Abstract

The dispersion and energies applied by the end-over-end shaking and ultrasonic methods of assessing aggregate stability were compared. The simple calculation of the kinetic energy of the falling water within the shaking cylinder (0·72 W) was found to underestimate the total energy associated with dispersion, which was estimated as the equivalent energy during the initial period of shaking, as 1·92±0·18 W. A range of mechanical energies up to 24·95 W was applied to suspensions of 2 Vertisols with contrasting stability using the ultrasonic and the end-over-end shaking techniques. Both power and total energy applied was found to affect significantly (P < 0·05) the dispersion of material sized <20 and <2 µm. The results confirmed the presence of aggregate hierarchy, with the end-over-end shaking treatment being unable to disperse completely the <2 µm material for either soil. An increase in the power applied by the ultrasonic probe increased the rate of aggregate breakdown for the stable soil but produced no effect on rate of breakdown in the unstable soil.