Study On Small-Scale Microseismic Monitoring And Application Of Roof Fracture In Fully Mechanized Mining Face

With the deep development of coal mining,the occurrence of coal becomes more and more complex.Under the influence of hard roof superposition,the strong mine pressure appears to bring great challenges to safe and efficient mining.Microseismic monitoring technology,as a large-scale and all-weather monitoring technology,can quickly determine the position and energy of rock stratum breaking in real time by receiving,processing and positioning microseismic waves,which provides a reliable criterion for safe and efficient mining in underground working face.Therefore,focusing on the small-scale microseismic monitoring and application of hard roof working face,theoretical analysis,laboratory test,numerical calculation,field test and other methods are adopted to reveal the propagation law of microseismic wave in layered rock mass.By establishing CNN model for automatic recognition of microseismic signals in small scale conditions and M-AIC arrival pickup method based on wavelet denoising,a source location algorithm based on NM-PSO algorithm in small scale non-benign array is proposed,and the experimental verification and field application are carried out.The mechanical model of microseismic wave propagation in layered rock mass is established.Theoretical and experimental results show that the equivalent wave velocity increases when microseismic wave propagates in layered rock mass.The shorter the distance between the seismic pick-up point and the focal point,the higher the peak value of the first wave of microseismic wave;The longer the propagation distance of microseismic wave,the lower the dominant frequency.Under the condition of small scale,the monitoring environment is complex,and microseismic signals include coal and rock fracture signals,blasting signals and interference signals.According to the characteristic differences between different microseismic signals,an automatic identification model for distinguishing three kinds of signals is established based on CNN.Field microseismic signal test shows that CNN identification model can effectively identify three types of coal and rock fracture signals,blasting signals and interference signals,and the accuracy has been effectively improved.Aiming at the problems of low signal-to-noise ratio of microseismic signal and low accuracy of signal arrival extraction,an improved M-AIC arrival pickup method based on wavelet denoising is proposed.The method is verified by laboratory vibration signal data and field microseismic data.The picking results show that the wavelet M-AIC method can effectively solve the problem of picking up microseismic signals with low amplitude and low signal-to-noise ratio in small scale,which is significantly improved compared with the conventional picking-up method.Aiming at different sensor arrays,the NM-PSO source location method based on non-benign sensor array is proposed.The source location test on two-dimensional plane strain similarity simulation platform shows that the NM-PSO source location algorithm can provide a general source location solution for different sensor arrays,and its accuracy can meet the requirements of small-scale source location accuracy.A coupling monitoring system of microseismic and electromagnetic radiation was established in 22116 working face of Luning Coal Mine.Through quantitative statistics of microseismic and electromagnetic data collected by it,the distribution law of microseismic events and the relationship between energy release with time and working face advancing distance were studied,and the correlation between the number of microseismic events,energy distribution and overlying strata breakage was analyzed by combining with mine pressure monitoring data.Comprehensive analysis shows that the number of microseismic events is proportional to the amount of energy released.When weighting occurs in the working face,its energy release increases sharply and gradually tends to be flat,but the periodic change of energy release is not completely consistent with periodic weighting,and the peak time of energy release lags behind the occurrence time of periodic weighting.The coupling events of microseismic and electromagnetic radiation can also be used to analyze the mine pressure behavior in fully mechanized coal face.By analyzing the synchronous monitoring data of microseismic and electromagnetic radiation in 22116 working face,it is concluded that the fracture span of main key strata is related to the nature and thickness of overlying strata.The thicker the weak strata,the smaller the fracture span.Therefore,in non-plain areas,the fracture span of main key strata after coal mining is non-average.The research results have important theoretical significance and application value for improving the accuracy of focal location and the accurate identification of micro-fracture under the small-scale condition of hard roof,promoting the global monitoring of microseismic monitoring technology and the application of local encryption,etc.