Disturbance characteristics of coal mining to the eco-phreatic flow field in adjacent regions

The natural runoff condition of high intensity mining in north Shaanxi coal energy base is easy to affect eco- phreatic in its adjacent regions. In this paper,aiming at the disturbance of coal resource exploitation to groundwater flow field around nature reserve,a mine field in Yushen mining area is studied. By constructing the hydrogeological model of coal-water spatial structure,the occurrence characteristics and its law of eco-phreatic in the study area are analyzed systematically. By means of physical simulation, numerical simulation and field measurement, the combined structure of coal overburden lithology,the distance between coal seam and key layer,the thickness of coal seam,the depth of coal seam,the length of coal face and so on are analyzed synthetically. The correlation analysis method is used to propose the height of the fractured zone suitable for the study area. According to the hydrogeological conditions and the mining mode of coal seam,the change of eco-phreatic flow field of Sarawusu formation after coal mining is simula- ted by using the method of numerical analysis of groundwater,and the characteristics of disturbance of eco-phreatic af- ter coal seam mining are analyzed. The results show that the eco-phreatic of Sarawusu formation is developed in the whole area and its occurrence is controlled by the form of bedrock surface,and the eco-phreatic level is affected by to- pography,aquifer thickness,groundwater watershed and surface water. Under the influence of sedimentation,the key layer is missing in the southeastern part of the study area to form a “ skylight” aqueduct. The overburden structure is mainly composed of hard-soft-hard and hard-hard-soft. The type of overburden structure plays an important role in the development height and shape of the water fractured zone. Based on the statistical analysis of the development height of several water fractured zone,it is proposed that the maximum fissure ratio is 28. 1 times in Yushen mining area,which has an important guiding significance for water-preserved mining and water hazard prevention in Yushen mining area. It is found that after coal seam mining, the loss of red soil in Baode formation in the southeast of the study area will re- sult in the loss of eco-phreatic water and the decline of water level,with a maximum depth of 10 m. In order to protect the eco-phreatic water resources,it is suggested that when mining the coal seam of the “ skylight” in the southeast part,the corresponding water-preserved mining method must be adopted.