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Cold regions involve hydrological processes that are not often addressed appropriately in hydrological models. The Cold Regions Hydrological Modelling platform (CRHM) was initially developed in 1998 to assemble and explore the hydrological understanding developed from a series of research basins spanning Canada and international cold regions. Hydrological processes and basin response in cold regions are simulated in a flexible, modular, object-oriented, multiphysics platform. The CRHM platform allows for multiple representations of forcing data interpolation and extrapolation, hydrological model spatial and physical process structures, and parameter values. It is well suited for model falsification, algorithm intercomparison and benchmarking, and has been deployed for basin hydrology diagnosis, prediction, land use change and water quality analysis, climate impact analysis and flood forecasting around the world. This paper describes CRHM’s capabilities, and the insights derived by applying the model in concert with process hydrology research and using the combined information and understanding from research basins to predict hydrological variables, diagnose hydrological change and determine the appropriateness of model structure and parameterisations.

Producción Científica, Este trabajo describe la metodología utilizada para cartografiar los suelos potencialmente helados en el valle de Tucarroya, en el Parque Nacional de Ordesa. Para cartografiar las formas asociadas a la presencia de hielo se combinó trabajo de campo, datos térmicos procedentes de sensores automáticos de temperatura del suelo y mediciones de la base del manto de nieve (BTS), así como variables predictivas obtenidas de un Modelo Digital de Elevaciones (MDE). La cartografía diferencia cuatro ambientes, suelo no congelado con actividad de la helada, suelos helados estacionales, permafrost posible y permafrost probable. El mapa revela una extensión del permafrost muy limitada, con escasez de formas asociadas. Solo se ha detectado por encima de los 2700 m de altitud en ambientes topográficos favorables, pendientessuaves y protegidos de la radiación solar. Los suelos helados estacionales son los ambientes más comunes y se desarrollan por encima de los 2500 m s.n.m., mientras los suelos no congelados,pero con heladas solo están presentes entre los 2570 y los 2750 m de altitud en laderas que reciben elevada radiación solar, Ministerio de Economía, Industria y Competitividad - Fondo Europeo de Desarrollo Regional (projects CGL2015-68144-R / CGL2017-82216-R), Geoparque de Sobrarbe (project R- ADM15/57)

Producción Científica, Este trabajo describe la metodología utilizada para cartografiar los suelos potencialmente helados en el valle de Tucarroya, en el Parque Nacional de Ordesa. Para cartografiar las formas asociadas a la presencia de hielo se combinó trabajo de campo, datos térmicos procedentes de sensores automáticos de temperatura del suelo y mediciones de la base del manto de nieve (BTS), así como variables predictivas obtenidas de un Modelo Digital de Elevaciones (MDE). La cartografía diferencia cuatro ambientes, suelo no congelado con actividad de la helada, suelos helados estacionales, permafrost posible y permafrost probable. El mapa revela una extensión del permafrost muy limitada, con escasez de formas asociadas. Solo se ha detectado por encima de los 2700 m de altitud en ambientes topográficos favorables, pendientessuaves y protegidos de la radiación solar. Los suelos helados estacionales son los ambientes más comunes y se desarrollan por encima de los 2500 m s.n.m., mientras los suelos no congelados,pero con heladas solo están presentes entre los 2570 y los 2750 m de altitud en laderas que reciben elevada radiación solar, Ministerio de Economía, Industria y Competitividad - Fondo Europeo de Desarrollo Regional (projects CGL2015-68144-R / CGL2017-82216-R), Geoparque de Sobrarbe (project R- ADM15/57)

Producción Científica, Este trabajo describe la metodología utilizada para cartografiar los suelos potencialmente helados en el valle de Tucarroya, en el Parque Nacional de Ordesa. Para cartografiar las formas asociadas a la presencia de hielo se combinó trabajo de campo, datos térmicos procedentes de sensores automáticos de temperatura del suelo y mediciones de la base del manto de nieve (BTS), así como variables predictivas obtenidas de un Modelo Digital de Elevaciones (MDE). La cartografía diferencia cuatro ambientes, suelo no congelado con actividad de la helada, suelos helados estacionales, permafrost posible y permafrost probable. El mapa revela una extensión del permafrost muy limitada, con escasez de formas asociadas. Solo se ha detectado por encima de los 2700 m de altitud en ambientes topográficos favorables, pendientessuaves y protegidos de la radiación solar. Los suelos helados estacionales son los ambientes más comunes y se desarrollan por encima de los 2500 m s.n.m., mientras los suelos no congelados,pero con heladas solo están presentes entre los 2570 y los 2750 m de altitud en laderas que reciben elevada radiación solar, Ministerio de Economía, Industria y Competitividad - Fondo Europeo de Desarrollo Regional (projects CGL2015-68144-R / CGL2017-82216-R), Geoparque de Sobrarbe (project R- ADM15/57)

Este trabajo describe la metodología utilizada para cartografiar los suelos potencialmente helados en el valle de Tucarroya, en el Parque Nacional de Ordesa. Para cartografiar las formas asociadas a la presencia de hielo se combinó trabajo de campo, datos térmicos procedentes de sensores automáticos de temperatura del suelo y mediciones de la base del manto de nieve (BTS), así como variables predictivas obtenidas de un Modelo Digital de Elevaciones (MDE). La cartografía diferencia cuatro ambientes, suelo no congelado con actividad de la helada, suelos helados estacionales, permafrost posible y permafrost probable. El mapa revela una extensión del permafrost muy limitada, con escasez de formas asociadas. Solo se ha detectado por encima de los 2700 m de altitud en ambientes topográficos favorables, pendientes suaves y protegidos de la radiación solar. Los suelos helados estacionales son los ambientes más comunes y se desarrollan por encima de los 2500 m s.n.m., mientras los suelos no congelados, pero con heladas solo están presentes entre los 2570 y los 2750 m de altitud en laderas que reciben elevada radiación solar., This paper shows the creation of a map of frozen ground potential for the Tucarroya valley in Ordesa National Park. To create this map, it was necessary to combine the identified landforms associated to the presence of frozen ground by fieldwork, ground temperature data continuously recorded during two years by automatic loggers, a Basal Temperature of Snow (BTS) survey, and predictor variables derived from a high resolution Digital Elevation Model (DEM). Four environments have been differentiated: unfrozen ground, seasonal frozen ground, possible permafrost and probable permafrost. The map confirms a very limited variety and extension of permafrost, above 2700 m a.s.l. on gentle and shadowed slopes. Seasonal frozen ground is the most common thermal regime, as it can be developed above 2500 m a.s.l. Snow-pack duration and thickness tightly control the duration of frozen ground and the freezing-thawing cycles. Frost activity and unfrozen ground is restricted from 2570 to 2750 m a.s.l.

