NH3.3

EDI
Rockfalls, rockslides and rock avalanches

Rockfalls, rockslides and rock avalanches are among the primary hazards in steep terrain. To better understand the processes driving rock slope degradation, mechanisms contributing to the triggering, transport, and deposition of resulting rock slope instabilities, and mitigation measures for associated hazards, we must develop insight into both the physics of intact and rock mass failure and the dynamics of transport processes.

This session aims to bring together state-of-the-art methods for predicting, assessing, quantifying, and protecting against rock slope hazards. We seek innovative contributions from investigators dealing with all stages of rock slope hazards, from weathering and/or damage accumulation, through detachment, transport and deposition, and finally to the development of protection and mitigation measures. In particular, we seek studies presenting new theoretical, numerical or probabilistic modelling approaches, novel data sets derived from laboratory, in situ, or remote sensing applications, and state-of-the-art approaches to social, structural, or natural protection measures.

Co-organized by GM3
Convener: Michael Krautblatter | Co-conveners: Anne VoigtländerECSECS, Axel Volkwein, Matthew Westoby
vPICO presentations
| Thu, 29 Apr, 15:30–17:00 (CEST)

vPICO presentations: Thu, 29 Apr

Chairpersons: Michael Krautblatter, Axel Volkwein, Anne Voigtländer
15:30–15:35
Weathering and detachment of rockfalls, rock slides and rock avalanches
15:35–15:40
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EGU21-15947
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ECS
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solicited
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Highlight
Andreas Ewald, Jan-Christoph Otto, Christoph von Hagke, and Andreas Lang

Global warming triggered retreat of alpine glaciers exposes large surface areas in the proglacial zone but also a significant headwall area above. The thermal and mechanical changes in the headwalls foster destabilisation and trigger rockfalls. Patterns of headwall destabilisation are complex due to variable rock strength and external atmospheric forcing and results are usually site-specific and do not allow regional scale stability assessments.

In order to understand sensitivity of alpine rock walls to instability following glacier retreat on a regional scale, we classify glacier headwalls based on a combination of surface and rock-mechanical characteristics. This includes (i) a semi-automatic detection of glacier headwalls using object-based image analysis, (ii) a morphometric analysis of headwalls, (iii) a regionalisation of rock-mechanical properties of the bedrock, and (iv) an analysis of other site conditions like potential permafrost occurrence and glacier retreat. We apply this workflow in the Hohe Tauern Range, Austria, to identify headwalls in recently deglaciated cirques and valleys with the highest potential for increased slope instability and rock fall processes.

For the central Hohe Tauern Range high-resolution digital datasets of topography, geology, glacier extent, and permafrost distribution are available. eCognition was used for semi-automatic headwall detection. Segmentation is derived from DEM derivatives like slope, aspect and a TPI-based landform classification. Headwall segments are classified based on slope and elevation thresholds that have been identified and validated using manual headwall mapping. Foliation information extracted from regional geological maps was compared to local geological surveys in order to specify type of foliation. Bedrock structure was interpolated based on a non-continuous azimuth distribution approach (NADIA). By combining topographic and geological data we derived a geotechnical classification scheme from cataclinal to anaclinal slopes with various dip-slope relations.

Preliminary results indicate that semi-automated headwall detection largely reproduces local observations. However, we observed an overestimation of 61% of total headwall area compared to the manually mapped headwalls. The rate of undetected areas is considered to be negligible. Overestimation mainly arises from inclusion of high-altitude profile straight slopes, matching the classification requirements without obvious glacial imprints such as schrundlines. Landform classification revealed a dominance of cataclinal slopes in the entire landscape. At steeper terrain, including glacier headwalls, anaclinal slopes prevail. Unstable situations such as overdip slopes are rare and predominantly found in the lower sections of glacier headwalls marked by schrundlines. Steep permafrost rock walls were found to be almost exclusively anaclinal, which might be considered as site-specific.

Our approach offers a new methodology to detect deglaciating headwalls and characterise their sensitivity to instability at a regional scale. Our classification can be used for up-scaling local headwall dynamics for a better anticipation of the destabilisation pattern of steep alpine slopes following glacier retreat.

How to cite: Ewald, A., Otto, J.-C., von Hagke, C., and Lang, A.: Combining surface characteristics and rock-mechanical properties to identify unstable glacier headwalls on a regional scale, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-15947, https://doi.org/10.5194/egusphere-egu21-15947, 2021.

15:40–15:42
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EGU21-14871
Oliver Sass

Rock moisture is an understudied factor governing weathering and rockfall. Many weathering processes like hydration, thermal and frost cracking are governed by moisture availability. However, weathering studies have primarily focussed on temperatures. The role of moisture supply has not been given the same attention, also because there is no humidity sensor that meets all requirements for application in rock.

In the sandstone area of Saxony in eastern Germany ("Saxonian Switzerland"), climbing on wet rock poses a safety problem as the sandstone loses stability when saturated. Visitor guidance measures ('rock traffic lights') were implemented to temporarily stop climbing at rocks that are too wet. To accompany this measure, we carried out a pilot study at the Gohrisch sandstone massif, involving moisture measurements in the four cardinal directions at the rockwall base and near the summit of the massif. We used a combination of (a) electrical resistivity electrodes, combined with wind-driven rain collectors; (b) 2D-electrical resistivity (ERT); (c) microwave sensors (MW) with four sensor heads for different penetration depth and (d) Schmidt Hammer (SH) measurements to assess rock stability. All techniques were accompanied by laboratory measurements at rock samples.

Electrical resistivity, MW readings and SH rebound all showed very good correlations with rock moisture in laboratory samples. However, the range of values measured in the field strongly differed from laboratory values so that the calibration curves could not be applied to field data. Presumeably this is due to lithological differences between the fresh quarry samples and the pre-weathered rock faces.  

ERT profiles using adhesive electrodes showed good reliability (RMS error 5-14%). Most sites were slightly wet at the surface, drier at 5-15 cm depth and moderately wet at 20-30 cm depth (1000 – 8000 Ohmm). The site Bottom North was much wetter than all others, and the two top positions were dried out at the surface probably due to wind. This distribution was roughly confirmed by microwave sensor data. Direct correlation between MW and ERT measurements was poor as measurement principle and geometry are very different.

