Tag Archives: 2013

Philippe Limousin: De la caractérisation du sol, à l’étude de propagation et des risques induits : Les cas du glissement de Pont Bourquin

Philippe Limousin
Supervisor: Prof. Michel Jaboyedoff
Co-supervisor: Bernard Vayssade

Les risques liés aux dangers naturels sont de plus en plus présents dans le monde mais encore plus particulièrement dans les pays de montagne, du fait de la multitude de dangers par lesquels ils peuvent être touchés notamment les chutes de blocs ou de pierres, les risques d’inondations, les tremblements de terre mais aussi les glissements de terrains. La caractérisation de ces phénomènes est une recherche qui prend de plus en plus d’importance. En effet pour définir les impacts qu’ils induisent sur la population ou la modification de l’environnement, il faut rechercher les zones où ces phénomènes peuvent se déclencher, trouver leur dynamique d’écoulement et leur propagation ainsi que les facteurs influençant ces différents paramètres.

Le thème principal est l’étude du glissement de terrain, de Pont Bourquin. Pour ce faire il a été analysé les caractéristiques du sol par des essais en laboratoire puis la propagation d’une possible coulée et enfin les vulnérabilités pour trouver finalement le risque induit.

La réflexion s’est articulée selon trois axes. Dans un premier temps, une analyse des comportements du sol et de ces caractéristiques. Dans un second temps, la modélisation du glissement de terrain. Pour finir, une étude de risque liée à la zone de glissements située à Pont Bourquin (Commune de Ormont-dessus), dans le canton de Vaud en Suisse, est réalisée.

Christopher Puglia: Multidisciplinary study of two anthropogenic landslides in Sindhupalchok and Ramecchap districts, Central Nepal

Christopher Puglia
Direction: Prof. Michel Jaboyedoff, Dr. Karen Sudmeier-Rieux, Dr. Marc-Henri Derron, MSc. Pierrick Nicolet

The purpose of this thesis is to explore the socio-economic and technical issues linked to landslides management in Sanusiruwari VDC (Sindhupalchock district) and Namadi VDC (Ramechhap district), central Nepal.

In Nepal, hydropower development is in expansion as it is a possibility to largely improve the electricity network. In the study, they aim for Sanusiruwari project is to supply the national grid and for Namadi to provide energy to the whole community. Nevertheless, their construction caused landslides in both sites making necessary to control and stabilize them.

The first part of the study is technical and it is intended to examine the landslides with observations and photogrammetry to have more information about its possible evolution and to find out if the plants’ construction is the only cause. Then, the Vetiver (Vetiveria ziznioides) is used as stabilization measure in both sites which will reveal issues regarding their maintenances and efficiency.

The second part is social and was conducted with interviews, discussion and participatory risk mapping. As the managers and communities are different for both sites, risks management differed, with different approaches, implications, priorities and opinions in slopes stabilization and hydropower matters. Communities’ involvement is important in Namadi because the project want to share knowledge which is not the case for the other project in Sanusiruwari which is a private sector project. In spite of that, issues related notably to the landslide management will turn out similar.

Alexandre Loye: Budgeting rockfall and modeling sediment delivery in torrent systems

Alexandre Loye
Director: Prof. Michel Jaboyedoff
Jury: Prof. Klaus Holliger, Prof. Michel Jaboyedoff, Dr. Marc-Henri Derron, Dr. Frédéric Liébault, Dr. Francesco Brardinoni, Prof. Oldrich Hungr

This thesis is a compilation of projects to study sediment processes recharging debris flow
channels. These works, conducted during my stay at the University of Lausanne, focus
in the geological and morphological implications of torrent catchments to characterize
debris supply, a fundamental element to predict debris flows. Other aspects of sediment
dynamics are considered, e.g. the coupling headwaters – torrent, as well as the development of a modeling software that simulates sediment transfer in torrent systems.