Producción Científica, Este trabajo describe la metodología utilizada para cartografiar los suelos potencialmente helados en el valle de Tucarroya, en el Parque Nacional de Ordesa. Para cartografiar las formas asociadas a la presencia de hielo se combinó trabajo de campo, datos térmicos procedentes de sensores automáticos de temperatura del suelo y mediciones de la base del manto de nieve (BTS), así como variables predictivas obtenidas de un Modelo Digital de Elevaciones (MDE). La cartografía diferencia cuatro ambientes, suelo no congelado con actividad de la helada, suelos helados estacionales, permafrost posible y permafrost probable. El mapa revela una extensión del permafrost muy limitada, con escasez de formas asociadas. Solo se ha detectado por encima de los 2700 m de altitud en ambientes topográficos favorables, pendientessuaves y protegidos de la radiación solar. Los suelos helados estacionales son los ambientes más comunes y se desarrollan por encima de los 2500 m s.n.m., mientras los suelos no congelados,pero con heladas solo están presentes entre los 2570 y los 2750 m de altitud en laderas que reciben elevada radiación solar, Ministerio de Economía, Industria y Competitividad - Fondo Europeo de Desarrollo Regional (projects CGL2015-68144-R / CGL2017-82216-R), Geoparque de Sobrarbe (project R- ADM15/57)

Este trabajo describe la metodología utilizada para cartografiar los suelos potencialmente helados en el valle de Tucarroya, en el Parque Nacional de Ordesa. Para cartografiar las formas asociadas a la presencia de hielo se combinó trabajo de campo, datos térmicos procedentes de sensores automáticos de temperatura del suelo y mediciones de la base del manto de nieve (BTS), así como variables predictivas obtenidas de un Modelo Digital de Elevaciones (MDE). La cartografía diferencia cuatro ambientes, suelo no congelado con actividad de la helada, suelos helados estacionales, permafrost posible y permafrost probable. El mapa revela una extensión del permafrost muy limitada, con escasez de formas asociadas. Solo se ha detectado por encima de los 2700 m de altitud en ambientes topográficos favorables, pendientes suaves y protegidos de la radiación solar. Los suelos helados estacionales son los ambientes más comunes y se desarrollan por encima de los 2500 m s.n.m., mientras los suelos no congelados, pero con heladas solo están presentes entre los 2570 y los 2750 m de altitud en laderas que reciben elevada radiación solar., This paper shows the creation of a map of frozen ground potential for the Tucarroya valley in Ordesa National Park. To create this map, it was necessary to combine the identified landforms associated to the presence of frozen ground by fieldwork, ground temperature data continuously recorded during two years by automatic loggers, a Basal Temperature of Snow (BTS) survey, and predictor variables derived from a high resolution Digital Elevation Model (DEM). Four environments have been differentiated: unfrozen ground, seasonal frozen ground, possible permafrost and probable permafrost. The map confirms a very limited variety and extension of permafrost, above 2700 m a.s.l. on gentle and shadowed slopes. Seasonal frozen ground is the most common thermal regime, as it can be developed above 2500 m a.s.l. Snow-pack duration and thickness tightly control the duration of frozen ground and the freezing-thawing cycles. Frost activity and unfrozen ground is restricted from 2570 to 2750 m a.s.l.

The conference included several papers on shaft projects in potash and precious metal mines and others on accessing salt, polyhalite, coal, base metal and alloy metal deposits, as well as presentations on particular aspects such as design and construction, mechanisation, theoretical approaches, blind sinking, ground freezing, raise drilling, drilling/blasting, sinking stages or Galloways, shaft bottoms, NATM lining design, lining deterioration assessment/remediation, closed shafts, rehabilitation, headframes, hoist capacity, hoist plants, piping, wireless communication, economics, standards, regulations and future developments. Projects discussed included mines in Saskatchewan (6 papers), Idaho, Nebraska, Mexico (2 papers), New South Wales, China (4 papers), South Africa (2 papers), Zambia, UK (2 papers), Belarus, Poland and Portugal., The conference included several papers on shaft projects in potash and precious metal mines and others on accessing salt, polyhalite, coal, base metal and alloy metal deposits, as well as presentations on particular aspects such as design and construction, mechanisation, theoretical approaches, blind sinking, ground freezing, raise drilling, drilling/blasting, sinking stages or Galloways, shaft bottoms, NATM lining design, lining deterioration assessment/remediation, closed shafts, rehabilitation, headframes, hoist capacity, hoist plants, piping, wireless communication, economics, standards, regulations and future developments. Projects discussed included mines in Saskatchewan (6 papers), Idaho, Nebraska, Mexico (2 papers), New South Wales, China (4 papers), South Africa (2 papers), Zambia, UK (2 papers), Belarus, Poland and Portugal.

This paper presents a procedure for determining unfrozen water saturation in a partially saturated frozen soil (clayey silt) using bulk electrical conductivity (EC) measurements. A modification of Archie’s law is proposed to describe the relationship between soil bulk EC, temperature, porosity and degree of unfrozen water saturation. Compacted samples have been prepared at a dry density around 1.90 Mg/m3 and at dif-ferent degrees of saturation. Samples have been then subjected to freezing paths up to -15 °C. Measurements of bulk EC along the temperature decrease and freezing paths have been used to calibrate parameters associ-ated with the proposed model. These calibrated models allow determining the amount of ice content for a given state of the partially saturated soil (porosity, initial degree of water saturation and temperature). The soil freezing retention curve has been also estimated by combining the Clausius-Clapeyron equation with water retention data on drying. A good agreement has been observed between the estimation based on EC measurements and results from water retention data, which validates the proposed procedure., Postprint (published version)

The Yellow River source region is located in the transition region between permafrost and seasonally frozen ground on the northeastern Qinghai-Tibet Plateau. The region has experienced severe climate change, especially air temperature increases, in past decades. In this study, we employed a geomorphology-based eco-hydrological model (GBEHM) to assess the impacts of climate change on the frozen ground and eco-hydrological processes in the region. Based on a long-term simulation from 1981 to 2015, we found that the areal mean maximum thickness of seasonally frozen ground ranged from 1.1-1.8m and decreased by 1.2cm per year. Additionally, the ratio of the permafrost area to the total area decreased by 1.1% per year. These decreasing trends are faster than the average in China because the study area is on the sensitive margin of the Qinghai-Tibet Plateau. The annual runoff exhibited variations similar to those of the annual precipitation (R2=0.85), although the annual evapotranspiration (ET) exhibited an increasing trend (14.3mm/10a) similar to that of the annual mean air temperature (0.66°C/10a). The runoff coefficient (annual runoff divided by annual precipitation) displayed a decreasing trend because of the increasing ET, and the vegetation responses to climate warming and permafrost degradation were manifested as increases in the leaf area index (LAI) and ET at the start of the growing season. Furthermore, the results showed that changes to the frozen ground depth affected vegetation growth. Notably, a rapid decrease in the frozen ground depth (< -3.0cm/a) decreased the topsoil moisture and then decreased the LAI. This study showed that the eco-hydrological processes in the headwater area of the Yellow River have changed because of permafrost degradation, and these changes could further influence the water resources availability in the middle and lower reaches of the basin.

The Yellow River source region is located in the transition region between permafrost and seasonally frozen ground on the northeastern Qinghai-Tibet Plateau. The region has experienced severe climate change, especially air temperature increases, in past decades. In this study, we employed a geomorphology-based eco-hydrological model (GBEHM) to assess the impacts of climate change on the frozen ground and eco-hydrological processes in the region. Based on a long-term simulation from 1981 to 2015, we found that the areal mean maximum thickness of seasonally frozen ground ranged from 1.1-1.8m and decreased by 1.2cm per year. Additionally, the ratio of the permafrost area to the total area decreased by 1.1% per year. These decreasing trends are faster than the average in China because the study area is on the sensitive margin of the Qinghai-Tibet Plateau. The annual runoff exhibited variations similar to those of the annual precipitation (R2=0.85), although the annual evapotranspiration (ET) exhibited an increasing trend (14.3mm/10a) similar to that of the annual mean air temperature (0.66°C/10a). The runoff coefficient (annual runoff divided by annual precipitation) displayed a decreasing trend because of the increasing ET, and the vegetation responses to climate warming and permafrost degradation were manifested as increases in the leaf area index (LAI) and ET at the start of the growing season. Furthermore, the results showed that changes to the frozen ground depth affected vegetation growth. Notably, a rapid decrease in the frozen ground depth (< -3.0cm/a) decreased the topsoil moisture and then decreased the LAI. This study showed that the eco-hydrological processes in the headwater area of the Yellow River have changed because of permafrost degradation, and these changes could further influence the water resources availability in the middle and lower reaches of the basin.

