programme interreg iva – alcotra 2007-2013 programme interreg iva – alcotra 2007-2013 m. a. s....
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PROGRAMME Interreg IVa – Alcotra 2007-2013 PROGRAMME Interreg IVa – Alcotra 2007-2013
M. A. S. S. A.
Discrete Modeling of Rock Avalanches
FEDERFonds Européens pour le
Développement Régional
Ensemble au-delà des frontièresInsieme oltre i confini
Guilhem Mollon, Vincent Richefeu, Pascal Villard, Dominique Daudon
3SR Lab, University of Grenoble, France
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Context of the study
Frank slide, 30 103 m3
Pirulli and Mangeney, 2007
103 m3- 105 m3
Purpose : numerical modeling of the propagation of a rock avalanche
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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
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Principles of the modeling
Discrete Element Modeling with
Coulomb friction coefficient and
normal damping
Bricks modeled by sphero-polyedra
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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
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Results of the fitting :
Vx Vy Vz
ωx ωy ωz
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
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Experimental measurements
Vx Vy Vz
ωx ωy ωz
Measured before impact
Vx Vy Vz
ωx ωy ωz
Measured after impact
Introduction in the discrete model
Numerical simulation for a given set of the
parameters (en2, μ, kn, kt)
Vx Vy Vz
ωx ωy ωz
Computed after impact
Comparison
Erreur function : err(en
2, μ, kn, kt)
Minimization
Determination of the contact parameters from the kinematics of the brick: back-analyse 2
Experimental identification of the parameters
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Result of the fitting
Example of result for a Brick-Support impact
Optimal parameters:
en2 μ kn kt/kn
Brick/Support contact 0,53 0,46 (φ=25°) 105 0,42
Brick/Brick contact 0,13 0,86 (φ=41°) 105 0,27
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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: 1mApparent volume: 40L
Number of particle: 6307Material density: 17kN/m3
“Smooth” support
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Results of the simulation:
Simulation of 6300 randomly poured bricks
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Comparison of the experimental and numerical deposits:
First information about the deposit kinematics
Simulation of 6300 randomly poured bricks
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Kinematics of the rock flow
Initial apparent volume : 40LFinal apparent volume : 57L
Volume change along time :
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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
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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
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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 ?
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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
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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
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Conclusion
Cutting Procedure
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Conclusion
Thank you
Guilhem Mollon