Spatial Variation Of Soil Structure And Soil Water Transport In Subsidence Area Disturbed By Extra-thick Coal Seam Mining

With ecologically fragile mining areas in western China as the research background,this thesis focuses on ecological and environmental problems such as soil structure destruction,soil water content reduction and intensified water and soil loss caused by surface subsidence caused by high-intensity coal mining activities.Dafanpu coal Mine in Ordos,Inner Mongolia is taken as the research object.Based on UAV image data and subsidence monitoring data,The spatial distribution characteristics of surface subsidence and surface cracks after mining of extra-thick coal seam are analyzed.The variation characteristics of soil physical structure parameters in different subsidence areas were analyzed based on measured soil physical parameters and laboratory experiments,and the spatial interpolation method was used to predict the subsidence areas.CT scanning technology was used to reconstruct the threedimensional spatial distribution of soil pores and quantified the characteristics of soil pore parameters,and the correlation between soil physical parameters and soil pore parameters was analyzed.With the Hydrus numerical analysis software,the variation of soil structure and the influence of soil water transport under the influence of fractures in the subsidence area were studied and determined.According to the characteristics of subsidence and soil structure variation in different subsidence areas,the regional remediation and treatment measures were proposed.The main research conclusions and achievements are as follows:(1)Based on the UAV image data and subsidence monitoring data,the spatial distribution characteristics of surface fractures in the subsidence area of extra-thick coal seam are studied as "inverted C-shape",and the formation reasons and development characteristics of fractures in different areas after mining are analyzed.It is concluded that the fractures in the subsidence stretch area at the edge of two roadway are obviously developed,and the fracture scale(crack width,crack length,crack drop,etc.)is large.The development of dynamic fractures above the working face is relatively small.(2)Through field measurement and laboratory experiments,the soil physical structure parameters in the subsidence area were tested.It was found that the variation characteristics of soil physical structure parameters in the subsidence stretch area were the most significant,which showed that soil moisture content decreased,soil bulk density increased,soil particle size increased,soil texture tended to sand,and soil aggregates were the most obvious failure characteristics.The spatial distribution and prediction of soil moisture content,soil bulk density and soil texture in the subsidence area were realized through spatial interpolation.(3)The 3D visualization model reconstruction of soil pores(cracks)in subsidence area was realized by using CT scanning 3D reconstruction technology,and the characteristic parameters of microscopic pore structure such as soil porosity,pore diameter,circularization rate and porosity connectivity rate were quantified under different subsidence positions and different vertical profile depths in subsidence area.It was found that the variation of soil pore parameters in subsidence stretching area was the most obvious.The porosity increased the most,the number of pores increased significantly,the size of pores increased significantly,the circular rate decreased,the Euler number increased,the proportion of macropores increased,and the pore connectivity network developed obviously.A Pearson correlation analysis model was established between soil physical structure parameters and soil pore structure parameters,and it was found that soil physical structure parameters were significantly correlated with soil pore structure parameters(P≤0.05).(4)Using the Hydrus soil water transport numerical analysis software,the soil water transport model under the variation of soil structure parameters in different regions of coal mining subsidence area and the soil water transport model under the influence of subsidence fractures were constructed.It was revealed that the more severe the influence of soil structure variation in subsidence area,the weaker the soil water holding capacity and the stronger the soil water dissipation capacity.The effect of drought stress on soil was more obvious,and the trend decreased with the increase of soil profile depth.However,under the influence of fractures,the dominant channels for soil water transport increased,and the soil water transport rate accelerated significantly,and the influence was most significant within 30 cm horizontal distance from fractures.There are 59 figures,14 tables and 101 references in this thesis.