Identifying the soil structure of the piedmont-plains by the fractal dimension of particle size

Soil structure fundamentally determines the hydrodynamic characteristics of the saturated-unsaturated zone, solute transport characteristics, and thermodynamic properties of the soil. Additionally, it regulates the process of transfer and conversion of matter and energy in the saturated-unsaturated zone. However, the quantification of soil structure is difficult because it depends on a combination of factors including soil particle sizes and types and spatial distribution of pores. In this study, the structural characteristics of the vadose zone are examined based on self-similarity in the soil and the fractal theory of non-linear science. This approach describes the soil particle sizes and spatial distribution of pores in the interior layers of the soil. The study area stretches across 165 km of the piedmont-plains of the Taihang Mountains. The particle sizes and volume percentages of particle sizes in 57 soil samples were measured using the Mastersizer 2000 laser diffraction particle size analyser (Malvern Instruments, U.K.). This information is then combined with the volume-based fractal dimension (D), calculated using the fractal theory, of the various samples. The results obtained indicate that: (i) the fractal theory can be used to effectively identify the characteristics of three-dimensional structural changes within the soil profiles. The average soil particle size decreases from the piedmont of the Taihang Mountains towards the plains. Similarly, the volume percentage of particle size and the maximum volume percentage of a single particle size decreases. Moreover, the D values show an overall declining trend; (ii) the D values of the soils of the piedmont-plains of the Taihang Mountains show significant spatial variations in the range of 1.037-1.925. Although there is no correlation between the D value and soil particle size, the D value is very sensitive to the soil structure uniformity. The higher the uniformity, the greater is the D value; and (iii) D values cannot be used as the sole basis for determining the soil hydraulic properties. The D values and soil hydraulic properties are correlated only for a particular range of soil particle sizes.