Microseismic Signal Identification And Location Method Of Coal Roof

With the depletion of shallow mining resources in North China mining area,the center of gravity of coal mining in China has shifted to the western mining area with abundant coal resources and good coal seam mining conditions,which has become the genuine coal strategic production base in China.In the process of mining,the western Jurassic coal seam is threatened by the pore-fracture water damage of its roof sandstone.Therefore,it is the key to prevent roof water inrush accident to find out the height of roof water conduction fissure zone.Microseismic signal will occur by roof rock failure during coal seam mining.Inversion location can achieve the purpose of exploring the height of the water-conducting fissure zone based on identifying the microseismic signal of roof.Therefore,the identification and location of roof microseismic signal is of great significance to prevent roof water inrush accidents.Based on the kinematics and dynamics of microseismic signals,this paper studies the identification method of microseismic signals on roof of working face.The roofcoal-floor model is established in numerical simulation.The wavelet source is used to simulate the microseismic source and then to obtain the roof microseismic signal and the floor microseismic signal.The difference of time-distance curve,energy difference and frequency of different components and different types of waves is analyzed.The results show that the microseismic signal of roof and floor has obvious difference in time-distance curve characteristics,and the time-distance curve of floor microseismic signal has obvious upward shift characteristics.Besides the Z component P wave signal,the energy and frequency of different components and different types of waves have obvious difference between roof and floor microseismic signals,and the difference of S wave is larger than of P wave.The position of the microseismic source of the roof is kept unchanged with the geophone arrangement.The change of the time distance curve,energy and frequency of the same microseismic source after passing through the coal seam is compared with the coal seam added to the roof of the above model.Based on the kinematics of seismic wave propagation and Fermat principle and quantum particle swarm optimization,a nonlinear piecemeal ray tracing method based on QPSO is formed.In this method,the source point of the layer is same as the geophone,the focal point is located in the upper layer of the geophone,and the focal point is located in the lower layer of the geophone.the method consider the refraction wave as the first-to-wave.Four kinds of horizontal layered model,dipping interface model and curved interface model are constructed to compare the time difference between nonlinear piecemeal ray tracing and high-order finite difference algorithm The result show that the two methods agree well.This ray tracing method can be applied to the calculation when the roof microseismic events are located.On the basis of the forward walking time calculation method,a time difference location method based on quantum particle swarm optimization is structured.This method can be divided into P wave travel time difference location and S-P wave travel time difference location according to the different objective functions.In this paper,the location error under the two objective functions and the value of the inversion position are analyzed in detail.The results show that the S-P wave travel time difference location error is smaller.Besides,this paper makes a detailed analysis of the observation system,initial pick-up and velocity model which affect the positioning accuracy.Aiming at the problem of positioning error caused by the inaccuracy of the initial velocity model,the calibration gun can be used for velocity correction,and a QPSO velocity model correction method is formed.The feasibility of the algorithm is verified by establishing a horizontal layered model.The results show that the error between the corrected velocity model and the actual velocity model is not more than 5%.Finally,the above velocity model correction method,forward walking time calculation method and time difference location method are applied to the detection of water conduction fissure zone height in the actual working face roof.The detection results are consistent with the network parallel electric method monitoring results.It shows that it has the ability to find out the height of roof water conduction fissure zone and can provide basis for the prevention and control of coal mine roof water hazard accident.