A review of the strength of iceberg and other freshwater ice and the effect of temperature

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Abstract

Based on literature results, the temperature of an iceberg around the Grand Banks of Newfoundland is shown to vary from about 0 °C at the water–ice interface to approximately − 20 °C in the interior. This temperature variation affects the strength of the ice. A review of the strength of iceberg ice shows that its uniaxial compressive strength is 1.7 times less than other freshwater ice at a strain-rate of 10 3 s 1, probably due to pre-existing healed cracks or flaws. Using an activation energy of 80 kJ/mol., the uniaxial compressive strength of iceberg ice is shown to vary from 5 MPa at 0 °C near the surface, to 8.5 MPa at − 20 °C, 10–20 m inside the iceberg.

Introduction

The temperature of the ice making up an iceberg is not constant. It has been found to vary significantly with depth. Since the properties of ice, particularly its strength, depend on temperature it follows that in an iceberg-structure collision the force generated may depend on the temperature of the ice.

This paper reviews the temperature data for icebergs, and then compares the uniaxial compressive strength of iceberg ice with other freshwater ice. The effect of temperature on the strength of iceberg ice is then discussed. It was not the intention to discuss failure mechanisms but to compare the strength of iceberg ice with other freshwater ice and to determine how the temperature variation with depth might affect the strength of the ice. The effect of confinement is neglected in this review. While it is an important consideration, the amount of data on the confined strength of ice, particularly iceberg ice, hardly warrants a review.

Section snippets

Iceberg temperatures

The temperature of an Antarctic iceberg was measured as long ago as 1902 (von Drygalski, 1983). He monitored the temperature of a large, probably tabular, 1 km long, iceberg at depths down to 20 m, over an extended period from April 1902–January 1903. Below a depth of 15 m the temperature was constant at about − 10 °C. Above this depth the temperature varied with the seasonal air temperature. While interesting, these large Southern icebergs are not subject to the same climate nor to the same

Compressive strength data

Fig. 3 shows the uniaxial compressive strength for all the iceberg ice data that were found in the literature. All data are for − 10 °C unless noted otherwise.

El-Tahan et al., 1984, El-Tahan et al., 1988 conducted three types of tests on iceberg ice as well as snow ice namely, uniaxial compressive, indentation, and impact tests. The compressive tests were done at − 5 °C, over a strain-rate range of 10 4 to 10 1 s 1. The ice had been collected from an iceberg that drifted around St. John's in

Effect of temperature on compressive strength

Barrette and Jordaan (2003) have tested iceberg ice as a function of hydrostatic confining pressure and of temperature, but unfortunately they gave no data at zero confining pressure. Their data, however, can be used to determine the temperature dependence of the strength of iceberg ice. They maintained a constant axial stress of 15 MPa and varied temperature from − 26 °C to − 5 °C, and confining pressure from 10 to 65 MPa. They interpreted their data using the well-known equation combining

Discussion and conclusions

The temperature of an iceberg on the Grand Banks of Newfoundland varies from about 0 °C at the water–ice interface to no lower than − 20 °C at a depth of about 20 m. This is, therefore, the temperature range of interest to iceberg-structure interactions.

The uniaxial compressive strength of iceberg ice is less than other freshwater ice, laboratory grown or natural. At − 10 °C, and at a strain-rate of 10 3 s 1, typical of many ice-structure interactions, iceberg ice has a strength approximately 1.7

Acknowledgment

I am grateful to the Institute for Ocean Technology, National Research Council of Canada, and to the ice-structure interaction activity of the Offshore Environmental Factors (OEF) program of PERD (Program of Energy Research and Development) for supporting this work. I am also grateful to two careful reviewers for their comments and corrections.

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