Candidate: Martin Kradolfer
Supervisors: Florian Amann, Kerry Leith
Institution: ETH Zurich
Activity: Beginning Fall 2017
Ice filled tension cracks are commonly observed in association with active or catastrophic rock slope failures located in potential permafrost regions of the Alps. Displacement or dislocation along cracks in many of these rock slopes has been observed to primarily occur when the crack top temperature or air temperature drops below zero in late fall to winter. Long-term temperature records from boreholes in active rock slope instabilities in permafrost regions suggest that the maximum temperature in the deeper underground occurs in late fall to winter (i.e. contemporaneous with the observed acceleration phases) due to a delayed temperature propagation into the rock mass. We suggest that the temperature gradient associated with higher temperatures in the deeper underground and sub-zero temperatures at the crack tops causes the migration of free water to the tension cracks, which then expands on freezing, causing the cracks to open. These processes are difficult to test and control on the field scale. Thus, we propose a laboratory test set-up that mimics these processes on the decimeter scale.
MSC Thesis goals:
The aim of the thesis is to conduct and analyse a series of laboratory tests that mimic different scenarios (i.e. moisture conditions in the crack; crack temperature variations, etc.). The test set-up consists of a temperature controlled water reservoir, a granitic rock block with a saw cut fracture, an air-gun that produces a cold air stream (i.e. -1 to -10°C) to cool the crack, extensometers and temperature sensors to monitor the thermo-mechanical response and time-lapse cameras to monitor the migration and freezing of water (which contains a tracer) in the tension crack.
Supervisors: Dr. Florian Amann, Dr. Kerry Leith