Search

Rockslides in intercalated carbonate rocks are among the most common and hazardous rock slide types in the European Alps and other mountains worldwide. Progressive shear plane development in marly or clayey interlayered limestones is an issue of debate, especially since the disastrous 200 million m³ carbonate rockslide in Vajont in 1963. Since interlayers are often not persistently developed, the processes controlling the progressive shear plane evolution in carbonate rockslides affecting acceleration and deceleration phases are poorly understood. This paper discusses 20 years of progressive shear plane development in a 10 million m³ multi-unit rockslide with marly interlayers (Hornbergl, Austria). We present a two-decade kinematic record, complemented with field mapping, surface geodetical observations, subsurface geophysical investigations, rock and soil mechanical laboratory testing, a snow-referenced infiltration model, as well as a resulting discontinuum mechanical model. Monthly tape extensometer measurements (3,300 individual measurements) from 1996 to 2016, mapping and geodetic investigations reveal mean absolute displacement rates of 0.2–14.5 mm/month between multiple units of the translational rockslide, often separated by >20 m deep and meter-wide open fractures. Electrical resistivity tomography (ERT) uncovers the geological and structural setting of the upper 40 m of the rockslide’s inner structure. Laboratory analysis shows that full (100%) saturation of marly interlayers decreases the cohesion from 65 to 21 kPa in comparison to 50% saturation, presumably explaining seasonal velocity variations. Correspondingly, infiltration models including snow accumulation and melt appear to control movement patterns in some years after snow melt and after heavy convective rainfalls. Discontinuum mechanical models based on mapping, geophysical reconnaissance and mechanical laboratory testing show that the multi-unit rockslide is at the fringe of stability with 50% water saturation in marly interlayers and that strain rates rapidly accelerate with the cohesion loss upon their full water-saturation matching with the described kinematic record. Over multiple years, compression and decompression waves between rockslide units become a first order control for progressive rockslide development. Here we show in a 20-year multi-unit rockslide record, that infiltration after snowmelt and extreme precipitation may control monthly and seasonal patterns of carbonate rockslide deformation, but compression and decompression waves may become key control on a multiannual time scale for progressive destabilisation. [ABSTRACT FROM AUTHOR]

Displacement rates of mountain slope deformations that can affect entire valley mountain flanks are often measured spatially distributed in‐situ without spatial significance. The spatially explicit measurement and recording of time series of slope deformations is a challenge, as the unstable slopes are often disintegrated into several subdomains, which move with different deformation rates. The current state‐of‐the‐art monitoring systems detect slow to very slow deformation rates between mm/a and several m/a. Using the examples of slope deformations in Saalbach‐Hinterglemm and the deep rock slide Marzellkamm in Austria this paper presents the results of terrestrial laser scans, extensometer measurements, Spaceborne InSAR data, unmanned Aerial System Photogrammetry (UAS‐P), and fixed‐point measurements. The different measurements complement each other and are optimally aligned for different application areas. InSAR data can help to identify hot spots on regional and local scale, while UAS‐P enables for spatially high level accuracy in the detection of subdomains moving at different speeds. For local warning systems TLS, extensometers and GBInSAR deliver higher accuracy. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

The Fernpass rockslide occurred about 4100 years ago and is one of the largest rock slope failures in the Alps, the run-out area being characterized by a hummocky surface with Toma Hills that were formed after the rockslide event. These hills, characterized by a cone-like shape with a flattened top, are typical for many rockslides, and the name "Toma" is derived from local dialects in Switzerland and Tyrol, Austria. So far, five hypotheses have been proposed for the formation of Toma Hills, the two relating to glacial activity being outdated meanwhile. These hypotheses cannot explain all features observed on site. Therefore, to investigate one of these hypotheses, a qualitative laboratory-scale analogue groundwater flow model with the size 1.5 × 1 × 0.8 m was used to investigate the contribution of internal erosion by suffosion to forming Toma Hills. From the model, hydrogeological calculations of Darcy velocity and hydraulic conductivity were determined to help understand the present study. The average hydraulic gradient of the experiments was close to that in reality. Hydraulic conductivities in the five experiments were comparable to the calculated field hydraulic conductivity (Bialas and Seelheim equations). A limnokrene like one south-west of Biberwier developed in all experiments. Development of lateral and transversal cracks, water-filled lateral depressions of the material in the model and discharge of finer material implicated that internal erosion is a substantial contribution to the Toma Hill formation. Based on the experimental results, we deduce that Toma Hill formation took between 140 and 580 years. [ABSTRACT FROM AUTHOR]