Thermo-active structures, such as energy piles, are used to store and extract heat energy from soil. In areas with seasonal freezing and thawing, such infrastructure is subjected to changes in the soil structure and, consequently, the soil strength. This research investigated the influence of repeated freeze-thaw (FT) cycles and different freezing rates on the shear strength of a frost susceptible Illite clay. Samples of saturated clay were subjected to between 1 and 20 FT cycles, and the shear strength was determined using undrained unconsolidated triaxial tests on the thawed samples. Soil subjected to freezing exhibited a reduction in shear strength compared to never-frozen soil. Slower freezing rates (warmer surface temperatures) resulted in lower shear strength. Results indicated an inverse relationship between the number of FT cycles and the shear strength with a constant applied freezing temperature. Strength recovery occurred between 1 and 3 freezing cycles. Between 3 and 7 FT cycles, the shear strength decreased, after which it approached an equilibrium shear strength between 7 and 10 FT cycles. The increase in shear strength between 1 and 3 FT cycles at a high freezing rate was not identified in the literature reviewed, but coincides with a decrease in stiffness and ice lens thickness. The reduction in shear strength with increasing FT cycles was attributed to movement of pore water through the sample and formation of ice lenses, which damaged the soil microstructure. The ice lenses formed via cryogenic suction pulling unfrozen pore water towards the freezing front and layer where a new ice lens was growing. Macro-CT scans showed decreasing size of ice lenses with increasing FT cycles, and denser ice lens formation near the freezing surface. The largest change in shear strength and ice lens formation occurred between a surface temperature of -5 and -10°C. Ice lenses increased in size moving away from the freezing surface, and a saturated ‘slurry’ layer form, Civil Engineering and Geosciences, Geoscience & Engineering

The present paper explores the use of the measurement of bulk electric conductivity and relative dielectric permittivity during freezing and thawing to estimate the ice content of two different partially saturated soils. The soils (Castelldefels fine sand and Barcelona clayey silt) were prepared at different degrees of saturation and dry densities at room temperature. Different target temperatures were used, which were reached at varying freezing rates and controlled with a thermal bath. Models were used to fit electrical conductivity and relative dielectric permittivity results under full unfrozen liquid and maximum ice conditions. The extension of these models allows estimating ice content on partially saturated soils at different porosities., Postprint (published version)

Thermo-active structures, such as energy piles, are used to store and extract heat energy from soil. In areas with seasonal freezing and thawing, such infrastructure is subjected to changes in the soil structure and, consequently, the soil strength. This research investigated the influence of repeated freeze-thaw (FT) cycles and different freezing rates on the shear strength of a frost susceptible Illite clay. Samples of saturated clay were subjected to between 1 and 20 FT cycles, and the shear strength was determined using undrained unconsolidated triaxial tests on the thawed samples. Soil subjected to freezing exhibited a reduction in shear strength compared to never-frozen soil. Slower freezing rates (warmer surface temperatures) resulted in lower shear strength. Results indicated an inverse relationship between the number of FT cycles and the shear strength with a constant applied freezing temperature. Strength recovery occurred between 1 and 3 freezing cycles. Between 3 and 7 FT cycles, the shear strength decreased, after which it approached an equilibrium shear strength between 7 and 10 FT cycles. The increase in shear strength between 1 and 3 FT cycles at a high freezing rate was not identified in the literature reviewed, but coincides with a decrease in stiffness and ice lens thickness. The reduction in shear strength with increasing FT cycles was attributed to movement of pore water through the sample and formation of ice lenses, which damaged the soil microstructure. The ice lenses formed via cryogenic suction pulling unfrozen pore water towards the freezing front and layer where a new ice lens was growing. Macro-CT scans showed decreasing size of ice lenses with increasing FT cycles, and denser ice lens formation near the freezing surface. The largest change in shear strength and ice lens formation occurred between a surface temperature of -5 and -10°C. Ice lenses increased in size moving away from the freezing surface, and a saturated ‘slurry’ layer form, Civil Engineering and Geosciences, Geoscience & Engineering

The present paper explores the use of the measurement of bulk electric conductivity and relative dielectric permittivity during freezing and thawing to estimate the ice content of two different partially saturated soils. The soils (Castelldefels fine sand and Barcelona clayey silt) were prepared at different degrees of saturation and dry densities at room temperature. Different target temperatures were used, which were reached at varying freezing rates and controlled with a thermal bath. Models were used to fit electrical conductivity and relative dielectric permittivity results under full unfrozen liquid and maximum ice conditions. The extension of these models allows estimating ice content on partially saturated soils at different porosities., Postprint (published version)

Tjällossning är ett stort problem för våra vägar idag och det är något som återkommer varje år. Tjällossning för med sig följder som i sin tur kräver mycket tid och resurser för att kunna återställa dessa vägar till att återigen kunna användas för trafik. Varje år förekommer stora skador på bl.a. vägar, gånggator, parkeringar samt övriga trafikytor, vilket kräver enorma summor av pengar för att åtgärda problemet. Byggnader får sättningsskador och VA-ledningar täpps till av stora isklumpar eller så fryser de sönder, och bara detta visar vad för stora problem tjällossning kan åstadkomma. Det innebär att vägarna måste vara underhållna och skötta ganska ofta av entreprenörföretag, vilket i sin tur leder till oönskade ekonomiska konsekvenser. I värsta fall stängs den tjäldrabbade vägen av under en viss tid, som är nödvändig för många att transportera sig genom till sina destinationer. I Sverige räknar man med att ca 15 - 20.000km väg berörs av just sådana tjälproblem varje år och dessa avstängningar på den skadade delen av vägnätet leder varje år till stora kostnader för samhället till följd av dålig framkomlighet. Idag används olika metoder för att lösa problemet med tjällossning på vägar och därmed måste olika ekonomiska summor betalas. Och frågan blir vilken/vilka metoder är mest effektivast och användbara i dagsläget, samt med bäst ekonomiskt vinst?, Soil frost thawing is a big problem for our roads today, and its something that comes over again every year on different type of roads. Soil frost thawing brings consequences, which in turn requires much time and resources to restore these roads to once again be used for traffic.Every year, big damages on the roads, streets, parking area, and ''traffic area'' usually occur and a great deal of money is spent to remedy these problems. Buildings are given damage-recompense 'and water and sewage pipes are closed off by big lumps of ice or they freeze until they break; this alone shows the extent of the problem that soil frost thawing can cause. This means that the roads must be maintained and managed quite frequently by entrepreneurial companies which in turn leads to great economic consequences and in worst case maybe the road has to shut down, that is very necessary for many people to transport themselves to their destinations during a period of time. In Sweden it is estimated that approximately 15 - 20.000km route affected by precisely such soil frost thawing every year, and these shutdowns on the damaged part of the road network leads every year to considerable costs for society due to poor accessibility.Today, they use different methods to solve the problem with the soil frost thawing on roads and thus have different economic sums paid. The question then becomes, which method is most effective and useful today as well as yields most economic profit?

