| Microseismic monitoring technology is one of the important technical means to analyze the stability of rock mass,which has been widely used in the field of safety monitoring of mines,dams,deep underground tunnels,rock slopes and so on.The advantage of micro-seismic monitoring technology over other monitoring technologies is that it can outline the process of rock burst preparation through the temporal and spatial positioning of microseismic events,and improve the reference for field support and construction.At the same time,it is convenient for scholars to analyze the mechanism of rock burst.Therefore,the accurate location of micro-seismic events is very important,and it is also a hot and difficult point in the research of micro-seismic monitoring technology.This thesis aims at how to further improve the positioning accuracy of microseismic events,on the basis of previous research and using the idea of active source technology for reference.Focusing on the arrival time,positioning algorithm and velocity model,the three main factors that affect the positioning accuracy of micro-seismic events are optimized from the algorithm and hardware.The main research work is as follows:(1)Aiming at the picking optimization of the arrival time,a single time window arrival time picking algorithm independent of the length of the time window is proposed by using the polarization analysis method to constrain the M-AIC algorithm.It overcomes the influence of data signal-to-noise ratio(SNR)and data trailing on M-AIC algorithm.At the same time,in view of the fact that the maximum picking accuracy of the current automatic arrival picking algorithm is limited by the sampling rate of the hardware,a high-speed micro-seismic data acquisition unit based on FPGA is designed to improve the time resolution of the data.At the same time,in order to reduce the data storage pressure at high sampling rate,FIR filter and STA/LTA algorithm are embedded in FPGA to distinguish noise data and vibration data.by selecting the way of storage,the data storage space occupation at high sampling rate is reduced.(2)Aiming at the optimization of velocity model and location algorithm,based on the active source technology,the "source-station" velocity model is proposed,and the positioning accuracy of the existing arrival time difference algorithm is improved by optimizing the velocity model;At the same time,referring to the main event location algorithm and the double difference location algorithm,a double difference single source location algorithm is proposed by reducing the number of parameters to be solved in the double difference algorithm by knowing the location of the active source event and the initiation time.The optimization algorithm is used to solve the source parameters,which further improves the positioning accuracy and calculation efficiency of the existing algorithms.In order to solve the problem of source and velocity model selection in the case of multi-active sources,in this thesis,a "source-station" mixed velocity model method based on arrival sequence and absolute travel time difference of source station and an optimal source selection method based on absolute travel time difference are proposed.It is used for velocity model selection of direct location algorithm and optimal source selection of double difference single source location algorithm respectively.(3)In order to solve the problem of establishing the velocity model of "sourcestation" in practical application,a source information recorder is designed to record the onset time of the source,and the source information recorder is synchronized with the acquisition equipment through PTP protocol.To ensure the unity of source recording time and data recording time.In order to verify the feasibility of miniaturized source in the establishment of velocity model,a small source based on piezoelectric ceramics is designed.The laboratory verification results show that the designed source has good repeatability.However because the power of the selected exciter is too small,it can not be applied in practical monitoring for the time being.(4)Through a large number of forward experiments,the forward verification of the algorithm in this thesis is completed,and the microseismic location experiments based on active source are carried out in the tunnel laboratory of Southwest University of Science and Technology and Baihetan Hydropower Station,and the forward results and the laboratory positioning results show that the positioning accuracy of the improved velocity model and positioning method is obviously improved,and the positioning results of Baihetan Hydropower Station show that the positioning accuracy of the improved algorithm is better than 7 meters for the excavation blasting source in the tunnel,the location accuracy is much better than the results of normal used speed model and location method in tunnel's MS events location.The positioning results of the excavation process events are consistent with the site construction progress.The main innovations of the research work are as follows:(1)The active source technology is introduced into the location of micro-seismic events,and the positioning accuracy of micro-seismic is optimized comprehensively from the level of algorithm and hardware.(2)An algorithm for picking up single-window microseismic data independent of the length of time window is proposed,which not only ensures the picking accuracy,but also ensures the computational efficiency.In the case of single-component data,the calculation speed is even better than that of the energy ratio method.(3)A high-speed micro-seismic data acquisition hardware embedded with STA/LTA algorithm is designed.by improving the time resolution of micro-seismic data,the picking accuracy of arrival time is improved.at the same time,due to the addition of STA/LTA algorithm,the noise data is filtered.While increasing the sampling rate,the occupation of data storage space is reduced.(4)A "source-station" velocity model and double difference single source location algorithm are proposed,as well as the velocity model under multi-active source and the selection scheme of the best source.After optimizing the velocity model and location algorithm,the positioning accuracy of microseismic events can be improved.(5)The source information recorder and a small active source based on piezoelectric ceramics are designed.The application of active source technology in the field of microseismic monitoring is solved from the hardware level,which provides hardware support for the realization of velocity model and algorithm. |
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