Formation processes, geomechanical characterisation and buttressing effects at the toe of deep-seated rock slides in foliated metamorphic rock

Zangerl, Christian; Chwatal, Werner; Kirschner, H.

doi:10.1016/j.geomorph.2015.03.030

Cited by 12 publications

(19 citation statements)

References 16 publications

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“…Both features are typical for deep-seated rockslides and were frequently mapped on surface as either downhill-or uphill-facing scarps or explored in the subsurface by boreholes as shear zones composed of low-strength fault breccias and gouges (Rechberger et al, 2021;Strauhal et al, 2017). The formation of slabs is a further indicator for increased fracturing and loosening of the rockslide mass, and it was determined by several case studies in crystalline rocks (Bonzanigo et al, 2007;Glueer et al, 2019;Zangerl et al, 2019). The obtained rock mass strength degradation process can be understood as the consequence of a complex interaction between pre-existing joints and brittle fracture propagation through intact rock bridges, herein modelled as block failure.…”

Section: Geomechanical Modellingmentioning

confidence: 99%

Geographic-information-system-based topographic reconstruction and geomechanical modelling of the Köfels rockslide

Zangerl

Schneeberger

Steiner

et al. 2021

Nat. Hazards Earth Syst. Sci.

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Abstract. The Köfels rockslide in the Ötztal Valley (Tyrol, Austria) represents the largest known extremely rapid landslide in metamorphic rock masses in the Alps. Although many hypotheses for the trigger were discussed in the past, until now no scientifically proven trigger factor has been identified. This study provides new data about the (i) pre-failure and failure topography, (ii) failure volume and porosity of the sliding mass, and (iii) numerical models on initial deformation and failure mechanism, as well as shear strength properties of the basal shear zone obtained by back-calculations. Geographic information system (GIS) methods were used to reconstruct the slope topographies before, during and after the event. Comparing the resulting digital terrain models leads to volume estimates of the failure and deposition masses of 3100 and 4000 million m3, respectively, and a sliding mass porosity of 26 %. For the 2D numerical investigation the distinct element method was applied to study the geomechanical characteristics of the initial failure process (i.e. model runs without a basal shear zone) and to determine the shear strength properties of the reconstructed basal shear zone. Based on numerous model runs by varying the block and joint input parameters, the failure process of the rock slope could be plausibly reconstructed; however, the exact geometry of the rockslide, especially in view of thickness, could not be fully reproduced. Our results suggest that both failure of rock blocks and shearing along dipping joints moderately to the east were responsible for the formation or the rockslide. The progressive failure process may have taken place by fracturing and loosening of the rock mass, advancing from shallow to deep-seated zones, especially by the development of internal shear zones, as well as localized domains of increased block failure. The simulations further highlighted the importance of considering the dominant structural features of the rock mass. Considering back-calculations of the strength properties, i.e. the friction angle of the basal shear zone, the results indicated that under no groundwater flow conditions, an exceptionally low friction angle of 21 to 24∘ or below is required to promote failure, depending on how much internal shearing of the sliding mass is allowed. Model runs considering groundwater flow resulted in approximately 6∘ higher back-calculated critical friction angles ranging from 27 to 30∘. Such low friction angles of the basal failure zone are unexpected from a rock mechanical perspective for this strong rock, and groundwater flow, even if high water pressures are assumed, may not be able to trigger this rockslide. In addition, the rock mass properties needed to induce failure in the model runs if no basal shear zone was implemented are significantly lower than those which would be obtained by classical rock mechanical considerations. Additional conditioning and triggering factors such as the impact of earthquakes acting as precursors for progressive rock mass weakening may have been involved in causing this gigantic rockslide.

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Section: Geomechanical Modellingmentioning

confidence: 99%

Geographic-information-system-based topographic reconstruction and geomechanical modelling of the Köfels rockslide

Zangerl

Schneeberger

Steiner

et al. 2021

Nat. Hazards Earth Syst. Sci.