Tjällossning är ett stort problem för våra vägar idag och det är något som återkommer varje år. Tjällossning för med sig följder som i sin tur kräver mycket tid och resurser för att kunna återställa dessa vägar till att återigen kunna användas för trafik. Varje år förekommer stora skador på bl.a. vägar, gånggator, parkeringar samt övriga trafikytor, vilket kräver enorma summor av pengar för att åtgärda problemet. Byggnader får sättningsskador och VA-ledningar täpps till av stora isklumpar eller så fryser de sönder, och bara detta visar vad för stora problem tjällossning kan åstadkomma. Det innebär att vägarna måste vara underhållna och skötta ganska ofta av entreprenörföretag, vilket i sin tur leder till oönskade ekonomiska konsekvenser. I värsta fall stängs den tjäldrabbade vägen av under en viss tid, som är nödvändig för många att transportera sig genom till sina destinationer. I Sverige räknar man med att ca 15 - 20.000km väg berörs av just sådana tjälproblem varje år och dessa avstängningar på den skadade delen av vägnätet leder varje år till stora kostnader för samhället till följd av dålig framkomlighet. Idag används olika metoder för att lösa problemet med tjällossning på vägar och därmed måste olika ekonomiska summor betalas. Och frågan blir vilken/vilka metoder är mest effektivast och användbara i dagsläget, samt med bäst ekonomiskt vinst?, Soil frost thawing is a big problem for our roads today, and its something that comes over again every year on different type of roads. Soil frost thawing brings consequences, which in turn requires much time and resources to restore these roads to once again be used for traffic.Every year, big damages on the roads, streets, parking area, and ''traffic area'' usually occur and a great deal of money is spent to remedy these problems. Buildings are given damage-recompense 'and water and sewage pipes are closed off by big lumps of ice or they freeze until they break; this alone shows the extent of the problem that soil frost thawing can cause. This means that the roads must be maintained and managed quite frequently by entrepreneurial companies which in turn leads to great economic consequences and in worst case maybe the road has to shut down, that is very necessary for many people to transport themselves to their destinations during a period of time. In Sweden it is estimated that approximately 15 - 20.000km route affected by precisely such soil frost thawing every year, and these shutdowns on the damaged part of the road network leads every year to considerable costs for society due to poor accessibility.Today, they use different methods to solve the problem with the soil frost thawing on roads and thus have different economic sums paid. The question then becomes, which method is most effective and useful today as well as yields most economic profit?

The frozen soil-structure interface is the key connecting component between structures and the soil in the permafrost regions. The soil-structure interface is usually subjected to seismic or wind loadings; consequently the cyclic shear properties of the interface are the key parameters of concern when considering the safety and durability of the structures in these permafrost regions. In this paper we present the results of measuring and analyzing the cyclic shear properties of an artificially frozen soil-structure interface; the experimental work being conducted on our self-developed, large-scale multi-functional direct shear apparatus (DDJ-1). These direct shear tests were conducted under conditions of constant normal stiffness, having a specific initial value for normal stresses (either 300, 500, or 700. kPa), and at a constant frozen temperature (i.e. -. 6, -. 10, or -. 14. °C) or a rising temperature (from -. 14. °C to -. 2. °C). Their cyclic shear stress and normal displacement were measured in 30. cycles for each of the constant frozen temperature settings, and in 13.25. cycles for the rising temperature. These test results show that: (1) The maximum shear stress is observed in the first cycle. This maximum shear stress is higher for lower frozen temperature and higher initial normal stress. Furthermore, the internal friction angle of the frozen soil-structure interface decreases with shear cycle and higher frozen temperature. (2) Under constant frozen temperature, the rates of increase of the normal displacement and normal stress slow down with cyclic loading time. However, these rates of increase are fast at the beginning, slow down, and then speed up again under the rising temperature. (3) The reversible normal displacement, expressed by the peak-to-trough distance of normal displacement, linearly increases with the initial normal stress when the frozen temperature is constant.

Construction of dams in permafrost regions provides an opportunity for frozen core or frozen foundation construction technology to be utilised. This technology ensures seepage control by taking advantage of extremely cold conditions to maintain and promote long-term ground freezing. Frozen-core dams are not new. They have been used in the Arctic regions of Russia, Canada and Alaska since the 1960s, and have been recorded as early as the 1790s. However, published literature about the design, construction and performance of these dams is in short supply. This, combined with concerns over climate change, makes owners and regulators nervous about the use of the technology. This paper summarises the historical use and performance of frozen dams, specifically frozen-core dams, and highlights specific elements of a recently completed, precedent-setting frozen-core dam in Nunavut, Canada. Unlike most existing frozen-core dams founded on bedrock, this dam has been constructed on thick, ice-rich saline marine sediments. Moisture-holding capacity is paramount for a suitable core material and field trials in advance of construction are invaluable., Construction of dams in permafrost regions provides an opportunity for frozen core or frozen foundation construction technology to be utilised. This technology ensures seepage control by taking advantage of extremely cold conditions to maintain and promote long-term ground freezing. Frozen-core dams are not new. They have been used in the Arctic regions of Russia, Canada and Alaska since the 1960s, and have been recorded as early as the 1790s. However, published literature about the design, construction and performance of these dams is in short supply. This, combined with concerns over climate change, makes owners and regulators nervous about the use of the technology. This paper summarises the historical use and performance of frozen dams, specifically frozen-core dams, and highlights specific elements of a recently completed, precedent-setting frozen-core dam in Nunavut, Canada. Unlike most existing frozen-core dams founded on bedrock, this dam has been constructed on thick, ice-rich saline marine sediments. Moisture-holding capacity is paramount for a suitable core material and field trials in advance of construction are invaluable.

Responsibility for the environmental management and remediation of the Colomac Mine site, Northwest Territories, reverted to the Government of Canada, following the bankruptcy of the former mine owner. Earthwork remediation of the tailings facility occurred from 2006 to 2007. One of the major components of the remediation plan was the construction of Dam 1B in the tailings containment area, downstream of an existing but leaky Dam 1A. Dam 1B functionally replaced a costly year-round pump-back system at the toe of Dam 1A. Seepage through Dam 1B is controlled by a geocomposite liner system that is keyed into permafrost. Thermosyphons were installed at the base of a key trench to prolong permafrost retention over the useful life of the dam and prevent underseepage. Open-graded rock fill was also placed on the downstream slope of Dam 1B to promote the ingress of cold air into the structure during the winter and further maintain a permafrost foundation. Thirteen ground temperature cables were installed at five sections along the dam to monitor temperatures within the dam. Measurements have been regularly recorded since January 2007. Temperatures below the dam have remained below –2 degrees C since construction and the dam foundation has cooled quicker than predicted during design. Natural air convection at the downstream toe is also proving to be an effective source of heat extraction., Responsibility for the environmental management and remediation of the Colomac Mine site, Northwest Territories, reverted to the Government of Canada, following the bankruptcy of the former mine owner. Earthwork remediation of the tailings facility occurred from 2006 to 2007. One of the major components of the remediation plan was the construction of Dam 1B in the tailings containment area, downstream of an existing but leaky Dam 1A. Dam 1B functionally replaced a costly year-round pump-back system at the toe of Dam 1A. Seepage through Dam 1B is controlled by a geocomposite liner system that is keyed into permafrost. Thermosyphons were installed at the base of a key trench to prolong permafrost retention over the useful life of the dam and prevent underseepage. Open-graded rock fill was also placed on the downstream slope of Dam 1B to promote the ingress of cold air into the structure during the winter and further maintain a permafrost foundation. Thirteen ground temperature cables were installed at five sections along the dam to monitor temperatures within the dam. Measurements have been regularly recorded since January 2007. Temperatures below the dam have remained below –2 degrees C since construction and the dam foundation has cooled quicker than predicted during design. Natural air convection at the downstream toe is also proving to be an effective source of heat extraction.

