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Les ‘glissements de type écoulement' dans les marnes noires des Alpes du Sud. Morphologie, fonctionnement et modélisation hydro-mécanique

Abstract : Flow-like landslides constitute a major natural risk in mountainous areas. This generic term gathers a variety of phenomena (earthflow, debris avalanche, debris flow) which may take place in a sequence and for which the common characteristic is the transport ‘en masse' of a highly concentrated mixture of water and solid particles. The considerable energy involved often renders inefficient any techniques of stabilisation or protection. It is therefore necessary to develop assessment and mitigation strategies. A variety of modelling studies has led to some progress, without however reaching completely satisfying results. Approaches through soil mechanics and fluid mechanics allow for a generally satisfactory representation of the flow motion at the laboratory scale, but care has to be taken when generalising these examples at the field scale, on observed events. These models suffer from a lack of calibration and validation. A scientific work has been carried out to deal with these questions on the basis of a better knowledge of the hydro-mechanical behaviour of these landslides. The approach is based on in-situ measurements, the statistical treatment of time series, hydrodynamical, geomechanical and rheological tests and numerical modelling. The Super-Sauze earthflow (South Alps), representative of viscous landslides in soft rocks has been chosen as experimental study site. A hydro-mechanical concept is proposed for the short- and long-term behaviour of earthflows. Constitutive equations of the materials are defined for various shear rates. The hydro-mechanical concept is introduced into several numerical codes to represent the different stages of movement (continuous slow-moving slide, fast-moving flow, spreading). Due to the complexity of these phenomena, the use of only one code is not possible. The groundwater and pore pressures fluctuations are modelled with the help of the distributed physically-based hydrological model STARWARS. The hydrological model is calibrated (soil moisture, pore pressures) on different internal variables, time steps and experimental points. The validity of the model is evaluated. The results are introduced as initial conditions in several mechanical models. An elastoplastic behaviour with viscous effects must be introduced to represent the ‘Pore Water Pressures/Displacements' relationships. The model is calibrated on an annual scale. Under specific circumstances, excess pore pressures are built up. This leads to intolerable movements and the static liquefaction of the material. The propagation and spreading of the released debris avalanches and debris flows are represented with the rheological models Bing and Cemagref-1D / 2-D. The runout distances and the thickness of the deposits can be correctly represented with a viscoplastic rheology (Herschel-Bulkley constitutive equation). Predictions and scenarios of events are proposed. Used in sequence, these different models allow to represent the successive stages of evolution of earthflows. They give ‘individually' good simulations and are calibrated on real observations. This cross-calibration allows to justify their performance and internal structure and to stress their advantages and inconvenience to the expert in charge of the hazard management.
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https://tel.archives-ouvertes.fr/tel-00010298
Contributor : Jean-Philippe Malet <>
Submitted on : Monday, September 26, 2005 - 7:38:02 PM
Last modification on : Monday, January 4, 2021 - 8:56:03 PM
Long-term archiving on: : Friday, April 2, 2010 - 9:58:50 PM

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  • HAL Id : tel-00010298, version 1

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Jean-Philippe Malet. Les ‘glissements de type écoulement' dans les marnes noires des Alpes du Sud. Morphologie, fonctionnement et modélisation hydro-mécanique. Géomorphologie. Université Louis Pasteur - Strasbourg I, 2003. Français. ⟨tel-00010298⟩

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