Special Issue "Rock Falls"

A special issue of Geosciences (ISSN 2076-3263). This special issue belongs to the section "Natural Hazards".

Deadline for manuscript submissions: 25 September 2022 | Viewed by 984

Special Issue Editors

Dr. Alexander Preh
E-Mail Website
Guest Editor
1. Institute of Geotechnics, Vienna University of Technology, 1040 Vienna, Austria 2. PI Geotechnics ZT GmbH, 1140 Wien, Austria
Interests: landslides; rockfall; natural hazard; numerical modeling
Dr. Johann Thomas Sausgruber
E-Mail Website
Guest Editor
Torrent and Avalanche Control and Protection Forest Policy, Agriculture, Regions and Tourism, Department of Forestry and Sustainability, Federal Ministry Republic of Austria, 6020 Innsbruck, Austria
Interests: engineering geology; natural hazards; landslides; monitoring

Special Issue Information

Dear colleagues,

We understand the process rock fall as the detachment of larger coherent rock masses and the following runout. Especially for this landslide type, the estimation of its hazard is difficult. Even though clear mechanical models are mostly available to deal with the detachment (e.g., limit equilibrium methods for analyzing rock wedges), it is often challenging to correctly identify the initial failure mechanism and estimate the potential volume of detachment. The runout process, in turn, is in most cases a process chain of moving individual fragments (fragmental rockfall), dynamic interaction of fragments, and mass flows of rock fragments (dry fractional flow). According to the prevailing dominant mechanism, conventional rockfall programs (lumped mass, rigid body, and hybrid models), the discrete element method as well as mass flow models (r.avaflow, Dan code, etc.) are used to calculate the runout. The extent to which the dynamic interaction between fragments and the progressive fragmentation of moving mass must be considered is not yet fully understood. Holistic models that are able to deal with the detachment and the following runout in a single computational run are extremely computationally intensive and are still partly experimental in nature.

This Special Issue aims to collect all research developments related to the whole rock fall process (detachment and runout) and provide a comprehensive update on the state of the art.

Dr. Alexander Preh
Dr. Johann Thomas Sausgruber
Guest Editors

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Keywords

  • rock fall
  • fragmental rockfall
  • mass flows
  • detachment mechanisms
  • runout
  • numerical models
  • landslides
  • natural hazard

Published Papers (2 papers)

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Research

Article
Challenges Assessing Rock Slope Stability Using the Strength Reduction Method with the Hoek–Brown Criterion on the Example of Vals (Tyrol/Austria)
Geosciences 2022, 12(7), 255; https://doi.org/10.3390/geosciences12070255 - 21 Jun 2022
Viewed by 177
Abstract
To estimate the hazard posed by rock slopes, it is essential to determine the overall stability and potential detachment volume. This is mostly solved using numerical methods together with the strength reduction method (SRM). Many calculation programs do not provide a direct implementation [...] Read more.
To estimate the hazard posed by rock slopes, it is essential to determine the overall stability and potential detachment volume. This is mostly solved using numerical methods together with the strength reduction method (SRM). Many calculation programs do not provide a direct implementation of the Hoek–Brown (HB) criterion. Equivalent Mohr–Coulomb (MC) parameters are often used. Especially for steep rock slopes, the use of equivalent MC parameters with numerical codes and the SRM lead to poor estimates of safety factors. The problem lies in the required and often difficult estimation of a suitable range of minor principal stresses over a ‘slope height’. In the example of the stability analysis of the rock slope Vals in Tyrol/Austria, we show the differences between the application of equivalent MC parameters and a direct application of the HB criterion with apparent MC parameters. The detachment volume and stability are overestimated when applying equivalent MC parameters, as confirmed by calculations with the continuum mechanics code FLAC3D (Itasca Consulting Group). However, the SRM with HB material (i.e., apparent MC parameters) results in a safety factor that cannot be applied to HB parameters. To date, it has not been possible to determine the HB parameters for limit equilibrium via the SRM. This challenge was overcome by fitting an HB envelope to the original HB shear envelope reduced by the safety factor. The envelope is adjusted by two HB variables: GSI and D. This allows to determine the HB parameters at limit equilibrium. It helps to make more realistic predictions about the detachment mechanism and volume. Full article
(This article belongs to the Special Issue Rock Falls)
Article
Impacts of Gravitational Mass Movements on Protective Structures—Rock Avalanches/Granular Flow
Geosciences 2022, 12(6), 223; https://doi.org/10.3390/geosciences12060223 - 25 May 2022
Viewed by 385
Abstract
Rock avalanches and landslides lead to gravitational flow into their runout areas, which poses increasing danger to settlement areas and infrastructure in the Alpine region as a result of climate change. In recent years, a significant increase in extreme events has been registered [...] Read more.
Rock avalanches and landslides lead to gravitational flow into their runout areas, which poses increasing danger to settlement areas and infrastructure in the Alpine region as a result of climate change. In recent years, a significant increase in extreme events has been registered in the Alps due to climate change. These changes in the threat to settlement areas in the Alpine region have resulted in the need for the construction of sustainable protective structures. Many structures are rigid, but others are now also increasingly flexible, e.g., net and dam structures, which are mainly earth dams with geogrids. In this study, empirical model experiments and numerical simulations were carried out to estimate the flow depth, the deposition forms and the effects on protective structures. Numerical programs usually require unknown input parameters and long computation times for a realistic simulation of the process. This study shows the results of model tests with different granular materials. Furthermore, different design approaches of different authors are presented. Finally, a design model based on the model tests of the University of Innsbruck for rigid barriers, nets and dams due to rock avalanches is presented. Full article
(This article belongs to the Special Issue Rock Falls)
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Planned Papers

