An integrated analysis of surface velocities induced by rainfall in the Séchilienne landslide (Western Alps, France)

International audienceAn integrated analysis on the relationship between rainfall and displacement in the most active area of the Séchilienne unstable slope was performed. This study combines several techniques and models to adequately reproduce the landslide movement induced by the rainfall. The analysis of available time series shows a long term trend and seasonal variations in the displacement, respectively independent and synchronous to precipitations. In particular wavelet analysis highlights that the movement is rather linked to groundwater recharge than to precipitation (rainfall + snowfall), involving then the importance of groundwater process in the area. A first and simple relationship between the water input and the fluctuations of displacements apart from the general trend is shown using a tank model. Moreover, a seasonal analysis of this relationship was performed, showing that displacement rate follows the behavior of the hydrological cycle. Two different models were applied to the long temporal series of extensometric and precipitation data: the FLAME model, from BRGM and the FORESEES model, from Univ. Lausanne. These tools are based on a combined statistical-mechanical approach to predict changes in landslide displacement rates from observed changes in precipitation amounts. The forecasting tool FLAME associates 1) a statistical impulse response (IR) model to simulate the changes in landslide rates by computing a transfer function between the rainfall and the displacements, and 2) a 1D mechanical (ME) model (e.g. visco-plastic rheology), in order to take into account changes in pore water pressures. The performance of different combinations of models was evaluated against observed displacement rates at the selected pilot study area. Our results indicate that both models are able to reproduce, with a high degree of accuracy, the observed displacement pattern in the general kinematic regime. Finally the variability of the results, depending in particular on the input data, is discussed

Toward a Generic Computational Approach for Flexible Rockfall Barrier Modeling

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Éditorial

La Revue Française de Géotechnique (RFG) est une publication scientifique parrainée par les comités français de mécanique des sols, de mécanique des roches, de géologie de l\textquoterightingénieur et des géosynthétique

Quantification des déplacements 3D par la méthode PLaS − application au glissement du Chambon (Isère)

Une méthode de suivi de l'évolution des mouvements de versant sans végétation, facile à mettre en œuvre et à bas coût, est développée : la méthode PLaS (Photogrammetry-based method for Landslide Study). Elle est basée sur le principe de la photogrammétrie qui est utilisée à la fois pour la génération du modèle 3D de la surface sous la forme de nuages de points et pour le calcul des déplacements 3D en surface pour le suivi de son évolution. Cette méthode est appliquée à l'étude de l'évolution du glissement du Chambon entre avril 2016 et juillet 2016. Elle permet d'identifier les zones stables et en mouvement et fournit une valeur et une direction des déplacements 3D sensiblement égales aux valeurs mesurées

EXTENDED EXPERIMENTAL STUDIES ON ROCKFALL FLEXIBLE FENCES

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Seasonal and long term analysis of precipitation-displacement relationships on a deep seated unstable slope (Séchilienne, French Alps)

National audienceTime series analysis and cross-wavelet analysis are used to characterize the relationship between water input and displacement in the most active zone of the Séchilienne unstable slope. Time series analysis shows a displacement long term trend and seasonal intra-annual variations, respectively independent and synchronous to precipitations. Wavelet analysis has allowed identifying and characterizing the precipitation-detrended displacement relationship which shows that the Séchilienne destabilisation is rather linked to effective rainfall than to raw precipitation (rainfall + snowfall), involving then groundwater process. Seasonal analysis of this relationship was performed, showing that displacement rate follows the behaviour of the hydrological cycle. Finally, trend was analysed and a weakening model approach was developed with an attempt to forecast the next modifications in unstable slope destabilisation behaviour

Comparison of two DEM modeling of flexible rockfall fences under dynamic impact

International audienceFlexible fences are efficient and cost-effective rockfall protection structures, but their complex response to impact remains difficult to predict. Models based on a discrete element method (DEM) of rock impact on a flexible fence are developed for a better understanding of the dynamic response of the structure under impact. Two of these models are introduced and compared in this paper

Étude expérimentale multi-échelle sur les écrans pare-blocs : comportement des ouvrages hors cadre ETAG27

