scholarly journals Review “Stability assessment of degrading permafrost rock slopes based on a coupled thermo-mechanical model.” by Mamot et al.

2020 ◽  
Author(s):  
Anonymous
Keyword(s):  
Mechanical Model ◽  
Stability Assessment ◽  
Rock Slopes ◽  
Permafrost Rock

Towards a benchmark mechanical model for warming permafrost rock slopes

2020 ◽  
Author(s):  
Michael Krautblatter ◽  
Benjamin Jacobs ◽  
Philipp Mamot ◽  
Regina Pläsken ◽  
Riccardo Scandroglio ◽  
...  
Keyword(s):  
Mechanical Properties ◽  
Fracture Toughness ◽  
Mechanical Model ◽  
Rock Slope ◽  
Limit Equilibrium ◽  
Mechanical Parameters ◽  
Rock Slopes ◽  
Permafrost Rock ◽  
Mechanical Models ◽  
Rock Mechanical Properties

<p>This paper discusses mechanical modelling strategies for instable permafrost bedrock. Modelling instable permafrost bedrock is a key requirement to anticipate magnitudes and frequency of rock slope failures in a changing climate but also to forecast the stability of high-alpine infrastructure throughout its lifetime.  </p><p>High-alpine rock faces witness the past and present mechanical limit equilibrium. Rock segments where driving forces exceed resisting forces fall of the cliff often leaving a rock face behind which is just above the limit equilibrium. All significant changes in rock mechanical properties or significant changes in the state of stress will evoke rock instability which often occurs with response times of years to 1000 years. Degrading permafrost will act to alter (i) rock mechanical properties such as compressive and tensile strength, fracture toughness and most likely rock friction, (ii) warming subcero conditions will weaken ice and rock-ice interfaces and (iii) increased cryo- and (iv) hydrostatic pressures are expected. We have performed hundreds of laboratory experiments on different types of rock that show that thawing and warming siginficantly decreases both,  rock and ice-mechanical strength between -5°C and -0.0°C.  Approaches  to calculate cryostatic pressure (ad iii) have been published and are experimentally confirmed. However, the importance and dimension of extreme hydrostatic forces (ad iv) due to perched water above permafrost-affected rocks has been assumed but has not yet been quantitatively recorded.</p><p>This paper presents data and strategies how to obtain relevant (i) rock mechanical parameters (compressive and tensile strength and fracture toughness, lab), (ii) ice- and rock-ice interface mechanical parameters (lab), (iii) cryostatic forces in low-porosity alpine bedrock (lab and field) and (iv) hydrostatic forces in perched water-filled fractures above permafrost (field).</p><p>We demonstrate mechanical models that base on the conceptual assumption of the rock ice mechanical model (Krautblatter et al. 2013) and rely on frozen/unfrozen parameter testing in the lab and field. Continuum mechanical models (no discontinuities) can be used to demonstrate permafrost rock wall destabilization on a valley scale over longer time scales, as exemplified by progressive fjord rock slope failure in the Lateglacial and Holocene. Discontinuum mechanical models including rock fracture patterns can display rock instability induced by permafrost degradation on a singular slope scale, as exemplified for recent a recent ice-supported 10.000 m³ preparing rock at the Zugspitze (D). Discontinuum mechanical models also have capabilities to link permafrost slope stability to structural loading induced by high-alpine infrastructure such as cable cars and mountains huts, as exemplified for the Kitzsteinhorn Cable Car and its anchoring in permafrost rocks (A). </p><p>Over longer time scales, the polycyclicity of hydro- and cryostatic forcing as well as material fatigue play an important role. We also introduce a mechanical approach to quantify cryo-forcing related rock-fatigue. This paper shows benchmark approaches to develop mechanical models based on a rock-ice mechanical model for degrading permafrost rock slopes.</p>

scholarly journals Brief communication: The influence of mica-rich rocks on the shear strength of ice-filled discontinuities

2020 ◽  
Vol 14 (6) ◽  
pp. 1849-1855
Author(s):  
Philipp Mamot ◽  
Samuel Weber ◽  
Maximilian Lanz ◽  
Michael Krautblatter
Keyword(s):  
Shear Strength ◽  
Failure Criterion ◽  
Rock Slopes ◽  
Surface Charges ◽  
Permafrost Rock ◽  
Rock Types ◽  
Negative Surface ◽  
The Stability ◽  
Stress Dependent ◽  
Dependent Failure

Abstract. A temperature- and stress-dependent failure criterion for ice-filled rock (limestone) joints was proposed in 2018 as an essential tool to assess and model the stability of degrading permafrost rock slopes. To test the applicability to other rock types, we conducted laboratory tests with mica schist and gneiss, which provide the maximum expected deviation of lithological effects on the shear strength due to strong negative surface charges affecting the rock–ice interface. Retesting 120 samples at temperatures from −10 to −0.5 ∘C and normal stress of 100 to 400 kPa, we show that even for controversial rocks the failure criterion stays unaltered, suggesting that the failure criterion is transferable to mostly all rock types.

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

2020 ◽  
Author(s):  
Philipp Mamot ◽  
Samuel Weber ◽  
Saskia Eppinger, ◽  
Michael Krautblatter
Keyword(s):  
Slope Stability ◽  
Rock Slope ◽  
Fracture Network ◽  
Slope Instability ◽  
Rock Slope Stability ◽  
Permafrost Degradation ◽  
Rock Slopes ◽  
High Mountains ◽  
Permafrost Rock ◽  
Wide Range

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.

scholarly journals Brief communication: The influence of mica-rich rocks on the shearstrength of ice-filled discontinuities

2020 ◽  
Author(s):  
Philipp Mamot ◽  
Samuel Weber ◽  
Maximilian Lanz ◽  
Michael Krautblatter
Keyword(s):  
Failure Criterion ◽  
Rock Slopes ◽  
Mica Schist ◽  
Surface Charges ◽  
Permafrost Rock ◽  
Rock Types ◽  
Negative Surface ◽  
The Stability ◽  
Stress Dependent ◽  
Dependent Failure

Abstract. A temperature- and stress-dependent failure criterion for ice-filled rock (limestone) joints was proposed in 2018 as an essential tool to assess and model the stability of degrading permafrost rock slopes. To test the applicability to other rocks, we now conducted experiments with mica schist/gneiss which provide the maximum expected deviation of lithological effects on the shear strength due to strong negative surface charges affecting the rock-ice interface. Retesting 120 samples from −10 to −0.5 °C and 100 to 400 kPa, we show that even for controversial rocks the failure criterion stays unaltered, suggesting that the failure criterion is transferable to mostly all rock types.

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

2021 ◽  
Vol 9 (5) ◽  
pp. 1125-1151
Author(s):  
Philipp Mamot ◽  
Samuel Weber ◽  
Saskia Eppinger ◽  
Michael Krautblatter
Keyword(s):  
Rock Slope ◽  
Slope Angle ◽  
Fracture Network ◽  
Slope Instability ◽  
Permafrost Degradation ◽  
Rock Slopes ◽  
High Mountains ◽  
Temperature Dependent ◽  
Permafrost Rock ◽  
Wide Range

Abstract. 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 sets). Here, we present a benchmark model capable of assessing the future destabilisation of degrading permafrost rock slopes.

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