Effect Mechanism And Evaluation Of Coal Mining Subsidence On Surface Ecological Environment

The effect of coal mining subsidence on the surface ecological environment is systematic and complex,involving water,soil,vegetation,and other ecological factors.Given the unclear understanding of the synergistic change patterns of the water-soil-vegetation ecological elements in the influence of coal mining in the west,this thesis studied on effect mechanism and evaluation of coal mining on surface ecological environment:Based on the FLAC^3D numerical simulation and surface measurement method,the surface subsidence characteristics and influence range of deep coal mining in the western wind and sand area were studied.The three-dimensional Empirical Bayesian Kriging method was used to construct a spatial interpolation model,which improved the prediction accuracy of soil moisture in the vadose zone and clarified the three-dimensional spatial variation of soil moisture.Using remote sensing inversion and geostatistical methods,the spatial distribution characteristics of vegetation-soil were analyzed,the response relationship between vegetation and soil under the influence of coal mining was analyzed,and the influence mechanism of coal mining on the surface ecological environment was revealed.The main results are as follows:（1）Characteristics and influence range of surface subsidence of coal mining based on FLAC^3D numerical simulationAiming at the problem of unclear understanding of surface subsidence characteristics of deep coal mining in the western wind and sand area,based on the FLAC^3D numerical simulation method and measured data,the dynamic characteristics and influence range of surface subsidence of deep coal mining were studied.The results show that:the surface subsidence in the study area was mainly controlled by working face inclination.The measured maximum subsidence of surface inclination was 2.72 m,and the maximum strike subsidence was 1.52 m.The coal pillar with a width of 20 m was reserved between the adjacent working face,which cannot effectively support the overlying rock,and a subsidence basin was formed above the goaf.The numerical simulation results showed that:the strike and dip reached the critical condition of full mining after mining in three working faces,and a flat bottom area appeared in the subsidence basin.The influence range of surface subsidence was 450 m outward expansion of goaf,and the subsidence area could be divided into uniform subsidence area and non-uniform subsidence area.（2）Spatial variability of soil moisture in vadose zone based on the three-dimensional Empirical Bayesian KrigingTo solve the problem that two-dimensional Kriging interpolation could not reflect the three-dimensional spatial variability of soil moisture,a three-dimensional Empirical Bayesian Kriging（3D EBK）spatial interpolation model was constructed to reveal the spatial variation mechanism of soil moisture in the vadose zone of subsidence area.The experimental results show that:the prediction accuracy of the 3D EBK model is higher than the two-dimensional Ordinary Kriging（2D Ordinary Kriging）model and the two-dimensional Empirical Bayesian Kriging（2D EBK）model,especially in the non-uniform subsidence area with great variability.Compared with the interpolation accuracy of the two-dimensional models,the root mean square error（RMSE）decreased from 1.37 and1.28 to 1.20,and the determination coefficient（R²）increased from 0.59 and 0.60 to 0.71,respectively.Soil moisture had weak spatial variability in the control area,and its distribution was mainly related to depth.Soil moisture had strong spatial variability in non-uniform subsidence area,and its distribution was not only related to depth,but also affected by surface subsidence,cracks,and other factors.The spatial variability of soil moisture in uniform subsidence area was between the control area and non-uniform subsidence area.The surface cracks caused by coal mining and the changes of soil texture and pore microstructure caused by non-uniform subsidence would lead to the change of soil moisture infiltration from uniform flow to preferential flow,increasing spatial variability of soil water.（3）The response relationship between surface vegetation and soil in the subsidence areaAiming at the problem of insufficient research on the response relationship between vegetation and soil factors under the influence of coal mining subsidence,based on remote sensing images and measured data,this thesis discussed the change law and spatial distribution characteristics of the physical and chemical properties of vegetation and soil and revealed the response relationship between vegetation and soil in the subsidence area.The results show that the influence of coal mining on vegetation in non-uniform subsidence area was greater than that in uniform subsidence area.The influence of coal mining on arbor growth was greater than shrub and herb.Mining subsidence significantly affected soil moisture but had little effect on soil p H values.The effects on soil nutrients were spatially specific.In the subsidence area,soil moisture fluctuation had a great effect on vegetation growth,while soil nutrient fluctuation had a small effect on vegetation growth,and the response relationship between soil moisture and nutrient was influenced by the type of vegetation.（4）Comprehensive evaluation of ecological environment quality in the subsidence areaIn response to the problem that the current research does not apply to the evaluation of surface ecological environment quality in small-scale subsidence area,a surface ecological environment quality evaluation model combining the hierarchical method and the weighted method was constructed to realize the comprehensive evaluation of surface ecological environment quality in small-scale subsidence area.The results showed that the change of soil and water environment caused by coal mining was the main factor affecting the ecological environment quality of the subsidence area.The evaluation results of ecological environment quality in the control area and the uniform subsidence area were grade III,which were the“general”levels.The evaluation result of the non-uniform subsidence area was gradeⅣ,which was the“poor”level.Coal mining subsidence had a greater effect on the ecological environment quality of non-uniform subsidence area.