A Comparison of the Ductile Compressive Strength of Columnar Saline Ice Under Proportional And Conventional Triaxial Loading

Much of the available triaxial compressive strength data for columnar saline ice has been generated from conventional triaxial tests. The advent of hydraulic "true" triaxial testing systems has allowed researchers to determine the compressive strength of ice using loading paths that were not accessible with conventional triaxial tests systems. The question that is considered here is whether data obtained from different loading paths can be directly compared. The deformation of laboratory-grown S2 columnar saline ice (LGSI) under triaxial compressive loading was investigated at a temperature of -10°C at a constant strain rate of 3.9 x 10.5 s-I applied in the direction of greatest load, using an MTS multi axial servo-hydraulic testing system. All of the tests were carried out on 160 mm cubic samples. In one set of tests the samples were proportionally loaded with confinement ratios of R21 = σ22/σ11=0.25 and 0.50, with R31=σ33/σ11 variable; σ11 and σ22 are the normal stresses applied in two orthogonal directions across the columns and σ33 is the normal stress applied along the columns. In this case the samples were loaded hydrostatically to an initial pressure 00 and then further loaded along XI at a constant strain rate of 3.9 x 10–5 s-I while σ22 and σ33 were held constant at σº. In this scheme x I and X2 are perpendicular to the long axis of the columns; x3 is parallel to the column axis. Comparison of the yield stresses from the proportional loading tests and simulated conventional loading tests did not reveal any significant difference in the yield strengths from the two loading paths, within experimental scatter. Further analysis has shown that there is statistically no significant difference in the flow stresses taken at other points on the stress-strain curve (σ11 vs. ε11), up to 2% inelastic deformation.