Rock slope failure in a recently deglaciated permafrost rock wall at Piz Kesch (Eastern Swiss Alps), February 2014

Abstract. Instability and failure of high mountain rock slopes have significantly increased since the 1990s coincident with climatic warming and are expected to rise further. Most of the observed failures in permafrost-affected rock walls are likely triggered by the mechanical destabilisation of warming bedrock permafrost including ice-filled joints. The failure of ice-filled rock joints has only been observed in a small number of experiments, often using concrete as a rock analogue. Here, we present a systematic study of the brittle shear failure of ice and rock–ice interfaces, simulating the accelerating phase of rock slope failure. For this, we performed 141 shearing experiments with rock–ice–rock “sandwich”' samples at constant strain rates (10−3 s−1) provoking ice fracturing, under normal stress conditions ranging from 100 to 800 kPa, representing 4–30 m of rock overburden, and at temperatures from −10 to −0.5 ∘C, typical for recent observed rock slope failures in alpine permafrost. To create close to natural but reproducible conditions, limestone sample surfaces were ground to international rock mechanical standard roughness. Acoustic emission (AE) was successfully applied to describe the fracturing behaviour, anticipating rock–ice failure as all failures are predated by an AE hit increase with peaks immediately prior to failure. We demonstrate that both the warming and unloading (i.e. reduced overburden) of ice-filled rock joints lead to a significant drop in shear resistance. With a temperature increase from −10 to −0.5 ∘C, the shear stress at failure reduces by 64 %–78 % for normal stresses of 100–400 kPa. At a given temperature, the shear resistance of rock–ice interfaces decreases with decreasing normal stress. This can lead to a self-enforced rock slope failure propagation: as soon as a first slab has detached, further slabs become unstable through progressive thermal propagation and possibly even faster by unloading. Here, we introduce a new Mohr–Coulomb failure criterion for ice-filled rock joints that is valid for joint surfaces, which we assume similar for all rock types, and which applies to temperatures from −8 to −0.5 ∘C and normal stresses from 100 to 400 kPa. It contains temperature-dependent friction and cohesion, which decrease by 12 % ∘C−1 and 10 % ∘C−1 respectively due to warming and it applies to temperature and stress conditions of more than 90 % of the recently documented accelerating failure phases in permafrost rock walls.

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Short Communication: Monitoring rockfalls with the Raspberry Shake

Earth Surface Dynamics ◽

10.5194/esurf-6-1219-2018 ◽

2018 ◽

Vol 6 (4) ◽

pp. 1219-1227 ◽

Cited By ~ 3

Author(s):

Andrea Manconi ◽

Velio Coviello ◽

Maud Galletti ◽

Reto Seifert

Keyword(s):

Seismic Data ◽

Slope Failure ◽

Rock Slope ◽

Low Cost ◽

General Information ◽

Swiss Alps ◽

Winter Period ◽

Critical Acceleration ◽

Progressive Rock ◽

Alpine Environments

Abstract. We evaluate the performance of the low-cost seismic sensor Raspberry Shake to identify and monitor rockfall activity in alpine environments. The test area is a slope adjacent to the Great Aletsch Glacier in the Swiss Alps, i.e. the Moosfluh deep-seated instability, which has recently undergone a critical acceleration phase. A local seismic network composed of three Raspberry Shake was deployed starting from May 2017 in order to record rockfall activity and its relation with the progressive rock-slope degradation potentially leading to a large rock-slope failure. Here we present a first assessment of the seismic data acquired from our network after a monitoring period of 1 year. We show that our network performed well during the whole duration of the experiment, including the winter period in severe alpine conditions, and that the seismic data acquired allowed us to clearly discriminate between rockfalls and other events. This work also provides general information on the potential use of such low-cost sensors in environmental seismology.

