Multi-fractal characteristics of reconstructed soil particle in opencast coal mine dump in loess area

Abstract: Reconstructed soil from an opencast mine dump in a loess area was a complex unity that was made up by humans using different reconstruction technology. It is composed by different soil particles with irregular shapes, and has a self-similar structure. The good soil structure for vegetation growth as reconstructed is the core work of land reclamation. In order to better quantify the soil structure reconstructed in a dump, the soil particle size distribution from four kinds of soil reconstruction modes in the Shanxi Pingshuo ATB Opencast Coal Mine dump was analyzed using the soil multi-fractal theory. Soil reconstruction modes included soil ccovered using loess with gravel, soil covered using loess with coal gangue, covering the whole soil with loess material, and soil covered using loess with Liao Jiangtu. Generalized dimension spectrum D(q), multi-fractal singularity exponent α(q), multi-fractal spectrum function f(α(q)) and other multi-fractal parameters were calculated, and the relationships among the different fractal parameters were analyzed in this paper. The results indicated the following conclusions. (1) The particle distribution of reconstructed soil had significant multi-fractal characteristics in an opencast coal mine dump in the study area. D(0), D(1), D(1)/D(0), Δα and Δf can reflect the non-uniform particle size distribution characteristics from different perspectives. (2) There was a smaller range of soil particle size distribution, a higher degree of measurement concentration, discrete to a lesser discretization extent, a lower non-uniformity of soil particle size distribution in the soil reconstruction mode of covering the whole loess material, and the function of the mode in changing soil particle size distribution was superior to the modes containing gangue and gravel. (3) The small probability subset of soil particles composition predominated and the soil contained more large particles in the reconstructed soil in the opencast coal mine dump of the loess area. (4) There were good correlations among the multi-fractal parameters of the reconstructed soil particles distribution. D(0), D(1)/D(0) and Δα(or D(0), D(1) and Δf ) can be simplified as three parameters to quantitatively express multi-fractal characterization of the reconstructed soil particle distribution in the study area. (5) The soil multi-fractal parameters in the reconstruction loess section 0-90 cm changed significantly, and the soil thickness covering loess should be more than 90 cm. Gangue and gravel have a certain impact on the dispersion degree of reconstruction soil particles distribution, and should be abandoned in the soil layers below 90cm to reduce its effect on soil particles composition and to improve vegetation restoration .This study can provides a theoretical basis for land reclamation and a quantitative expression of reconstruction soil quality in an opencast coal mine dump of a loess area.