Processus Gravitaires et Évaluation de la Stabilité des Pentes : Approches Géologique et Géotechnique. Application à la marge algérienne et à l'effondrement de l'aéroport de Nice en 1979

The present work consists of two areas of interest: the Algerian margin and the area affected by the 1979 Nice slide. The first scientific survey, MARADJA, took place in 2003 in order to characterize the Algerian margin from a morpho-sedimentary point of view and to map the presence of mass-wasting deposits. Based on other two scientific surveys, PRISMA and MARADJA 2, the mechanical and physical properties of the Algerian sediment were defined. The geotechnical properties were used to identify the triggering mechanisms of the observed mass-wasting deposits and to assess the present-day slope stability. The main results are: • The sedimentary processes are clearly influenced by the morphology of the margin, which is controlled by the tectonics. The sedimentation is heterogeneous and controlled by two different processes: (a) gravity processes including the turbidity currents and the mass-wasting deposits and (b) the hemipelagic sedimentation. • Numerous mass-wasting deposits exist throughout the study area. They are characterized by small size, with an average surface calculated at 0.2 km². Only one mass-wasting deposit observed on the continental slope, offshore Dellys town, is more significant. • The presence of silt and sand layers, which are susceptible to liquefy, correspond to a major triggering factor. The evaluation of the potential of liquefaction shows that for an earthquake characterized by a PGA of 0.2 g, liquefaction may appear within the silt and sand layers. • The slope stability assessment shows the failure may occur for an earthquake characterized b only 0.1 g of PGA. In contrast, the Nice area was exceedingly studied in order to describe the 1979 Nice event. The present work presents a geological and geotechnical description of the available data. These data were used to model the slope stability of the Nice airport area in order to understand the role of the new harbour construction. We advanced a new hypothesis to explain the triggering mechanisms: a the creeping of the sensitive clay layer under the loading of the new harbour construction. The role played by other triggering factors is discuss for the present-day slope stability assessment.