Field experiences in a few particular areas of Slovenia have shown that during periods of snowfall some overhead lines are randomly exposed to short-circuit events between conductors that lie in a vertical disposition. This paper presents two practical approaches to reducing the probability of these inter-span contacts that result from the snow shedding. Both approaches refer to the same overhead line, so that a direct comparison can be made. The first overhead-line circuit is equipped with phase spacers; the second one is equipped with V strings. Up to now, both approaches have served well in practice. In this paper a transmission line is presented, and the differences between the two approaches with regard to the design parameters are given. The advantages and disadvantages of both approaches are summarized.
The presence and distribution of airborne and surface contaminants can often be inferred from their effects on vegetation, and this is particularly true in areas of frozen ground where the vegetation is especially vulnerable. In this paper, we take as a study area the region around the city of Noril'sk in northern Siberia. Non-ferrous metal smelting has been carried out extensively in Noril'sk since the 1930s, and it is now one of the world's largest producers of nickel. The principal contaminants, which are extensive, are sulphur dioxide and heavy metals. Heat contamination from buildings and industrial activity is also significant in the immediate surroundings of the city where it has led to degradation of permafrost.We describe two approaches to the use of satellite imagery to monitor vegetation degradation in the Noril'sk region. The first of these compares a panchromatic spy satellite image from 1961 with a multispectral satellite image acquired 34 years later to quantify the gross changes in land cover around Noril'sk. This analysis shows a decrease of approximately 80 km2 in the vegetated area around the city. The second approach is a regional multitemporal study based on the use of the Normalised Difference Vegetation Index, to which we apply a new correction for phenological variation. This analysis is used to identify a previously unreported area of vegetation decrease to the southwest of Noril'sk.
From strain rate measurements at two firn pits, the effective shear viscosity and the effective bulk viscosity for temperate firn of high density were calculated, depending upon the depth and the in-situ state of stress. At densities from 640 to 840 (kg/m3) the effective shear viscosity increases from 0.2×1010 to 1.5×1010 (kPa s) and the effective bulk viscosity from 4.4×1010 to 65.1×1010 (kPa s). From these viscosities, the effective compative viscosity and the effective uniaxial viscosity were calculated and compared with the values of other types of snow.
On April 12, 1986, the Molikpaq, a caisson-type offshore drilling structure, experienced a series of loading events when second-year and multi-year ice moved against the structure. The highest loads that the Molikpaq experienced during the 1985–86 season were during this day. Extensive ice thickness measurements had been taken in the ice around the Molikpaq prior to April 12. Thickness of up to 6 m were measured and 8 to 12 m estimated for a multi-year hummock. MEDOF panels on the outer face of the caisson and strain gauges on inner bulkheads of the structure were the primary instrumentation used to calculate forces on the faces. Detailed analysis of strain gauge and extensometer data indicated that the maximum global force on the Molikpaq was no more than 420 MN and most likely was 380 MN. This is in contrast to higher and lower values quoted in the literature for the April 12th event. Other loading events during the day when multiple strain gauges and MEDOF panels were being recorded produced global loads of the order 250 MN. Global ice pressures for the 8 to 12 m thick multi-year hummock crushing on the 59 m long east face were not greater than 0.8 MPa.
This compilation of US ice mechanics investigations over 1987–1990 focuses on efforts that support the development of our understanding of sea ice interaction. Both ice-structure and ice-ice interaction studies have been included in hopes that insights from one area will complement developments in the other. The work discussed in the area of ice-structure interaction was intentionally limited to lateral movement of the ice against a vertical structure. It is these results that can be most easily extended to ice-ice interaction events.
During the 1994 and 1995 spring breakup events, ice jams were formed on the lower Matapedia River and remained in place long enough to permit collection of detailed field data on jam thickness as well as on water surface elevations. Together with bathymetric data that were obtained in the following summers, the spring measurements form one of the most complete ice-jam data sets that have been obtained to date. This allowed examination of how well current understanding of the hydromechanics of ice jams, incorporated in a numerical model, can describe the results of the measurements. The availability of jam thickness data was particularly advantageous because it removed the ambiguity associated with model calibrations that are solely based on water level measurements. With suitable choice of the model parameters, the model reproduced the measured water level profiles of the jam very closely, while providing reasonable simulations of jam thickness. The selected values of the model parameters were consistent with values established by previous applications on other rivers, and almost identical between the two Matapedia jams, despite contrasts in jam severity and river flow. Model sensitivity was explored using the more complete 1995 data set and found to be moderate. The detail of the available data also made it possible to scrutinize hydraulic resistance characteristics of flows underneath ice jams, and confirm earlier formulations specifically designed to address extreme-roughness conditions.
On January 28, 1998, an avalanche accident occurred near the Japanese ski resort Niseko Alpen in Hokkaido. The following morning, a snow-pit was dug through the fracture line and the snow cover analysed. There was a weak layer of faceted crystals at a depth of 1 m and it was this weak layer that became the slide plane. Meteorological and snow-pit data from a nearby (1 km) site are used with the Crocus model to explain the formation of the faceted crystals as follows. A period of slow surface warming followed by rapid cooling created a large temperature gradient in the layer near the surface of the snow cover which formed a thin layer of faceted crystals near the surface. The large gradient remained as the layer became buried and the faceted crystals survived in the snow cover for 9 days until increasing load from snow accumulation led to failure and the avalanche occurred.
