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

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

10.5194/esurf-2020-70 ◽

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.

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Assessment of Slope Instability and Risk Analysis of Road Cut Slopes in Lashotor Pass, Iran

Journal of Geological Research ◽

10.1155/2014/763598 ◽

2014 ◽

Vol 2014 ◽

pp. 1-12 ◽

Cited By ~ 3

Author(s):

Mohammad Hossein Taherynia ◽

Mojtaba Mohammadi ◽

Rasoul Ajalloeian

Keyword(s):

Rock Mass ◽

Risk Analysis ◽

Rock Slope ◽

Classification Systems ◽

Slope Instability ◽

Rock Slope Stability ◽

Rock Slopes ◽

The Stability ◽

Cut Slopes ◽

Road Cut Slopes

Assessment of the stability of natural and artificial rock slopes is an important topic in the rock mechanics sciences. One of the most widely used methods for this purpose is the classification of the slope rock mass. In the recent decades, several rock slope classification systems are presented by many researchers. Each one of these rock mass classification systems uses different parameters and rating systems. These differences are due to the diversity of affecting parameters and the degree of influence on the rock slope stability. Another important point in rock slope stability is appraisal hazard and risk analysis. In the risk analysis, the degree of danger of rock slope instability is determined. The Lashotor pass is located in the Shiraz-Isfahan highway in Iran. Field surveys indicate that there are high potentialities of instability in the road cut slopes of the Lashotor pass. In the current paper, the stability of the rock slopes in the Lashotor pass is studied comprehensively with different classification methods. For risk analyses, we estimated dangerous area by use of the RocFall software. Furthermore, the dangers of falling rocks for the vehicles passing the Lashotor pass are estimated according to rockfall hazard rating system.

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Microseismic activity analysis for the study of the rupture mechanisms in unstable rock masses

Natural Hazards and Earth System Science ◽

10.5194/nhess-10-831-2010 ◽

2010 ◽

Vol 10 (4) ◽

pp. 831-841 ◽

Cited By ~ 56

Author(s):

D. Amitrano ◽

M. Arattano ◽

M. Chiarle ◽

G. Mortara ◽

C. Occhiena ◽

...

Keyword(s):

Monitoring System ◽

Rock Slope ◽

Western Alps ◽

Permafrost Degradation ◽

High Mountains ◽

Significant Damage ◽

First Results ◽

Microseismic Activity ◽

North Western

Abstract. Rockfalls are common instabilities in alpine areas and can cause significant damage. Since high mountains have been affected by an increasing number of these phenomena in the last years, a possible correlation with permafrost degradation induced by climate change has been hypothesized. To investigate this topic, a monitoring system, made of 5 triaxial geophones and 1 thermometer, was installed in 2007 at the Carrel hut (3829 m a.s.l., Matterhorn, North-western Alps), in the frame of the Interreg IIIA Alcotra project n. 196 "Permadataroc". The preliminary data processing relates to the classification of recorded signals, the identification of the significant microseismic events and the analysis of their distribution in time and space. The first results indicated a possible correlation between clusters of events and temperature trend, and a concentration of events in specific sectors of the rock mass. Research is still in progress. The recording of data for a longer period is planned to fully understand seasonal trends and spatial distribution of microseismic activity, and possible relations with permafrost degradation. Nevertheless, the preliminary observations prove that the monitoring system can detect noises generated by rock slope deformation. Once fully developed, this technique could become a helpful tool for early warning and preliminary stability assessments.

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Multiple rock-slope failures from Mannen in Romsdal Valley, western Norway, revealed from Quaternary geological mapping and 10Be exposure dating

The Holocene ◽

10.1177/0959683618798165 ◽

2018 ◽

Vol 28 (12) ◽

pp. 1841-1854 ◽

Cited By ~ 13

Author(s):

Paula Hilger ◽

Reginald L Hermanns ◽

John C Gosse ◽

Benjamin Jacobs ◽

Bernd Etzelmüller ◽

...

Keyword(s):

Slope Failure ◽

Rock Slope ◽

Significant Risk ◽

Geological Mapping ◽

Slope Instability ◽

Permafrost Degradation ◽

Geomorphological Mapping ◽

Exposure Dating ◽

Western Norway ◽

Air Temperatures

Oversteepened valley walls in western Norway have high recurrences of Holocene rock-slope failure activity causing significant risk to communities and infrastructure. Deposits from six to nine catastrophic rock-slope failure (CRSF) events are preserved at the base of the Mannen rock-slope instability in the Romsdal Valley, western Norway. The timing of these CRSF events was determined by terrestrial cosmogenic nuclide dating and relative chronology due to mapping Quaternary deposits. The stratigraphical chronology indicates that three of the CRSF events occurred between 12 and 10 ka, during regional deglaciation. Congruent with previous investigations, these events are attributed to the debuttressing effect experienced by steep slopes following deglaciation, during a period of paraglacial relaxation. The remaining three to six CRSF events cluster at 4.9 ± 0.6 ka (based on 10 cosmogenic 10Be samples from boulders). CRSF events during this later period are ascribed to climatic changes at the end of the Holocene thermal optimum, including increased precipitation rates, high air temperatures and the associated degradation of permafrost in rock-slope faces. Geomorphological mapping and sedimentological analyses further permit the contextualisation of these deposits within the overall sequence of post-glacial fjord-valley infilling. In the light of contemporary climate change, the relationship between CRSF frequency, precipitation, air temperature and permafrost degradation may be of interest to others working or operating in comparable settings.

