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The response of a 0.6 m thick floating ice cover in a small lake is described, when 60,000 spectators gathered to witness a concert on stages built on the ice. To monitor and evaluate safety, deflection and surface strain on the ice cover were recorded continuously in front of the stages. The data illustrates the effect of crowd movement on the deformation of the ice cover and emphasizes the importance of careful planning of events, as well as crowd control by the organizers., 9th International Conference on Offshore Mechanics and Arctic Engineering (OMAE '90), February 18, 1990, Houston, TX, USA

An investigation was undertaken of the creep of columnar-grained ice under constant compressive stresses of 98 and 59 kPa in order to extend the observed relationship between strain-rate and stress further into the low-stress region. Stress was applied perpendicular to the long direction of the grains. Observations were made for temperatures between -5 and -40°C. The steady-state creep rate for secondary creep was not yet attained for strain of 1.4% and stress of 98 kPa. An initial yield was observed at that stress in the strain range of 0.2 to 0.3%, similar to that seen at higher stress. The observations showed that the strain-rate tended to a linear dependence on stress below 49 kPa and that more than one dislocation process with different values for the stress exponent may contribute to the strain at higher stresses. An activation energy of 63 kJ mol−1 was consistent with the observed temperature dependence of the strain-rate. Straining ice to a given strain under a stress of about 0.3 MPa and then reducing the load may be a convenient way to study the stress, strain and temperature dependence of the strain-rate at low stress.

This paper describes the growth of sea ice and the salinity profiles observed in Eclipse Sound near Pond Inlet, Baffin Island, Canada, during the winter of 1977–78. A numerical method of calculation has been developed to incorporate the variations in snow conditions and physical properties of ice and snow during the growth season. It is shown that the growth rate can be predicted reasonably well. It is also shown that the vertical salinity profile in the ice towards the end of the season, provides a record of previous climatological conditions. A dependence has been shown between the predicted growth rate and the measured salinity.

A simple numerical integration method has been developed for predicting growth of ice under snow cover where solar radiation does not play a dominant role. The method is capable of incorporating variations in snow conditions and physical properties of ice and snow during the growth period. Theoretical predictions compare favourably with field observations in Eclipse Sound, Baffin Island, for the winter seasons of 1977–78 and 1978–79.

Deformation characteristics of polycrystalline ice and their dependence on time, temperature, and stress have been analysed on the basis of a phenomenological relation which describes creep in terms of initial elastic, delayed elastic, and permanent strain. It is shown that the effective modulus of ice observed in the laboratory or in the field can be examined on the basis of this model. The model also provides a basis on which the observed flow law of ice can be examined conveniently. Some apparent inconsistencies in the results of earlier investigations of the mechanical property of ice appear of be reconciled by the model.

Tests have been performed on fine-grained, columnar, freshwater ice sheets 40 to 70 mm thick grown in a refrigerated model basin. Cantilever beams of various geometries were tested for lengths ranging from 200 to 2 000 mm and widths of 50 to 250 mm. Analysis of the results in terms of simple elastic beam theory indicated that modulus increased with increasing beam length and decreasing bean width. An analytical model for beam deflection was developed, taking into account the effects of buoyancy, shear, and rotation and deflection at the root. This model satisfactorily explained the observed deflection behaviour and the apparent geometry dependence of the modulus. Flexura! strength was independent of beam length, but decreased with increasing beam width. Flexural strength was independent of loading rate, whereas modulus decreased with increased loading time.

A method is described for preparing the surface of ice and for forming etch pits on the prismatic surfaces with whisker replicas that correspond to basal dislocations. The technique removes the ambiguity sometimes associated with etch pits and dislocations, and allows direct observation of dislocation glide, pile-up against barriers, and other features in deformed ice.