Schmidt Hammer data was very consistent with microwave moisture in the lab (lower rebound at wetter surfaces); however not in the field, where the wetter Bottom North site showed highest rebound values. The summit positions showed significantly lower rebound which we attribute to stronger weathering (more dry-wet cycles). Lab results show that the sandstone loses stability (SH rebound) mainly between 60% and 100% pore saturation. Currently we cannot reliably determine if this saturation was actually reached in the field.

The combined interpretation of all measurements, even if imperfectly calibrated, points to surface-parallel weakness zones that have developed at all sites except of Bottom North which is almost never hit by sunlight. Water supply by rainfall is weak at the almost vertical sites; water rather seems to infiltrate in flat areas and to seep out at the base of the massif. The results help to understand the distribution of dampness in the rock and will be supplemented by continuous monitoring and numerical simulations.

How to cite: Sass, O.: Measuring rock moisture using different techniques in the sandstone area of Saxony, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-14871, https://doi.org/10.5194/egusphere-egu21-14871, 2021.

15:42–15:44
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EGU21-4999
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ECS
Quantifying and characterising contemporary rockfall supply to a debris-covered glacier catchment
(withdrawn)
Rebecca Stewart, Matthew Westoby, Stuart Dunning, Francesca Pellicciotti, and John Woodward
15:44–15:46
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EGU21-8304
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ECS
Li Fei, Marc-Henri Derron, Tiggi Choanji, Michel Jaboyedoff, Chunwei Sun, and Charlotte Wolff

Freezing-thaw weathering is recognized as one of the most significant factors in the fatigue of rock mass in areas where the temperature periodically fluctuates around the freezing point. 
A one-year monthly SfM monitoring program from December 19, 2019, to January 7, 2021, was done to detect rockfall activity on a rockslide cliff composed of marl-sandstone at La Cornalle, Switzerland. More than one hundred rockfall events were detected during this period with the volumes varied from 0.005m3 to 4.85m3
We texture all the rockfalls on the 3D SfM model. It is shown that most of them are mainly located in three areas:  the top of the cliff, the foot of the cliff, and the medium-left part of the cliff. The common feature of these three parts is that the layers are more or less overhanging with dense fractures around them. At the same time, the meteorological data collected by a weather station on site is correlated with the rockfall events to figure out the relationship between each other. Actually, about 30% of total rockfall volume fell during winter on this site. The triggering factor of rockfall during winter is related to freezing-thaw cycling. This kind of weathering can be understood as an interplay between rock properties and its dynamic environment.
In order to make clear the role of freezing-thaw played on the rockfall generation, an on-site 24h monitoring measurement program that consists of two crack meters, one rock thermal sensor, and thermal camera monitoring is installed in January 2021. Those datasets will help to understand how the crack grows with the changing temperature. In addition, freezing-thaw cycling laboratory experiments for the rock samples taken from different areas of the cliff will be done with an environmental test chamber. The topography of the rock samples before and after the experiments will be acquired by a 3D handheld scanner. This work will benefit to reveal the rock surface evolution during the freezing-thaw cycling in a dynamic environment with varied humidity and number of cycles. 
In conclusion, the combination of on-site measurements and laboratory freezing-thaw experiments will provide a good basis for a better understanding of the rockfall triggering mechanism led by physical weathering.

How to cite: Fei, L., Derron, M.-H., Choanji, T., Jaboyedoff, M., Sun, C., and Wolff, C.: The role of freezing-thaw cycling in rock samples topography evolution and rock cliff retreat, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-8304, https://doi.org/10.5194/egusphere-egu21-8304, 2021.

15:46–15:48
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EGU21-8260
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ECS
Nader Saadatkhah and Aaron Micallef

Groundwater seepage has been shown to unambiguously lead to channel formation inunconsolidated sand to gravel sized sediments. However, its role in the evolution of bedrocklandscapes remains controversial. In this study, we use the coastline of the Maltese Islands as a case study to establish if and how groundwater seepage can form box canyons in limestones. The study area comprises up to 40 m high coralline limestone cliffs, with a mean fracturedensity of 1 in 5 m, overlying a ductile marl layer. The permeability contrast promotes the development of a perched aquifer and groundwater seepage at the cliff face. We  ran numerical simulations using a 3D distinct element model based on geological, geotechnical and hydrological baseline information from the study state, and explored three potential mechanisms: (i) fracture widening by fluid pressure and dissolution associated to groundwater flow and seepage, (ii) fracture widening by loss of support at the base due tomarl displacement resulting from increased water content, and (iii) a combination of (i) and (ii). We also took into consideration two scenarios: (a) uniform groundwater seepage, and (b)focused groundwater seepage. Our results suggest that the combination of mechanisms (iii) and the scenario with focused groundwater seepage (b) give rise to the box canyonmorphology observed at the site. Box canyons thus initiate and grow via detachment of limestone blocks and their toppling, which is more concentrated at the head where groundwater seepage occurs.

How to cite: Saadatkhah, N. and Micallef, A.: Formation of box canyons by mass failure in limestone: A modelling study of the role of groundwater seepage, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-8260, https://doi.org/10.5194/egusphere-egu21-8260, 2021.

