Refinement and re-evaluation of the drop-shatter soil fragmentation method

Abstract

The drop-shatter method was re-evaluated since data were reported of degrees of soil fragmentation, obtained by using this method, showing a dependence on the total specific energy input, defined as the cumulative drop height. A new definition of the specific energy input based on the kinetic energy of the soil clods available for fragmentation upon impact is presented. The kinetic energy is calculated from the air-resistance dependent falling velocity of the soil units upon impact. Better correlations were found for the median aggregate diameter and specific surface area with the kinetic energy than with specific energy input. Notwithstanding that improvement, a drop height dependence of the degree of soil fragmentation was found for drop heights > 1.5 m. Compression stress loading rate as the stress-fracturing mechanism is suggested as a possible explanation for that dependence. It is concluded that (a) drop heights should not exceed 1.5 m, and (b) in analyzing soil fragmentation-energy input relationships obtained by the drop-shatter method, the refined method for calculating the kinetic energy available for fragmentation should be used instead of the cumulative height.