The air content of sea ice can be measured directly by melting a sample and collecting the released air, provided the air saturation ratio in the meltwater is known. The saturation ratio was found experimentally to be a function of three parameters: the time after an ice sample was melted, the average bubble size, and the air porosity of the sample. Since the last parameter is the term to be determined, an iteration method was employed in calculations of porosity. The bubble pressure was assumed to be at one atmospheric pressure. The vertical profile of air porosity was thus obtained for first-year sea ice in the Arctic. The results were in good agreement with estimations of porosity made from density values measured for the same samples. This indicates that the bubble pressure is near one atmospheric pressure.

Observations are reported on the failure and use of freshwater ice covers for vehicular traffic. The study showed that good quality ice covers can support loads of up to P = 250 h2, where P is the total load in pounds and h is the thickness of the ice in inches. Failures were reported, however, for loadings as low as P = 50 h2. Factors contributing to the failure of covers for loading less than P = 250 h2 were: vehicle speed, thermal stress due to drop in temperature, and fatigue and quality of the cover. The results are discussed with reference to Westergaard's equations for the maximum stress due to circular loads on an elastic plate resting on an elastic foundation. Information is presented on the elastic and strength properties of ice covers required for theoretical calculations. Experience in the construction and use of ice roads and parking areas is described.

Observations were made at one temperature on the cracks that form in ice during creep under constant compressive load. The ice had a hexagonal symmetry with respect to the grain boundaries. The load was applied perpendicular to the long axis of the grains. A piezoelectric crystal was used to detect the cracking activity in the ice.Two stages of cracking were observed. The first occurred during the transient period of the creep, and the plane of these cracks tends to be parallel to the grain boundaries and to the direction of the stress. The rate at which these cracks formed decreased very markedly as the creep rate approached a constant value. Above a certain stress, the creep rate continuously increased with time. Under this condition the second stage of cracking was observed. These cracks tend to be more irregular in direction and to occur in planes that are at 45° to the applied stress.

Information is presented on the failure behavior of columnar-grained ice during compressive creep and constant strain rate tests. The role of crack formation in establishing the failure condition is briefly described. Breakdown of structure is responsible for a marked change in the creep behavior of ice in the stress range of 10 to 12 kg/cm2. A ductile-to-brittle transition is observed at a strain rate of about 5 × 10−3 min−1. The upper yield stress in constant strain rate tests is shown to increase with increase in rate of strain up to the ductile-to-brittle transition.

Stress relaxation experiments are carried out on single, bi, tri and quadri crystals of ice to obtain information on the rate controlling process. The results are analyzed with the rate theory developed previously. The study indicated that the energy barrier is asymmetrical and that the rate controlling process is associated with the Peierls barrier, with the dislocation intersection mechanism, or with the non- conservative motion of jogs. It seems unlikely that climb would control the dislocation motion in ice.

SYNOPSIS Maximum heaving pressures caused by ice lens growth were determined experimentally for saturated specimens consisting of fragmental particles in several size ranges. Theoretical predictions show that the pores produced by the smaller particles in the system are responsible for the maximum heaving pressures measured. The suggestion is that the ice-water interface assumes an undulating configuration over the smaller pores when ice proliferation stops, and hence heaving pressures rise to a maximum. Particle size seems to be an adequate basis for predicting frost susceptibility in practice although the exact amounts and size limits permissible have not been evaluated. The nature of the failure caused by frost action is not the same for all engineering structures. Failures by “rate of heave” and “heaving pressure” should both be considered if the possibility of frost damage exists. The results substantiate earlier conclusions that there is no sharp dividing line between frost-heaving and nonfrost-heaving soils. Recent studies by the author have shown that the theory of Everett (2) and Everett and Haynes (3) provides a realistic basis for the growth of ice lenses from pure water in porous systems of simple and uniform geometry. Difficulties arise when the theory is applied to soils which have a more complex porous structure because a grain size, and hence a pore size, distribution exists. For a porous system of this complexity, the theory as it stands is not adequate for prediction, since little is known about the size of pores, in a given pore size range, that determine the heaving pressure characteristics. The two laboratory approaches for assessing frost susceptibility (“rate of heave” and “heaving pressure”) are not entirely compatible, but it is clear and consistent that soils which are not frost-susceptible should not exhibit any measurable heaving pressure or rate of heave. Soils that have a low heaving pressure may show a considerable rate of heave under little or no restraint. On the other hand, some soils that exhibit a high heaving pressure from ice lens growth, such as dense clays, may due to permeability limitations have a sufficiently low heaving rate to be acceptable for some engineering structures subject to freezing conditions, (Fig. 1). The trend in soil engineering has been to predict the frost susceptibility of a soil from its particle size characteristics through relationships determined by “rate of heaving” experiments. Many organizations have carried out such tests but there are no generally-accepted limits to particle size or percentage of fines which determine frost susceptibility. In this paper attempt is made to elucidate further the mechamism of heaving, particularly the development of “heaving pressures” by ice lens formation in relation to the particle size distribution of the sample. It will be shown that from measurements of heaving pressure it is possible to obtain an estimate of the sizesof particles which are responsible.