Knowledge about action undergone by an obstacle impacted by an avalanche is still insufficient to allow civil engineers to design really efficient and resistant structures. The main difficulty is to take into account the mutual interactions that occur between the structure and the flow and the influence of the obstacle on the avalanche action itself. An original back-analysis principle is proposed to obtain information on avalanche action from real destructive event and to ensure that the result is effectively what is undergone by the structure and not only what could be generated by the phenomenon. In that way, the destruction of two deflective walls in Taconnaz site by the 11th of February 1999 exceptional avalanche is studied with several parts: firstly, a large site investigation program is conducted to gather observations including material specimen's tests and to exhibit two collapse scenarios. Then, laboratory experiments are performed to confirm failure mechanisms. Finally, numerical simulations used a rigorous three-dimensional finite elements model and a realistic representation of the concrete behaviour to evaluate the effective resistance of the structures under different conditions, including quasi-static, cyclic and dynamic influences.
We evaluated how climate change resulting from increased greenhouse gas (GHG) emissions may affect the timing of wet avalanches and snow quality at Aspen Mountain in the years 2030 and 2100. Snow quantity was evaluated using the Snowmelt Runoff Model and snow quality was evaluated using SNTHERM. We determined the timing of wet avalanche activity by examining changes to historical average temperatures and snow quality by calculating the bulk density of the top 10 cm of the snowpack. Climate changes were evaluated using MAGICC/SCENGEN and the output from five General Circulation Models (GCMs). The climate change estimates were run using the relatively low, mid-range, and high GHG emissions scenarios: B1, A1B, and A1FI. To get higher resolution estimates of changes in climate, we used output from a regional climate model (RCM, MM5), which is nested in the Parallel Climate Model (PCM).We defined wet avalanches as likely to occur when average daily temperature exceeds 0 °C and investigated three scenarios: first day when daily average temperature exceeds 0 °C, first three consecutive day period when average temperature exceeds 0 °C, and the day after which average temperature remains greater than 0 °C. By 2030 at the top of Aspen Mountain, wet avalanches are likely to occur between 2 and 19 days earlier than historical averages, with little difference across the GCMs. In 2100, the occurrence of wet avalanches at the top of the mountain varies strongly by CO2 emissions scenario. The low and mid-range emissions scenarios show that wet avalanches at the top of the mountain start 16 to 27 days earlier than historical averages. In contrast, the high emissions scenario shows wet avalanches occurring 41 to 45 days earlier. In spite of earlier melt initiation and the reduction in snowpack, snow density in the top 10 cm increased by less than 20% by 2030.
Cryoconite holes form on ice due to enhanced ablation around particles deposited on the surface, and are present in the ablation area of glaciers worldwide. Here we investigate the use of Ground Penetrating Radar (GPR) as a non-destructive method to monitor and map cryoconite holes. We compare GPR data obtained from the Jutulsessen blue ice area in Dronning Maud Land, Antarctica, with modeled GPR data. The modeled GPR response to cryoconite holes is numerically calculated by solving Maxwell's equations with a 3D Finite-Difference Time-Domain (FDTD) scheme. The model includes a realistic shielded bowtie antenna and dimensions and constituent parameters of cryoconite holes excavated in the field. We have performed what-if scenarios with controlled variation of single parameters. We show that GPR can be used to determine the horizontal extent, depth and whether a cryoconite hole is frozen or contains liquid water, information unavailable from visual surface inspection. The cryoconite thickness can, for completely frozen holes, be determined to within a 1/4 of the GPR center frequency wavelength. The exact water content is not readily extractable because the GPR response is influenced by many other factors such as: cryoconite thickness, shape and roughness, as well as antenna ground coupling.
A three-dimensional model developed for the slow deformation, without macroscopic failure, of a stratified snow cover has been used to simulate laboratory mechanical tests performed on sieved snow. The model is based on a non-linear visco-elastic constitutive law for snow whose parameters depend on the snow temperature and density. Snow densification is derived from the bulk viscous strain. The model has been implemented in the Flac3D finite-difference code. The experimental device is a convergent channel in which snow is forced at a constant velocity in the range 1–100 μm s− 1. Although snow is compressed under plane strain conditions, the channel geometry allows obtaining a multi-axial stress-state. Since the testing conditions involve ranges of variation of both the snow density and the strain-rate wider than those encountered for a natural snowpack, the constitutive relations of the model had to be modified. In this paper we present the constitutive model for snow, some details about its implementation into the Flac3D code, and its application to the numerical simulation of the mechanical tests. The comparison of the model and experimental results shows a relatively good agreement, although snow microstructure is accounted for only through its density. However, the treatment of the non-linearity of the viscosity must be improved. This 3D numerical model can be regarded as an interesting tool for assessing a constitutive law for snow on the basis of cold-room experiments, as well as for studying natural snow covers.
Using Synthetic Aperture Radar (SAR) images from ERS-1, we render high resolution motion fields of sea ice using a multi-resolution processing system. The results are provided at a 400 m resolution, which is an order of magnitude greater than the standard SAR motion products (5–10 km). An error propagation experiment shows a standard deviation of 1.3% day− 1 for the noise in invariant shear resulting from position uncertainties and processing techniques. We use this noise level to determine a significant lower threshold when identifying shear zone discontinuities. As example, a 24-day sequence of images is processed using this system to examine the development and evolution of a shear zone. This evolution is in response to the topographic steering caused by ocean circulation and wind forcing along a continental shelf break. In addition, we adapt the Line Integral Convolution (LIC) to depict flow patterns present in the motion field. Collectively, these motion products provide valuable descriptions of the non-rigid dynamics taking place within the sea ice. Our goal is to complement the existing RADARSAT Geophysical Processing System (RGPS) motion products and aid in the validation and further development of the most progressive “lead-resolving” sea ice models currently available. This form of sea ice visualization is important for understanding air–ice–sea momentum transfer processes that transcend through small-scale to large-scale fracture events with application to ship navigation.