Rock mass and pre-failure rock slide characterisation for rockfalls, rock slides and rock avalanches
15:48–15:50
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EGU21-9096
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solicited
Federico Agliardi, Rou-fei Chen, Chiara Crippa, De-Cheng Yi, and Ching-Weei Lin

Deep-seated gravitational slope deformations (DSGSD) gained increasing attention in Taiwan due to their catastrophic impacts on lives and infrastructures during Typhoon Morakot in 2009, when over 2700 mm of rainfall in 5 days were recorded. As the main Taiwan island is located on a complex convergent plate boundary, available data suggest that the island’s strong tectonic activity has contributed, along with its subtropical climate and intense human activity, to the onset and destabilization of deep-seated landslides. These are widespread in high-relief mountain areas where Miocene to Eocene meta-sandstone and slate successions outcrop. Slopes at Tienchih (Lalong River of Kaohsiung) and Yakou (few km east in Taitung County) were affected by significant slope collapses and impending instabilities after the heavy precipitation of Typhoon Morakot. This led to severe damages and closure of the South Cross Island Highway No.20, a critical roadway connecting the western and eastern sides of S Taiwan, where continuing slope instability has been observed after 2009. At Tienchih, 240 mm of displacement over an area of 6.7 ha were recorded in 2016 by continuous GPS measurements after a heavy rainfall event. At Yakou, the middle slope sector including the road experienced a major collapse in 2018. At both sites, morpho-structural evidence identified in 1-m resolution LiDAR DEMs suggest that long-term slope deformations occurred well before catastrophic slope destabilization. This is supported by spectacular gravitational deformation structures (i.e. kink folds and shear zones), well exposed at Yakou, and by continuous slow movements detected at Tienchih by multi-temporal TCPInSAR analyses on ALOS/PALSAR images (2007-2011). On the other hand, dense vegetation and limited rock outcrops make an accurate assessment of the geometry, controls, mechanisms and style of activity of these landslides difficult. To overcome this difficulties, we carried out a systematic geomorphological mapping of the two areas through ortho-photos and HRDEMs derived from aerial LiDAR (2012 and 2019), and field surveys to characterize the local structural geology (ductile and brittle features), rock mass strength and gravitational morpho-structures. We performed a local-scale analysis of displacement patterns and rates by combining traditional radar interferometry (D-InSAR on ALOS and Sentinel-1 imagery), improved TCPInSAR analyses, GPS data, Digital Image Correlation between DEMs and change detection analysis of LiDAR point clouds. Our results suggest that long-term progressive failure of slopes was promoted by high tectonically-forced erosion rates and constrained by inherited ductile structures. These preconditioned the location, size and mechanisms of slope sectors more prone to catastrophic failure due to intense rainfall and river bank erosion. A systematic characterization of long-term slope deformation can thus provide key information to assess the hazard related to deep-seated landslides in Taiwan.

How to cite: Agliardi, F., Chen, R., Crippa, C., Yi, D.-C., and Lin, C.-W.: Mechanisms and activity of deep-seated landslides at Tienchih and Yakou (S Taiwan) revealed by structural geology and remote sensing, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-9096, https://doi.org/10.5194/egusphere-egu21-9096, 2021.

15:50–15:52
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EGU21-8179
Tiggi Choanji, Charlotte wolff, Li Fei, Lidia Loiotine, Amalia Gutierrez, Chunwei Sun, Marc-Henri Derron, Dario Carrea, and Michel Jaboyedoff

Lithology identification and discontinuity mapping are necessary for rockfall hazard assessment in tunnels. However, the restricted exposure and variability of rock face orientation in tunnels ought to be taken into account. Therefore, using Light Detection and Ranging (LiDAR) technique may significantly contribute to this task.

A historical carved tunnel in the Upper Marine Molasse (a poorly consolidated sandstone) of the City of Fribourg (Switzerland) was then investigated by fieldwork and LiDAR. Interestingly, it appears that in addition to joints and layering, some specific sedimentary structures, i.e. cross-bedding, have an important role in the tunnel roof stability. Cross-bedding is a sedimentary structure that can be identified clearly by the geometry of layer within one or more beds in a series of rock strata that does not run parallel to the plane of stratification.

In order to detect and analyse these sedimentary structures, the intensity of the backscattered LiDAR signal is analysed using the Oren-Nayar reflectance model, which considers range, incidence angle, scanned surface geometry (i.e. roughness). It provides corrected values of intensities that make possible to distinguish and identify geometry of cross-beddings in the tunnel.

An analysis of structural discontinuities was also performed using Coltop Software which identified joint sets developed inside the tunnel. Based on this approach, lithology characterizations, orientation of each discontinuity and bedding structures could be identified in point clouds confidently for understanding the mechanisms of potential rockfalls in the tunnel.

How to cite: Choanji, T., wolff, C., Fei, L., Loiotine, L., Gutierrez, A., Sun, C., Derron, M.-H., Carrea, D., and Jaboyedoff, M.: Cross-Bedding and Structural Mapping for Rockfall Assessment of a Tunnel using Hi-Resolution LiDAR (Fribourg, Switzerland), EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-8179, https://doi.org/10.5194/egusphere-egu21-8179, 2021.

15:52–15:54
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EGU21-2589
Emmanuel Wyser, Lidia Loiotine, Charlotte Wolff, Gioacchino Francesco Andriani, Michel Jaboyedoff, and Mario Parise

The identification of discontinuity sets and their properties is among the key factors for the geomechanical characterization of rock masses, which is fundamental for performing stability analyses, and for planning prevention and mitigation measures as well.
In practice, discontinuity data are collected throughout difficult and time-consuming field surveys, especially when dealing with areas of wide extension, difficult accessibility, covered by dense vegetation, or with adverse weather conditions. Consequently, even experienced operators may introduce sampling errors or misinterpretations, leading to biased geomechanical models for the investigated rock mass.
In the last decades, new remote techniques such as photogrammetry, Light Detection and Ranging (LiDAR), Unmanned Aerial Vehicle (UAV) and InfraRed Thermography (IRT) have been introduced to overcome the limits of conventional surveys. We propose here a new tool for extracting information on the fracture pattern in rock masses, based on remote sensing methods, with particular reference to the analysis of high-resolution georeferenced photos. The first step consists in applying the Structure from Motion (SfM) technique on photos acquired by means of digital cameras and UAV techniques. Once aligned and georeferenced, the orthophotos are exported in a GIS software, to draw the fracture traces at an appropriate scale. We developed a MATLAB routine to extract information on the geostructural setting of rock masses by performing a quantitative 2D analysis of the fracture traces, based on formulas reported in the literature. The code was written by testing few experimental and simple traces and was successively validated on an orthophoto from a real case study.
Currently, the script plots the fracture traces as polylines and calculates their orientation (strike) and length. Subsequently, it detects the main discontinuity sets by fitting an experimental composite Gaussian curve on histograms showing the number of discontinuities according to their orientation, and splitting the curve in simpler Gaussian curves, with peaks corresponding to the main discontinuity sets.
Then, for each set, a linear scanline intersecting the highest number of traces is plotted, and the apparent and real spacing are calculated. In a second step, a grid of circular scanlines covering the whole area where the traces are located is plotted, and the mean trace intensity, trace density and trace length estimators are calculated.
It is expected to test the presented tools on other case studies, in order to optimize them and calculate additional metrics, such as persistence and block sizes, useful to the geomechanical characterization of rock masses.
As a future perspective, a similar approach could be investigated for 3D analyses from point clouds.