An unusual humped formation of floating ice, about 10 m. high, 100 m. wide and 1,200 m. long. was observed on the Ottawa River, Canada. Some characteristics of this formation are described. The cause of the humps was found to be frazil ice deposited in a trench about 90 m. wide, 90 m. deep and 1,200 m. long. The frazil ice was formed in rapids up-stream from the humps.

The gradual breakdown of a material during creep due to the formation of cracks is a subject receiving widespread attention. Although considerable information has been obtained on how individual cracks are nucleated, grow, and ultimately join together to cause failure, not much attention has been given to the possible interrelation between crack formation and the stress and time dependence of the deformation. Information has recently been presented on crack density and creep behaviour for an aluminium-zinc alloy. The author has obtained similar information for ice. In addition to demonstrating a correlation between cracking activity and deformation, these observations show an interesting similarity in behaviour, even though the mode of crack formation is different for the two materials.

Observations are reported on the stress–strain behavior at −9.5 ± 0.5 °C of four types of ice obtained from the St. Lawrence River. The ice was subject to nominal rates of strain covering the range 2.1 × 10−5 min−1 to 5.8 × 10−2 min−1. A ductile-to-brittle transition was observed for strain rate of about 10−2 min−1. In the ductile range the four types had an upper yield stress that increased with strain rate according to a power law.

Observations were made on the creep behavior of columnar ice beams of different thicknesses subjected to repeated and reversed loading. More than half of the beams tested showed unusual creep behavior. During transient creep the strain rate increased to a maximum value and decreased only thereafter. It was established that this behavior was not a permanent property of ice. On reloading, the same beams exhibited normal creep behavior. For the conditions of the experiments, the deflection was very sensitive to the thickness of the beams. It was found that the neutral axis was located at the center of the beam when the maximum strain was less than 1%.

Salinity/electrical conductivity, oxygen isotope and grain structure analysis of ice cores recovered from the surface of an ice island showed the ice to be of freshwater origin. The grain structure of the ice was somewhat columnar; density ranged from 875 to 900 kg/m[3]. Seven uniaxial compression tests were done on specimens 60 mm in diameter, 110 mm to 160 mm long and oriented vertically with respect to the surface of the ice island. Compressive strengths ranged from 1.4 MPa to 3.5 MPa (at epsilon [nom] = 10[-5]s[- 1], comparable to values for iceberg ice., Proc. 9th Int. Symp. on Ice: 23 August 1988, Sapporo, Japan

The flexural behaviour of ice covers is often determined by in situ cantilever beam tests. Finite element analysis of such test geometries was used to investigate the influence of the elastic connection between the beam and the ice cover. Where beam lengths were short, i.e., less than ten times the ice thickness, the finite element analysis showed that deflection and moment distribution differ substantially from that predicted, assuming a clamped cantilever beam. Results of full-scale experiments performed on beams of various lengths and widths confirmed that the finite element solution best describes the measured deflections.

