Mechanisms governing failure of ice beneath a spherically-shaped indenter

Small-scale laboratory ice-indentation tests were conducted on freshwater granular and freshwater columnar S2 ice at − 10 °C and − 40 °C. Tests were performed on confined and unconfined laboratory-grown ice using semi-spherical indenters (hemispherical-ended rods) of radii 12.7 and 5 mm and accompanied by a study of angle of repose (AOR) of crushed ice. This paper describes experimental procedure, presents and discusses the results of experiments with specific focus on the micromechanical processes underlying the indentation pressure as a function of indentation speed, penetration depth and the size of the indenter and the relevance to those processes at larger scales. The experiments indicate that the presence of lateral confinement during indentation is an important factor, as confinement suppresses ice failure by splitting. It is shown that during indentation, there are regions of Columbic and plastic faulting in ice. At small penetration depths of ~ 1 mm, the transition between these two regions is in agreement with earlier experiments under homogeneous triaxial loading and is governed by the degree of confinement. The AOR study shows that flowability of crushed ice particles is mainly controlled by the contact forces between the grains and varies with particle size and time.