02 Increasing the usability of flexible nets in natural terrain by large-scale rock impact tests

Sanchez Miguel1, Bartelt Perry1, Caviezel Andrin1, Lanter Andreas2

  1. WSL Institute for Snow and Avalanche Research SLF, Davos, Switzerland
  2. Geobrugg AG, Romanshorn, Switzerland

Rockfalls are a geological phenomenon that can be a major hazard and a threat to life, properties and infrastructure. Despite their relatively small size compared to other mass movements, rockfall can be very destructive as high velocities and consequently, high energies can be reached during their propagation [1].  At the core of the rockfall problem is the ability to model contact-impact phenomena. Rock contact with the ground defines the runout distance, dispersion and velocity of falling rocks. 

SLF is conducting detailed field studies of rockfalls at different natural alpine sites to investigate the dynamics and runout behavior of different rock shapes [2]. Through real scale testing, we are gaining better insights into the rockfall motions detailing impact interactions with different terrains.  The full-scale rockfall tests are being used to validate mixed hard/soft-contact approaches [3]. These models treat the ground as a deformable layer that compacts under the dynamic action of the rocks [4]. When the ground can no longer deform, the hard-contact approach is used to simulate the rock rebound.    

In September 2019, a flexible rockfall barrier was installed at the Chant Sura test site. The testing aims to reproduce and understand impact loadings in a more realistic setup compared to current certification methods using vertical drop tests. The first tests show low impact energies for blocks of 800 kg. For blocks of 2700 kg, the energies can reach up to 1000 kJ. Calculated energies obtained from the tests show that rotational energies can amount for 15 to 30% of the block energy. Thus, even the first tests reveal the importance of studying the role of rotational energies in rockfalls in general and barrier interaction in particular.

References

[1]     Cruden, David. 1996. “Cruden,D.M.,Varnes, D.J.,1996, Landslide Types and Processes, Transportation Research Board, U.S. National Academy of Sciences, Special Report, 247: 36-75.” Special Report - National Research Council, Transportation Research Board 247.

[2]    Leine, R.I.; Schweizer, A.; Christen, M.; Glover, J.; Bartelt, P.; Gerber, W., 2014: Simulation of rockfall trajectories with consideration of rock shape. Multibody System Dynamics, 32, 2: 241-271. doi: 10.1007/s11044-013-9393-4

[3]    Lu, G.; Caviezel, A.; Christen, M.; Demmel, S.E.; Ringenbach, A.; Bühler, Y.; Dinneen, C.E.; Gerber, W.; Bartelt, P., 2019: Modelling rockfall impact with scarring in compactable soils. Landslides, 16: 2353-2367. doi: 10.1007/s10346-019-01238-z

[4]   Caviezel, A.; Demmel, S.E.; Ringenbach, A.; Bühler, Y.; Lu, G.; Christen, M.; Dinneen, C.E.; Eberhard, L.A.; Von Rickenbach, D.; Bartelt, P., 2019: Reconstruction of four-dimensional rockfall trajectories using remote sensing and rock-based accelerometers and gyroscopes. Earth Surface Dynamics, 7, 1: 199-210. doi: 10.5194/esurf-7-199-2019