Study On Seepage Evolution Law Of Coal Seam Roof In Changzhi Lu’an Mining Area

Located in Changzhi basin of Shanxi Province,lu ’an mining area is a typical representative of north China type coal field.Due to the sharp increase in the amount of coal mining,a lot of problems emerge in the mining area driven by coal mining,which is mainly reflected in the decrease of groundwater level in the mining area,and the original groundwater that can be supplied to the residents in the mining area turns into polluted mine water and is discharged.The main reason is that the overburden of the roof of the coal seam is deformed and destroyed under the mining operation,which influences the circulation mode of groundwater and destroys the recharge,runoff and discharge of groundwater.Therefore,the study on the distribution of fractures and the evolution of groundwater seepage under coal mining is carried out to reveal the evolution law of groundwater seepage under coal mining,so as to provide theoretical basis and scientific support for the development,utilization and protection of groundwater resources in the future as well as the safety of coal mining and the sustainable utilization and management of regional water resources.Based on the collection of relevant data in the study area and the full understanding of the hydrogeological conditions in the study area,this paper sorted out and analyzed the distribution characteristics of cracks in the roof of coal seam and the evolution law of groundwater seepage under the driving of coal mining.Taking changzhi luan mining area as the research object,relevant indoor similar simulation experiments were carried out.Due to the restriction of actual experimental conditions,the laboratory experiments simulated the mining conditions of single ore.The corresponding conclusions were obtained through sorting and analyzing the experimental data.Then the whole research area is simulated by computer,and the simulation results are analyzed and the corresponding conclusions are drawn.The main research results are as follows:(1)Through the indoor similar simulation test,and through the analysis and research on the variation of groundwater flow under the two mining modes,I summarized the variation rule of groundwater seepage direction.The law is that the groundwater flow changes from the direction of original runoff to the direction of lateral recharge at the mining face,and the curve equation of the depth of groundwater drop and the distance from the mining hole satisfy certain conditions.The results of test show that the groundwater downstream of the mining hole is more affected than that of the upstream.When the miningwidth is 300 m and the mining length is 450 m,the influence on the groundwater downstream and upstream is the least.(2)The software used in this numerical simulation is MODFLOW.By simulating the water level before and after coal mining in lu ’an mining area of Changzhi basin,the groundwater head value under different conditions is simulated.By comparing the simulated groundwater level before and after mining,it is found that the groundwater level in the study area decreases after mining,and the water level drops more deeply as the water level is closer to the mining face.In addition,the direction of groundwater flow changes from the original direction of runoff to confluence at the coal mining face.(3)By analyzing and studying the section drawing of the groundwater head calculated by the numerical model,the seepage evolution law of the roof of the coal seam under the mining action can be obtained.The law is that the area of clay rock at the bottom of the upper aquifer is decreasing under the action of mining-induced fractures for a long time.Although some areas still form a diving aquifer,the capacity of groundwater regulation and storage is greatly weakened,and the stability is poor.In some areas,the diving aquifer has dried up.The mining of deep coal seam results in only a small range of lateral runoff in the overlying aquifer,most of which flows into the mine through vertical infiltration to form mine drainage,and the drainage of groundwater evolves into mine drainage.At present,the floor of no.3 coal seam becomes the final water-proof layer in the area.The original lateral runoff of the submersible aquifer controlled by topography and landform is reduced,and it is mainly collected into the underground goaf through vertical infiltration along the artificial channel of water guide fissure,forming a falling funnel centering on the goaf.As a result,the underground water level drops,and the runoff of surface water is greatly reduced or even broken.