THE FAILURE OF FRESH-WATER GRANULAR-ICE UNDER MULTIAXIAL COMPRESSIVE LOADING

The failure of fresh-water granular ice under multiaxial compressive loading was investigated at -10, -20 and -40 degrees C at 10(-3) s(-1), using a true multiaxial servo-hydraulic testing system. The tests were carried out on cubic samples proportionately loaded under different confinement ratios R = sigma(3)/sigma(1) = sigma(2)/sigma(1). Two regimes were revealed at all three temperatures. Under lower confinement the failure stress, sigma(1f), increases sharply with R, whereas at higher confinement sigma(1f) is roughly constant. Both brittle and pseudo-ductile behavior were observed under lower confinement, depending upon the confining stress and the temperature, while the behavior was brittle under higher confinement. An analysis of the brittle to pseudo-ductile transition within the lower confinement regime was performed in terms of the frictional crack sliding/wing-crack mechanism. The high-confinement regime is characterized by intense intergranular damage. The final failure, however, is caused not by the linking of the uniformly distributed microcracking, but by damage localized at the ice/platen interface. The saturation in the failure stress with increasing confinement is attributed to a mechanism specific to the boundary conditions and not to the ice per se.