| The mining explorations in North China were generally threatened by floor Karst water disaster; but as for Hydrogeological and engineering geological conditions had differences in various mines, the water inrush type, mechanism, damage degree and prevention technology also had divergences. Huai Bei mine is the classical mine which is watery in North China mines. There were large water inrush disasters of floor Karst to cause submergence. As enlarging mining depth and raising water pressures, Karst damage would be more serious. Based on the complications of Hydrogeological and engineering geological conditions of depth mining and water inrush mechanisms of floor Karst, it refers that present specific methods have been not adapted to evaluate water inrush risks.The paper studies floor water inrush of typical mine limestone aquifer in the Huai Bei mining areas, utilizing research methods which include theoretical analysis, field geological survey, coal mine field underground test, physical simulation and numerical simulation to deeply explore the mechanism, evaluation methods, and governing modes for the water-inrush at Taiyuan Formation limestone, and derives the following results:(1) Through several tests including the ground pumping test, underground combined dewatering test, underground simplified water detection and water release test, the single-layer water yield property and vertical variations in water yield property of the aquifer at the upper member of Taiyuan Formation were studied. It pointed that the main water inrush sources in Huaibei 6(10) coal mine are located in the L3~L4 limestone layers of the upper member of Taiyuan Formation. At the upper member of Taiyuan Formation limestone, the water yield capacity decreases as the burial depth increases, and referred to Hydrogeological environment of‘high pressure and low water yield’in the deep structure.(2) Through analyzing the unit water inflow quantities, inflow rate, rock core and Karst survies of the upper member of Taiyuan Formation limestone drilling holes, the Karst development type were confirmed:L1~L2 limestone were pore and fissure Karst; L3~L4 limestone were Karst fissure and reticular type. The studies found Karst development degree were decreasing with increasing mining depth. So it put up the varieties of depth and recharging were main facters to affect the change of Karst development and aquifer watery.(3) Through analyzing the water inrush characteristics of the working face in the Huaibei mining area, the article puts forward that the working face at the thin-bedded limestone floor in Huaibei demonstrated a regular pattern of mining under overpressure and floor breaking with each water inrush. The water inrush volume is generally consistent with the zoned characteristics of the water yield property of upper member of Taiyuan Formation. The statistics and analysis on the characteristics of water inrush working face provide reliable reference for the governing of coal floor water hazards under different hydrogeologic conditions.(4) On the basis of analyzing the water inrush case at the thin-bedded limestone floor in the North China inundation mine area, it was found that using constant critical water inrush coefficient to predict water inrush risks of different aquiclude thickness is seriously conformed to facts; the paper studied mechanics of critical water inrush coefficient caused by aquiclude thickness, and set up modified formulas what critical water inrush coefficient varies with its aquiclude thickness, enriching and developing water inrush coefficient theories, improving the accurate of floor water inrush predictions.(5) Through employing the RFPA2D-Flow numerical simulation software, water inrush models were established based on the floor with different thickness of water-resisting layer but the same water inrush coefficient.The simulation results shown that on the condition of the same water inrush coefficient, the risk for water inrush increased as the thickness of water-resisting layer decreases, which was generally in line with the results derived by the TS-M method. The comparison analysis of the fissure development features of the single weak water-resisting floor(mudstone) and the soft-hard alternant stratum demonstrated that when both the thickness of water-resisting layer and the water inrush coefficient were the same, the soft-hard alternant stratum had a smaller possibility of developing fissure connection.(6) The similar material simulation on fault water inrush shrew the internal water pressure and the permeability coefficient of the fault during water inrush present regular variation. As the transfusion starts, the water pressure increased at first and maintains a stable level while the permeability coefficient remains almost unchanged. As the transfusion converts, the water pressure dropped rapidly, the permeability coefficient increased significantly. During the inrush period, the water pressure and the permeability coefficient tent to remain stable. The article put forward the ‘permeability-seepage pressure balance’ theory on the fault water inrush and elaborates on the mechanism of water inrush. under ‘permeability-seepage pressure balance’theory and explores the water inrush prediction at first step, monitoring and warning methods for fault water inrush based on this theory.(7) Through the coal mining field fault water pressure test, the similar material simulation on fault water inrush, and the analysis on the fault permeability theory, a correlation have been found between the permeability coefficient and the critical water inrush coefficient. The critical water inrush coefficient TS decreased nonlinearly as the permeability coefficient K increased. Based on this research, a TS-K method for evaluating the fault water inrush was put forward, which made up for the deficiency of the water inrush coefficient theory in the research on the seepage features of fracture zone of geological structures and provides reference for the fault inrush prediction and the fault grouting effect evaluation.(8) The article put forward the water governance prospecting concept based on unit working face. It also laid out three coal floor water hazard governance modes which included the‘watering and depressurization for mining under limited pressure mode’,the‘local grouting and pressure-resisting mining mode’and the‘overall grouting reconstruction and pressure-resisting mode’.It defined the application conditions for each mode and regulates the technical requirements for the governance modes. Based on the specific water hazard governance case, the article laid out several key technologies for the governance modes including the‘economical drainage’,local grouting comprehensive evaluation technique, and the flexible drilling pipe horizontal drilling, forming supporting technological systems for different governance modes. |
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