Garry Timco

A review of sea ice density

Abstract The density of sea ice is an important property in many applications. However, due to its multi-phase composition of solid ice, solid salts, liquids and gas, the definition and measurement of density is not straightforward. The reported values vary over a wide range from 0.72 Mg m−3 to 0.94 Mg m−3, with an average of approximately 0.91 Mg m−3. The reasons for the spread are partly real, and partly a function of the test technique used for determining the density. Accurate measurements which represent the in situ density of first-year sea ice range from 0.84 to 0.91 Mg m−3 for the ice above the waterline, and 0.90 to 0.94 Mg m−3 for the ice below the waterline.

Flexural strength equation for sea ice

Abstract The measured flexural strengths of freshwater ice and sea ice have been compiled with a view towards correlating the measured results. Two thousand, four hundred and ninety-five experimentally measured data points from nineteen investigators have been used. This correlation has been done as input for a new system being developed to quickly characterize sea ice properties. The results indicate a very good correlation (r2= 0.77) between the flexural strength (σf) and the brine volume (νb) with a functional form σf = 1.76 e−5.88√νb where the flexural strength is in MPa, and the brine volume is expressed as a brine volume fraction. The value of 1.76 MPa for zero brine volume is in excellent agreement with the average value (1.73 MPa) measured for freshwater ice.

An analysis of the shapes of sea ice ridges

Abstract An analysis has been made of the salient features of 112 first-year and 64 multi-year sea ice ridges. Based on this information, the important characteristics of the ridges have been related through simple equations. In particular, the ratio of the keel-depth to sail-height was found to be 4.4 for first-year ridges, and 3.3 for multi-year ridges; the ratio of the keel-area to sail-area was 8.0 for first-year ridges and 8.8 for multi-year ridges. Also, for first-year ridges, the ratio of the keel-width to sail-height was approximately 15, and the ratio of the keel-width to keel-depth was 3.9. An analysis of the sail and keel angles indicates a distribution of values with an average sail angle of 21° for temperate ridges, and 33° for ridges in the Beaufort Sea. In this paper, the results of this analysis are described, and the important ridge characteristics are discussed.

Compressive strength of sea ice sheets

Abstract A model has been developed for predicting the large-scale compressive strength of sea ice sheets. The only inputs which are required to calculate the strength are the air temperature, the ice thickness and the strain rate. The model makes use of the results of 283 small-scale strength tests and the relationships between the intrinsic and extrinsic properties of the ice sheet. A comparison of the results of the model to large-scale measured compressive strengths shows excellent agreement. A parametric variation is performed on all of the factors affecting the compressive strength. In addition, using available meteorological information for the Arctic, the compressive strength of a typical sea ice sheet is predicted throughout a winters season.

Confined compression tests: Outlining the failure envelope of columnar sea ice

Abstract A series of confined compression tests has been performed on columnar sea ice over a range of nominal strain rates of 10 −5 to 10 −3 s −1 at a temperature of −2°C. Both the applied load and side confining load were measured. These are used to outline the full 3-dimensional failure envelope of the ice. The results are discussed in terms of loading rate effects, temperature, brine volume and air porosity. A strength index is introduced which correlates the present results in terms of these parameters. This leads to an empirical relationship which gives the functional dependence of the uni-axial compressive strength in terms of strain rate, loading direction, salinity, temperature and ice density. A mathematical description of the failure envelope is presented using a modified n -type yield function.

EG/AD/S: A new type of model ice for refrigerated towing tanks

Abstract 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.

Ice loads on the Molikpaq in the Canadian Beaufort Sea

The Molikpaq is a steel caisson structure that was used in the 1980s in the Canadian Beaufort Sea for exploration drilling of oil and gas. It was very extensively instrumented. Part of the instrumentation was designed to measure the ice loads. This paper presents an overview discussion of the characteristics and instrumentation of the Molikpaq. It presents detailed information on 188 ice loading events from both first-year and multi-year ice for different ice macrostructures including level ice, ridges, hummock ice and isolated floes. Investigation of the ice loads has shown that the Line Load (global load per unit length of the structure) increases with increasing ice thickness. The analysis of the ice loads in terms of the failure mode of the ice provides additional insight and explains some of the scatter in the ice load data.

Flexural strength and fracture toughness of sea ice

Abstract A series of mid-winter experiments were carried out on the ice in the rubble field around Tarsiut Island in the Beaufort Sea. The tests included grain structure determinations, salinity and density of the ice, small beam flexural strength and fracture toughness. Typical values for flexural strength and fracture toughness were 0.6–1.0 MPa and 100–140 kPa m 1 2 respectively. Both properties were dependent on brine volume and depth in the ice sheet. In comparing these results with identical tests on finegrained freshwater ice it was found that for comparable loading conditions, the strength of the sea ice was significantly lower than the strength of the freshwater ice, whereas the fracture toughness of the sea ice was higher than the fracture toughness of the freshwater ice.

Comparative strengths of fresh water ice

Abstract In order to gain a quantitative comparison among the various mechanical properties of ice, a series of tests was performed on fresh water ice in which several of the mechanical properties were tested under identical experimental conditions. In particular, the tests were standardized with respect to ice growth conditions, ice type, grain size and orientation, sample size, test temperature and strain rate. The average results of the test were: flexural strength − cantilever beam = 770 ± 150 kPa; flexural strength − simple beam (top tension) = 2200 ± 320 kPa; flexural strength − simple beam (bottom tension) = 1770 ± 190 kPa; fracture toughness = 83 ± 7 kPa m 1 2 ; shear strength = 500 ± 220 kPa; compressive strength (horizontal loading) = 4400 ± 700 kPa and strain modulus − cantilever beam = 1.6 ± 0.4 GPa. Since most of the tests were performed using a portable compression test machine, the strength values can serve as baseline values for comparison with field results.

An investigation of the failure envelope of granular/discontinuous-columnar sea ice

Abstract The three-dimensional failure envelope for granular/discontinuous-columnar sea ice has been investigated over a range of nominal strain rates from 9 × 10−6 s−1 to 4.4 × 10−4 s−1 by using confined compression tests. Both the applied load and side-confining load were measured. The tests were performed on samples cut from a solid block of ice in the Beaufort Sea which structurally was granular with some banding of discontinuous-columnar ice to a depth of 1.2 m. The results indicate the overall shape and size of the failure envelope of this ice, and show that although the shape is independent of loading rate, the size increases with loading rate. An analytical expression is derived which mathematically describes the failure envelope in three-dimensional space.