Tag Archives: 2012

SafeLand – Living with landslide risk in Europe

SafeLand was a Large-scale integrating Collaborative research project funded by the The Seventh Framework Programme for research and technological development (FP7) of the European Commission. The project team, composed of 27 institutions from 13 European countries, was coordinated by Norwegian Geotechnical Institute (NGI).

SafeLand aimed at developing generic quantitative risk assessment and management tools and strategies for landslides at local, regional, European scales. It also established the baseline for the risk associated with landslides in Europe, and improved our ability to forecast landslide and detect hazard and risk zones.

During this 3-years project, our group mainly contributed to the following deliverables:

  • D 1.6: Analysis of landslides triggered by anthropogenic factors in Europe
  • D 2.10: Identification of landslide hazard and risk “hotspots” in Europe
  • D 4.1: Review of Techniques for Landslide Detection, Fast Characterization, Rapid Mapping and Long-Term Monitoring (as Editor)
  • D 4.4: Guidelines for the selection of appropriate remote sensing technologies for monitoring different types of landslides
  • D 4.8: Guidelines for landslide monitoring and early warning systems in Europe – Design and required technology
  • D 5.1: Compendium of tested and innovative structural, non-structural and risk-transfer mitigation measures for different landslide types

All deliverables and more information about the SafeLand project can be found on www.safeland-fp7.eu.

Featured image: Landslide in Namsos, Norway (copyright SafeLand)

Andrea Pedrazzini: Characterization of gravitational rock slope deformations at different spatial scales based on field, remote sensing and numerical approaches.

Andrea Pedrazzini
Director: Prof. Michel Jaboyedoff
Jury: Prof. Torsten Venneman, Dr. Marc-Henri Derron, Dr. Federico Agliardi, Prof. Masahiro Chigira, Prof. Giovanni Crosta

Rock slope instabilities such as rock slides, rock avalanche or deep-seated gravitational slope deformations are widespread in Alpine valleys. These phenomena represent at the same time a main factor that control the mountain belts erosion and also a significant natural hazard that creates important losses to the mountain communities. However, the potential geometrical and dynamic connections linking outcrop and slope-scale instabilities are often unknown. A more detailed definition of the potential links will be essential to improve the comprehension of the destabilization processes and to dispose of a more complete hazard characterization of the rock instabilities at different spatial scales.

In order to propose an integrated approach in the study of the rock slope instabilities, three main themes were analysed in this PhD thesis: (1) the inventory and the spatial distribution of rock slope deformations at regional scale and their influence on the landscape evolution, (2) the influence of brittle and ductile tectonic structures on rock slope instabilities development and (3) the characterization of hazard posed by potential rock slope instabilities through the development of conceptual instability models.

To prose and integrated approach for the analyses of these topics, several techniques were adopted. In particular, high resolution digital elevation models revealed to be fundamental tools that were employed during the different stages of the rock slope instability assessment. A special attention was spent in the application of digital elevation model for detailed geometrical modelling of past and potential instabilities and for the rock slope monitoring at different spatial scales. Detailed field analyses and numerical models were performed to complete and verify the remote sensing approach.

In the first part of this thesis, large slope instabilities in Rhone valley (Switzerland) were mapped in order to dispose of a first overview of tectonic and climatic factors influencing their distribution and their characteristics. Our analyses demonstrate the key influence of neotectonic activity and the glacial conditioning on the spatial distribution of the rock slope deformations. Besides, the volumes of rock instabilities identified along the main Rhone valley, were then used to propose the first estimate of the postglacial denudation and filling of the Rhone valley associated to large gravitational movements.

In the second part of the thesis, detailed structural analyses of the Frank slide and the Sierre rock avalanche were performed to characterize the influence of brittle and ductile tectonic structures on the geometry and on the failure mechanism of large instabilities. Our observations indicated that the geometric characteristics and the variation of the rock mass quality associated to ductile tectonic structures, that are often ignored landslide study, represent important factors that can drastically influence the extension and the failure mechanism of rock slope instabilities.

In the last part of the thesis, the failure mechanisms and the hazard associated to five potential instabilities were analysed in detail. These case studies clearly highlighted the importance to incorporate different analyses and monitoring techniques to dispose of reliable and hazard scenarios. This information associated to the development of a conceptual instability model represents the primary data for an integrated risk management of rock slope instabilities.

 

 

Murielle Voutaz: Etude d’une déformation gravitaire profonde de versant (DGPV) dans la région du Simplon par une approche structurale et cinématique.