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Short Communication: Monitoring rock falls with the Raspberry Shakes

10.5194/esurf-2018-62 ◽

2018 ◽

Author(s):

Andrea Manconi ◽

Velio Coviello ◽

Maud Galletti ◽

Reto Seifert

Keyword(s):

Seismic Data ◽

Slope Failure ◽

Rock Slope ◽

Low Cost ◽

Late Summer ◽

Swiss Alps ◽

Rock Fall ◽

Rock Falls ◽

Monitoring Period ◽

Seismic Sensors

Abstract. We evaluate the performance of the low-cost seismic sensors Raspberry Shake (RS) to identify and monitor rock fall activity in alpine environments. The test area is a slope adjacent to the Great Aletsch glacier in the Swiss Alps, i.e. the Moosfluh deep-seated instability, which is undergoing an acceleration phase since the late summer 2016. A local seismic network composed of three RS seismometers was deployed starting from May 2017, in order to record rock fall activity and its relation with the progressive rock slope degradation potentially leading to a large rock slope failure. Here we present a first assessment of the seismic data acquired from RS sensors after a monitoring period of 1-year. A webcam was installed on the opposite side of the active slope, acquiring images every 10 minutes to validate the occurrence and identify rock falls as well as their location and approximate size. Despite seismic data were collected mainly to identify rock fall phenomena, other event types were recorded during the monitoring period. Thus, this work provides also general insights on the potential use of low cost sensors in environmental seismology investigations.

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A temperature- and stress-controlled failure criterion for ice-filled permafrost rock joints

10.5194/tc-2018-57 ◽

2018 ◽

Cited By ~ 2

Author(s):

Philipp Mamot ◽

Samuel Weber ◽

Tanja Schröder ◽

Michael Krautblatter

Keyword(s):

Failure Criterion ◽

Slope Failure ◽

Rock Slope ◽

Shear Failure ◽

Shear Resistance ◽

Stress Conditions ◽

Rock Joints ◽

Normal Stresses ◽

Permafrost Rock ◽

Limestone Sample

Abstract. Instability and failure of permafrost-affected rock slopes have significantly increased coincident to warming in the last decades. Most of the observed failures in permafrost-affected rock walls are likely triggered by the mechanical destabilisation of warming bedrock permafrost including effects in ice-filled joints. The failure of ice-filled rock joints has only been observed in a small number of experiments, often using concrete as a rock analogue. Here, we present a systematic study of the brittle shear failure of ice and rock-ice interfaces, simulating the accelerating phase of rock slope failure. For this, we performed 141 shear experiments with rock-ice-rock sandwich samples at constant strain rates provoking ice fracturing (10−3 s−1), under relevant stress conditions ranging from 100 to 800 kPa, i.e. 4–30 m rock overburden, and at temperatures from −10 to −0.5 °C, typical for recent rock slope failures in alpine permafrost. To create close to natural but reproducible conditions, limestone sample surfaces were ground to international rock mechanical standard roughness. Acoustic emission (AE) was successfully applied to describe the fracturing behaviour, anticipating rock-ice failure as all failures are predated by an AE hit increase with peaks immediately prior to failure. We demonstrate that both, the warming and unloading (i.e. reduced overburden) of ice-filled rock joints lead to a significant drop in shear resistance. With a temperature increase from −10 °C to −0.5 °C, the shear stress at failure reduces by 64–78 % for normal stresses of 100–400 kPa. At a given temperature, the shear resistance of rock-ice interfaces decreases with decreasing normal stress. This can lead to a self-enforced rock slope failure propagation: as soon as a first slab has detached, further slabs become unstable through progressive thermal propagation and possibly even faster by unloading. Here, we introduce a new Mohr-Coulomb failure criterion for ice-filled rock joints that is valid for joint surfaces which we assume similar for all rock types, and which applies to temperatures from −8 to −0.5 °C and normal stresses from 100 to 400 kPa. It contains a temperature-dependent friction and cohesion which decrease by 12 %/°C and 10 %/°C respectively due to warming and it applies to temperature and stress conditions of more than 90 % of the recently documented accelerating failure phases in permafrost rock walls.

