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

Context of the study Frank slide, m 3 Pirulli and Mangeney, m m 3 Purpose : numerical modeling of the propagation of a rock avalanche

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

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

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

Results of the fitting : V x V y V z ω x ω y ω z Before and after impact Determination of the kinematics of the brick from the trajectories of the points : back-analyse 1 Experimental identification of the parameters

Experimental measurements V x V y V z ω x ω y ω z Measured before impact V x V y V z ω x ω y ω z Measured after impact Introduction in the discrete model Numerical simulation for a given set of the parameters (e n 2, μ, k n, k t ) V x V y V z ω x ω y ω z Computed after impact Comparison Erreur function : err(e n 2, μ, k n, k t ) Minimization Determination of the contact parameters from the kinematics of the brick: back-analyse 2 Experimental identification of the parameters

Result of the fitting Example of result for a Brick- Support impact Optimal parameters: en2en2 μknkn k t /k n Brick/Support contact 0,530,46 (φ=25°)10 5 0,42 Brick/Brick contact 0,130,86 (φ=41°)10 5 0,27

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

Results of the simulation: Simulation of 6300 randomly poured bricks

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

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

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

Energy considerations The numerical results provide the evolution of the energy levels in the flow: -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 time: Along the X-axis: -There is a peak of energy dissipation around the transition zone -This peak is related to inter- particle energy dissipations

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 ?

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

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

Conclusion Cutting Procedure

Conclusion Thank you Guilhem Mollon