7 - Complex States of Stress and Triaxial Tests

Summary

The states of stress in high-pressure zones involve a combinations of volumetric and deviatoric stresses. Modelling of ice behaviour under these states of stress is essential for developing proper mechanics of failure of high-pressure zones. Past triaxial tests are reviewed. There is a lack of information for higher confining pressures. The microstructural changes of microcracking and recrystallization needed to be studied in terms of past stress history. These were addressed in a special series of tests, which showed that microcracking at low confinements causes increase in compliance, which decreases with increasing confinement, but that at higher confinements, pressure softening, associated with melting, results in much increased compliance. Tests in which the activation energy at various confinements was measured using tests at a range of temperatures showed that the addition of pressure to ice resulted in behaviour similar to less confined ice at a higher temperature (pressure–temperature equivalence). Ice is prone to localize and small irregularities are sufficient to trigger this behaviour, as observed in some triaxial tests.