Multi-fractal characteristics of the particle distribution of reconstructed soils and the relationship between soil properties and multi-fractal parameters in an opencast coal-mine dump in a loess area

Abstract

Soil reconstruction is at the core of mine land reclamation. Reconstructed soil from an opencast mine dump in a loess area is a complex composite that was assembled by humans, using multiple reconstruction technologies. The soil is composed of varied soil particles with irregular shapes and has self-similar structure. To better quantify the characterization of reconstructed soil in this dump, the soil particle-size distribution from four modes of soil reconstruction in the Shanxi Pingshuo Antaibao opencast coal-mine dump was analyzed using multi-fractal theory. Soil reconstruction modes included loess material containing gravel (LG), loess material containing coal gangue (CG), total loess material (AL) and loess material containing ginger stone (LGS). Soil particle composition, gravel content, field water capacity, soil bulk density, soil organic matter, total nitrogen (TN), soil pH and electrical conductivity (EC) of different soil layers from different reconstruction modes were measured. A generalized dimension spectrum D(q), multi-fractal singularity exponent α(q) and multi-fractal spectrum function f(α(q)) were calculated. Relationships between soil properties and fractal parameters were analyzed. The results led to the following conclusions: (1) the soil particle distribution of reconstructed soil had significant multi-fractal characteristics in an opencast coal-mine dump in a loess area. D(0), D(1), D(1)/D(0), Δα and Δf can reflect the non-uniform particle-size distribution characteristics. D(0), D(1)/D(0) and Δf (or D(0), D(1)/D(0) and Δα) can be simplified as three parameters to quantify the multi-fractal characterization of the reconstructed soil particle distribution. (2) After reclamation, the soil quality from different layers of different profiles in different reconstruction modes shows some improvement. (3) There were strong correlations between multi-fractal parameters and soil properties. D(1) and Δα increased and D(1)/D(0) and Δf decreased with increasing gravel content, soil bulk density, organic matter, TN and soil EC; however, it was opposite for pH and field water capacity. Gangue and gravel have a definite impact on the dispersion degree of soil particles in reconstruction. This study provides a theoretical basis for land reclamation and quantitative expression of reconstructed soil particles’ distribution in opencast coal-mine dumps in loess areas.