Tag Archives: 2017

David Médico: Caractérisation des avalanches de neige mouillée

David Médico
Director: Prof. Michel Jaboyedoff
Assistant: MSc. Antoine Guérin

The winter 2011-2012, relatively rich in snow, was very marked in the spring by the avalanches of wet snow especially on the Swiss part of the Portes du Soleil (Valais). The following winters also had a lot of heavy snow avalanches in the spring. The first findings of the zones exposed to failure were made during the winter 20I3-20I4.

ln order to characterize snowpack movements and identify areas of rupture, a series of LiDAR scans were carried out at various locations in the Crosets (Portes du Soleil – Valais) with the help of the domain trackers. For logistical and practical reasons, only the Vaillime sector was monitored thereafter. Several scans were carried out at regular intervals throughout the sector. During the non-consecutive 4 days of monitoring, 2 avalanches occurred and a creeping zone was identified. With georeferencing on a digital terrain model (DTM), it was possible to identify the slopes in which these events occurred. The volumes in motion could also be calculated.

ln addition to LiDAR investigation, the thermal imaging technique was used to detect warmer areas in the snowpack before a crack could open. Unfortunately, this was not possible, but the thermal imaging analysis still showed differences in snow temperatures between the shaded areas protected from rocks and open areas.

The last technique used during the same winter is Structure-from-Motion. A large number of photographs were taken in areas where an avalanche was possible. At first, the expected results were not sufficient, it is only during the following winter that new reconstruction tests were more relevant, even if the technique still needs some improvements.

During the winter 20I5-2016, that work was reoriented toward the study of snow melt. An
experimental table was built since it is neither possible to predict how the winter will be (e.g the number of wet snow avalanches) nor possible to control the necessary parameters continuously. lt was a tilting table and allowed the control of meltwater, climate data from the weather station (that collected data continuously) and the change in snow volume through the use of a LiDAR. ln parallel, an experiment took place to continuously measure the temperature of the snow through a probe coupled to a logger. The latter resulted in the loss of data due to a power failure. Coupling of the weather station, LiDAR and meltwater volume has been successful, although the system can be improved, e.g snowfall harvesting.

Patrick Huber: Exploitation du LIDAR embarqué dans l’étude des falaises littorales de Seine-Maritime; Normandie, France

Patrick Huber
Director: Dr. Marc-Henri Derron
Expert: Dr. Clément Michoud

The coastal chalk cliffs in Normandy located in the North-West of France, is an area especially affected by the erosion. lt inducts a rapid retreat of coastline. Due to its important anthropization, this coastline is an essential area in risk management and land use planning.

Coastal erosion is influenced by many interrelated factors. Due to its complexity, the coastal erosion is still a relatively unknown phenomenon.

This work aims to study the modalities of the erosion of the coastal cliffs of Normandy usíng data acquired between 2012 and 2015, thanks to a LiDAR (Light Detection and Ranging) installed on a boat. This study aims to:
1) Define the limitations of acquired data
2) Locate and characterize the main detected collapses
3) Study the role of lithology in the dynamics of erosion
4) Study the role of human activities in the dynamics of erosion
5) Perform a diachronic analysis of a major landslide near Dieppe
5) To use the LIDAR intensity for detecting the lithology and the ground movements
7) Define the role of lithology and general orientation of the cliff on fracturing.

Amin Mudaqiq: Rockfall risk analysis along road cantonal between Aigle and Le Sépey

Amin Mudaqiq
Director: Prof. Michel Jaboyedoff

This study aims to identify the risk of rockfall alongside a road on a regional scale. On first step, rockfall source areas was identified, using slope angle distribution (SAD) procedure and then it was cross checked with orthophotos and field observation. Later, three software l) CONEFALL (Jaboyedofl 2003) 2)Flow-R (Horton, et al., 2013) and 3) Rockyfor3D (Dorren, 2015) were used to investigate the maximum possible of runout distance of rockfalls. Except  CONEFALL, the two-other softwares provide the reach probability of rockfall to the road, made it possible to analyze the rockfall risk alongside the road.

