Study On Method Of Water Inrush Risk Assessment Of Mining Above Confined Aquifer

With extensive, large-scale, high strength of exploration and development around decades, most of coal bases have been into deep-well development and it became more greatly difficult to mine. Especially for Karst coalfields restricted by complex geological and hydrogeological conditions in North China, many mining areas suffer varying degrees of threat from Ordovician aquifer underlying the coal seam.In view of mining under complex geological environment and high water pressure from Ordovician aquifer with large static reserves in the research area, the controlling factors of floor-water-inrush are discussed and water-resisting ability of the floor block is emphatically explored. On the basis of analyzing the water-inrush mechanism, a risk assessment of floor water-inrush is conducted with knowledge of Mine Hydrogeology and Rockmass Mechanics and methods of practical tests, artificial intelligence, water-bursting coefficient, numerical simulations and analytical hierarchy process.Firstly, a detection and research on deformation characteristics of floor failure of three mining faces under different conditions is carried out. With the comprehensive analysis of injection test results, it shows that deformation of the mining faces is mainly affected by mining depth, mining width and water pressure,.particulariy close to characteristics of the roof above the coalbed.Secondly, 74 groups of measured data of floor failure depth are collected to be loaded into the artificial intelligence platform—MATLAB. Then a nonlinear model for prediction of floor damage depth is constructed. After model training and random samples testing, prediction errors are analyzed. And the relative error percentage is the maximum of 7%.Thirdly, guided by the essence of floor water-inrush and with water-inrush coefficient formula based on“Down Three Zones”principles and numerical simulation and analytical hierarchy process, a pattern of risk assessment for predicting wether water-inrush occurs is established as well the access to the evaluation parameters in the research area.Finally, take 4# coal mining face in M1 as an example to carry a risk assessment. As for water-inrush coefficient formula, it calculates T=0.107 MPa, greater than the critical coefficient value Ts=0.076 MPa, indicating that it’s more likely to suffer floor water-inrush in the mining face. For computing results of water-inrush mechanics model in FLAC3 D show that the minimum principal stress value of the floor rocks is 7~8 MPa, less than the water pressure of 9 MPa; but the maximum floor failure depth of 26 m is less than thickness of 110.05 m of water-resisting layers. As a result, it’s not likely to lead to water inrush. For the AHP model, the largest eigenvalue of the judgment matrix for floor water-inrush assessment is 0.3004, in correspondence to the assessment level “Dangerous”, showing a large probability of water-inrush. Considering all of assessment results, is’ s supposed that 4# coal mining face in M1 is more likely to suffer water-inrush without appropriate measures.