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“…volume gain due to failure, computed similar to recommendations by Hungr and Evans (2004); Jaboyedoff et al (2019). The used 3D volume balancing (difference of elevation models, cf., Zangerl et al, 2015) stands in contrast to the standard 2D volume balance cross section method using one single cross section for a respective site ('section area balance', cf., Zangerl et al, 2015). The reason for the application of the 3D volume balance method is the central source zone of the failure together with the lateral expansion of the landslide mass at the foot of the slope, i.e.…”

Section: Slope Reconstructionmentioning

confidence: 99%

Dynamic numerical modelling of co-seismic landslides using the 3D distinct element method: Insights from the Balta rockslide (Romania)

Mreyen

Donati²,

Elmo³

et al. 2022

Engineering Geology

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“…During the Holocene, i.e. several thousand years after the Last Glacial Maximum (LGM), several deep-seated rock slides were formed in the Kaunertal valley region (Strauhal et al 2017;Zangerl et al 2010;Zangerl et al 2015). Like many rock slides in this region, the Bliggspitze rock slide originated in mica-rich meta-sedimentary rocks (i.e.…”

Section: Geological and (Peri-)glacial Characterisationmentioning

confidence: 99%

“…Typical geomorphological and structural features are stepped slope profiles, horst and graben structures, and/or secondary shear zones representing distinct boundaries of rock slide slabs/blocks of individual deformation and activity characteristics. As opposed to the formation of Bsingle block^rock slides, the deformation behaviour of compound rock slide systems composed of individual slabs is different and complex (Zangerl et al 2015). Herein, Brock slide slabs^are defined as individual parts of rock/soil masses which are delimited to other parts of the slide by shear zones composed of loose and non-cemented fault breccias and gouges.…”

Section: Introductionmentioning

confidence: 99%

“…These data can be obtained from different in situ methods, such as geomorphological and geological mapping, geophysical surveys, geodetic monitoring, and borehole drilling with geophysical logging, hydraulic packer testing, and inclinometer as well as piezometer measurements. Exemplarily, comprehensive rock slope investigations were performed at the Randa landslide in Switzerland (Willenberg et al 2008;Gischig 2011), La Saxe in Italy (Crosta et al 2014), La Clapiere in France (Palis et al 2017), and in the Kaunertal valley in Austria (Strauhal et al 2017;Zangerl et al 2010Zangerl et al , 2015. Although extremely useful and often a requirement for a comprehensive rock slide investigation campaign, these direct methods are costly and require direct access to the slide.…”

Section: Introductionmentioning

confidence: 99%

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Deformation characteristics and multi-slab formation of a deep-seated rock slide in a high alpine environment (Bliggspitze, Austria)

Zangerl

Fey

Prager

2019

Bull Eng Geol Environ

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This study presents the results of a more than 10-year-long field investigation and remote sensing monitoring campaign of a highly active deep-seated rock slide located in a glacial to periglacial environment (Bliggspitze, Tyrol, Austria). Data concerning (i) the terrain surface displacements based on imagery (webcam time-lapse, ortho-images) and both terrestrial and airborne laser scanning, and (ii) the geological-structural and geomorphological situation were analysed to develop a geological-geometrical model of the rock slide and to study the temporally variable activity behaviour and the formation of individual rock slide slabs. Results clearly show that at least seven rock slide slabs were formed at different times and under different slope stability conditions. Some of these rock slide slabs were displaced at slow to moderate velocities and reached scarp offsets of several tens of metres, whereas other, shallower slabs collapsed and formed extremely rapid rock falls and avalanches. Generally, the rock slide is affected by rock mass cataclasis, fracturing and loosening, which in turn cause extensive mass loss accompanied by debris accumulation at lower parts of the slope. The cause for the development of the Bliggspitze rock slide is poorly understood. However, there are clear indications that permafrost degradation and/or glacial retreat, particularly at the foot of the slide, during the recent decades may have adversely affected the slope stability situation. Keywords Deep-seated rock slide . Metamorphic rock . Rock slide slab formation . High alpine environment . Glacial changes . Remote sensing . Monitoring . Airborne and terrestrial laser scanning * C. Zangerl

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Formation processes, geomechanical characterisation and buttressing effects at the toe of deep-seated rock slides in foliated metamorphic rock

Cited by 12 publications

References 16 publications

Geographic-information-system-based topographic reconstruction and geomechanical modelling of the Köfels rockslide

Geographic-information-system-based topographic reconstruction and geomechanical modelling of the Köfels rockslide

Dynamic numerical modelling of co-seismic landslides using the 3D distinct element method: Insights from the Balta rockslide (Romania)

Deformation characteristics and multi-slab formation of a deep-seated rock slide in a high alpine environment (Bliggspitze, Austria)

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