A test series has been carried out to investigate the load and deformation behaviour of thin freshwater ice sheets loaded to ultimate failure in a buckling-type failure mode. The tests were conducted with loading rates giving failure times of less than one-half second. Considerable microcracking was observed in the ice thickness, were measured at failure. The load and ice deformation profile are given for twelve different buckling events., Proc. 7th Int. Conf. on Offshore Mechanics and Arctic Engineering: OMAE: 07 February 1988, Houston, Texas, USA

Observations on the nearshore movement of an ice cover were made at two locations in the North Baffin Area of the Canadian Arctic. These measurements were made at half hourly and hourly intervals for periods up to 24 hours. From these measurements, a consistent pattern of offshore ice cover movement has been observed. This has been related to a concommittant lateral shortening of the ice sheet itself. These short term measurements tend to support a tidal jacking mechanism as the cause of the observed movements., Proc. 9th Int. Symp. on Ice: 23 August 1988, Sapporo, Japan

This paper sets forth the results of ice properties measurements carried out during the ice breaking trials of the "CANMAR KIGORIAK" in the winter of 1979-80. The measurements included crystallographic analysis to establish ice type and structure, temperature and salinity profiling of ice cores, and uniaxial compression and "Brazil" strength tests. These measurements were all performed on board ship at the time of the trials. The ice analyzed included samples from both first-year ice covers and multi-year pressure ridges. Strength results were found to generally agree with values in the literature.

Creep of the columnar-grained ice, under uniaxial compressive force normal to the columns, is shown to be composed of an instantaneous elastic response followed by a delayed elastic and viscous deformation. Both the delayed elastic and viscous strains are shown to have equal activation energies. Thus, this ice can be considered as a thermo-rheologically simple material with a nonlinear stress dependence. A simple phenomenological relationship has been developed that can be used for further analysis of the creep compliance function presented in a normalized form.

Work on the mechanics of ice, has resulted in a number of significant advances in the last 10 years. The factors influencing the growth of various types of sea ice have been quantified fundamentally and methods for examining the resulting material structure have been developed. Extensive work has been done on strength and deformation characteristics of ice. A significant effort has been the development of analytical expressions to describe the rheological behavior of ice. Elastic modulus, Poisson's ratio, and creep were also treated. A great deal has been done on measuring the compressive strength of various types of naturally occurring ice and subsequently these data were combined into a suitable description of a failure envelope. Work has also been done on measuring the flexural strength, shear strength, adhesion and fracture toughness. Methods for laboratory testing and in situ measurements of mechanical properties have been developed. The problem of defining ice forces on structures has been the primary motivation for research on ice. Analytical modelling, physical modelling, laboratory studies and very extensive field studies have been used. Work done in this area has included development of methods and their application to actual problems and has benefitted greatly from the integration of all four approaches. Ice and ice covers have been successfully used to support various offshore activities: drilling of floating ice platforms, stabilizing grounded rubble fields to protect structures and transporting large loads over ice., Sixth 1987 International Symposium & Exhibit on Offshore Mechanics and Arctic Engineering, Houston, Texas, March 1-6, 1987

A non-linear viscoelastic creep equation for polycrystalline material is presented. It incorporates the effect of cracking and is capable of describing primary, secondary and tertiary behaviour. The model predicts the formation of microcracks and thus the damage state due to the high temperature grain-boundary embrittlement process. This paper describes its application in formulating crack- enhanced creep and material response under constant strain- rate loading conditions (theoretically the simplest case but actually the most difficult to maintain). The formulation makes it possible to define the rate effect on stress-strain response and the rate sensitivity of strength, failure time, failure strain, damage and damage rate, strain recovery, etc. Numerical correspondence between theory and experiment was observed when predictions were compared with availible closed-loop, controlled, constant strain-rate strength and deformation data on pure ice. Calculations made use of material constants determined from independent constant-load creep tests.

Problems involving sublimation of ice in porous media arise in a number of engineering contexts. This paper reviews the theoretical basis necessary for a mathematical description of the phenomena concerned and presents data on sublimation rates for pure ice. A numerical model for computing sublimation rates in non-isothermal conditions is described briefly., Proceedings of the 4th International Symposium on Ground Freezing: 05 August 1985, Sapporo, Japan

The stress-strain relationship to fracture for polycrystalline ice in tension has been shown to be governed by elastic and delayed elastic deformation with negligible viscous flow. Delayed elasticity, associated with grain boundary sliding, dominates the deformation process as the grain size decreases leading to an apparent transition from brittle to ductile with the decrease in grain size.

