Multi-method characterisation of an active landslide: Case study in the Pays d'Auge plateau (Normandy, France)

Abstract : Shallow landslides are among the most frequent natural hazards in the Pays d'Auge plateau (Normandy, France) but no study has yet focused on the functioning of these phenomena at a detailed scale. This study aims to identify the structure and mechanical properties of a representative case study in the region. The main objective is to understand landslide dynamics and behaviour in order to assess triggering conditions and quantify triggering thresholds. The results will help complement the regional landslide hazard mapping based on landslide statistical susceptibility mapping and quantification of triggering thresholds. The landslide morphology and internal structure were identified using a multi-method approach. A morphodynamic map was produced in the field using car-tographic GPS to depict the surface morphology and map the estimated landslide activity. These field measurements were completed by an analysis of all available aerial-photo images from the French National Geographic Institute (IGN) to identify the occurrence dates and possible landslide reactivations. The landslide structure was defined using multiple electrical tomography profiles, boreholes, augerings and penetration tests. Despite the overall low electrical resistivity of the landslide materials (i.e. ± b 80 Ω·m), the electrical profiles showed good agreement with the interpreted structure based on direct observations (augerings and penetration tests). The landslide slip surface, internal morphology and palaeotopography were identified. A finite slope model was used to calculate the landslide safety factor based on the internal structure and geotechnical data. The evolution of this safety factor according to the rainfall and the groundwater levels shows that the landslides are more likely to occur after long episodes of high cumulative precipitations with an important role being played by the preliminary conditions and the rise of the surficial groundwater table level.
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Soumis le : jeudi 1 septembre 2016 - 14:46:27
Dernière modification le : vendredi 14 septembre 2018 - 10:56:08

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Mathieu Fressard, Olivier Maquaire, Yannick Thiery, Robert Davidson, Candide Lissak. Multi-method characterisation of an active landslide: Case study in the Pays d'Auge plateau (Normandy, France). Geomorphology, Elsevier, 2016, 270, pp.22-39. 〈10.1016/j.geomorph.2016.07.001〉. 〈hal-01358915〉

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