The below list represents only planned manuscripts. Some of these manuscripts have not been received by the Editorial Office yet. Papers submitted to MDPI journals are subject to peer-review.

1. Title: The unusually long runout of the Alpl rock fall (Tyrol, Austria).  An analysis of the underlying mechanisms

Authors: Alexander Preh, Thomas Sausgruber

Abstract: On 22nd March 2012, shortly before midnight about 33 km west of Innsbruck (Tyrol, Austria), a rock fall occurred in the Mieminger mountain chain. Despite the relatively small detached volume of about 75.000 m³, this “rock fall” had an exceptional long runout of 2.6 kilometres. This event would normally be described as a rock fall or a rock avalanche in the literature. Interestingly, after detailed field investigations it turned out that in real it was a process chain. The process started as a fall. However, the falling rock mass was rapidly and heavily fragmented by the massive impact on the flatter toe of the rock slope. The process then rapidly transitioned into a mass flow/rock avalanche due to the heavy fragmentation and sliding onto old snow. It turned out, that the entire process (the process chain) can be calculated with sufficient accuracy using mass flow models such as the DAN code or r.avaflow. The extreme mobility of the process can be explained by the cover of old snow on the runout path, which was not eroded but acted as a sliding medium and significantly reduced the basal shear resistance.

2. Title: Challenges assessing rock slope stability using the Strength Reduction Method with the Hoek-Brown criterion on the example of Vals (Tyrol/Austria)

Authors: Mariella Illeditsch, Alexander Preh, Thomas Sausgruber

Abstract: Since many calculation programs do not provide a direct implementation of the Hoek-Brown (HB) criterion, equivalent Mohr-Coulomb (MC) parameters are often used. Especially for steep rock slopes, it is known that the use of equivalent MC parameters with numerical codes and the Strength Reduction Method (SRM) leads to poor estimates of safety factors. The problem lies in the required estimation of a suitable range of minor principal stresses over a slope height. On the example of the stability analysis of the rock slope Vals in Tyrol/Austria, the differences between the application of equivalent MC parameters and a direct application of the HB criterion with apparent MC parameters are shown. Calculations with the continuum mechanics code FLAC3D (Itasca Consulting Group) have confirmed that the detached volume and stability are potentially overestimated when equivalent MC parameters are applied. However, SRM with HB material (i.e. apparent MC parameters) results in a safety factor that cannot be directly applied to either HB or apparent (local) MC parameters. So far, it was not possible to determine HB parameters for limit equilibrium via the SRM. This challenge was overcome by fitting a HB envelope to the original HB shear envelope reduced by the safety factor, by varying two variables (GSI and D). This allows the HB parameters at limit equilibrium to be determined to make more realistic predictions about the detachment mechanism and volume.

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