Dans le cadre du projet national C2ROP, une large campagne d’essais expérimentaux a été conduite. Des essais sous sollicitations quasi-statiques et dynamiques ont été réalisés sur les composants les plus critiques des écrans pare-blocs (filets, dissipateur d’énergie) et sur un ouvrage complet selon différentes configurations. Une dizaine d’essais d’impact a été réalisée sur un écran développé spécifiquement pour étudier expérimentalement le comportement de ce type d’ouvrage. Des méthodes d’acquisition de données spécifiques ont été mises en place, et une grande quantité de données a été recueillie puis exploitée. La force d’impact utile pour le dimensionnement des composants, le phasage de la déformation de l’ouvrage (de l’impact à l’arrêt du bloc), et la cinématique des dissipateurs d’énergie ont ainsi pu être étudiés. Des configurations d’impacts inhabituelles représentatives des conditions de sollicitation de l’ouvrage dans son contexte de mise en œuvre ont été réalisées et comparées aux configurations de certification prescrites par l’ETAG27. Des coefficients ont été proposés afin de quantifier l’endommagement de l’ouvrage par rapport à la configuration de certification en fonction du type d’impact. Les résultats obtenus mettent en évidence que la configuration définie par l’ETAG27 n’est pas nécessairement la configuration la plus défavorable

Managing Rockfall Hazard on Strategic Linear Stakes: How Can Machine Learning Help to Better Predict Periods of Increased Rockfall Activity?

International audienceWhen rockfalls hit and damage linear stakes such as roads or railways, the access to critical infrastructures (hospitals, schools, factories …) might be disturbed or stopped. Rockfall risk management often involves building protective structures that are traditionally based on the intensive use of resources such as steel or concrete. However, these solutions are expensive, considering their construction and maintenance, and it is very difficult to protect long linear stakes. A more sustainable and effective risk management strategy could be to account for changes on rockfall activity related to weather conditions. By integrating sustainability principles, we can implement mitigation measures that are less resource-intensive and more adaptable to environmental changes. For instance, instead of solely relying on physical barriers, solutions could include measures such as restriction of access, monitoring and mobilization of emergency kits containing eco-friendly materials. A critical step in developing such a strategy is accurately predicting periods of increased rockfall activity according to meteorological triggers. In this paper, we test four machine learning models to predict rockfalls on the National Road 1 at La Réunion, a key road for the socio-economic life of the island. Rainfall and rockfall data are used as inputs of the predictive models. We show that a set of features derived from the rainfall and rockfall data can predict rockfall with performances very close and almost slightly better than the standard expert model used for operational management. Metrics describing the performance of these models are translated in operational terms, such as road safety or the duration of road closings and openings, providing actionable insights for sustainable risk management practices

An integrated analysis of surface velocities induced by rainfall in the Séchilienne landslide (Western Alps, France)

International audienceAn integrated analysis on the relationship between rainfall and displacement in the most active area of the Séchilienne unstable slope was performed. This study combines several techniques and models to adequately reproduce the landslide movement induced by the rainfall. The analysis of available time series shows a long term trend and seasonal variations in the displacement, respectively independent and synchronous to precipitations. In particular wavelet analysis highlights that the movement is rather linked to groundwater recharge than to precipitation (rainfall + snowfall), involving then the importance of groundwater process in the area. A first and simple relationship between the water input and the fluctuations of displacements apart from the general trend is shown using a tank model. Moreover, a seasonal analysis of this relationship was performed, showing that displacement rate follows the behavior of the hydrological cycle. Two different models were applied to the long temporal series of extensometric and precipitation data: the FLAME model, from BRGM and the FORESEES model, from Univ. Lausanne. These tools are based on a combined statistical-mechanical approach to predict changes in landslide displacement rates from observed changes in precipitation amounts. The forecasting tool FLAME associates 1) a statistical impulse response (IR) model to simulate the changes in landslide rates by computing a transfer function between the rainfall and the displacements, and 2) a 1D mechanical (ME) model (e.g. visco-plastic rheology), in order to take into account changes in pore water pressures. The performance of different combinations of models was evaluated against observed displacement rates at the selected pilot study area. Our results indicate that both models are able to reproduce, with a high degree of accuracy, the observed displacement pattern in the general kinematic regime. Finally the variability of the results, depending in particular on the input data, is discussed