We present technical methods aiming at a reduction of snow and ice ablation within an Austrian glacier ski resort. From April 2004 to September 2005 we carried out field studies at Schaufelferner (2870 m a.s.l.) and Gaiβkarferner (3100 m a.s.l.), two glaciers situated in the Stubai Alps. We injected water into the winter snow and studied the effects of compaction and artificial surface cover blankets. Results demonstrate a high efficiency of special blankets (geotextiles) that are placed on the snow surface in spring. Average melt rates and total ablation are reduced by 60%, conserving around 300 kgm− 2 of winter snow over the ablation periods 2004 and 2005, respectively. Crucial material properties are identified that play an important role in the performance. It is possible to increase glacier mass balance using a 0.004 m thin cover material.
Faceted crystals are observed to grow above crusts. These crusts can result from the release of latent heat from a freezing-layer of wet snow. Thus, the formation of an icy layer could trigger the onset of the growth of a layer of faceted crystals above the icy layer. Once started, the growth of faceted crystals might then be enhanced due to the low thermal conductivity of the faceted layer in relation to the icy layer. The presence of a faceted layer can lead to the release of an avalanche through either failure within the faceted layer or between the faceted layer and the crust.
A physically based, numerical snow-transport model (SnowTran-3D) is used to successfully simulate the above treeline snowdrift evolution around Montgomery Pass in the Northern Colorado Rocky Mountains. The model accounts for key snow-transport components including: saltation, suspension, deposition, erosion, and sublimation. The snow-transport model requires static inputs of vegetation type and topography, and temporally evolving spatial distributions of air temperature, humidity, precipitation, wind speed, and wind direction. A simple wind-flow model, driven by data from a ridge-top meteorological station, is used to simulate the flow field over the topographic drift catchment. The snow-transport model outputs include the spatial and temporal evolution of snow depth resulting from variations in precipitation, saltation and suspension transport, and sublimation. The model is forced using SNOTEL and meteorological data from the 1997–1998 winter, and the resulting model outputs are compared with observed snowdrift distributions.
This paper presents an overview of bergy bit impact trials carried out on the CCGS Terry Fox off the northern tip of the island of Newfoundland in June 18–23, 2001 and is meant to accompany the five papers that follow. The trial consisted of impacting target iceberg ice masses ranging from roughly 100 t (growlers) to 22,000 t (bergy bits) on an instrumented bow area of the ‘Terry Fox’ at various forward speeds. Parameters measured included impact forces, pressures and contact areas, ship motions with six degrees of freedom, ship forward speed, and ambient environmental factors. In addition, extensive video and photographic records were compiled, including stereo photographs of the bergy bits. Furthermore, a multi-beam sonar was used to determine underwater profiles of some of the targeted ice masses. Temperature profiles were obtained for a number of bergy bits and some ice samples were collected from undamaged and impacted ice. The details and data associated with the various components of the field study are presented in the 5 accompanying papers. Below are brief descriptions of the ‘Terry Fox’, the instrumentation/set-up used and ice characterization techniques employed. This overview is condensed from a more detailed one [Gagnon, R., Cumming, D., Ritch, R., Browne, R., Johnston, M., Frederking, R., McKenna, R. and Ralph, F., 2002. Overview of Bergy Bit Impact Trials. Proceedings of the 16th International Symposium on Ice, Ice in the Environment, IAHR 2002, Dunedin, New Zealand, Vol. 1, 458–465.] presented at IAHR 2002 in New Zealand.
Local pressures are generally determined based on extreme pressures obtained in measurements. The exposure of structural components is an issue that needs attention. Exposure can be considered in everyday terms as “the longer you fish, the bigger the fish you catch.” In the case of design of offshore structures for ice environments, the more numerous the number of ice–structure interaction events, the greater the likelihood of a particular load being exceeded. The number of interactions with multiyear ice is different for say the Beaufort and Chukchi Seas, and varies with location within these areas. These differences are expressed in terms of the exposure of the structure to multiyear ice. Exposure may also vary depending on location within the structure. Structure above or below the ice belt may receive few interactions resulting in small local pressures.The paper presents a generalization of a method for accounting for exposure, originally developed for ship rams. The particular application is multiyear ice interacting with a structure. The panel data from the Beaufort Sea experience of the Molikpaq structure is used as an example. Exposure is an important parameter that can be taken into account with the method. The previous relationship α = 1.25a− 0.7 obtained for ship rams can be reasonably applied to multiyear ice, where 10 min of multiyear ice interaction is approximately equivalent to 1 Kigoriak ship ramming event. The method is promising for use in codes, for example with the new ISO Code 19906.
Scanning electron microscopy and X-ray microanalysis were employed to investigate the morphology of impurities present in pond and river freshwater ice. Several structural features, 0.4 to roughly 1.2 mm in diameter, with distinct morphological characteristics were identified in the pond ice. The features reside both in the interior of the grains as well as at grain boundaries. In river ice, the impurity aggregates were significantly smaller than in the pond ice (the majority with sizes ⪝20 μm) with no particular shape and were concentrated in the grain boundaries.
The effects of extreme meteorological phenomena covering a vast area may cause a huge failure of a power system. The blackout dated the 8th of April 2008, which took place in the large Polish city Szczecin and the surrounding areas, requires analysis of its causes as well as its direct and indirect effects. This article presents proposals for transmission network operators aimed at improving the effectiveness of action taken during a crisis or disaster caused by meteorological phenomena.