The study area is mainly covered by a forest, and the effect of the forest on rockfall propagation have been tested by help of Rockyfor3D. To define the characteristics of forest (DBH and forest density), field observation and a software called FINT(Donen, 2014) were used. The results of the study showed that forest has a big protective effect on rockfall propagation specially on big and medium size of rocks.

On the study area of Aigle, it was not clear to find a rockfall with a distinct source areas to calibrate rockfall propagation using Rockyfor3D, to solve this problem another similar site was chosen (Frenieres sur Bex) and the position of rocks based on their volume were marked by GPS, then calibration was done on this area and parameters were changed to conespond the observed rocks positions on the field. Parameters used for simulation in area of Frenieres sur Bex were used for rockfall propagation in Aigle area.

For validation of the results from Rockyfor3D, two other softwares were used 1) RockforNET (Berger & Dorren, 2007) and 2) RocFall (rocscience, 2017). RockforNET showed that the protection effect of forest can stop the rocks with 5 m3 volume, confirming the simulations results from Rockyfor3D, and RocFall results for maximum possible of runout distance were corresponding the results from simulations done by Rockyfor3D.

Risk analysis along road showed that small rocks cost more than the medium and big rocks per year, and risk of driving heavy cars is higher than driving motorcycles or normal cars on the road between Aigle and Le SéPey.

Olivier Dubas: La thermographie infrarouge dans le domaine du rocheux: éléments d’influence et corrections de la température apparente en température réelle

Olivier Dubas
Director: Dr. Marc-Henri Derron
Experts: Prof. Michel Jaboyedoff, MSc. Antoine Guerin

In the field of risk analysis related to rock instabilities, temperature measurement can yield useful information in terms of stability. Indeed, temperature differentials can sometimes indicate elements that are invisible to the naked eye (eg presence of discontinuities, voids, fractured zones or exfoliation layers in certain geologies). Therefore, measuring large-scale temperatures could be beneficial in this area.

In this perspective, infrared thermography appears to be a particularly suitable tool. Indeed, the infrared thermography is a method of remote sensing that allows the instantaneous measurement of the temperature over an entire surface. This one results from the recording of a signal which is a function of the amount of infrared radiation received at the surface of the sensor. By transforming the latter into temperature using calibration curves specific to each thermal camera, this technique makes it possible to measure the surface temperature of an object remotely and rapidly.

However, this method is very sensitive to many parameters which, if not taken into account, can distort the measurement and cause artefacts. Therefore, a good understanding of the influencing parameters is necessary in order to bring the measured temperature closer to the actual temperature of the object under study. To do this, a good parameterization of the camera is necessary and this results from a good understanding of the phenomena that can influence the thermographic measurement. These may be related to 1) the nature of the surface studied (type of rock, alteration, roughness, oxidation) 2) the state of the environment in which the measurement is carried out (influence of the environment) and 3) The geometrical arrangement between the camera and the object studied (distance, angle of incidence).

The objective of this work is to: understand the theoretical notions specific to infrared thermography, assimilate the operation of the camera used and propose an adequate acquisition protocol, evaluate the impact of different influential parameters with the achievement of some experiments, propose a three-dimensional model of correction of apparent temperatures using a coupling between the thermal camera and a terrestrial laser scanner and finally propose a method to achieve thermal panoramas on a large scale thanks to the coupling between the thermal camera and a “GigaPan” panoramic head device.

Roya Olyazadeh: Natural hazards and open source development: adoption and application of mobile and Web-GIS technologies in risk management

Roya Olyazadeh
Director: Prof. Michel Jaboyedoff 
Jury:  Dr. Marc-Henri Derron, Dr. Christian Kaiser, Dr. Anne Puissant, Prof. Suren Erkman

