Shear faulting and localized heating in ice: The influence of confinement

Systematic experiments on laboratory-grown polycrystalline granular ice and columnar S2 ice loaded triaxially at -10 degrees C at a strain rate (epsilon) over dot(11) = 2.2 x 10(-2) s(-1) under increasing levels of confinement have established two distinct modes of brittle-like shear faulting. One mode, termed Coulombic (C) or frictional faulting, develops under lower degrees of confinement and is characterized by macroscopic faults, comprising a narrow band of microcracks, oriented similar to 30 degrees from the direction of maximum shortening; and by pressure hardening, grain-size-dependent strength, localized heat production and the creation of fault gouge. The second mode of faulting, termed plastic (P) or non-frictional faulting, develops under higher degrees of confinement and is characterized by macroscopic faults, comprising a fine band of recrystallized grains, oriented similar to 45 degrees to the direction of maximum shortening; and by pressure and grain-size-independent strength and localized heat production. The transition from C-faulting to P-faulting corresponds to the level of confinement required to suppress frictional sliding. (C) 2010 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.