This paper describes a semi-empirical model capable of predicting the local heat transfer and ice accretion rates over aircraft wings (airfoils) under a host of environmental conditions. The model is particularly useful when the equilibrium surface temperature of the airfoil is in the vicinity of the freezing temperature in that it considers different scenarios involving the simultaneous occurrence of freezing, sublimation, and evaporation for high-speed subsonic flows over airfoil surfaces. Profiles of evaporation and sublimation fractions as well as ice accretion and liquid runoff rates are presented and general conclusions are reached.
The main objective of this paper is to introduce a new 2-D icing model, of which the primary purpose is the simulation of the ice accretion process on overhead power line cables. The parameters of the model, such as the Local Collision Efficiency (LCE) and the local Heat Transfer Coefficient (HTC), were evaluated on the basis of time-dependent airflow computations and water droplet trajectory calculations. For wet accumulations, the movement of a surface water film was monitored at each time step so as to obtain the film's thickness and direction. In order to validate the present model, a number of experimental tests were carried out at the CIGELE Atmospheric Icing Research Wind Tunnel (CAIRWT). The results show that, on the whole, the proposed ice model performed well in simulating and predicting ice-grown shapes under dry and wet icing conditions.
The shapes and density of ice accretions on an H.V. conductor is closely related to the electrical corona activities on ice asperities. We will present some effects of positive and negative corona discharges on a tip of conical ice as a function of corona current, temperature and atmospheric conditions. Firstly, the loss in the volume of the icicle and corona wind velocity were measured. Secondly, the influence of corona activities on the ice accretion was observed. The initial charge of water droplets impinging on the tip was also examined. It will be shown that the presence of corona activities does not promote ice accumulation and that the ice structure is independent of corona discharge.
This paper presents a one-dimensional numerical model for simulating dynamic ice jam formation. The formulation is unique in that a purely Eulerian finite element method is used for both the hydrodynamic and the ice dynamics components of the model. A new constitutive model for determining the internal resistance of moving ice accumulation is formulated, and its suitability is explored based on stress and strain rate data obtained from experimental data describing ice jam formation dynamics. The proposed model is validated with a hypothetical idealized ice jam scenario, for which an analytical solution is available. Additional model validation is achieved using a series of experimental ice jam consolidation events.
Acoustic emission events were measured during the cyclic loading of cantilever beams of sea ice. The events were detected with resonant transducers, with bandwidth 20 kHz to 150 kHz, which are predominantly sensitive to the vertically polarized component of the Rayleigh surface wave. This confinement to the surface, along with the linear geometry of the beam, make it possible to estimate a one dimensional source location with only two tranducers.We define an event magnitude and find that this magnitude increases as the load increases, with the largest energy release occurring during the fracture of the beam. The measurement of magnitude requires an estimate of the high frequency attenuation of the Rayleigh waves in sea ice. In the absence of existing data in the literature, we make our own estimate and compare this with suitably adjusted data for compressional waves.The sources of the events are precursors to the eventual fracture of the sea ice, having highest density at the location of the final failure of the beam. We speculate that the emissions originate either from dislocation breakaway or the microcracking associated with this dislocation motion. By measuring the slope of the cumulative magnitude-frequency plot we may surmise that our data are consistent with the view that the system is organising itself into a stationary critical state.
This paper investigates the use of a sensor based on acoustic technology to record the transport rate of blowing snow in the field. Particle flux is important but poorly documented information, as it is one of the most essential parameters of certain predictive numerical models. Therefore, extensive field data are needed, which requires accurate remote-controlled sensors. Flowcapt is the best-known acoustic sensor able to make such measurements and it has been in widespread use for practical purposes. This paper establishes a no exhaustive list of the limits attributable to the device's design, such as poor treatment of particle velocity, resulting in aberrations in the recorded data. As a consequence, and even if the sensor provides good information in operational use, a regrettable inaccuracy in the collected data prevents the use of such measurements for research purposes. Nevertheless, a correction algorithm based on a statistical calibration of the sensor is proposed, which should make it possible to use the recorded data for preliminary approximations.
Acoustic emission techniques have been used for several decades in the nondestructive testing of materials. The purpose of this project is to apply these techniques to sea ice subjected to cyclic loading due to moving vehicles. Preliminary results show that acoustic emission events are recorded which are clearly associated with the strain field established by the vehicle. A time delay of the order of a second is measured between the maxima in surface strain and surface strain rate and the peak acoustic emission count rate. However the strain amplitude has a maximum at the critical velocity of the vehicle while the peak acoustic emission count rate increases with vehicle speed. Further work is being initiated to address some of the questions raised by this study.
Wind can create even greater unstable accumulations of snow in mountainous areas than heavy snowfalls. But knowing wind conditions is not sufficient to predict these accumulations because their formations also depend on the snow quality of the snowpack surface upwind of the release zone. Consequently, assessment of snowdrift is required to improve avalanche forecasting. In accordance with this assumption, a new acoustic sensor was developed. The sensor includes a mechanical part designed to form a closed acoustic enclosure. The acoustic enclosure contains microphones connected to an electrical amplifying and filtering device. Because the output information delivered by the instrument is proportional to the wind velocity and to the flux of solid particles (ice grains) drifted by the wind, the instrument is called an anemo-driftometer. Prototypes of the instrument were first tested in a wind tunnel and then at an experimental site in the Alps. Then an operational version, called FlowCapt, was developed and connected to an automatic weather station at 2700 m in the Aminona ski resort (Switzerland). During the winter, snowdrift is recorded on the test site along with other meteorological parameters, and avalanche activity, to provide extensive on-site calibration and testing of the sensor. The experiment demonstrates that the instrument is a useful component of the avalanche forecasting chain.
