Analysis Of The Safety Of Mining Under A Reservoir And The Influence Of Surface

Mining activities of coal mines under reservoirs not only threaten the safety of underground production,but also affect surface water bodies,dams and other buildings and structures to varying degrees.Due to the complexity of various mining conditions under the reservoir,there are many factors affecting the mining process and the characteristics of abrupt changes,the realization of safe and green mining under the reservoir undoubtedly puts forward higher requirements on mining technology,mining methods and monitoring and prediction work accompanying the mining process.In this paper,the mining activities under the reservoir in 3301 working face of a coal mine are taken as the research background.Firstly,the safety of mining under the reservoir is analyzed.According to the geological and mining conditions of the working face,the maximum development height of the water flowing fractured zone above 3301 working face was detected and predicted by empirical formula method,field measurement and nonlinear GA-SVM model prediction.According to the results obtained by different methods,the maximum development height of water-conducting fracture zone in 3301 working face is determined to be 85m,and the thickness of waterproof coal rock pillar and other indexes are calculated.Finally,combined with the predicted results of mining surface fracture depth in working face,the safety of coal mining under reservoir in 3301 working face is comprehensively evaluated.According to the actual occurrence conditions of coal seam in 3301 working face,the UDEC software is used to establish a numerical model to analyze the development characteristics of plastic failure zone of overlying strata in the process of pushing and mining.The simulation results show that the process of increasing the height of the plastic zone in the overlying strata of the working face is consistent with the fracture of the roof strata,and generally presents the characteristics of phased upward development along the advancing direction.When the working face reaches full mining,the plastic zone reaches the maximum height and remains unchanged when the pushing mining continues.Based on the numerical simulation results,the displacement curves of the strata above the working face and the surface during mining are drawn.By analyzing the displacement characteristics of the strata,it is found that the mining caving zone height of the working face is about 33m.In addition,the surface subsidence speed is faster when the working face is advanced to 200m to 400m m.When the working face is advanced to 500 m to 600m,the maximum surface subsidence change tends to be stable,and the corresponding subsidence curve is in the shape of a flat bottom bowl.The observation stations were established on the surface above 3301 working face to periodically monitor the surface subsidence and dam damage caused by coal mining.The network RTK system is used to measure the first elevation of 3301 working face surface monitoring station,and compared with the leveling results of the same period.The error analysis results show that the network RTK can meet the requirements of mining area elevation monitoring in the survey area where observation conditions permit and terrain changes are gentle.According to the measured data in the mining process of the working face,the subsidence curves of each monitoring line on the surface of the working face are drawn,and the mining influence of 3301 working face is deeply analyzed by combining the surface images before and after mining and the field investigation results of dam damage.Finally,the probability integral method is used to predict the degree and scope of surface deformation and damage,and the research results have important guiding significance for mining scheme design and surface subsidence control in mining areas.