The 1979 Nice harbour catastrophe revisited: Trigger mechanism inferred from geotechnical measurements and numerical modelling

In 1979, a catastrophic event occurred on the Nice continental slope (French Riviera) generating the lost of human lives and important material damages. Part of the new harbour constructed at the edge of the International Airport of Nice collapsed into the sea. The main aim of this work was 1) to present a review of facts and details related to the 1979 accident and a review of the geological setting, and 2) to evaluate the slope stability before and after the new harbour construction, by taking into account new available data such as sediment cores and piezocone CPTU data. The CPTU data were of great value to understand the origin of the 1979 event. They show the existence of a sensitive clay bed between 30 mbsf and 45 mbsf Under high deviatoric load a sensitive clay layer underwent an important creep, which dramatically decreased its resistance and caused the slope failure. This working hypothesis was supported by the good agreement between the maximum thickness of the failure surface and the depth of the sensitive clay layer. Slope stability assessment using the finite element model Femuslope show the metastable state of the Nice slope before the harbour extension. Numerical calculations demonstrated that creeping of the sensitive clay layer could be at the origin of the 1979 slide. In addition, the exceptionally heavy rainfall which occurred before the accident and consequently the seepage of fresh water probably induced the decrease of the effective stress and accelerated sediment creeping and triggered the Nice slope failure. A progressive and relatively long-term creeping failure scenario is in good agreement with the official report mentioning cracks, settlements, failures and embankment collapses occurred during land filling operations. (C) 2007 Elsevier B.V. All rights reserved.