The acoustic emission response from fine-grained polycrystalline ice subjected to constant compressive loads was examined. A number of tests were conducted with the nominal stress ranging from 0.8 to 3.67 MPa at a temperature of −5°C. The acoustic emission response was recorded and the data are presented with respect to time and strain. The source of acoustic emissions in ice is considered in terms of the formation of both microfractures and visible fractures that develop without catastrophic failure of the ice. A model to describe the acoustic emission response is developed.
Measurements were conducted to determine the effect of a snow cover on acoustic wave propagation during a 50 day period in Alaska. Acoustic waveforms produced by a blank pistol shot were recorded after propagating horizontally over various snow-covered propagation paths and were used to determine the snow cover parameters by comparison with theoretically calculated waveforms. This automatic comparison procedure was successful in determining the average snow cover permeability and depth even when the snow cover depth varied greatly across the propagation path. Although the snow cover properties remained relatively constant during the measurement period, the acoustic measurements were able to determine the changes caused by wind events and new snowfall. Acoustic measurements can provide a rapid, accurate method for determining and monitoring snow cover characteristics. The excess attenuation produced by the snow cover was generally about − 30 dB for 100 m distance and frequencies above 100 Hz. Theoretical calculations also show that even a thin snow cover only 0.02 m thick will affect acoustic pulse propagation. The attenuation and distortion caused by a snow cover can degrade passive acoustic sensor identification and distance estimation, but these detrimental effects can be mitigated by proper design of signal processing algorithms.
Human observations and records of sea ice conditions from ships of opportunity in polar regions have been formalized under ASPeCt (Antarctic Sea Ice Processes and Climate) protocols as part of the Scientific Committee on Antarctic Research (SCAR) initiative, Global Change in Antarctica. Human observations, however, are subject to both bias and level of expertise. In support of ASPeCt observations, a ship-based, ice condition imagery acquisition, processing and analysis system is developed and presented in this paper. Digital images captured from recorded oblique-view video of sea ice during the inbound and outbound transits of the icebreaker NB Palmer, during the 2007 SIMBA (Sea Ice Mass Balance in Antarctic) cruise, were used to demonstrate the method. The resultant orthorectified and spatially registered images can thus be used to derive ice concentration, ice types, floe sizes, and area of deformed ice, parameters recorded by an ASPeCt observer based on experience. An assessment of total ice concentration, utilizing a digital number threshold method, for a 30 image sequence spanning 10 min, was compared to the corresponding ASPeCt observation and found good agreement. A k-means unsupervised classification technique was employed to evaluate the spectral separability of pixels associated with differing ice types. A significant source of visual perspective bias was discovered in associated with uneven spatial distribution of open-water leads. Convolution spatial filtering was employed to assess area of deformed ice during night-time conditions, when ship's floodlights illuminate the ice field. Transformation of individual image elements, such as floes, to vector-based polygons enabled accurate measurement of dimension, thus providing a frequency distribution of floe sizes, currently not possible with existing ASPeCt protocols. Limitations of this acquisition and analysis technique, future improvements, and coordination with the ASPeCt program were discussed.
The segregation potential, SP, has been used to solve two-dimensional frost heave problems. SP-based approach to predict frost heave has been extended to 2-D problems such as freezing around chilled pipelines buried in unfrozen ground. It requires, however, the input of non-linear stress-strain-strain rate-temperature relations for characterizing the behavior of the frozen soil and an incrementally deforming mesh. Simulations of actual field tests using burial chilled pipelines were successfully performed with the newly developed 2D-SP frost action model and provide distributions of ice content, stresses and displacements.Assuming a bi-linear stress-strain relationship for the frozen soil, parametric studies have shown that frost heave was more sensitive to post-yield characteristics of the frozen soil than to the magnitude of its yield stress.
Freezing behavior and frost shattering of rocks were studied in the laboratory. Rates of frost shattering were determined for 47 different samples of saturated rocks partially immersed in water by a decreasing rate of the longitudinal wave velocity during freeze-thaw cycles. The ratio of surface area per unit volume to tensile strength gives a good estimation of the frost shattering rate. This indicates that water migration caused by adsorptive suction participates in the frost shattering, as well as the 9% volumetric expansion. Frost shattering occurred in porous rocks despite the lower saturation level than the theoretical value derived from the volumetric expansion theory. Furthermore, the open system was much more effective in frost shattering than the closed system was. Such moisture effects also demonstrate the large role of water migration in frost shattering.The linear strain of some saturated rocks during a freeze-thaw cycle was measured with foil strain gauges. Immersion in water increased the freezing expansion of tuffs, although it affected the strain of a shale and an andesite only little. Low cooling rates resulted in small freezing expansion of rocks placed under the closed system because of creep of pore ice. These results suggest that the freezing expansion of a rock consists of three components: two positive strains due to the 9% volumetric expansion of water, and water migration controlled by adsorptive suction, and a negative strain due to creep of ice. The frost shattering of the tuffs would be primarily controlled by the water migration, and that of the shale and andesite is probably caused by the volumetric expansion. The relative contribution of the two processes on frost shattering may depend on the surface area per unit volume of the rocks.
A wavelet cross-correlation analysis was applied to ice loads and corresponding acceleration signals measured at the Norströmsgrund lighthouse in the Gulf of Bothnia, Sweden. It was shown that the excitations of the lighthouse by actions from ice floes are influenced by structural responses with dominant excitation frequencies in the same range as the frequencies of the responses. The lengths of intervals with synchronized excitations and responses are predicted to be from 1.9 to 8.6 s. Local ice loads were found to be synchronized in the same intervals and for the same frequencies, but for a slightly shorter time. This synchronization causes simultaneous ice actions which can trigger higher global ice loads on the structure than has been obtained during brittle non-simultaneous crushing.