Following a rockslide in a former quarry near the town of Dürnstein/Wachau, extensive remedial measures were necessary to restore the damaged rail infrastructure and ensure long term safety. To provide for safe working conditions during the phase of construction of additional protection measures, a geotechnical risk management system based on the observational method per EC 7 was developed and implemented. Geotechnical monitoring was a key safety management element. The paper discusses the specific challenges, practical approaches and general experiences associated with the use of the observational method for the monitoring of cliff faces. Nach einem Felssturz in einem ehemaligen Steinbruchgelände nahe der Ortschaft Dürnstein/ Wachau waren umfangreiche Maßnahmen zur Wiederherstellung und langfristigen Sicherung der stark beschädigten Bahnlinie erforderlich. Um während der Sanierungsphase die Sicherheit gewährleisten zu können, wurde ein Risikomanagement in Anlehnung an die Beobachtungsmethode nach EC 7 geplant und umgesetzt. Zentraler Bestandteil des Sicherheitsmanagementplans waren geotechnische Messungen. Der vorliegende Beitrag berichtet über die speziellen Herausforderungen, konkreten Problemlösungsansätze und allgemeinen Erfahrungen bei der Anwendung der Beobachtungsmethode zur Überwachung von Felswänden. [ABSTRACT FROM AUTHOR]

After heavy rainfalls, a rock slide and a consecutive debris flow a mudslide comprising a volume between 3,5 and 5 million m3 was reactivated in Gschliefgraben valley (Gmunden, Upper Austria province) in 2007/2008. The mudslide moved downwards with displacement velocities of some metres per day, until it could be stopped finally. The geologic-geotechnical model for the mudslide as well as the mechanisms and processes are described. They are influenced essentially by the pore water pressure and by the hydrostatic head. Comprehensive investigations showed that the clayey-silty-sandy-pebbly masses in the Gschliefgraben are especially sensible to changes of water content and acting stresses. Based on these geologic-geotechnical models for the movement process the mitigation measures carried out are described and their effects as well as their success are evaluated critically. Im Gschliefgraben (Gmunden, Oberösterreich) wurde nach starken Niederschlägen und einer Felsgleitung sowie einem anschließenden Murgang 2007/2008 ein Erd- und Schuttstrom mit einem Volumen zwischen 3,5 und 5 Mio. m3 wieder aktiviert. Dieser Erd- und Schuttstrom erreichte Bewegungsraten von mehreren Metern pro Tag, bis er schließlich gestoppt werden konnte. In dem Beitrag werden das geologisch-geotechnische Modell für den Erd- und Schuttstrom sowie die Mechanismen und Prozesse aufgezeigt. Diese werden wesentlich vom Porenwasser- und Wasserdruck beeinflusst. Umfangreiche Untersuchungen haben ergeben, dass das Material ein besonders sensibles Verhalten gegenüber Änderungen des Wassergehalts und den auftretenden Spannungen hat. Aufbauend auf diesen geotechnisch-geologischen Modellen für den Bewegungsprozess werden die durchgeführten Stabilisierungsmaßnahmen beschrieben und deren Wirkung kritisch untersucht. Darauf aufbauend wird deren Erfolg dargestellt und bewertet. [ABSTRACT FROM AUTHOR]

Abstract: In this paper, we present a structurally controlled, deep-seated, gravitational slope deformation, located in the Fusch Valley, Eastern Alps, Austria, which is potentially endangering infrastructure. In the framework of a landslide risk analysis, a danger characterisation of this slope is presented. The characterisation is based on strong geomorphological, geological, and hydrological evidence, on which both a kinematical and a stability model of that slope could be developed. Unlike the majority of case studies where type and position of basal slip surfaces remain unknown, the present models seem capable of delivering characterisations on the classification of the potential slope instability, its spatial extents, and likely physical reasons for its pre and post failure behaviour with high consistency and likelihood. [Copyright &y& Elsevier]

Abstract: One of the largest mass movements in the Alps, the fossil Fernpass rockslide in the Northern Calcareous Alps (Tyrol, Austria), was dated absolutely for the first time. Three independent radiometric dating methods were applied to geologically individual sample sites and enabled a cross-checking of the results. Close to the scarp-front, rockslide-dammed torrent deposits indicate a 14C minimum age of at least 3380–3080 cal. yrs BP. The chronostratigraphic base of this backwater sequence has not been dated yet, but is assumed to date somewhat older into the middle Holocene. However, this coincides with two cosmogenic radionuclide 36Cl ages of sliding planes at the steep and rugged scarp. Exposure data thus obtained are 3400±900 and 4800±1200 yrs respectively with an arithmetic mean of 4100±1300 yrs. Additional age data were acquired from post-depositional calcareous cements, which locally lithified the rockslide debris. These meteoric cements contain remarkably high Uranium total contents and yielded a 230Th/234U minimum age of about 4150±100 yrs for the accumulation of the rockslide deposits. All dating data agree well and indicate that the Fernpass rockslide is of Subboreal age. Thus the intensively structured present morphology, characterised by the well-known cone-shaped Toma-hills and several lakes in the depressions, is indicative of primary rockslide morphology and clearly not shaped by late-glacial ice as assumed formerly. [Copyright &y& Elsevier]

