Comparing stress wavelets with fragment fractals for soil structure quantification

A laboratory test following a field experiment was conducted to investigate the performance of stress wavelets as a tool for soil structure quantification. Based on the test, comprehensive calculations of indices were performed, including per fragment surface contacting energy, fragment fractal dimensions and specific fragmentation energies. Fragment fractal dimensions were 2.46 for autumn-tilled soil and 1.86 for spring-tilled, showing the improvement of soil structure from winter process, mainly from statistical point. Specific fragmentation energy ranged from 78.72 to 1135.44 J/kg, depending both on the way of field treatment and initial size ranges of soil been fragmented. Compared with these, stress wavelets analysis was capable of distinguishing, specifically from mechanical points, differences between autumn-tilled and spring-tilled soils. s shown that fractal dimensions provided information on soil fragment size distributions, bearing no significance on soil mechanical properties. Stress wavelets, on the other hand, permitted calculations of specific fragmentation energy and per fragment surface contacting energy, which had a uniquely straight-forward connection with soil mechanical properties. The low per fragment contacting energies possessed by autumn-tilled soil, as compared with spring-tilled soil, indicated that winter process reduced soil contacting energies significantly. But a negative value of per fragment contacting energy for autumn-tilled soil was un-interpretable. The combination of stress wavelets and fractals may serve as a fundamental quantitative index for modeling soil structures in its thorough dimensions. The difference between autumn-tilled and spring-tilled soils also indicated that tillage alone should not be taken as a sole way for the improvement of soil qualities.