Experimental study on rockfall fragmentation: In situ test design and first results

Ripoll, José Antonio Gili; Carulla, Roger Ruiz; Casado, Gerard Matas; Dulcet, Jordi Corominas; Lantada, Nieves; Andrés, María Amparo Núñez; Mavrouli, Olga; Pozuelo, Felipe Buill; Sánchez, José Moya; Valls, Albert Prades; Moreno, Sjædric

doi:10.1201/9781315375007-106

Cited by 7 publications

(19 citation statements)

References 1 publication

Supporting

Mentioning

Contrasting

Order By: Relevance

“…With 3–6 events/yr, flake‐like to pebble‐size events onto the upper talus segment are most frequent, whereas return periods of bigger boulders decrease non‐linearly up to 250 years (on T1) with increasing distance to the source rockwalls. Following André (), the frequent supply of apical clasts could result from surficial rockwall flaking, although fragmentation of larger rockfall events after their first ground impact and associated dust clouds need to be taken into account (Gili et al ., ).…”

Section: Discussionmentioning

confidence: 97%

“…Comparing the largest boulder of 11 m 3 at T1 (Figure a) with the maximum Jv of its source rockwall (Figure a) suggests a block size decrease of up to 92%. Similar orders of rockfall fragmentation have been found by numerical (Wang and Tonon, ), experimental (Giacomini et al ., ; Gili et al ., ) and direct field observations (Corominas et al ., ). Nevertheless, the intense surface weathering of large boulders at the talus toe (Figures b and c) may support our calculation in Figure that boulder falls and larger events occur relatively rarely with long return periods of several 10–100 years.…”

Section: Discussionmentioning

confidence: 99%

See 1 more Smart Citation

Structural and thermal controls of rockfall frequency and magnitude within rockwall–talus systems (Swiss Alps)

Meßenzehl

Dikau

2017

Earth Surf Processes Landf

View full text Add to dashboard Cite

Both from a systemic and natural hazard perspective, it is essential to understand the causes and frequency of rockfalls in mountain terrain and to predict the block sizes deposited at specific locations. Commonly, rockfalls are studied either retrospectively, using talus slopes, or directly by rockwall surveys. Nevertheless, our understanding of rockfall activity, particularly at the lower magnitude spectrum, is still incomplete. Moreover, the explanatory framework is rarely addressed explicitly. In this study, we investigate two rockwall-talus systems in the Swiss Alps to estimate the rockfall frequency-magnitude pattern and their key controls. We present a holistic approach that integrates deductive geotechnical and thermal investigations of the source rockwalls with abductive talus-based explanations of rockfall volume and frequency.The rockwalls' three-dimensional (3D) joint pattern indicates that 75% of the blocks may be released as debris fall (< 14 m 3 ) and boulder falls (14-61 m 3 ), which is mirrored in the corresponding talus material. Using two-year records of near-surface rockwall temperatures as input for a 1D heat conduction model underlines the destabilizing role of seasonal ice segregation. Deepest frost cracking of 300 cm may occur on the north-northeast (NNE)-exposed, snow-rich rockwall, with peaks at the outermost surface. The synthesis of all data suggests that infrequent, large planar slides (approximately every 250 years) overlain by smaller, more frequent wedge and toppling failures (approximately every 17-50 years) as well as high-frequency flake-like clasts (3-6 events/year) characterize the rockfall frequency-magnitude pattern at Hungerli Peak.Here, we argue that small-size rockfalls need more scientific attention, particularly in discontinuous permafrost zones. Our study emphasizes that future frequency-magnitude research should ideally incorporate site-specific structural and thermal properties, rather than just focusing on climatic or meteorological triggers. We discuss how holistic rockwall-talus approaches, as proposed here, could help to increase our process understanding of rockfalls in mountain environments.

show abstract

Section: Discussionmentioning

confidence: 97%

Section: Discussionmentioning

confidence: 99%

Structural and thermal controls of rockfall frequency and magnitude within rockwall–talus systems (Swiss Alps)

