Water-richness evaluation of sandstone aquifer based on set pair analysisvariable fuzzy set coupling method:A case from Jurassic Zhiluo formation of Jinjiaqu coal mine in Ningdong mining area

During the exploitation of Jurassic coal resources in Northwest China,many water inrush disasters,which are related to the hydrogeological structure of the overlying strata of coal seam,threaten the safe mining. The effective prediction and evaluation of water richness of the coal seam roof aquifer is conducive to making scientific decisions on the prevention of water disaster and realizing the safe mining of coal seam. A case of evaluation of water-richness of the sandstone aquifer in the Jurassic Zhiluo Formation overlying the main coal seam from Jinjiaqu coal mine in Ningdong mining area was studied. Based on the aquifer lithology,three evaluation factors,including the equivalent thickness of sandstone,the lithological coefficient of sandstone and the numbers of exchange layers between sandstones and mudstones,were selected to establish the lithological index. Based on the faults and folds structure,three factors including fault frequency density,fault scale density and the variation coefficient of the slop of the coal seam were selected as the evaluation index. Set pair analysis-variable fuzzy set coupling method was applied to establish the water-richness evaluation model and reveal the water abundance zones. The degree of connection was used to realize the connections between the water richness evaluation index and the evaluation grades,and the relative membership function was used to realize the integration among the evaluation index values. On the basis of relative zonation,the water yield evaluation zones in the study area was determined by referring the actual yields measured from borehole pumping tests. The prediction results show that the water abundance of Zhiluo formation can be divided into low and medium water abundance classes. The medium water richness areas were mainly distributed in the middle and north of the study area,while the low class of that were distributed in the south,east and west of the study area.