Murielle Voutaz
Direction: Prof. Michel Jaboyedoff
Rapporteur: Prof. Jean-Luc Epard
Suivi: Andrea Pedrazzini, Battista Matasci

Deep-seated gravitational slope deformations (DSGSD) are poorly understood. Induced by gravity deformation mechanisms, the susceptibility of DGPV increases with many factors; the most important are decompressing ice, seismic and regional tectonics.

The relationship between regional tectonics and DSGSD is studied in this work through the characterization of morphostructures produced by rock slope failures and DSGSD located on the left bank of Haut-Valais. The direction of these morphostructures was compared with the direction of morphological lineaments of the same area. It shows two main directions of lineaments: NE/SW and NW/SE. The first one corresponds to the direction of the main schistosity, related to the second phase of deformation described by Steck (1984). The morphostructures of rock slope failures and DSGSD show also this direction, confirming the influence of tectonics on this kind of instabilities. The second direction of lineaments can be linked with the expansion phase that occurs in the central Alps from the Miocene.

The DSGSD of Wasenalp has developed significant morphostructures: big scarps with a throw of more than 10 m which share the pasture of Wase and two rock glaciers from east to west and counterscarps which induced horst and grabens morphology in the central part of the slope. Significant signs of instability also characterize the toe of the DSGSD including paleolandslides and still active landslides.

Three sagging areas are also located on the DGPV: the sagging area of Mäderhorn, the sagging area of Scheen Biel and the sagging area of Hohture. While the first two have only little morphostructures, the sagging area of Hohture shows serious gravity forms, including counterscarps and tensile cracks parallel to the crest line.

Besides the study of morphostructures, DGPV analysis was performed on the basis of structural data of the rock mass. This method allowed identifying the orientation of the main schistosity and 6 sets of discontinuities. At least two of the joint sets, J1 and J6, are directly related to the extension tectonics of the area. The measurements of the main schistosity have also revealed a significant flexural toppling in the lower part of the DSGSD.

The analysis of the deformation is carried out from the geomorphological analysis and the structural characterization of the DSGSD; several assumptions of deformation were developed to understand the DSGSD. The more consistent one define a deep shearing zone with kink structures which results from the diffusion in depth of the shear constraints from the main scarps. From this scarp the deformation follows first the main schistosity plans and then spread in the shearing zone. The flexural toppling results from the deep shearing zone.

Léonard Jaton: Development and application of a hydrological and slope stability model using Matlab

Léonard Jaton
Supervisor : Prof. Michel Jaboyedoff
Expert : Pascal Horton

This master thesis is focused on the development and application of a hydrological and slope stability model for use on catchment basins.

In the field of natural risks analysis, and particularly those of quick rises in river water levels and resulting floodings as well as landslides, a modeling of the hydraulic processes taking place in a catchment area during periods of rainfalls is a crucial point. This allows a better comprehension of the way water is transported downhill, and so permits to better identify and predict dangerous areas and events.

A computer program is therefore developed in Matlab to model the various intervening principles and obtain results of flow rates and slope stability from precipitation data on the area of study.

The following paper is made up of a first chapter presenting the theoretical concepts used as well as their adaptation for the model. The program and its functions are then detailed and explained, fol-lowed by a section of tests and application of the model to firstly theoretical then natural basins. In a last chapter, several criticisms of the model and other development ideas are proposed.

Jérémie Voumard: Simulation dynamique du trafic routier pour l’estimation du risque sur les routes de montagne

Jérémie Voumard
Supervisor : Prof. Michel Jaboyedoff
Experts : Dr. Marc-Henri Derron, Dr. Luuk Dorren, Olivier Caspar

The main theme of this Master thesis is the calculation of risk generated by natural hazards on roads. While it is common to assess risk incurred by the road users through static calculations, a new approach based on a dynamic calculation of risk is proposed here. Risk is usually calculated at a so-called macroscopic scale, i.e. with general parameters representing the road and its related traffic. The new approach presented here is to consider the traffic at a microscopic scale, taking into account risk for each vehicle traveling on the road. This new dynamic approach ensures a more realistic application of the theoretical concept of risk calculation. For this purpose, a road traffic model was created and implemented into a simulator specially conceived in this Master thesis. An analysis of various models used for traffic simulation, a reminder of fundamental concepts of computer simulation and a presentation of software able to simulate road traffic are also presented.

In a first, the existing context around risk calculation on the roads is explained and highlighted by:

  • A reminder about the history of roads with a focus on mountain roads in Switzerland,
  • A description of natural hazards that may occured in the three geographical areas of Switzerland and worldwide,
  • An inventory of natural events on roads in Switzerland between winter 2011 and summer 2012,
  • An analysis of the Swiss inventory of road accidents caused by rockfall.

