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

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

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 :

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

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

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

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

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 : 40LFinal 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