Finite element analysis of beams subjected to four-point asymmetric loading has been used to calculate the internal stress fields for different specimen and loading geometries. The shear stresses determined from these stress fields were significantly different from those calculated from simple beam theory. Laboratory experiments done on samples of columnar-grained fresh water ice showed that consistent values of shear strength were obtained provided specimen and loading geometries did not vary beyond a particular range. At -10 deg C an average shear strength of 600 kPa was determined. Special measures taken to reduce stress concentrations at the load application points resulted in an increase of the average shear strength to 1100 kPa. Based on this experience, a shear testing method for ice is proposed., Reprinted from: Proceedings of the 9th International Symposium on Ice, Sapporo, Japan, August 23-27, 1988, IAHR Committee on Ice Problems, vol. 3, p. 76-88, 9th International Symposium on Ice, August 23-27, 1988, Sapporo, Japan

During the period December 1979 to June 1980, five visits were made to observe and measure ice behaviour around the wharf at Nanisivik, on Baffin Island. The measurements included ice thickness, temperature, salinity, and density, as well as horizontal movements of the ice cover. In March 1980, additional measurements and observations were made of tides, rotations of the ice sheet, and grain structure of the ice. A model for the formation of an active zone of ice between the wharf and the adjacent ice cover has been proposed, based on the observed evolution of ice conditions and internal structure of the active zone. Horizontal growth of the active zone displaces the adjacent ice cover away from the wharf, and in so doing, generates ice pressures estimated at 69 kPa on the wharf. Key words: ice forces, wharves, ice behaviour, ice properties.

The search for hydrocarbons in the Arctic offshore has increased substantially in the last 15 years. The presence of large ice features separates the systems required in the Arctic from those available for other offshore areas. The ice environment and the interaction between ice and proposed exploration and production systems are briefly reviewed. Requirements of exploration and production are contrasted. A number of the systems proposed or actually realized are examined, with attributes or problems noted. Particular emphasis is placed on actual experience with exploration and production systems. Development has been careful, and significantly there have been no major problems resulting from ice., 7th IAHR International Symposium on Ice, August 27, 1984, Hamburg, West Germany

A model test study has been done to investigate the ridge-building processes in ice. Ridge geometries and the associated forces have been determined throughout the formation of pressure ridges. The results indicate that the forces appear to be proportional to the sail and keel heights of the ridge raised to a power greater than one. In its formation, the sail height and keel depth increased until they reached limiting values whereupon they grow horizontally., 8th IAHR Ice Symposium: 18 August 1986, Iowa City, Iowa, USA

Ice stresses and environmental factors at Nanisivik wharf on Strathcona Sound in the Canadian Arctic are reported for the winter 1985/86. The ice regime is that of landfast first- year sea ice that attains a maximum thickness of 1.6 m in May. The primary mechanism of generating ice loads at this location appears to be temperature-induced strains in the ice cover. A thermal analysis based on secondary creep behaviour predicts thermal stresses lower than those measured., Proc. 9th Int. Symp. on Ice: 23 August 1988, Sapporo, Japan

The current basis for design of ice bridges and ice platforms is considered. Experience and performance observations showing that the moving load problem can be treated analytically using the theory of thin elastic plates on an elastic foundation are summarized, and an opinion is expressed as to the information still required. The basis for the design of ice platforms, for which a validated analytical method has not yet been established, is reviewed; and the possibility of progress on the problem, provided by the capability for measuring strains in ice covers, is pointed out., Proceedings, IAHR International Symposium on Ice: 27 July 1981, Quebec, Quebec, Canada