This study presents a multi-disciplinary approach for combining geological-geomorphological field mapping with different surface deformation monitoring techniques (i.e. extensometer, tachymetry, photogrammetry, airborne laser scanning (ALS), terrestrial laser scanning (TLS), uncrewed aerial vehicle (UAV)) to evaluate the impact of structural features on the formation process and deformation behaviour of the deep-seated Marzellkamm rock compound slide. The investigated rock slide is located in a high-alpine, glacier retreat environment in Northern Tyrol (Ötztal Alps, Austria) and formed in a well-foliated, fractured metamorphic rock mass. The total volume of the rock slide of approximately 13 Mm3 was estimated based on geographic information system (GIS) analysis by comparing the surface topography and reconstructed geometry of the basal shear zone. In the upper part of the rock slide, annual mean velocities of up to 0.3 m/year were measured by a combined tachymetric-global navigation satellite system (GNSS) procedure. Based on multi-temporal terrain model analyses, the highest sliding velocities were obtained at the central slope foot area, reaching more than 1 m/year. Geological-geomorphological field mapping showed that the rock slide can be subdivided into two large rock slide systems with different geometry, formation age, and current activity. Furthermore, structural and geomorphological features (i.e. main and minor scarps, graben-structures, downhill- and uphill-facing scarps, tensile fractures, trenches), as well as surface deformation data, indicate the formation of six rock slide slabs. These slabs move downwards at different velocities and are separated by discrete shear zones, where slope displacement primarily accumulates. Large offsets along these shear zones indicate that internal slab deformation has only limited influence on the overall rock slide behaviour. At the Marzellkamm rock slide, pre-existing tectonic fault zones and planes were reactivated and used as weakness zones, playing a crucial role in the overall rock slide geometry and internal separation of the rock mass into slabs. Field survey and monitoring data suggest that a fully persistent, curved, non-circular basal shear zone has developed. Based on comprehensive analyses of mapping and deformation monitoring data, a geological-geometrical and kinematical model of the Marzellkamm rock slide was developed, providing a basis for site-specific hazard assessment and numerical modelling. • Two rock slide systems of six rock slide slabs of different deformation behaviour • Significant influence of pre-existing geological structures on rock slide formation • Deformation is controlled by the magnitude of shearing on separating shear zones. • Field survey indicates a fully persistent, curved, non-circular basal shear zone. • Two rock fall/avalanche events occurred at the lower part of the most active slabs. [ABSTRACT FROM AUTHOR]

In the former quarry near Spitz an der Donau (Austria), many rockfalls have occurred during operation as well as after closure. They have endangered a railway, the Wachau bicycle route, an important road, and the left Danube riverbank. Thus, future detachment scenarios were investigated and, in addition, weather and occurrence statistics were analyzed to determine the occurrence probabilities of these scenarios. Simulations of possible future rockslides were performed using the Distinct Element Code 3DEC in order to estimate the damage caused by these events. Based on these results, the risks of the scenarios were calculated according to the definition of risk as the product of damage and occurrence probability. By this means, the profitability of mitigation measures (e.g., a massive retaining structure fixed to the ground by bored piles) can be evaluated. [ABSTRACT FROM AUTHOR]

