Experimental Study of Rock Sheds Impacted by Rock Blocks

Abstract. In the framework of rockfall trajectory modelling, the bouncing phenomenon occurring when a rock block impacts with the slope surface is the most difficult to predict, owing to its complexity and its very limited understanding. To date, the rebound is commonly quantified by means of two coefficients of restitution estimated from a rough description of the ground material. To acquire a better knowledge of the bouncing phenomenon and to investigate the influence of various impact parameters, a comprehensive experimental study was undertaken at the LMR-EPFL (Rock Mechanics Laboratory -Swiss Federal Institute of Technology Lausanne).After a summary of the main conclusions drawn from a small-scale study, the paper focuses on half-scale experiments, describing first the testing device and the data processing and analysing then the influence of several impact parameters. It is observed that the rebound and the commonlyused coefficients of restitution expressed for the mass centre of the block depend not only on slope material characteristics, but also on factors related to the kinematics (slope inclination and impact velocity) and to the block (weight, size and shape). As many trajectory computer codes consider constant coefficients of restitution only function of the outcropping material, the trajectory results should be interpreted with caution and always checked against field observations.

Section: Testing Devicementioning

confidence: 99%

Half-scale experimental study of rockfall impacts on sandy slopes

Labiouse

Heidenreich

2009

“…The δ P value can be obtained by evaluating the peak force that acts during the stopping phase (F max ) and by balancing 80÷85% of the kinetic energy of the block and the plastic deformation work done by the stopping force, which is assumed to have a triangular shape: of the multiplicative coefficient derives from the energy impact level: 0.85 is chosen for an impact with less energy than 5000 kJ and 0.80 for an impact with more energy than 5000 kJ. In order to compute F max , it is possible to use the formula developed from the model proposed by Montani et al (1996) and by Labiouse et al (1996), which was derived from studies on rockfall shelter cover thickness:…”

Section: Design Guidelinesmentioning

confidence: 99%

Design of reinforced ground embankments used for rockfall protection

Ronco

Oggeri

Peila

2009

Abstract. The prediction of the effects of rockfall on passive protection structures, such as reinforced ground embankments, is a very complex task and, for this reason, both full-scale tests and numerical dynamic modelling are essential.A systematic set of numerical FEM models, developed in the dynamic field, has been implemented in this work to evaluate the conditions of an embankment that has been subjected to the impact of rock blocks of various sizes at different speeds. These analyses have permitted design charts to be obtained. Furthermore, a simplified analytical approach, based on an equilibrium analysis, has been proposed and its results are compared with numerical data in order to assess its feasibility. A good correspondence between the results has been obtained.

“…A relatively common way of preventing and controlling rockfall hazard in an open-pit mine is to lay an energy-consuming layer on a safety platform (Labiouse et al, 1996). However, research into such cushions seldom considers the effects of the particle size of the cushion on the characteristics of rockfall movement.…”

Section: Introductionmentioning

confidence: 99%

The effects of gravel cushion particle size and thickness on the coefficient of restitution in rockfall impacts

Zhu

Wang

Xia

et al. 2018

Abstract. Gravel cushions are widely used to absorb the impact energy of falling rocks in open-pit mines. A particularly important application is to enhance the energy-absorbing capacity of rockfall sheds. In this paper, we study how varying the thickness and particle size of a gravel cushion influences its energy-consumption and buffering effects. We performed a series of laboratory drop tests by dropping blocks from a fixed height onto cushions of different thicknesses and particle sizes. The results indicate that, for a given impact energy, the cushion thickness has a strong influence on the measured coefficient of restitution (COR) and therefore impact pressure. Additional tests were performed to study how the radius of the block and the height it is dropped from affect the measured COR. This showed that as the movement height of the block is increased the COR also increases, and blocks with larger radii exhibit a larger variability in measured COR. Finally, we investigated the influence of rockfall block radius, r, movement height, H , cushion thickness, h, and particle size, d, on the COR and the damage depth, L, of the cushion. The test results reveal that the cushion thickness is the primary design parameter, controlling not only COR, but also the stability of the cushion material. The results provide a theoretical and practical basis for the design of gravel cushions for rockfall protection.