The sediment activity at Manival, an active torrent system of the northern French Alps,
was investigated using terrestrial laser scanning and supplemented with geostructural investigations and a survey of sediment transferred in the main torrent. A full year of sediment flux could be observed, which coincided with two debris flows and several bedload transport events. This study revealed that both debris flows generated in the torrent and were preceded in time by recharge of material from the headwaters. Debris production occurred mostly during winter-early spring and was caused by large slope failures. Sediment transfers were more puzzling, occurring almost exclusively in early spring, subordinated to runoff conditions, and in autumn during long rainfall events. Intense rainstorms in summer did not affect debris storage that seems to rely on the stability of debris deposits.

The morpho-geological implication in debris supply was evaluated using DEM and field
surveys. A slope angle-based classification of topography could characterize the mode
of debris production and transfer. A slope stability analysis derived from the structures
in rock mass could assess susceptibility to failure. The modeled rockfall source areas
included more than 97% of the recorded events and the sediment budgets appeared to be
correlated to the density of potential plane failure. This work showed that the analysis
of process-related terrain morphology and of susceptibility to slope failure document the
sediment dynamics to quantitatively assess erosion zones leading to debris flow activity.

The development of erosional landforms was evaluated by analyzing their geometry with
the orientations of potential rock slope failure and with the direction of the maximum
joint frequency. Structure in rock mass, but in particular wedge failure and the dominant
discontinuities, appear as a first-order control of erosional mechanisms affecting bedrockdominated catchments. They represent some weaknesses that are exploited primarily by mass wasting processes and erosion, promoting not only the initiation of rock couloirs and gullies, but also their propagation. Incorporating the geological control in geomorphic processes contributes to better understand the landscape evolution of active catchments.

A sediment flux algorithm was implemented in a sediment cascade model that discretizes
the torrent catchment in channel reaches and individual process-response systems. Each
conceptual element includes in a simple manner geomorphological and sediment flux information derived from GIS complemented with field mapping. This tool enables to simulate sediment transfers in channels, considering evolving debris supply and conveyance, and helps reducing uncertainty inherent to sediment budget prediction in torrent systems.

This thesis aims in a modest way to shine light on some aspects of sediment dynamics of
torrent systems.

 

Marc Choffet: Cost of Natural Hazards to Building and Influence of Risk Factors in the Context of Building Insurance

Marc Choffet
Director: Prof. Michel Jaboyedoff
Jury: Prof. Michel Jaboyedoff, Prof. Eric Verrecchia, Prof. Franco Romerio, Prof. Jean Ruegg, Dr. Markus Imhof

In Switzerland, the annual cost of damage by natural elements has been increasing for several years despite the introduction of protective measures. Mainly induced by material destruction, building insurance companies have to pay the majority of this cost. In many European countries, governments and insurance companies consider prevention strategies to reduce vulnerability. In Switzerland, since 2004, the cost of damage due to natural hazards has surpassed the cost of damage due to fire; a traditional activity of the Cantonal Insurance company (ECA). Therefore, the strategy for efficient fire prevention incorporates a reduction of the vulnerability of buildings. The thesis seeks to illustrate the relevance of such an approach when applied to the damage caused by natural hazards. It examines the role of insurance place and its involvement in targeted prevention of natural disasters.

Integrated risk management involves a faultless comprehension of all risk parameters. The first part of the thesis is devoted to the theoretical development of the key concepts that influence risk management, such as: hazard, vulnerability, exposure or damage. The literature on this subject, very prolific in recent years, was taken into account and put in perspective in the context of this study.

Among the risk parameters, it is shown in the thesis that vulnerability is a factor that we can influence efficiently in order to limit the cost of damage to buildings. This is confirmed through the development of an analysis method. This method has led to the development of a tool to assess damage to buildings by flooding. The tool, designed for the property insurer or owner, proposes several steps, namely:

  • Vulnerability and damage potential assessment;
  • Proposals for remedial measures and risk reduction from an analysis of the costs of a potential flood;
  • Adaptation of a global strategy in high-risk areas based on the elements at risk.

The final part of the thesis is devoted to the study of a hail event in order to provide a better understanding of damage to buildings. For this, two samples from the available claims data were selected and analysed in the study. The results allow the identification of new trends. A second objective of the study was to develop a hail model based on the available data. The model simulates a random distribution of intensities and coupled with a risk model, proposes a simulation of damage costs for the determined study area.

