BRITTLE COMPRESSIVE FAILURE OF SALT-WATER COLUMNAR ICE UNDER BIAXIAL LOADING

The brittle failure of saline columnar ice was investigated under biax ial compression at epsilon =10(-2) s(-1) and -10 degrees and -40 degre es C, over the range 0 less than or equal to R(A) < 1 where R(A) is th e ratio of the intermediate to major principal compressive stress. The major principal stress and the intermediate (confining) stress were o rthogonal to the columnar axes (type-A confinement); both stresses and the c-axes of the grains were co-planar. The results confirm earlier work by Hausler (1981) and Timco and Frederking (1983, 1986) on saline ice and follow similar behavior to fresh-water columnar ice found by Smith and Schulson (1993) and Frederking (1977). Failure stress and fa ilure mode are sensitive to the confinement and two regimes of behavio r are found: the failure stress first rapidly increases with R(A) in t he range 0 less than or equal to R(A) < R(t) and then tends to decreas e for R(A) > R(t). The transition stress ratio, R(t), changes from app roximate to 0.2 at -10 degrees C to approximate to 0.1 at -40 degrees C. The failure mode changes from axial splitting to shear faulting in the loading plane for 0 < R(A) < R(t). Above R(t), failure changes to a combined mode of splitting across the columns and shear faulting out of the loading plane. The failure-stress envelope is of a truncated C oulomb-type. Damage studies show wing cracks and local fragmentation o f grains involving the brine pockets. The results are explained in ter ms of Coulombic sliding and Hertzian crack mechanics.