Design of an experimental procedure and set up for the detection of ice segregation phenomena in rock by acoustic emissions

Large slope failures in steep alpine bedrock present a significant geological hazard in many high mountain areas throughout the world. An increased number of periglacial rock falls have been identified in recent decades as a consequence of climate changes. Starting from the Matterhorn site field observations (Italy), a comparative analysis between temperature spatial-temporal distribution and microseismic activity, showed that the hypocentres seemed to be localized close to the permafrost boundary. Ice segregation has been interpreted as one of the mechanisms involved in high mountain bedrock degradation and its associated instability. The aim of this research is to design and set up a down scaled physical simulation of this frost weathering mechanism. Ice segregation phenomenon has been analyzed in depth through numerical simulations and laboratory tests. Fully coupled thermo-hydro-mechanical analyses have been carried out using the FEM code CODE_BRIGHT, by coupling a description of transient heat and mass transfer in porous, freezing media. These studies have addressed the mechanics of ice growth, particularly the role of the premelted films in lens growth, in order to do some prediction of the timing and depth of potential macrocrack originating perpendicular to the water flow from ice segregation processes. Uncoupled numerical analyses have also been performed using the FEM code ABAQUS: they highlighted how steady temperature gradients play a fundamental role in crack propagation and they permitted to chose the temperature interval that would maximize the frost cracking mechanism in the rock sample. Finally, two long-term freezing tests has been set up: the first experimental test was aimed to reproduce the ice lens growth mechanism due to the onset of ice segregation processes at the interface active layer-permafrost table, building up a physical model. During the second trial, acoustic emission monitoring system has been installed, deepening the understanding of the processes operating in evolving fault zone due to the ice lens growth.