| At the distribution adjustment stage of national coal resource development,in order to ensure the security of the national coal supply,the eastern mining area still needs to maintain a stable production period of about 20 years,and many mines will inevitably enter deep mining.This study centres on scientific and technological problems such as the dynamic formation mechanism of the water inrush channel of the deep coal mining floor and the evaluation and prevention of the water disaster of the floor,and uses the representative mines in the eastern margin of North China type coalfield as an example.Field investigation,theoretical analysis,in-situ test,laboratory test,numerical simulation and other methods were used to carry out the research according to the following aspects: 1)The characteristics of coal bearing geological structure in the eastern mining area of North China coalfield;2)Dynamic monitoring method for the deformation and failure of floor in deep coal mining;3)Temporal and spatial evolution characteristics and water inrush model of deformation and failure of floor strata in deep coal mining;4)Prediction method for failure depth and risk assessment method for water inrush from mining floor in deep coal seam;5)Control mode of floor water hazard in deep coal seam mining and evaluation method for control effect sequence verification.The main achievements are as follows:(1)In this paper,the dynamic monitoring method for floor deformation and failure in deep coal mining is proposed by using the Brillouin optical time domain reflectometry(BOTDR).According to the research,the dynamic deformation and strain distribution of BOTDR system are consistent with the stress-strain characteristics of the coal seam floor,which is a new scheme to effectively monitor the deformation and failure of the coal seam floor.BOTDR system shows that in the process of mining,the coal seam floor strata show the strain trend of "compression-tension-compression" from top to bottom.At the same time,the maximum failure depth of the coal seam floor is obtained,which provides effective in-situ test data for the accurate prediction of the failure depth of the deep coal seam mining floor.(2)The temporal and spatial evolution characteristics of complete floor failure in deep coal mining were revealed: 1)The influence range of high stress area before mining is about 38 m in front of coal wall;2)The position of the first breaking point of the mining floor rock is 29.07 m in front of the coal wall of the working face and 9.24 m below the coal seam,with the failure of coal seam floor starting from brittle rock;3)The development trend of mining floor breaking is from the first breaking point to the top and to the bottom,simultaneously.4)The maximum failure depth of coal mining floor is in the high stress area before mining,and the maximum failure depth is near the peak stress propagation line in the high stress area before mining(in general).According to the temporal and spatial evolution characteristics of coal seam mining floor failure,the failure characteristics of coal seam mining floor under the conditions of complete floor and fault floor are compared and analyzed;at the same time,the coal mining floor was divided horizontally,the regional names in turn are original rock stress balance area,high stress area before mining,post mining stress release area and post mining stress re balance area.(3)By using BP neural network,analysis of stress helix of coal mining floor,air bag-solution leak detection method,empirical formula method,multi-factor regression and distributed optical fiber measurement method,the effective prediction model and method of deep coal mining floor failure depth are obtained.The prediction method with small prediction error also includes a new mathematical theoretical model analysis method and a BP neural network prediction model.(4)The risk of floor water inrush in deep coal mining was comprehensively evaluated by means of analytic hierarchy process,entropy weight method,geographic information system,etc.in combination with the effective thickness of aquiclude and other factors that affect the floor water inrush,two risk assessment models of water inrush from the floor of deep coal seam mining,AHP-EWM and IAHP-VI were obtained.Both of them have a certain practical value.In the actual application process,one of them can be selected according to the actual situation of the research area,and the other can be combined according to the prediction results of the two models,which can further improve the safety degree of evaluation.(5)Based on the formation mechanism of water inrush channel and water inrush mode of deep coal seam mining floor in the eastern margin of North China coal accumulating area,the “coordinated advanced area control of water-filled aquifer and water-conducting structure” mode was proposed and defined.Based on the existing control technology of water hazard in deep coal seam mining,according to the factors such as the structure of the target layer of grouting transformation,regional geostress,the original rock hydrodynamic field and so on,the scientific and effective optimization research was carried out on the setting of the borehole direction and the borehole spacing of the controlled directional drilling on the ground.(6)This paper puts forward "the sequential verification evaluation method of the effect of water hazard control in the floor of deep coal seam mining",a scientific and systematic evaluation method established by using the GIS system to study comprehensively the permeability coefficient and permeability rate of the target layer,the water resistance capacity of the coal seam floor,the detection of mine electrical method,and the inspection of borehole data.(7)By using the mode of “the coordinated advanced area control of water-filled aquifer and water-conducting structure”,the water hazard of deep coal seam floor in the east mining area of North China coal accumulation area is controlled,and the result shows that the control effect is good and the deep coal seam coalface of the research mining area has realized safe mining.The results of this paper can provide a reference for the prevention and control of water hazard in the floor of the lower group coal mining in the eastern mining area of the North China coal accumulation area. |
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