Impacts of natural disasters have increased worldwide in the past decades. Risk assessments and analysis have been effectively pursued by research institutions, national and local governments, NGOs and different stakeholders for some time and a wide range of methodologies and technologies are proposed consequently. Nowadays, risk and disaster management including risk reduction mitigation and alternative selections are becoming more useful with World-Wide-Web and Geospatial Technologies. Web-GIS technologies offer a wide range of solutions to map the disasters, damages, analyze data and publish the results on the web. Open-source Web and Mobile GIS tools can help to improve the analysis of data and reduce the time and cost required. Open-source platforms and data have been widely used today because they stay free and facilitate access to data especially significant in developing countries. This research explores the applications and adoptions of Mobile and Web GIS technologies in the field of risk and disaster management. The purpose of this research is: (l)To review different open source web and mobile GIS systems related to Risk and Disaster management; (2) to explore the adoption and application of web and mobile GIS technologies for the collection, analysis, and decision making in disaster management; (3) to manage risk analysis using open data such as OpenStreetMap (OSM); (4) to apply advanced visualization, central database, fast and easy data and information acquisition. This research was carried out in 3 major phases: risk identification, assessment, and evaluation, which includes developing different platforms using open-source Web-GIS technologies such as OpenLayers, Leaflet maps, Cordova, GeoServer, PostgreSQL as the real DBMS (Database Management System) and PostGIS as its plugin for spatial database management. The first study presents a Web-GIS prototype using OSM data to evaluate the rapid impact of naturally produced disasters like an earthquake for the estimation of total damages. For this purpose, expert knowledge such as earthquake intensifies and vulnerability inputs are imported into the system. The second study uses the same methodology as the first platform and is applied in a teaching project (FIP) at University of Lausanne. Its purpose is to discover the relation between an open-source platform/data and students. The third application reviews the implementation and selected results of a secure Mobile map application called ROOMA (Rapid Offline-Online Mapping Application) for the rapid data collection of landslide hazard in Nepal. This prototype assists the quick creation of landslide inventory maps (LIMs) by collecting information on the type, feature, volume, date, and patterns of landslides. This application comprises Leaflet map coupled with satellite images as a base layer, drawing tools, geolocation (using GPS and the Internet), photo mapping and events clustering. The fourth study presents an improved version of ROOMA for Canton Vaud, Switzerland to collect all events and hazards such as landslide, floods, avalanches, and etc. The last platform reviews an implementation of a decision analysis module based on Multi-Criteria Decision Analysis (MCDA) in the platform of a Natural Risk Management Spatial Decision Support System (SDSS) called “RiskChanges”. This platform involves changes in hydro-meteorological risk and delivers tools for indicating the best risk reduction alternative. This module assists the users by importing the essential factors, such as risk and cost-benefit values from other modules. Besides the combination of the multi-criteria analysis and possible future scenarios in group sessions and comparison the results by means of a numerical and graphical view are carried within the system. The results of these different platforms clarify how open- source GIS technologies can be easily adopted on different levels of risk and disaster management such as post-disaster management, teaching, decision support systems and, etc. Moreover, the results present the technical difficulties to adapt these technologies to real-life situations.

Cécile d’Almeida: Model and cartography of the Saint-Eynard cliff erosion by rockfalls

Cécile d’Almeida
Supervisors: Prof. Michel Jaboyedoff, MSc. Antoine Guerin

Rockfall hazard is a major concern in mountainous area and its characterization is needed to set proper safety dispositions. An estimation of the erosion dynamic of the Saint-Eynard cliff near Grenoble in France, is performed using a lidar detection method of rockfall between 2015 and 2017. The detection of the rockfall allows to set an inventory of past events. Based on this inventory, a power law is fitted to model the frequency-magnitude of the fallen blocks. A stability analysis of the fitted power law distribution is performed making the use of a eight years database on the Saint-Eynard cliff from previous studies. Further, the use of the lognormal distribution to model the frequency-magnitude is evaluated and compared to the power law fittings. It appears that both the power law and the lognormal distribution model with the same order of accuracy the frequency-magnitude distribution of the rockfalls. Finally, a preliminary work on a semiquantitative analysis of propagation hazard is performed using the Rockyfor3D and Trajecto3D model.

