Effect of Hydrostatic Confining Pressure on the Failure Mode and Compressive Strength of Polycrystalline Ice

Abstract

Compressive tests were performed on fine and coarse-grained granular ice with grain size of 1 and 10 mm and coarse-grained columnar ice at strain rates from 3 × 10-4 to 5 × 10-2 s-1 under hydrostatic confining pressure from 0.1 to 50 MPa, at −11 ± 0.5 °C. The effect of hydrostatic confining pressure on the failure mode and the compressive strength were examined with reference to grain size and strain rate. At a constant strain rate, the compressive fracture/yield stress increased with increasing confining pressure up to a critical confining pressure at which the stress attains a maximum and the process of failure changes from brittle to ductile. Above the critical confining pressure, the compressive stress was not changed by confining pressure at lower strain rates, while it decreased at higher strain rates as the confining pressure increased. The critical confining pressure increased with increase in strain rate and grain size. A higher confining pressure was required to inhibit brittle failure for columnar ice and coarse-grained granular ice than for fine-grained granular ice at the same strain rate. Application of a confining pressure above 20 MPa caused fine-grain ice to deform in a ductile manner for the strain rate applied; a confining pressure of 50 MPa was required at 2.5 × 10-2 s-1 for coarse-grained granular ice and 1 × 10-2 s-1 for columnar ice. The correlation between the deformation behavior and the change in the internal structure was examined.