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PROGRAMME Interreg IVa – Alcotra 2007-2013

PROGRAMME Interreg IVa – Alcotra 2007-2013. FEDER Fonds Européens pour le Développement Régional. M. A. S. S. A. Discrete Modeling of Rock Avalanches. Guilhem Mollon, Vincent Richefeu, Pascal Villard, Dominique Daudon 3SR Lab, University of Grenoble, France.

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PROGRAMME Interreg IVa – Alcotra 2007-2013

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  1. PROGRAMME Interreg IVa – Alcotra 2007-2013 FEDER Fonds Européens pour le Développement Régional • M. A. S. S. A. • Discrete Modeling of Rock Avalanches • Guilhem Mollon, Vincent Richefeu, Pascal Villard, Dominique Daudon • 3SR Lab, University of Grenoble, France Ensemble au-delà des frontières Insieme oltre i confini

  2. Pirulli and Mangeney, 2007 103 m3- 105 m3 Frank slide, 30 103 m3 • Context of the study Purpose : numerical modeling of the propagation of a rock avalanche

  3. Experiences performed at EPFL Base of the study: experimental device from EPFL Manzella and Labiouse 2009 Materials: Object of the study: propagation and deposit of the granular mass

  4. Principles of the modeling Discrete Element Modeling with Coulomb friction coefficient and normal damping Bricks modeled by sphero-polyedra

  5. Experimental identification of the parameters 4 parameters to determine for each type of contact : Experimental device of controlled fall • Filmed by 2 cameras, 1000 frames/seconde • Tracking of 3 points on each frame, and 4 points in total • Back-analysis of the 3D trajectory to obtain the model parameters

  6. Experimental identification of the parameters Determination of the kinematics of the brick from the trajectories of the points : back-analyse 1 Vx Vy Vz ωxωyωz Before and after impact Results of the fitting :

  7. Experimental identification of the parameters Determination of the contact parameters from the kinematics of the brick: back-analyse 2 Experimental measurements Vx Vy Vz ωxωyωz Measured before impact Vx Vy Vz ωxωyωz Measured after impact Comparison Introduction in the discrete model Vx Vy Vz ωxωyωz Computed after impact Erreur function : err(en2, μ, kn, kt) Numerical simulation for a given set of the parameters (en2, μ, kn, kt) Minimization

  8. Result of the fitting Example of result for a Brick-Support impact Optimal parameters:

  9. Simulation of 6300 randomly poured bricks Simulation of the EPFL experiment (Manzella and Labiouse 2009) with bricks randomly poured in the starting box Parameters of the simulation: Release height: 1m Apparent volume: 40L Number of particle: 6307 Material density: 17kN/m3 “Smooth” support

  10. Simulation of 6300 randomly poured bricks Results of the simulation:

  11. Simulation of 6300 randomly poured bricks Comparison of the experimental and numerical deposits: First information about the deposit kinematics

  12. Kinematics of the rock flow Volume change along time : Initial apparent volume : 40L Final apparent volume : 57L

  13. Kinematics of the rock flow Close study of the velocities, angular velocities, and solid fraction during the flow -Velocity is maximum before the transition zone, constant in the deposit -Important angular velocities at the angle, no more rotation in the deposit -Solid fraction decreases in the slope, and slightly increases in the deposit

  14. Energy considerations The numerical results provide the evolution of the energy levels in the flow: Along time: -The kinetic energy is maximal just after the impact on the horizontal plane -The kinetic energy related to rotations is negligible -Most of the energy dissipation is related to basal friction Along the X-axis: -There is a peak of energy dissipation around the transition zone -This peak is related to inter-particle energy dissipations

  15. Influence of the basal friction Introduction of a « macro-roughness » at the blocks scale: Question: How does it compare with a simple increase of the friction coefficient on a regular slope ?

  16. Influence of the basal friction Case A: Increase of the friction coefficient of the slope Deposit Shape Case B: Introduction of a « macro-roughness » Volume Change Energy Balance

  17. Perspectives - Work in progress Modeling of a rock avalanche in a real context Use of a digital Elevation Model Short-term application: Rock avalanche on the Néron (Grenoble, France) in 2011

  18. Conclusion Cutting Procedure

  19. Conclusion Thank you • Guilhem Mollon

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