Characterizing effects of mechanical compaction on macropores of reclaimed soil using computed tomography scanning

To study the effects of mechanical compaction on soil macropore structure in the process of reclamation, this study investigated reclaimed soil mechanically compacted in coal mining area with high groundwater level. The computed tomography scanning technology was employed to get soil slice images, and ArcGIS® was used to analyze the porosity, number, size, morphology, and distribution of macropores in reclaimed soil, at different compaction times (0, 1, 3, 5, 7, and 9) and depths (0–20, 20–40, and 40–60 cm). Our results proved that the mechanical compaction could decrease the macroporosity, number, and equivalent diameter (ED) of the macropores in reclaimed soil, while the morphology became rounded. The distribution of macropore ED was steeper and more asymmetrical than macropore circularity. However, mechanical compaction could make them flat and symmetrical. The macroporosity, number, ED, and circularity of macropores in packing layer (40–60 cm) were smaller than backfilling top layer (0–20 cm) and sublayer (20–40 cm). Thus, we suggest that subsoiling in packing layer is responsible for the improved macropore characteristics. Moreover, these macropores will possess better permeability if the compaction times are controlled.