A temperature-dependent mechanical model to assess the stability of degrading permafrost rock slopes

• Published in: Earth Surface Dynamics
• Main Authors: P. Mamot, S. Weber, S. Eppinger, M. Krautblatter
• Format: Article in Journal/Newspaper
• Language: English
• Published: Copernicus Publications 2021
• Subjects: Dynamic and structural geology; QE500-639.5; Ice; permafrost
• Online Access: https://doi.org/10.5194/esurf-9-1125-2021; https://doaj.org/article/8774097d3fc54b98a64af98dddaf909a

Over the last 2 decades, permafrost degradation has been observed to be a major driver of enhanced rock slope instability and associated hazards in high mountains. While the thermal regime of permafrost degradation in high mountains has been addressed in several modelling approaches, no mechanical models that thoroughly explain rock slope destabilisation controls in degrading permafrost have been developed. Meanwhile, recent laboratory studies have shown that degrading permafrost affects both, rock and ice mechanical strength parameters as well as the strength of rock–ice interfaces. This study presents a first general approach for a temperature-dependent numerical stability model that simulates the mechanical response of a warming and thawing permafrost rock slope. The proposed procedure is exemplified using a rockslide at the permafrost-affected Zugspitze summit crest. Laboratory tests on frozen and unfrozen rock joint and intact rock properties provide material parameters for discontinuum models developed with the Universal Distinct Element Code (UDEC). Geophysical and geotechnical field surveys reveal information on permafrost distribution and the fracture network. This model can demonstrate how warming decreases rock slope stability to a critical level and why thawing initiates failure. A generalised sensitivity analysis of the model with a simplified geometry and warming trajectory below 0 ∘ C shows that progressive warming close to the melting point initiates instability above a critical slope angle of 50–62 ∘ , depending on the orientation of the fracture network. The increase in displacements intensifies for warming steps closer to 0 ∘ C. The simplified and generalised model can be applied to permafrost rock slopes (i) which warm above −4 ∘ C, (ii) with ice-filled joints, (iii) with fractured limestone or probably most of the rock types relevant for permafrost rock slope failure, and (iv) with a wide range of slope angles (30–70 ∘ ) and orientations of the fracture network (consisting of three joint ...