Modelling geophysical mass flows : current challenges and insights from well-controlled experiments
Numerical modelling of geophysical mass flows such as debris flows, rock avalanches, or snow avalanches, generally relies on hydraulic-type depth-averaged approaches based on a shallow-flow approximation. Such modelsa are increasingly being used in an operational context to assess hazards and risks, design protective measures, or anticipate evolutions in the context of global change. However, although certainly successful to some extent, current numerical tools still face numerous challenges that can hinder their prediction capabilities and limit their applicability. One can mention, in particular, shortcomings related to the complex rheological behavior of the materials, the heterogeneity of the flows, the role played by erosion and entrainment processes, etc. I will illustrate some of these issues, and show how they can be alleviated through small-scale and well-controlled experiments designed to improve the understanding of underlying physical processes. I will focus on the particular case of viscoplastic flows and describe two recent projects that allowed us to gain new insights into the dynamics of gravity-driven surges characterized by this rheology. The first project was concerned with the internal dynamics of the surges and involved monitoring the evolution of unyielded regions in the front region using a specific laboratory setup. The experimental data can be used directly to test and improve the asymptotic approximations underlying the shallow-flow models. The second project consisted of investigating the interaction between a surge and a mobile bed through SPH numerical experiments. The simulations revealed a wide variety of entrainment regimes, which can lead to a decrease or increase in overall flow mobility.
Contact Nathanael Machicoane for more information or to schedule a discussion with the seminar speaker.