Frocasting The Phreatic Water Field Effect On Xiao Baodang Coal Mine Coal Mining

As the large-scale of developing of coal resources, the Xiaobaodang well field, located in the yulin-shenmu coal mine areas of northern shaanxi energy chemical industry base center,has triggered many environmental geological problems such as mining depression and underground water loss and of these problems, the contradiction between coal seam mining and the protection of local main unconfined aquifer(The unconfined aquifer of upper pleistocene series Sarah Wu Su group) is pretty sharp. Facing this serious situation, this paper,based on the present situation of Xiaobaodang well field and the summary of pre-existing geological and hydro-geological data, studied the occurrence and structural characteristics of the main working bed overburden in detail to evaluate the effect of coal mining(before and after) to the flow field change of ground water operation through the method of numerical simulation technique. This paper reached the following conclusions:Through the analysis of the spatial distribution and structure of strata in the study area,the paper focused in its water abundance and hydro-geological characteristics of water bearing/resisting layer. It turned out that the Baode group red soil water resisting layer is the key layer to the aquifer in this area, but it scatters uneven in space with ‘karst window' in partial and the Sarah Wu Su group is the important unconfined aquifer and widely distributed which has great influence on the ecological environment and industrial and agricultural production in this area.The paper predicted the maximum growth height of water-flowing fractured zone in the Xiaobaodang coal field 2-2 seam after mining is 146.1m and the ratio of the height of the fractured zone to the mining height is 24.35 through the method of empirical formula and theoretical mechanics. After overall consideration of the spatial distribution characteristics and the development of conductivity fracture zone in the water resisting layer, the paper systematically divided the safe mining areas of Xiaobaodang well field.After building a three dimensional hydro-geological model, simulating researching on the groundwater flow field using the Visual Mod Flow software, and predicting the influence of Xiaobaodang well field coal mining to unconfined aquifer flow field, it turned out that the water resisting layer in most of the coal field will not cause a loss of underground water except there is small landing funnel in the ‘ karst window' part of the middle east of coal field and a modest decline of phreatic level in the east of coal field because of the water resisting layer thinner.