A series of tests have been performed to measure the plane strain critical stress intensity factor (KIC) for columnar freshwater ice as a function of loading rate and loading direction. The results indicate that KIC decreases with increasing loading rate and grain size, and that for comparable conditions, KIC is higher for crack propagation extending along the plane of the ice cover as opposed to crack propagation through the thickness of an ice cover. A separate series of tests indicated that increasing microcrack density resulted in a decrease in the apparent fracture toughness of ice., Proc. 5th Int. Offshore Mechanics and Arctic Engineering Symp. (OMAE): 13 April 1986, Tokyo, Japan

Brine layer spacing has been measured in a core sample taken 19 January 1978 from Eclipse Sound, Baffin Island, Canada. Observations on snow and ice conditions and a record of air temperatures for the entire growth season allowed correlation of the brine layer spacing with the growth rate of the sea ice. Growth rate is related to climatology, and the vertical brine layer spacing profile in the ice provides a record of previous weather conditions. It is suggested that the spacing is inversely proportional to the growth rate, and could also be dependent on crystallographic orientation. The spacing decreased rapidly with depth near the bottom of the core sample, and this is not compatible with a general relation between spacing and growth rate. Before a definitive statement can be made, cores from a variety of locations, grown in a range of meteorological conditions, will have to be studied.

The literature reporting scientific and engineering investigations on ice has grown rapidly in the past 50 years, and increased by a factor of at least ten in the past 20 years. A review is presented of advances in engineering for ice problems during this period, including ice formation in rivers, lakes, and oceans; ice forces on structures; bearing capacity of ice covers; and atmospheric icing. The difficulties faced by engineers due to the unique physical and mechanical properties of ice and its normal thermal state are emphasized.

Pack-ice driving forces are synonymous with the limiting forces that can be transmitted through pack ice. Knowledge of this topic is important in relation to: ice loads on structures (the limiting driving force approach); ice motion modelling and forecasting; arctic ship routing. Until recently, limiting pack-ice forces had been speculated upon but never measured. This paper describes a pilot experiment to measure typical values for pack-ice driving forces across a width of several kilometres in the southern Beaufort Sea. In-situ ice pressure sensors were installed near the middle of a multi-year floe. The floe was subject to converging ice conditions and pressure ridging occurred around it. Corresponding compressive ice stresses in the floe were measured from which the average pack-ice forces associated with the observed ridging could be inferred. The paper describes the background to the project, the general approach, the equipment used, and the results obtained., Proc. 9th Int. Conf. on Port and Ocean Engineering under Arctic Conditions (POAC-87): 17 August 1987, Fairbanks, Alaska, USA

In order to evaluate the utility of remote sensing methods for the detection and identification of ice flaws, a series of research flights was conducted using a high resolution thermal infrared scanner and an impulse radar from airborne platforms. The airborne data missions were then compared with surface truth observations. This paper will discuss the results of that research and present examples of the specific ice features that were clearly identified by the remote sensing technique., ASPRS-ACSM Fall Convention: 28 September 1986, Anchorage, Alaska, USA

A test series has been carried out to study the behaviour of a rigid structure on a compliant foundation. The model, a 60-mm diameter cylinder, was attached to a base whose compliance could be varied. Ice loads on the structure were measured as a function of foundation stiffness (natural frequencies 9 to 50 Hz) and velocity (10 to 270 mm/s). EG/ AD/S model ice with an average flexural strength of 50 kPa and thickness 40 mm was used. Both longitudinal and transverse loads were measured. The dynamic characteristics of the system were measured and the transfer function determined and subsequently used to obtain corrected ice loads using Fourier techniques. The mode of ice failure was found to be a function primarily of velocity and to a lesser extent foundation stiffness. For high velocities and compliant foundations the ice load transferred through the foundation was magnified by as much as one third., 9th Int. Conf. on Port and Ocean Engineering under Arctic Conditions 1987 (POAC-87): 17 August 1987, Fairbanks, Alaska, USA