The objective of the study has been to investigate whether cold-adapted microorganisms (CAMs) are metabolising hydrocarbons in situ at sub-zero temperatures. Since the summer 2001, soil temperatures and soil gas concentrations of oxygen (O2) and carbon dioxide (CO2) at various depths at a petroleum hydrocarbon contaminated permafrost site at Longyearbyen, Spitsbergen, have continuously been measured and compared to data from a nearby non-contaminated site. We have previously reported on unchanged microbial O2 consumption in the active layer for about 12 days after the soil temperatures decreased below 0 °C in late October 2001 and we are now reporting on the microbial activity in the soil profile from January to September 2002. The empirical data have been compared to theoretical simulations of O2 concentration as a function of soil depth and time from when the CAMs became active in spring until steady-state conditions were achieved in the summer. At the 0.7 m depth in the oil-plume site, microbial O2 consumption started in the middle of April, about 45 days before the soil thawed. There was no coincidence between the microbial activation time and the thawing time of the soil. The CAMs became active at temperatures of about −6 °C, but the main degradation activity occurred at temperatures between −1 and −3 °C. When the soil thawed, the hydrocarbon degradation was probably limited by the O2 supply. In the summer months where we expected the greatest degradation activity to occur because of positive temperatures and access to water, the degradation was limited by O2 depletion. The overall data from this arctic permafrost site indicate that without other limiting conditions such as O2 and substrate availability, the active biodegradation period can be extended to about 6 months despite periods with sub-zero soil temperatures.
The sensitive permafrost environments along the Qinghai–Tibet Engineering Corridor (QTEC) from Golmud to Lhasa are controlled by periglacial processes, geography, geocryology and the local climate. During the past 50 years, permafrost has been degrading at a rapid rate due to the combined influences of steadily increasing human activities and persistent climatic warming, and extensive accelerated degradation has been observed along the QTEC. In many locations, the surface vegetation and the top soils have been completely removed, or destroyed, and have led to significantly increased water and soil erosion, with extensive and serious environmental and engineering impacts. The vegetation along the QTEC is dominated by alpine grasslands and meadows. The alpine grasslands have a better capability for recovery from the damages than the meadows. At sections where the vegetation and soils were severely damaged, it will take 20–30 years for alpine grasslands to recover their ecological structures and biodiversity similar to that of the original conditions, whereas it will take 45–60 years for the alpine meadows. The environmental management and protection along the QTEC are urgent and important for the long-term stability of engineering foundations, and for the sustainable development on the Qinghai–Tibet Plateau (QTP). The proper protection and management requires the development of a non-interference plan and acceleration in the enactment and enforcement of environmental protection (laws, regulations and stipulations) based on an extensive and thorough understanding and practical rehabilitation techniques for disturbed or damaged permafrost environments.
The estimation of recoverable mobile free product or light non-aqueous phase liquid (LNAPL) is important in monitoring and selecting appropriate remedial techniques. This study used a field empirical approach to estimate the actual product thickness at the Colomac mine site in the Northwest Territories (NWT), which has extensive fuel contamination. The empirical approaches used are described by Hughes et al. (1988) and the modified Gruszczenski method. Of the two, only the latter provided useful estimates of actual LNAPL thickness in the tank farm area where most of the contamination occurred. The estimated LNAPL thickness at the site is 8 cm. Later excavation at the site corroborated this estimated value.
A new type of model ice has been developed for use in refrigerated towing basins. The ice is grown from an aqueous solution containing three different chemical dopants - ethylene glycol (EG), aliphatic detergent (AD) and sugar (S). In this paper, the concepts and development of this model ice are discussed. Analysis of the structure of the ice indicates that it is single layered, fine-grained and strictly columnar. A number of the mechanical properties of EG/AD/S model ice have been measured including the flexural strength, uni-axial and confined compressive strength, strain modulus and critical stress intensity factor. The results of these tests are compared to appropriately scaled sea ice values and the corresponding properties for carbamide (urea) model ice. This comparison shows that this new ice is far superior to urea model ice in all respects.
Spatial estimation of snow water equivalent SWE at six different dates from February 1st to June 1st is tackled using Kriging from a sparse network of 14 snow stakes with density within the Adamello Natural Park of Italy. Therein, SWE is measured at these six dates for the period 1967–2009. Second order statistics of SWE are evaluated and linked to physiographic features. The covariance of the SWE field within the Park is studied, necessary for Kriging, and its regularization provided based upon geomorphic attributes. Seasonal dependence of the covariance of the SWE field is observed, and taken into account for optimal estimation. Then, a Kriging procedure based upon the so obtained covariance fields is developed and cross-validated. The accuracy of Kriging estimates is then compared against that of other commonly adopted methods for spatial interpolation. Kriged SWE maps are then produced at the six dates for two sample years, to demonstrate use of the method. Snow Cover Area SCA from the MODIS® satellite is used to constrain Kriging procedure upon snowed areas. The procedure provides well estimated, least variance SWE values and it is relatively simple and fast because it uses only information of physiography of the area. The so obtained maps can be used for spatial estimation of SWE within the investigated region for water availability conjectures, for constraining hydrological models simulating runoff at thaw, for ecological conjectures upon snow cover related species within the Park, and to evaluate snowpack dynamics for avalanche risk assessment.