How to cite: Wyser, E., Loiotine, L., Wolff, C., Andriani, G. F., Jaboyedoff, M., and Parise, M.: 2D quantitative analysis of fractures from high-resolution photos for the geomechanical characterization of rock masses, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-2589, https://doi.org/10.5194/egusphere-egu21-2589, 2021.

15:54–15:56
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EGU21-5622
Klaus Voit, Christine Fey, Christina Rechberger, Volkmar Mair, and Christian Zangerl

In Alpine areas, deep-seated rockslides are relatively common. They are mostly based on geological and tectonic conditions and triggered by permafrost degradation, snowmelt or heavy rainfall events. A striking example is situated near Laatsch, South Tyrol, at the valley entrance of the Münstertal at close range to the national road SS41 leading to the Swiss border. The activation of the movement occurred in the year 2000, showing a rapid expansion since the year 2012 causing a relocation of the road in 2014.

The U-shaped valley of the Münstertal was formed by glaciers, the valley floor is filled with alluvial sediments. The Mountain ridge runs approx. 2,100 m above the Adriatic Sea, valley floor at approx. 1,000 m above Adriatic Sea. The slope gradient varies between 30 and 50°. The rockslide situated in this slope is approx. 400 m wide, approx. 700 m in height at its longest extension, with a slide surface ca. 50 - 100 m deep summing up to an instable rock volume of approximately 5 to 10 million m³ and monthly average movement rates of 0.1 to 0.55 m.

Geological mapping and analysis were performed for the detailed identification of the cause of failure and occurring failure types such as sliding, falling, toppling and flow. The different gneiss bedrock types mainly consist of Quartz, Feldspar, Muscovite and Calcite, foliation is mainly caused by Muscovite layers. Muscovite-rich shearing planes could also be identified via thin section analysis. The foliation dips with a dip of ca. 10-20° mainly towards Northeast and therefore is orientated towards the slope. Two sets of very steep dipping joins are present deeply fragmenting the rock mass providing starting points or lines for the development of scarp surfaces. Deep weathering of the disintegrated gneiss bed rock could be observed at tectonically induced fracture surfaces. Weathering progresses along scarps and developed tension cracks further eroding and dissembling the rock mass.

Movement analysis of different slabs were performed twice a year using multi-temporal terrestrial laser scanning (TLS) between 2017 and 2020. Along this sliding surface, rock material is transported as individual slabs showing mainly a translational movement behavior with minor internal deformation. These slabs are visually recognizable on site as well as during the analysis of movement rates of laserscanning series measurements.  Main mass transport occurs from upper steep slope areas to areas of lower slope angle within and at the foot of the rockslide. General movement occurs via a basal slip surface with an average thickness of failure volume of approx. 50 to 100 Meters.

Volume of displaced material during accompanied processes of rock fall and rock topple events amounts to 2,000 - 5,000 m³ depending on the size of the event. These types of rock movement mainly take place along outbreak recesses at the rockslide flanks, scarps and at the internal slab margins. These falls and topples can also be detected through several laserscanning measurement series.

How to cite: Voit, K., Fey, C., Rechberger, C., Mair, V., and Zangerl, C.: Geological investigation and movement analysis of the deep-seated compound rockslide Laatsch, South Tyrol, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-5622, https://doi.org/10.5194/egusphere-egu21-5622, 2021.

15:56–15:58
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EGU21-13425
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ECS
Danilo D'Angiò, Luca Lenti, and Salvatore Martino

Rock mass damaging investigation is a main research topic in the ambit of rock fall hazard assessment. Roads and railways interruptions, as well as damages of buildings, are among the main inconveniences due to the detachment of unstable sectors of highly jointed rock masses. The contribution of rock mass creep together with natural and anthropic forcings leads to the accumulation of inelastic strain within the rock mass and to the formation of new joints or to the extension and movement of the pre-existing ones. The associated stress release produces tiny vibratory signals (known as microseismic emissions) that can be detected by on-site installed microseismic monitoring networks. Monthly and annual microseismic monitoring data can provide information on seismicity increase over certain periods and on the deterioration of rock properties as the elastic moduli. However, other seismic attributes may support the comprehension of rock mass damaging processes. In particular, the analysis over time of the damping ratio associated with the microseismic emissions could indicate transient and permanent changes within the micro-joint network. This analysis approach has been already conducted on a three-month long microseismic dataset collected at the Acuto field-lab, which is hosted in an abandoned quarry and is mainly exposed to environmental forcings (rainfalls and thermal cycles); moreover, to account also for anthropic vibrations, preliminary studies were carried out on a rock mass located in proximity of a railway. As a further perspective, the investigation of multi-year seismic dataset acquired on unstable rock masses will allow to better inspect the reliability of this analysis approach for rock mass damaging assessment.

How to cite: D'Angiò, D., Lenti, L., and Martino, S.: Rock mass damaging investigation through the analysis of microseismic monitoring data collected on rock masses, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-13425, https://doi.org/10.5194/egusphere-egu21-13425, 2021.