The interaction of an ice cover and a fixed narrow structure was modelled by edge loading large rectangular (0.4 m × 0.5 m) plates of columnar-grained ice. The plates were set on one of the long edges and the load was applied to the opposite edge by means of indentors of widths varying between 12 and 150 mm. Ice plates 25 to 100 mm thick were used. Observations were made of the dependence of the indentation load on indentor width and ice thickness. All loading was within the range of ductile behavior of the ice. The study indicated that the indentation pressure was a function of the width of the indentor, but not of the thickness of the ice plate. The mode of deformation was observed to be primarily two dimensional. The results of this study are in contrast to observations under field conditions, from which it is concluded that the indentation pressure depends on the ratio of the width of the indentor to the thickness of the ice cover. This suggests the presence of an effect which must be given attention in the development of modelling techniques for the ice pressure problem.

A method has been developed for making a dogbone or dumbell- shaped specimen with a uniform gauge section made of any natural ice to be tested in tension. The specimen ends are made of built-up ice and the cross-sectional geometry is compatible with the grain structure of the ice. The gauge section is large enough to contain a sufficient number of grains to avoid any geometric effect and to mount the displacement gauge for conducting tests under closed-loop controlled constant strain rates. The application of the technique is illustrated by examples of test results on columnar-grained sea ice obtained from a multi-year floe in the High Arctic in the form of 300 mm diameter cores. The paper also describes methods of carrying out post-test microstructural analysis., Proc. 8th Int. Conf. on Offshore Mechanics and Arctic Engineering: 19 March 1989, The Hague, The Netherlands

The use of general purpose bonded resistance foil gauges has been examined for measuring small strain in both laboratory made pure ice and natural Arctic sea ice. A method for mounting the gauges on ice has been developed. Experiments were carried out under uniaxial loading conditions in a wide stress rate range of 1 x 10 [-3] to 1.25 x 10 [2] MN m [-2] s [-1] at -20!C and the responses of the foil gauges were compared with those of a displacement gauge also mounted on the ice. Observations indicated that the foil gauges can be used reliably for stress rates less than 1 x 10 [-1] MN m [- 2] s [-1]. Analysis of the system indicates that weak bond at the interface between the gauge carrier and the adhesive layer of ice results in damped response of the gauges and limits their use at higher loading rates. This test series has also provided, for the first time, experimental data on the dependence of effective modulus of ice on stress rate up to 1.2 x 10 [2] MN m [-2] s [-1] or a frequency of about 100 Hz.

Canada and the Soviet Union share similar geographical positions and likewise similar problems with ice loads on structures. Soviet experience in dealing with ice problems has resulted in the publication of ice codes in 1959, 1967 and now most recently in 1976. There are now efforts in Canada to revise and update existing ice codes here. It was felt that the translation of this most recent Soviet Code would be a useful contribution to Canadian engineers and code writers. Only the part on ice of a chapter in SNiP II - 57-75, which includes, as well, wave and vessel effects on hydraulic structures, has been translated and printed in this publication. It should be pointed out, that the literature on which the Soviet Code is based is not readily available for evaluation. Therefore it is not possible to judge how applicable the recommendations are to Canadian conditions. This document should only be considered as an additional source of experience either in formulating guidelines for Canada or in assessing ice forces for particular locations in Canada.

A program to determine ice forces and behaviour was carried out on a wharf at Strathcona Sound on Baffin Island during the winter 1975-76. Observations at the site revealed that tidal action resulted in the formation of an increasingly wide and thick zone of ice between the wharf and the natural ice cover. A qualitative model for developing ice pressures is postulated based on this behaviour. The gauges selected to measure horizontal ice pressures proved to be unsatisfactory so no direct measurements were obtained. It was possible however, from secondary calculations, to establish that horizontal ice pressures of the order of 500 kPa were developed.

Delayed elastic phenomenon during high-temperature creep of polycrystalline materials is correlated with strain due to grain boundary sliding. This correlation has been used to develop a phenomenological viscoelastic model that includes the grain-size effect. With ice as a reference material, it is shown that the contribution of the grain-boundary sliding strain to the total strain, and its dependence on stress, time, temperature and grain diameter can be systematically analysed by the proposed model. The results appear to agree with the observed trends in other materials.

