Change in Aggregates Structure of Kuroboku Soils with Drying and Compaction Treatment Related to Fractal Dimension

Abstract

(i) Earthworm In order to understand the response of Kuroboku soil to external mechanical forces, the changes in soil aggregate shapes caused by drying and compaction have been analyzed by the Mandelbrot fractal dimension procedure.
Samples of aggregates, 2-1mm in size, were separated by wet sieving from topsoil and subsoil samples of allophanic and non-allophanic Kuroboku soil.
(1) Mandelbrot fractal dimension procedure proved to be useful in the quantitaive formulation of the change in the shape of soil aggregates ocurring on drying and compaction. Themagnitude of fractal dimension (D) obtained for the samples used were 1.9-1.3.
(2) The fractal dimension (D) changed, as a function of drying, in the form of a curve with an exsreme value (maximum or minimum) at the maximum dry density (ρ_{d max}) for topsoil, but in a linearly decreasing way for the subsoil samples. Such a difference was presumed to be due to the difference in the microstructure of aggregates between topsoil and subsoil.
(3) Relationship between fractal dimension (D) and water content (ω) of the samples after compaction was expressed by a concave curve with a minimum at the maximum dry densityn (ρ_{d max}) for all samples used. The sample from allophanic topsoil showed, however, a small convex at the maximum unconfined strength (q_{u max}). The fractal dimension attained a maximum when the non-allophanic samples were compacted at an air-dry state.