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Does climate change influence the frequency of large rock slope failures?

10.5194/egusphere-egu2020-7361 ◽

2020 ◽

Author(s):

Simon Loew ◽

Nora Buehler ◽

Jordan Aaron

Keyword(s):

Slope Failure ◽

Rock Slope ◽

Negative Temperature ◽

Climatic Conditions ◽

Swiss Alps ◽

Rock Fall ◽

Mean Annual Temperature ◽

European Alps ◽

Depth Range ◽

Slope Failures

A large number of scientific contributions (e.g. BAFU 2017, Speicher 2017, Phillips et al. 2017, Ravanel et al. 2017, Haque et al. 2016) have suggested that many recent rock slope failures in the European Alps have been triggered by climate warming. For example, Huggel et al. 2012 and Fischer et al. 2012 could show that rock fall frequencies above 2000 masl increased significantly since 1990 at regional (Swiss Alps and adjacent areas) and local (Mont Blanc) scale, based on 52 events larger than 1000 m3 (PERMOS data base) covering the period 1900-2010. This increase in frequency could be correlated with a significant departure of mean annual temperature from the 1960&#8211;1990 average, based on a dataset describing conditions in Switzerland. Paranunzio et al. 2016 systematically studied the climatic conditions and anomalies occurring before 41 rock fall events in the Italian Alps with volumes of several hundred to several million m3. They show that positive and negative temperature anomalies triggered the majority of analysed rock fall events in a complex manner, but that melting of permafrost was clearly not the only rock fall trigger.However, there have been no studies which systematically investigate changes in the frequency of rock fall events based on complete inventories covering a large range of rock fall volumes. To fill this gap, we have generated a new database for rapid rock slope failures in the Swiss Alps covering events larger than 100&#8217;000 m3 (B&#252;hler 2019, BSc Thesis ETH 2019). This catalogue covers the period between 1700 and 2019 and includes 86 events with reliably estimated volume, date and location of occurrence, and pre-disposing factors (such as slope orientation, permafrost occurrence and geological setting). Volume-cumulative frequency plots of the events demonstrate completeness of the catalogue for all size classes, and significant changes in the ratios between large and small events through time.An enhanced frequency of the volume class of 105 m3 (100&#8217;000-999&#8217;000 m3) is observed starting from 1940, predominantly occurring in permafrost areas and elevations ranging between 2800 and 3200 masl. This increasing frequency signal with time disappears for increasing volumes beyond a magnitude of about 400&#8217;000 m3 and is clearly absent for very large rock slope failure of millions to tens of millions of m3.The volume dependence of climate sensitivity can be physically explained, as larger volume slope failures tend to have deeper failure surfaces. Typical failure depth for multi-million m3 slope failures in crystalline rocks are up to a few 100 meters, and beyond the depth of Alpine permafrost. Direct impacts of surface temperature changes on permafrost are mainly manifested through a minor thickening of the active layer, typically ranging between 1 and 10 meters, but indirect effects at the depth range of decameters (i.e. the depth of failure surfaces for events of the 105 m3 class) have been assessed and demonstrated in a large number of studies.

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ROCK SLOPE SURFACE STABILITY ANALYSIS: A CASE STUDY ON HON LON ISLAND, KIEN HAI DISTRICT, KIEN GIANG PROVINCE, VIETNAM

Journal of Southwest Jiaotong University ◽

10.35741/issn.0258-2724.56.5.29 ◽

2021 ◽

Vol 56 (5) ◽

pp. 340-350

Author(s):

Ngoc Binh Vu ◽

Truong Thanh Phi ◽

Thanh Cong Nguyen ◽

Hong Thinh Phi ◽

Quy Nhan Pham ◽

...