For the design of deep frozen shafts through unstable rocks and/or water-saturated soils, core samples from a borehole at or near the proposed shaft centre need to be as undisturbed as possible so that laboratory tests of frozen and unfrozen conditions can be carried out. A single borehole may be inadequate if geology changes over short distances, as proved the with the Gorleben nuclear waste disposal shaft in Germany at the top of a clay dome. Cores may be unobtainable from the overburden where the greatest risk of problems lies. Highly sophisticated borehole geophysical measurements are helpful but cannot provide simple input parameters such as cohesion in the unfrozen and frozen state, internal friction, thermal conductivity and creep, as illustrated by a Saskatchewan potash project. A modern programme for parameter evaluation must combine on-site geological and engineering survey results from core drilling with geophysical survey evaluation and laboratory testing to internationally accepted standards, as exemplified by a Russian potash project along the Kama river., For the design of deep frozen shafts through unstable rocks and/or water-saturated soils, core samples from a borehole at or near the proposed shaft centre need to be as undisturbed as possible so that laboratory tests of frozen and unfrozen conditions can be carried out. A single borehole may be inadequate if geology changes over short distances, as proved the with the Gorleben nuclear waste disposal shaft in Germany at the top of a clay dome. Cores may be unobtainable from the overburden where the greatest risk of problems lies. Highly sophisticated borehole geophysical measurements are helpful but cannot provide simple input parameters such as cohesion in the unfrozen and frozen state, internal friction, thermal conductivity and creep, as illustrated by a Saskatchewan potash project. A modern programme for parameter evaluation must combine on-site geological and engineering survey results from core drilling with geophysical survey evaluation and laboratory testing to internationally accepted standards, as exemplified by a Russian potash project along the Kama river.

A new method for calculating the thicknesss of shaft linings is introduced for use in mining of Chinese coal deposits located at depths of around 500-1 000 m beneath deep alluvium. Chinese achievements in ground freezing are outlined with reference to around 700 deep shafts sunk since 1955 and design details are presented for the Zhaogu No.2 mine auxiliary shaft, sunk through 527.5 m of alluvium. As depths have increased, progressively higher groundwater pressures have required thicker frozen walls to be accommodated into excavation methods and schedules. Temperature calculation formulae have been adapted to take into account an inner ring of anti-spalling auxiliary freezing boreholes within the main borehole ring. The shaft liner at the freezing section consists of reinforced concrete inner and outer liners with a plastic sliding layer between them and a polystyrene yielding layer to buffer and insulate the outer liner from the surrounding rock. Tables are presented from Zhaogu for alluvial composition, freezing design technical indices, frozen soil connection times, freezing wall formation indices for a clay soil layer, adjustment and control of saline water temperature and flow, and test results for the inner and outer concrete liners., A new method for calculating the thicknesss of shaft linings is introduced for use in mining of Chinese coal deposits located at depths of around 500-1 000 m beneath deep alluvium. Chinese achievements in ground freezing are outlined with reference to around 700 deep shafts sunk since 1955 and design details are presented for the Zhaogu No.2 mine auxiliary shaft, sunk through 527.5 m of alluvium. As depths have increased, progressively higher groundwater pressures have required thicker frozen walls to be accommodated into excavation methods and schedules. Temperature calculation formulae have been adapted to take into account an inner ring of anti-spalling auxiliary freezing boreholes within the main borehole ring. The shaft liner at the freezing section consists of reinforced concrete inner and outer liners with a plastic sliding layer between them and a polystyrene yielding layer to buffer and insulate the outer liner from the surrounding rock. Tables are presented from Zhaogu for alluvial composition, freezing design technical indices, frozen soil connection times, freezing wall formation indices for a clay soil layer, adjustment and control of saline water temperature and flow, and test results for the inner and outer concrete liners.

Sub-aerial deposition of tailings in the dam at Cameco's Rabbit Lake uranium mine in Saskatchewan, Canada, occurred throughout the year. Those tailings deposited during the winter month formed a frozen layer, which was prevented from thawing by the subsequent deposition of tailings during warmer months. The frozen material has to be thawed before the dam is decommissioned, partly to consolidate the tailings but also to recover the space currently occupied by ice. The suitability of electric resistance heating for this purpose was tested in two laboratory studies. The tests showed that there were negligible geochemical effects associated with thawing, and a field trial is due to be carried out in summer 2010 to obtain further data on aspects such as long-term geochemical and geotechnical effects and the economics of the process., Sub-aerial deposition of tailings in the dam at Cameco's Rabbit Lake uranium mine in Saskatchewan, Canada, occurred throughout the year. Those tailings deposited during the winter month formed a frozen layer, which was prevented from thawing by the subsequent deposition of tailings during warmer months. The frozen material has to be thawed before the dam is decommissioned, partly to consolidate the tailings but also to recover the space currently occupied by ice. The suitability of electric resistance heating for this purpose was tested in two laboratory studies. The tests showed that there were negligible geochemical effects associated with thawing, and a field trial is due to be carried out in summer 2010 to obtain further data on aspects such as long-term geochemical and geotechnical effects and the economics of the process.

Cameco's Cigar Lake property is located in the Athabasca Basin of northern Saskatchewan, Canada. The high-grade deposit, up to 16 m thick, consists of massive pitchblende, clay and sand and is overlain by thick zones of sandy clay, unconsolidated sandstone and altered sandstone. Work is currently in progress to restore the underground workings, following water inflows in 2006 and 2008. Ground freezing will be used to support the weak rock and to minimise the risk of further water inflows during mining. Testwork carried out on drill core sample to improve knowledge of the behaviour of the frozen ground is presented and discussed., Cameco's Cigar Lake property is located in the Athabasca Basin of northern Saskatchewan, Canada. The high-grade deposit, up to 16 m thick, consists of massive pitchblende, clay and sand and is overlain by thick zones of sandy clay, unconsolidated sandstone and altered sandstone. Work is currently in progress to restore the underground workings, following water inflows in 2006 and 2008. Ground freezing will be used to support the weak rock and to minimise the risk of further water inflows during mining. Testwork carried out on drill core sample to improve knowledge of the behaviour of the frozen ground is presented and discussed.

