Experimental Study On The Propagation Law Of Microseismic Signals In Layered Rock Mass

Rock burst is one of the main dynamic disasters associated with coal mining,so the accurate location of the seismic source is of great practical significance to the monitoring and warning of rock burst,assessment of impact risk,disaster prevention and reduction.Most studies on source location are based on the assumption of wave velocity model,without considering the influence of the complexity of geological structure on the propagation law of microseismic waves,which often leads to the unacceptable positioning error.The propagation law of microseismic signals in layered rock mass is studied by combining theory with experiment.The following main conclusions were obtained:(1)Based on BP neural network technology to predict rock wave velocity,the mechanical parameters of each rock layer in the wave velocity model are taken as test samples,and the output value of the test sample is compared with the rock wave velocity measured by rock wave velocity test.The results show that the predicted rock wave velocity is close to the measured wave velocity and meets the accuracy requirements.The effectiveness of BP neural network method in wave velocity prediction research is verified.(2)In order to pick up the first arrival of microseismic signals accurately,the entropy method is improved to pick up the process.At the same time,the influence of the sampling frequency of the signals on the pickup results and the influence of the change of picking parameters on the pickup results of signals with different frequencies are studied.The results show that the improved entropy method reduces the influence of partition and region width on the pickup results,and the pickup precision is improved significantly.The higher the sampling frequency,the more accurate the first arrival of the signal.In terms of the influence of pickup parameters,the larger the sampling frequency,the smaller the influence of the pickup parameter change on the pickup result.(3)The propagation law of microseismic signals in layered rock mass is studied through laboratory experiment.The experimental results show that for complex media,there are differences in the corresponding propagation velocity of sensors arranged in different coordinates for the same seismic source.The propagation velocity of microseismic signals decreases with the increase of rock strength in a single rock layer.The stronger the strength is,the smaller the propagation velocity attenuation of microseismic signals will be.(4)In the study of propagation law of microseismic signals,instantaneous energy,marginal spectrum and marginal entropy are analyzed.The results show that the measured signals mainlyinclude low frequency signals and high frequency signals.After the microseismic signals passes through the structure surface,the low frequency signals decreases and the main frequency shifts to low frequency direction.The marginal entropy of signals with less structure surface is smaller and the signals frequency distribution is more uniform.On the contrary,the marginal entropy value of the signals is larger and the disorder of the frequency distribution of the signals is larger.There are 59 pictures,33 tables and 70 references in this paper.