The critical state concept and the behaviour of powders in the ring shear cell test

Abstract

In this paper, the powder ring shear cell test is interpreted in terms of the critical state concept. The critical state line is found when the powder (Snowcal 3ML) reaches an ultimate condition of shear at no volume change. The critical state line is shown to be parallel to the virgin consolidation line in void ratio/ log (normal stress) space. To the right of the critical state line, the Roscoe surface is identified at the onset of plastic yielding, accompanied by the onset of volume decrease of the powder. To the left of the critical state line, the Hvorslev yield surface cannot be identified in the ring shear cell, but rather a surface describing failure on discrete planes is found. The shape of the failure surface may differ according to the stress conditions, but in the usual mode of powder shear testing will assume the classical ‘powder yield locus’ form.