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.
This new project, started in June 2019, is a pilot study to develop techniques in order to (1) harmonize the 1:25000 geological maps and (2) to improve the Quaternary mapping of the region of “canton de Vaud” in Switzerland. This region includes 3 geographic zones: the Jura mountain, the Pre- Alpes and the molasse Plateau. During the XX century, geological maps have been produced by different authors over decades. Then, limits or stratigraphical attributions may differ from one map to another. In addition, new types of data are now available, in particular a high resolution LiDAR digital elevation model over the entire canton, and geophysical or boreholes data. Three pilot zones have been selected (one by geographic zone) to test new approaches to improve the mapping of geological formations and Quaternary deposits. Field surveys are also planned for the selected zones. Valérie Baumann, a new post doctoral researcher at UNIL, has an extensive experience in geological and Quaternary mapping. She will be in charge of the project, with the contributions of Michel Jaboyedoff, Jean-Luc Epard and Marc-Henri Derron from the Institute of Earth Sciences.
Detail of the union (red line) between the geological maps Monthey (1960; left side) and Diablerets (1990; right side) at scale 1:25000. Note the mismatch between the same geological units.
3D shaded relief from the summits and three old glacial cirques located in the Préalpes obtained from high resolution LiDAR data
View of the old glacial cirque located between the Tour d´Aï and Tour de Mayen
Professor Michel Jaboyedoff and Ph.D student Li Fei from our Risk Analysis Group participated to the 2nd Badong International Geohazards Symposium (BIGS) held in Badong County, Hubei Province, China, from August 24-25, 2019. As a invited speaker, Michel Jaboyedoff delivered a keynote speech with the title “Estimating initial failure surface depths and volumes based on surface information” and visited the landslide in-situ experiment site in Three Gorges Reservoir Area. This conference was a good chance for our group to exchange ideas, experiences on issues related to geohazards with worldwide scholars.
Once again the field course for master students in risk took place in the beautiful valley of Ubaye this year. During 11 days (end of May – beginning of June 2019), 12 students from environmental risk or geological risk had the opportunity to study the landslide of Lavalette, work on rockwall stability and discover the processes leading to debris flows. We had the pleasure to be hosted at the scientific center of Seolane in Barcelonnette.
Like every year, The European Geosciences Union (EGU) General Assembly in Vienna 2019 (7 – 12 April) was a great opportunity for our Risk Group to present recent researches and to interact with the international and multidiscipline platform of experts and scientists.
This assembly was a record-breaking meeting, with 16,250 presentations: 5,531 orals, 9,432 posters, and 1,287 PICOs. The program featured 683 unique scientific sessions together and received 16,273 scientists from 113 countries.
The Risk Group members presented 10 contributions as first authors whose titles are below.
The usual fieldtrip for bachelor students in risk took place in Les Diablerets . About twenty students took part to this course on 1-3 May 2019. The Pont Bourquin landslide was used for a mapping exercise and as a starting point for a risk analysis.
Example of a landslide map produced by students during 1 day mapping
Ryan Kromer is PhD graduate of Queen’s University and a post doctoral researcher at the Colorado School of Mines. He was a visiting PhD student at the University of Lausanne during 2015 and 2016 and is now visiting the Risk group from April to June 2019. During his visit, he will be conducting research on automated monitoring of landslides using terrestrial LiDAR and photogrammetry. The research visit is supported by the Herbette Foundation. Ryan is looking forward to another fruitfull visit with the group.
Active mountain fronts are subject to large scale slope collapses which have the capacity to run long distances on piedmont areas. Over time, fluvial activity and other gravitatory processes can intensively erode and mask primary features related to the collapses. Therefore, to reconstruct the history of their occurrence, further analyses are needed, like sedimentologic analyses. This work focuses on the occurrence of large rock avalanches in the Vinchina region, La Rioja (28°43’27.81” S / 68°00’25.42” W) on the western side of the Famatina range (Argentina). Here, photointerpretation of high-resolution satellite images (Google Earth) allowed us to identify two rock avalanches, with their main scarps at 2575 and 2750 masl. There are no determined absolute ages for these deposits, however by comparing their preservation degree with those dated further north (in similar climatic and landscape dynamics contexts), we can suggest these rock avalanches took place during the Pleistocene.We carried out a fieldwork survey in this remote area, including classical landslide mapping, structural analysis, deposits characterization and sampling. The deposits reach the valley bottom at around 1700 masl. with runouts about 5 km and 5.3 km long. In one of the cases, the morphology of the deposit is well preserved, allowing to accurately reconstruct its extension. However, in the second case, the deposits are strongly eroded by sources draining from the mountain front, therefore further analyses should be done to reconstruct its extension. In addition to morphologic interpretations, a multiscale grainsize analysis was done to di?erentiate rock avalanches from other hillslope deposits: first 3D surface models of surface plots (5x5m) were built with SfM (structure from motion) photogrammetry; then classical sieving and finally laser grain-size analysis of deposits were performed. Samples were collected on different parts of the slope, but also along cross sections throughout the avalanche deposit. This deposits characterization was combined with results from mapping and image analysis to provide a first description of the sequence and the extension of events related to the evolution of this mountain front. The collected data helped to create a series of propagation models with the software DAN3D, developed by Hungr (2009). We chose a Voellmy rheology for the model with f = 0.10 ± 0.05 and ? = 100 (m/s2) ± 50 (m/s2) for the rock avalanches and f = 0.10 ± 0.05 and ? = 500 (m/s2) ± 200 (m/s2) for the debris flow. The results show a good propagation with more dispersion that we can see on the field. Part of the cover on the numerical model is not visible on the field, probably due to erosion and transport having moved the material, resulting in the current landscape.
Author: José Pullarello Director: Marc-Henri Derron, Michel Jaboyedoff. External Supervisor: Ivanna Penna.
Jérémie Voumard Director: Prof. Dr. Michel Jaboyedoff Jury: Dr. Marc-Henri Derron, Dr. Andrea Pedrazzini, Dr. Nicolas Pollet, Prof. Dr. Suren Erkmann
Geological and hydro-geological natural hazards, as landslides and floods, are a threat to many transport networks built in mountainous areas. These risks, that are often small in intensity, are poorly evaluated or unknown. This doctoral thesis focuses on the characterization and quantification of natural hazards that impact Swiss communication tracks. It also explores various remote sensing techniques dedicated to the survey of areas around traffic lanes. A database has been created to characterize the many small events that regularly affect roads and railway lines in order to compensate the lack of knowledge. The number of events and their trends – such as their spatio-temporal distribution, the weather, the geology, the direct damages or the types of affected tracks- are thus known at the national level over a period of five years (2012-2016). It shows that a natural event, on average, disrupts the traffic every 2.1 days and that the events occur mostly during the months of June and July, late afternoon. Direct costs were estimated at CHF 4 million per year, with an average cost per event estimated at 23 400 francs. In order to characterize the approaches to roads and railways, we have developed and tested the photogrammetric technique “on-motion Structure from Motion”, whose cost is reasonable. This remote sensing technic makes possible to obtain colorized and georeferenced 3D point clouds from images taken by four action cameras placed on a moving vehicle. Its accuracy has been evaluated in laboratory conditions and on many sites. It was also compared with seven other traditional surveillance techniques to identify advantages and disadvantages. This work highlights the impact and consequences of small-scale natural hazards that, taken as a whole, are not negligible for society. In addition, this study demonstrates that low-cost survey technic can compete with more expensive traditional survey techniques.