Changes Of Upper Aquifer Parameter Caused By Coal Mining

Stratigraphic disturbance,large-scale pumping test and long-term mine drainage activities change the feature of aquifers.We try to analyze the change of parameters of cover aquifers in mining conditions,using a method of obtaining aquifer parameters by tidal effects inversion,based on the theory of micro-behavior of groundwater.The study area is located in the south wing of Ningtiaota mine field.The research focus on the fractured confined aquifer of Zhiluo Formation,which is overlaying on a coal seam.The data series of groundwater level dynamics were identified from observation wells in this area.The well water level of earth tide were separated from the observation well water level after removing long period trend and the barometric pressure effect of groundwater.And the tidal factor and phase lag of MZ wave were calculated to solve the specific storage and transmissibility in confined aquifer with the Hsieh model.After the study on changes of aquifer parameters during coal mining,as well as period before and after pumping test,we reacied the following conclusions:1)The specific storage of cover aquifer in coal mine unevenly distributed in space and fluctuated over time in the condition of mining.The cover aquifers in the area of observation well Q3,J13,J17 and SKI 6 is more sensitive to stress and strain than other areas and similar fluctuations occur in January 2013.We speculate that regional stress changed in this period and cause a compression-expansion change of the aquifer.We get the permeability by the parameter of phase lag and find that penmeability in the area of observation well J7 is consistent with the result of pumping test,while the permeability in the area of observation well SK8 is poor.We speculate that the area is affected by curtain grouting works.2)The specific storage of Zhiluo fractured confined aquifer gradually deteriorate in the direction of well J17,SK16 and J14,in the west side of the roadway.While,in the east side of the roadway,the area of J13 has a good storage and the aquifer near the coal seam,in this case,we should prevent the incidents of water inrush in mining.3)The parameters changed after a large-scale drainage test in the area of about 50m from observation well SKI 1 and about sixty percent reduced in specific storage and several times increased in transmissibility.And the parameters gradually restored to its original level two months after the drainage test.