A methodology to obtain the block size distribution of fragmental rockfall deposits

Ruiz-Carulla, Roger; Corominas, Jordi; Mavrouli, Olga

doi:10.1007/s10346-015-0600-7

Cited by 73 publications

(62 citation statements)

References 23 publications

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“…Budetta, 2004;Lan et al, 2010) or expert opinion (e.g. Romana et al, 2003). Furthermore, several techniques exist based on which the depositional ages of rocks can be reconstructed in absolute terms (e.g.…”

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confidence: 99%

Quantifying the effect of forests on frequency and intensity of rockfalls

Moos

Dorren

Stoffel

2017

Nat. Hazards Earth Syst. Sci.

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Abstract. Forests serve as a natural means of protection against small rockfalls. Due to their barrier effect, they reduce the intensity and the propagation probability of falling rocks and thus reduce the occurrence frequency of a rockfall event for a given element at risk. However, despite established knowledge on the protective effect of forests, they are generally neglected in quantitative rockfall risk analyses. Their inclusion in quantitative rockfall risk assessment would, however, be necessary to express their efficiency in monetary terms and to allow comparison of forests with other protective measures, such as nets and dams. The goal of this study is to quantify the effect of forests on the occurrence frequency and intensity of rockfalls. We therefore defined an onset frequency of blocks based on a powerlaw magnitude-frequency distribution and determined their propagation probabilities on a virtual slope based on rockfall simulations. Simulations were run for different forest and non-forest scenarios under varying forest stand and terrain conditions. We analysed rockfall frequencies and intensities at five different distances from the release area. Based on two multivariate statistical prediction models, we investigated which of the terrain and forest characteristics predominantly drive the role of forest in reducing rockfall occurrence frequency and intensity and whether they are able to predict the effect of forest on rockfall risk. The rockfall occurrence frequency below forested slopes is reduced between approximately 10 and 90 % compared to non-forested slope conditions; whereas rockfall intensity is reduced by 10 to 70 %. This reduction increases with increasing slope length and decreases with decreasing tree density, tree diameter and increasing rock volume, as well as in cases of clustered or gappy forest structures. The statistical prediction models reveal that the cumulative basal area of trees, block volume and horizontal forest structure represent key variables for the prediction of the protective effect of forests. In order to validate these results, models have to be tested on real slopes with a wide variation of terrain and forest conditions.

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confidence: 99%

Quantifying the effect of forests on frequency and intensity of rockfalls

Moos

Dorren

Stoffel

2017

Nat. Hazards Earth Syst. Sci.

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“…Two main consequences of the fragmentation are the generation of multiple fragments and the divergence of the fragment trajectories downhill from the impact point. After an impact involving fragmentation, the initial rock mass generates a number of block fragments that can be characterized by a volume distribution (Ruiz-Carulla et al 2015a). Further features are higher bounces, higher post-impact velocities and the ejection of small fragments.…”

Section: -Block Shapementioning

confidence: 99%

“…During the propagation of the mass downslope, the original distribution may be modified by the disaggregation of the rock mass along pre-existing discontinuities and the breakage of intact rock. The resulting distribution after the fragmentation, including disaggregation and breakage, is the Rockfall Block Size Distribution (RBSD) (Hantz et al 2014, Ruiz-Carulla et al 2015a). Fig.…”

Section: Conceptual Fragmentation Frameworkmentioning

confidence: 99%

RockGIS: a GIS-based model for the analysis of fragmentation in rockfalls

et al. 2017

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ABSTRACT:A Rockfall is a mass instability event frequently observed in road cuts, open pit mines and quarries, steep slopes and cliffs. After its detachment, the rock mass may disaggregate and break due to the impact with the ground surface, thus producing new rock fragments. The consideration of the fragmentation of the rockfall mass is critical for the calculation of the trajectories of the blocks and the impact energies, for the assessment of the potential damage and the design of protective structures. In this paper, we present RockGIS, a GIS-Based tool that simulates stochastically the fragmentation of the rockfall, based on a lumped mass approach. In RockGIS, the fragmentation is triggered by the disaggregation of the detached rock mass through the pre-existing discontinuities just before the impact with the ground. An energy threshold is defined in order to determine whether the impacting blocks break or not. The distribution of the initial mass between a set of newly generated rock fragments is carried out stochastically following a power law. The trajectories of the new rock fragments are distributed within a cone. The fragmentation model has been calibrated and tested with a 10,000m 3 rockfall that took place in 2011 near Vilanova de Banat, Eastern Pyrenees, Spain.

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“…11 Rockfall Block Size Distribution (RBSD) from 6 fragmental rockfalls events inventoried in Catalonia (from Ruiz-Carulla et al 2017) number of fragments generated is an order of magnitude bigger than the original IBSD. Most of the new fragments are small and appear concentrated forming a young debris cover at the base of the cliff (Ruiz-Carulla et al 2015a). The number of fragments smaller than 0.01 m 3 represents more than 60% of the total.…”

Section: Fragmentation In Rockfallsmentioning

confidence: 99%

“…The rock fragments were measured directly in the field one by one with a tape. In case the deposit formed a continuous young debris cover with a high number of blocks to be measured, the methodology proposed by Ruiz-Carulla et al (2015a) was followed. The rockfall volume involved in these events ranges from 2.6 m 3 to 10,000 m 3 .…”

Section: Fragmentation In Rockfallsmentioning

confidence: 99%

Rockfall Occurrence and Fragmentation

Corominas

Mavrouli

Ruiz-Carulla

2017

Advancing Culture of Living With Landslides

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Rockfalls are very rapid and damaging slope instability processes that affect mountainous regions, coastal cliffs and slope cuts. This contribution focuses on fragmental rockfalls in which the moving particles, particularly the largest ones, propagate following independent paths with little interaction among them. The prediction of the occurrence and frequency of the rockfalls has benefited by the rapid development of the techniques for the detection and the remote acquisition of the rock mass surface features such as the 3D laser scanner and the digital photogrammetry. These techniques are also used to monitor the deformation experienced by the rock mass before failure. The quantitative analysis of the fragmental rockfalls is a useful approach to assess risk and for the design of both stabilization and protection measures. The analysis of rockfalls must consider not only the frequency and magnitude of the potential events but also the fragmentation of the detached rock mass. The latter is a crucial issue as it affects the number, size and the velocity of the individual rock blocks. Several case studies of the application of the remote acquisition techniques for determining the size and frequency of rockfall events and their fragmentation are presented. The extrapolation of the magnitude-frequency relationships is discussed as well as the role of the geological factors for constraining the size of the largest detachable mass from a cliff. Finally, the performance of a fractal fragmentation model for rockfalls is also discussed.

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A methodology to obtain the block size distribution of fragmental rockfall deposits

Cited by 73 publications

References 23 publications

Quantifying the effect of forests on frequency and intensity of rockfalls

Quantifying the effect of forests on frequency and intensity of rockfalls

RockGIS: a GIS-based model for the analysis of fragmentation in rockfalls

Rockfall Occurrence and Fragmentation

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