The second part is about the numerical simulator itself. The simulator, developed using the programming software MATLAB®, is based on two different scenarios: the first simulating the effect of a rock on the road traffic and the second modeling an alternating traffic governed by traffic lights. The simulator includes two categories of vehicles for which the dynamic variables and those related to traffic and speed limits are freely configurable. Reductions in visibility and curve speed are taken into account.

Dynamic risk is based on the vehicles number in the danger zone as well as their speed. Standard risk is also calculated to compare the two results. Thereby, an almost infinite number of real traffic situations can be simulated, such as:

  • A straight road without obstacles,
  • A curve section with a high rate of slow vehicles,
  • A rockfall cutting one or two lanes,
  • A road where traffic is controlled by two alternating traffic lights, etc.

In the third part, the simulator model was calibrated and validated with data from the main road linking the town of Aigle in the Chablais Vaudois to the tourist resort of Les Diablerets. Various data relating to the speed of vehicles and their behavior were collected in the field on several sections relevant to the evaluation of natural hazards threat on the road. Otherwise, a history of the road, completed with traffic statistics and socio-economic data contributed to understand the acceptability of risks on the road by the population.

The results of the dynamic calculation of risk from different simulations were compared with results of standard calculations and the most dangerous situations, for instance a column of vehicles stopped at a red light in a dangerous area, were highlighted.

To conclude, a critical assessment of the simulator, with its perspectives, is proposed with a discussion about the risk calculation on the roads.

Virgile Nanchen: Application de la technologie LIDAR à la méthodologie Matterock

Virgile Nanchen
Co-supervisors : Prof. Michel Jaboyedoff
Experts : Alex Loye, Andrea Pedrazzini

The rockslide of 1991 in Randa motivated the development of Matterock methodology (Rouiller et al. 1998). Based on the principle that there is no hazards without discontinuity, this evaluation method of rock walls is based of the structural pattern of the cliff to identify the compartments favourable to rockslide Within the framework of the methodology and as a complement to field studies, some altitude numerical models and statistical methods has been used in order to create automatically hazard’s map.

Since the establishment of the methodology, tools for automatic detection have been highly improved, the resolution of terrain numerical models has increased, and new instruments based on laser technology have been developed, enabling to make 3D models of rock faces. The LIDAR (Light Detection and Ranging) system has shed a new light in terrain analysis. It enables to create point’s cloud with a centimetre resolution, representing the surface geometry of rock walls.

Jointly to the development of such a technology, several methods, based on clusters of points and high resolution MNTs, have been developed in order to identify the structural pattern of the cliff. Within the framework of this work, several on these methods have been applied on the site where the Matterock methodology has been developed. Results are compared to those of 1998 in order to outline the contribution of these new technologies. The objective of this work is to evaluate if such new tools are comparable to the Matterock methodology.

Romain Chenillot: Analyse des aléas rocheux des falaises du Grand Bois du Ban, Lavey Village

Romain Chenillot
Co-supervisors: Prof. Michel Jaboyedoff, Prof. Vincent Labiouse, Dr. Mario Sartori

This analysis of rock falls hazards relates to cliffs of the Grand Bois du Ban, located by the city of Lavey, in the canton of Vaud, Switzerland. The activity of this site was established on the basis of observations of blocks and traces of impacts carried out in wood. The purpose of this study is to determine the various elements characteristic of the phenomenon, thus allowing the development of hazard maps based on two softwares of trajectographic modelings and two methods of zoning.

The cliffs are located in the Helvetic’s tectonic whole, on the level of the Morcles’ klippe. They are made primarily of massive and compact limestones. It was made possible to characterize five families of discontinuities, and the stratigraphy based on the structural analysis, the field’s observations and the LiDAR scans treated by Coltop3D. The whole zone is affected by a rather important fracturing, but also by the presence of folds.

Field’s observations and LiDAR analysis made it possible to determine three formations processes of dihedral slip and a process of planar slip related to stratigraphy. Matterocking software could give potential rock instabilities on the basis of these observations.

At this point, the trajectographic’s tests is feasible. Two softwares were used. Initially Rocfall, limited to a modeling 2D, then Rockyfor3D allowing the taking into account of three-dimensional trajectories. The comparison of the results between these two models shows good similarities of the blocks stopping limits. Although the disparities of the energy intensities are sometimes important.