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Permafrost distribution in steep rock slopes in Norway: measurements, statistical modelling and implications for geomorphological processes

Earth Surface Dynamics ◽

10.5194/esurf-7-1019-2019 ◽

2019 ◽

Vol 7 (4) ◽

pp. 1019-1040 ◽

Cited By ~ 6

Author(s):

Florence Magnin ◽

Bernd Etzelmüller ◽

Sebastian Westermann ◽

Ketil Isaksen ◽

Paula Hilger ◽

...

Keyword(s):

Rock Slope ◽

Multiple Linear Regression Model ◽

Permafrost Degradation ◽

Rock Slopes ◽

Northern Norway ◽

Precise Knowledge ◽

Discontinuous Permafrost ◽

Southern Norway ◽

Steep Slopes ◽

North And South

Abstract. Permafrost in steep rock slopes has been increasingly studied since the early 2000s in conjunction with a growing number of rock slope failures, which likely resulted from permafrost degradation. In Norway, rock slope destabilization is a widespread phenomenon and a major source of risk for the population and infrastructure. However, a lack of precise knowledge of the permafrost distribution in steep slopes hinders the assessment of its role in these destabilizations. This study proposes the first nationwide permafrost probability map for the steep slopes of Norway (CryoWall map). It is based on a multiple linear regression model fitted with multi-annual rock surface temperature (RST) measurements, collected at 25 rock slope sites, spread across a latitudinal transect (59–69∘ N) over mainland Norway. The CryoWall map suggests that discontinuous permafrost widely occurs above 1300–1400 and 1600–1700 m a.s.l. in the north and south rock faces of southern Norway (59∘ N), respectively. This lower altitudinal limit decreases in northern Norway (70∘ N) by about 500±50 m, with a more pronounced decrease for south faces, as a result of the insolation patterns largely driven by midnight sun in summer and polar night in winter. Similarly, the mean annual RST differences between north and south faces of similar elevation range around 1.5 ∘C in northern Norway and 3.5 ∘C in southern Norway. The CryoWall map is evaluated against direct ice observations in steep slopes and discussed in the context of former permafrost studies in various types of terrain in Norway. We show that permafrost can occur at much lower elevations in steep rock slopes than in other terrains, especially in north faces. We demonstrate that the CryoWall map is a valuable basis for further investigations related to permafrost in steep slopes in terms of both practical concerns and fundamental science.

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Repeat Glacier Collapses and Surges in the Amney Machen Mountain Range, Tibet, Possibly Triggered by a Developing Rock-Slope Instability

Remote Sensing ◽

10.3390/rs11060708 ◽

2019 ◽

Vol 11 (6) ◽

pp. 708 ◽

Cited By ~ 6

Author(s):

Frank Paul

Keyword(s):

Satellite Data ◽

Temperature Increase ◽

Rock Slope ◽

Slope Instability ◽

Mountain Range ◽

Rock Slopes ◽

Direct Response ◽

Hill Slope ◽

Eastern Tibet ◽

Regional Temperature

Collapsing valley glaciers leaving their bed to rush down a flat hill slope at the speed of a racing car are so far rare events. They have only been reported for the Kolkaglacier (Caucasus) in 2002 and the two glaciers in the Aru mountain range (Tibet) that failed in 2016. Both events have been studied in detail using satellite data and modeling to learn more about the reasons for and processes related to such events. This study reports about a series of so far undocumented glacier collapses that occurred in the Amney Machen mountain range (eastern Tibet) in 2004, 2007, and 2016. All three collapses were associated with a glacier surge, but from 1987 to 1995, the glacier surged without collapsing. The later surges and collapses were likely triggered by a progressing slope instability that released large amounts of ice and rock to the lower glacier tongue, distorting its dynamic stability. The surges and collapses might continue in the future as more ice and rock is available to fall on the glacier. It has been speculated that the development is a direct response to regional temperature increase that destabilized the surrounding hanging glaciers. However, the specific properties of the steep rock slopes and the glacier bed might also have played a role.

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STABILITY OF RUBBLE MOUND BREAKWATERS WITH A BERM

Coastal Engineering Proceedings ◽

10.9753/icce.v33.structures.10 ◽

2012 ◽

Vol 1 (33) ◽

pp. 10

Author(s):

Marcel Van Gent ◽

Gregory M. Smith ◽

Ivo Van der Werf

Keyword(s):

Rock Slope ◽

Slope Angle ◽

Rock Slope Stability ◽

Rock Slopes ◽

Test Results ◽

Physical Model Tests ◽

Rubble Mound ◽

The Stability ◽

Rubble Mound Breakwaters ◽

Rock Size

The stability of rock slopes with a horizontal berm has been studied by means of physical model tests. This paper is focussed on the rock slope stability of the slopes above and below the berm. By applying a berm the rock size can be reduced compared to the required rock size for a straight slope without a berm. This reduction can be significant for the slope above the berm. The influence of the slope angle (1:2 and 1:4), the width of the berm, the level of the berm, and the wave steepness have been investigated. Based on the test results prediction formulae have been derived to quantify the required rock size for rubble mound breakwaters with a berm.

