Research On Influence Mechanism Of Coal Ming In Thick Loess Region On The Overlying Loose Aquifer

In the Loess Plateau area covered by thick loess, the loose aquifer is one of the main sources of water for many people’s life and production.In Shanxi and other great province of energy resources, coal seam mining influenced and even damaged overlying aquifer. In the past, the influence of coal mining on the groundwater resources was mostly focused on the aquifer, within the water flowing fractured zone, but it had no influence on the aquifer above the zone.However, a large number of facts have proved that the phenomenon of regional water loss had appeared in the aquifer region that water flowing fractured zone has failed to communicate with or not fully communicated with.In this paper, based on the research background of thick loess covered area in Tunliu County, Changzhi City, the influence mechanism of coal mining on the loose aquifer was studied by means of similar simulation experiment.Coal seam mining are divided into three layers Overlying strata is symmetrical in a figure-eight pattern after collapsing, and the caving angle is between 50~60 degrees.Three dimensional photogrammetry system was introduced in this paper to accurately measure the displacement variation of the overlying strata.Through the analysis of the change of overlying strata displacement monitoring line, the horizontal displacement and vertical displacement law of the overlying strata under stratified mining were studied.Besides, the height change of water flowing fractured zone of overlying rock after coal seam mining was also studied.Based on the length and area of the fracture under different advancing distance of the coal seam, the development rules and development degree of the overlying rock fissure at different thickness of the coal seam were studied.Taking the goaf area as the independent variable, the length and area of overlying strata are the dependent variables, and the development process curve of the goaf area and overlying strata fissure was established. We can draw the conclusion that the length of the overlying rock and the goaf area of the coal seams are three polynomial relations, and the relationship between the fracture area and the goaf area is quadratic polynomial.Contrasting the relationship between the height of the overlying strata fissure and the infiltration rate of the loose aquifer under the different mining distance, we can see that when the second layer of coal were mined to 220 m, the height of water flowing fractured zone is 89.9m, which is far from the loose aquifer water resisting floor, but the permeability rate of loose aquifer increases from the original 0.0278cm/h to 0.0712cm/h at this time. In the process of the third layer coal seam mining, the average infiltration rate of aquifer suddenly increased to 5.5cm/h when the advancing distance is 160 m.Meanwhile, the loose aquifer at the bottom would be drained and lose the role of water conservation.The horizontal deformation, inclined deformation and curvature of the waterproof clay layer were studied in the experimental process.When the curvature of the aquifer is greater than-0.13m-1, the permeability coefficient of the aquifer will be affected. When the curvature of the water-resisting layer is greater than 0.22m-1, the permeability coefficient of the aquifer will increase, which will seriously damage the structure of the water resisting layer. Conclusion can be used as a basis for judging whether the aquifer is affected.The results of similar simulation experiment show that the effect of coal mining on the loose aquifer is not only based on the height of the water flowing fractured zone.