Keyword(s):

Slope Failure ◽

Rock Slope ◽

Slope Surface ◽

Plane Failure ◽

Surface Stability ◽

Average Percentage ◽

The Road ◽

Wedge Failure ◽

Analytical Results

The research aimed to study 24 rock slope surfaces along the road around Hon Lon Island, Kien Hai district, Kien Giang province, Vietnam. The analytical results have determined slope failure, wedge failure, and toppling, which occurred on almost slope surface and the average percentage of plane failure is the largest. The average percent of plane failure is 19.23%, the wedge failure is 15.35%, and the toppling fault is 6.73%. Besides, the analytical results have also identified the slope surfaces which can be the key blocks: ND-13, 18, 23, 25, 34, 37, 45, 51, 62, 63. The other analytical results show that the existence of key blocks at the rock slope surfaces in the N-S direction, dip to E at the survey locations: ND-13, 23, 63 and dip to W at the survey locations: ND-37, 45; in the NE-SW direction, dip to SE at the survey locations: ND-15, 62 and dip to NW at the survey locations: ND-18, 34; in the NW-SE direction, dip to SW at the survey location ND-51. These results have important significance to support for protecting slope surface safety.

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High alpine rock-wall retreat rates over millennia through thermo-cryogenic pre-conditioned rock fall (Mt. Eiger, Switzerland)

10.5194/egusphere-egu21-5908 ◽

2021 ◽

Author(s):

David Mair ◽

Alessandro Lechmann ◽

Romain Delunel ◽

Serdar Yeşilyurt ◽

Dmitry Tikhomirov ◽

...

Keyword(s):

Swiss Alps ◽

Rock Fall ◽

Rock Wall ◽

Rock Face ◽

Depth Profiles ◽

Weathering Processes ◽

Temperature Conditions ◽

Low Efficiency ◽

Cryogenic Processes

Rock fall processes of various size and magnitude control retreat rates of high alpine rock-walls. For millennial time scales, these retreat rates can be quantified in-situ from concentrations of cosmogenic nuclides along bedrock depth profiles (Mair et al., 2019). We measured cosmogenic 36Cl and 10Be along several such profiles at Mt Eiger in the Central Swiss Alps to study the local rock-wall retreat on this time scale (Mair et al., 2019; 2020). The resulting spatial pattern shows that rock-wall retreat rates are low (0.5 to 0.6 &#177; 0.1 mm/yr) in the higher region of the NW rock-wall, in contrast to both the lower part of the NW rock-wall and the SE face, where rates are high (1.7 &#177; 0.4 to 3.5 &#177; 1.4 mm/yr). We link these retreat rates to differences in local temperature conditions, because the patterns of faults and fractures and the lithology of the bedrock are similar at all sites, and thermo-cryogenic processes are known to weaken the bedrock through fracturing, thereby preconditioning the occurrence of rock fall (e.g., Draebing and Krautblatter, 2019). However, it is still unclear how effective and at which rate individual thermo-cryogenic processes contribute to the preconditioning through fracturing. Therefore, we investigate several processes and estimate the probability of bedrock fracturing through the employment of a theoretical frost-cracking model, which predicts cracking intensity from ice segregation. The model results infer a low efficiency in the higher region of the NW rock-wall, but a relatively high one in the lower section of the NW wall and on the SE rock face of Mt. Eiger. Although the model is rather generic, the results disclose a significant control of temperature conditions on the erosional processes and rates. Furthermore, temperature conditions for the last millennia have been similar to present day conditions, as our reconstructions disclose, therefore the cosmogenic-nuclide-based long-term differences in rock-wall retreat rates predominantly stem from large contrasts in the microclimate between the NW and SE walls of Mt. Eiger. Accordingly, the site-specific differences in microclimate conditions could explain the lower retreat rates in the upper part of the NW rock-wall and the rapid retreat in the SW face and in the lower part of the NW rock face.ReferencesDraebing, D. and Krautblatter, M.: The Efficacy of Frost Weathering Processes in Alpine Rockwalls, Geophys. Res. Lett., 46, 6516&#8211;6524, doi:10.1029/2019GL081981, 2019.Mair, D., Lechmann, A., Yesilyurt, S., Tikhomirov, D., Delunel, R., Vockenhuber, C., Ak&#231;ar, N. and Schlunegger, F.: Fast long-term denudation rate of steep alpine headwalls inferred from cosmogenic 36Cl depth profiles, Sci. Rep., 9, 11023, doi:10.1038/s41598-019-46969-0, 2019.Mair, D., Lechmann, A., Delunel, R., Ye&#351;ilyurt, S., Tikhomirov, D., Vockenhuber, C., Christl, M., Ak&#231;ar, N. and Schlunegger, F.: The role of frost cracking in local denudation of steep Alpine rockwalls over millennia (Eiger, Switzerland), Earth Surf. Dyn., 8, 637&#8211;659, doi:10.5194/esurf-8-637-2020, 2020.