This project concerns the effect of freeze-thaw cycles on the pore-scale structure of nonaqueous phase liquid (NAPL) contaminants in water-saturated porous media. This problem is of critical importance to the entrapment of such contaminants in cold temperate, polar and high altitude regions, and has not been examined in the literature to date. This research work is conducted in three stages: (i) two-dimensional nondestructive visualisation of residual light non-aqueous phase liquid (LNAPL), and dense non-aqueous phase liquid (DNAPL), in porous media subject to successive freeze-thaw cycles; (ii) three-dimensional experiments on LNAPL in porous media subject to freeze-thaw, with quantification of phase volumes by X-ray micro-computed tomography (micro-CT); and (iii) the explanation of results by several pore scale mathematical and conceptual models. The two-dimensional cell experiments (using a monolayer of 0.5 mm diameter glass beads held between two glass sheets), and three-dimensional X-ray micro-CT experiments reveal a substantial mobilisation and rupture of ganglia during successive freeze-thaw cycles; this includes the detachment of smaller ganglia from larger ganglia and the mobilisation of NAPL in the direction of freezing front. The experiments also reveal significant shedding of numerous single/sub-singlet ganglia along narrow pore corridors, their entrapment in growing polycrystalline ice, and the coalescence of such small ganglia during thawing to form larger singlets. These changes were more predominant where the freezing commenced. The results of the experimental studies were interpreted by developing several mathematical and conceptual models, including freezing-induced pressure model, Darcy's law model, multipore ganglia model (rupture coefficient) and ice-snap off model.

By employing a combination of ice pressure, liquid pressure and total stress as state variables, a new thermoplastic constitutive model has been developed that encompasses frozen and unfrozen behaviour within a unified effective-stress-based framework. It has been incorporated into a fully coupled thermo-hydro-mechanical (THM) finite element formulation that considers freezing and thawing in water-saturated soils and applied to a large-scale pipeline frost heave test., Peer Reviewed, Postprint (published version)

[EN] Wedge-like structures occur in raised beach gravels near Rio Grande, eastern Tierra Del Fuego (latitude 53°50′S; longitude 67°5′W). They vary in dimension, being approximately 1.0–1.5 m deep and 0.3–0.8 m in apparent width. Some are closely spaced, while others are as much as 5.0–8.0 m apart. The infill is predominantly fine and coarse sand, together with silt, all of local provenance. There is little evidence of secondary infill. It is unclear whether these structures are soil wedges, sand wedges, or composite wedges. Their significance as regards the possible previous occurrence of perennially-frozen ground in the lowlands of Tierra del Fuego has yet to be determined.

Problems are discussed relating to the coordination of excavation and lining operations to achieve good excavation productivity with rapid lining installation to avoid stability problems caused by thawing of the rock around the tunnel. Finite element analyses of the temperatures inside a tunnel, verified by physical measurements in a tunnel in permafrost on the Qinghai-Tibet railway, were used to determine stability conditions relating to the thawing depth. Four safety conditions were identified, a safety phase, relative safety phase, safety precaution and potential safety problem, which showed strong agreement with the conditions actually observed during construction., Problems are discussed relating to the coordination of excavation and lining operations to achieve good excavation productivity with rapid lining installation to avoid stability problems caused by thawing of the rock around the tunnel. Finite element analyses of the temperatures inside a tunnel, verified by physical measurements in a tunnel in permafrost on the Qinghai-Tibet railway, were used to determine stability conditions relating to the thawing depth. Four safety conditions were identified, a safety phase, relative safety phase, safety precaution and potential safety problem, which showed strong agreement with the conditions actually observed during construction.

The following papers are included: Selbaie mine closure plan for the long-term, by Caron D., Adam D. and Wiber M., p.725-734; Mine closure in the Arctic, by Reshetnyak S.P. and Fedotova Y.V., p.735-741, 3 refs.; Reclamation of frozen sulphidic tailings area - Nanisivik mine, northern Canada, by Claypool G., Cassie J. and Carreau R., p.743-754, 4 refs.; Closure of Nanisivik mine in the Canadian Arctic - progress and costs, by Carreau R., Markle M., Cassie J. and Claypool G., p.755-766, 3 refs.; Tailing facility closure in arid environments - research and outcomes, a review of sites closed through this process in Western Australia's arid regions, by Lacy H.W.B. and Barnes K.L., p.767-775, 15 refs.; and Abandoned mines in northern Canada - programme challenges and case studies, by Nahir M. and David C., p.777-785., The following papers are included: Selbaie mine closure plan for the long-term, by Caron D., Adam D. and Wiber M., p.725-734; Mine closure in the Arctic, by Reshetnyak S.P. and Fedotova Y.V., p.735-741, 3 refs.; Reclamation of frozen sulphidic tailings area - Nanisivik mine, northern Canada, by Claypool G., Cassie J. and Carreau R., p.743-754, 4 refs.; Closure of Nanisivik mine in the Canadian Arctic - progress and costs, by Carreau R., Markle M., Cassie J. and Claypool G., p.755-766, 3 refs.; Tailing facility closure in arid environments - research and outcomes, a review of sites closed through this process in Western Australia's arid regions, by Lacy H.W.B. and Barnes K.L., p.767-775, 15 refs.; and Abandoned mines in northern Canada - programme challenges and case studies, by Nahir M. and David C., p.777-785.

The Terrestrial hydrothermal processes and systems reviewed are associated with submarine, sub-aerial and sub-volcanic settings, intra- continental rifts and geothermal springs. Systems that most closely approximate Martian conditions include the Dresser Formation and the Sulphur Springs Group in the Pilbara Craton, Western Australia. The East African rift system may be considered as an analogue for the great rift system of Valles Marineris on Mars. A summary of the geology of Mars is presented and the types of hydrothermal systems that may occur are discussed, in particular around Tharsis volcanoes and caldera floors and in fractures and rift valleys. The discovery of crystalline haematite and sulphate deposits indicates chemical precipitation analogous to that of banded iron formation and/or hot spring sinter-like deposits. The interaction of hot magmas with the cryosphere is proposed as a mechanism to explain many of the surface features and a model is presented for the widespread deposition of sulphates as hydrothermal precipitates, generated through the interaction of magmatic H2S in hydrothermal solutions with water in the cryosphere., The Terrestrial hydrothermal processes and systems reviewed are associated with submarine, sub-aerial and sub-volcanic settings, intra- continental rifts and geothermal springs. Systems that most closely approximate Martian conditions include the Dresser Formation and the Sulphur Springs Group in the Pilbara Craton, Western Australia. The East African rift system may be considered as an analogue for the great rift system of Valles Marineris on Mars. A summary of the geology of Mars is presented and the types of hydrothermal systems that may occur are discussed, in particular around Tharsis volcanoes and caldera floors and in fractures and rift valleys. The discovery of crystalline haematite and sulphate deposits indicates chemical precipitation analogous to that of banded iron formation and/or hot spring sinter-like deposits. The interaction of hot magmas with the cryosphere is proposed as a mechanism to explain many of the surface features and a model is presented for the widespread deposition of sulphates as hydrothermal precipitates, generated through the interaction of magmatic H2S in hydrothermal solutions with water in the cryosphere.

The international mine ventilation congresses cover the topics of mine ventilation and the working environment, as well as the ventilation- related aspects of fires and explosions. A total of 64 papers were presented at the eighth congress, with 5 in each of the following sessions: Cooling I and II, Heat, Respirable dust, Case studies I and II, Gases, Diesel, Fires, Spontaneous combustion, Monitoring and control, and Poster papers. There were 4 papers in the Spontaneous combustion workshop., The international mine ventilation congresses cover the topics of mine ventilation and the working environment, as well as the ventilation- related aspects of fires and explosions. A total of 64 papers were presented at the eighth congress, with 5 in each of the following sessions: Cooling I and II, Heat, Respirable dust, Case studies I and II, Gases, Diesel, Fires, Spontaneous combustion, Monitoring and control, and Poster papers. There were 4 papers in the Spontaneous combustion workshop.