Blowing snow is a process, which can be observed during the entire winter season in Arctic catchments. On Spitsbergen at 78° North, the ground is bare of tall vegetation and the snow is easily moved by the wind. During frequent storms, large masses of snow are relocated from erosion to deposition areas. In this study, the mass of snow, transported out of an Arctic valley to the open sea is estimated via direct measurements and model calculations. The study area is a valley on Spitsbergen in the high Arctic. The valley is approximately 4 km wide and 10 km long and ends in a fjord arm. The wind direction in the valley is very uniform. During the winter season, the wind is blowing out of the valley 80% of the time. There is one permanent automatic weather station located in the valley. In addition, three automatic weather stations were installed in the valley during a study period of 2 months in February and March 2000. These stations measure, in addition to wind speed and direction, the snow drift flux with acoustic snow drift sensors. The results of the study period are related to those of the permanent station to quantify the accumulated snow mass passing from the valley to the open sea for the entire season. The results show that the transport snow mass equals 0.2% of the annual precipitation in the catchment. Thus, the losses due to snow drift to the open sea are of little importance to the valleys water balance.
This paper evaluates the use of waste materials such as silica fume, fly ash, and red mud in the modification of granular soils in order to remove the effects of freezing–thawing cycles. In this study, two granular soils obtained from primary rock were stabilized by silica fume–lime, fly ash–lime, and red mud–cement additive mixtures. Natural and stabilized soil samples were subjected to freezing–thawing cycles after curing for 28 days. After the freezing–thawing cycles, compressive strength, California bearing ratio, freezing–thawing, ultrasonic wave, and resonant frequency tests were performed to investigate effects of additive mixtures on the freezing–thawing properties of natural and stabilized soil samples. The experimental results show that stabilized samples with silica fume–lime, fly ash–lime, and red mud–cement additive mixtures have high freezing–thawing durability as compared to unstabilized samples. These additive mixtures have also improved the dynamic behaviors of the soil samples. Consequently, we conclude that silica fume–lime, fly ash–lime, and red mud–cement additive mixtures, particularly silica fume–lime mixture, can be successfully used as an additive material to enhance the freezing–thawing durability of granular soils for road constructions and earthwork applications.
Under satisfactory technical and ecological conditions, a coastal airstrip with the necessary security requirements for medium carriers will be constructed in Terre Adélie by October 1992. Inspired by the “Terres Australes et Antarctiques Françaises” (TAAF), it will provide better opportunities for scientific research with air access from Dumont d'Urville to Dome “C”, the planned research base. It will enable summer campaigns to benefit fully from the season without ice restrictions and it will reduce the need for a passenger cargoboat. The only possibility for achieving this is to connect islands by means of a causeway along the same axis as the prevailing wind. The “Expeditions Polaires Françaises” have thoroughly researched the site in “Pointe Geologie Archipelago” and have carried out a complete study of the local environment by collating all the observations concerning wind, sea swell, current, pack ice and geological features. These have led to a theoretical causeway model and consequently to an “experimental model” where studies of swell-ice-structure interactions, stability in the presence of ice and measurements of swellings, tide and porosity of the embankment have been made. Revetment tests have allowed for the construction of a bi-layered roadway. To date, the causeway reaches the last island. The main island has been blasted and a zone has been prepared for the future hangar and control tower. Nearly 4% of the cost of the project will be used to protect the fauna (new nesting zones, movement to protected areas and enclosure of the airstrip). Observations made during the 1989 winter show that this causeway does not disturb the migration of Emperor penguins.
In this paper, the finite-element formula of convective heat transfer in porous media is obtained by using the Galerkin's method according to the continuity, momentum and energy equations of fluid heat convection for solving the computational problem of temperature field on the ripped-rock revetment embankment in Qing–Tibetan railway. The temperature changes of the ripped-rock revetment and common ballast embankments with south and north slopes have been investigated in coming 24 years, respectively. The results indicate that the ripped-rock of 10 cm diameter is paved on the south and north side slopes of common embankment ballast with the corresponding thickness of 1.6 and 0.8 m, respectively, when the temperature difference of the south and north slopes is 1.8 °C, which is able to make the temperature field distribution symmetrical during summertime, permafrost table greatly raised above the native ground surface with frost-susceptible sub-clay (the active layer before embankment construction) completely frozen under embankment during the time, and eliminate the disasters of longitudinal cracks resulting from the uneven settlement of embankment. Thus, we strongly suggest that the ripped-rock revetment embankment be adopted as a kind of embankment structure of Qing–Tibetan railway with south and north slopes in permafrost regions in order to protect the railway as much as possible.
Adsorption force fields that (i) decay with distance and (ii) act preferentially on liquid water relative to ice should cause “ordinary” water and ice to behave in a manner often perceived as incompatible with expected behavior, especially when viewed from outside the force field. This illusion, its relationship to freezing temperature and to the mechanism of frost heave, is demonstrated using a simple example in which earth and its gravitational field interact with water and ice.
Presented in this paper are the theorization of a traditional concept of the mechanics of frost heaving, as well as a critical review of the recent developments in this field. The key to the theorization is the following: (1) the film water adsorbed on soil particles can build up an internal solid-like stress, and (2) the flow of film water is different from the conventionally accepted flow of pore water. It is expected that modern continuum mechanics will, in the future, improve the theory of film water which, in this paper, has been formulated by use of the classical method.The freezing film water, trying to retrieve the loss of its thickness to the frozen ice, generates a suction force that draws water to the freezing front where the frost-heaving pressure pushes up the overburden. The temperature of the freezing film water that has generated the solid-like stress, is lower than the temperature of the freezing pore water. This distribution of freezing temperatures in the region of film and pore waters explains the observation that the freezing front causing frost heaving is not a planar surface but a three-dimensional zone diffused in the direction of heat transfer. Frost-heaving pressure can be derived as part of the solution of the boundary-value problem of the frost-heaving differential equations.
Snow depth was measured with an L-band frequency-modulated continuous wave (FMCW) radar operating from an aerial tramway up to 70 m above the ground. Snow depth, wetness, and slope varied greatly along the 2.4-km transect, with 640 m of relief. Radar measurements taken in the morning, when the snowpack was frozen were compared against concurrent manual depth probes, and good agreement was found between the estimates. The results suggest that deep snowpacks in rugged terrain can be accurately and safely surveyed by helicopter-borne radar.