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Palaeoclimatic and morphodynamic implications of Holocene boulder-dominated periglacial and paraglacial landforms in Rondane, South Norway

10.5194/egusphere-egu21-12172 ◽

2021 ◽

Author(s):

Philipp Marr ◽

Stefan Winkler ◽

Svein Olaf Dahl ◽

Jörg Löffler

Keyword(s):

Slope Failure ◽

Rock Slope ◽

Control Point ◽

Alluvial Fan ◽

Age Dating ◽

The Holocene ◽

Holocene Thermal Maximum ◽

Exposure Age ◽

Thermal Maximum ◽

Exposure Ages

Periglacial, paraglacial and related boulder-dominated landforms constitute a valuable, but often unexplored source of palaeoclimatic and morphodynamic information. The timing of landform formation and stabilization can be linked to past cold climatic conditions which offers the possibility to reconstruct cold climatic periods. In this study, Schmidt-hammer exposure-age dating (SHD) was applied to a variety of boulder-dominated landforms (sorted stripes, blockfield, paraglacial alluvial fan, rock-slope failure) in Rondane, eastern South Norway for the first time. On the basis of an old and young control point a local calibration curve was established from which surface exposure ages of each landform were calculated. The investigation of formation, stabilization and age of the respective landforms permitted an assessment of Holocene climate variability in Rondane and its connectivity to landform evolution. The obtained SHD age estimates range from 11.15 &#177; 1.22 to 3.99 &#177; 1.52 ka which shows their general inactive and relict character. Most surface exposure ages of the sorted stripes cluster between 9.62 &#177; 1.36 and 9.01 &#177; 1.21 ka and appear to have stabilized towards the end of the &#8216;Erdalen Event&#8217; or in the following warm period prior to &#8216;Finse Event&#8217;. The blockfield age with 8.40 &#177; 1.16 ka indicates landform stabilization during &#8216;Finse Event&#8217;, around the onset of the Holocene Thermal Maximum (~8.0&#8211;5.0 ka). The paraglacial alluvial fan with its four subsites shows age ranges from 8.51 &#177; 1.63 to 3.99 &#177; 1.52 ka. The old exposure age points to fan aggradation follow regional deglaciation due to paraglacial processes, whereas the younger ages can be explained by increasing precipitation during the onset neoglaciation at ~4.0 ka. Surface exposure age of the rock-slope failure with 7.39 &#177; 0.74 ka falls into a transitional climate period towards the Holocene Thermal Maximum (~8.0&#8211;5.0 ka). This indicates that climate-driven factors such as decreasing permafrost depth and/or increasing hydrological pressure negatively influence slope stability. Our obtained first surface exposure ages from boulder-dominated landforms in Rondane give important insights to better understand the palaeoclimatic variability in the Holocene.

