| It is of great significance for safety and expeditious production in coal mine to study the prevention and in Carboniferous Permian coalfield in North china.At this stage,in the light of mining rock mass mechanics theory,there are three difficulties and challenges of this project to prevent and control the limestone water disasters,namely the study on identification and formation of water flowing channels induced by induced by coal mining,the determination of the failure depth in floor location of strata and damage and the height of water flowing fractured zone.Water inrush in coal mines results from the stress perturbation caused by mining,which induces the initiation,development and coalescence of micro-cracks.Based on the academic thought that micro-breakup precursor information is the common feature of mine dynamic disasters,such as water inrush,the microseismic monitoring technique,combined with means of the monitoring techniques of water flow and pressure,are adopted in the No.22517 working face of Dongjiahe coal mine.From the essence that the water inrush is induced by geological environment deterioration due to micro-breakups during mining process,the study on the precursory seismic information of the failure degree in floor,the dynamic failure process and activation law of the water inrush channel,was carried out.Based on the inner cause and precursor law of water inrush,the study aims at forming a dynamic prediction and forecast approach using micro-seismic monitoring to deal with the hazard caused by water inrush and the following work has been carried out.(1)Based on the academic thought that key stratums are the dividing line of the two zones in the roof,a zoning method is established for strata movement in roof along the vertical directions by analyzing the distribution pattern of the number and energy of microseismic events.According to this zoning method,the height of water flowing fractured zone can be determined effectively.On the basis of the horizontally zoning three-zoning model,an improved horizontally zoning model is proposed,which divides the roof strata into 4 zones,i.e.the in-situ stress zone,the coal pillar supporting zone,the separation zone and the re-compaction zone.Based on the different stress states and the different fracture distribution of the four zones in the improved horizontally zoning model,the horizontal distribution model of the microseismic events in the roof strata can be established,which divided the roof strata face into three zones,i.e.the calm zone,the generation zone impacted by working face and the historical generation zone.According to the relationship between the improved horizontally zoning model and mining subsidence,a method to determine the displacement angle using the microseismic monitoring technology is proposed.(2)The relationship between Microseismic monitoring results,the floor failure stratum(strength key stratum in floor)and the failure depth in floor,was studied.It can be found that the vast majority of microseismic events distributed failure above the floor failure stratum(strength key stratum in floor),and the failure depth is equal to the depth of the floor failure stratum.On this basis,the method of determining the depth of coal floor failure is established by combining the results of microseismic monitoring and the geological histogram in working face.By analysis of the relationship between the energy density contour of microseismic events in floor and the inflow of water in working face,the position of water channel in floor can be determined and the formation and development process of water channel can be revealed,which provide the basis for prevention and control of water.(3)The microseismic monitoring technology is an effective way to detect micro-fracture signals at up to 200 m ahead of a buried fault.Therefore,microseismic monitoring technology can be regarded as a passive,geophysical exploration.Based on the above principle,a method of buried faults recognition based on microseismic monitoring is proposed.By analyzing the relationship between the distribution of time,space and energy of microseismic events induced by fault activation and the position of working face,it can be determined that the active phase of buried fault.By analyzing the focal mechanism of the microseismic events caused by the buried fault activation,some parameters of the buried fault can be determined.On this basis,the method of determining the buried fault parameters is established,which is based on the focal mechanism analysis of microseismic events and geological analysis.(4)Based on the analysis of results of biaxial compression,acoustic emission test,the double peak model of microseismic events was introduced to study the relationship between the double peak model of microseismic events and the stability of rock in coal mine.It can be found the stability of rock mass can be evaluated by analyzing the ratio between the microseismic events of high energy and that of low energy.Therefore,the risk assessment method of water inrush in floor in coal mine based on energy of microseismic events is established.On this basis,the risk prediction method of water inrush in floor in coal mine based on microseismic monitoring,was established to determine the risk of water inrush in floor.Based on the concentration areas of energy density in floor and the distribution of the water inrush coefficient in floor,the danger zones of water inrush in floor were determined.By the methods of apparent stress and apparent volume,Gutenberg-Richter b value,the local and dynamic evaluation of water inrush in danger zones of floor is studied and the formation of water channel in the water inrush danger zone is predicted.Based on the above work,we can get the following conclusions:I.By microseismic monitoring,the height of water flowing fractured zone and leading infection zone of coal mining at working face can be determined effectively.Based on this,methods for determining the height of water flowing fractured zone and the displacement angle by microseismic monitoring technology is established.II.By microseismic monitoring,the failure depth and the water channel in floor can be determined effectively.Based on this,methods for determining the failure depth and the water channel by microseismic monitoring technology is established.III.The microseismic monitoring technology,as a passive,geophysical exploration,can identify hidden buried in advance.By analyzing the focal mechanism of the microseismic events caused by the buried fault activation,some parameters of the buried fault can be determined.On the basis of the above analysis,a new method to identify hidden faults based on microseismic monitoring is proposed.IV.The risk prediction method of water inrush in floor in coal mine based on microseismic monitoring was established. |
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