Slope instabilities mapping using GIS, Differential SAR Interferometry methodologies and field investigations along the National Road N7, Mendoza Province, Argentina

This project was carried out with the collaboration of the Group Risk from the University of Lausanne and the Argentinean Geological Survey (SEGEMAR). The main goals of this project are:

  1. Identification of deep-seated gravitational slope deformation and structures displacements by advanced differential SAR Interferometry (PS and SBAS approaches).
  2. Rockfall hazard mapping: detection of source areas by quantitative DEM analysis (Loye et al 2009) and estimation of propagation zones by 3D numerical modeling.
  3. Debris Flow susceptibility mapping (source areas and propagation zones) by an energy-controlled numerical model (Horton et al., 2008).
  4. Snow avalanche susceptibility mapping (source areas and propagation zones) with Flow-R.
  5. Field investigations along the road N7: detailed studies on identified hotspots by the regional mapping and the knowledge of the Geological Survey of Argentina.

Main findings of the project can be found here:

Baumann, V., Jaboyedoff, M, Oppikoffer, T, y Altobelli S. 2006. Potenciales caídas de rocas determinadas con el método Conefall para el área de Puente del Inca., S. IGRM-SEGEMAR y IGAR-FGSE. En Estudio Geocientífico aplicado al ordenamiento territorial en Puente del Inca, provincia de Mendoza, Argentina. SEGEMAR (Servicio Geológico y Minero Argentino) y MAP (Multinacional Andean Project), Anexo I, Buenos Aires.

Baumann, V., Wick E., Derron M.H., Horton P., Jaboyedoff  M., Rosas M. y Marengo H., 2011. Cartografía de la susceptibilidad  a las avalanchas de nieve a lo largo de la ruta nacional 7 En: Actas del XVIII Congreso Geológico Argentino (Eds. Leanza, Franchini, Impiccini, Pettinari, Sigismondi, Pons y Tunik), p. 345. Neuquén, Argentina.

Baumann, V., Wick, E., Horton P. y M. Jaboyedoff,  2011. Debris flow susceptibility mapping at a regional scale along the National Road N7, Argentina. Pan-Am CGS Geotechnical Conference 2011, Toronto.

Wick, E., Baumann, V. and Jaboyedoff, M., 2010. Brief Communication: Report on the impact of the 27 February 2010 earthquake (Chile, Mw 8.8) on rockfalls at far distance, Natural Hazards and Earth System Sciences, 10: 1989-1993.

Wick, E., Baumann, V., Favre-Bulle, G.,Jaboyedoff, M., Loye, A., Marengo, H., and Rosas, M. 2010. Flujos de detritos recientes en la Cordillera Frontal de Mendoza: un ejemplo de riesgo natural en la Ruta 7. Revista de la Asociación Geológica Argentina.

Baumann, V., Favre-Bulle, G., Oppikofer, T. , Altobelli, S., Rosas, M. , Jaboyedoff, M. , Hermanns, R. , Coppolecchia, M. ,  y Fauqué, L., 2008. Estudio de las caídas de rocas sobre la ruta Nacional N°7, en las áreas de Polvaredas y Puente del inca (Mendoza) usando un modelo digital del terreno. In: Zappettini et al. (eds) XVII Congreso Geológico Argentino – Acta, Tomo I, p. 259-260.

The project is funded by the Group Risk from the CRET Institute (University of Lausanne).

 

Lauren Gavillet: Dynamique d’érosion et étude de stabilité d’un petit bassin versant alpin: le cas du Courset (VD, Switzerland)

Lauren Gavillet
Supervisor: Prof. Michel Jayboyedoff
Internal Experts: MSc. Pierrick Nicolet, MSc. Benjamin Rudaz
External Expert: Marcel Burri

The landslide triggered on August 26, 2005 by a heavy rain event, in the watershed of the Courset is the origin of this master thesis. To determine if this event was exceptional or if we can expect an intensification of erosion processes, the activity of the watershed is analyzed through its dynamic erosion and through analysis of the stability of slopes.

To collect interesting and useful informations on the watershed, a history of developments and events that have affected the watershed of the Courset is established. Geotechnical analyzes are performed to characterize the soils of the watershed. These results are then used to model the stability of slopes. Rainfalls in the region are also analyzed to be used in this modeling.