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Towards a benchmark mechanical model for warming permafrost rock slopes

10.5194/egusphere-egu2020-17616 ◽

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

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.&#160;&#160;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,&#160; rock and ice-mechanical strength between -5&#176;C and -0.0&#176;C.&#160; Approaches&#160; 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.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).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 m&#179; 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).&#160;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.

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Discrete Element Modelling of Complex Failure Mechanism at Quarry Slope

Jurnal Teknologi ◽

10.11113/jt.v72.4010 ◽

2015 ◽

Vol 72 (3) ◽

Cited By ~ 1

Author(s):

Rini A Abdullah ◽

Mohd For Mohd Amin ◽

Ahmad S.A. Rashid ◽

S.M. Yahya

Keyword(s):

Slope Stability ◽

Failure Mechanism ◽

Rock Slope ◽

Water Pressure ◽

Research Work ◽

Slope Angle ◽

Discrete Element ◽

Slope Instability ◽

Open Pit ◽

Open Pit Mining

Road cutting, open pit mining, quarrying and various other constructions in hilly terrain demand special attention in terms of slope stability. The analysis of slope stability is of great significance not only for ensuring safe design of excavated slope, but also for preventing potential hazards. This research was undertaken to identify the controlling parameters affecting the slope instability. As the rock slope behaviour is mostly governed by discontinuities, discontinuum numerical technique such as Discrete Element Method (DEM) which has the ability to address discontinuity controlled instability is well suited for this case. This study investigated the failure pattern and its responsible factors leading to failure of a slope at a slate quarry situated in Wales, United Kingdom as a case study. The research work consisted of field investigation, laboratory experiments and parametric analysis by powerful and renowned distinct element computational tool Universal Discrete Element Code (UDEC). Evidence showed that complex failure mechanism involving distinct planar sliding surface along with block-flexural toppling contributed to the instability at the studied slate quarry. Dip of discontinuity, presence of water, weathering state and slope angle were the significant factors found in this study to have profound impact on controlling rock slope instability. The modelling results also indicated that the influence of structurally dipping at 78° of cleavage in slate and the water filling in the crack which developed excess water pressure have triggered the failure.

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Influences of Joint Persistence and Groundwater on Wedge Failure Potential of Jointed Rock Slope

10.5194/egusphere-egu2020-7303 ◽

2020 ◽

Author(s):

Yu-Hsuan Chang ◽

Cheng-Han Lin ◽

Ming-Lang Lin

Keyword(s):

Rock Slope ◽

Water Pressure ◽

Jointed Rock ◽

Slope Instability ◽

Rock Slope Stability ◽

Rock Slopes ◽

Wedge Failure ◽

Large Landslide ◽

Potential Failure ◽

The Stability

Joint persistence and groundwater are critical factors that influence the stability of rock slope. Persistence dominates the extent of pre-existing potential failure surfaces. Under certain conditions, slope instability may vary with time, as the propagation of existing joints leads to the development of fully persistence failure surfaces. At the same time, groundwater may travel through the fracture network and provides an external force to unstable rock masses, resulting in the damage of rock slope failure hard to predict. In general, when a rock slope consists of two or more sets of joints, the wedge failure often becomes the initial structurally controlled failure of a progressive large landslide. A classic case, which was occurred at a steep cut rock slope on 32.5k, Provincial Highway 7, Taiwan, had been completely recorded with UAV-surveys, field investigations and witness. The landslide first occurred on 13th May 2019 as a wedge failure with the magnitude of the volume of 892 m3 and resulted in a large landslide on 29th July 2019 with the magnitude of the volume of 37234 m3, destroyed the protection measures and roads. According to the field investigation, groundwater was discovered flowing out from the line of intersection of persistence joints, which could be the main reason leads to the wedge failure and the progressive large rockslide. Hence, the couple mechanics-hydraulic behavior in a rock slope should be studied in more detail to mitigate such hazards.In this study, sandbox model was applied to clarify the effects of the groundwater and joint friction on failures of single rock wedge. In addition, the software 3DEC, which is based on Distinct Element method, was carried out to extent the analysis conditions. The results of sandbox simulations were used to calibrate the performance of the numerical model, especially the coupled hydro-mechanical analysis. The stability of jointed rock slopes under different persistence and various water pressure conditions has been studied. It is believed that the study can enhance the way for stability analysis and monitoring of the potential failure of jointed rock slopes.Keywords: Wedge failure; Joint persistence; Groundwater; Rock slope stability.&#160;

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