The aim of the GéoCoD team’s project is twofold, focusing on knowledge, prevention and management of gravitational risks such as land movements in relation to adaptation to climate change and on management, optimisation, modernisation and design of infrastructures and structures.
The GéoCoD team’s research programme deals with several major economic, societal and strategic issues.
The societal issues are:
Knowledge, management and prevention of natural gravitational risks
One of the major issues the team is tackling is knowledge, management and prevention of natural gravitational risks. Although gravitational risks cause less damage than risks with an atmospheric origin (flooding and storms), their cost amounts to several million euros per year (source: Caisse centrale de réassurance).
Road and rail infrastructures are very much exposed to these risks, in particular in mountainous areas, in the form of rockfalls, rock slides, debris flows and avalanches, which may lead to occasional closure as well as significant damage to property and people, with major repercussions for the local or national economy. Due to the position of the French mountain ranges, often at the national borders, and the increase in international travel by road and rail, communication routes of the utmost importance are located in these areas. Every day of the year they are used by thousands of railway carriages and trucks and hundreds of thousands of motorists, particularly during the mass migrations that take place during holiday periods. In addition, the mountainous regions make a major contribution to the French economy.
In a context of long-term and undoubted climate change, it is likely there will be an increase in rockfall events, collapses, rock slides and landslides. This is caused by the rise in the rain-snow line by an average of 300 metres over the last few decades and the increase in the number of violent events characterised by substantial and intense impluvium, even though the quantity of precipitation remains constant. In coastal areas there are also major protection issues, and the effects of climate change are also evident. In this context, the ambition of the GéoCoD team is to contribute to knowledge about mechanisms that trigger instabilities, to prediction of events, and to development of counter-measures by specifying the dimensioning methods.
Renewal and maintenance of geotechnical structures linked to transport infrastructures and to improvement activities in areas at risk.
The second major subject the team is focusing on is renewal and maintenance of geotechnical structures linked to transport infrastructures and to improvement activities in areas at risk. In particular, since the new regulatory seismic zoning was defined in 2010, many sites in France are subject to seismic risk. Complex demands must therefore be taken into account when dimensioning and reinforcing these structures. New research issues are therefore coming to light, directly linked to the concerns of companies working in the field. The responses provided will make it possible to build or rehabilitate better, taking account of the complex demands in areas where there are more and more restrictions and a high level of urbanisation, characterised by natural materials with often poor mechanical properties. These responses will also provide an opportunity to optimise dimensioning and reinforcements. This research is therefore positioned as a preliminary to a more global scientific and technical approach seeking to meet “the needs of the present without compromising the ability of future generations to meet their own needs” (Brundtland Report, 1987).
The GéoCoD team is working to find answers to the following research question: Faced with exposure to risks and with land-use planning requirements, how can we dimension and optimise the means of protection against gravitational risks and the geotechnical structures, taking account of durability and ageing?
This question of dimensioning requires prior knowledge of the behaviour of geomaterials and the site. These are the input data for definition of a suitable structure. In order to provide answers to the research question that is posed, it is essential for the team’s work to focus on identifying the mechanical parameters, the changes they undergo over a period of time and the relevant uncertainties.
Then it is also necessary to better understand the behaviours of the support, reinforcement and protection solutions in order to guarantee reliable dimensioning and controlled durability, while optimising construction and maintenance costs.
The GéoCoD research team project consists in characterising the mechanical behaviour of geomaterials when they are subjected to various loads or external aggressions, and then defining protection solutions and protective dimensioning methods. The mechanical behaviour of the geomaterials and structures is therefore defined according to the interaction between multi-physical phenomena (Axis 1), and then according to dynamics (Axis 2):
Axis 1: Consideration of hydric, chemical, thermal and mechanical interactions (THMC) in the behaviour of geomaterials and sites.
Axis 2: Dynamic behaviour of soils, rocks, structures and sites.
The main objectives of the project are therefore as follows:
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to take account of seismic, cyclical and dynamic loads in the dimensioning of geotechnical structures,
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ageing of geomaterials in their environment and durability of the associated geotechnical structures,
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behaviour of protection structures subjected to impacts,
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understanding of mechanisms triggering gravitational instabilities and identification of warning signs.
In this context the expected results are as follows:
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Identification of thresholds for triggering gravitational instabilities;
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Introduction of multi-physical digital models describing variations in the mechanical properties of geomaterials over time (environment, internal processes);
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Identification of mechanical parameters of soils subject to cyclical and dynamic loads and quantification of the associated uncertainties;
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Quantification of the inertial and kinematic effects of soil-structure interactions when subjected to seismic loads;
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Development of a method for dimensioning rockfall protection netting screens integrating the variability of the impacts;
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Introduction of tools to detect movements in the same order of magnitude as data noise.
Gustave Eiffel University, EDF, INRAE, GéoCorail, Géolithe, Ineris, BRGM
Louis Zadi (2019-2022), University of La Rochelle, “Modélisation numérique des processus physico-chimiques impliqués dans la formation d'un écomatériau sédimentaire généré en milieu marin” (Digital modelling of physico-chemical processes involved in the formation of a sedimentary eco-materials generated in the marine environment), A. Soive (Cerema co-supervisor) and Philippe Turcry (University of La Rochelle co-supervisor)
Haytam Tribak (2019 – 2022), University of Fez – University of Côte d’Azur, “Influence de la géologie et de la géotechnique sur les instabilités des versants du Rif marocain” (Influence of geology and geotechnics on instabilities in the hillsides of the Moroccan Rif), M. Gasc (Cerema co-supervisor) and Prof. Abdelkader El Garouani co-supervisor for Moroccan University of Sidi Mohamed Ben Abdellah)
Claudia Villarraga-Diaz (2018), University of Toulouse, “Effet des cycles thermiques sur la stabilité des massifs rocheux” (Effect of thermal cycles on stability of rock masses), supervised by M. Gasc (Cerema), José Darrozes (University of Toulouse) and J. Vaunat (Universitat Politècnica de Catalunya)
Jibril Coulibaly (2017), University of Grenoble Alpes, “Modélisation numérique discrète du comportement mécanique sous impact des structures d'écrans de filets pare-pierres” (Discrete digital modelling of mechanical behaviour of rockfall prevention netting screens subjected to impacts), supervised by F. Nicot (INRAE), MA Chanut (Cerema), S. Lambert (INRAE)
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