Motion and trajectory modelling of rockfalls, rock slides and rock avalanches
15:58–16:00
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EGU21-10791
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ECS
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solicited
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Highlight
Adrian Ringenbach, Peter Bebi, Perry Bartelt, and Andrin Caviezel

Forests with a high density and basal area of living trees are known for their function as natural and cost-efficient protection against rockfall. The role of deadwood, however, is less understood. We address this knowledge gap in this contribution as we present the results of repeated real-scale experiments in a) a montane beech-spruce forest with and without deadwood and b) in a subalpine scrub mountain pine-spruce forest with deadwood. We used artificial rocks with either an equant or platy shape, masses between 45 kg and 800 kg (≈ 0.3 m3), and equipped with in-situ sensors to gain insights into rotational velocities and impact-accelerations. Clusters of deadwood and erected root plates reduced the mean runout distance at both study sites. For site a), we found that more rocks were stopped behind lying than living trees and that the stopping effect of deadwood was greater for equant compared to platy rock shapes. Site b) revealed a braking effect of scrub mountain pines for relatively small (45 kg), but also a visible reduction in rotational velocities for the 800 kg rocks sensor stream. We conclude that deadwood must be taken into account in rockfall modeling and the management of rockfall protection forests.

How to cite: Ringenbach, A., Bebi, P., Bartelt, P., and Caviezel, A.: The role of forest deadwood in rockfall protection, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-10791, https://doi.org/10.5194/egusphere-egu21-10791, 2021.

16:00–16:02
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EGU21-9731
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ECS
Andrea Valagussa, Giuseppe Dattola, Paolo Frattini, Elena Valbuzzi, Alberto Villa, Federico Agliardi, and Giovanni Crosta

Rockfalls are severe and common dangerous events in mountain areas which are strongly controlled by geological and weather conditions. Remotely sensed data allows to identify slowly moving block volumes and to characterize the evolution towards collapse. The commonly adopted approaches for time to failure estimations generally rely on the inverse velocity approach. In this study we investigate the capabilities of a viscoplastic model to simulate the progressive evolution of the block instability with time. We use the monitored time series to calibrate the model parameters and then we pass to the modeling of the entire rockfall events and to the design of mitigation countermeasures. To this aim we study the May 29th 2018 Gallivaggio rock fall (San Giacomo Filippo, Sondrio, Italy) when about 5,000 m3 of rock detached from a 400 m high cliff, causing considerable damage to the area of the Sanctuary of Gallivaggio and closure of the main mountain route (S.S.36).

The area was monitored by the Regional Environmental  Protection Agency since 2011 by using a ground-based radar (GB-InSAR, LisaLab srl), and it was affected by a 150 m3 rockfall event in the last months of 2019.

GB-InSAR data, multiple laser scanner surveys and drone images of the rock cliff recorded before the event allow to identify the source area, to define and characterize the potentially detachable block volumes and their evolution through time. Thanks to the continuous GB-InSAR monitoring which started well before the event, we calibrated the parameters of a 1d multi-block model whose behaviour is governed by time-dependent visco-plastic constitutive law based on the Perzyna’s approach. This model is subsequently employed to reproduce the mechanical response of the block masses until their detachment from the vertical wall by using different constitutive laws.

At the same time, the comparison between the size distributions of the detached and the deposited blocks and the dust sampling and characterization allowed us to evaluate the degree of comminution due to fragmentation. This information, which is rarely available, made possible to calibrate the fragmentation algorithm of the code HY-STONE, which simulates fragmentation of the falling blocks overcoming a certain energy threshold and the dynamic behaviour of the resulting fragments. We first applied the code to replicate the rockfall events, being able to simulate the large spreading of the block that was impossible to simulate without the fragmentation algorithm. Then we applied this modelling approach for the design of a ditch-embankment countermeasure, simulating different scenarios with and without fragmentation. The results show that fragmentation induces an increase in the number of blocks impacting the embankment, in the heights, and in the velocity, but a decrease of the kinetic energy since each fragment has a smaller mass than the original blocks.

How to cite: Valagussa, A., Dattola, G., Frattini, P., Valbuzzi, E., Villa, A., Agliardi, F., and Crosta, G.: Accelerating phase displacement prediction and 3D rockfall modelling of the large Gallivaggio rockfall, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-9731, https://doi.org/10.5194/egusphere-egu21-9731, 2021.

16:02–16:04
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EGU21-5572
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ECS
Su Yang, Xiaoliang Wang, and Qingquan Liu

Natural disasters such as landslides dominated by granular material may cause catastrophic consequences. Therefore, the protection of human-made facilities in mountainous areas is of great significance. An effective protective measure is to install an array of obstacles upstream of the structure that needs to be protected. We need to numerically simulate the interaction between granular flow and obstacle array, and forecast the flow path and stacking position of granular flow after interacting with an array of obstacles. The constitutive behavior and structure-interaction mode of granular material differs substantially from water flow-dominated hazards (e.g., floods). We have developed a depth-averaged model that can accurately simulate the interaction between granular flow and obstacles. Numerical simulations were performed for the case of granular flow facing a large number of different obstacles arrays to produce a dynamical process of granular flow and the depth changes of fixed detection points. We obtain different obstacles arrays by changing, including but not limited to, the type, geometric size of the obstacles, and row spacing of the arrays. We found that obstacles play roles of dissipation, deflection and hindrance, on the granular flow. For some types of obstacles, such as tetrahedron, the previous two mechanisms are dominant. Our research results show that the existence of obstacle arrays can indeed protect specific areas downstream. Furthermore, we can achieve better protection effects by changing the parameters of the array. These research results help us better forecast the result of the interaction between granular flow and an array of obstacles in space, and provide guidance for the structural design and assessment for hazard mitigation in mountainous regions. These findings advance the understanding of flow structures of fast granular flow facing obstacles, which provides guidance for structural design and assessment for hazard mitigation in mountainous.

How to cite: Yang, S., Wang, X., and Liu, Q.: Forecasting granular flow on steep terrains after interacting with an array of obstacles, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-5572, https://doi.org/10.5194/egusphere-egu21-5572, 2021.

16:04–16:06
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EGU21-12604
Giuseppe Dattola, Giovanni Battista Crosta, and Claudio Giulio di Prisco

Rockfall is one of the most common hazards in mountain areas causing severe damages to structures/infrastructures and, human lives. For this reason, numerous are the papers published in the last decades on this subject, both introducing reliable approaches to simulate the boulder trajectory and defining design methods for sheltering structures. As is well known, the most popular strategy to simulate the block trajectory and velocity is based on the lumped mass material point approach. This is capable of describing the block trajectory, before either its natural arrest or impact against an artificial/natural obstacle, by suitably considering its interaction with soil/rock materials, interaction always dynamic, very often highly dissipative and defined, according to its nature, as sliding, rolling or impact.

