Research On Elastic Wave Propagation Characteristics And Rockburst Monitoring And Early Warning Under Complex Medium Conditions

As a real-time,dynamic and continuous geotechnical monitoring method,the greatest advantage of microseismic monitoring technology is that it can locate the rupture source and decribes the process of deformation and failure directly.However,due to the complexity of coal mine environment,it is difficult to guarantee the location accuracy,which will affect the accuracy of source analysis and disaster early warning.Therefore,the dissertation takes complex media condition as the research background,and studies microseismic monitoring technology from three aspects,including wave propagation characteristics,source location algorithm,and evolution law of source.It is measured that wave velocity in different direction at different stress state,and mechanism of wave velocity anisotropy is studied.The research results show that the wave velocity has obvious anisotropy during loading process,which is caused by closure and growth of microcracks.When microcracks close,wave velocity in the corresponding direction increases;when microcracks grow,wave velocity in the corresponding direction decreases.A coupling model between stress and wave velocity is built.There is a good exponential function relationship between stress and wave velocity.Based on wave velocity data,stress state of coal and rock samples can be inversed accurately.It is studied that change of time-frequency parameters of waveform with stress.During the loading process,the first wave amplitude show downtrend after upward trend.The dominant frequency is not sensitive to changes of stress state,while the centroid frequency is sensitive to changes of stress state,which presents downtrend after fluctuation.Wavelet energy distribution has obvious multifractal characteristics,and multifractal parameter ?? of receiving wave is less than that of transmitting wave.In the end stage of loading,multifractal parameter ?? of receiving wave decreases obviously.The change of time-frequency parameters is caused by damage degree of samples.It is analyzed that the influence of macro defects on wave propagation paramenters.With the angle,number and length of crack increasing,wave velocity and the first wave amplitude decrease gradually.Centroid frequency decreases gradually with the number and length of crack increasing,but centroid frequency shows downtrend after upward trend with the angle increasing.With diameter of the hole increasing,wave velocity,the first wave amplitude and centroid frequency decreasing.However,these parameters will increase when the hole is filled with the coal.The source location algorithm under complex medium conditions is studied.Divide the monitoring area into grids,and calculate the minimum travel time path from sensors to nodes based on Dijkstra algorithm.The location source is the node with the smallest overall deviation from the observed arrival time difference.Because the positioning results obtained based on different scale grids are evenly distributed around the real source,average location theory is proposed.The location source is weighted average of many location results using grids with different scale.Average location theory has the advantages of high accuracy,small amount of calculation,and low hardware configuration requirements.Because location accuracy is affected by the density of grids,overall-local joint location method is proposed and is vertified.The research results show that overall-local joint location method can improve location accuracy.The evolution and mechanism of acoustic emission events are studied.Single-linkage clustering method is introduced and four parameters are defined,including spatial correlation length ?,information entropy H,fractal dimension of single links distribution D and b value.During the whole loading process,the b value shows a change of “first high value fluctuation,then gradually decrease,and finally significant decrease”.The ? value shows a change of “first rise,then fluctuation,final rise”,and H value decreases after it fluctuates.Combining with 3-D crack growth theory and microcrack aggregation critical conditions,the essence of deformation and failure of coal and rock samples is revealed.The essence is transform process from small-scale fracture to large-scale fracture and from local damage to overall damage.The change of spatial correlation length ?,information entropy H and b value can reflect this transform process well.In the end stage of loading,D value shows obvious downtrend.The main reason is that a large number of microcracks grow along axial direction,and the disorder of single link is weakened and the order is enhanced.According to formation conditions and mining data in a Coal Mine,the microseismic sources are relocated using average location method,and precursor law of microseismic events is calculated using single-link cluster method.The results show that the relocation results are more consistent with the description of the field damage record,and the precursory law based on the relocation results is more obvious."Microseismic Location Monitoring and Rockburst Early Warning Software" is written,which is applied to microseismic monitoring in the Coal Mine.The results show that good precursor law can be obtained before the occurrence of rockburst.The research results are of great theoretical significance and reference value for locating source accurately and conduct effective early warning in complex medium conditions.