ESR12: irstea (IRSTEA), France & Grenoble Institute of Technology (INPG), France

Modeling of the mechanical behavior of flexible structures against debris flows

Supervisor: Dr. Ing Stéphane Lambert (IRSTEA),  Prof. Francois Nicot (IRSTEA) & Ass. Prof. Bruno Chareyre (Lab. 3SR)

Objective: Realistic assumption of impact force, Validation and new designs of protection structures, Guideline for dimensioning of protection structures;

Methodology:  Debris flows are one of the most severe risks affecting mountainous areas. Strongly dictated by the weather conditions (storms, rainfalls), predicting and preventing the occurrence of such eventsemain very difficult tasks. Mitigation actions consist usually in setting up specific structures in torrent beds in order to control debris flows when occurred. An innovative solution consists in flexible structures, for instance made up of wire nets placed across the torrent bed section. Such open structures make water flows possible, but can control more viscous flows such as debris flows with a possible fraction of gravel or rocks. The thesis will focus on the mechanical behavior of such structures, by developing a numerical tool with engineering purposes. To this aim, a discrete element method will be used (YADE open software), to describe both the mudflow and the flexible structure in interaction (Nicot et al., 2004 and 2007). A specific attention will be given to the modeling of debris flows, described as a saturated granular assembly. Recent developments (Chareyre et al., 2012) carried out to model saturated granular materials with internal flows will be accounted for. Finally, comparisons with case studies will be done in order to validate the numerical tool, and practical recommendations (geometrical configuration, size, constitutive materials) will be drawn in order to optimize the resultant forces developed in the different parts of the structures.

Deliverable: Validation of protection structure designs based on impact forces from WP3, Guidelines for dimensioning of protection structures;

Secondments: INPG: 12 p-ms (numerical simulation), ETHZ: 2 p-ms (DEM crosslink), GEOB (protection systems)

References: Chareyre, B., Cortis, A., Catalano, E., Barthélemy, E. (2012): Pore-scale modeling of viscous flow and induced forces in dense sphere packings. Transport in Porous Media, Vol. 9(2), pp. 473-493. Nicot, F. (2004) : From constitutive modelling of a snowcover to the design of flexible structures. Part II, Some numerical aspects. International Journal of Solids and Structures, Vol. 41, pp. 3339-3352. Nicot, F., Bertrand, D., Gotteland, P., and Lambert, S. (2007): Multiscale approach for geo-composite cellular structures subjected to rock impacts. Int. J. Num. Anal. Methods in Geomechanics, Vol. 31, pp. 1477-1515.