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Combined rock slope stability and shallow landslide susceptibility assessment of the Jasmund cliff area (Rügen Island, Germany)

Natural Hazards and Earth System Science ◽

10.5194/nhess-9-687-2009 ◽

2009 ◽

Vol 9 (3) ◽

pp. 687-698 ◽

Cited By ~ 27

Author(s):

A. Günther ◽

C. Thiel

Keyword(s):

Slope Stability ◽

Landslide Susceptibility ◽

Slope Failure ◽

Rock Slope ◽

Shallow Landslide ◽

Material Strength ◽

Spatial Integration ◽

Inventory Data ◽

Susceptibility Analysis ◽

Susceptibility Model

Abstract. In this contribution we evaluated both the structurally-controlled failure susceptibility of the fractured Cretaceous chalk rocks and the topographically-controlled shallow landslide susceptibility of the overlying glacial sediments for the Jasmund cliff area on Rügen Island, Germany. We employed a combined methodology involving spatially distributed kinematical rock slope failure testing with tectonic fabric data, and both physically- and inventory-based shallow landslide susceptibility analysis. The rock slope failure susceptibility model identifies areas of recent cliff collapses, confirming its value in predicting the locations of future failures. The model reveals that toppling is the most important failure type in the Cretaceous chalk rocks of the area. The shallow landslide susceptibility analysis involves a physically-based slope stability evaluation which utilizes material strength and hydraulic conductivity data, and a bivariate landslide susceptibility analysis exploiting landslide inventory data and thematic information on ground conditioning factors. Both models show reasonable success rates when evaluated with the available inventory data, and an attempt was made to combine the individual models to prepare a map displaying both terrain instability and landslide susceptibility. This combination highlights unstable cliff portions lacking discrete landslide areas as well as cliff sections highly affected by past landslide events. Through a spatial integration of the rock slope failure susceptibility model with the combined shallow landslide assessment we produced a comprehensive landslide susceptibility map for the Jasmund cliff area.

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Comprehensive Method to Test the Stability of High Bedding Rock Slop Subjected to Atomized Rain

Applied Sciences ◽

10.3390/app10051577 ◽

2020 ◽

Vol 10 (5) ◽

pp. 1577

Author(s):

Zheng-jun Hou ◽

Bao-quan Yang ◽

Lin Zhang ◽

Yuan Chen ◽

Geng-xin Yang

Keyword(s):

Slope Failure ◽

Rock Slope ◽

Evaluation Method ◽

Failure Modes ◽

Similarity Theory ◽

Fem Simulation ◽

Strength Reduction ◽

Comprehensive Method ◽

The Stability ◽

Bedding Rock Slope

In the construction of high dams, many high rock slope failures occur due to flood discharge atomized rain. Based on the steel frame lifting technique and strength reduction materials, a comprehensive method is proposed in this paper to study the stability of high bedding rock slope subjected to atomized rain. The safety factor expression of the comprehensive method and the evaluation method for deformation instability were established according to the similarity theory of geomechanical model, failure criterion, and mutation theory. Strength reduction materials were developed to simulate the strength reduction of structural planes caused by rainfall infiltration. A typical test was carried out on the high bedding rock slope in the Baihetan Hydropower Station. The results showed that the failure modes of the bedding rock slope were of two types: sliding–fracturing and fracturing–sliding. The first slip block at the exposed place of the structural plane was sliding–fracturing. Other succeeding slip blocks were mainly of the fracturing–sliding type due to the blocking effect of the first slip block. The failure sequence of the slip blocks along the structural planes was graded into multiple levels. The slip blocks along the upper structural planes were formed first. Concrete plugs had effective reinforcement to improve the shear resistance of the structural planes and inhibit rock dislocation. Finite element method (FEM) simulation was also performed to simulate the whole process of slope failure. The FEM simulation results agreed well with the test results. This research provides an improved understanding of the physical behavior and the failure modes of high bedding rock slopes subjected to atomized rain.

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