The energy applied to a soil-water suspension by an ultrasonic probe was determined for seven vertisol soils using calorimetric techniques. The rate of energy consumed by aggregate dispersion during sonification was calculated as the difference between the energy components measured before and after complete dispersion. Dispersive energy consumption was found to vary significantly during sonification and significant differences (P
The application of ultrasonic energy to soil-water suspensions for particle size analysis has been widely adopted and more recently applied to aggregate stability assessment. However, suspension properties have been reported to affect both the energy applied and the degree of aggregate breakdown. This paper investigates the effect of suspension concentration, suspension volume, gas saturation, depth of ultrasonic probe insertion and particle size distribution on the power (energy per unit time) applied by an ultrasonic probe. It also investigates the effect of suspension concentration, suspension volume, gas saturation and method of wetting the soil on the dispersion produced by ultrasonic energy applications. Where the power applied was expressed per unit soil mass, the quantity of dispersed material released by ultrasonic action was not affected by either the volume or concentration of the suspension. However, decreasing the dissolved gas concentration in suspension decreased the dispersion produced. The method of soil wetting significantly affected initial disruption but had no effect on the maximum amount of <2 and <20 �m material produced by sonification. The power applied by the ultrasonic probe was found to decrease with suspension temperature, increase with dissolved gas concentration and increase with the depth of probe insertion. Recommendations are made on the range of suspension properties that should be used for standard measurements of aggregate stability assessment using ultrasonic energy.
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.
The end-over-end shaking technique has been widely used to provide a measure of soil dispersibility. However, results are dependent on the specific methodology employed. This paper investigates the effect of various physical parameters on the dispersion produced using an end-over-end shaking technique. Significant (P < 0·05) increases in the percentages of clay (D2) and silt+clay (D20) particles dispersed as a proportion of the total soil weight were observed with increasing period of shaking, suspension concentration, container size, and air-gap above the suspension. However, differences due to suspension temperature and soil texture were either relatively minor or insignificant (P > 0·05). To enable better comparison of results from different workers, the following methodology for end-over-end shaking studies is proposed as a standard. The soil sample should be air-dried and crushed to pass through a 2-mm sieve. The air-dried equivalent of 50 g oven-dried soil should then be immersed in 1 L double-deionised water at 20°C within a 1·425-L cylinder (70 mm internal diameter) and shaken end-over-end at 20 rpm for 30 min before measuring the amount of dispersed <2 and <20 µm material produced. The amount of dispersed material should be expressed as a proportion of the total soil material.
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