Brittle failure of columnar saline ice under triaxial compression

The brittle compressive failure of cubes of columnar saline ice was studied under triaxial (proportional) loading where the ratio of normal stresses (sigma(11):sigma(22):sigma(33)) was varied in a systematic manner using a true multiaxial loading system. The strain rate in the direction of the greatest applied compressive stress was 6 x 10(-3) s(-1) and the temperature was -10 degrees C. The failure surface is faceted and reveals three regimes: (1) of lower across-column confinement where the along-column confinement has no significant effect on the major across-column stress at failure, but where the minor across-column stress raises the strength; (2) of higher across-column confinement where along-column confinement now raises the major across-column stress at failure; and (3) of predominantly along-column loading where the along-column failure stress increases in proportion to the smaller of the two across-column confining stresses. Each regime shows a high sensitivity of strength to the appropriate confining stress. The behavior is explained in terms of the frictional crack sliding-wing crack mechanism of brittle compressive failure.