The negative effects of ice accretion on wind speed measurements by a cup anemometer have been indicated by analyses of field test results and already been studied numerically and experimentally by the authors of this paper. Implementation of calculations of the dynamic behavior of a cup anemometer with or without ice was carried out employing the fictitiously altered aerodynamic characteristics of an iced or clean cup based on NACA test results for a conical cup because no information covering the aerodynamic characteristics of an iced cup had been provided up to that point. In light of the absence of solid data, wind tunnel tests of the aerodynamic characteristics of iced cup-shaped bodies were performed. Imitated ice models were built and used for the test based on test results from an icing wind tunnel test conducted separately. We found that, depending on its amount, ice accretion in dry-growth conditions results in big penalties to the aerodynamics of cup-shaped bodies, while ice deposits of wet growth cause little effect, regardless of the thickness of ice.
In cold regions, biodegradation of fuel spills can take a prolonged period of time. Conventional fuels and crude oil contain contaminants such as aromatics and PAH which can pose risks to humans and the environment. The goal of the present study was therefore to investigate the biological degradation of an alternative synthetic fuel, Syntroleum, which is less toxic and, as shown in this study, more easily biodegradable than conventional diesel fuel. Use of alternative fuels such as Syntroleum would be especially beneficial in sensitive regions where spills of conventional fuel are highly undesirable. Gravel and sand from Interior Alaska were spiked with diesel and synthetic diesel fuel (arctic-grade Syntroleum). After adding an inoculum, samples were incubated in the laboratory at different temperatures (6 °C and 20 °C), contamination levels (2000 mg and 4000 mg of fuel/kg dry soil), nutrient dosages (300 mg N/kg soil and 0 mg N/kg soil) and moisture contents (2%, 4%, 8% and 12% gravimetric water content). The objective of this research was to investigate the effect of physical and chemical environmental conditions on the biodegradability of contaminants and to determine optimal conditions for biodegradation by indigenous microorganisms. The respiration rate (CO2 production) was measured as an indicator of microbial activity and mineralization of contaminants, and complemented by analysis for hydrocarbons at the end of the experiment by gas chromatography/mass spectrometry. Both fuel types were biodegraded, with up to 75% mineralization after 17 weeks. The faster degradation rate was achieved in Syntroleum-contaminated soils with a degradation-rate constant of 0.0064–0.0106 d− 1 at 20 °C. At 6 °C, diesel fuel showed minimal degradation during several short-term studies (4–6 weeks), less than 5% total mineralization of the hydrocarbons in the fuel. The average degradation-rate constant for Syntroleum at 6 °C was 0.0016 d− 1 during a 4-week study, while the degradation-rate constants became much higher (0.0045–0.005 d− 1) for the long-term experiments (12–17 weeks), resulting in significant mineralization of total carbon present. The different moisture contents in the sandy soil showed no significant impact on respiration. The addition of fertilizer was essential to achieve good degradation rates. After the end of the 17-week experiment, the recovered contaminant was approximately 50% less in the case of Syntroleum when nutrients were added to the soil as compared with nutrient-deficient conditions. Respiration rates were higher in sand than in gravel, which may be due to differences in soil porosity and the available surface area for more even hydrocarbon distribution. Degradation rates varied significantly over time. A first-order model, which used different rate constants for three growth phases, was able to model cumulative carbon dioxide production quite well over a period of four months. In the carbon mass balance, the sum of the diesel range organics recovered from the soil plus the produced carbon dioxide accounted for approximately 30–85%. The remaining amount of carbon either was incorporated into biomass, degraded incompletely, or evaporated.
A laboratory investigation was carried out in order to evaluate the quality of concrete with 10%, 20% and 30% combination of pumice aggregate and expanded perlite aggregate instead of fine aggregate (0–2 mm), and 0.1% air-entraining agent ratio. Several properties related to durability were determined, and particular attention was put on the resistance of the concrete mixes to the freezing and thawing cycles based on ASTM C 666, procedure B. Compressive strength and unit weight of concrete were decreased with increase of LWA but water absorption and sorptivity coefficient of concrete were increased before and after 100 freeze–thaw cycles. After 100 cycles of freeze–thaw 10% pumice aggregate and expanded perlite aggregate increased compressive strength of samples 3 and 4% respectively when compared to control samples. Reduction in the compressive strength due to the air-entraining agent was around 9% after 100 freeze–thaw cycles.
The physical characteristics of air inclusions embedded in the ice covers of the Saint François River (Quebec, Canada) and the Athabasca River (Alberta, Canada) are studied because of the importance of such inclusions to the analysis and interpretation of Synthetic Aperture Radar satellite images used to characterize river ice. Studies of ice cores sampled from these two rivers show that the concentration of air inclusions in the ice cover is highly dependent on both the ice type as well as the rate of freezing. When this rate is slow, the ice cover will have few air inclusions. However, when it is rapid and sustained in duration, the amount and cross sectional diameter of these inclusions increase. Air inclusions in the snow ice were found to be spherical and ranging in size from just a few millimetres up to about a centimetre. Generally, air inclusions formed in the sampled columnar ice were sparse and either spherical or tubular in shape. Air inclusions in the frazil ice were found to present a different structure from those formed in the other ice types. In most cases, their shape were irregular and their distribution was inhomogeneous. The study of these inclusions under a microscope showed them to have angular boundaries with a whitish appearance. These results will be valuable to the development of radar backscatter analysis algorithms for river ice characterization.