After a description of the watershed dynamics, longitudinal profiles and their knickpoints are identified in order to locate areas of the profiles that will be affected by erosion. The erosion potential of the entire watershed is also estimated. Past erosion is studied in light of the observed current activity.

A synthesis of the controversial quaternary filling hypothesis of the Lavey-Le Châtel glacial trough is established, and a new reconstitution is proposed.

Tiziana Egli: Cartes de danger de chutes de blocs sur le village des Morgnes (Bagnes)

Tiziana Egli
Co-supervisors : Dr. Vincent Labiouse, Prof. Michel Jaboyedoff
Experts : Dr. François Joseph Baillifard, MSc. Clément Michoud

The alpine village of Les Morgnes is dominated by a long cliff. Some previous reports and blocks present in the forest below the cliff informs that the village is threatened by this cliff. The aim of this study is to establish the rockfall hazard map for this place combining two different methodologies: the Matterock approach and the CADANAV approach.

The studied cliff is located in an old glacial valley and it’s surrounded by landslides. The cliff is mainly composed by quartzite and past tectonic conditions has created a significant schistosity. According to the Matterock methodology, field campaigns and LiDAR scans establish the structural conditions and the potential localized sources. The susceptibility mapping was performed with a software according to kinematic tests. Toppling and wedge sliding are the principal failure mechanisms. 2D trajectography were simulated along predefined paths. The hazard assessment, based on the trajectography studies, demonstrate that no building is in a dangerous zone. According to the CADANAV approach, 3D trajectography studies were performed. The semi-automatic hazard assessment shows that depending on the return period, some buildings are located in a high danger zone.

Maria Ponzio: Etude des instabilités du Val Canaria (Tessin, Suisse) et analyse de la stabilité de l’éboulement de Sotto Corte

Maria Ponzio
Supervisor : Prof. Michel Jaboyedoff
Rapporteur : Prof. Stefan Schmalholz

La zone d’étude se trouve dans le Val Canaria, au Nord du Tessin (proche du village d’Airolo). Cette zone est caractérisée par plusieurs phénomènes d’instabilités.

Le but de ce travail de master est de comprendre les mécanismes qui agissent sur la formation des instabilités. Pour l’atteindre une étude basée sur les observations de terrain et les méthodes de télédétection (Lidar aérien et Lidar terrestre) a été réalisé. Une carte des principales instabilités est proposée. Les deux flancs de la vallée sont affectés par une Déformation Gravitaire Profonde de Versant (DGPV) qui comprend, en son sein, différentes autres instabilités, notamment des glissements profonds, des glissements superficiels, d’éboulements rocheux et des érosions de berge.

Une carte géologique a été aussi été réalisée pour comprendre la potentielle corrélation entre instabilités et lithologies. De plus, cette carte a été utilisée pour créer un modèle géologique en 3D. Les principales lithologies présentes dans la zone d’études sont des roches sédimentaires mésozoïques (dolomie, cornieule, gypse, anhydrite, Bündnerschiefer et Quartenschiefer), ainsi que les roches constituent le massif du Gothard (métapélites, gneiss, amphibolites) et la nappe du Lukmanier (gneiss et micaschistes).

Une dynamique de l’activité instable du flanc droit voit la présence de plusieurs plans de glissements qui sont liés au contact entre les dépôts non consolidés quaternaires (principalement des colluvial) et la roche, la dissolution des roches carbonatées (dolomie et cornieule) et des roches sulfatées (gypse, anhydrite) et l’activité tectonique de compression. Les facteurs dégradants agissant sur le versant sont principalement les infiltrations d’eau, l’état de la fracturation de la roche et l’érosion de pied du versant par la rivière.

Le flanc gauche se caractérise par une zone affectée par un glissement superficiel très étendu qui est principalement causé par l’activité érosive de la rivière. Les plans de glissements sont multiples et le glissement est en train d’évoluer en direction de l’amont de la pente. Comme dans le cas du flanc droit, les facteurs dégradants sont principalement la présence d’eau dans la couche de matériel meuble ainsi que la forte fracturation de la roche.