In this framework, this study focusses on impacts and, in particular, on the role of block geometry in affecting the block kinematic response. The problem is approached numerically; by modifying a previously conceived elastic-viscoplastic constitutive model, based on the macro-element concept. and capable of satisfactorily simulating impacts of spherical blocks.

The modified constitutive model relaxes the assumption of spherical block by assuming an ellipsoidal shape and by allowing for the boulder rotation. These two changes make the problem more complex but allow to model more realistically the impact. For the sake of simplicity, the results shown in this work consider the block motion to be planar, but the model already allows to include general three dimensional conditions.

In this work, the model is briefly outlined and the procedure for calibrating the model constitutive parameters described. Then, the results of an extensive parametric analysis, employing constitutive parameters calibrated on experimental data taken from the literature, are discussed. In particular, the role of (i) the inner block orientation, and (ii) the inner impact angle is considered in terms of both kinematic variables and restitution coefficients. Finally, interpolation functions to compute restitution coefficients, once both block shape and inner impact block orientation are known, are provided.

How to cite: Dattola, G., Crosta, G. B., and di Prisco, C. G.: Modeling of the impact of rigid ellipsoidal blocks by means of an elastic-visco-plastic constitutive model , EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-12604, https://doi.org/10.5194/egusphere-egu21-12604, 2021.

16:06–16:08
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EGU21-14683
Shiva P. Pudasaini and Michael Krautblatter

Erosion can dramatically change the dynamics and deposition morphology and escalate the destructive power of a landslide by rapidly amplifying its volume, turning it into a catastrophic event. Mobility is the direct measure of the thread posed by an erosive landslide as it plays a dominant role in controlling the enormous impact energy. However, no clear-cut mechanical condition has been presented so far for when and how the erosive landslide gains or loses energy resulting in enhanced or reduced mobility. We pioneer a mechanical model for the energy budget of an erosive landslide that delineates the enhanced or reduced mobility. A fundamentally new understanding is that the increased inertia due to the increased mass is not related to the landslide velocity, but it is associated with the distinctly different entrainment velocity emerging from the inertial frame of reference. The true inertia can be much less than incorrectly proposed previously. We eliminate the existing erroneous perception and make a breakthrough in correctly determining the mobility of the erosive landslide. We reveal that the erosion velocity plays an outstanding role in appropriately determining the energy budget of the erosive landslide. Crucially, whether the erosion related mass flow mobility will be enhanced, reduced or remains unaltered depends exclusively on whether the newly constructed energy generator is positive, negative or zero. This provides a first-ever explicit mechanical quantification of the state of energy, and thus, the precise description of mobility. This becomes a game-changer and fully addresses the long-standing scientific question of why and when some erosive landslides have higher mobility, while others have their mobility reduced. By introducing three important novel mechanical concepts: erosion-velocity, entrainment-velocity and energy-velocity, we demonstrate that the erosion and entrainment are essentially different processes. With this, we draw a central inference: that the landslide gains energy and enhances its mobility if the erosion velocity is greater than the entrainment velocity. The energy velocity delineates the three excess energy regimes: positive, negative and zero. We establish a mechanism of landslide-propulsion that emerges from the net momentum production, providing the erosion-thrust to the landslide. Analytically obtained velocity quantifies the effect of erosion in landslide mobility and indicates the fact that erosion can have the major control on the landslide dynamics. We have also presented a full set of dynamical equations in conservative form in which the momentum balance correctly includes the erosion induced change in inertia and the momentum production. This is a great advancement in legitimate simulation of landslide motion with erosion.

How to cite: Pudasaini, S. P. and Krautblatter, M.: The Mechanics of Landslide Mobility with Erosion, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-14683, https://doi.org/10.5194/egusphere-egu21-14683, 2021.

16:08–16:10
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EGU21-10215
Franck Bourrier and the Members of task A.3.1 of C2ROP project

A comparative analysis between block propagation experiments and predictive simulations of block trajectories was conducted to evaluate the predictive capacities of block propagation analyses. Approximately one hundred blocks were released on two propagation paths with topographical discontinuities and configurations promoting block rolling. The block propagation was analysed at specific locations of the paths, called evaluation screens. A significant variability of the block velocities was measured at the screens and bimodal distributions of the velocities were observed for the screens located downhill topographical discontinuities.

The comparative analysis between the experimental results and the predictive simulations shows a large variability of the simulations results, that illustrates the uncertainties related with these predictions, done without calibration data. Specific limitations of the block propagation models were shown as regards to the modelling of block propagation similar to rolling motion on soft soils. Finally, the simulations were shown more predictive for extreme velocities than for mean ones and for block passing probabilities.

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How to cite: Bourrier, F. and the Members of task A.3.1 of C2ROP project: Benchmark of predictive simulations of block trajectories using field experiments , EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-10215, https://doi.org/10.5194/egusphere-egu21-10215, 2021.

16:10–16:12
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EGU21-10619
Vincent Acary, Franck Bourrier, David Toe, and Francois Kneib


Block propagation models are routinely used for the quantitative assessment of rockfall hazard. In these models, one of the major difficulties is the development of physically consistent and field applicable approaches to model the interaction between the block and the natural terrain. For most of propagation models, a thorough calibration of the input parameters is not available over the wide range of configurations encountered in practice. Consequently, the parameters choice is strongly depending on expert knowledge. In addition, most of models exhibit substantial sensitivity to some parameters, i.e. small changes of these parameters entail large differences in the simulation results.

The trajectory analysis platform Platrock, freely available upon request (contact: franck.bourrier@inrae.fr), allows performing 2D and 3D simulations using both material point rebound models and models, based on non-smooth mechanics, that explicitly account for block shape. This platform provides several simulation tools for detailed analyses of block propagation on study sites.

