Microstructure Characteristics Of Reclaimed Soil In CT-based Coal Mining Areas

Mining and reclamation process can create a tremendous disturbance on soil environment and affect the soil physical and chemical properties and biological conditions of the reclamation soil.Therefore, the comprehensive quality of reclamation soil has always been the focus of scholars both at home and abroad.Soil structure is the intuitive performance on the micro scale of land using, which contains a lot of information such as mineral composition, material migration, farming, soil fertility and the way of land use.Soil structure and properties is an important index of soil fertility.The composition of different soil particle structure and pore condition is different, so the holding water and fertilizer characteristics is also different.So studying on the reclamation of soil mechanical composition particle and pore condition is of great realistic significance.This study selected typical reclamation project area under different reclamation years(1year, 3 years, 5 years, 10 years) and not subsided land in the city of Zoucheng.While we established reclamation simulation test area of different reclamation mode.The study get undisturbed soil pore structure characteristics,using non-destructive imaging technique,the computer X-ray computed tomography(computerized tomography, CT) and obtained the distribution of reclaimed soil particles using winner2000 laser particle analyzer.While we take soil samples outdoor for the determination of other physical and chemical properties of soil bulk density, soil nutrients and so on.Finally, we analysised the soil structure under different conditions reclamation change models quantitatively using fractal geometry. And to establish its relationship with the number of other physical and chemical characteristics of the soil.The results show that:(1)Microstructure characteristics of soil under different reclamation yearsWith increasing age of reclamation, soil clay, silt content increased, but sand content reduced which showed a thinning phenomenon in the particles.The fractal dimension of soil particles and the clay, silt, unit weight or organic matter content present a significant positive correlation extremely,and the fractal dimension of soil particles and soil nitrogen, potassium,available phosphorus was positively correlated,while with sand content, porosity was significantly negatively correlated.Fractal dimension of soil particles of different reclamation years is different, reclamation 1year, 3 years, 5 years, 10 years, not subsided land to the soil particles fractal dimension were2.4959,2.5005,2.5177,2.6211,2.6270.The fractal dimension of soil particles also increased with increasing reclamation years.Fractal dimension and soil fertility showed a strong correlation between soil particle fractal dimension and organic matter, nitrogen, potassium,available phosphorus were significantly positively correlated.So we can use soil particle fractal dimension variation as an evaluation for mine subsidence area reclamation soil fertility characteristics.With the reclamation age increases, soil porosity round rate increased.Soil porosity round rate for 1-year reclamation,3 years,5 years,10 years were respectively0.7141,0.7379,0.7507,0.7589, and the fractal dimension of soil pore were1.5113,1.6057,1.7290,1.7531,which explained with increasing reclamation years, soil pore shape gradually improved and closed the circle, and 5 years after reclamation soil morphology gradually became good.Due to mechanical compaction, soil reclamation round rate of 1-year reclamation was different to the other three years of reclamation.(2)Microstructure characteristics of soil under different mechanical reclamationTaking the silty loam as the cover soil, with compaction by dump truck in three times and crawler bulldozer in five times, the composition of soil particles is most similar to the natural land. The similarity were 0.9537 and 0.9945.If we increase the number of rolling, can cause serous soil compaction and poor soil structure.The uniformity index of soil particle change like the "W" type with the increase of dump truck’s compaction times, but it changed like a converse "V" type when using crawler bulldozer as reclamation machinery.Compared to the two reclamation machinery, on the mechanical composition of the soil particles,crawler excavators reclaimed soil fraction dimension(2.785) <dump truck reclaimed soil fractal dimension(2.843), the role of the soil under the dump truck to refine than the track-type tractors.Soil particles fractal dimension under the both mechanical action were of larger changes in the vertical profile, changes were 0.026,0.077. Changes in the soil under thelower dimension dump truck role is much greater than the track-type tractor.Compared with mechanical particles fractal dimension of soil pore composition varied greatly between the layers, and the fractal dimension was between 2.3-2.7, while the changes in the upper and lower were in the range of 0.378,which denoted that the composition of soil porosity was complex than soil particle size composition between the layers.Fractal dimension of soil porosity under crawler bulldozer(2.586)> Fractal dimension of soil porosity under the dump truck role(2.446),so it means that soil of crawler bulldozer reclamation compared Dump Truck were relatively uniform and the permeability wre relatively good.(3)Microstructure characteristics of soil under different filling materialsIn the block of using coal gangue as a filler, content of physical clay were significantly higher than those of filled with construction waste and ash.Fractal dimension of soil particles:reclaimed ash soil <construction waste Reclaimed soil<gangue Reclaimed soil <control soil.The correlation coefficient was 0.7867,it showed that between uniformity Index and fractal dimension of soil particles had a certain degree of correlation.Fractal dimension of soil pores using gangue,ash,construction waste are1.526,1.406,1.492.The better soil structure, the higher the clay content, the greater the pore fractal dimension.Data showed that gangue reclaimed soil is better than the other two materials.This study indicated that fractal dimension of soil particles and soil pore fractal dimension can be the evaluation factors of soil fertility in mine subsidence reclamation area.