Preprints
https://doi.org/10.5194/esurf-2020-70
https://doi.org/10.5194/esurf-2020-70

  28 Sep 2020

28 Sep 2020

Review status: this preprint is currently under review for the journal ESurf.

Stability assessment of degrading permafrost rock slopes based on a coupled thermo-mechanical model

Philipp Mamot, Samuel Weber, Saskia Eppinger,, and Michael Krautblatter Philipp Mamot et al.
  • Chair of Landslide Research, Technical University of Munich, 80333, Germany

Abstract. In the last two 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 already been intensively investigated, the mechanical consequences on rock slope stability have so far not been reproduced in numerical models. Laboratory studies and conceptual models argue that warming and thawing decrease rock and discontinuity strength and promote deformation.

This study presents the 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 applied to 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 the discontinuum model developed with the Universal Distinct Element Code (UDEC). Geophysical and geotechnical field surveys deliver information on the permafrost distribution and fracture network.

The model demonstrates that warming decreases rock slope stability to a critical level, while thawing initiates failure. A 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 zero degree.

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, (iv) with a wide range of slope angles (30–70°) and orientations of the fracture network (consisting of three joint sets). The presented model is the first one capable of assessing the future destabilisation of degrading permafrost rock slopes.

Philipp Mamot et al.

 
Status: final response (author comments only)
Status: final response (author comments only)
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Philipp Mamot et al.

Philipp Mamot et al.

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Short summary
The mechanical response of permafrost degradation on high-mountain rock slope stability has not been calculated in a numerical model yet. We present the first approach for a model with thermal and mechanical input data derived from laboratory and field work, and existing concepts. This is applied to a test site at the Zugspitze, Germany. A numerical sensitivity analysis provides the first critical stability thresholds related to the rock temperature, slope angle and fracture network orientation.