L’étude en détail d’un éboulement rocheux de Sotto Corte dans le flanc gauche a permis d’interpréter le mécanisme de rupture, ce qui permet d’émettre des hypothèses sur une possible évolution future de cette instabilité.

Le monitorage par LiDAR terrestre a montré que l’activité de chutes de blocs est importante dans la partie supérieure de la niche d’arrachement. Dans le cône d’éboulis, les ruissellements d’eau superficielle engendrent l’érosion du matériel fin déposé lors de l’éboulement survenu en 2009. Les discontinuités présentes dans la zone peuvent géométriquement provoquer des glissements de type plan ou dièdre. La stratigraphie plonge dans la même direction de la pente.

Le modèle géomécanique, par la méthode des éléments finis, a permis de comprendre la dynamique qui a amené à la rupture du 2009. Le plan de cisaillement se trouvera à la limite entre le gypse et l’anhydrite et les fractures, ne contrôlent que partiellement l’instabilité. Ces informations ont permis permettre d’estimer les volumes instables encore présents dans la zone. Deux compartiments avec des volumes maximaux de 90’000 m3 et 26’000 m3 ont été identifiés.

Aucun facteur déclenchant n’a été identifié pour cette instabilité. Plusieurs facteurs déstabilisant sont présents, en particulier l’effet de l’eau, qui joue un rôle principal pour l’instabilité. La circulation dans le massif provoque la dissolution du gypse, ainsi que l’hydratation de l’anhydrite, qui se transforme en gypse. L’érosion du pied de la pente par la rivière amène à une perte de stabilité. Le phénomène de gel-dégel provoque la fracturation de la roche, et en conséquence, augmente sa perméabilité. Le modèle géomécanique montre aussi que la dégradation des paramètres de résistance au cisaillement de la roche et la présence de la nappe phréatique provoquent la rupture.

Une évolution possible future est la propagation progressive de cette instabilité en direction le Nord-Est, zone où se trouvent plusieurs failles et fractures. A plus à courte terme trois possibles scénarios sont possibles. Un effondrement simultané de deux compartiments ou l’effondrement individu de l’un au l’autre des compartiments.

Camille Perraudin: Characterization of Montset rock slope instability in Hérémence valley.

Camille Perraudin
Supervisor: Prof. Michel Jayboyedoff
Experts: Dr. Marc-Henri Derron, MSc. Dario Carrea

The study focuses on the characterization of Montset rock slope instability in Hérémence valley. The first part of the work aims to determine, on the basis of geomorphological and geometrical characteristics, what kind of instability is that of Montset, which at first looks like a Deep Seated Gravitational Slope Deformation. The next step is to determine its level of activity, i.e. if the movement can be measured and / or observed, and, if necessary, to locate them. Signs of activity, in terms of surface and deep instabilities are detected by field observations and also from the information obtained with LiDAR. This provides a series of measurements of high density accuracy for the creation of a point cloud of the topography. The detected instabilities are described and their susceptibility to failure is evaluated. A hazard map for rockfall in the study area has been created. Following this, a model of instability is constructed. This model incorporates field observations, displacement measurements, information from the geological map and subsurface data. These data were acquired during the visit of a hydraulic gallery underlying the eastern part of the Montset. Finally, based on the synthesis of information from the study, assumptions about the history of instability and the reasons that led to its development are proposed.

Line Rouyet: Monitoring and characterization of rock slope instabilities in Norway using GB-InSAR.

Line Rouyet
Co-supervisors: Prof. Michel Jayboyedoff, Dr. Marc-Henri Derron
Experts: Dr. Lene Kristensen, MSc. Clément Michoud

The master thesis named “Monitoring and characterization of rock slope instabilities in Norway using GBInSAR (Ground-Based Interferometric Synthetic Aperture Radar)” aims (1) to improve the knowledge about the advantages and limitations of a GB-InSAR system (©LiSALab-Ellegi) for the monitoring of instable rock slopes; (2) to contribute to the understanding of two large rock instabilities, especially in terms of behavior and geometry.

The work includes (1) the processing and interpretation of GB-InSAR data for two main case studies of major rockslides in Norway, as well as for a third test case involving rockfalls; (2) the comparison of GB-InSAR results with other available monitoring data (GPS, crack/extenso-meters, lasers-reflectors, tiltmeters and meteorological data), as well as the integration of structural analyzes (using Terrestrial and Aerial Laser Scanning data); (3) the global synthesis of the results and the comparison with the conclusions of precedent studies in order to reach the two objectives previously highlighted.