Maxime Collombin: De l’affleurement à la caractérisation réservoir : étude de fracturation sur la base d’une acquisition LiDAR

Maxime Collombin
Supervisor: Dr. Marc-Henri Derron

The study of fractured reservoirs is of primary importance for hydrocarbons, water and geothermal exploration.

The investigation of natural fracture networks affecting potential reservoir is a key point in the present field of research since fracturing may constitute preferential flow paths for fluids consequently to an increase of the secondary permeability.

Performed in the context of a geothermal project in the Western Alps of Switzerland, the present work focuses on the characterization of the fracturing pattern in order to better understand water circulations affecting a gneissic geology (tectonic unit of the “Aiguilles Rouges Massif”). The fracturing interpretation is here mainly based on a terrestrial LiDAR survey of outcrops close to (future) production wells as well as on discrete fracture
network (DFN) modelling.

The different sets of fractures are characterized in terms of orientation and density. In addition, traditional field survey observations and measurements from outcrops allow documenting the fracture aperture, types of fillings and the evidences of past and present-day fluid circulations. Fracturing patterns from outcrops and LIDAR analysis are then compared to regional structures observed on a DEM.

Main objectives of this study are: (1) to compare and check the consistence of various sets of fracturing data, acquired by various methods at different scales; (2) to develop the most representative fracture model (DFN), taking into account these datasets.

Pierrick Nicolet: Quantitative risk analysis for natural hazards at local and regional scales

Pierrick Nicolet
Director: Prof. Dr Michel Jaboyedoff
Jury: Prof. Dr Paolo Frattini, Dr Alexander Garcia Aristizabal, Dr Markus Imhof, Dr Farrokh Nadim, Prof. Dr Suren Erkman, Prof. Dr Jean-Luc Epard

Natural hazards can have damaging consequences for human activities, causing death or economic losses. This PhD thesis concentrates on the risk of natural hazard, where risk is defined as the combination of the likelihood of a damaging event and its negative consequences. The types of hazards considered in this work are mostly geological hazards such as landslides and sinkholes, but hail is also investigated.

The first part of this work focuses on the local scale, where local stands for a small group of objects, typically a few houses or a road. First, in order to improve the characterisation of the hazard, the potential of the photogrammetric method, which consists in retrieving the 3D position of objects from a set of 2D pictures, is tested. Together with this promising method, Unmanned Aerial System (UAS) are presented, since they permit to carry a camera and thus to take pictures for a photogrammetric analysis. Then, a tool to calculate the risk at local scale is presented. This tool is designed in Microsoft Excel an aims at calculating rapidly the risk using hazard maps produced according to the Swiss guidelines. A particular aspect of this model is presented in the next chapter; it reviews the methods used to calculate the conditional probability for a falling object, such as a rock block, to impact a moving vehicle, taking into account the dimensions of the block and of the vehicles. Then, prospective aspects of such a risk model are presented and deal with the addition of multiple risk scenarios and the inclusion of uncertainty in the risk analysis using a Monte-Carlo approach. To conclude this part, a method which aims at taking the protection measures into account in the hazard maps without losing the initial hazard level is presented.

The second part of this work presents risk analyses at regional scale, where the region varies from the size of a canton to the size of a (small) country. The first study concerns the risk induced by evaporite sinkholes on a building portfolio. An inventory of damaged buildings is built from different sources and projections are made to estimate the losses that the public building insurance company could face if this type of hazard was insured. Then, a stochastic model which aims at modelling shallow landslides with regard to a precipitation event, and at calculating the probability of impact with buildings is presented. It shows that the location of the landslides which occurred during the precipitation event considered in this study is positively correlated with the building location, suggesting a human influence in the landslides. To conclude this part, an analysis based on a hail event is presented and aims at relating the radar-derived maximum hailstone size reached during an event with the losses, at calculating the mean annual risk using this relation and at modelling random event to refine the risk analysis.

Although the basic principles of risk analysis are relatively simple, this work highlights the diversity of the risk analyses procedure and the need to adjust the procedure to the research question. In addition, it highlights the need for good inventories of events and consequences, since these inventories are crucial to perform a good risk analysis.

Download the PhD manuscript here