Study On Character, Disaster Mechanism And Prevention Of Water Inrush During Mining Under Coal Seam Roof Of Unconsolidated Confined Aquifer

There are rich coal reserves in China, but a lot of coal mines facing with complex hydrogeological conditions, such as threatened by water hazard. In a certain degree, the area, type and degree of the water hazard during mining activities in China are most specially and rarely than other place of the world. Specially, an unconsolidated confined aquifer with sand and gravel at the bottom of thick alluvium, which located at the top of coal seam in most coal mine. Water inrush from coal seam roof is one of the most important factors threatening the safety during mining process. Water flowing fractured zone developed during mining activities, which lead the water of unconsolidated confined aquifer over the coal seam swarmed into the working surface, which cause significant casualties and economic losses.Therefore, the unconsolidated confined aquifer of Qi-dong coal mine has been selected as the research background of this thesis, based on analysis of the mining engineering geological and hydrogeological conditions, the main feature and characteristics of water bursting, seepage field, supports jammed, mechanism and prevention of water inrush have been studied. The main research work and results are summarized as follows:(1) Based on analysis the morphological characteristics, physical and mechanical properties, mineral composition and provenance of loose layer, the thickness, floor level, the effective thickness of aquifer, the thickness of clay layer have been studied. The type and flow of water inrush has been analyzed with lots cases. And the relationship between water quality and time of water inrush has been investigated, which helping to determine the water source of water inrush.(2) Based on the analytic hierarchy process and fuzzy comprehensive evaluation method, the 4th aquifer has been divided as 10 hydrological geological units, and the average value of hydrological parameters of each hydrological geological unit has been got, considering the influencing factors of specific water inflow, stratum lithology, coefficient of permeability, thickness and water level of the 4th aquifer. The groundwater flow of Qi-dong coal mine has been simulated with FEM software of FEFLOW, with the generalized hydrogeological model of the study area. The result of simulation has been verified by monitoring data.(3) The character of supporting jammed and water inrush has been analyzed with the case of 6130 working surface, based on the statistics of different cases. Furthermore, the mechanism of supporting jammed and water inrush has been studied with software UDCE and field testing data. It can be found that the special structure of overlying strata with primary key stratum and inferior key stratum controlled the abnormal phenomenon of water inrush at Qi-dong coal mine. There is linkage effect between roof pressure at working surface and water level of the 4th aquifer.(4) There is great influence of key stratum breaking distance by thickness of bedrock. The compound breakage would not easily happened in multi key stratum structure when hard rock layers increased or the distance between each hard rock layer bigger than a critical value.(5) Based on the theory of coal mining under unconsolidated confined aquifer and existing experience, the synthetical technology of prevention and control of water have been proposed individually in this thesis. And early warning of height of fracture zone with electric field has been detailed and especial introduced, mining technical measures and waterproof measures have also been presented.Through those work, the following understanding and results had been got:(1) The partition characteristics of hydrogeological units of Qi-dong mine have been revealed, and average value of hydrological parameters of each hydrogeological unit have been got. Furthermore, the groundwater flow field of Qi-dong mine had been identified and verified with numerical model.(2) It had been found that composite structure with main key stratum and subordinate key stratum is the main reason of Qi-dong mine with anomaly pressure frame and water inrush. In a certain degree, the small periodic pressure of roof strata is induced by broken of subordinate key stratum, while the big periodic pressure of roof strata is induced by broken of main key stratum. The most important factors influencing the height of vertical fracture is the distance between key stratum and the 4th aquifer and the location of key stratum.(3) Synthetical and complete technology of prevention and control of unconsolidated confined aquifer water have been proposed, including prediction of supports jammed and water inrush, comprehensive drainage, pre-blasting of coal seam roof, using high resistance of supports, designing safety coal pillars, optimum speed of coal mining, etc. Each technology has its own advantages and insufficiency. Therefore, comprehensive prevention and control method should be used according to different situations, in order to ensure that coal mining with safety and high efficiency under unconsolidated confined aquifer.