On the relationship between particle breakage and the critical state of sands

Ring shear and shear box tests were used to investigate the relationship between volume change and particle breakage during the shearing of two sands. One sand was a carbonate sand which was sheared under a high confining stress to examine whether, in the region of compressive shearing behaviour due to particle breakage, the breakage would ever cease and the soil reach a stable grading. The other sand tested was a quartz sand that was sheared at low confining stresses, to investigate whether a dilatant sand would also be subject to particle breakage. In both cases breakage was found to continue to very large strains, with no evidence of a stable grading being reached within the range of strains used. While the breakage was very small for the quartz sand it was large for the carbonate, emphasising that any definition of a critical state by means of conventional triaxial or shear box testing would be approximate only, because of the limited strains that they allow.