The rigidity modulus is determined for simply supported, circular ice plates 0.5 and 1.22 m in diameter. Measurements for the 0.5 m diameter plates were made at -10 deg.C and for the 1.22 m plates in the range of -7 to -37 deg.C. The elastic moduli and Poisson's ratio, calculated from the rigidity modulus, are in the range of 6.0-12.0 GPa and 0.29-0.60 respectively, depending on ice type, temperature, and grain size. The plate characteristic lengths calculated from the measured values of the elastic moduli are compared with characteristic lengths determined from field measurements of the deflection of ice covers under load.

A series of model tests has been carried out on downward breaking conical structures using low salinity model ice. Comparison with information in the literature showed that a downward breaking cone experiences lower ice forces than an upward breaking cone. Fixed cones of angles of 15, 30, 45 and 60 deg were tested in 50-mm-thick ice of 60 kPa flexural strength at velocities ranging form 0.01 to 0.5 m/s. The effects of thickness and flexural strength variations were also investigated. Horizontal forces were observed to increase with increasing velocity. Ice thickness variation was observed to have a stronger influence on the vertical forces than on the horizontal forces. Vertical and horizontal forces showed a decrease with decreasing flexural strength. Two test series were run with the 45 deg conical structure arranged so that it oscillated. Horizontal force reductions of up to two thirds were observed.

Laboratory tests were conducted to investigate the effects of displacement rate, ice thickness and pile diameter on the adhesion of a saline ice sheet to wooden piles. The ice used was representative of naturally formed columnar-grained sea ice. Cylindrical piles having diameters between 30 and 145 mm were pulled up at constant nominal displacement rates between 1.5X10-4 and 7.8X10-2 mm/sec, for ice thicknesses from 58 to 170 mm. The failure mode, either shear at the pile-ice interface or flexural in the ice was observed to depend upon the test parameters. The adhesion strength was observed to increase with increasing pile displacement rate, increasing ice thickness and decreasing pile diameter. The adhesion strength of saline ice was found to be smaller by a factor of at least 3.5 than that of fresh-water columnar- grained ice measured earlier under similar conditions., Proc. 8th Int. IAHR Symposium on Ice: 18 August 1986, Iowa City, Iowa, USA

The cantilever beam test has been used very extensively in both the field and laboratory to investigate the flexural strength and strain modulus of sea ice. Shortcomings in the test are generally recognized, hence these measurements are used only as index values. One problem with flexural tests is that some prior knowledge about the material properties is required before they can be analyzed. The first part of this paper considers the elastic theory of a beam on an elastic foundation. Various factors that affect the interpretation of cantilever beam tests are examined, i.e., beam geometry, elastic foundation effect, and nonhomogeneity of elastic modulus through beam thickness. The second part of the paper presents results from in situ cantilever beam tests in Isfjorden, Spitsbergen, conducted during full scale trials with the offshore supply vessel M.V. "Werdertor" by a German group of investigators under the management of the Hamburgische Schiffbau-Versuchsanstalt. Field tests were carried out on 0.4 m thick sea ice with beam lengths up to 12 m. Load and beam deflections at up to three points were measured versus time. From these measurements strength and modulus index values were determined and the behaviour of a long cantilever beam on a foundation was confirmed. Frankenstein's approach of relating strength and strain modulus to the brine volume of saline ice was found to be quite applicable., Ice Forces on Structures. Proceedings Part 1 IAHR Symposium on Ice Problems: 07 August 1978, Lulea, Sweden

Methods of conducting and analysing uniaxial compressive strength and deformation measurements in the field and in the laboratory by means of conventional and closed-loop controlled test machines, respectively, are described, plus procedures for sampling, shipping, storing specimens and microstructural studies. Reliable measurements of the rate sensitivity of strength and deformation modulus of young congealed frazil sea ice can be obtained irrespective of location. Observations of Poisson's ratio, its variation during the tests, and its dependence on rate of loading are discussed.