Simple-shear box experiments with floating ice rubble

Abstract

A simple-shear box was used to study the shear strength characteristics of floating layers of vertically unconstrained ice rubble comprised of parallelpiped ice blocks. A comparative set of experiments was also performed using floating layers of parallelpiped plastic blocks in order to determine the origin of cohesion in ice rubble. Experiments were also performed using mushy ice. However, the shear-box proved not to be useful for determining the shear testing of mushy ice. The shear strength of a layer of ice rubble was found to depend on normal stress, which in turn was found to depend on rubble thickness, layer porosity, and shear rate. The dependence on shear rate of normal stress and, as a consequence, of shear strength of a layer of floating ice rubble is attributed to the development of freeze-bonds between the ice blocks comprising the rubble layer. It is argued that, at slower shear rates, more and stronger freeze-bonds develop than at higher shear rates, thus enabling the layer to withstand larger normal stresses and, consequently, shear strengths that increase with decreasing shear rates. If the influence of freeze-bonding on normal stress is taken into account, and if a Mohr-Coulomb failure criterion is used to characterize shear strength, it is found that a floating layer of ice rubble undergoing continuous-shear deforms as a cohesionless material; or at least as a material with unique cohesive properties.