Meßenzehl

Dikau

2017

Earth Surf Processes Landf

View full text Add to dashboard Cite

show abstract

“…At Foj, the number of impacts on the slope (before the main one on the quarry floor below) was 1 or 2, whereas at Ponderosa it was always 1. See Gili et al () for further details on the experiment itself.…”

Section: Methodsmentioning

confidence: 99%

Seismic Energy Analysis as Generated by Impact and Fragmentation of Single‐Block Experimental Rockfalls

et al. 2018

Self Cite

View full text Add to dashboard Cite

The analysis of seismic signals obtained from near‐source triaxial accelerometer recordings of two sets of single‐block rockfall experiments is presented. The tests were carried out under controlled conditions in two quarries in northeastern Spain; in the first test (Foj limestone quarry, Barcelona), 30 blocks were released with masses ranging between 475 and 11,480 kg. The second test (Ponderosa andesite quarry, Tarragona) consisted of the release of 44 blocks with masses from 466 to 13,581 kg. An accelerometer and three high‐speed video cameras were deployed, so that the trajectories, velocities, and block fragmentation could be tracked precisely. These data were used to explore the relationship between seismic energy and rockfall kinetics (the latter obtained from video analysis). We determined absolute and relative values of seismic energy and used them to estimate rockfall volumes. Finally, the seismic signature of block fragmentation was assessed in both the frequency and time domains. The ratios of seismic energy after impact to kinetic energy before impact ranged between 10−7 and 10−4. These variables were weakly correlated. The use of seismic energy relative to impacting kinetic energy was preferred for the estimation of volumes. Block fragmentation impacts were dominated by higher acceleration spectrum centroid frequencies than those of nonfragmentation impacts: 56.62 ± 2.88 and 48.46 ± 4.39 Hz at Foj and 52.84 ± 12.73 and 38.14 ± 4.73 Hz at Ponderosa.

show abstract

“…Crosta et al () and Hogan et al () found that the integral size distribution for grains produced during low‐energy impact experiments against rock is well fitted by a power law whose exponent is the fractal dimension with a power spectrum of about 2 when the integral fraction is plotted as a function of the particle diameter. Gili et al () propose a similar power law with an exponent ranging between 0.18 and 0.69 for much larger clasts (between several centimeters to meters in diameter) that chip off boulders during artificial rock falls. However, the size range where these power law functions hold is never wider than 2–3 orders of magnitude in terms of clast diameter.…”

Section: Impact Study and Fragmentationmentioning

confidence: 96%

Extremely Energetic Rockfalls

2018

View full text Add to dashboard Cite

Extremely energetic rockfalls (EERs) are defined here as rockfalls for which a combination of both large volume and free fall height of hundreds of meters results in energy larger than about 80 GJ released in a short time. Examples include several events worldwide. In contrast to low energy rockfalls where block disintegration is limited, in EERs the impact after free fall causes immediate release of energy much like an explosion. The resulting air blast can snap trees hundreds of meters ahead of the fall area. Pulverized rock at high speed can abrade vegetation in a process of sandblasting, and particles suspended by the blast and the subsequent debris cloud may travel farther than the impact zone, blanketing vast areas. Using published accounts and new data, we introduce physically based models formulated on analogies with explosions and explosive fragmentation to describe EERs. Results indicate that a portion of the initial potential energy of the block is spent in rock disintegration at impact (typically 0.2%–18%), while other sources of energy loss (air drag, seismic, sound, and ground deformation) are negligible; consequently, more than 80% of the potential energy is converted to kinetic energy of the fragmented block (ballistic projection, shock wave, sand blast, and dust cloud). We also propose simple estimates for the flow of the dust cloud associated with an EER and its long settling time. The areal extent of the affected zone is estimated from the energy balance and an empirical power law relationship.

show abstract

Experimental study on rockfall fragmentation: In situ test design and first results

Cited by 7 publications

References 1 publication

Structural and thermal controls of rockfall frequency and magnitude within rockwall–talus systems (Swiss Alps)

Structural and thermal controls of rockfall frequency and magnitude within rockwall–talus systems (Swiss Alps)

Seismic Energy Analysis as Generated by Impact and Fragmentation of Single‐Block Experimental Rockfalls

Extremely Energetic Rockfalls

Contact Info

Product

Resources

About