Strength and Failure Modes of Pure Ice and Multi-Year Sea Ice Under Triaxial Loading

Abstract

Following a brief description of a new servo-controlled triaxial testing system for large ice samples (ca. 40mm diameter) with facilities for acoustic emission (AE) observations, and of a technique for manufacturing pure ice samples, laboratory results are presented for the strength of ice under uniaxial tension, and under uniaxial and triaxial compression. Data has been gathered using strain rates up to 10^-2/s, confining pressures up to 30MPa and temperatures down to -40°C. The pure ice had a uniform grain size of about 1mm and a high density. The sea ice, collected from the Canadian High Arctic, had a large natural variability of structure, salinity and density. The test conditions straddle the boundary between brittle cracking and fracture behaviour, and high temperature plasticity. The behaviour shows some similarities with that of silicate rocks and covalent oxides. At low temperatures and high strain rates ice fracture exhibits a pressure dependence similar to that of brittle rocks, with strength increasing as confining pressure increases. AE is also similar to that of brittle rocks. However, at higher temperatures and pressures, where ductile behaviour occurs, increasing pressure leads to decreasing strength. The peak strengths observed during ductile behaviour are not yet fully understood. The results are discussed in terms of Griffith crack theory.