Triaxial experiments on iceberg and glacier ice

Abstract

Triaxial experiments, at confining pressures in the range 0–13.79 MPa, have been performed on glacial ice collected from four icebergs and one glacier. Tests were conducted at strain rates in the range of 5 × 10−5 to 5 × 10−5s−1 and at four temperatures in the range of −1° to −16°C. Depending on test conditions, the ice failed by one of four possible modes ductile deformation, due to extensive non-interacting microcracks; fracture along a shear plane followed by continuous or stick-slip sliding; large-scale brittle fracture; and combined ductile and shear-plane fracture and slip The strength Increased with decreasing temperature, increasing strain rate up to 5 × 10−3s−1 and increasing confining pressure at the lower temperatures. The strength at 5 × 10−2s−1 was lower than at 5 × 10−3s−1 probably because extension and interaction of microcracks is enhanced at the higher rate. For higher confining pressures at −1°C, the strength decreased due to freezing-point depression. The ice from the different sources exhibited different mean uniaxial compressive strengths. The mean number of air bubbles per unit volume correlated with the mean uniaxial compressive strengths and this may be the dominant factor distinguishing the strengths of the various ice types.

Fracture of multiyear sea ice

“…The stress-strain curve shows anelastic strain hardening up to peak stress, followed by strain softening at a rate that decreases with strain. This type of behavior has been described as plastic/shear slip by Gagnon and Gammon [1995]. At 20 MPa, creep deformation occurs with no visible cracking activity.…”

The structure and mechanical behavior of ice

“…The brittle compressive strength rises sharply under a small amount of confinement in a Coulombic manner. [42][43][44][45][46][47] This implies that the deviatoric stress at failure increases with increasing hydrostatic stress and means that frictional crack sliding is an important element in the failure process. Again, the strength decreases with increasing grain size in a Hall-Petch manner.…”

“…The confinement raises the failure stress, as noted above, with the effect being greater within the regime of brittle behavior. Envelopes and surfaces describing both ductile and brittle failure under both biaxial 32, 34,35,42 and triaxial 30, 31,36,[43][44][45][46][47]49,50 loading have now been obtained and can be understood within the context of the mechanisms that are described herein. The challenge is to incorporate them in models of ice loads.…”

Micromechanical model for sintering and damage in viscoelastic porous ice and snow. Part I: Model and calibration

“…The activation energy was sugested to be 120J/mol for temperatures above −8 and 78J/mol for temperatures below. Other researchers found much lower values for the activation energy 120J/mol for −40 to −20 o C [44] and 101J/mol for temperature range of −16 to −1 o C by [45]. The difference in activation energy is believed to come from some liquid at grain boundaries.…”

“…Time-temperature superposition can be used to establish the relation between viscosity and temperature. For ice, the Arrhenius relation have been used [19,44,45]. The Arrhenius type creep rate relation :…”