Abstract
Ice samples were extracted from a land-fast ice sheet of 90 cm thickness at Lutzow-Holm Bay in the Antarctica. The ice samples were then shipped to a cold room in Tokyo, and unconfined uniaxial compression tests and fracture toughness tests were performed for a wide range of loading rate under temperature varying from −5°C to −30°C. During the tests limited in number, acoustic emission measurements were also carried out. On the other hand, distributions of salinity, density, air content, fabric structure and grain size were examined along the thickness direction of the ice sheet. The ice sheet consisted of fine-grained granular ice at the top surface layer and columnar grains below it. The grain size was less than 1 mm for the granular ice and the columnar ice grain size increased linearly with the depth from about 1 mm just beneath the transition zone to about 13 mm at the bottom surface. The density and the air content also varied showing its maximum or minimum value, respectively, at the mid-thickness position along the thickness direction of the ice sheet. Thus, correlations between the mechanical properties and the physical features were studied. The fracture toughness (KIC) of the columnar grained ice showed a strong dependence on the grain size (diameter of the columnar ice). Namely, the KIC decreased in proportion to the inverse square root of the grain size. The compressive strength showed a linear relationship with the density, which was a function of not only the brine volume, but also the air content. Accordingly, the compressive strength was recognized to decrease with an increase in the sum of the square root of brine volume and the square root of air content. The other ice samples were also extracted from one of icebergs in Lutzow-Holm Bay. And the compressive strength and the fracture toughness were measured and reported in this paper.
