All posts by Emmanuel Wyser

Preliminary numerical simulation of landslides using an MPM framework

The Material Point Method (MPM), which is an extension of the particle-in-cell method , provides a promising numerical framework which can naturally handle classical problems involving severe deformations, such as landslides. Interested readers may refer to a general introduction by Fern et al. about MPM here. We are  currently developing an MPM matlab solver capable of solving a variety of elastoplastic problems, ranging from granular impacts to granular collapse.

We here only intend to show some preliminary results of a typical slumping process governed by a Coulomb type material with a non-associated flow rule, considering i) a weak layer with a lower internal frictional angle,  (ii) an heterogeneous cohesion field and, iii) a strain weakening behavior of the material.

The initial geometry of the problem is described in the Figure below. We can set different value for the basal friction, i.e., mu is ranging from 0 (free slip boundary) to 0.5 (increasing stick-slip behavior at the interface). The mass instantly deforms under self-weight loading, i.e., the solver does not iterate to converge toward a force equilibrium before plastic loading to occur.

The two following numerical solution after 6 seconds shows naturally an important contribution of the basal friction both on the strain localization and the runout distance of the slumping mass. This also suggest different modes of deformation regarding the frictional behavior at the basal interface.

Deeper investigations are now required to fully understand the complex nonlinear behavior of a slumping mass.

Accumulated plastic strain considering a lower basal friction coefficient, i.e., mu=0.1
Accumulated plastic strain considering a higher basal friction coefficient, i.e., mu=0.3

Fieldwork in Barcelonnette during September 2018

François Noël, Teresa Gracchi and Emmanuel Wyser of the Risk Analysis Group (UNIL) went to Barcelonnette (France) from the 23rd to the 27th of September for an amazing experimental work in the field dealing with rock fall trajectories and associated topics (e.g. impact response, energy transfer, etc.), amongst other French researchers from Active Deformation Group of the University of Strasbourg (EOST, leaded by Jean-Philippe Malet) and the IRSTEA Institute of Grenoble (leaded by Franck Bourrier).

Several (30) rocks were thrown down into a short but steep gully while seismic signals (EOST) and high-speed imaging (IRSTEA & UNIL) were acquired. High resolution 3D imagings  were acquired thanks to TLS and SfM.

Accelerometers (ISTE & EOST) were also included in few rocky blocks to monitor and acquire data to better understand impact response, angular velocity changes and other exciting data.

 

New staff members at the Risk Analysis Group

The Risk Analysis Group welcomes three new members.

The group welcomes from April 25 to May 27, Melanie Mayers, a master student from Laval University in Québec. Her master project under the direction of Jacques Locat contributes to the Parachute research project. The aim of this project is to integrate various technologies into a workflow for rockfall characterization along linear infrastructures, using a 260 km-long railroad as the study site which is located on Québec’s North Shore, Canada.

Caroline Lefeuvre a master student from the École nationale supérieure des mines d’Alès (EMA, France) is visiting the group from April 11 until September 9 . She will investigate various influences such as thermal incidences over rock slope stability at the study site of La Cornalle (Vaud). Hazards related to rockfall events will also be addressed.

Emmanuel Wyser is starting his Ph.D under the supervision of Prof. Michel Jaboyedoff. His research is oriented toward the study of granular flows and particle-based methods, with numerical and analogue models.