Glacier retreat is one of the most significant consequences of 20th and 21st century temperature rise in the European Alps, most obvious at glacier tongues but also at glacier cirques. As cirque headwalls deglaciate, internal stress redistribution occurs and atmospheric forcing intensifies rendering deglaciating headwalls particularly prone to rock slope failure. Fractures intersecting these rock masses represent potential planes of weakness. Their dynamics may thus reveal information about the magnitude and timing of stability-relevant processes. The present study focuses on the need for quantitative data from unstable, recently deglaciated rock slopes, essential for better understanding the increasing risk on high-alpine infrastructure.Here, we investigate the deformation regime of an open fracture, which is of direct geotechnical relevance for a popular cable car station at the Kitzsteinhorn (3203 m a.s.l.). The fracture is situated immediately up slope of the detachment zone of a recent rock slide (2012) and was glacially covered until the 1980s. Two crackmeters are operated to measure horizontal and vertical crack deformation with a resolution of ±0.003 mm as well as crack top temperature. To decipher thermo-mechanical from cryogenic forcing, thermal expansion coefficients for both horizontal and vertical directions were calculated in order to model purely thermomechanical deformation. Based on a 2.5-year monitoring campaign, this study aims to decipher and quantify stability-relevant processes and their temporal occurrence, and addresses the following research questions: (i) Are fracture dynamics dominated by thermo-mechanical expansion/contraction of the inter-cleft rock mass? (ii) Do cryogenic processes, i. e. freeze-thaw dynamics and ice segregation, affect fracture opening/closing? (iii) Can irreversible crack deformation patterns and destabilisation be observed?(i) Fracture dynamics are dominated by thermo-mechanical expansion and contraction of the inter-cleft rock mass during sustained snow-covered and snow-free periods. Calculated thermal expansion coefficients of 7E-006 along and 14E-006 perpendicular to foliation highlight material anisotropy of the calcareous micaschist.(ii) Significant deviations from the thermo-mechanical deformation regime occur mainly during spring and autumn zero curtain periods due to freeze-thaw action. Peak vertical deformations are triggered by rainfall events providing liquid water onto the rock surface and into the fracture system. Subsequent refreezing rather than hydrostatic pressure build-up is assumed to cause the mechanical response of the rock. Lower magnitude deviations in the horizontal component arise in autumn and early winter, which are referred to segregation ice growth. Besides cryogenic processes, other mechanisms seem to affect fracture dynamics such as wedged rock fragments impeding maximum fracture-closing during snow-free periods.(iii) Irreversible fracture opening, pointing towards acute, high magnitude rock slope instability, was not observed. However, enhanced cryogenic deformation in spring and autumn may lead to shallow, low magnitude rock detachments. Our results highlight the importance of liquid water intake in combination with subzero-temperatures on the destabilisation of glacier headwalls. Randkluft systems may favour intense frost action and ice segregation, serving as important preparatory factors of paraglacial rock slope instability. [ABSTRACT FROM AUTHOR]

In order to understand and identify the influence of the structure of the rock mass on rock slide formation and deformation processes, the highly active, deep-seated "Marzell" rock compound slide in the Ötztal valley (Tyrol, Austria) has been examined. The investigated rock slide is situated at the SE-facing slope above the Marzell valley glacier and measures about 400 m in width and 600 m in height (main scarp at 2850 m a.s.l.). Geologically, the rock slide is located within the fractured, foliated poly-metamorphic rocks of the Ötztal Crystalline basement (i.e. paragneisses, mica schists and banded amphibolites).A multi-disciplinary approach comprising of i) geological-geomorphological mapping, ii) tachymetric and GPS survey campaigns, iii) analyses of airborne laserscanning data (ALS), iv) analyses of historic and current ortho-images, and v) manual wire-extensometer measurements, was applied to reconstruct the rock slide evolution and to develop a geometrical-kinematical rock slide model. Given that rock discontinuities influence the geomechanical failure behaviour and thus the failure geometry, a major focus was set on rock mass characterization based on discontinuity mapping. Additionally, kinematical analyses considering the structural inventory was carried out to identify modes of rock mass failure and preliminary discrete element modelling (UDEC) was performed to study rock slide kinematics and failure mechanisms.Geomorphological features such as primary and secondary scarps, uphill and downhill facing scarps, graben structures, trenches and tension fractures indicate the evolution of two time-delayed rock slide systems. Geodetic survey results show a high recent activity of the rock slide of several decimetres per year. Based on the geological structures and the measured displacement rates, six individual rock slide slabs can be identified. These slabs are separated by discrete failure surfaces/shear zones that were formed partly or totally along pre-existing NNE-SSW and E-W trending fault systems. The detailed discontinuity analyses of foliation planes, joints, and brittle fault zones show a major influence on the rock slide failure mechanism, failure geometry and kinematics. Kinematically, the SE directed slope movement caused extensional structures near the head scarp (horst and graben, trenches, fractures) and to bulging and slope steepening at the lower part of the rock slide. Results from the numerical 2-D discontinuum model are discussed with respect to: i) the structural influence on failure geometry (from pre-failure to current failure state), ii) the internal structures (e.g. horst and graben) and deformation behaviour of the sliding mass, and iii) the existence and formation process of a basal shear zone. [ABSTRACT FROM AUTHOR]