The possibilities of the predictive capabilities of different block propagation modelling approaches integrated into the Platrock platform have been assessed on a well-documented study site, where a benchmark of propagation models has been done in the context of C2ROP research project. This analysis emphasized the capacities of trajectory analyses to traduce block propagation but also demonstrated their substantial sensitivity to model parameters. The results from these simulations cannot be relevantly interpreted if they are not accompanied with calibration proofs, sensitivity analysis, and detailed interpretation of the results from the expert in charge of the study.

How to cite: Acary, V., Bourrier, F., Toe, D., and Kneib, F.: Comparing different block propagation modelling approaches using the Platrock simulation platform , EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-10619, https://doi.org/10.5194/egusphere-egu21-10619, 2021.

Deposition and impact of rockfalls, rock slides and rock avalanches
16:12–16:14
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EGU21-8442
Peter Tropper, Kurt Krenn, and Diethard Sanders

The Tsergo Ri rockslide represents one of the world's biggest rockslides in crystalline rocks (original volume: 1010 m3). The mass movement comprises migmatites, leucogranites, orthogneisses and paragneisses (Weidinger et al. 2014). During mass-wasting, frictionites and microbreccias formed at the base of the rockslide. The frictionite is mainly composed of a glassy matrix containing biotite, quartz, and abundant plagioclase and K-feldspar. Biotite locally shows a transformation to spinel + glass in highly glassy microdomains. Fe-rich layers in the glass indicate melting of biotite-rich layers of the protolith biotite-bearing orthogneiss. Locally, quartz grains are rimmed by a thin layer of SiO2 glass (lechatelierite).

Investigations by McMillan et al. (1991) and Kowitz et al. (2013) have shown that shocked quartz shows a shift in the main A1 Raman mode down to lower wavenumbers with increasing pressures. Tropper et al. (2017) and Sanders et al. (2020) found that quartz from the frictionites in the Köfels landslide (Austria) shows a significant shift of up to 4 cm-1 in the main A1 Raman mode. Therefore micro-Raman spectroscopy was applied to quartz crystals with and without lechatelierite rims in the Tsergo Ri frictionites. Raman maps of quartz grain areas were prepared using a HORIBA Jobin Yvon LabRam HR800 micro-spectrometer equipped with a 30 mW He-Ne laser (633 nm emission).

Micro-Raman spectroscopy of 'normal' quartz yielded an intense A1 Raman mode at 464 cm-1, whereas  quartz without lechatelierite rims shows a shift of this band down to 461.5 cm-1. The highest shifts down to 460.5 cm-1 were observed in quartz grains rimmed by lechatelierite. It is also noteworthy that these grains show an internal gradient of Raman shift of up to 3 cm-1 from the core (463.5 cm-1) to the rim (460.5 cm-1) to just below the lechatelierite rims. This is an important observation since lechatelierite formation in frictionites from rockslides was considered so far to be a function of temperature only. Because lechatelierite only rims quartz with strongly shifted A1 band numbers, we interpret lechatelierite formation to be driven by both temperature and pressure, at least under frictionite conditions. The completely molten granitic matrix and the breakdown of biotite to spinel + melt indicates minimum temperatures of 900-1000°C. Sanders et al. (2020) showed that the shifted A1 mode of quartz is stable only below 1100°C, thus giving an upper limit of the temperature range. The observed Raman shift of the A1 mode and the presence of lechatelierite strongly suggest that a pressure of possibly >24-26 GPa was attained (cf. McMillan et al. 1991, Kowitz et al. 2013). The data from Köfels and Tsergo Ri provide the first quantitative estimates of peak pressures during frictionite formation, and show that UHP-modified quartz associated with lechatelierite is common in landslides of silica-rich rocks.

 

 

References:

Kowitz et al. 2013: Earth and Planetary Science Letters, 384:17

McMillan et al. 1992: Physics and Chemistry of Minerals, 19:71

Sanders et al. 2020: EGU2020-4831

Tropper et al. 2017: Mitteilungen der Österreichischen Mineralogischen Gesellschaft, 163: 89

Weidinger et al. 2014: Earth and Planetary Science Letters, 389:62

How to cite: Tropper, P., Krenn, K., and Sanders, D.: Beyond ultra-high pressure metamorphism: evidence for extremely high pressure conditions during frictional fusion in gigantic landslides using micro-Raman spectroscopy of quartz: the Tsergo Ri (Langtang Himal, Nepal) rockslide, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-8442, https://doi.org/10.5194/egusphere-egu21-8442, 2021.

16:14–16:16
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EGU21-4759
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ECS
Camilla Lanfranconi, Paolo Frattini, Giovanni Battista Crosta, Gianluca Sala, Davide Bertolo, Marco Paganone, Michel Stra, and Patrick Thuegaz

Despite their centrality to rockfall risk management, two issues are frequently overlooked: the role of forests in rockfall dynamic and the fragmentation phenomenon. To investigate the importance of these issues we have developed advanced modelling case studies in two representative sites that have been recently affected by rockfall events in the Aosta Valley Region (Western Italian Alps). In the Saint Oyen case study, about 17,500 m3 of rock detached in March 2019 and reached a service road and the sport center in the lower part of the slope, passing through a mature fir forest. The presence of the forest has significantly influenced the rocks distribution along the slope, increasing the lateral dispersion of trajectories and reducing the mobility. For the design of defensive works, 3D rockfall models of three future potential risk scenarios were therefore performed by using the tree-impact algorithm of the code HY-STONE (Frattini et al., 2012). This algorithm provides the location of impacts on trees, the absorbed energy, and the deviation angle. The input parameters (i.e., the value of diameter at breast height and the forest density) were based on direct measurements of the fir forest. Compared with a traditional simulation without the protective role of forests, the results of 3D numerical modelling with tree-impact algorithm show a decrease in the number of blocks impacting the barriers (91%), no variations in the bouncing heights (for 95th percentile), and an increase in the kinetic energies due to a filter effect by the forest (85% for 95th percentile). In the Roisan case study, about 1,050 m3 of rock toppled in October 2019. While the main body of the rockfall stopped in a relatively flat area close to the failure, two blocks were exceptionally able to reach the foot of the slope causing the interruption of a municipal road. An attempt to back-calibrate this event with HY-STONE showed difficulties to describe the behaviour of these isolated blocks with respects to the main landslide body. A possible explanation for this behaviour is that the detached volume fragmented soon after impacting the slope, giving rise to flying fragments with higher mobility. To test this hypothesis we accounted for fragmentation through a specific algorithm of HY-STONE that fragments the falling blocks when their energy overcomes a certain threshold and simulate the behaviour of the resulting fragments. This approach allowed to accurately replicate the rockfall event. We therefore adopted this approach for defensive-works design, simulating all the unstable volumes overhanging the municipal road. Compared with a traditional simulation, the results of 3D numerical modelling with fragmentation algorithm show an increase in the number of blocks impacting the barriers (86%) and in the bouncing heights (96% for 95th percentile), with a decrease of the kinetic energy due to comminution (39% for 95th percentile). These two case studies demonstrate the importance of accounting for the forest or for fragmentation in the design of cost-effective defensive works.

