A triaxial investigation of kinematic yielding in sand

The elastic-plastic behaviour of a reconstituted sand is considered under triaxial conditions, covering a wide range of strains. Monotonic probing tests are used to identify two types of kinematic yield surface for samples with loose and dense initial states, under drained and undrained conditions and after different patterns of consolidation. Plastic strain development and global stiffness degradation are found to be closely interrelated, and the interpretation involves decoupling the elastic and plastic strain components. The sizes and the shapes of the loci are strongly affected by effective stress states and histories, including any periods allowed for creep and ageing. A tentative qualitative micromechanical explanation is offered for the phenomena observed.