Effects of land reclamation time on soil pore number and porosity based on computed tomography images in opencast coal mine dump

Abstract: Opencast coal mining is an anthropogenic activity that changes the antecedent soil profile, and the physical, chemical and biological properties. The compaction activities of large machinery play a great effect on reconstructed soil pore structure in opencast coal-mine dump, so it is an important work to reconstruct a suitable soil pore structure for vegetation growth during the land reclamation for dump. In order to make a quantitative analysis on the pore number and porosity of reconstructed soils in dump, high precision and lossless computed tomography (CT) was used to study the effect of opencast coal-mining, land reclamation and dumping on soil pore number and porosity by scanning the soils in Antaibao opencast coal mine in Pingshuo mining area, Shanxi Province, China. The soils were taken from the dump platform covered by loess parent material, which were the ones with different reclamation time (0, 20 and 23 a) and the one of original landform. The softwares, including Photoshop 7.0, ArcGIS 10 and AutoCAD 2010, were used to process the scanned image and carry out statistical analysis for soil pore properties, and the image characteristics of soil pores and the changes in the number of soil pores and the porosity were analyzed. The changes in macropores, mesopores and micropores of reconstructed soils were also studied in this paper. The results indicated that: 1) Applying the combination method of high precision CT scan imaging technology and computer graphics software could accurately analyze the size, number and distribution of reconstructed soil in opencast coal-mine dump; 2) The number of soil pores and the porosity in original landform were the largest, followed by the soils reclaimed for 23 and 20 years, and the soils after dumping before reclamation were the lowest; 3) Opencast coal-mining and dumping activities reduced the number of soil pores and the porosity because of the effects of large mechanical compaction, especially for macrospores, and land reclamation had a certain function of increasing soil pore size and improving soil porosity; 4) The effect of mining, dumping and other activities on the number of soil pores and the soil porosity for surface soils was higher than that for the bottom soils. During the land reclamation process, subsoiling, planting green manure, applying organic fertilizer and other land reclamation measures should be used to increase the number of reclaimed soil pores and the porosity of macropore on surface soils. This research can provide theoretical reference for the quantitative expression of reconstructed soil pores' distribution, the selection of land reclamation measures, and the optimization of reconstructed soil structure in opencast coal-mine dumps in loess areas.