 

Frattini P, Crosta GB, Agliardi F (2012) Rockfall characterization and modeling. Landslides: types, mechanisms and modelling 22:267-281

How to cite: Lanfranconi, C., Frattini, P., Crosta, G. B., Sala, G., Bertolo, D., Paganone, M., Stra, M., and Thuegaz, P.: Advanced rockfall modelling for risk mitigation: tree impact and fragmentation, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-4759, https://doi.org/10.5194/egusphere-egu21-4759, 2021.

16:16–16:18
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EGU21-2431
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ECS
Chung-Hsun Lee, Cheng-Han Lin, and Ming-Lang Lin

The past decade has witnessed increasing case studies on the application of 3D discrete element modeling to assess potential rockslide disasters. The assessment is usually based only on the influence area related to kinematic process and final deposition by the simulation. Currently, the hazard of the rockslide-structure interaction is not well defined, and only a few studies have quantality this behavior with a parametric analysis. A dip slope disaster case history on 18 August 1997 in Taiwan was simulated in this study using discrete element method (DEM). The landslide intensely damaged a five-floor building complex of the Lincoln community and caused 28 death. This study first gathered historical aerial images, geology maps of 1:50,000 scale, post-disaster investigation reports, and in-situ photos to clarify the geological and geometry conditions of the dip slope and its spatial relationship to the Lincoln community. Most importantly, a 3D geomechanical model was developed for the numerical study. With the advantage of DEM analysis on large deformation problems, the entire impact process of the dip slope failure was simulated, starting from rock mass sliding to collision and breaking during movement, impacting on the structural buildings and progressive failure of the structures. The simulated results agree well with the field observation after the incident in 1997. The parametric results show that the configuration of the geological discontinuity dominates the magnitude of the potential sliding block, and the rockslide-structure interactions are affected by the relative location between rock slope and buildings and the strengths of rock mass and structure elements. Overall, the 3D DEM-based simulation provides qualitative information on the impact process of the rockslide and the damage states of the building complex. This validated numerical approach can be a valuable tool for assessing the building vulnerability to rockslide with scenario study.

How to cite: Lee, C.-H., Lin, C.-H., and Lin, M.-L.: A Numerical Study of Rockslide-Structure Interactions in a Dip Slope Disaster by 3D Discrete Element Modeling , EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-2431, https://doi.org/10.5194/egusphere-egu21-2431, 2021.

Societal consequences of rockfalls, rock slides and rock avalanches
16:18–16:23
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EGU21-15575
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ECS
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solicited
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Highlight
James Glover and Christoph Nänni

Rockfall modelling draws on the experience of researchers, geologists, engineers and authorities to provide protection solutions for rockfall hazards. Decision making when dealing with rockfalls is aided with sophisticated rockfall models. While there are a number of modelling tools available. The ability to make informed decisions on appropriate protection measures is dependent on the user, available data, scenario setting and post processing of simulation results. Despite the advances in the capabilities of rockfall models, there is often disparity between the state of the art in research and rockfall management in practice. With the use of a series of case studies along roadways in Switzerland, we explore some of the issues and challenges in modelling rockfalls. From defining initial conditions for rockfall simulations, the use of simplified empirical methods and advanced modelling techniques and the need for probabilistic data for design decisions, we provide insights into the application of rockfall modelling in practice.    

How to cite: Glover, J. and Nänni, C.: Challenges in rockfall modelling for roadway management, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-15575, https://doi.org/10.5194/egusphere-egu21-15575, 2021.

16:23–16:25
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EGU21-3179
Nikolai Voronov and Valentin Sapunov

The course "Life Safety" was introduced in higher educational institutions of Russia in the 1990s. It combined information from sanitary medicine, criminology and was aimed at developing self-safety in students. The realities of 2020 required the creation of an anti-virus safety section within the course. The teaching of this problem had experienced in some Russian institutions and universities. This topic is taught to students both through personal contact with the lecturer and on-line. The branch of course is based on the following sections of modern science and practice: 1. Virology, 2. Global ecology, 3. Sanitation and preventive medicine. Teaching contributes to the formation of an objective view of the dangers of viruses in young people, without diminishing or exaggerating the real dangers of infectious diseases. Much attention is paid to the following sections of modern science: 1. The theory of the biosphere by Vladimir Vernadsky, 2. The doctrine of genetic instability and "horizontal transmission", providing informational unity of the biosphere, supported by viruses (Nobel Prize for Barbara McClintoch, 1983). Teaching is combined with practical exercises on the use of personal protective equipment against viral infections. The idea is brought to the students that viruses are a necessary component of the biosphere. They cannot be suffocated and it is impossible to be completely isolated from them. Teaching this course will contribute to improving the health indicators of the population. At the sessions of the European Geosciences Union, it is planned to hold a presentation of programs and teaching textbooks for this course.

How to cite: Voronov, N. and Sapunov, V.: Teaching the basics of anti-virus safety in the course "Life Safety", EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-3179, https://doi.org/10.5194/egusphere-egu21-3179, 2021.

16:25–17:00