Dust is carried into the airways of underground Arctic placer mines by moisture evaporating from the frozen ground. A mathematical analysis of heat and mass transfers between the ventilation air and frozen ground shows that climatic conditions play a major role in both dust generation and suppression. This analysis allows methods of dust control to be identified, such as the injection of steam into ventilation air in winter. The steam deposits a film of moisture on the walls of the airway, trapping dust on the walls., Dust is carried into the airways of underground Arctic placer mines by moisture evaporating from the frozen ground. A mathematical analysis of heat and mass transfers between the ventilation air and frozen ground shows that climatic conditions play a major role in both dust generation and suppression. This analysis allows methods of dust control to be identified, such as the injection of steam into ventilation air in winter. The steam deposits a film of moisture on the walls of the airway, trapping dust on the walls.

A short outline is given of the development of mathematical models by the Institute of Mining of the North, part of the Russian Academy of Science, for use in mines within the permafrost region. These take into account the water phase transformations within the frozen host rocks. One example calculates the temperature variations within a ventilation air distribution network. Another covers heat transfer between backfill and the host rock, accounting for both the heat released during hydration of the backfill and the water phase transformations in the frozen host rocks., A short outline is given of the development of mathematical models by the Institute of Mining of the North, part of the Russian Academy of Science, for use in mines within the permafrost region. These take into account the water phase transformations within the frozen host rocks. One example calculates the temperature variations within a ventilation air distribution network. Another covers heat transfer between backfill and the host rock, accounting for both the heat released during hydration of the backfill and the water phase transformations in the frozen host rocks.

Changes in the hydraulic conductivity were studied of three non-compacted clay covers located on a sodic/saline overburden fill at the Syncrude oil sands mine, Alberta. Monitoring of the covers for temperature, matric suction, and water content has been ongoing for more than three years. The three covers were constructed in 1999 and are 35, 50, and 100 cm thick. The covers are comprised of a surface layer of reclaimed peat/mineral mix over a secondary reclaimed mineral soil (glacial till or glaciolacustrine clay), placed over a sloping shale surface. Field measurements of hydraulic conductivity within the secondary layer were obtained during the 2000, 2001, and 2002 summer field seasons. The hydraulic conductivity values for the covers were similar during each of the field study seasons. The mean hydraulic conductivity of the secondary layer increased every year. Soil temperature data shows that one freeze/thaw cycle occurred each year at the measurement depths. The results indicate that an extensive and evenly distributed soil structure has developed throughout the secondary cover material. It is anticipated that future freeze/thaw cycles will not affect the hydraulic conductivity of the cover system., Changes in the hydraulic conductivity were studied of three non-compacted clay covers located on a sodic/saline overburden fill at the Syncrude oil sands mine, Alberta. Monitoring of the covers for temperature, matric suction, and water content has been ongoing for more than three years. The three covers were constructed in 1999 and are 35, 50, and 100 cm thick. The covers are comprised of a surface layer of reclaimed peat/mineral mix over a secondary reclaimed mineral soil (glacial till or glaciolacustrine clay), placed over a sloping shale surface. Field measurements of hydraulic conductivity within the secondary layer were obtained during the 2000, 2001, and 2002 summer field seasons. The hydraulic conductivity values for the covers were similar during each of the field study seasons. The mean hydraulic conductivity of the secondary layer increased every year. Soil temperature data shows that one freeze/thaw cycle occurred each year at the measurement depths. The results indicate that an extensive and evenly distributed soil structure has developed throughout the secondary cover material. It is anticipated that future freeze/thaw cycles will not affect the hydraulic conductivity of the cover system.

Arsenic trioxide dust from the roaster at the gold mine in the Northwest Territories, stored underground from 1951 onwards in shallow chambers thought to be protected by permafrost, is now threatening groundwater as the permafrost degrades. A large number of options have been reviewed and the best in-situ and ex-situ alternatives identified as artificial ground freezing and surface encasement in cement. Both would demand long-term water treatment and site monitoring., Arsenic trioxide dust from the roaster at the gold mine in the Northwest Territories, stored underground from 1951 onwards in shallow chambers thought to be protected by permafrost, is now threatening groundwater as the permafrost degrades. A large number of options have been reviewed and the best in-situ and ex-situ alternatives identified as artificial ground freezing and surface encasement in cement. Both would demand long-term water treatment and site monitoring.

The foundations of the shaft head-frame at the Internationalny underground mine in Yakutia are situated in permafrost. The head-frame base is built on 132 piles, each with a load-bearing capacity of 100 tons. Frozen ground has little or no bearing strength when thawed, so the foundation base is to be maintained in a frozen state by the application of two concentric freezing holes. These were designed using parameters obtained by mathematical simulation of the dynamic temperature field. An automated thermo-measurement system will allow the foundation's temperature regime to be controlled., The foundations of the shaft head-frame at the Internationalny underground mine in Yakutia are situated in permafrost. The head-frame base is built on 132 piles, each with a load-bearing capacity of 100 tons. Frozen ground has little or no bearing strength when thawed, so the foundation base is to be maintained in a frozen state by the application of two concentric freezing holes. These were designed using parameters obtained by mathematical simulation of the dynamic temperature field. An automated thermo-measurement system will allow the foundation's temperature regime to be controlled.

Regulation of the thermal regime is extremely important for assuring the stability of mine openings in permafrost. The thermal regime around an airway with thermosyphons installed on the surface is examined. The results of finite element analysis indicate that where thermosyphons are installed, a cold area develops at the top of the roof, in some ways resembling a dome covering the roof. The development and maintenance of this cold dome must be carefully considered when planning the support system for a near-surface underground mine opening in frozen ground., Regulation of the thermal regime is extremely important for assuring the stability of mine openings in permafrost. The thermal regime around an airway with thermosyphons installed on the surface is examined. The results of finite element analysis indicate that where thermosyphons are installed, a cold area develops at the top of the roof, in some ways resembling a dome covering the roof. The development and maintenance of this cold dome must be carefully considered when planning the support system for a near-surface underground mine opening in frozen ground.

Permafrost features that influence the deposition of sulphidic wastes liable to create acid mine drainage include processes within the active layer that produce pathways for reactants and contaminants, barriers such as snow and ice covers, and low temperatures that slow most chemical and biological processes. Primary issues for disposal of sulphidic mine tailings are summarised and strategies for controlling the oxidation of sulphide minerals at sub-zero temperatures are discussed. Results from Nanisivik in Canada illustrate the possibilities of keeping tailings permanently water-saturated or frozen, as well as problems such as the enhancement of bacterial activity under an insulating cover of snow. Future research should focus on rates of generation of acid mine drainage at sub-zero temperatures and on solute migration in frozen media., Permafrost features that influence the deposition of sulphidic wastes liable to create acid mine drainage include processes within the active layer that produce pathways for reactants and contaminants, barriers such as snow and ice covers, and low temperatures that slow most chemical and biological processes. Primary issues for disposal of sulphidic mine tailings are summarised and strategies for controlling the oxidation of sulphide minerals at sub-zero temperatures are discussed. Results from Nanisivik in Canada illustrate the possibilities of keeping tailings permanently water-saturated or frozen, as well as problems such as the enhancement of bacterial activity under an insulating cover of snow. Future research should focus on rates of generation of acid mine drainage at sub-zero temperatures and on solute migration in frozen media.

