Rock slope dynamics in bedrock permafrost: Insights across scales

• Main Author: Weber, Samuel
• Format: Doctoral or Postdoctoral Thesis
• Language: English
• Published: 2018
• Subjects: Ice; permafrost
• Online Access: https://zenodo.org/record/2552150; https://doi.org/10.5281/zenodo.2552150

Rock slope failure poses a potential risk to the safety of local communities and infrastructure in populated mountain regions. There is evidence that climate-related change of thermal conditions in steep bedrock permafrost leads to increased rock slope destabilization. The presence of permafrost supports the infill of fractures with ice, which can act as preferential failure planes when exposed to increasing temperatures. Permafrost also affects the hydrological and mechanical properties, which are sensitive to a changing climate. Therefore, characterizing and monitoring the dynamics of steep rock slopes is relevant for assessing rock slope stability and for detecting precursory behavior prior to slope failure. In this thesis, multi-year time series of field measurements and a comprehensive set of laboratory shear strength experiments were acquired and analyzed. The longer-term evolution of fracture kinematics in steep bedrock permafrost was analyzed with an unprecedented level of detail thanks to a unique multi-year time series of fracture displacements, rock temperatures and environmental conditions at the Matterhorn Hörnligrat field site. In the wider context of rock slope stability assessment, a new metric was proposed to quantify irreversible displacement of fractures based on the statistical separation of reversible components, caused by thermoelastic strains, from irreversible components due to other processes. Passive monitoring of acoustic emission and micro-seismology, recorded for the first time simultaneously in steep bedrock permafrost, covers the broad frequency range of 1-105Hz. These measurements provide important subsurface information on fracturing and therefore complement surface displacement data. The analysis of artificial forcing (rebound hammer) at the Matterhorn Hörnligrat field site led to two major findings: Firstly, the lack of cross-correlation between signals indicates that waveforms change strongly with propagation distance. Secondly, a significant amplification was found in the ...