Hazard maps were carried out according to two methodologies respectively the Matterock Modified based on the results of Rocfall and the new Cadanav methodology based on Rockyfor3D. The analysis of the results shows a less favourable mapping for Modified Matterock, especially if blocks of great volumes are taken into account with one great period of return. This element brings the fore on one of the essential differences between the two methodologies. Namely taking into direct account the period of return in the case of Cadanav, which is left aside using Modified Matterock.

Lastly a second series of hazard maps was carried out in order to test the impact of the variation of a parameter on the results of mappings using the Original Matterock which takes all blocks into account. This differs from the Modified Matterock withdraws the 10 % of the modeled extreme blocks. Concerning Cadanav, the periods of return values estimated based on field’s observations were divided by 5. The results show important mapping variations, illustrating these methods great sensitivity to the fluctuation of its parameters mainly based on estimations.

As a conclusion of this analysis of rock falls the village of Lavey is located out the dangerous perimeter. However all limits previously mentioned must be taken into account and decisions made accordingly.

Tristan Burnand: Étude des processus érosifs et bilan sédimentaire au Vallon de Nant

Tristan Burnand
Supervisor: Prof. Michel Jaboyedoff
Expert: Alexandre Loye

This master thesis studies the Vallon de Nant, a glacial valley located in the Vaud Alps on the border with the canton of Valais. Within this valley, the different erosion processes are studied.

In context, the processes related to erosion are mapped on the basis of field visits, orthophotos and digital terrain model (DTM) high precision (spatial resolution of 1 m).

A qualitative study, by means of indicators such as the stream power and the erosion index are used globally in the Vallon. This allows you to split the catchment into three distinct zones (A, B and C), governed by different dominant processes. Within each zone, a secondary watershed is studied in more detail to test the assumptions for each predetermined area. The first area is dominated by gravity processes and mobilization of sediments. A second area is dominated by large geological structures and high sediment yield. The last zone corresponds to the system of glacial and paraglacial glacier des Martinets.

These three areas have in common, however, that the sediments that eventually come into the riverbed of the Nant Avançon are then transferred down by fluvial processes. The interaction of these erosion processes can be considered as a sediment cascade, where various sedimentary reservoirs and fluxes are combined.

The method of local base level (SLBL) is used to determine the volume of sediment present in the valley floor. This amount is used to calculate an average denudation rate since the glaciers last retreated, and a sediment yield.

A sediment budget, based on the mapping of phenomena established, is performed using the loss of potential energy concept. It is made for a single secondary catchment. The results give an average erosion rate of 0.74 mm/year, with a minimum of 0.24 mm/year and a maximum of 1.24 mm/year.

On the same secondary catchment, modeling the spread of rock falls is made. Then, based on the concept of the sediment cascade modeling the spread of sediment remobilization, by debris flow processes, is undertaken.

Statistical precipitation forecasting for the Minerve project

The upper Rhone catchment is sometimes subject to heavy precipitation that can eventually result in floods. The MINERVE project, to which this work belongs, aims at providing tools for flood forecasting and management. For this purpose, actions can be undertaken on dam storage, but this requires forecasting precipitation accurately days beforehand. This is currently done by the numerical weather prediction model of MétéoSuisse. However, due to large uncertainties in the forecasting of extreme events, it was decided that a parallel forecast based on a statistical approach could complement the information available.

Therefore, we adapted a technique of statistical precipitation forecasting, namely the analogue method, to the alpine context of our catchment. Several parameterizations of the method have been documented and calibrated.

A substantial part of this study was devoted to programming a forecasting software, which was called Atmoswing. It is designed to process automatically forecasts by means of the analogue method, and to provide a tool for visualizing the results on maps and graphs. It can process many different versions of the analogue method. The software has been operational since mid-2011, and has allowed us to confirm the interest of prediction by analogy.

As the method is applied here to a new geographical context, a large number of synoptic variables were evaluated. We then confirmed the relevance of the traditional two levels of analogy, which are related first to the atmospheric circulation, and next to the humidity flux, while making improvements to them. As a result, we created new parameterizations that have better forecasting skills than the reference methods considered so far. We also evaluated other improvements, such as the introduction of a shifting time window to find better synoptic analogues at other hours of the day, which show some potential. A 6-hourly time step forecast has been evaluated and was found to bring useful information on precipitation characteristics.

Finally, we introduced a technique of global optimization: genetic algorithms. These were found to be able to calibrate the analogue method by considering jointly all parameters of the different analogy levels. With that kind of tool we can approach an objectively optimal parameterization.

As the choice of atmospheric levels and time windows is automated, this technique can result in a gain of time, even if it is relatively demanding in calculations. Thus we were able to improve the analogue method, and to add new degrees of freedom.