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Auscultation d'un versant rocheux soumis aux sollicitations thermiques naturelles. Cas des Rochers de Valabres (Alpes-Maritimes)

Abstract : The present work focuses on the monitoring of a rockslope, prone to instability, named Rochers de Valabres, subjected to natural thermal fluctuation at the rock surface. Thermal variations are supposed to be a preparatory factor for rockfalls. Their action is continuous, slow and imperceptible. This phenomenum is not widly studied and seldom quantified. As a first step, investigations, based on topographic survey using Lidar, stress measurements and laboratory testing, have been performed. They reveals parameters of the rockslope, as well as the stress field at shallow depths, characterized by high magnitudes, high turnover of the principal orientations and affected by topography and geological heterogeneities. Thermomechanical monitoring was performed by a network composed of strain cells and thermal sensors, deployed in boreholes. Thermal data give us information about thermal transfer, as a function of time or space. Strain variation data, although affected by thermal artefacts, give quantitative information on strains, equivalent stresses and depth of influence, on daily and seasonal basis. In order to evaluate the assumption of fracture propagation on thermal loading, an analytical model, based on fracture mechanic, is suggested. Using specific conditions and assumptions, this model reveals that measured stress and strains are sufficient to lead to propagation of pre-existing discontinuities. Consequently, this study confirms that thermomechanical variations can be considered as a non negligible preparatory factor for rockfall and can contribute to mechanical degradation of the rock masse and discontinuities
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https://hal.univ-lorraine.fr/tel-01748693
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Cécile Clément. Auscultation d'un versant rocheux soumis aux sollicitations thermiques naturelles. Cas des Rochers de Valabres (Alpes-Maritimes). Sciences de la Terre. Institut National Polytechnique de Lorraine, 2008. Français. ⟨NNT : 2008INPL051N⟩. ⟨tel-01748693⟩

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