Multi-fractal characteristics of three-dimensional distribution of reconstructed soil pores at opencast coal-mine dump based on high-precision CT scanning

The pore conditions of reconstructed soils can reflect the quality of rehabilitated soils. In this paper, high-resolution and non-destructive computed tomography (CT) images were used to conduct three-dimensional reconstruction of soil pore distribution by scanning soils from the Antaibao Opencast Coal-mine in the Pingshuo mining area, and multi-fractal theory was used to analyze the distribution characteristics of soil pores. The soils were taken from one unmined site, one unrehabilitated site and two rehabilitated sites. All of the unrehabilitated and rehabilitated sites were on the dump platforms using a loess parent material covering, and two rehabilitated sites had the rehabilitation time of 20 a and 23 a, respectively. The three-dimensional distribution of the reconstructed soil pores followed the multi-fractal theory, and the entropy dimension (D1), difference between capacity dimension minus entropy dimension (D0-D1), variation degree of generalized dimension spectra (ΔD), width of singularity spectra (Δα) and symmetry of singularity spectra (Δf) can reflect different aspects of the soil pore distribution characteristics. Compared to unmined soils, the multi-fractal parameters of soil pore distribution (D1, D0-D1, ΔD, Δα and Δf) significantly decreased after mining and dumping, and soil micropores dominated with uniformity. However, D1, D0-D1, ΔD, Δα and Δf had significant increase during rehabilitation, and the pore conditions of rehabilitated soils were improved significantly with increasing rehabilitation time, increasing macropore ratio and becoming heterogeneous.