Behaviour of a sensitive marine sediment: microstructural investigation

The aim of this study is to characterise along various stress paths the microstructural evolution of a deep-water marine sediment from the Gulf of Guinea (GoG). Results obtained at the macroscopic level have shown that the phenomenological behaviour of the GoG sediment is explained by the properties of remoulded samples given by the isotropic and critical state lines, and by the properties of the intact samples given by the damage evolution of the inter-aggregate bonds. Microstructural investigations conducted by mercury intrusion porosimetry and scanning electron microscopy demonstrate that the volumetric strains measured at the macroscopic level come from inter-aggregate pore variations associated with the degrading of the inter-aggregate bonds. The mechanism responsible for reorienting the particles appears to apply in the case of the remoulded sediment. As for the natural sediment, it is first necessary to increase the isotropic consolidation stress towards higher values in order to break the bonds between the aggregates before it becomes possible to activate the particle reorientation mechanism and thus approach the remoulded behaviour.