| Coal floor water disaster has attracted extensive attention and research with respect to its great damage to mining safety.Mining of some key coal seams at Huobao Ganhe coal mine,one of the key mines of Shanxi Jiaomei group has suffered great threat from the karst water in the confined aquifers under the coal seams.Based on the above reason,hydrogeological drilling,pumping test,hydrogeological logging,rock and water samples testing,theoretical calculation and RFPA-2D FEM numerical modeling of the floor damage depth under the mining,vulnerability index method and five-map and two-coefficient method were applied to zone the mining area of the key coal seams,i.e.,the 2nd coal seam and 10 th coal seam,suffered the different-level threat of the karst water in confined aquifers under the key coal seams,i.e.,Carboniferous Taiyuan group limestone aquifer and Ordovician limestone aquifer.Forthermore,the evaluation results were validated hy the hydrogeological condition exposed under the underground coal mining.The results have proviede great technical support for the mining safety.The key results can be extracted as following based on the comprehensive research in this paper.? Based on the hydrogeological drilling,the pumping test,the hydrogeological logging,rock and water samples testing,the thickness and formation lithology and water abundance of the aquifers,i.e.,Carboniferous Taiyuan group limestone aquifer and Ordovician limestone aquifer,were identified.The water adundance of the former is weak and that of the latter is rich.The thickness,formation lithology,mechanical parameters and water resistance features of the strata between the key coal seam and their underlying confined aquifers were identified.The hydraulic connection of the main confined aquifers were identified.The former aquifer is recharged by the latter aquifer through some vertical structures in part of the coal field.? The floor damage depth triggered by the 2nd coal seam mining was identified by applying the FEM software,RFPA-2D.The result of the numerical simulation was compared and validated by the result of theoretical calculation and field testing at neighbour coal mines.The depthes of the floor damage in the numerical models are about 14 m and they are smaller than that of the theoretical calculation and field testing,i.e.,about 22~25m.For the reliability of the following evaluation and the mining safety,the results of the theoretical calculation and field testing are adopted as the main bases of the following zoning evaluation.The results here provide a useful support to the following research.? The probability zonings of the floor water inrush from the coal seams,i.e.,the 2nd coal seam and the 10 th coal seam,were conducted by applying the Vulnerability Index Method.The results show that the probability of the floor water inrush of the 2nd coal seam increases from the south to the north of the coal field.In addition,the locations of faults and folds are almost in the relative vulnerable zone and vulnerable zone.The probability of the floor water inrush of the 10 th coal seam is very high as a whole.In detail,the southeast of the coal field is relative safe.However,the central north part of the coal field is relative danger and the north and the other part of the coal field is in the vulnerable zone.? The probability zonings of the floor water inrush from the coal seams,i.e.,the 2nd coal seam and the 10 th coal seam,were also conducted by applying the five-map and double-coefficient method.The results show that a floor water inrush is prone to form in 2nd coal seam form the Carboniferous Taiyuan group limestone aquifer in the centralnorth part of the coal field.However,the floor water inrush from the Ordovician limestone aquifer in 2nd coal seam is highly possible.The danger zone is located at small part of the north.A floor water inrush with a direct passage in 10 th coal seam is likely to form at the west part of the coal field and a normal floor water inrush is likely to form at the central-east part of the coal field.? The results based on the above two methods were campared to the hydrogeological conditions exposed by the underground mining.The comparison show that the controlling factors included in the Vulnerability Index Method are more than that of in Five-map and Double-coefficient Method.The variation feature which is very essential in geological analysis is embodied sufficiently in the former method rather than in the latter method.The tectonic feature is not embodied in the latter method and it will lead to a distortion among its evaluation results.The nonlinear fearture and multi-factor feature are embodied well in the former method and the feature are very important factors in the process of the evaluation of the floor water inrush.The evaluation results of the latter method is relative safer.However,the results lead to a great waste of the underground coal resources.However,the results of the former method can save much coal resources and behave a considerable economic efficiency.Therefore,the results of the former method can be a important reference for the following underground coal mining.? Refering the mining practice,some countermeasures are put forward based on the above comprehensive evaluation results.Firstly,in relative safe area,unnormal variation features of the water inflow and water table of the Taiyuan group limestone aquifer should be reported in time.Secondly,in transition area,the unnormal variation features of the above content should be reported in time and some countermeasures should be applied to strengthen the aquiclude.For example,grouting technique and reform of the aquifers.Thirdly,in relative fragile area,the following countermeasures should be conducted.Water abundance and passage exploitation in advance should be done in process of underground coal mining.Geophysical exploitation and drilling should be applied to identify the poor distribution of the aquicludes,rich water abundance and possible water passage,continuity of the floor rock strata and fracutures distribution.Grouting should be conducted in the fractured area and the water resistance of the rock strata will be strengthened.As a result,the mining safety can be guaranteeed.In process of coal mining,some aquifers should be discharged to get a safe water pressure.In case of the complicated area,water detection and discharge in advance should be conducted and a water proof door should be build according to the circumstance.Fourthly,in vulnerable area,the following countermeasures should be conducted.Grouting should be conducted in a aquiclude with poor thickness to strengten the rock stratum to a safe mining level.Grouting should also be conducted in a aquiclude with a poor fragile rock stratum to strengthen the aquiclude.The mining accomapied by water discharge and water pressure decreasing is a good choice for a rich water abundance area.The method can also be conducted in a high water pressure area.Finally,in a faults and folds developed area,the following countermeasures should be conducted with respect to some possible water passage formed here.Water proof coal pillar should be retained in normal circumstance.Grouting in advance in two parts of the structure or water discharge and water pressure decreasing locally should be applied in some serious areas.Geophysical exploitation and drilling should be applied to identify the distribution of the structures to dectect and discharge the water in advance when coal mining is near them.Water proof pillars and doors should also be applied to ensure the mining safety with respect to some special circumstances.Detailed observation should be done to the structures where a water inrush has not formed in case of a delaying water inrush. |
PDF Full Text Request