The first case study is the site of Indre Nordnes (Troms County, northern Norway) which is affected by a large rockslide above Lyngenfjord generating a significant risk of tsunami. Its volume is estimated to be around 10-15 millions of m3. Two intermittent GB-InSAR campaigns were performed in summer 2011 and their results are compared and integrated with the large monitoring database available since the end of 2007 for the crackmeters, the beginning of 2010 for the GPS, since mid-2011 for the extensometers and tiltmeters.

Generally, the results show that the rockslide is slow (6-7 mm/year) with accelerations during the thaw periods (May-June). The year 2011 is an exception with an important acceleration in June (up to 14 mm in only 2 weeks according to GB-InSAR data). These values can be related to the exceptionally high temperatures in 2011. Moreover, GB-InSAR data allow giving new information about the extent and the repartition of movements of instable area. Finally, thanks to the structural analyzes two discontinuities sets are supposed to be mainly involved in the sliding. It suggests a stair-steps geometry of the sliding surface.

The second case study is the large Børa/Mannen area (Møre of Romsdal County, western Norway), which includes the rockslide of Mannen (15-25 millions of m3) as well as the Børa plateau located on the southwest side of Mannen. Because Børa area showed some signs of activity, intermittent GB-InSAR campaigns were performed in summer 2011 and 2012. Their results are compared and integrated with the large monitoring database including GPS campaigns between 2003 and 2010 on Børa plateau, various in situ data in Mannen since the end of 2010 and permanent GB-InSAR data since the beginning of 2010. This second GB-InSAR system is located about 2 km more northeastern than the one of Børa and aims to monitor the Mannen rockslide. It has the advantage to be in overlap with the Børa GB-InSAR view and to provide continuous images between 2010 and 2013.

Overall, a good concordance is found between the results of the two GB-InSAR systems. In the overlap part, a coherent and progressive pattern is highlighted in the middle of the slope. During the August 2011 campaign, positive displacements (increasing of distance between the GB-InSAR and the target) are recorded and exceed +8 mm in two weeks. With data integration at long-term, it is shown that this part is affected by large variations and inversions of movements, which can be related to seasons. These effects could be linked to water circulation in the rock slope, but the explanations are not yet clear.

For the Mannen rockslide, it is possible to distinguish two parts with different behaviors in terms of velocities and orientations of movement. It highlights that the most upper and southwestern part is the most active (>20 mm/year). Otherwise, thanks to the structural analyzes three discontinuities sets are supposed to be mainly involved in the sliding.

For Børa area, GB-InSAR recorded higher displacements (25-90 mm/year) than those estimated from GPS campaigns (mainly no significant displacements with a maximum velocity of 14.6 mm/year). In any case, it appears that the area is generally moving slowly and quite regularly.

Finally, high variations at short-term and long-term are visible on the interferograms which cast doubts on the data quality. A case of loss of coherence probably due to snowfalls in October is also detected. This underlines the high potential of researches to improve the removing of atmospheric effects and the capability of the GBInSAR in case of external perturbations.

The third test case of Sunndalsøra-Oppdølsstranda (site C along the road 70 between the two localities, Møre of Romsdal County, western Norway) is studied in order to improve the knowledge of the potential of GBInSAR for the detection and analysis of rockfalls. Between April 2010 and October 2011, five GB-InSAR campaigns were performed and give information about a rockfall event of 15-20 m3 which occurred the 8th of June 2011. The results confirm the capability of the system to record precursor movements to failure, but highlighted also various operational limitations.

Overall, the joined analysis of the three different case studies allows having a good overview of the potential and limitations of the GB-InSAR system. Moreover, because of their respective advantages and limitations (in terms of kind of recorded information, temporal sampling, accuracy, spatial coverage, etc.), it appears that the GB-InSAR and the in situ monitoring devices have a good complementarity. The integration of their results therefore allows giving new inputs about the behavior and geometry of the Indre Nordnes and Børa/Mannen sites.