As part of a flood alleviation scheme on the River Thames in southern England, a large box culvert was jacked through an embankment under the Great Western railway. To maintain the embankment's stability, ground freezing was adopted. The structural strength and deformation of the frozen ground around the culvert was calculated to ensure its support would be adequate during the jacking process. Its thermal behaviour was also predicted to ensure freeze growth could be controlled and would be satisfactory. Ground heave and thaw settlement estimates were made to ensure the level and alignment of the railway tracks could be maintained during jacking. Performance monitoring gave actual values close to those predicted and the project was successfully completed in August 1999., As part of a flood alleviation scheme on the River Thames in southern England, a large box culvert was jacked through an embankment under the Great Western railway. To maintain the embankment's stability, ground freezing was adopted. The structural strength and deformation of the frozen ground around the culvert was calculated to ensure its support would be adequate during the jacking process. Its thermal behaviour was also predicted to ensure freeze growth could be controlled and would be satisfactory. Ground heave and thaw settlement estimates were made to ensure the level and alignment of the railway tracks could be maintained during jacking. Performance monitoring gave actual values close to those predicted and the project was successfully completed in August 1999.

The mine, which has produced over 16 000 000 tonnes of ore since 1976, is located at 73 degrees N in the Canadian Arctic, where the rock is permanently frozen to depths of 500 m or more. Rock mechanics studies for pillar recovery began in 1989 and the first pillars were mined from 1992, but a roof fall in 1994 led to further work on determining a means for safe sequencing of pillar extraction. The use of hydraulic radius was considered reliable for calculating Rock Mechanics Rating (RMR) values for entry-type excavations in dolostones and shales, and a pillar index number system was developed during 1997 for comparing different pillars and deciding their extraction sequence. Real-time ground movement monitoring was installed, with the underground leaky feeder system transmitting data from monitors to computer. Since 1997, pillar recovery has progressed successfully on a continuous basis., The mine, which has produced over 16 000 000 tonnes of ore since 1976, is located at 73 degrees N in the Canadian Arctic, where the rock is permanently frozen to depths of 500 m or more. Rock mechanics studies for pillar recovery began in 1989 and the first pillars were mined from 1992, but a roof fall in 1994 led to further work on determining a means for safe sequencing of pillar extraction. The use of hydraulic radius was considered reliable for calculating Rock Mechanics Rating (RMR) values for entry-type excavations in dolostones and shales, and a pillar index number system was developed during 1997 for comparing different pillars and deciding their extraction sequence. Real-time ground movement monitoring was installed, with the underground leaky feeder system transmitting data from monitors to computer. Since 1997, pillar recovery has progressed successfully on a continuous basis.

The underground mining of frozen placers in Alaska eliminates major pollution by silt discharged into water bodies, but creates new problems related to the excessive convergence and potential instability of openings in ice-rich silts and gravels. It is necessary to predict seasonal temperature variations in ventilation air and the heat transfer from air to rock masses of particular thermo-physical properties. Finite element analysis of temperature distributions around a deep airway and sensitivity analysis of the thermal regime, using two types of frozen soils and three heat transfer coefficients, shows that the asymmetry of the model in the y-direction does not significantly influence temperature distribution. For all the cases investigated, the processes of heat transfer eventually reached a steady state., The underground mining of frozen placers in Alaska eliminates major pollution by silt discharged into water bodies, but creates new problems related to the excessive convergence and potential instability of openings in ice-rich silts and gravels. It is necessary to predict seasonal temperature variations in ventilation air and the heat transfer from air to rock masses of particular thermo-physical properties. Finite element analysis of temperature distributions around a deep airway and sensitivity analysis of the thermal regime, using two types of frozen soils and three heat transfer coefficients, shows that the asymmetry of the model in the y-direction does not significantly influence temperature distribution. For all the cases investigated, the processes of heat transfer eventually reached a steady state.

As East Twin Lake is used to extract drinking water for the mine, the tailings disposal area in the adjacent West Twin Lake has been divided into an upper surface cell for solids retention and a lower reservoir for the disposal of supernatant water, to keep the water level below that of East Twin Lake. An upstream-constructed dyke of frozen shale is used to retain the solids and to separate the surface cell from the reservoir. A review is presented of the construction methodology used for this novel retention dyke, its performance to date, a seepage event that occurred in 1999 and the lessons learnt. Two possible mechanisms for the seepage were considered and it was concluded that tailings discharge water ponded against the dyke had infiltrated the upstream side of the shale fill and flowed downward. A bentonite seal was therefore constructed along the upstream face of the dyke., As East Twin Lake is used to extract drinking water for the mine, the tailings disposal area in the adjacent West Twin Lake has been divided into an upper surface cell for solids retention and a lower reservoir for the disposal of supernatant water, to keep the water level below that of East Twin Lake. An upstream-constructed dyke of frozen shale is used to retain the solids and to separate the surface cell from the reservoir. A review is presented of the construction methodology used for this novel retention dyke, its performance to date, a seepage event that occurred in 1999 and the lessons learnt. Two possible mechanisms for the seepage were considered and it was concluded that tailings discharge water ponded against the dyke had infiltrated the upstream side of the shale fill and flowed downward. A bentonite seal was therefore constructed along the upstream face of the dyke.

Static strength testing and dynamic model simulations were carried out. The frozen fill materials exhibited superior structural performance, particularly at low temperatures. Fill was prepared at water contents of 5 and 10 wt%, lower than typical, to evaluate the possibility of minimising water run-off. Frozen limestone fill was capable of providing structural support for a stope under variations in temperature from -12.9 to -0.2 degrees C, but frozen siltstone fill did not provide the required support when temperatures were elevated to -0.7 degrees C. While both fill materials exhibited comparable uniaxial compressive strengths, their dynamic performances were very dissimilar., Static strength testing and dynamic model simulations were carried out. The frozen fill materials exhibited superior structural performance, particularly at low temperatures. Fill was prepared at water contents of 5 and 10 wt%, lower than typical, to evaluate the possibility of minimising water run-off. Frozen limestone fill was capable of providing structural support for a stope under variations in temperature from -12.9 to -0.2 degrees C, but frozen siltstone fill did not provide the required support when temperatures were elevated to -0.7 degrees C. While both fill materials exhibited comparable uniaxial compressive strengths, their dynamic performances were very dissimilar.

It is not always true that permafrost contains water only in the solid phase and is impermeable, and therefore effective in preventing movement of ground water. As the temperature of the frozen ground increases, mining conditions change. The filtration capacity of underlying, fissured bedrock is of critical importance and may disappear on thawing. The mine may then begin to fill with water entering through the thawed surface deposits and the fractured bedrock. Infiltration of water through fine-grained soil and bedrock increases the ground temperature, increasing permeability. A mathematical model has been developed which describes the simultaneous transport of heat and water in frozen porous material. The physical basis for the model is the analogy between the mechanism of water transport in unsaturated porous media and in partially frozen, porous media. The model also takes account of thermal effects resulting from heat transport by infiltrating water., It is not always true that permafrost contains water only in the solid phase and is impermeable, and therefore effective in preventing movement of ground water. As the temperature of the frozen ground increases, mining conditions change. The filtration capacity of underlying, fissured bedrock is of critical importance and may disappear on thawing. The mine may then begin to fill with water entering through the thawed surface deposits and the fractured bedrock. Infiltration of water through fine-grained soil and bedrock increases the ground temperature, increasing permeability. A mathematical model has been developed which describes the simultaneous transport of heat and water in frozen porous material. The physical basis for the model is the analogy between the mechanism of water transport in unsaturated porous media and in partially frozen, porous media. The model also takes account of thermal effects resulting from heat transport by infiltrating water.