layered construction of road construction, including one shoulder, on a permafrost foundation;
Figure 2 is an alternative construction to that shown in figure 1 using a high conducting fin at the shoulder;
Figure 3 is another alternative using a wick--type : geofabric at the shoulder;
Figure 4 is an alternative construction using geotextile wick at the shoulder;
Figure 5 is a computer simulation slowing -thermal : 1~ behaviour of permafrost roads constructed using a normal : insulation layer;
Figure 6 is a compu-ter simulation showing thermal behaviour of permafrost roads constructed using a heat-sink layer; and Figure 7 is a computer simulation showing thermal behaviour of permafrost roads constructed using a variable K layer according to the embodiments of Figure 1 to 4.
2 ~ 2 ~
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
Referring to Figure 1, which shows a transversal half section including one shoulder (hatching has been omitted for clarity), a sub~rade or permafrost layer 10 has a layer 11 of coarse grained material such as gravel S laid on top. On top of layer 11 a variable K layer is constructed which cornprises an impermeable membrane 12 on top of which is a layer 13 consisting of a free draining porous thermal insulating strands, pellets or the like such as superexpanded polystyrene beadboard pellets manufactured by BASF and identified by it as drainage board. Extruded polystyrene strands or flexible polyurethane foam are also useable. On top of the layer 13 there is another coarse grained layer 1~
such as gravel, which provides the top surface layer of the road construction. At the shoulder, zones 15 and 16 are constructed of conventional insulating materials having conductivities not significantly dependent on temperature . Zone 17 at the shoulder is a continuation of the variable K layer 13 and, due to the provision underneath of the insulting zone 16, follows more closely the atmospheric (air) temperature, thereby allowing it (zone 17) to block drainage of the layer 13 as temperatures drop at -the beginning of winter. The water retained in the layer 13 therefore freezes and causes the layer 13 to become highly conductive in contrast to its previous low conductivity in summer.
In order to aid the draining blockage provided by the zone 17, an improvement is added as shown in Figure 2, wherein a highly conductive fin or heat pipe 18 is 2 ~ 2 ~
g provided to conduct heat ~rom close to the road surface down to the zone l7. The in 18 is perforated at its base (between the layer 13 and the zone 17) in order to continue to allow drainage of the layer 13 in summer.
The fin 18 could be rrleta1~ or totally made of or include wick-type geofabrics in conjunction with perforations to enhance blockage.
Figure 3 shows an embodiment wherein the shoulder drainage/blockage is achieved by means of a wick-type geofabric layer 19 delimiting the variable K layer 13 at the shoulder, and freezing due to its proximity to the top surface thereby blocking drainage.
In Figure 4, the variable K layer 13 continues down the shoulder of the embankment, but is interrupted by lS geotextile wick barriei^s 20 and 21, which freeze due to their contact with a similar barrier 22 that is close to the exposed embankment shoulder 23 and the atmospheric cold air in winter.
Figure 5 shows the result of a computer model simulating equilibrium thermal behaviour of permafrost construction using a conventional insulating layer in place of the variable K layer 13. The dotted curve F
shows the protile after the first five years, while curve E shows the profile of temperature vs. depth after equilibrium has been reached.
In Figure 6 the thermal behaviour simulation is that using a heat sink layer rather than an insulating 2 ~ 2 ~
layer as in Figure 5. As may be seen, the thermal behaviour is quite similar at a depth of lm down to 8m, where the equilibrium temperature is slightly above 0C.
Figure 7, on the other hand, shows the results of simulation using the variable K layer 13 of the present invention, where at 8m depth the equilibrium temperature is below 0C, with an improved (lower) temperature profile above, including a lower temperature than surface temperature in contrast to the results of the simulation as shown in Figures 5 and 6.
Claims (7)
1. A method of reducing mean annual temperature of permafrost comprising laying insulating material over the permafrost, said insulating layer exhibiting variable heat conductivity (K) value, with a lower K
value in the warmer season, and a higher K value in the colder season.
value in the warmer season, and a higher K value in the colder season.
2. A surface construction for permafrost (or near permafrost) ground, and exhibiting reduced mean annual temperature of the permafrost, said construction comprising a layer of insulating material overlaying the permafrost, said insulating material exhibiting variable heat conductivity value (K), with a lower K value in the warmer season and a higher K value in the colder season.
3. A surface construction as in claim 2 adapted to stabilize a trafficked surface against seasonal partial thawing of the underlying permafrost, said construction comprising a layer of insulating material overlaying the permafrost, said insulating material exhibiting variable heat conductivity value (K), with a lower K value in the warmer season and a higher K value in the colder season;
wherein said variable K insulating layer retains water for freezing during the colder season to provide a higher K value; and drains melted water during the warmer season to provide a lower K value.
wherein said variable K insulating layer retains water for freezing during the colder season to provide a higher K value; and drains melted water during the warmer season to provide a lower K value.
4. A surface construction as in claim 3, comprising an impermeable membrane overlaying the permafrost, and on said impermeable membrane a layer of porous support material whereby the porous material exhibits a relatively low K value when drained during the warmer season, and a higher K value during the colder season.
5. A construction as in claim 4 for an embankment having one or more downwardly sloping sides; said embankment being exposed at its exterior face to ambient temperatures, means adjacent to the exterior face comprising means adapted to carry heat between the surrounding air and a side edge of the variable K
insulating layer, whereby during the warmer season the heat pipe means provides melting of the water at the edge of the insulating layer, permitting melt water to flow away; and provides freezing of the water at the edge of the insulating layer during the colder season, thus immobilizing the edge water, which collects and freezes water which accumulates in said porous insulating layer.
insulating layer, whereby during the warmer season the heat pipe means provides melting of the water at the edge of the insulating layer, permitting melt water to flow away; and provides freezing of the water at the edge of the insulating layer during the colder season, thus immobilizing the edge water, which collects and freezes water which accumulates in said porous insulating layer.
6. A construction as in claim 5, wherein said means adapted to carry heat is a metal or the like fin.
7. A construction as in claim 5, wherein said means adapted to carry heat is a heat pipe.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA 2051024 CA2051024A1 (en) | 1991-09-10 | 1991-09-10 | Variable conductivity trafficked surface for permafrost regions |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA 2051024 CA2051024A1 (en) | 1991-09-10 | 1991-09-10 | Variable conductivity trafficked surface for permafrost regions |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2051024A1 true CA2051024A1 (en) | 1993-03-11 |
Family
ID=4148335
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA 2051024 Abandoned CA2051024A1 (en) | 1991-09-10 | 1991-09-10 | Variable conductivity trafficked surface for permafrost regions |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA2051024A1 (en) |
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US5697730A (en) * | 1995-07-21 | 1997-12-16 | University Of Alaska | Roadway having convection cooling for permafrost regions |
| WO2011079468A1 (en) * | 2009-12-31 | 2011-07-07 | 中交第一公路勘察设计研究院有限公司 | Method for protecting roadbeds in frozen soil area and pavement structure |
-
1991
- 1991-09-10 CA CA 2051024 patent/CA2051024A1/en not_active Abandoned
Cited By (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US5697730A (en) * | 1995-07-21 | 1997-12-16 | University Of Alaska | Roadway having convection cooling for permafrost regions |
| WO2011079468A1 (en) * | 2009-12-31 | 2011-07-07 | 中交第一公路勘察设计研究院有限公司 | Method for protecting roadbeds in frozen soil area and pavement structure |
| CN102084064B (en) * | 2009-12-31 | 2012-09-05 | 中交第一公路勘察设计研究院有限公司 | Method for protecting roadbeds in frozen soil area and pavement structure |
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